280
THE EXCHANGE OF DISSOLVED SUBSTANCES
BETWEEN MUD AND WATER IN LAKES
BY CLIFFORD H. MORTIMER
BiologicalAssociation,WrayCastle,Ambleside
Freshwater
Figuresin theText)
(Withforty-six
CONTENTS
PAGE
280
Introductior.
of dissolved
I. The distributionof some physlcalvariables and concentratiOns
.
283
substancesin EsthwalteWater,April1939-February 1940
.
..
283
Methods
287
Results ..
.297
..
Discussion
(a) Deductions from the distributionof temperatureand dissolved
.297
.
substancesin the hypolimnion .
(b) Seasonal variations in rate of exchange of dissolved substances
.
.301
betweenmud and water.
..309
(c) Events underice
II. Changesin redox potentialand m concentrationsof dissolvedsubstancesin
312
artificialmud-watersystems,subjected to varyingdegreesof aeration
.312
.
.
.
Methodsand experimentalprocedure
.318
..
Results
324
.
Discusslon..
III. The relation of seasonal variationsini redox conditionsin the mud to the
distributionof dissolved substancesin Esthwalte Water and Windermere,
Northbasin
Samplng techniqueand othermethods
Results
(a) Esthwaite Water, 1940-41
(b) Windermere,Northbasin, 1940-4
Discussion
IV. Generaldiscussion
Summary
References
Note. SectionsIII and IV, Summaryand References,will appear in the followingnumberof
this Journal.
INTRODUCTION
conclusionsofresearchon the physicsand chemistryoflakes during
the past fortyyears have been reviewedby Welch (1935). Water movements
inducedby windand the turbulenceassociatedwiththemare the main agents
transportingheat and dissolved substances in lake water. Until density
is set up by surfacewarmingin the spring,the dis(thermal)stratification
tributionof heat and dissolved substances,includingoxygenabsorbed from
the atmosphere,is practicallyuniformfromtop to bottom. In typical lakes
developsduringsummer,and the zone in freecirculation
thermalstratification
withthe atmosphereis confinedto a surfacelayeror epilimnion.Below this a
GENERAL
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
281
whichoffers
narrowzone existswithlargetemperaturegradient(thermocline),
considerableresistanceto wind mixingand separatesthe epilimnionfromthe
The latteris almost entirelyisolated fromthe atmosphere,and
hypolimnion.
is destroyed
water movementis very much reduced. Thermal stratification
as a resultofsurfacecoolingin the autumn. Decompositionoforganicmatter,
largelyderivedfromdead plankton,depletesthe storeof oxygenavailable in
and at the
the hypolimnionduringthe developmentof thermalstratification
same timeliberatesinorganicmaterialswhichaccumulatein the hypoliminion
plants extractdissolvedsubduringthe periodof stratification.Concurrently
which
cannot
receivemuchreplenishin
the
epilimnion,
stancesfromsolution
ment frombelow. This depletionof plant nutrientsmay limit organicproduction. Circulationbetweenepilimnionand hypolimnionmay come too late
in the year to revive plant growth;thus the seasonal cycle of thermaland
oftenimposesa seasonal cycle on plant production.
chemicalstratification
organicproduction
that the factorscontrolling
It may be concludedfurther
circuin lakes are divisibleintotwo groups,namely,climaticfactors,affecting
lation and exchange,and geochemicalfactors,which include processesboth
in the lake and its drainage area, controllingthe rate 6f supply of essential
aspect
nutrients.To completethe causal descriptionof the physico-chemical
of organicproductionin lakes two categoriesof knowledgeare required:first,
ofthephysicaland chemicalvariableswhichlimitplant growthin any specified
set of conditions,and second, of the factorscontrollingthe rate of supply of
nutrientelementsto surfaceilluminatedwaters. This paper seeks to supply
information
on the second category.
Recently,Muller(1938), Einsele & Vetter(1938), and Pearsall & Mortimer
(1939) have shown that exhaustionof dissolved oxygenin the hypolimnion
is attendedby reductionprocessesas well as by
duringthermalstratification
considerableincreasesin the concentrationsof dissolvedsubstances,including
some,e.g. bases, silica and phosphate,whichcould not be regardedas primary
conditions
productsof reduction. Hence it appears that oxidation-reduction
may exercisea profoundinfluenceon organicproduction,not only in determiningthe freeenergyof the environment,but also in affectingthe rate of
supply of nutrients.The work describedin this paper is an attemptto gain
informationon the mechanismsinvolved in the apparent release of plant
nutrientsto thewaterunderreducingconditions,by a studyofthe distribution
of physicalpropertiesand dissolvedsubstancesin lakes whichare subject to
wide seasonal fluctuationsbetweenoxidized and reducedconditions.In basepoor regions,such as the English Lake District,only relativelyshallowlakes
show completereductionof oxygenin the hypolimnion.Thereforemost ofthe
workwas carriedout on EsthwaiteWater and Blelham Tarn,maximumdepth
16 and 15 m. respectively. Observations on mud-water systems in the
laboratoryand on otherlakes in the-Lake District are included in ?? II-IV
forcomparison.
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
282
Exchangeof dissolvedsubstancesin lakes
in outline,ofa theoryofchemical
Theresultshaveledto thepresentation,
fromthistheoryhave,as far
Deductions
exchangebetweenmudand water.
workers.Earlyinthiswork,
ofprevious
beentestedonthefindings
as possible,
at the mudsurfaceand in the muditselfwas
of conditions
the importance
Thefirst
essentialwas
devisedfortheirinvestigation.
and methods
recognized
sampleofthemudsurface
a sampling
devicecapableofraisingan undisturbed
whose
it. Thishas beenachievedbyMrB. M. Jenkin,
andthewateroverlying
an
in? III, represents
described
His apparatus,
acknowledge.
helpI gratefully
equipment.
additionto hydrobiological
important
(Pearsall& Mortimer,
was drawnin a previouscommunication
Attention
electrodes
platinum
bright
at
measurable
ofpotentials
1939)to thecorrelation
with chemicalevidenceof oxidationor reductionin soil and mud-water
systems.It was suggestedthat,althoughthesepotentialsare not,thermotheyrepresent
is difficult,
reversibleand theirinterpretation
dynamically
reversible
andarerelatedto ecologically
potentials
(redox)
oxidation-reduction
it
systems.Theirpracticalvalue lies in the factthatby theirmeasurement
systemis capablesoil or mud-water
whethera naturals
maybe determined
of oxidationor reduction.It has been possibleto studyin detailthe redox
of a fewmillimetres
withinthedimensions
whichmaybe confined
gradient,
of the
than the confirmation
nearthe mud surface.The resultsgo further
theysuggestthat the
practicalvalue of redox potentialmeasurements;
processesand thatthe conpotentialitselfcontrolsmanyphysical-chemical
on
exertsitsinfluence
ofoxygen,
oranyotheroxidantorreductant,
centration
its effect
on thepotential.
thesystemlargelythrough
of
to theimportance
was also directed
earlyin theinvestigation
Attention
and dissolvedsubin the transport
ofphysicalproperties
watermovements
stanceswithinthelake system(waterand mud),and to thevalueofthecon(Schmidt,
ofmeteorology
appliedto problems
originally
cept'eddydiffusion',
in
(literature
to oceanography
1925; G. I. Taylor,1915),and morerecently
and heat
Defant,1929).Theseauthorshave shownthatthelawsofdiffusion
analysis
whichhave beenthe subjectof detailedmathematical
conduction,
mixingin fluids.The
(Carslaw,1921),also applyto problemsof turbulent
by Schmidt(1925). Lna future
was firstattempted
to limnology
application
in prep.I) is is hopedto explainmorefullythe
communication
(Mortimer,
problems.
to limnological
integrals
applicationofcertaindiffusion
inthree
theresultsofthisinvestigation
to present
It wasfoundconvenient
ofmethodsand somediscussion.A
eachwitha separatedescription
sections,
Forreasonsofspace,publication
discussion-follows.
fourth
section-general
untilthenextnumber
is deferred
andreferences
of??III andIV withsummary
ofthisJournal.
withchemical
I wishto acknowledge
the help of Miss W. Pennington
on occasionsof my absence,and the
analysisand othermeasurements
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
283
painstakingworkof G. Thompsonand the laboratorystaffat Wray Castle in
collectingsamples. I am indebtedto Dr C. B. Taylorforpermissionto publish
the temperatureand dissolved oxygen data obtained in connexionwith a
bacteriologicalinvestigationon EsthwaiteWater,1939,and to K. Lee forthese
determinations.
I. THE DISTRIBUTION OF SOME PHYSICAL VARIABLES AND CONCEN-
TRATIONSOF DISSOLVED SUBSTANCESIN ESTHWAITEWATER,
AP-RIL1939-FEBRUARY1940
METHODS
obtainedat approximatelyweeklyintervals
was
A verticalseriesofsamples
at a fixedstation near the deepest point in the lake (see map, Fig. 1). A
Friedingerwatersamplerwas employedand portionsof the sample wererun
offintotwo 100 c.c. stopperedbottles,takingthe usual precautionsto exclude
to screw-caprectangular
air. A thirdportionof the sample was transferred
bottlesof350 c.c. capacity,ofconvenientsize and shape forpacking. Samples
wereobtainedat the followingdepths: 1, 5, 6, 7, 8, 9, 10, 11, 12 and 13 m.; the
last depthwas 1 m. above the mud. On each samplingoccasion the depth of
all samples below 6 m. was adjusted forvariationsin lake level so that they
were at whole-metreintervalsabove the mud surface. The temperatureof
the waterat these depthswas determinedat the same timewith a reversing
thermometer.On some occasions a sample was taken just over the mud
surfacewithan apparatus describedin ? III. The mud temperaturesobtained
during 1940 were measured by allowing the thermometerto sink into the
softmud surface,withdrawingit slightlyand at the same time reversingit.
gradientinthemudinvestigatedbyothermeans
Evidencefromthetemperature
representthetemperatureat approximately
indicatesthatthesemeasurements
10 cm. below the mud surface.
On returnto the laboratory,one of each set of 100 c.c. bottleswas used for
dissolved oxygen determination(unmodifiedWinkler),the reagentshaving
been added in thefield.The other100 c.c. bottlewas used forthedetermination
of redox potential by the potentiometricmethod described by Pearsall &
Mortimer(1939) and outlinedin ?? II and III. A spade-typebrightplatinum
electrode1 sq. cm. in area was introducedinto each bottle,the neck of which
was then sealed fromthe atmosphereby a little medicinal paraffin.The
potentialwas measured2 hr. afterthe insertionof the electrodes,whichwere
acid and well rinsed.
then cleaned in dichromate-sulphuric
In orderto make this chemicalsurveyas extensiveas possible,a plan for
a selectednumberof determinations
by rapid methodson a large numberof
was
in
to
adopted preference a more completeanalysis of a smaller
samples
numberof samples. Attentionwas confinedto the determinationof (a) the
general charactersof the water: electricalconductivity,alkalinity(titration
pH, colourand
withN 100 HCl to pH 4 withbenzene-azo-oc-naphthylamine),
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
284
Exchange of dissolved substances in lakes
0~~~~~~~~~~~~~~~~~~~
A
dl~~~~1
oO
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. 'MORTIMER
285
turbidity;(b) estimations,on filteredsamples,of those substanceslikelyto be
involved in redox reactions: ammonia (directNesslerization),nitrite(GreissIlsovay), nitrate(phenoldisulphonicacid), manganese(potassiumperiodate),
ferric,ferrousand total iron,sulphideand sulphate;.(c) otherplant nutrients:
silicate (ammoniummolybdate),phosphate (Denige's method). Brackets indicate standard methods which are described in American Public Health
the Lovibond Nesslerizer
Association(1936). For the followingdeterminations
with colouredglass standardswas used and effecteda considerablesaving in
time-ammonia, nitrite,silicate, phosphate and pH. The silicate disk was
calibratedfornitrateestimation,as the yellowtint producedin both determinationsis identical. Difficultywas experiencedin nitrate estimationin
waters containingconsiderabledissolved organic matter,due to disturbing
browncolourationsproducedwith the acid. This disturbancewas minimized
whenammoniawas employedforneutralizationand in most cases the brown
tintcould be distinguishedfromthe picricacid yellow,especiallyas the latter
developedmorerapidlyafterneutralization.
Fuller descriptionsof non-standardmethods will be given elsewhere.
Colourwas determinedin arbitraryunits usingthe ammonia standarddisk of
the Lovibond Nesslerizer,the tint beingvery similarto water colour. 'Turphotobidity' or 'transparency'was determinedby means of a photo-electric
in prep. II). The total transmission
meterdesignedforthe purpose(Mortimer,
of white lightthrougha column of the sample (350 c.c.) was measured and
expressedas a percentageof transmissionthroughdistilledwater,measured
under identical conditions.This result included absorptiondue to turbidity
and colour. A correctionforthe lattermay be made by a transparencydeterminationon a filteredsample.
An instrumenthas been designed (Mortimer,in prep. III) to determine
the electricalconductivityofwaterand mud sampleswitha d.c. galvanometer
and to,correctthe readingsto 180 C. Beforepassingto the electrodesthe d.c.
was convertedinto a.c. by means of a commutatordrivenby a gramophone
motor.The electrodes,whichconsistedoftwo sheetsof brightplatinum,total
area approximately1 sq. cm. wrapped round and fusedto a glass tube (Fig.
robust to be loweredinto mud cores withoutdamage.
16), were sufficiently
whichmay also be used in the field,possessescertainadvanThis instrument,
tages forthe rapid evaluationofconductivityand the studyofits distribution
in undisturbedmud-watersystems. Expressed as reciprocal megohmsat
180 C. (K18x 10-6), the conductivityvalue may be taken to be almost exactly
1 6 times the total concentrationof dissolvedsalts in watersin whichbicarbonate is the main anion (Kitto, 1938).
Tests for free ferriciron with potassium thiocyanate were invariably
negative,althoughferricions appeared in many cases aftertreatmentwith
or similarcomplex.
acid, whichprobablyreleasedthemfroma ferric-organic
'Ferrous iron' was estimatedby the increasein colour with potassiumthio-
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
286
Exchangeof dissolvedsubstancesin lakes
cyanate afteroxidationof the sample withhydrogenperoxide (one drop of
From
Perhydrol,Merck). 'Ferrous iron' was also detectedwithoc-oc'-dipyridyl.
the conclusionsof Cooper (1937) and the findingsof Coolidge(1932) it is clear
that much of the ferrousiron musthave been in complexformat the pH of
the Esthwaitesamples. Total ironwas estimatedwithpotassiumthiocyanate
afterpreliminarydigestionof 50 c.c. sample (less in samples with high iron
concentration)with0 5 c.c. concentratednitricacid, A.R.
Perhaps the most sensitivetest forhydrogensulphideis smell. Although
traces of 112S weredetectedin thisway in some samples,no sulphidecould be
detectedwith cadmiumsulphate by the methoddescribedby Ohle (1936a).
It is probablethat in the presenceof freeferrousions at the pH of the water
concernedalmostall sulphidewas precipitatedas ferroussulphide.
of
ofsulphatein waterswithlow concentration
Hithertothe determination
this ion has been a tedious matter. Nevertheless,estimationof sulphate is
necessaryfora studyof redox reactionsin naturalwaters. Duringthe course
of this investigationa conductimetricmethod was developed (Mortimer,in
prep. IV). 25 c.c. of sample, to whichan equal volume of ethylalcohol had
been added, was titratedagainststandardbariumchloride.The rate ofchange
of conductivity,measuredduringthe titrationby means of the instrument
already described,exhibiteda sharp discontinuityat the end-point. By this
the low concentrationsof sulphate encounteredin the waters inmaiethod
vestigated(0-10 mg./l.S04) could be estimatedto within02 mg./I.S04. A
took about 5 min.
singledetermination
thermal
ofresults.The usual practiceofrepresenting
Noteonthepresentation
becomes
by a seriesof verticaldistributiongraphs
or chemicalstratification
impracticablewhen detailedresultsforfrequenttime and depth intervalsare
presented. One method,adopted by Birge& Juday(1911), is to plot the value
of the physicalvariable or concentrationon the ordinate,and time along the
axis, and thento join the plottedvalufesforeach depthby a singlelinelabelled
forthat depth. Anothermethodemployedhere(cf.Yoshimura,1936a), offers
certainadvantages. As before,timeis plottedalongthe axis, but the ordinate
is depth in metres.The diagram thus representsa depth-timechart,and a
separate one is prepared for each investigatedpropertyof the water. The
value of this propertyin each sample is writtenon the diagram at the
appropriate depth and time. Isothermsor isopleths (lines of equal concentration)are then drawnfreehandby inspection. In this way tables have
been eliminatedand the diagram provides a pictureof the developmentof
of the
verticaldistributionwith time. With practice,detailed interpretation
diagrambecomes easy. Thus isothermsor isoplethsbunchedtogetherat one
at that depth; changesin slope
depth indicate markedverticalstratification
fromabove or below,and verticallinesshow
of the lines may indicatemixingr
uniformdistributionthroughoutthe water column.
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
287
H. MORTIMER
RESULTS
Only a selectionof the resultscan be presentedhere and only some of the
of the depthconclusionscan be indicatedin the text. Furtherinterpretation
4-202
Tempera-Lure
Mmtempatmght
was- 210C
+10-
Rainfall
2-0
I1-0
onWindermereO=Flatcalm. I=Calm,
Conditions
I
rough
2=Moderate.3=Choppy,4=Rough, 5=Very
I May. I June I July I Aug I Sept I Oct I Nov, I Dec
Apr
F
Feb I
I Jan
Fig. 2. Meteorologicalrecords, 1939-40; air temperature(9 a.m. Ambleside), rainfall (daily
totals Ambleside)and observationson Windermere(estimateof mean daily condition).
0.
168
190
185
200
Ice
-
822
4
39
319
6~~~~~~~~~~~~~
P_(O
38
10
12
44
42~~~~~~~~~~~~~~~~~~~~~~~
108
7
Mud
1
1
14117
i71 AI
16rl681'5222
2i22
63
May
Apr
dates.
Sampling
June
h 7J39 172i5,14
July
Aug.
-9-
2q5 1219 I
Sept
Oct.
Nov.
4
-
8
Dec
2j
12I'171
Jan.
I
2I
Feb.
Fig. 3. EsthwaiteWater, 1939-40. Depth-timediagramof the distribution
of temperature (' C.).
time diagramsis leftto the reader. The full data may be inspectedat Wray
Castle.
and dissolvedoxygen.The influenceof weather
Weather,lake temperature
on lake temperatureis clear froma comparisonof Figs. 2 and 3. Data for
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
288
windare clearlyinadequate. Daily observationsof conditionson Windermere
do not necessarilyhold for Esthwaite Water 3 miles away, but the major
oscillationsin windforcemay be consideredto apply equally to both lakes.
The main featuresof the temperaturecycle were as follows: Isothermal
conditionscontinuedinto April. Thermal stratificationcommencedat the
beginningof May, was destroyedby a gale in the middleof that month,but
was re-establishedduringthe calm warm spell that followed.The epilimnion
was deepened by rough weather at the end of June, the thermoclinewas
pusheddownto about 8 m. and throughoutthe summerwas notverynarrowly
defined.Stability,i.e. thermalresistanceto windmixing,was highestbetween
8 and 12 m. As a resultof surfacecoolingduringSeptemberthe epilimnion
deepeneduntilgalesinthebeginningofOctoberre-established
was progressively
completecirculation.
11 9
1
10
2
4
~~Io
12
~
/
1
0
/
are thesameas thoseshownin Fig 3
figures
Samplmgdatesin thisandsubsequent
Junel
Oct.
I
Aug I Sept I
Apr I May
I July
Nov. i
Dec
Ilan.
IFeb.
by Winklerprocedurewithno preliminaryoxidation
Note. Deternmnations
of reducmgsubstances.
Fig. 4. EsthwaiteWater, 1939-40. Depth-timediagramof the dcstribution
of dissolvedoxygen(mg./l.).
was establishedthe concentrationof disAs soon as thermalstratification
solved oxygenbelow the thermoclinebegan to fall (Fig. 4). The rate of fall
at each level was progressivelygreater as depth increased. By methods
in prep.I) it has been deduced
illustratedin a latercommunication(Mortimer,
took
place at the mud surface. Oxygen
that most of the oxygenabsorption
in the lowest
was completelyconsumed(unmodifiedWinklerdeterminations)
sample by the end of July. Afterthis the de-oxygenatedzone increasedin
destroyed
heightto above the 11 m. level in September,but was progressively
by mixingwithoxygenatedwaterfromabove at the end ofthat month,finally
foundat
disappearingat the overturnon 5 October.The highconcentrations
the surfaceduringthe summerrepresentedpercentagesaturationvalues of
over 100 at the temperaturesconcerned,produced in part at least by the
activityof phytoplankton.
photosynthetic
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
289
The increasein oxygenconcentration
throughoutthe wholelake duringthe
a
earlywinterwas resultofthe greaterabsorptioncapacityofthe wateras the
temperaturefell. The concentrationsfound representpercentagesaturation
values varyingbetween90 and 95. The decrease in concentrationin surface
layers duringSeptembermay be consideredto have been the result of the
progressivemixingof these layerswith de-oxygenatedhypolimnionwater as
the level of the thermoclinefell.The high concentrationsof iron encountered
in the surface waters duringthe same period (Fig. 6) indicates that the
substances whichabsorbed oxygenwere associated withiron,which did not
disappearfromthese watersuntil some monthslater. As inorganiciron is
practicallyinsolublein oxygenatedneutralor alkaline water,it must be supposed that the relativelyhigh concentrationsin surfacewaterswere present
either as colloidal ferrichydroxideor as soluble or colloidal ferric-organic
complexes,probablysimilarto thoseformedin watersand soilsin the presence
of humus. Such colloidsor even floceswould be kept in suspensionby wind
circulation,and the sharp fall in concentrationwhich occurred under ice
(Fig. 6) may be interpretedas the resultof settlingof thesematerials. In any
case the mechanismis of interestin suggestingthe mannerin whichironmay
be suppliedto the phytoplankton(cf. Hutchinson,1941).
Redoxpotentialand iron. As a resultoftheinsolubilityofferricironin most
natural waters,the concentrationof iron remainedlow in all samples from
Esthwaite Water in whichthe oxygenconcentrationhad not fallenbelow a
certainlevel,say 5 mg./l.The mud,however,in commonwithmostlake muds,
is anaerobicjust below the surfaceand containsferrousiron,whichis soluble.
be assumed,and observationhas confirmed
the assumption,
It musttherefore
that ferrousiron cannotpenetrateinto oxygenatedwater,but is precipitated
in ferricformon the mud surface(Einsele, 1938; Pearsall & Mortimer,1939).
High concentrationsof iron in the water are only maintainedin the absence
of oxygen.Thaf highconcentrationsoccurin the de-oxygenatedhypolimnion
of lakes has been observedby various workers(Muller,1938; Einsele, 1938;
Yoshimura,1936b; Stangenberg,1936; Pearsall & Mortimer,1939). The latter
authorsfoundthat ferrousiron appeared in the water of Blelham Tarn, and
also in soils and muds, only if the redox potential fell below E7= 0-23V.,
which correspondedin Blelham Tarn to an oxygen concentrationof about
0 5 mg./l.
The controllinginfluenceof the concentrationof dissolvedoxygenon the
distributionof redox potentialand iron and of otherdissolvedsubstancesin
EsthwaiteWater (1939) is demonstratedby the similarcourseofthe isopleths
in Figs. 4-6 and subsequentdiagrams. Afterthermalstratification
had commenced,the risein concentrationof ironin the bottomsample was relatively
slow until the dissolvedoxygenconcentrationhad fallento about 1 mg./l.in
the middleof July. At thistimethe ironconcentrationin the bottomsample
was 0 75 mg./l.,and the redox potentialhad onlyfallenapproximately0.1 V.
J. Ecol. 29
19
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
290
water(E7=0 5 V.). From
fromthe value usuallyfoundin well-oxygenated
was morerapid. It
thispointonwardsthe risein totalironconcentration
iron
yetno ferrous
As
to
0-25
fell
the
potential
and
a
fortnight
trebledin
V.
be assumedthatthe
had appearedin the bottomsample. It musttherefore
ironfromthemud
offerrous
diffusion
fromincreased
increasein ironresulted
I
..L
d_~~~~~~~~~~~~~~~~~~~~~~-c
....
148\50
052
050
4
06
10
0*4 0
12
06~~~~~~~~~~~
Q~~~~~~52 016
IJune
'
\k
0
~ ,,,T
Aug.
I
juIy
4
o.
,~,
Sept
05
\~~~~~~~~~~~~~~
0
\
,
IOct
Nov.
I
Dee
I
I
Jan
5
2
FebI
Fig. 5. EsthwaiteWater, 1939-40. Depth-timediagramof the distribution
of redox potential(E7 in V.).
0
r
Tr
Tr
Highest level
* =
0 40
0 38
at whichferrous lronTr 'aI 0d04
0 061
fee
[CC
Snow
Snow
I
4
P-4
0..I
,
.
~~I0
Fig.
1
.
.
ea.~~~~~~~
I
.
...........
Wo
,
,
*
I
,
.........
I
Tn
Tr
o~~~~~~~~~~~~~~
12
4- 010
-
oftotaan
'June' 1ul;
. .H 6
'Aug
' eru
Sept!
15
io
Oct
4
47
mg/.F)~~~0
Nov
'Dec
an
Feb
0= Highestlevel at whichferrousironwas detected.
Fig. 6. EstliwaiteWater, 1939-40. Depth-timediagramof the distribution
of total and 'ferrousiron' (mg./I.Fe).
nearthe mud surface,and its oxidationat
at loweroxygenconcentrations
higherlevels. As a resultofthisthewaterbecamecloudyand colouredwith
ironfirstappearedin the bottomsampleon
ferrichydroxide.Free ferrous
27 July,whenthe oxygenhad disappearedand the potentialhad fallento
E7 =0418 V. The rapid rise in iron concentrationwas maintainedthroughout
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
291
the summer,reachinga maximumvalue in the bottomsampleof 12-5mg./l.on
28 September,by whichdate the potentialhad fallento E7 = 005 V.
For reasons of space, data forferrousiron are included on the total iron
diagram (Fig. 6). As the summerproceeded it made up a progressively
increasingpart of the total iron in the hypolimnion(see Fig. 11) until on
28 Septemberall the iron in the bottomsample was in the ferrousor ferrous
complex state. The persistenceat otherlevels of the de-oxygenatedzone of
some iron not in 'ferrous' form may have resulted fromthe presence of
unionized ferrouscomplexes or from the slow rate of reduction of ferric
complexesproducedfromthe large-scaleoxidationofferrousironduringJuly
and fromthe continuousoxidation and precipitationof iron,whichmay be
level. A turbiditymaximum(cf.Fig. 11)
expectedto occurat the thermocline
indicatedthat oxidationof ironwas in fact proceedingin the upper layersof
the hypolimnion.These layerswereconsiderablymoreturbidthan the bottom
water, which became clearer but more coloured as the summerproceeded.
Possible accumulationof plankton at the thermoclinelevel should also be
bornein mind. The upper limitsof occurrenceof ferrousiron coincidedwith
an oxygen concentrationof approximately0-5 mg./l. and a potential of
approximatelyE7 = 0-25V. An exceptionto thisruleoccurredduringunstable
conditionsresultingfromactive mixingin the 10-13 m. layeron 28 September,
a few days beforethe overturn. Ferrous iron was detected at 10 m. at a
potentialof 0 37 V. and oxygenconcentrationof 8-4mg./I.
The restorationof dissolved oxygento the mud surfaceat the overturn
effecteda rapid oxidation and precipitationof the iron, most1of which was
depositedon the mud surface(see Fig. 12). Nevertheless,as was pointedout
in thewholelake remainedrelativelyhighduring
earlier,theironconcentration
the earlypart of the winter. A sharp rise in redox potentialwas observedat
the time of oxidationand precipitationof the iron,althoughthe high spring
values were not equalled until about 2 monthslater. These values are comparable with those obtained in oxygenated sea water (Cooper, 1938) and
oxygenateddistilledwater (Richards, 1928) if correctionsare made forpH
value. The factthat thesepotentialswerenot attaineduntilDecembermay be
consideredas furtherevidence that reducingmaterialswere presentin the
water duringthe precedingmonths.
Colour. The time-depthdistributionof colour is not figured.Colourwas
negligiblein surfacewaters. In the hypolimnionit was partly due on some
occasions to the presenceof colloidal ferrichydroxideand partlyto coloured
out of the mud. Colourdue to this latter
soluble organicsubstancesdiffusing
cause increasedin the hypolimnionto a maximumjust above the mud at the
end of the stagnationperiod. Afterthe overturnit was decreasedto less than
one-tenthof this value. A typical vertical distributionof colour during
is shownin Fig. 11, and a graph showingthe seasonal
summerstratification
variation of the 'total colour' in the water column is included in Fig. 13.'
19-2
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Exchange of dissolved substances in lakes
292
it is apparentthatmuchof
Fromthesharpfallin totalcolourat theoverturn
thesolubleorganicmatteris removedat thesametimeas iron.
increasein concentration
from
Silica (Fig. 10) also showeda progressive
1 to over3 mg./l.SiO2in thehypolimnion
duringthecourseofthesummer.
a
afterthe overturn
was 2-0mg./l.Thisrepresents
The meanconcentration
4
66
67
66
70
2
Ie
So
75.,68-
7O
4
65
69
6~~~~~~
-4~
May
June
Aug'
July
Sept
105
'Oct'
Nov
1
Dec
Jan
Fig. 7. EsthwalteWater, 1939-40. Depth-timediagramof the distribution
(K18x 10-6).
of electricalconductiviity
Snow
Ie
41
L
05
68.
2
81
28
o-i
?
?
oz0 '0l
W
003
02
~~~0
oq0J
0 2
d 001
;
0
j
5
0oW
002
,0
0 05
i
i
0
N1
T
JueJul;
4'Spt0
1
01
Nov
Dec
J..
Fe
Fig. 8. EsthwaiteWater, 1939-40. Depth-timediagramof the distribution
of ammonia(mg./I.NH,. N).
slightdecreasein mean concentrationof silica in the whole water columnof
0-1 mg. as a resultof the overturn.The correspondingdecrease during1940
was greater(Fig. 12). This pointis discussedlater.
Electricalconductivity
( x 0-63= total dissolved salts; cf. Kitto 1938) rose
at the mud surface from about '70 at the beginningof June to 109 on
28 September. This correspondsto an increase in total dissolved salts of
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
293
H. MORTIMER
CLIFFORD
approximately60 mg./l. It is shownin laterdiscussionthat this increasecan
be accounted forby the observedincreasesin iron,ammoniaand otherbases.
At the overturntherewas a sharpfall in the mean conductivityof the whole
water columnfrom76 to 67, a decrease of 12 %. It is suggestedin later discussionthat this amountmusthave been absorbedby the mud, as the period
28
0
t,0 07/
of
025 0.0
N
I
I
~
a
3N)k
~
~
~
~
~
O3~~~~~~~~~~~~~
12
14-
_________
between
-S.now
36
.2%
10
8
6o
0/
fe
I
\JI
Q
J
~
~
1
~
0
0
0I2
.
~
N0
26
11*
28 SeptemberI
Snd5Octobert
wasnoct
Nov
Dec
Jan
Febi
ofdetectable
nitrite,* > 0 0005 mg/1JNO2N, & > 0 005 mg/i NO2 N
---=Limit
{\/~
:Fig. 9. Esthwaite Water, 1939-40. Depth-timediagramof the distribution
of nitrate(NO03.N)and nitrite(N0m.N).
045
2/Fig
4/
0
I
6
0
8
beg0 1s5
1 32
15k6/'
10. Esha.t
et-ledi.r
Watr3990
ftedsrbto
-
err
rm5
12
2
Ma;
I Jne 1
JI
'1
Ag
I
Sept.''
c'
Nov. I
Dec
Fig. 10. Esthwaite Water, 1939-40. Depth-timediagramof the distribution
of silicate(SiO2).
between28 Septemberand 5 Octoberwas not long enoughforany change in
the conductivityof the inflowwaterto have caused this decrease.
Ammonia,nitriteand nitrate(Figs. 8, 9, 11). The rise in ammoniaconcentrationin the hypolimnion
followeda similarcourseto that ofiron,althoughit
began somewhatearlier,reachinga maximumof 2-6 mg./I.Nil3. N just above
thiemud surfaceon 22 September. In the epilimnion,and in the whole lake
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
22 June
2
0 2 b' 0
x
14
12.
F
pH
67075
ho
612
1
?,
7:
#50
eWater,1639.
V
t
0
T6
?281
54, ig /1K18
~
?,6
Iron
mg
/1
2
i
8
N x1
.
I
pi
me
iO
P0008910
e
14
10
02ou (abtandS0
Kms
X0
0
0
70
6~~~~0
1
0-62
80 0
-10 0
rnprnc
1
?Oo
12
6o5disle
usacsa
or
ek
2
ue
n
hren
ek
2
141
di
~ ~ ~ ~ ~ ~
&
isildwtrvle
F ig .EtwieWtr199Vetclcsrbtoofsmphsclvralsadcnetain
ofdsole
ubtnesa
esabihmntotera
ou eks(2Jne
ugs)afenh
sraiictin
n titenwes
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
2
uut
feh
CLIFFORD
295
H. MORTIMER
afterthe overturn,the ammonia concentrationwas normallyabout 1/100of
this value. It will be seen that the increasein ammoniawas about ten times
the equivalentamount of nitratereducedin the hypolimnion.This point will
be discussedlater. The nitratediagramshowsthat rapid reductionof nitrate
occurredin the hypolimnionwhen the oxygen concentrationand the redox
potentialhad fallenbelow approximately2 mg./l.and E7= 0-4 V. respectively.
Depletion of nitratealso occurredin the epilimnion.This may be mainlydue
werefoundin the
to assimilationby algae. Hence the highestconcentrations
i 8-
Overturn
16
0
Total
14
iron/
~12
>iZ
--
Sihcate
(I 94O>./
]
_
t0Cconcentr2ati/on
0~~~~~~~~~~~~~~~~~~~~~~
t
6
V|l
ez
NE /?
\
IN
j
L
004
V
2"-ta 13m3'02
Ph
Ete/
.60
~~~~~~~~~~~~~~~~~~~~~
Ca
>,
Ca
Tz~~~~~~~~~~~~~~~~
~June
July
Aug.
Sept.
Oct.
Nov.-
Fig. 12. EsthwaiteWater,1939 and 1940. Variationin total contentofironand ammonia(1939),
silicate and phosphate(1940), in the water column(0-13 in.) above 1 sq. m. of mud surface
at the samplingstation.This is comparedwiththe oxygenconcentration
and redoxpotential
in the lowestsample (13 in.).
thermoclineregion,wherea slow increaseduringAugustwas observed.There
was a steadyincreasein the nitratecontentofthe wholewatercolumnduring
the earlywinter,althougha lag ofabout 1 monthintervenedbetweenthe overturnand the commencement
ofthisincrease.Thus on 28 Septemberthe mean
N)
concentration(NO3. throughoutthe whole water columnwas O-068mg./1.
and by 19 Octoberit had onlyrisento O 079.
Data for nitritehave been included on the nitratediagram. Nitritewas
onlyfoundin verysmallconcentrations
and, as the diagramshows,the greatest
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
296
Exchangeof dissolvedsubstancesin lakes
region,usuallya metreor so above
amountswerefoundin the thermocline
reducedand a risein ammonia
that level at whichnitratewas completely
observed.This supportsthe view,expressedby Pearsall &
concentration
and not
(1939),thatthemainsourceofnitriteis nitratereduction
Mortimer
shown
have
later
in
discussion,
mentioned
oxidation.
Experiments,
ammonia
thatlittleoxidationofammoniatakesplacein thewater.Nitritewas absent
but traceswereoftenfoundin surface
fromthe fullyreducedhypolimnion,
waters.These may have been associatedwiththe activitiesof the phytoplankton.
andsulphide.
The conductometric
methodofsulphateestimation
$u7phate
herefor
of1939,and thedata presented
was notdevelopeduntilthesummer
August(Fig.11).
to a typicalverticaldistribution
during
thatyearareconfined
duringthecourse
depletedin thehypolimnion
Sulphatebecameprogressively
recordedwas 2-6mg./l.S04 just
of the summer.The lowestconcentration
the
throughout
The concentration
overthe mud surfaceon 28 September.
to thewinter
aftertheoverturn
wholewatercolumnrosealmostimmediately
value ofabout9 mg./l.S04. Morecompletedata forsulphateare presented
in prep.I) it willbe demonin ? III. In a latercommunication
(Mortimer,
Water,1940
ofsulphateinthehypolimnion
ofEsthwaite
stratedthatdepletion
in
reduction
at
mud
and
that
for
reduction
the
be
accounted
surface,
can
by
sulthe waterwas negligible.Neitherduring1939norduring1940was the
reduced.
completely
phatein thehypolimnion
weretoo smallto
ofsolublesulphidesin thehypolimnion
Concentrations
H2Swasdetectedbysmellin the
although
be estimated
bystandardmethods,
and black cloudinessdue to
lowestsamplesduringAugustand September,
duringthelatter
sulphideappearedin thelowerhypolimnion
colloidalferrous
offerrous
month.Production
sulphidein thewaterwas notobservedduring
was about6-9. As
duringSeptember
1940.ThepH ofthelowerhypolimnion
coefficient
offerrous
low solubility
sulphideat this
a resultoftheextremely
pH, almostcompleteremovalof sulphideions fromsolutionoccursin the
ions (cf.Einsele,1937). This probablyexplainswhyno
presenceof ferrous
solublesulphidecouldbe detected.
in thehypooccurred
risein alkalinity
andpH. A progressive
Alkalinity
fall
Thecourseofthisriseand ofthecorresponding
limnion
duringstagnation.
in
almost
detail
to
that
described
similar
already
was,
every
aftertheoverturn
is omitted.The
Hencea time-depth
diagramforalkalinity
forconductivity.
is discussedlater. In the absenceof
and conductivity
relationof alkalinity
offree
freemineral
ororganicacids,pH dependsontherelativeconcentrations
carbondioxideand alkalinity.In fact,if any two membersof thistriple
graphsin Moore,
relationareknown,thethirdmaybe computed(convenient
of dissolved
1939).Thusit wouldbe possibleto computethe concentration
found.
Thishas
values
from
the
and
in
Water
Esthwaite
alkalinity
pH
C02
in
are
described
of
direct
determinations
the
results
CO2
not been done,as
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
297
? III. 'It willbe showntherethattherateofCO2productionin thehypolimnion
was high whilethe dissolved 02 was being reduced,but that littleanaerobic
CO2productiontook place subsequently.This explains why,during1939,the
pH at 13 m. was observedto fall from6-9 to 6-5 duringJune,as a resultof
C02 accumulationin the hypolimnion.Later, as the alkalinityincreased,the
pH at 13 m. roseto 6-9at the end of September.This difference
in the vertical
distributionof pH at the beginningand towards the end of stagnationis
illustratedin Fig. 11.
Phosphate.Estimationsofphosphatewereonlycarriedout on a fewsamples
fromEsthwaiteWater during1939. Distributionofphosphatewas studiedin
more detail during1940 and discussionis deferreduntil ? III. During both
yearsthephosphateconcentration
in the hypolimnion
rosefromthe extremely
low values prevalentin oxygenatedwater (about 0001 mg./l.P) to over a
hundredtimes this concentrationin de-oxygenatedlayers. This agrees with
previous findings(Pearsall & Mortimer,1939) and with the explanation
advanced by Einsele (1938). He showed that under oxidizing conditions
phosphateis precipitatedin the presenceof ironas insolubleferricphosphate
on the mud surface.When this is reduced,soluble phosphateis liberated.
Manganese. Discussionofthe distributionofmanganeseis postponeduntil
? III.
DISCUSSION
(a) Deductionsfromthedistribution
oftemperature
and dissolved
substancesin thehypolimnion
The courseof the isoplethsin Figs. 4-10, and indeed the fact that vertical
chemicalstratification
is maintainedin the water column,suggeststhat the
main agents of productionor depletionof dissolvedsubstancesare located at
the lower boundaryof the column,at the mud surface. If the water were
completelystagnant,i.e. in the absence of motionof water masses,transport
of dissolved substancesto and fromthe mud surfacewould be the resultof
moleculardiffusion,
the laws of whichcan be deduced fromconsiderationof
the random movementsof molecules (Mortimer,in prep. I). In lakes this
mode of transportis confinedto the water withinthe intersticesof the mud.
In the waterabove the mud some motionofwatermassesoccursunderalmost
all natural conditions,and it may be demonstratedthat even the slowestof
thesemovements,e.g. convectioncurrentsunderice,producesturbulenteddies
whichare instrumentalin spreadingheat, dissolvedsubstancesor otherpropertiesin thewater. In a watercolumn,ofsufficient
magnitudecomparedwith
the mean diameterof the eddies, the spread of a propertyby 'turbulent' or
' eddydiffusion',
consideredovera periodsufficiently
longto averageout shortterm fluctuations,approximates,to that produced by random motion. In
otherwordsthe laws of diffusion
and heat conductionmay be directlyapplied
(Schmidt,1925). The fundamentalassumption,verifiedby experiment,at the
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
298
Exchange of dissolvedsubstancesin lakes
basisoftheselawsis thattheamount(F) of substanceor heat,etc.,passing
acrossa boundaryofunitarea in unittimeis theproductoftheappropriate
coefficient
ofconduction
ordiffusion
(K) andthegradient
oftemperature,
concentration,
etc.,existingat the boundaryalongancaxis normalto it. Thus
considering
diffusion
ofa dissolvedsubstanceand employing
c.g.s.notation:
Amountingramsdiffusing
across1 sq. cm.=Ft=Kt (gradient,
g./cm.), (1)
wheret is the durationof the periodin secondsand K may eitherbe the
coefficient
of moleculardiffusion
or the coefficient
of turbulentdiffusion.
FollowingSchmidt(1925) the letterA is employedfor the latter (A=
'Austauschkoeffizient')
to distinguish
it fromK,the coefficient
of molecular
diffusion.
Changesin the verticaldistribution
of dissolvedsubstancesand temperature
may,infavourable
instances,
be usedin conjunction
withformula
(1)
to obtainan estimateofA. Themethodat thebasisofall suchestimations
in
thispaperis illustrated
bythefollowing
calculation
ofa meanvalueofA at the
12 m. levelin EsthwaiteWaterduringtheperiod27 Julyto 31 August1939.
Data fortotalironwereutilizedandc.g.s.notationwasemployed
throughout.
Thisperiodwasselected
as oneduring
whichfreeexchange
ofironbetweenmud
and wateroccurred
(see laterdiscussion)
and becausetheincreasein theiron
contentofthewatercolumnabove 12 m. duringtheperiodwas considerable.
As the mudwas the onlysourceofiron,thisincrease(6.4x 10-4g./sq.cm.,
obtainedbysumming
themeanironcontentofeachmetrepanelabove12 m.)
musthavebeentransported
The
the12 m.levelbyeddydiffusion.
up through
meanconcentration
gradient
at thislevelmaybe takenas roughly
themean
ofthedifferences
in concentration
between11 and 12 m. and 12 and 13 m. on
all thesampling
datesduringtheperiod,and was computed
as 0-84mg./l./m.
or 8-4x 10-9 g./c.c./cm.
Substituting
in formula(1), where86-4x 103 is the
numberofsecondsin a day and 34 daysthelengthoftheperiod,
A-
6-4x 10-4
2-6xlo-2
8-4x 10-9 x 34 x 86-4x103
Similarestimates
can be madein all casesin whichit is certainthatall of
theincreasein heatorconcentration
ofdissolvedsubstanceon onesideofthe
has beenderivedfromthe othersideby diffusion,
levelinvestigated
and as
oftemperature
longas thestratification
orconcentration
in theregionofthat
levelis largeenoughto enablereliableestimatesofthegradient
to be made.
casesa roughestimateofA can be mademorerapidlyfromthe
In favourable
orisopleths
ona depth-time
spacingandslopeoftheisotherms
Values
diagram.
A + K, at variouslevelsin thehypolimnion
of A, or morestrictly
speaking
of
EsthwaiteWater,estimatedas above fromthe distribution
of variousproperties,are collectedin Table,1. ValuesforSchleinseewereestimated
from
of Einsele& Vetter's(1938) diagramsand are
data obtainedby inspection
ncludedhereforcomparison.
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
299
CLIFFORD H. MORTIMER
Estimations of A during stagnation under ice are presented later in
Table 2. It willbe seen in Table 1 that estimatesofA, obtainedfromthe considerationof heat passing down throughlowerlevels of the hypolimnion,are
consistentlylowerthan those obtained fromthe upward spread of dissolved
substances. As thereis good agreementbetweenestimatesof the latterclass,
it is likelythat the low values obtainedfromtemperaturedistribution
resulted
fromthefailureto accountforheat passingintothe mud (cf.Birgeetat. 1928).
The discrepancydisappears when the upward flowof heat under ice is considered(Table 2). It shouldbe emphasizedthat the data onlypermitapproximationsto the mean value ofA at a certainlevel and fora certainperiodto be
Table 1. Estimatesoftheeddydiffusion
coefficient
(A x 100) at various
levelsin thehypolimnion
ofSchleinseeand EsthwaiteWater
Lake
.
...
...
...
Depth of bottomat sampling
station(m.) ...
...
...
Year
...
...
...
...
Period ...
...
...
...
EsthwaiteWater
11-6
14-0
1939
8. vi.-29. vi.*
-
f,
Lower limitof thermocline(m.)
Depth of estimation(n.)
... 13
Data employed:
Ammonia
Total iron
Conductivity
Phosphate
Sulphate
Temperature
Schleinsee
7
12
10
1940
1935
27. vii.-29. viiLi. 3.viii.- 15.iv.- 24.v.,
29. viii. 24.v. 6.viii.
10
9
7
13
12
10=
13
11
11
thermocine
Mean values of A x 100 forperiod
4
4
3
3
3
2
2.8
2-6
2-6
3-3
10
-
-
3-8
3-6
2-5
-
1-5
1-8
1-6
3-7
2-3
0-8
1-8
10
(12 m.)
* Data duringthis period only allow the orderof magnitudeof A to be roughlyestimated.
Estimationsduringotherperiods may only be consideredsignificantto one figure.The second
figureis includedin thistable and in Table 2 to demonstratethemagnitudeof differences
between
estimatesderivedfromdifferent
data.
-
-
-
-
made. The agreementbetweenestimatesderivedfromdifferent
data indicates,
as would be expected,that A is the same if computedfromany conservative
propertyofthe water; it is solelyan index ofthe rate ofexchangeofthe water
masses bearingtheseproperties.The value 3 x 10-2 may thereforebe taken as
a roughestimateof A in the lowerhypolimnionduringsummerstratification.
It may be an under-estimate,
as the above calculationshave taken no account
of salts diffusing
throughthe thermoclineand lost at the outflow.The value of
these estimateslies in the fact that they demonstratethat water movement
and eddy diffusioncontinuein the hypolimnionafter thermal stratification
has become established,fortheyyield a value of A which is over 20 times
as great as the correspondingcoefficient
of molecularheat conduction,and
approximately2000 times as great as the coefficientof molecular diffusion
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
300
Exchangeof dissolvedsubstancesin lakes
betweenthe rate of
difference
of most commonsolutes.This considerable
alone is
transportof substancesin the mud, wheremoleculardiffusion
stratification,
of
thermal
under
conditions
even
and in the water,
operative,
and discussedlater.
described
explainsmanyofthephenomena
thatA,is
givetheimpression
shouldnot,however,
The abovecalculations
in valueat anypointforthewholeoftheperiodsinvestigated.
at all constant
in the hypolimnion
laterin ? IV thatwatermovements
It willbe suggested
there
region.Although
inthethermocline
instability
resultfromwind-induced
of
therelationofweatherand themagnitude
is notspacehereto demonstrate
andisopleths
ofthecourseoftheisotherms
an inspection
A inthehypolimnion,
occurand
variations
diagramswillshowthatconsiderable
on thedepth-time
in windforce.Examplesofthismay
thattheseareassociatedwithvariations
increased
be foundin theincreasein slopeoftheoxygenisoplethsindicating
(11-12m.) at theendofJune1939,and a
mixingin thecentralhypolimnion
at theendofAugust1940,bothas a
similarincreasein slopeoftheisotherms
resultofroughweather.Neithershouldit be assumedthatA has the samle
It is to be expectedthatA is convalue at all levelsof the hypolimnion.
as
stratification,
(density)
thermal
reducedin regionsofconsiderable
siderably
turbulent
exchangein suchregionsalso involvesworkagainstgravity.The
region,
ofA inthethermocline
themagnitude
resultsofattempts
to determine
on somewhat
inadequatedata,areincludedin Table L Thelowvaluesfound
fromthe
in isolatingthehypolimnion
ofthethermocline
theeffect
illustrate
A
circulation
winter
andinthewholelakeduring
In theepilimnion
epilimnion.
1925).
(Schmidt,
timesas greatas in thehypolimnion
maybe severalhundred
withvaryingwindforce.A
It will,ofcourse,fluctuate
in valueconsiderably
is thevirtualdisappearvalues
ofthesehighA
directresultoftheoccurrence
in the water. A
or temperature
gradients
ance of detectableconcentration
consideration
offormula(1) willshowthat,iftherateofsupplyofheator a
soluteat a terminal
boundaryofthewatercolumn(i.e. lake surfaceor mud
gradient
surface)variesonlywithinfairlynarrowlimits,the concentration
levels
at different
mustvaryinversely
as A, whichclearlyvariesenormously
and seasons. In the mud,on theotherhand,wheretheexchangecoefficient
gradientsare
steepconcentration
is reducedto that of moleculardiffusion,
of
few
millimetres
('microinto the dimensions a
foundto be compressed
Alsterberg,
1927,1930),cf.? III.
stratification',
in the lake systemwillbe
The distribution
of properties
and transport
in prep.I). By
in moredetailin a latercommunication
(Mortimer,
considered
ofmethodsofmathematical
physicsit is possibleto
meansoftheapplication
of reactionsin the mud and in the wateron
assess the relativeinfluence
in themud-water
in
the
of
dissolvedsubstances
system.
distribution
changes
are
mud
in
the
largely
responsible
The conclusions
reachedarethatreactions
of watermassesin the
in the water;movement
forchangesin distribution
and thisis sufficient
to maintainan eddy
is mainlyhorizontal
hypolimnion
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
301
diffusioncoefficient
and a rate of spread of dissolvedsubstancesroughlytwo
thousand times as great as would occur if molecular diffusionalone were
operative. How these watermovementsmay be producedis discussedlater.
(b) Seasonal variationsin therateofexchangeofdissolved
substancesbetween
mudand water
In Fig. 12 variationsin total contentof certaindissolvedsubstancesin the
water columnof 1 sq. m. cross-section,extendingfrom13 m. to the surface,
are plottedforEsthwaite Water, 1939. If these are comparedwith the dissolved oxygenconcentrationand redoxpotentialin the lowestsample (13 m.),
certaincorrelationsbecome apparent.
Only the more strikingchanges may be correlatedwith redox conditions
in the hypolimnion,
as the effectof slow changesresultingfromvariationsin
compositionof inflowwater has not been considered.The sequence of events
may be describedas follows:Removal of oxygenfromthe hypolimnion(see
Fig. 13) commencedas soon as thermalstratificationwas established.The
depletionrate was fairlyconstant duringthe initial stage, but became less
at the point whenthe oxygenconcentrationin the bottomsample had fallen
to abo4t 2 mg./l.This reductionin depletionrate may have been the result
decreasein the concentrationgradientat the mud surface.
of a corresponding
Up to this time (stage I), alkalinity,iron and colour had increasedslightly.
and redoxpotential
The nextstage (II), duringwhichtheoxygenconcentration
at 13 m. fell to 0 5 mg./l.and E7= 0-25V. respectively,was marked by an
accelerationin oxygendepletionrate (Fig. 13) and the beginningof a sharp
rise in the contentof iron, and an increasedrate of accumulationof 'total
salts' (conductivityx 0-63; cf.Kitto, 1938),alkalinityand colour(Figs. 12-14).
Turbidityalso increasedduringstage II. From the data forphosphateand
silicateforEsthwaiteWater,1940 (includedin Fig. 12, because theyare more
completethan data for1939) it may be assumedthat stage II also marksthe
beginningof a rise in silicateand a considerablerisein phosphatecontent.
It is suggestedhere and proved in later sectionsthat stage II is initiated
by a fallin oxygenconcentrationand redox potentialat the mud surfaceto a
level at whichoxidized insolubleferricsubstancesincludingferricphosphate
are reducedin the mud surface.This liberatessolubleferrousironand probably
otherreducingsubstancesinto the water. As long as the potentialat the mud
surfaceis maintainedbelowthislevel,i.e. untilthe autumnoverturn,diffusion
of ferrousiron,phosphate,etc., frommud into the water continues. It has
been shown earlierthat the rate of spread of these reducingsubstanceswas
increasedroughly2000 timesas soon as theyleftthe mud and came underthe
influenceof eddy diffusionin the water. The acceleration in the oxygen
depletionrate between 6 and 13 July,was probably a directresult of this
liberationand acceleratedspreadofferrousironand otherreducingsubstances
into the water. The oxygen concentrationand redox potentialat 13 m. fell
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
302
andfrom0-42to 0-25V. respectively.
duringthisperiodfrom2*5to 0*5mg./l.
valuesat themudsurface(.14m.) were
It is probablethatthecorresponding
lowerat thistime.
ironproduceda markedincreasein turbidity
The oxidationofthisferrous
in colloidalor finely
hydroxide
offerric
and colourdue to the precipitation
ironwas notdetectedin thewaterin amounts
suspendedstate. Freeferrous
until27 July.Afterthisdatetherateofincreaseof
forestimation
sufficient
ofit consisted
proportion
totalironbecameevenmorerapidandan increasing
30(tcl
0-13
m.
~
25
~
Colour
3
Ar
A
?\
"
20C
III
StageII Sitage
stageu
fr~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1
andammniaoxygen
atthe
Ammoniat
C
I0
5
1Nitrate.
June
July
Aug
~~Sept
Oct.,
Nov
Fig. 13. EsthwaiteWater,1939. Variationin total contentof oxygen,ammonia and nitratein
the hypolimnionwater columnabove 1 sq. m. of mud surface.These totals were estimated
by summationof concentrationsat 10, 11, 12 and 13 m. Fig. 13 also includestotal colour
in the column0-13 m.
of ferrousiron(Fig. 14). A largeincreasein ammoniacontentalso occurredat
this time. The water became clearerlater in the summer,but the colourstill
continued to increase, indicating the accumulation of dissolved organic,
possiblypeaty, materials.
The slowingup of the rate of increaseof most substances(stage III) was
observedduringSeptember. It cannotbe readilyestimatedhow far this was
due to the gradual destructionof the hypolimnionby the progressivefall in
level ofthe thermocline.A veryrapid fallin total contentof iron,phosphate
on 5 October,and
and ammonia occurredat the completionof the overturnL
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
303
H. MORTIMER
duringthe periodimmediatelyprecedingit. The fall was correlatedwith the
rise in oxygencontentin the hypolimnion,and may be consideredas a rapid
reversalof the changesproduced by reductionin the spring. Corresponding
decreases in alkalinityand conductivityare also apparent (Fig. 14). Total
colour contentof the water columnfelloffless rapidly,reachinga minimum
afterthe completionof the overturn,and it was not until
value a fortnight
afterthisthat the total nitratecontentbegan to rise. It is not certainwhether
the fallin total silicatecontentat the overturncan be regardedas significant.
4
v
or
equivalent
Conductivity
='total salts'(K8 X 10-6XO-63,
as CaCO3)
expressed
&=Jalkalinity
. 2
///
>
\sS'B
\
+El
-[~~~~~~D
ie_
(j=
ron
totaliron
=ammonia
1June
'July IAug.
Sept. I
__
Oct.
_
I
Nov.
Fig. 14. EsthwalteWater,1939. 'Total salt' and total 'excess base' (alkalmity)contentsof the
ofironand ammonia.
watercolumn,comparedwiththe respectivecontributions
hypolimnion
Totals obtainedby summationof 10, 11, 12 and 13 m. values and expressedin g.-equiv./sq.m.
of mud surface. Iron otherthan 'ferrous'is assumedto be trivalent.
It is clear, however(Fig. 10), that the summerrise was due not only to probut also to an increasein silica in the epilimnion
ductionin the hypolimnion,
fromthe minimalspringvalues. This riseoccurredduringboth 1939 and 1940,
and in spiteofabsorptionby diatoms. Inflowwaterand littoralmudsmustbe
regardedas probablesourcesof this silica.
A considerationofthe nitrogenrelationships(Fig. 13) showsthat ammonia
productionduringstage II is much greaterthan the equivalent amount of
be producedby the mud. Under
nitratereduced. A large part musttherefore
oxidizingconditionsonlytracesofammoniaare foundin the waterand during
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
304
Exchange of dissolvedsubstancesin lakes
no largeincreaseoccurredbeforeAugustwhenthe
thermalstratification
ironhad appeared
had fallento a lowleveland ferrous
oxygenconcentration
(ammoniaoxidation)occurs
in the water.This suggeststhat nitrification
to anygreatextentin thewater
forifit occurred
mainlyat themudsurface,
i.e. if ammoniaweregivenofffromthe mudand
duringwintercirculation,
oxidizedin the water,it would be expectedthat ammoniawould have
of thermal
rightfromthe commencement
accumulatedin the hypolimnion
Theview
time.
this
at
commenced
as
nitrate
reduction
especially
stratification,
by
is
supported
nitrification
of
seat
main
the
is
surface
mud
oxidized
thatthe
that
was
found
it
which
in
here,
not described
the resultsof experiments,
additionsofammoniato naturalwatersin vitrowerenotoxidized,but that
mudwere
ifsmallamountsofsurface
occurred
nitrateproduction
considerable
maybe takenas a faircomparison
added. If theperiodOctoberto November
to thewater
withAugust,it appearsthattherateofsupplyofsalinenitrogen
(August)thanas
is muchgreaterin theformofammoniaduringstagnation
and thistakesno accountof
(October-November),
nitrateduringcirculation
to an increasein
attributed
be
must
increase
winter
of
the
part
thefactthat
that,under
This
suggests
1939).
nitratecontentof inflowwater(Mortimer,
into
diffusing
ammonia
at the mudsurface,not all the
oxidizingconditions
surfaceis oxidized,butthata largepartmustbe adsorbed.
themiiud
maybe derivedfroman analysisoftheincreasesin
Furtherinformation
stratification
thermal
during
observed
('totalsalts')andalkalinity
conductivity
(Fig. 14). In mostnatural
decreasesat the overturn
and the corresponding
watersonlya portionofthecations(bases)is balancedby availablemineral
acidanions(-C1, 3S04,-NO3,TPO4,etc.).Thisportionwithequivalentanions
the'neutralsaltcontent',bearingin mindthatin mostwaters
maybe termed
dissociated.Bases in excessof this
dissolvedsalts are almostcompletely
ormorecommonly,
withcarbonate,
to be combined
portionmaybe considered
thatmeasured
Theamountofthis'excessbase' is approximately
bicarbonate.
It is clearthatpartoftherisein alkalinity
determination.
by thealkalinity
ofEsthwaiteWatermusthavebeendueto theincreasein
in thehypolimnion
to be intheformofbicarammonia
(whichmaybe considered
and
ferrous
iron
as well. In orderto
of
ferric
hydroxide
bonates)and possiblyto thepresence
as
(expressed
howlargethispartis, thetotalcontentofalkalinity
determine
m.
in gram-equivalents
persq.
ironand ammonia,
CaCO3),totaliron,ferrous
m.,have beenplottedagainsttimein Fig. 14.
forthewatercolumn9-5-13-5
(1936)thata part
it waspointedoutbyRuttner(1921)and Niumann
Further,
of a wateris due to substancesproducing
of the electricalconductivity
to the 'neutralsalt content'.By
the otherpartbeingattributed
alkalinity,
it
value(assuming
of
equivalent' thealkalinity
the'conductivity
determining
relative
the
enabled
have
authors
these
all to be due to calciumbicarbonate),
to be assessedfrom
of the alkalinityand neutralsalt fractions
magnitudes
In all watersinwhichbicarbonate
determinations.
andalkalinity
conductivity
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
305
is the main anion (mostfreshwaters)a closelysimilarresultmay be aehieved
by multiplyingthe conductivityby Kitto's (1938) factor,0-63,to convertit
into 'total salt', and comparingthis with alkalinity,both being expressedas
CaCO3. This has been done in Fig. 14 and, as only.a relative comparisonis
requiredhere, 'total salt (as CaCO3)' has been plotted on the same scale of
per sq. m. as alkalinity,iron,etc.
gram-equivalents
Comparisonsyieldthe followinginformation.'Total salt' minus-alkalinity
(line A - B) representsthe equivalent contentof the 'neutral salt fraction'.
Bearing in mindthe limitationof this comparison,no markedchange in the
' neutralsalt content'is apparentthroughoutthe wholeperiodunderreview.
The slightdecrease observed duringthe stagnationperiod may have been
partly due to the fact that the alkalinityvalue may have included some
substances,e.g. ferrichydroxide,in precipitatedor unionizedcomplexform,
not includedin the conductivityvalue, and partlydue to sulphatereduction
and precipitationas ferroussulphide.
The line B - (C + D) representsthe alkalinityequivalent with the equivalentsof total ironand ammoniasubtracted.The markedrise shownby this
line after13 Julymusthave been theresultofthe additionofbases otherthan
iron and ammonia to the water column. The apparent fall after17 August
mightbe attributedto one or both of two causes. Either some part of the
total iron,e.g. precipitatedferriciron,was not includedin the alkalinityvalue,
or bases otherthan ironand ammoniawereremovedfromthe water column.
The possibilityof adsorptionon colloidal ferroussulphideor humus colloids
in wateror mud shouldbe bornein mind. No evidenceis available to showto
what degreethe firstcause may have been operative. If it is assumedthat all
the 'ferrousiron' (line E, Fig. 14) is includedin the alkalinityvalue, but that
ferricironis not,thenthe contentof 'excess base' otherthan ferrousironand
ammonia,line B - (D + E), remainedmore or less constantuntil the middle
ofSeptember,afterwhicha decreaseoccurredat the overturnto a value which
was almostidenticalwiththat on 13 July,beforethe summerincreasebegan.
This markeddecreaseat the overturnis clearlydue to re-adsorptionof bases,
presumablymainlyon the re-oxidizedmud surface.The slow progressivefall
in alkalinityduringthe earlywinterreflectsa changewhichoccurredthroughout the wholeofthe watercolumnand, as the conductivityremainedconstant
duringthisperiod,thisfallin alkalinityprobablyrepresentsfurtheradsorption
betweenalkalinityand conof bases at the mud surface. As the difference
ductivity(A - B) was even greaterat the beginningof June,it may be supposed that this adsorptionof bases proceedsthroughoutthe winter.
The above considerationssuggestthat the sudden increaseof bases other
than ironand ammoniawhichoccurredafter13 Julyrepresentsthe liberation
of an adsorbed store of bases fromthe mud at a time when the adsorbing
agents,possiblycolloidalferriccomplexesin the mud surface,were destroyed
by reduction. It will be rememberedthat other evidence (accelerationof
20
J. Ecol. 29
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
306
Exchangeof dissolvedsubstancesin lakes
oxygendepletionand ironproduction)
suggested
thatthe mudsurfacehad
becomecompletely
reducedon thisdate.
Thefollowing
description
ofeventsinthehypolimnion
ofEsthwaiteWater
maybe advancedas a working
hypothesis
applicableto lakesin whichdeoxygenation
occurs.In theearlystage(I) ofoxygendepletion,
during
whichthe
oxygenconcentration
and the concentration
gradientat the mudsurfaceis
relatively
high,depletion
proceedsat a relatively
highrate.Thisratedecreases
as theconcentration
gradient
at themudsurface
falls.Activenitrate
reduction
occursduringthisstage.The nextstagein reduction(II) is initiatedwhen
ferric
ironis replacedby ferrous
at themudsurface,
whichoccursat a fairly
definite
redoxpotentiallevel (about E7= 0-25V.) and low oxygenconcentration(about05 mg./l.).
Thereduction
offerric
ironresultsinthedestruction
ofinsoluble
ferric
complexes
previously
existing
inthemudsurface,
andinthe
liberation
to thewaterofbases,including
ammonia,adsorbedon thesecomplexes,as wellas ferrous
ironand otherreducingmaterial.The morerapid
spreadofthesereducing
substances
by eddydiffusion
in thewateraccelerates
oxygendepletion.
The depletion
of
slows
as theavailrate, course,
up finally
able oxygendisappears.The removalof adsorbingcomplexesin the mud
surfaceallowsa morefreeexchangeofionsto take place betweenmudand
water. Rise in ionicconcentration
is mainlydue to risein alkalinity.The
concentration
ofionsinthewaterincreases
rapidlyat first(stageII), andthen
moreslowly(stageIII), untiloxygenis re-introduced
intothehypolimnion
at
theoverturn.
If thepotential
fallslowenoughbefore
thisoccurssulphatemay
becomereducedand,ifpH is sufficiently
high,thesulphide
maybe precipitated
as ferrous
sulphide,
whichmaycausea decreasein ironconcentration.
A rapidreversalof thesechangesoccursat the overturn.Iron is precipitated
from
thewater.Insolubleferric
re-form
inthemudsurface,
complexes
muchof the base contentliberatedduringstagnationand rere-adsorbing
an adsorbentbarrierin the sutfacemudlayerto freeexchange
constituting
ofionsbetweenmudand water.Slowadsorption
ofbasesfromthewaterby
thislayercontinues
the winter.At the sametimenitrification
through
of a
portionof the ammoniasupplyfromthe lowermud proceedsat the mud
surface.
bothin EsthwaiteWaterand in
Workdesignedto testthishypothesis
is described
in succeeding
-artificial
mud-water
sections.An attempt
systems
as faras possible,whether
thesedeductions
is madehereto ascertain,
maybe
ofpublisheddata forotherlakes. In one case
confirmed
by theexamination
fora detailed
onlyhave sufficient
physicaland chemicaldata beenpublished
is especiallyvaluableas the lake
to be made. This comparison
comparison
in question,Schleinsee(Einsele& Vetter,1938),is in manywayssimilarto
coincidence
EsthwaiteWater,a factwhichis notso mucha fortunate
as might
at firstbe supposed.The firstauthorhas alreadypointedouttheimportance
of the ironcyclein lakes (Einsele,1938) and has realizedthat oxidation-
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
307
H. MORTIMER
CLIFFORD
reductionprocessesand their influenceon organic productionare best displayed forstudy in lakes representinga transitionbetweenoligotrophicand
eutrophictype and shallowenoughto produceoxygendepletionin the hypolimnion.
The seasonal variationin total contentof certaindissolvedsubstancesin
the wholewatercolumn(0-11 m.) of Schleinsee,1935, computedfromvalues
derivedby inspectionof Einsele & Vetter'gfigures,
has been plotted (Fig. 15)
18
?_
1
StageI
/
\Overturn
StageII
StageIII
0~~~~~~~~~~~~~/3
Z
144
Oxygen
(~~~E7-1lm.
Silicate
12
08
8
\_<
0P
j
~~6oxygen~~Oxygen
1
concentro tion
Fig 1.
2sg/q
oye
chlineeay195.Toalconen
Ap.
June
.o
h
rontntoate
a\
hyol
o Jul
irn,slicae,phspatanammonia
Au.
Sp.
wt
/xetoh
cl
wderes
emlydfrEtwiedt
Fig..
152lise,13.Ttlcotnfio,
yolumnio (0-11in.) above1sql.ofwmda
cnn
Ot i
Pos phopate
)a
h
ae
ta
concentration
siliate phopae
aeleindo amoniae
in thewae
surflarcoatrtesapln sthatifoun,
comparedwithte
isug./sq.,m.uothe sametl scgaie(wihpteexption
ofdin phihosphate)da
bthatn
24 May and 4 Julymust have been the resultof some additionof oxygento
20-2
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
308
Exchangeof dissolvedsubstancesin lakes
As in Esthwaite
fromaboveorbyphotosynthesis.
bymixing
thehypolimnion
aftertheoxygen
ofoxygendepletionoccurred
Water,a markedacceleration
and
in the bottomsample(11 m.) had fallenbelow0 5 mg./l.,
concentration
precededa rapidrisein ironand phosphatecontentand the
thisimmediately
appearanceof ferrousironin the water.The slow springrise in ammonia
was notobservedin EsthwaiteWater,
in Schleinsee,
whichoccurred
content,
but a markedincreaseduringAugust,risingto a maximumin September,
was about50 % higherin
in bothlakes.Total ammoniaproduction
occurred
ammoniaand alsosilicaexhibited
ofiron,phosphate,
Thecontents
Schleinsee.
similarto thatobservedin EsthwaiteWater.
a markedfallat the overturn
by Einsele& Vetterto
Decreaseof silicaduringthe springwas attributed
between
difference
The mostimportant
diatomgrowthin the epilimnion.
and EsthwaiteWaterconsistsin thehighercalciumcontentofthe
Schleinsee
is abouttentimesthatin EsthwaiteWater.
in Schleinsee
former.Alkalinity
is also aboutten
production
in Schleinsee
It willals? be notedthatphosphate
is onlyaboutone quarterof,thatin Esthwaite.
times,whileironproduction
may be correlatedwiththe highercalciumcontentof
These differences
Schleinsee. (For convenienceof plotting,phosphate is shown as P205 and
by 0 44 reducesthese
scalesin Figs. 12 and 15. Multiplication
on different
values to P.) Thus the Fe: P ratio in Schleinseewas about 8: 1, while
in EsthwaiteWater,taking1939valuesnotshownin Fig. 12, the ratiowas
about200: 1.
and a simultaneous
A striking
increaseof alkalinityin the hypolimnion
theperiodofthermalstratification.
during
occurred
decreaseintheepilimnion
precipitation
biochemical
thesechangestoresultfrom
Einsele& Vetterconsider
ofexcess
inthepresence
andre-solution
intheepilimnion
ofcalciumcarbonate
in thewholewatercolumn(not
The totalalkalinity
C02 in thehypolimnion.
sharpfallat the
exceptforan unexplained
here)showedlittlevariation
figured
as a resultof
Thusa releaseofadsorbedbasesto thehypolimnion
overturn.
The
the reductionof ferricadsorbingcomplexescannotbe demonstrated.
was
approximately
Water
dueto thiscausein Esthwaite
increasein alkalinity
with
m. (Fig.14). It is possiblethatthisamountis correlated
0 5 g.-equiv./sq.
adsorbing
or morecloselywiththeamQuntofferric
thetotalironproduction
so thatthe equivalent
materialpresentin themudsurfacebeforereduction,
m. In any
amountliberatedin Schleinseemaybe lessthan0 5 g.-equiv./sq.
inthatlake,
case thisamountmakesup onlyabout3 % ofthetotalalkalinity
couldnotbe detected.
duetobaseliberation
andthismayexplainwhyan effect
Japaneselakes,inwhichthemasking
Froman extensive
studyofbase-poor
(1932a, b)
is absent,Yoshimura
ofhighalkalinity
inSchleinsee
observed
effect
observedin thehypolimnia
in alkalinity,
thattheincreases
has demonstrated
couldbe accountedforby
occurred,
ofthoselakesin whichde-oxygenation
not
increases
in Fe, Mn,Ca and otherbases.Theincreasein Ca wasconsidered
ofCaCO3fromhigherlevels,butto 'someother
to be due to theprecipitation
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
309
cause'. The descriptionof eventsin EsthwaiteWater suggeststhat this cause
was liberationof adsorbedbases fromthe reducedmud surface.
Furtherevidenceofsimilarityin the developmentofde-oxygenation
in the
hypollmniaof widelyseparatedlakes is affordedby computations(resultsnot
given in detail) of the total oxygendepletionrate in those lakes, forwhich
oxygen data have been publishedin sufficientdetail, e.g. Wisconsin lakes;
Mendota,Long Lake, RainbowLake (Birge& Juday,1911),Schleinsee(Einsele
& Vetter,1938) and Waskesiu (Rawson, 1936). These computations,compared
withthoseforEsthwaiteWater 1939 and 1940, show that althoughconsiderable variationsin the depletionrate occurred,therewas in all cases a general
tendencyforthe depletionrate to decreaseas the oxygenconcentrationofthe
bottomsample (usually 1 m. fromthe mud) fellfromabout 5 to about 1 mg./l.
This was probably due to the decrease of the oxygen gradientat the mud
surfaceand was equivalentto stage I, alreadydescribedforEsthwaiteWater.
This stage was followedin all cases by one of acceleratedoxygendepletion
(stage II). It has been suggestedthat this is the result of the liberationof
reducingsubstancesfromthe mud surface,afterit has become reduced,and
the increasein the rate of spread of these substancesunder the influenceof
eddy diffusion.
Aftercompletionof this manuscript,an importantcontributionto the
study of stratifiedlakes has appeared (Hutchinson,1941). Althougha fuller
discussion of this paper must be postponed, it is clear that Hutchinson's
in Linsley Pond is in many
descriptionof the developmentof stratification
ways similarto that givenforEsthwaite Water.
(c) Eventsunderice
Conditionsunder ice provide opportunitiesfor testing some of the deductions arrived at earlier. It was suggestedthat turbulencein the hypolimnionwas induced chieflyby wind action. As this is absent under ice, it
coefficient
A wouldbe lower,that the
may be expectedthat the eddy diffusion
spread of substances derived fromthe mud would be slower and that deoxygenationwould be confinedto a narrowerzone than was the case during
the corresponding
periodofsummerstratification.An examinationofFigs. 4-9
forEsthwaiteWater 1939-40 showshow farthese expectationswererealized.
During 7 weeks under ice, reductionat the mud surfacehad not proceeded
as far,and the spread of ironand ammoniain the waterwas not as extensive
as during the first7 weeks after the commencementof summerthermal
at the end of May. The redox potentialat the mud surfacefell
stratification
only to E7=049 V. and nitratewas not appreciablyreduced. A comparison
of Fig. 7 withotherfiguressuggeststhat the rise in conductivitywas greater3
relativelyto other dissolved substances,duringthe ice period than during
June.Thereis some evidencehowever(Table 2) that not all thisincreasecould
be attributedto the mud. The only explanationthat can be offeredforthe
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
310
Exchangeof dissolvedsubstancesin lakes
factthattheoxygenconcentration
was apparently
lowerand concentrations
ofotherdissolvedsubstances
wereapparently
higheron 27 Januarythanon
5 February,
in all samplestakenbetween11 m. and the bottom,is thatan
errorin depthdetermination
occurred
on theformer
date.
The conclusions
in thepreceding
paragraphmaybe substantiated
by the
calculationofA usingmethods
indicatedpreviously.EstimatesofA in both
in
EsthwaiteWaterand BlelhamTarn 1940 (in whichlake the findings
EsthwaiteWaterwereconfirmed)
are summarized
in Table 2. Resultsfor
Schleinsee
from
dataobtainedbyinspection
ofEinsele& Vetter'sfigures
(1938)
have beenincludedforcomparison.
Table2. Estimates
oftheeddydiffusion
coefficient
(A x 100)in lakes
undercoverofice
Lake
EsthwaiteWater
Bottom (m.) at samplingstation...
14 0
Year.
...
...
1940
Period .
22. i -22. ih.
..
...
...
13
...
Depth of estimation((m.)
Data employed:
Ammoma
Total iron
Conductivity
Phosphate
Alkalinty
Temperature
Blelham Tarn
13 2
1940
6. i.-20. ii.
12
Schleinsee
11 6
1935
15. i.-15. nI.
11
Mean values of A x 100 forperiodunderice
,
I
05
1-8
0-8
0-6
1-4
1-2
1.0
1.0
05
1.0
thehighvalue derivedfromconductivity
Ignoring
data,whichmayhave
been the resultof a conductivity
increasefroman unknownsourcein the
water,the meanforEsthwaiteWatermay be taken as 5 x 10-3. This is
aboutone-sixth
ofthatfoundat a similarlevelduringsummer
stratification
of molecular
(Table 1), but is stillover200 timesas greatas the coefficient
diffusion
andaboutfourtimesas greatas molecular
heatconduction
in water.
This indicatesthat convection
currents
preventcompletestagnationunder
ice. The distribution
oftemperature
(Fig. 3) and thefactthatthe mudwas
at a highertemperature
consistently
thanthewaterjust overit,suggestthat
theheatgivenoffto thewaterby themudmaybe responsible
forsuchslow
convection
currents.
Thisheat represents
that storedby the mudsincethe
and possiblyalso someheatproducedby organicdecomposition.
A
summer,
morerapidloss of heat fromthe mud duringthe autumnis prevented
by
slowconduction
inthemud(cf.Birgeetal. 1928). Othersuppliesof
extremely
heatmaybe neglected.It is hopedto discussthissubjectin moredetailin a
latercommunication
in prep.I).
(Mortimer,
It willbe notedthat A in BlelhamTarn is appreciably
higherthan in
lessthan
A underice is notsignificantly
EsthwaiteWater.Alsoin Schleinsee
No
can be
thatin thehypolimnion
Table
duringAugust(cf.
1).
explanation
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
311
H. MORTIMER
but in Blelham Tarn it was noted that
offeredat presentforthis difference,
numerouslarge marsh gas bubbles collectedunder the ice, especiallyin the
neighbourhoodof the inflowstreams,but also in the middle region at the
samplingstation. It is probable that turbulenceassociated with the rise of
to increase A significantly(cf.
these bubbles to the surfacewas sufficient
Rossolimo& Kusnetzowa,1934). The organiccontentof Blelham Tarn mud is
appreciablyhigherthan that of Esthwaite Water (Misra, 1938), but it seems
increasein heat of deproducesa sufficient
doubtfulwhetherthis difference
compositionto affectconvectioncurrentsabove the mud significantly.
The rise in concentrationof certain solutes observed in the water just
under the ice is of interest(see Figs. 4, 7). To determinewhetherthese had
been eliminatedfromthe ice duringthe freezingprocess,blocksofice werecut
out with a narrow-bladedsaw, commencingthe cut in a hole bored with a
brace and bit. The blockswerewashedwithdistilledwaterand meltedin clean
Table 3. Dissolvedcontentof (a) ice, (b) waterjust belowice and (c) water
at 5 m. depthin EsthwaiteWater,12 January1940
Results of chemicalanalysisexpressedin mg./l.of water.
41
(a) Ice (molten)
A
Water
_
Lower cloudy
layer,con(b) Immediately
Upper clear
tamingbubbles
underice
layer
1*4
Assumedto be 0
Temperature,? C.
Dissolved oxygen,mg./l.
10 0
14*3
5.3
Dissolved oxygen,% saturation 35
68
103
4
3
75
Conductivity(K18x 10-8)
0*7
15-6
05
Alkalmity(CaCO3)
0.01
Colour (arbitraryunits)
None
None
0.10
Ammonia(NH3)
None
None
Nitrate(NO3)
None
None
1*4
9-3
None
None
Sulphate (SO4)
0*24
None
None
Iron (total Fe)
6.9
6*0
pH
A
(c) At 5 m.
depth
3-9
11.5
88
65
13-6
0 01
0-06
1-2
8-8
Trace
6-8
blocks were washed,
Pyrex vessels. For 'dissolved' oxygen determinations,
dried and meltedundermedicinalparaffin.To obtain an undisturbedsample
of water fromjust underthe ice some distancefromthe hole, a rubbertube
about 2 m. long,one end ofwhichwas mountedin a cork,was insertedthrough
a small hole in the ice. The corkwas designedto floatthe end of the tube up
against the lowersurfaceof the ice some distancefromthe hole. The sample
was then sucked throughsamplingbottlesby means of a bicyclepump with
in the next section.The resultsare summarizedin
reversedvalve, as described,
Table 3.
The removalofdissolvedsalts fromice on freezingwas therefore
practically
complete.These salts accumulatedin the waterjust underthe ice. From its
chemicalcompositionthe watexobtainedfromEsthwaiteice would be classed
as good quality distilledwater. It is probable that the oxygenfoundin the
ice was not in truesolutionbut entrappedin the formofbubbles,whichwere
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
312
Exchange of dissolved substances in lakes
seento have accumulated
in the lowercloudylayer.The pH (6.0) in water
derivedfromice meltedunderparaffinsuggeststhat some CO2 was also
retained.
II. CHANGES IN REDOX POTENTIAL AND IN CONCENTRATIONS OF
DISSOLVED SUBSTANCES IN ARTIFICIAL MUD-WATER SYSTEMS,
SUBJECTED TO VARYING DEGREES OF AERATION
It was suggested
in thepreceding
sectionthatchangesin redoxconditions
at ornearthemudsurface
dccurring
during
ofthehypolimnion
de-oxygenation
in lakesareassociatedwithand probablycontrolmarkedchangesin therate
of exchangeofionsbetweenmudand water.The following
was
experiment
to studythesechangesmorecloselyin 'artificial
designed
lakesystems'under
laboratory
control.
METHODS
AND EXPERIMENTAL
PROCEDURE
SeveralPetersen
mudweretakenfrom
grabsamplesoftypicalWindermere
about 30 m. depthoffWrayCastleBoat House. The surfacebrownlayer
ferricironwas scrapedoffand kept separatelyfromthe lower
containing
reduceddarkgreymud,whichwas stirredto obtaina uniform
sampleand
thenpouredinto threeglass tanks (rectangular
batteryjars, 15x 20 cm.,
25 cm.deep)to a depthofabout3 cm.Thetankswerethenslowlyfilledwith
tap waterwithout
themud.Thesurface
disturbing
werealsostirred,
scrapings
mixedwitha littletap waterand dividedintothreeapproximately
equal
oneofwhichwas addedto thewaterofeachtankin sucha waythat
portions,
an evenlayerwas depositedon themudsurface.In thiswayan attemptwas
madeto imitatea naturalmud.The waterin thetankswas siphonedoffand
themudallowedto standexposedto theairforseveraldays. Afterthis,but
it was foundpossibleto runlakewaterintothetanksveryslowly
notbefore,
to a depthof20 cm.(6 1.in all) so thatit remained
clear.Thetankswerekept
inthelaboratory,
exposedto light,butshieldedfromdust.Thetemperature
of
thewaterinthetanksrosegradually,
withslightvariations,
from14 to 20?C.
duringthe courseof the experiment.Afterstandingfora weekto attain
stableconditions,
approximately
the surfacebrown'oxidizedlayer',viewed
theglasssides,was about7 mm.deepin all tanks.The mudsurface
through
showeda tendencyto crumbleand becomedetachedin smallcakes when
instruments
wereinserted
measuring
and removed,
and was notas flocculent
as thenaturalmudsurfacein thelake.
At thisstagea seriesofdeterminations
werecarriedouton all threetanks.
Theresults(zeroonthetimescale,Figs.18-20)showedthatconditions
in each
tankweresufficiently
forthepurposesoftheexperiment.
comparable
Each
tankwas thensubjectedto a different
treatment,
describedbelow,and the
determinations
following
repeatedon all threetanksat intervals.
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H.
MORTIMER
313
Electricalconductivity.With the instrumentand electrodespreviously
described,measurementswere made at various points in each tank, in the
waterand at threedepthsin the mud (0.5, 1P5and 2-5cm.). It was foundthat
horizontalvariationwas negligiblein the waterand small in the mud. Values
givenin Fig. 18 are mean values foreach level. The electrodes,whichwereof
robustpattern,are shownin Fig. 16 C.
Redox potential. Following the potentiometrictechnique employed by
Pearsall & Mortimer(1939), using a saturated KCl-calomel half-celland
saturated KCl agar bridges,redox potential was measured at small depth
intervalsabove and below the mud surfacewith a seriesof brightplatinum
electrodes,the arrangementof whichis shown diagrammaticallyin Fig. 16,
A
hB
|
CX
Hg
a
C
1cm.
Fig. 16. Electrodes for the measurementof redox potential and electrical conductivity.
a = frameof s.w.g. Pt. wire; b = copperlead enclosedin glass tube; c = glass seal around
42 s.w.g. Pt. wire.
and in Fig. 24, ? III. Each electrode consisted of a strip of platinum
foil 10 x 2 mm., welded on to a frameof stout platinum wire of the same
dimensionsforsupport. An efficient
weld was achievedby hammeringthe red
hot pieces of metaltogetheron a carbonblock. The electrodewas mountedas
shown in Fig. 16B by fusingthe wire into the end of a narrowglass tube
(75 cm. long foruse withthe surfacemud samplerdescribedin the following
section),and internalconnectionwas made witha drop ofmercuryand copper
wire in the normalway. Twelve such electrodeswere arrangedaround cork
centresin sucha mannerthatthe metalblades radiatingfromthe centrecame
to lie at fixeddepth intervalson a descendingspiral, as shownin Fig. 16A
and Fig. 24, ? III. Thus, when this 'compound electrode' was lowered
verticallyinto the mud, the electrodeat each level cut edge-on into mud,
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
314
Exchangeof dissolvedsubstancesin lakes
may
bythepassageoflowerelectrodes.Each electrode
whichwasundisturbed
the meanpotentialof a panel 2 mm.deep at the
to register
be considered
were
depthto whichit is lowered.Thedepthsusuallychosenformeasurement
50, 10 and 1 mm. above and 1, 2, 3, 5, 7, 10, 13, 16, 19 mm. belowthe
in thenextsectionon lake muds
mudsurface.For measurements
described
in situinthesampling
foursimilarelectrodes,
mudsampler,
tubeofthesurface
levels,wereaddedto thesystem
whichcouldbe readilyadjustedat different
Thesewerearranged
depthsbelowthemudsurface.
at greater
formeasurements
of the
to slideup and downin holesin the corkcentres.The arrangement
is shownin Fig. 24, ? III. The copper
electrodesforthesemeasurements
depthon a celluloid
was fixedin orderofelectrode
lead fromeach electrode
terminal
by
withthepotentiometer
strip,and couldbe selectedforconnection
meansofa cliplead.
Both in naturalmuds(see nextsection)and in mudsin the tanksthe
Usuallya
thefirst
hourafterinsertion.
potentials
fellrapidlyduring
electrode
wasobserved
drift
fairly
steadystatewasreachedafter1-2hr. A slownegative
overa periodofdays. Potentialvaluesgiveninthisandthenextsectionrefer
pH were
to measurements
made2 hr.afterinsertion.Eh and,wherepossible,
recordedand all potentialswere reduced to a comparativebasis of E7, i.e.
a risein onepH unitto be equivalentto a decrease
Eh at pH 7*00,assuming
in volts,was chosen
of58 mV.(cf.Pearsall& Mortimer,
1939). E7,expressed
in preferenceto E5 (cf. Pearsall & Mortimer,1939) as 7 00 was nearerthe
the
actual pH of the mediainvestigated.Aftereveryfewdeterminations
themin a wellmixedsampleofreducing
electrodes,
weretestedbyimmersing
on all electrodes
mudofsufficient
volumeto coverthemall. Usuallyreadings
ofsingleelectrodes
behaviour
agreedtowithin+ 10 mV. Occasionalanomalous
in prep.V), in which
willbe discussedin a futurecommunication
(Mortimer,
andpH in lakemuds
and interpretation
ofredoxpotentials
themeasurement
oftheaboveorderwasnotobtained
willbe dealtwithmorefully.If agreement
acid and rinsedwell.
the electrodes
werecleanedwithdichromate-sulphuric
in distilled
water.
werekeptimmersed
Betweendeterminations
theelectrodes
methodof
It is probablethat the mostsatisfactory
pH determination.
pH at smalldepthintervalsabove and belowthe mud surface
measuring
ofsuitable'micro'pattern.In theabsenceof
wouldbe witha glasselectrode
methodusedfor
ofthequinhydrone
a modification
thenecessary
equipment,
ofthismethodto muds
soilswasemployed.A criticalstudyoftheapplication
characters
of mostof
showedthat,owingto the reducingand unbuffered
it was necessaryto maintainthe mud/quinhydrone
the mudsinvestigated,
results. Even so, the
ratio withinnarrowlimitsto obtain reproducible
results
which
were
normally
onlyreproducible
techniqueproduced
following
5 c.c.ofmud
onthesamemudsampleto within041pH unit.To approximately
waterandfrom30 to 50 mg.quinhydrone
an equalvolumeofdistilled
roughly
was added in a glass dipper.The mixturewas shakenand the potential
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
315
measuredin the usual mannerafter2-5 min. Difficulty
in the measurementof
pH in lake mudsby the quinhydronemethodwas also experiencedby Karsinkin & Kusnetzow(1931). Howeverno advantagewas discovered,in thepresent
work,in employingthetechniquesuggestedby them,namelythe measurement
of the potentialin the supernatantliquid afterthe quinhydrone-mud
mixture
has been allowed to settle.
ExtremelyhighapparentpH values (between8 and 9) werefoundwiththe
quinhydroneelectrode at the oxidized surface of some muds. These were
almost certainlyanomalous and probably due to the presenceof manganic
compounds. Such compoundsin soils (Wright,1939) are reduced by quinhydroneto manganoushydroxidewhichraisesthe pH. In these cases the pH
ofthe mud was eitherassumedto be the same as that ofthe waterjust overit,
or colorimetric
determinations
were made withindicatorsin 0 5 % agar. This
methodwill be describedlater (Mortimer,in prep. V).
In the workon coresofnaturalmudsdescribedin the nextsection,pH was
determinedon samples obtained by slicingthe core up into layers,usually
approximatelyat centimetredepthintervals.The samplefromeach layerwas
well mixed and its pH value was taken to be the mean value forthe depth
panel concerned.From this data, the probablepH at the depthsat whichEh
had been made was determined
measurements
-bygraphicalinterpolation.The
probableE7 value was thencomputedand the resultexpressedto two figures.
A considerationof the reproducibilityof Eh and pH values shows that in
manycases it is doubtfulifthe secondfigureis significant.Even so the results
are sufficiently
accurate for the purposes of this paper, as the range of Eh
values encountered
was large. pH in thewaterwas determinedcolorimetrically.
Duringthe experimentdescribedin this sectionit was not possibleto remove
samples of the mud forpH determination.Determinationsmade with the
quinhydroneelectrodeat the end of the experimentshowed that the mean
value of the surfaceand lower mud in the aerated tanks was 6-3 and 6-4
respectively,while in the anaerobic tank the equivalentvalues were 6-6 and
6-7. These pH values were employed to calculate a probable E7 value at
different
depthsin the mud throughoutthe courseof the experiment.
Chemicalanalysis was carriedout on samples of water removedfromthe
tanks immediatelyafterdeterminationsof redox potentialand conductivity
had been made. The samplingarrangementemployedconsistedof a glass tube
supportedwithone end an inch or so above the mud surface.This lowerend
was turnedup to avoid disturbanceof the mud duringthe samplingoperation.
The tube was connectedby rubbertubingthrougha tap to (1) a 125 c.c. bottle
of the type used for oxygen determination,(2) a 50 c.c. flaskfor C02 determination(describedbelow) and (3) a bottle of 400 c.c. capacity,in that order
in such a mannerthat, whenthe systemwas partiallyevacuated by means of
a bicycle pump with reversedwasher, water was sucked firstthroughthe
oxygen bottle and then throughthe C02 flask,expellingthe air in both of
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
316
Exchangeof dissolvedsubstancesin lakes
thesein theprocess.The tap was keptcloseduntila slightvacuumhad been
therewas
createdin the systemby a fewstrokesof the pump. Otherwise
until400c.c.
themudsurface.Waterwassuckedthrough
dangerofdisturbing
had arrivedin the last bottle.The tap was thenclosedand the apparatus
oftheoxygenbottleand C02
In thiswayan adequateflushing
disconnected.
weretreatedintheusual
flaskwasensured.Samplesforoxygendetermination
according
withbromine,
tankbeingpre-oxidized
theanaerobic
way,thosefrom
(Ohle,1936b). Duringthelatterstagesof
procedure
modified
to Alsterberg's
ofsolutesintheahaerobictankrosesufficiently
concentration
theexperiment,
to be carriedout on smallersamples.
to enableall determinations
made on the samplein the largerbottleare listedin
The estimations
orthose
wereeitherstandardmethods
employed
Figs.19 and20. Themethods
section,withthe exceptionof 'oxygenabsorbed
describedin the preceding
on a 50 c.c. sample,to which
whichwas determined
frompermanganate'
5 c.c. N/80 KMnO4 and 5 c.c. 25 % H2SO4 had been added, and which was
incubatedat 400 C. for4 hr.
of standard
by a modification
Dissolvedcarbondioxidewas deterrmined
with
(titration
procedure
standard
in
principle,
simple
Although
procedure.
of
difficulty
the
involves
standardalkalior carbonateusingphenolphthalein)
of atmospheric
C02. In the nmethod
withoutintroduction
adequatestirring
vessel.The standard
adoptedherethesamplingvesselwas also thetitration
with
weighted
alkaliwasweighted
withGlauber'ssaltandthephenolphthalein
of Maucha(1932).The samplingand
to theinstructions
according
glycerine
wax (p in Fig.
titration
flaskwas preparedas follows:Pure moltenparaffin
flaskand
in thebottomofa 100c.c. volumetric
17 A) was allowedto solidify
(g),wereembeddedin thewax
as baffles
stripsofglass,designedto function
in themannerindicated.Afterthesamplehad beenobtainedin themanner
describedabove, a portionwas removedby pipetteforpH determination,
was added.
leaving50 c.c. in theflaskto which10 dropsofphenolphthalein
shownin Fig. 17A, withthe
was carriedoutwiththearrangement
Titration
underthe surfaceoftheliquid.The bulb (b) on
tip oftheburetteextension
ofthe
belowthesurface
ensuredthatall thealkaliwasdelivered
thisextension
sampleand thatnonecollectedon the side ofthe neck. Due to its greater
densitythealkalisankto thebottomoftheflask.Rotationoftheflaskwith
mixingof the
the neckheld betweenthe handsensureda rapidthorough
heavierreagentsand thesamplewithoutundueagitationofthesmallsurface
to
necessary
exposedto theairin theneckoftheflask.It was notconsidered
thiscouldbe donein cases
although
paraffin,
withmedicinal
coverthissurface
in thecomby similarmethods
to carryouta titration
in whichit is required
pleteabsenceofair.
seriesofdeterminations
thepreliminary
After
Further
treatment
ofthetanks.I
in
all threetanks,each
identical
shown
conditions
were
had
that
practically
aeratedtank',was
was subjectedto different
treatment.One,the'artificially
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
317
subjectedto continualaerationby meansofthe apparatusshownin Fig. 17 B.
The wide tube (a) was adjusted at such a heightthat, when suctionfroma
filterpump was applied at b, waterwas sucked up fromthe tank throughthe
tube c of 4 mm. bore. This continueduntilthe level of waterin the tank had
to admit air throughc. In this way the partial vacuum
fallen sufficiently
inside a was destroyedand the water began to flowback to the bottomofthe
tank throughtube d of 2 mm. bore. The waterlevel in the tank of courserose
at the same time, but an intervalelapsed beforestable conditionswere reestablishedat the lowerend of c, so that in practiceair continuedto bubble
throughthe water in a and no water was sucked up until a was practically
empty.The rate ofthiscontinuousaerationand circulationcould be variedby
varyingthe suctionof the filterpump.
of 'artificially
Fig. 17. Titrationflaskforcarbon dioxide determinationArrangement
aerated' and ' anaerobic' tanks. w =paraffinwax; I = liquid paraffin
A second tank ('aerated tank') was allowed to stand with the water
surfaceexposedto the air. All threetankswereshieldedfromdust The water
surface in the third tank ('anaerobic tank') was covered with medicinal
paraffinto a depth of about 2 cm., aftera wide glass tube had been fittedas
shownin Fig. 17 C to act as a shaftforthe insertionof measuringinstruments
and samplingtube into the tank withoutbringingtheminto contactwiththe
liquid paraffin.Aftermeasurements,the water level in the shaftwas raised
by suction until all the air was withdrawn;the tap was then closed. Just
beforeeach series of measurements,air was admittedto the shaft and the
water level was allowed to fall graduallyin order not to disturbthe mud
surface.The rubberbungwas thenremovedand electrodesinserted.Naturally
some air was introducedduringmeasurement,but this did not disturbthe
course of the experiment.More serioustroublewas encounteredwhenit was
discoveredthat the liquid paraffinlayer was not an effectivebarrierto the
diffusionof atmosphericoxygen. It was found necessary to employ an
done by runningmolten
wax. This was conveniently
additionalseal ofparaffin
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
318
Exchange of dissolved'substances in lakes
wax downa widegentlyinclinedplaneofcardboardon to thesurfaceofthe
liquidparaffin.
Moreviolentpouringcausedthewax to plungedownintothe
solidcrustofwax,whichformed
waterandsolidify
thereinlumps.Thissurface
be made to
of gases,could sometimes
an effective
barrierto the diffusion
but
duringsamplingand measurement,
followchangesin level occurring
cracksoftendevelopedand thewax had to be removedand thecrustrecast.
RESULTS
in Figs. 18-20,in whichconcentrations
ofdissolved
Resultsarepresented
in the waterare plottedagainsttime. Redoxpotentialand consubstances
in depth-time
on the same time
diagramas
ductivitydata are incorporated
in thefigures
areexpressed
in the
recorded
as mg./l.
scale.Theconcentrations
forchangesinrelativevolumeof
actualsample.Theyhavenotbeencorrected
fromtheremovalofsamples.It is clearthata part
waterand mudresulting
intheanaerobictank,fromwhich
oftheincreasein somedissolvedsubstances
moresamplesweretaken,was due to the decreasein watervolume.As the
was to detectlargequalitativedifferences
between
purposeoftheexperiment
has been made forthis. If the
aeratedand anaerobictanks,no correction
forvolume,it is by no meanscertainthat the
resultshad been corrected
valueswouldbearanyrelationto naturalratesofproduction,
as it
corrected
theconcentration
ofanyoneioninthewaterrepresents
is notknownwhether
the wholemud+watervolume,or an
concentration
a uniform
throughout
betweenmud and water,whichis maintainedirrespective
of
equilibrium
For
estimations
in
the
water.
of
the
natural
ionic
production
volumechanges
withlargertanksand witha deeper
ratesoflake muds,similarexperiments
in orderthatthevolumeofwaterremovedin the
layerofmudare necessary,
to the totalvolume,and thatthe prosamplemaybe smallin comparison
ductionofionsby themudshallnotbe limitedby shallowmuddepth.
aeratedtank' havebeenomittedhere,as they
Data fromthe 'artificially
wereverysimilarto thoseobtainedinthetankwhichwasaeratedbyexposure
wasthatthechangesoccurring
in both
to theair.The onlymarkeddifference
the
in
aeratedone. It therefore
tankstook place morerapidly
artificially
to maintainfullyaerated
weresufficient
appearsthat convectioncurrents
tank('aeratedtank' in Figs. 18-20).
in thestanding
conditions
in (a) theaeratedtank.Isovoltsare drawnin Fig. 18 for
Redoxconditions
intervalsof0-06V. The depthoftheisovolt(E7=0024V.)-thick linein the
with the lower limit of the surface
corresponded
figure-approximately
'oxidized layer', containingferrichydroxide,as viewed
chocolate-brown
withthefinding
ofPearsall&
thesideofthetank.Thisis inagreement
through
ironreplacedferricif the redoxpotentialfell
Mortimer
(1939)thatferrous
belowthislevel.The depthoftheisovoltE7= 024 V. belowthemudsurface
to register
ofthe oxidizedsurface
be considered
thethickness
maytherefore
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
319
HI. MORTIMER
~~~~~~~o~~~~~~~~~c
a9
O
I~~~~~~~~~~~~~~~~~~~c
o
Ca
o
Ca
Ca
l0
0
-c~~~~~~~~~
cc
~ ~
0
o
T II
III
I
I,
~~-=
L~~~~~~~~~~~~~~
~~ ~ ~ ~
C)
~
OCf%'.00%
~
~
0C
C)
~
l
p0j,JQJ
0~~~~~~~~~~~~~~~~~~~~~~~~~~~04..
C-~
~
~~~~~~~~~~~~~~~~~.1
~
~
~
C>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~c
CI
~~~~~
I
I
I>(>
0
JA,
~~~~~~~~~~~~4
C)~
0~~~~~~~~~~~~~~"
C
AlVQJM
uinsptu0ql0
0
-
E-i
?
0~~~~~~
~~~~~~~~~~~~~~~~~~~
0
PA
~~ ~ ~ ~ ~
I4hr
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
~
C
P
co~~~~~~c
Exchange of dissolvectsubstances in lakes
320
CN
It
CO)
%
co
4
pq
0
P4
-4
PA
Ca
0
Ca
CN
.,Ca
>
W)
Ca
4
Ca
Ca
Hd
CN
anoloo
CV
Ca
paqiosqu uo2f.,xo
CN
I- !i
CN
C
0
A,:tTATjonpuo3
O/
co
uoavd9uvjL
P-1
x
C)
CN
W)
E.
0
P-1 Ca
0)
0 .0
C)
Ca
W)
bD
cn
cn
2
Ca
W)
>
Ca
P-1
0
Pr4
cn
CN
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Ca
CLIFFOR.DH.
321
MORTIMER
bi)~~~~~~~
0'
2'
1
0(
\
0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~C1
~~~~~~~~~~~~~~~~~~0~~~(
N~~~~~~~~~~
i~~~~~~~~~~~~~~~~
*
0
Cu~~~~~~~~~~~~~~~~~~C1
Cu~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Nc
ci
Cul
0%
c'c
C
u
I
0
e
I ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I
Cu~~~~~~~~~~~~~~~~~~~~~~
CZ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~C
o
cn
1
1
-0
Cu~~~~~~~C>
4
C
0~~~~~~~~0C
CZ
~
0
~
~
~~~~~~~~~~~~~~~~~
C
0
aq
'C'~~~~~~~~~~~~~~~~~~1
J. Ecol. 29
21
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
322
Exchangeof dissolvedsubstancesin lakes
layer. In the aerated tanks this graduallyincreasedduringthe course of the
experiment.
(b) The anaerobictank. Fromthe timewhenthe tank was effectively
sealed
fromthe atmosphereby paraffin
wax (27 days), the isovoltE7 =0-24 V. began
to rise to the mud surface,reachingit at 70 days, at which time the mud
surfacehad considerablydarkenedin colour and the dissolvedoxygenin the
water had disappeared. Previouslyto this, nitratehad become completely
reduced in the water (51 days) and the ammonia concentrationhad begun
to rise(Fig. 20); at this time the potentialin the water was approximately
betweenthe markedverticalstratification
of redox
E7-036 V. The difference
in
the
mud
and
is
potential
in thewater striking.
the lack of suchstratification
The potential values at 50 mm. above the mud surfacehave been omitted
fromthe figureas they were almost invariablythe same as those found at
+ 10 mm. This difference
may be consideredto be due to the fact that much
of thereducingmaterialis in immobileformin the mud and that transportof
dissolved substanceswithinthe mud by moleculardiffusionis slow in comin the water.
parisonwith convectioncurrentsand associated eddy diffusion
Changestn thewateroftheanaerobictank.The mQststrikingresultobtained
duringthe experimentwas the rapid rise in concentrationof iron,ammonia,
silicate, phosphate, alkalimty, conductivityand substances reducing permanganateobservedin the waterofthe anaerobictank, afterthe potentialat
the mud surfacehad fallenbelow E7=024 V., i.e. afterthe oxidized surface
was maintained,althoughfor
layerhad disappeared.This risein concentration
most substancesat a slowerrate, duringthe subsequentcourseof the experiment. As statedearlier,a partoftheconsiderablerisein concentration
observed
in some cases towardthe end of the experimentmustbe attributedto a considerabledecreasein watervolumeresultingfromthe removalof samples.
A moredetailedexaminationof eventsafterthe destructionofthe surface
oxidized layer shows other points of interest.These events also exhibit a
markedparallelismwith those foundto occur duringreductionin the hypolimnionin Esthwalte Water during1939. The rise in ammonia-nitrogen
far
exceeded the equivalent amount produced by nitratereduction,and must
thereforehave originatedfromthe mud. Nitriteappeared in small quantities
duringthe period of nitratereduction,but had disappearedby the time the
potentialin the water had fallenbelow 0 30 V. The rate of increaseof iron,
silicate and phosphate,as well as of substancesreducingpermanganatewas
greatestwhilethe potentialin the waterfellfrom0-18 to 0-12V. Iron, phosphate and manganesecontinuedto increasein concentration
afterthis,whereas
silicateshowedno furtherrise and substancesreducingpermanganateshowed
a decrease All the iron was in ferrousformafterthe potential had fallen
below 0-12V.
During the imtlalstages of the experiment,the rate of increaseof C02 in
the anaerobictank was approximatelyproportionalto the decreasein oxygen
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
323
concentration.This resultmightbe expectedifit is assumedthat most ofthe
oxygenwas absorbedin the oxidationoforganicmaterialand in such reactions
as the productionof ferrichydroxidefromferrousbicarbonate.The slow rise
afterthe disappearanceofthe oxygencannotbe taken as
in C02 concentration
evidence of anaerobic C02 production,as it is probable that this increaseis
due to the accumulationof C02 producedas a resultof the introductionof a
littleoxygenat each seriesof measurements.
A crackwhichdevelopedin the wax seal just before83 days had an interestingeffecton conditionsin the water. The isovolt E7 = 024 V. was pushed
downto the mudsurface,a small amountof oxygenwas detectedin the water,
and traces of mtriteand nitratewerefound.The introductionof oxygenalso
resultedin the oxidation of a large amount of iron,whichwas foundin suspensionin ferricform,resultingin a decreasein transparencyof the water. A
decreasein silicateconcentrationalso occurredat the same time.
The sulphate concentrationbegan to fall slowlyafterthe tank had been
effectively
sealed fromthe atmosphere.This fall may have been due to the
diffusionof sulphateinto the mud and its reductiontherein regionsof lower
potential. Afterthe potentialin the waterhad fallenbelow 0410V., reduction
of sulphate proceededmore rapidly. It had disappeared when the potential
in the waterhad fallento 0-06V. The sharpfall in iron (mainlyferrous)concentration,which occurred at the same time may be consideredto have
the precipitationofferroussulphide.This was associatedwitha
resultedfromn
in
fall conductivityand transparency,and with a sharp rise in ammoniaand
alkalinity.Duringthlsperiodthe mud surfacebecame black,presumablyas a
resultof accumulationof ferroussulphide.
ofthemud tntheanaerobictankrose steadilyduring
Electricalconductivity
the periodof reductionof the mud surface,later risingrapidlyto over 200 at
the mud surface.This rise may have been partly due to the liberationof
adsorbedions as adsorbingcomplexesweredestroyedby reduction.The sharp
fall in conductivitywhichoccurredafterthe maximumat 117 days may have
been the result of the precipitationof ferrousand sulphide ions as ferrous
sulphide. It is also possible that some adsorptionof ions on colloidal ferrous
sulphidetook place.
Conditionsin theaeratedtank. None of the changesdescribedabove were
observedin the aerated tank,in whichthe oxygenconcentrationin the water
remainedhighand the isovoltE7=0024 remainedwell below the mud surface.
Apart froma slightinitialfallin conductivity,a morerapid initialfallin pH,
alkalinity,nitrateand ammonia and a subsequentslow rise in sulphate and
conductivity,little change occurredin the concentrationsof dissolved substances in the water.
21-2
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
324
Exchangeof dissolvedsubstancesin lakes
DIsCUSSION
Changesin the 'aeratedtank' maybe interpreted
as follows:The imtial
fallin alkalinity
was considerably
fallin
morerapidthanthecorresponding
This indicatesadsorptionof bases,of whichammoniaformed
conductivity.
a largeproportion.
Thisresultedin a fall in pH, as the CO2 concentration
remained
fairly
constant.
Thestrongly
adsorbent
oflacustrine
properties
muds,
inthesurface
in commercial
especially
fishlayers,havelongbeenrecognized
pondpractice.Inorganicfertilizers
addedto pondsare strongly
adsorbedon
mudandreleasedto thewaterat a slowrate For instance,
thebeneficial
thke
effect
on the fishcropof limingor phosphatemanuring
in one yearcan be
detectedin subsequent
years(Demoll,1925). Fromtheexperiment
described
hereandalsofromobservations
thewinter
of1939inEsthwaiteWater,
during
is exercisedby the
thereis reasonto supposethat-thisadsorbing
influence
oxidizedmud surface.It is clear that continuousadsorptiona
musthave
occurredin the mudsurfaceof the aeratedtank,forthereis no reasonto
supposethatorganicdecomposition
in themudhad stopped,and thereis no
otherexplanationof the lack of rise of conductivity
in the wholesystem,
themud.
including
The decreasein nitratein the aeratedtank may,at firstsight,appear
as it has beenshownin experiments
surprising,
mentioned
in the preceding
sectionthatnitrification
occursat theoxidizedmudsurface.A similarobservationofthedisappearance
ofnitrateabovepondmudswithoxidizedsurface
was madeby Lind (1940). Someofthemtrateproducedat themudsurface
mustdiffuse
downintothelowermudand becomereducedthere.It maybe
that
suggested
bothin thisand in Lind's experiment,
in whichthe water
volumewas comparatively
small,therateofnitrification
was notsufficient
to
makegoodthelossofnitratefromdiffusion
intoand reduction
in themud.
Theresultsobtainedin theanaerobictankshowthat,whentheconnection
betweenthe mud surfaceand the atmosphere
throughthe wateras interis interrupted,
the adsorbing
mediary
influence
ofthemudsurface(observed
in the aeratedtank)is removed.As events,whichmaybe describedas the
rapidreleaseof adsorbedmaterials,occurredat the timewhenthe isovolt
ironin the
E7= 024 V. had reachedthemudsurfaceand whenall theferric
it maybe suggested
mudhadbecomereduced,
thattheadsorbent
properties
of
the oxidizedmudsurfaceare largelydue to the presenceof colloidalferric
The removalofthesecomplexes
on reduction
complexes.
ofthemudsurface,
to result,notonlyin theliberation
maybe considered
ofadsorbedions,but
alsoina muchlessimpededexchange
ofionsbetween
mudandwater,as shown
rise
in
most
the
dissolved
continued
by
constituents
theinitialrapid
following
hadbecomereduced.Thiscontinuous
risejustafterthemudsurface
production
was ofcourseslower,expressedper
duringthelatterpartoftheexperiment
unitarea ofmud,thanthatindicatedin Figs. 19 and 20. If corrections
had
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
325
moreclearly
beenmadeforchangein watervolume,thiswoulddemonstrate
slowincreasein
the contrastbetweentheinitialrapidriseand thefollowing
concentration
of the adsorbingagentsin the mud
Whilea moredetaileddescription
surfacemustbe leftto futurework,somespeculationas to theirnatureis
complexwhich
thattheadsorbent
permissible.
Mattson(1935)has suggested
It is
is transported
in peatypodsolsis a ferri-silico-humate.
and precipitated
possiblethata similarcomplexexistsintheoxidizedmudsurface.If thisis so,
the risein silica concentration
duringthe periodof reductionof the mud
ofthiscomplex.
to resultfromthe destruction
-surface
mightbe considered
precipitation
of
associatedwithconsiderable
The fallin silicaconcentration
of oxygenthrougha crackin the wax at
ferricironafterthe introduction
83 days,mayhave resultedfromthe re-formation
of thiscomplex,and the
subsequent
rapidrisein silicamayhavebeenproducedwhenthecomplexwas
again reduced No markedincreaseof silica occurredafter110 days The
it mayhavebeen,appearstohavebecomeexhausted.
sourceofsilica,whatever
Mentionshouldalso be madeofthe existenceofferrichydroxide
and ferric
is
phosphate
in theoxidizedmudsurface(cf.Einsele,1938) Ferrichydroxide
adsorbing
probablylargelyin colloidalformand may exerta considerable
at the same timeas
influenceThe sharprise in phosphateconcentration
with
ironin thewater(97-102days)is in agreement
disappearance
offerric
thatlargeamountsof phosphateare boundas
Einsele's(1938) observation
insolubleferricphosphatein the surfaceof oxidizedmuds,and liberatedin
possibly
thatan organicconstituent,
solubleformonreductionThepossibility
ofthehumustype,forms
a partoftheadsorbing
complexin oxidizedmuds,is
ofsubstances
reducing
suggested
bytheriseincolourandintheconcentration
permanganate
whichoccurredin the waterafterthe mudsurfacehad been
reduced.The increasein permanganate
was considerably
greater
reduction
thantheequivalentreduction
due to ferrous
ironcontentalone.
The similarity
of eventsin the waterof the anaerobictank and in the
of EsthwalteWaterhas been pointedout before.Thereare,
hypolimnion
is madebetweenthe
differences.
In Fig 21 a comparison
however,
important
and otherbases (ammonia,
increasein conductivity
('total salts'),alkalinity
iron and manganese)The assumptions
involvedand the methodof conofa similar
struction
ofthefigure
are thesameas thosefortheconstruction
figureforEsthwalteWater(see ? I, Fig 14 and relevantdiscussion).Concentrations
of the substancesconcernedare plottedforcomparisonon a
The differences
betweenthe equivalentsof
commonscale of mg.-equiv./l.
ironetc. are not plottedin Fig. 21 as was donein
conductivity,
alkalinity,
strikingwithoutthis. As in
Fig. 14, as relativechangesare sufficiently
decreased
between'totalsalts' and alkalinity
EsthwaiteWater,thedifference
andthesameexplanation
ofthemudsurface,
forthisdecrease
afterreduction
namely,that it may be partlydue to the reductionof
may be suggested,
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
326
/
Conductivityequivalent or 'total salts'
--
/ \
(K18x 10-6 x 063, expressedas CaCO3)
1*0
I
- i- o Alkalinity
-
'Ferrous'iron
/
I3
/
all except
Total iron,assuming
'ferrous'ironto be trivalent-
/
/
*A Ammonia
0*8
/
* Manganese
o-4
A~~~~~~~
_
A~~~~~~~~~
I'12
2'7
/
6973 83 9970101
394i55
Duration of experimentin days
3
Fig. 21. 'Total salt' and 'excess base' contentof the anaerobic tank, comparedwith the respective contributionsof iron, ammoma and manganese. All concentrationsexpressedas
mg -equiv./l.
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
327
sulphateor partlyto the inclusionofsomeun-ionizedbasic material(e.g. ferric
hydroxide)in the alkalinityvalue.
It is in the comparisonofthe equivalentsof total alkalinityand the other
betweenEsthwaite Water and the anaerobic
bases that the main difference
tank appears. In the formercase (Fig. 14), total iron(even whenconsideredto
be trivalentand whollyactive in the alkalinitytitration)plus ammoniaonly
made up a portionofthe total alkalinity,the residuebeingattributedto other
bases. In the anaerobictank (Fig. 21) ammoniaalone was almost equivalent
to total alkalinity,leaving iron, manganese and possibly other bases unaccountedfor.This considerablediscrepancycannotbe explainedsatisfactorily
research. It may,however,be suggestedthat a large part of
withoutfurther
the ironmay be in complexformand not includedin the alkalinityvalue. The
same may also be true of manganese. Even so, ifit is assumedthat ammonia
is fullyionized,thisdoes not leave muchresidualalkalinityas evidenceforthe
presenceof otherbases. It is possiblethat, in confined,base-poorsystemsof
this kind withno outsidesourceof supplyof monovalentand divalentbases,
the available bases are bound by bacteria or in other ways. Another
lies in the way of the assumptionthat the ironis in complexform.
difficulty
This is the strongpositive colour reaction which was obtained with oc-oc'dipyridyl,whichis usually consideredto be a specificindicatorof Fe++. It is
of interestin this connexionthat Coolidge (1932), duringthe study of iron
type in yeast,foundthat ferrousironexistedin
complexesofthe iron-protein
It is also of
un-lonizedform,but gave a positivereactionwithoc-oc'-dipyridyl.
interestthat the Eo value (potentialat whichequal quantitiesof oxidizedand
reduced phase exist in equilibrium)of these complexesand also of artificial
iron-albumincomplexeswas foundto be about 02 V. at pH 7. This E0 value,
which is approximatelythe same as that observed for the iron systemsin
1939),is muchhigherthan
naturalwaters,mudsand soils(Pearsall & Mortimer,
Eo-0- 6 V.
the E0 ofmostbetterknownironcomplexes(e.g.ironpyrophosphate,
at pH 7) and much lowerthan the E0 of the inorganicFe+++ Fe++ system
(0.75 V. at pH 4). Recent workon the chemistryof humus (Waksman,1936)
complex as the essentialconstituent.The similar
recognizesa lignin-protein
behaviour of iron-proteincomplexes(Coolidge,1932) and iron complexesin
natural muds, suggeststhat the latter may be essentiallyiron-humuscomplexes.
The behaviourof samplestaken fromthe anaerobictank duringthe latter
betweenthe
part ofthe experimentprovidesfurtherevidenceofthe difference
state ofthe ironin thesesamplesand in samplesfromthereducedhypolimnion
in Esthwaite Water. On exposureto the air, the iron in lake samples was
almost all precipitatedas ferrichydroxidewith a correspondingfall in conductivityand alkalinity. During a similar period of exposure to the air,
precipitationdid not occurin a reducedsampletakenfromthe anaerobictank
at 110 days, but the colour was trebledand the alkalinityand conductivity
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
328
Exchange of dissolved substances in lakes
fellslightly.Althoughthis difference
in behaviourcannotbe explained,it
mayhavebeendueto the'protective'actionontheferric
colloidsofa higher
concentration
oforganicmatterinthewaterofthetank. A fullerexplanation
ofthewayin whichtheferric
ironwas keptin 'sol-ation'maythrowlighton
problems
oftransport
ofironin peatywatersand soils.
In a stimulating
paper,Ohle (1937)has described
phenomena
associated
withthe colloidalproperties
of mud constituents,
and has emphasizedthe
importance
oftheseproperties
inthecontrol
oftheexchangeofplantnutrients
in lakes. In particular
he has demonstrated
the 'ampholytic'natureofthe
ferric
hydroxide
in acid and electro-negative
in
gel,whichis electro-positive
alkalinesolution.Thus in the presenceof CO2at pH 4, negatively
charged
phosphate
ionsaddedto ferric
hydroxide
gelwerestrongly
adsorbed,
although
someoftheironwentintosolution.AfterraisingthepH to 9 bytheqddition
ofcalciumbicarbonate,
a largepartofthephosphate
wasliberated.Thismay
in partexplainthefundamental
influence
ofthepresenceor absenceofbases
(calcium)on thedegreeofproductivity
in freshwater.In thewaterofbasepoorhumuslakesphosphateand otherplantnutrients
are adsorbedon iron
gelswhicharethemselves
attachedto electro-negative
humuscolloids.Hence
productivity
is low. It is possiblethatan essentially
similarprocessoccursin
theoxidizedmudsurfaceofotherlaketypes,producing
theadsorption
effect
described
inthepresent
paper. Ohlehas also shownthatin higher
pII ranges,
manganic
ions,whichbeginto precipitate
as hydroxide
at pH 8, alsoexercise
an adsorptive
influence.In manycases the phosphorus
cyclemay be more
closelycoupledwiththemanganese
cyclethanwithiron,especially
ifsufficient
organiccolloidsare notpresentto 'protect'theironfromrapidprecipitation
and removal.Ohle'sresultsand thosein the presentpaperare sufficient
to
indicatetheimportant
partwhichcolloidchemistry
is destinedto playin the
studyoflake 'metabolism'.
As a resultofobservations
ontheanaerobic
tankitis nowpossibleto define
morecloselythepotential
reductions
rangeswithin
whichthefollowing
maybe
expectedto occurin mud-water
systems.These rangesin E7 V. unitsare
givenbelowin brackets.The firstpotentialgivenis thatbelowwhichactive
reductionmaybe considered
to have occurredin the water,i.e. wherethe
fallin concentration
intothemud.
wastoo rapidto be explainedby diffusion
The secondpotentialis thatbelowwhichnoneoftheoxidizedphasecouldbe
detectedin the water. Nitrateto nitrite(0.45-0.40V.); mtriteto ammonia
(0.40-0.35V.); ferriccomplexto ferrouscomplexor Fe++ (0X30-0X20
V.);
associatedwith
sulphateto sulphide
(0X10-0X06
V.). Theoxygenconcentrations
thesepotentialrangesin the anaerobictankwereapproximately
4, 04, 0X1
and zeromg./l.
In
respectively. EsthwaiteWater1939(seepreceding
section)
it was observedthatthefirstappearanceofferrous
ironat 13 m. (1 m. above
the mud)occurred
at a potentialbetweenE7=0-3-0-2V. and was associated
ofapproximately
withan oxygenconcentration
a muchhighercon1 mg./l.,
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
329
centrationthan that observedat the same stage in the anaerobictank. It is
possiblethatthe conditionsfoundin Esthwaiterepresentan unstablestate due
to mixingby eddy diffusionof water containingferrousiron, and at a low
redox potential near the mud surface,with water containingmore oxygen
fromhigherlevels. This presupposesthat ferrousiron is not oxidized instantaneously,a suppositionwhichwas justifiedby conditionsfoundduring
mixingprecedingthe overturn,at which time ferrousiron was detected in
watercontaining8&4mg./l.of oxygen.
(To be conttnued)
This content downloaded on Tue, 5 Mar 2013 12:33:17 PM
All use subject to JSTOR Terms and Conditions
147
THE EXCHANGE OF DISSOLVED SUBSTANCES
BETWEEN MUD AND WATER IN LAKES1
BY CLIFFORD H. MORTIMER
BiologicalAssociation,WrayCastle,Ambleside
Freshwater
?? III AND IV, SUMMARY AND REFERENCES
III. THE RELATION OF SEASONAL VARIATIONS IN REDOX CONDITIONS IN
THE MUD TO THE DISTRIBUTION OF DISSOLVED SUBSTANCES IN
THE WATER OF ESTHWAITE WATER AND WINDERMERE
demonstratedin ? II, betweenchangesin concentration
THE interdependence,
of dissolved substancesin the water and redox conditionsin the mud, and
also the similarityof these changesto those observedin the hypolimnionof
Esthwaite Water and otherlakes (? I), suggeststhat redox conditionsin the
mud also control the distributionof dissolved substances in natural lake
systems.The workdescribedin this sectionwas designedto obtain information on this point. A chemicalsurveyon Esthwaite Water, similarto that
carriedout during1939, was repeatedduring1940, and at the same time the
distributionof redox potential and other variables was investigatedin undisturbedshortcores of the surfacemud and overlyingwater,obtained with
samplingapparatus designedforthis purpose. EsthwaiteWater and lakes of
similartype (e.g. Blelham Tarn) were chosenfordetailed study,because the
rangeofvariationofredoxconditionsand distributionofdissolvedsubstances
is sufficiently
wide to allow significantcorrelationsto be recognized. It is,
however,of equal importanceto attemptto discoverthe reasonsforthe small
seasonal amplitudeof physical-chemicalvariationobservedin lakes of oligotrophictype. Accordingly,the investigationof seasonal changesin the mud
and water,by methodsdescribedin this section,has been extendedto lakes
and the changesassociated with
in whichde-oxygenationof the hypolimnion,
it, does not occur. 'Resultsofinvestigationon Windermere(northernbasin)a representativeof this type of lake-have been selectedhereforcomparison
with EsthwaiteWater. A chemicalsurveyextendingover the years 1936-40
has been carriedout on Windermerein connexionwith bacteriologicaland
algological investigations.The full results of this survey will be published
later. Some data fortemperature,dissolvedoxygenand distributionof bacteriahave alreadybeen publishedby Taylor(1940). In addition,P. M. Jenkin
(unpublishedresults) studied the distributionof temperatureand dissolved
northand south basins,during1931-2.
oxygenin Windermere,
1
Continuedfromthe previousnumberof this Journal(Aug. 1941).
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
10-2
Exchangeof dissolvedsubstancesin lakes
148
SAMPLING TECHNIQUE
Thefirstessentialforthisworkwas a method
mudsampler.
Jenkinsurface
by meansofwhicha sampleofthe surfacemudand thewaterimmediately
it could be obtainedforlaboratoryexaminationwiththe least
overlying
ofphysical-chemical
variables.Thisproofstratification
possibledisturbance
whoseassistancein
solvedby MrB. M. Jenkin,
blemhas beensatisfactorily
C
B
A
k
ml
k
d
Cl
ILI'
~b,~~~
Fig. 22. Diagram of surfacemud sampling apparatus. A. Details of lid. B. Open position.
C. Closed position,with sample. For otherletterssee text.
this matter I gratefullyacknowledge.The firstexperimentalmodel of the
' surfacemud sampler', whichhe designedand constructedand whichis shown
and was employedthroughoutthis investigain Fig. 22, workedsatisfactorily
tion. It is of use in all cases wherean undisturbedsample of the surfacemud
and water in contact with it is requiredfor chemical,faunisticor otherinvestigation.The apparatuswillbe describedmorefullyelsewhere.Its working
principlesare outlinedhere.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
149
The sampleis takenin a glasstube (Fig. 22, a), 2 ft.longand 3 in. diameter.
Each end is groundflatand providedwitha lid (Fig. 22 A) whichconsistsof
a glass disk over whicha wide rubberband is slippedto give the lid a facing
of rubber.This lid formsa watertightseal with the end of the tube, and is
backed by a metal disk, which carries cross-bars(b, b,) projectingbeyond
the rim of the lid, attachments(c, cl) for springs,and a metal heel (d), the
purpose of whichis explained later. Each lid is held tightlypressed against
the end of the tube by a pair of steel springs(e, el) on eitherside, stretching
betweenthe lid attachments(c, cl) and attachments(f) at the middle of the
tube on a strip-metalharness,in whichthe tube is enclosed (Fig. 22 B). The
tube with its lids and attachmentsformsa containerin which the sample
may be transportedwithoutloss.
to whichfourlegs(o,ol) are rigidlyfixed
The tabe is mountedin a framework
and tube are supportedverticallyduring
in such a mannerthat the framework
carriesan upperand a lowerpairof
manipulationandtransport.Thisframework
arms,pivotedat (g,gl), each pair beingconnectedtogetherby cross-struts.In
addition,the upperpair is gearedto thelowerpair by gearwheelsat (g,gl); the
two pairs are also linkedby a dashpot (h) (consistingof the barreland piston
of a cycle pump). At its distal extremityeach arm carries a plate (i, i1)
arrangedin such a mannerthat, when the arms are rotatedin the direction
away fromthe tube (clockwiseas Fig. 22) the plates firstmake contact with
the cross-bars(b, bl) on eitherside of the lids. As describedabove, the arms
are geared to move together,and furtherrotationof the arms in the same
directionliftsthe lids away fromthe tube, against the tensionof the springs
to the 'open' position (Fig. 22 B). The arms are held in this positionby a
trip-catch
(j).
In this position,withthe samplingtube completelyopen,the apparatusis
lowered to the mud surface. As long as the winch cable remains taut, a
weight(k), which slides on a verticalrod (1), is held in a raised positionby
a metal bracket(in) attached to the winchcable. The frameworklegs are so
weightedwith lead wrappingsthat, when the apparatus.reaches the mud
surface,its momentumcarriesthe samplingtube to about one-quarterof its
lengthintothe softmud. The winchcable goes slack and the weight(k)fallsand
releasesthe trip-catch(j). The tensionof the springs(e, el) thenpulls the arms
thus closingthe tube (Fig. 22 C, arrows
carryingthe lids counter-clockwise,
indicatedirectionofmotion).To avoid disturbanceofthe sample,the dashpot,
whichis at this stage full of water,ensuresthat this closingoperationshall
proceedslowly.The rate may be regulatedby a valve (n) on the outletof the
powerfulto cause the bottomlid
dashpot barrel.The springsare sufficiently
to slice throughthe softsurfacemud and close the bottomof the tube. The
heel (d, Fig. 22 A) preventsthe lids frompassingbeyondthe ends ofthe tube.
Operated by a separate pair of springs(not shown in figure),the arms pass
on and leave the lids to close down on the ends of the tube an4 to keep it
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
150
Exchangeofdissolvedsubstancesin lakes
closed by the tensionof theirsprings.The plates (i1) on the bottomarms are
so arrangedthat the bottomlid closes slightlybeforethe top one. The apparatus is then hauled up and the tube and its contentsmay be removedfrom
the framework.
Samples obtained in this mannerappeared to be undisturbed,except for
a littlesmearingofsurfacemud to lowerlevelsat the side ofthe tube. Stratification of colour and texturewas preserved,the surfaceflocculentlayer includinginsecttubes and casts appeared undisturbedand the waterwas clear.
observedjust above
Also,thepreservationofthe markedverticalstratification
and below the mud surfaceis evidence of the undisturbedconditionof the
sample.
Immediatelyaftersampling,i.e. in the boat, the top lid was removedand
waterfromjust above the mud surfacewas
/
siphonedthrougha rubbertube into100 c.c.
bottlesfor 02, C02 and redoxpotentialdea
- terminations.In all three cases the same
a
_ bprecautionswere observed as in sampling
for dissolved oxygen determination. In
order to obtain the volume of sample
necessaryfor all determinationsfromthe
lower part of the tube only, the three
100 c.c. bottles,afterhavingbeen carefully
washed on the outside and inside, were
placed as shownin Fig. 23 in a clean glass
funneland held togetherby a rubberband.
The overflowfromflushingthe bottles,to
s,
_
expel air and waterwhichhad been in contact with it, was collected in the funnel,Fig. 23. Arrangementforsamplingwater
fromjust above the mud surface.
passed into a larger sampling bottle and
a, C02-bottlewith glass bafflestrips
used for other determinations. Another
in paraffin
supported
wax; b,rubber
ofofmud
mud and overlying
sample
verlylngwater
ater was
sample
band; c, siphon fromnsamnplingtube.
then taken, with the apparatus already
described,and transportedto the laboratory. Samples fromEsthwaiteWater
and Windermerewere usually examinedwithin30 min. of sampling.
-
-=
-
OTHER METHODS
Redoxpotentialaboveand belowthemud surface
Brightplatinumelectrodes,describedin ? II (Fig. 16), were loweredinto
the mud core (Fig. 24) as soon as it had arrivedin the laboratory,and the
potentials at small depth intervalsabove and below the mud surfacewere
measured 2 hr. afterthis. During this period the water at the top of the
samplingtube had been exposed to air. Study of the rate of changeof distri-
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
151
bution of redox potentialand conductivityin samples examined at varying
time intervalsaftersampling,showedthat conditionsin the mud and in the
water a centimetreor so above it, after transportand the 2 hr. interval
necessaryforthe electrodepotentialsto attain a relativelysteady value, representedfieldconditionssufficiently
closelyforthe purposesof this investigation. This conclusionis consistentwiththe slow rate of diffusionofsolutes
in the mud and withthe slowrate ofoxidationor reductionofthe mud surface
(cf. Fig. 28 and later discussion).The above measuringtechnique,however,
caused considerablechange in the distributionof redox potential and conductivityat higherlevels in the water. Consequently,only those samples
on conditions
siphonedoffin the fieldwerereliedupon to supplyinformation
in the waterjust overthe mud. The values indicatedforwaterabove the mud
surfacein Figs. 28, 30, 32 and 33 were obtained fromthese samples, using
methodsdescribedin ? I.
aboveand belowthemud surface
Electricalconductivity
Beforeinsertingthe redox-potentialelectrodes,the conductivityat each
centimetrelevel in the mud core was determinedwith the apparatus and
electrodesdescribedearlier (Fig. 16). It was arrangedthat the electrodes
should penetratethe core at points removedfromthe regionin which the
redox electrodeswere subsequentlyinserted. Usually the mean of two or
three vertical series was taken. Measurementsat the same level normally
showed close agreement.The conductivityvalues enteredin Figs. 30, 33, 34,
35 and 45 representthe apparentconductivityof the mud,assumingthat the
temperatureof the whole core is the same as at the surface.This value is not
necessarilythe same as the conductivityof the interstitialwaterin the mud,
as the maskingeffectof the mud solids on the electrodeshas not been considered. However,the resultsare reproducible,comparableand adequate for
the studyof seasonal and regionalvariation.
pH of mud core
Afterthe measurementsof redox potentialand removalof the electrodes,
the waterwas siphoned out of the samplingtube as completelyas possible
and the mud core was pushed up to the top of the tube by meansof a piston.
This operationapparentlycaused littledisturbanceof the core except at the
sides. The core was then sliced with a thin metal plate into approximately
-centimetre
layers,or otherconvenientthicknesses,as it emergedfromthetube.
pH estimationwas carriedout with a quinhydroneelectrode.The procedure
mud levels was describedin ? II.
and the calculationof E7 values fordifferent
Estimationofdissolvedsubstancesin thewater
The methodsand extentof the chemicalsurveyin the water,carriedout
at the same time as the investigationof the mud, in Esthwaite Water were
closelysimilarto thosedescribedfor1939 in ? I. Many ofthe resultsobtained
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
152
Exchangeofdissolvedsubstancesin lakes
aX=;a
526
Fig. 24. Arrangementforthe investigationof the distributionof redox potentialand electrical
conductivityin surfacemud cores. a, samplingtube; b,redoxelectrodes;c, calomelelectrode;
d, leads to potentiometer;e, conductivityelectrodes;f, KCl-agar bridge.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
153
in 1940. Only a selectionof theselatterresults,suffiin 1939 were confirmed
will be
cient to indicate the course of thermaland chemical stratification,
includedhere. Manganese,and occasionallychloride,was added to the routine
determinationsduring 1940: CO2 was estimated by a modificationof the
methoddescribedin ? II. 100 c.c. bottleswere fittedwith glass bafflestrips
supportedin paraffinwax, as shown in Fig. 23. Samples were collectedin
these with the same precautionsused in the collectionof oxygen samples.
Titrationwas carriedout in the samplingbottle,by the methoddescribedin
pH determination.Alster? II, after5 c.c. had been removedforcolorimetric
berg's modificationof Winkler'smethod (cf. Ohle, 1936b) was employedfor
dissolved oxygen determinationin all cases where the presenceof reducing
substanceswas suspected. 'Biochemical oxygen demand' was estimatedby
a standardmethod(Amer.Publ. Hlth Ass. 1936) on the same samplein which
redox potential had previouslybeen measured,care having been taken to
exclude air duringthe measurement.Oxygenintroducedwiththe electrodes
was neglected.
Similar series of determinationswere carried out at various depths in
Blelham Tarn, Windermerenorthand south basins and otherlakes, at the
same time as an investigationof the mud surfaceby the methodsdescribed
above.
RESULTS
A. EsthwaiteWater,May 1940-March1941
Weatherand thermalstratification.
Except forone stormduringMay, calm
at an earlierdate than in 1939.
fineweatherinitiatedthermalstratification
The hypolimnionwas also much colder and less stratifiedthan during1939
may
(cf. Figs. 3, 26). Furthercorrelationsbetweenweatherand stratification
be observedby comparisonof Figs. 25 and 26.
Distribution
of(a) dissolvedoxygen,(b) redoxconditionsnearthemudsurface
and (c) concentration
of solutesin thewaterjust abovethemud (Figs. 27-29).
Soon afterthermalstratification
had become establishedand the oxygenconcentrationjust above the mud had begunto fall (Fig. 27), the oxidizedsurface
mud layer,the bottomof whichmay be taken (cf. ? II) approximatelyas the
isovolt E7= 0.20 V. (thickenedline in Fig. 28), was reduced to a thin layer
at the mud surface,finallydisappearingon 12 June. Afterthis date the
concentrationsof iron,carbon dioxide and colour in the water began to rise
morerapidly; dissolvedoxygenconcentrationand transparencybegan to fall
more rapidly,and manganese appeared (Fig. 29). However, probably as a
resultof roughweatherand relativelyhighturbulencein the hypolimnionat
the end ofJune,the isovoltE7 = 0-20V. did not riseintothe wateruntilnearly
a monthafterit had appeared at the mud surface. By this time (July)the
oxygenconcentrationabove the mud had fallento just below 1-0mg./l.,and
ferrousironwas detectedin the water. During the weeks precedingthis,the
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeofdissolvedsubstancesin lakes
154
concentrationsof iron,ammonia,colour,silicate,conductivityand alkalinity
of nitrateand sulphate
had shownmarkedincreases,whilethe concentrations
OC OF
+20-
0-
Tempei ature
7
3-0 Rainfall
on Windermere 0=Flat calm, I1'Calm, 2='Moderate, 3=Choppy, 4=Rough, 5=Veryrough
Conditions
June
May
Apr
July
Aug
Oct
Sept
I
INov
Dc
lan
Feb
Fig. 25. Meteorologicalrecords, 1940-1. Air temperature(9 a.m. Ambleside), ramfall (daily
totals Ambleside)and observationson Windermere(estimateof mean daily condition).
;:
4?0X
4-
180
l7s
13
21 3
t^1Sl
17
1:^12
7
t54
16
15
993
94
19
383
7t1
13
42
6
66
0 9 87
6
5
6)
14.
o5
od
Date
77
7
)2
'
86
ii
2
4
_
i
886
9
2
i
tt16 tO;
7
11
0
93 82l 71l
77X1
2I 8
19
65
69
6 5
_43
4
Fig. 26. Esthwaite Water, 1940. Depth-timediagram of the distributionof temperature(0 C.)
m waterand mud surface(approx. 10 cm. below the surface).
had decreased (Fig. 29). Transparencyhad also considerablydecreasedowing
to thepresenceofcloudinessresultingfromtheprecipitationofferrichydroxide
producedby oxidationof ferrousironat the mud surface.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
155
CLIFFORD H. MORTIMER
Apartfromthe suddenincreasesin concentration
offerrousiron,phosphate
and reducingsubstances(oxygendemand),whichoccurredduringsubsequent
weeks,the initial rate of increase,at the beginningof July,in concentration
1101
10
988
1
94
10
r
. ,
jl
10
97
CD 1 0
6-
9
j
124
2
113
10
Overtrl
Partial Conplete
2
11
12
94
1
)
010
+0061111
~~~~~~~/OS81
+5
74 and
14~~~abv
May
ue
luy
h
Aug
u
ufc,
S-ept
~
in 0
05
00632 10703
o
40
4m
t
E
Nov
0
ot)
Dee~
a
eb
Mr1
Fig. 27. Esthwaite Water, 1940. Depth-time diagram of the distributionof rhsledopotyenta
Fig.m27.Esthwite Wter, 1940.dDept-tier
diagreame
of
ithe
dstribu
ututionso,soleoxyge
periiodatslowe
some.fluctugatios,oc-hi
oWinclreasme,wtho)
sumer./.During
Althibrgs
us ntFigth
currd
anrrdinumseqet
submseqet
casues
figues
asuntFig.
ovrur6
26.vrtrFi.2)Fg.2)
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeofdissolvedsubstancesin lakes
156
Overttirt
12
Paitial Cotiiplete
10-
30
4 |
Alaiit
?
82-
_30
-7
_
CCO)7
\O~~xygen
(K1s_L0_6
Conductivit
______________________
Totaliron
Iron
Manganese
Colour
20
60
8
=
Alaint
ACaCs3
8-
=
'
dioxidle
~~~~Carboti
,-#Ferrousiron
/
8il0 Transpareny
Sulhate
(S(14) \_ \\=
' .; |
v
(S0)%
0
24-
_
Ot
-
08
4
~~~~~~~~~~~~~ f
0
6H0.
/_\ \
~~~~~~~~~~~~~~~~~~-0-
0~~~~~~~~~~~~~~~~~~~~~~~~~~*8'
~~Ammoniia
Amm?nia/
N
41-55 |
zNH3
5
t;0-5
-
<
J
Nitrite (NO2
\Nitrate (NO3
|
0015
N)
-005
N)
~~~~~~~~~~~~~~~~~~~
0
16
1l2
R
B 0 D (5 days200C)
Oxygenabsorbed
C
FromKMnO4(4 hr 400C)
May
1?
June
' ' 'I''
/
\
12
Chloride(Cl)
/
gmulgm.(m./l..
July
Sept
Aug
sufc,
11
Oct
4.
1.
Nov
Dec
1
-0
Fig. 29. Esthwalte Water, 1940. Concentrationsof dissolved substancesin water Justover the
mud surface, 14 m. (mg./I.).
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
157
Changes in total content of phosphate and silicate in the whole water
columnare shownin Fig. 12, ? I.
The same seriesof changes observedat the overturnin Esthwaite Water
1939 wererepeatedduring1940. A partial overturnoccurredas the resultof
a gale on 17 September,followedby a calm spell (see Figs. 25-27). Circulation
was not completeuntilthe stormyweatherafter5 October.The effectofthese
weather oscillationson the redox potential and concentrationof solutes at
the mud surfacemay be seen in P-igs.28 and 29. A change in the ratio of
alkalinityto conductivitywas observedafterthe overturn(1940), indicating,
as in 1939, the adsorptiveremoval of bases fromthe water by the oxidized
mud surface.The fall in ammonia concentrationat the partial overturnwas
followedby a nitritemaximum,itselffollowedby a comparativelyhighnitrate
maximum3 weeks later. Ferrous iron disappeared at the partial overturn,
later. A fallin transparency
but manganesedid not disappearuntila fortnight
at the end of Septemberwas associated with the oxidation of ferrousiron.
Phosphate concentrationfell to minimalvalues afterthe overturn,and the
concentrationsof silicate, colour and reducingsubstances (oxygen demand)
also decreased. Sulphate, which had only been reduced to half its original
springconcentration,
approximatelydoubled in concentrationafterthe overturn.
Redoxconditionsaftertheoverturn
(Fig. 28). It was some weeks afterthe
overturnbeforethe oxidizedlayerbecame fullydevelopedat the mud surface,
and the isovolt E7= 0-20 V. remained at a relativelysteady 'winter' level
below the mud surface,comparable with that observed during May. The
thicknessofthe oxidizedlayerwas subjectto considerablefluctuations.During
a calm spell in Decemberit consistedonly of a surfacescum containingferric
hydroxide,and it was again almost destroyedduringstagnationunder ice
from3 Januaryto 15 February1941. Samples were taken on the latterdate
whilethe ice was still breakingup and beforecirculationof the lowerwater
had begun. The last sample on 12 March completedthe investigationof an
annual cycle, as it may be assumed that the oxidized layer remained at
approximatelythe same thicknessfromMarch until thermalstratification
and de-oxygenationrecommencedin the spring.
Conductivity
of the mud (Fig. 30) increased at all the levels investigated
had been establishedand rose to a maximumat
afterthermalstratification
the mud surfaceon 24 July. Possible reasons for this considerableincrease
and forthe subsequentfall in the conductivityof surfacelayers will be discussed later. Some considerableoscillationsin conductivityvalues were observed at the periodof the overturn,followedby a fall in conductivityat all
levels to low values comparablewith those found at the beginningof May.
Anothermarkedrisein conductivityat all levelswas observedafterthe period
of stagnation under ice. This was followedby a decrease in conductivity
similarto that observedafterthe overturn.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchange of dissolved substances in lakes
158
B
l ffi
May
June 'July
~~~
~
~~~304
Overturn
PartialComplete
1
Icecover
69
65
~lMud-surfaee
Feb
Jan
Dec.
Aug'Sept'Oct'INov
'Mar
Fig. 30. Esthwaite Water, 1940-1. Depth-timediagram of the distributionof electricalconx 10-6).
ductivityabove and below the mud surface,14 m. (l
0
0-~~~~1
255
A
75
0
679Overturn
9
1
511
8
partial
Assumed
complete
B
2
91%
/
_
Oxygen
~
Alkalinity (CaCO3)
8
-_
_
sat.
f93%
sat.
_ _ _ .^
_
Oct.
_
=
__4
52
~~~~~Sulphate
(SO4)
4 C ductivity(K280x 106)
(SiO2) e, _>=
Silicate (NO3)
_ Nitrate
Sept.
_
48
Carbondioxide
Nov.
Dec.
Jan.
R
L46
Feb).
Fig. 31. Windermere,North Basin, 1940-1. A. Weather observations(estimateof meandaily
condition). B. Concentrationsof dissolved substances n water Justover the mud surface,
65 m.
(mg./A.).
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
159
B. Windermere,
NorthBasin (25 September1940 to 6 February1941)
Seasonal changesin physicaland chemicalvariablesin the surfacemud and
the water immediatelyoverlyingit were investigated,by the same methods
employedon Esthwaite Water, at a station (65 m. depth) in the deep region
of the NorthBasin of Windermere,over a period whichincluded 21 months
beforeand afterthe overturn. From Fig. 31, which indicates (a) weather
conditionson Windermereand (b) concentrations
ofsome dissolvedsubstances
2
Overturn
Partial
0
I
055
_
07
02i07
0-40
O=_______8051
0*50
0-08
0.04
T~o*0
0-03
1
Oct.
053
0*54
~~~~~~~~~0-52
_
0
Spt.
I
04
0~~~~~~~~02
43
-4
4,
052
=~
Complete
1
Nov.
=
|''/
0*04 0*03
D.
0.02
O*05
Jn.Feb.
Fig. 32. Windermere,North Basm, 1940-1. Depth-timediagram of the distributionof redox
potentialabove and below the mud surface,65 m. (E7 in volts).
in the water siphonedfromjust over the mud in the samplingtube, it may
be assumed that the overturnoccurredas a resultof a gale on 21 November
and was completedby the gale on 5 December.
The oxygenconcentrationabove the mud at the end of thermalstratification was 8-8mg./l.or 71 % saturationat 6.40 C. The oxidizedlayer(Fig. 32)
was not destroyedduringthe stagnationperiod,but it may be assumed that
it had becomegraduallyreducedin thickness,forafterthe overturnits thickness was approximatelydoubled.
Changesin concentrationof dissolved substancesin the water above the
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
160
Exchangeof dissolvedsubstancesin lakes
smallcombutextremely
weredefinite
at theoverturn,
mud,whichoccurred
paredwiththosewhichoccurredduringthe overturnin EsthwaiteWater.
A fallin the concentration
of carbondioxideand iron,and slightdecreases
wereobserved.
and conductivity
of silicate,alkalinity
in the concentrations
can be accountedforby the
Calculationshowsthatthefallin conductivity
alkalinity.This suggests
decreasein concentration
of substancesproducing
ofbases,observedin EsthwaiteWateraftertheoverturn
thattheadsorption
also occursin Windermere,
at themudsurface,
to adsorption
and attributed
is muchlessmarkedinthelattercase. Duringthe2 months
although
theeffect
remained
alkalinityfellslowly,whilethe conductivity
afterthe overturn,
constant.Data fromanalysesof inflowwatersare not availableto decide
of
ofbasesand liberation
adsorption
whether
thischangeis due to continued
anionsotherthan bicarbonate(noteincreasein sulphateduringthe same
ofinflow
to changesin composition
it mustbe attributed
period),orwhether
aftertheoverturn.
slightly
water.Sulphateand nitraterosein concentration
and phosphatewereonlypresentin tracesbeforeand after
Ammonia,
nitrite
theperiodaftertheoverturn
theoverturn.
ofoxygenduring
Theconcentration
represented
percentagesaturationvalues of about 92 at the temperatures
concerned.
of the mud core showedsome fluctuations
Althoughthe conductivity
in all but the
(Fig. 33), therewas clearevidenceof a fall in conductivity
theoverturn.A risewas notedat
surfacelayersduringthemonthfollowing
in
theend ofJanuary.Furtherevidenceofseasonalchangein conductivity
themudis afforded
(Figs.34,35) oftheverticaldistribution
bythecomparison
in a numberof surfacemudcoresfromthe deep regionof
of conductivity
Allthesamples
beforeandaftertheoverturn.
theNorthBasinofWindermere
within
sextant
the
50 m. contour,
weretakenat points,fixedby
bearings,
1 km.2 Fig. 34 indicatesthe degreeof
i.e. withinan area of approximately
local variationwhichwas found,but showsthat,in spiteof thisvariation,
betweenthegroupofcorestaken(A) at theendof
thereis littleoverlapping
summerstagnation(autumn1939)and (B) at the end dfwintercirculation
in Fig. 35.
(spring1940). Mean curvesforthesetwo groupsare presented
ofionsat different
levelsin the mud
Usefuldata on therateofproduction
analysisofsuchcurves(see ? IV).
maybe obtainedby mathematical
DISCUSSION
ofrelatively
The occurrence
slightchangessimilarto thosejust described
NorthBasin,was confirmed
forWindermere,
by a similarstudyin the~South
of singlesamples
overthe sameperiod. Investigation
Basin of Windermere
Crummock
takenonotherlakes(Thirlmere,
Derwentwater)
Water,Ennerdale,
thatsimilarchangesoccurin all lakes
timesoftheyear,suggests
at different
doesnottakeplace. On theother
ofthehypolimnion
wherede-oxygenation
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
coMud
Overturn
surface
~~1:
49'
0
47
-
48
49
481
n-~
-
-
11"
1
Partial Complete
-
50
~
-
-
-
50
2~~~~~~~~~~~~~8
100
4
120
6
140
8:
150
187
18460
19
12.
196
~
170
~ ~
~
200
~
~
~
~
~
~
~
~
~
~
~
~
~
~
9
0
2020
8
21
22
Sept.
~
~ ~
~
~
~
~
~~1
230~~2020
Oct.
NOV.
Dec.
Jan.
I
of electrical
NorthBasin, 1940-1. Depth-timedliagramof the clistribution
Fig. 33. Windermere,
65 m. (Ki8' X 1-)
aboveand belowthemudsurface,
conductivity
11
J. Ecol. 30
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeofdissolvedsubstancesin lakes
162
hand,themarkedseasonalchanges,foundto be associatedwithde-oxygenain EsthwaiteWater,
ofthemudsurface
andreduction
tionofthehypolimnion
in waterand mud
by a detailedstudyofconditions
werealso demonstrated
samplesfrom
of
occasional
of BlelhamTarn and also by the examination
40
60
80
100
120
160
140
180
200
220
_II.
0::.:.
2
-
**W
x XRIA
Mudsurface
o .1-17
.\11-
A_^
XV
*A
B
E
0O
00
\
xxxxx uo 0
19 Aprito4May1940
KA8?
Nov.1939
A
xX80 6
1*00
2
x
14
$'
40
60
80
100
120
10-6
K1-X
140
160
180
200
220
conofthe distribution
of electrical
NorthBasin,1939-40.Comparison
Fig. 34. Windermere,
than50 m., (A) at theend ofsummer
mudcores,fromdepthsgreater
in surface
ductivity
period(spring1940s
(autumn1939,8 cores)and (B) at theendofthecirculation
stagnation
1939.
about20 November
occurred
9 cores).Theoverturn
ofthehypolimnion
occurs(RydalWater,
otherlakesin whichde-oxygenation
and
in Windermere
found
that
the
conditions
Loweswater).This suggests
oftwofundamentally
as representative
EsthwaiteWatermaybe considered
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
163
H. MORTIMER
differentlake types. The causes of these differencesand their relation to
organicproductionwill be discussedin ? IV.
Discussion of theresultsfromEsthwabteWater.The considerableincrease
in the concentrationof certain solutes in the water over the mud, which
60
40
80
100
140
160
180
200
220
I
I
I
I
180
200
220
surface
~~~~~~Mud
E1
I
180
40
120
60
80
I
I
160
140
120
100
40 in caseofA-B)
x 10-6(subtract
North Basin, 1939-40. Mean distributionof electrical conductivityFig. 35. Wmndermere,
computedfromFig. 34-n surfacemud cores,fromdepths greaterthan 50 in., (A) at the
end of summerstagnation (autumn 1939) and (B) at the end of the circulationperiod
(spring1940).
occurredafterthe mud surfacehad becomereducekd-or,moreprecisely,after
the isovolt E7= O*20V. had risen to the mud surface-is in close agreement
(? II), and substantiates
withthe findingsin the anaerobic tank experimentX
11-2
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
164
Exchangeof dissolvedsubstancesin lakes
the suggestion,made in ? I, that similarincreasesobservedin 1939 resulted
from the reductionof adsorbingferriccomplexes in the mud surface. In
short,resultsfromall threesectionsare consistentwith the view that comparativelylarge amounts of materialare liberatedduringthe destructionof
the oxidizedsurfacemud layer.The rate ofincreasein concentrationof many
substances in the water duringthe later summerwas usually much slower.
This may be taken to representthe steady rate of supply fromcontinuous
processes in the mud, the products of which were free to diffuseinto the
water unhamperedby the stronglyadsorptive effectof the oxidized mud
surface.
In contrastto this, conditions(a) in Esthwaite Water afterthe overturn
whenthe surfaceoxidized layer had re-formed,
where
and (b) in Windermere,
the oxidizedlayerwas nevercompletelydestroyedthroughoutthe year,were
similarto those observed in the aerated tank (? II). Althoughcontinuous
productionof ions must have been takingplace, concentrationin the water
was littleaffected,
as precipitationand adsorptionin the oxidizedmud surface
had immobilizeda large part of these products.This process,and its reversal
afterthe onset of thermalstratification,
also appears to have affectedionic
concentrationin the mud itself.Thus the generalrise in conductivityof the
mud in Esthwaite Water duringMay and June (Fig. 30) may be attributed
to the decrease in thicknessof the oxidized layer,resultingin the liberation
of adsorbed ions and to a correspondingdecrease in capacity of the surface
layer to adsorb productsof continuousmud processes. A converseexplanation may apply to the general fall in conductivityafter the overturn. It
appears unlikelythat these changes can be explained by changes in temperatureat the mud surface,as this was fairlyconstantthroughoutspring
and early summer,risingto a maximumat the overturn.This rise in temperaturemightbe expected to increaseionic productionin the mud; but in
fact a decreasein conductivityoccursat this time. Similarseasonal changes
in the conductivityof Windermeremuds (Fig. 33), althoughnot so marked
as in Esthwaite,may be consideredto be associated in a similarmannerwith
changes in thickness,and thereforein total effectiveness
as an adsorbent
blanket,of the surfaceoxidizedlayer.
It will be observedthat both in EsthwaiteWater and Windermere(Figs.
30, 33, 34, 35) thegreatestchangesin the concentration
(conductivity)gradient
occurredat and near the mud surface,suggestingthat the amplitudeof seais greatestin thisregion.Thesefluctuations
sonalfluctuations
maybe considered
to result partly from the physical-chemicalchanges in the mud surface,
described above, and partly from seasonal changes in the eddy diffusion
in the waterjust above the mud. The rateof removalof ions from
coefficient
the mud depends on the product of this coefficient
and the concentration
gradientin the waterin contactwiththe mud.
The reason for the rise to the high conductivitymaximumobserved at
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
165
the mud surface on 24 July (Fig. 30) is obscure. The oxidized layer was
destroyedand the ions adsorbed in it presumablyreleased a monthearlier.
These high values cannot be due to contamination,as they were found on
two samplingoccasions,and theireffecton the mud surfaceis apparent for
some time afterwards. It is possible that a large plankton crop produced
duringthe long calm finespell in the latterhalfof Julymay have settledand
no data on the plankton
decomposed on the mud surface. Unfortunately,
populationis available. The fall in conductivityafterthis period may have
been the result of diffusionof the products of this decompositioninto the
water,in which a marked increase in conductivitywas noted at this time,
and also partly to the cause, to which a similarfall in conductivityin the
anaerobictank was attributed(? II), namely,precipitationofferroussulphide.
The fall is greatestin the top few centimetresof the mud, in which most
precipitationmightbe expectedto occur,and in whichconsiderableaccumulationsofblack ferroussulphidewereobservedtowardsthe end ofthe summer.
Fluctuationsin conductivitythroughoutthe whole mud core at the time
to explain. The partial overturn(23 September)
of the overturnare difficult
was associated with a fall in conductivity,anotherrise occurringduringthe
period beforecompletecirculationof the bottomwater had been established
(cf. Figs. 27, 30). This was followedby a sharp fall, then a slightrise and a
slow fall duringthe early winter.Without furtherstudy it cannot be said
how far these variations may be attributedto local variations near the
sampling point. Such variation is, however,relativelysmall in the deep
regionof Windermere(Fig. 34). If local variationis made responsibleforthe
fluctuationobserved duringthe month ending 21 October,it is difficultto
explain why such fluctuationswerenot observedat othertimesof the year.
The explanation of the rise in conductivitywhich occurredin the mud
duringthe periodunderice is consideredto be the same as that givenforthe
duringMay and June. Partial reductionof the
similarrise which occurfred
mud surfaceand decrease in eddy diffusionin the water over the mud were
probably both contributoryfactors. If the results from one sample (15
February) are consideredto be representative,the rise in mud conductivity
under ice was greaterthan duringa comparableperiod.in the spring.This
cannot be explained'by a morerapid reductionof the mud surfaceunderice
in eddy
(cf. Figs. 28, 30), but must have been the result of the difference
in the waterjust above the mud duringthe two periods.
diffusioncoefficient
was certainlyconsiderablylowerthanduringsummer
Underice thiscoefficient
stratification
thermal
(cf. Tables 1 and 2, ? I).
Otherpoints of interestarisingfromchangesin the distributionof redox
potential and concentrationsof dissolved substances are brieflydealt with
below. The lag (Fig. 28) in the formation,afterthe overturn,of a surfaceoxidizedlayer,comparablein thicknessto that foundat the end ofthe winter,
may be consideredto be the result of the slownessof diffusionin the mud
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
166
Exchangeofdissolvedsubstancesin lakes
and of the slownessof oxidationof the accumulatedproductsof summer
reduction.Of these,ferroussulphideprobablyformsan important
part.
Similarly,
the lag in reduction
processesduringtheinitialstagesQfsummer
stagnation(Figs. 12, 28) maybe largelydue to the slownessofreduction
of
ferrichydroxideand otherferriccomplexesundernaturalconditions.A
similarobservation
was madeby Pearsall& Mortimer
(1939,p. 493).
No explanation
can be offered
in concentration
forthelargefluctuations
ofsomesubstances,
notablyphosphorus,
ironandreducing
substances
('oxygen
demand')in the waterabove the mudduringsummer.Such largefluctuationswerenot observedduring1939. It is probablethat,comparedwith
1939,conditions
in the hypolimnion
wereunstableas a resultof poorlydevelopedstratification
(cf.Figs.3, 26). Augustwas also exceptionally
stormy.
However,estimhtes
oftheeddydiffusion
coefficient
forthatmonthat 13 m.,
obtainedby methodsdescribed
in ? I, are notconsiderably
greaterthanestimatesfora similarperiodin 1939 (see Table 1, ? I). The meanestimates
of [A] for August 1940 and 1939 may be taken as 4 x 10-2 and 3 x 10-2
respectively.
A comparison
ofthegraphsof02 and C02 concentrations
(Fig.29) suggests
thatlittle,ifany,anaerobicC02 production
occurred.
In mostnaturalwatersmanganese,
like iron,is practically
insolublein
trivalent
(oxidized)form,but is solublein manganous(reduced)form.The
appearanceof manganesein the waterat an earlierdate thanferrous
iron,
and its persistence
ironhad disappearedat the
forsometimeafterferrous
in the oxidizedmud
overturn,
suggeststhatinsolublemanganiccompounds
surfaceare reducedmorereadily,i.e. at a higherredoxpotential,thanthe
to notethatsulphate,
ferric
complexes.It is ofinterest
although
considerably
in
the
reduced
water
above
the mud during
depleted,was not completely
summerstagnation.It may also be notedthatthe redoxpotentialin the
waterdid notreachthepotential,
E7=0-06V., at whichsulphatecompletely
disappearedin the anaerobictank experiment
(? II), untiljust beforethe
overturn.
Chlorideshowedlittleseasonalchangein concentration
(Fig. 29). This
of Ohle(1933-4).The chlorideion is apparently
agreeswiththefindings
not
in seasonalredoxand associatedchanges.
concerned
Theresultsobtainedon EsthwaiteWater1940haveconfirmed
thedescriptionofeventsin thehypolimnion,
suggested
by thestudyofthedistribution
of redoxpotentialand dissolvedsubstancesin the waterduring1939 (? I).
withand largelycontrolseasonal
Seasonalchangesin themudare correlated
variationsin concentrations
of solutes
changesin the water. In particular,
in the hypolimnion,
detectedduring1939and confirmed
during1940,were
at the mudsurface.Almostall
on redoxconditions
foundto be dependent
of
the phenomenain mud and water,describedduringthe development
in an artificial
mud-water
anaerobicconditions
system(? II), werefoundto
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
167
be repeated in the same orderin Esthwaite Water duringthe development
of de-oxygenationin the hypolimnion.One exceptionwas that the complete
reduction of sulphate with precipitationof ferrolussulphide in the water,
observedin the experimentaltank, did not occurin EsthwaiteWater during
1940,althoughthereis some evidencethat it occurredduringSeptember1939.
This may be explainedby the highermean potentialin the lowerhypolimnion
duringSeptember1940. The mean potentialat 13 m. duringthe monthprecedingthe overturnin 1940 and 1939 was approximatelyE7= 0 17 and 0 09 V.
respectively.The latterpotentialis not far removedfromthat (E7 = 006 V.)
at whichsulphatedisappearedfromthe water of the experimentaltank. The
in behaviour between successive years may have
reason for this difference
been the conditionsunder which thermal stratificationwas set up in the
spring. From the outset the hypolimnionwas thermallystratifiedto a far
higherdegreeduring1939 than during1940 (cf. Figs. 3, 26).
Discussionofresultson Windermere.If the explanationof eventsin Esthwaite Water is a true one, thenthe fact that the surfaceoxidizedlayer of the
mud was not reduced in Windermereexplains the absence of large seasonal
ofdissolvedsubstancesin thewater.The relatively
variationsin concentrations
lhighconcentrationof dissolved oxygen,which was maintainedat the mud
was responsiblefor the
surface duringthe period of thermalstratification,
failureof the lower mud-the reducingintensityof which,as will be shown
later,is notfarbelowthat ofEsthwaiteWater-to reducethe ferriccomplexes
in the mud surface.When, undersuitable conditions(anaerobictank experiment),reductionof Windermeresurfacemud did take place, markedchanges
occurredin the mud-watersystem similar to those already described for
Esthwaite Water. The small seasonal variationswhich were found to occur
under natural conditionsin Windermereare probably largelythe result of
seasonal changes in degree of eddy diffusionand in oxygen concentration
gradientat the mud surface.
mud layermay be takento represent
The thicknessofthe surface-oxidized
a balance between(a) the rate of diffusionof oxygeninto the mud, whichis
a functionof the concentrationgradientat the mud surface,and (b) the reducingpowerofthe mud. Seasonal variationof(b) is notknown,but probably
not large. When the rate of supply of oxygento the mud surfaceby eddy
the concendiffusionfromabove is decreased duringthermalstratification,
trationgradientat the mud surfacedecreasesto an extentdeterminedby the
degree of eddy diffusionin the water and the rate of oxygenabsorptionby
layerthendecreases,adjusting
the mud. The thicknessofthe surface-oxidized
itselfto the new balance between oxygen supply and consumption. It is
possiblethat the slownesswith whichinsolubleferriccompoundsare reduced
imposesa lag on this adjustment.The decreasein thickness,of course,takes
place frombelow,and may be expectedto resultin some liberationof soluble
ions previouslyadsorbedor precipitated(Fe, Mn, P04 and bases), and also in
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
168
substancesin lakes
Exchangeofdissolzved
somedepletion
ofthetotalcapacityoftheoxidizedlayerto bindtheproducts
ofcontinuous
processes
in thelowermud. One demonstrable
resultofthisis
a risein ionicconcentration
(conductivity)
in the mudand a slightincrease
in concentrations
of certainsubstances(cf.alkalinity,
conductivity,
C02) in
the water.The bulk of the materialliberatedin thisway,however,is reabsorbedby the surfaceoxidizedlayerthat remains.The main difference
betweenlakesofthetwotypes,exemplified
by EsthwaiteWaterand Windermere,is thatin theformer
thesupplyofdissolvedoxygento themudsurface
is morelimitedand the oxygenconcentration
gradientfallssufficiently
low
forthewholeofthe surfaceoxidizedlayerto becomereduced,initiating
the
markedchangesin ionicexchangebetweenmudandwater,alreadydescribed.
At the overturn
bothlake typesexhibita reversalofthe changeswhich
tookplace in mudand waterduringthermalstratification.
The reversalin
the mud appearedto be morerapidin Windermere
thanin Esthwaite(cf.
Figs. 28, 32). This maybe becauseno considerable
sulphatereduction
and
accumulation
of insolubIk
ferroussulphidein the mud surfaceoccurredin
Windermere.
IV. GENERAL DISCUSSION
Factsandcorrelations
disclosed
by thefindings
in preceding
sections,
and
further
data obtainedfromotherlakesin the EnglishLake District,linked
together
byhypothesis,
helpto providea description
in outlineandinphysicochemicaltermsof one aspectof the cycleof organicproduction
in lakes.
Roughlyspeaking
thisdescription
appliesto a reversible
system,
thechemical
cyclein the lake basin,whichis insertedinto and maintained
by a larger
basin.
relatively
irreversible
geochemical
process,
enactedinthewholedrainage
As a hydro-electric
planttransforms
and accumulates
a portionofpotential
energy,
whichwouldotherwise
be (relatively)
irreversibly
wasted,so a lake
a partoftheavailable'chemicalpotential'ofa
trapsfororganicproduction
be morerapidlylost to the sea.
drainagesystem,whichwouldotherwise
Variousfactors,includingthe peculiarproperties
and stabilityof humus,
oforganicmaterialin lakedeposits,
lead to theaccumulation
normally
whichl
a portionofthe 'chemicalpotential'for
function
as accumulators,
defraying
in thewater,andthemselves
organicproduction
beingcontinually
replenished
oforganicmatterand siltfromabove.Thusanabolicprocesses
by deposition
a reversible
in thewaterand katabolicprocessesin the mudconstitute
lake
of which,relativeto irreversible
maintenance
system,the importance
processesin thedrainagearea,maybe expectedto varywiththeage ofthelake
of the mudand the ratioof its watervolumeto inflow.The constitution
water-atmosphere
system,and the factthatkatabolicprocessesinvolverplinkedwiththelake
duction,explainswhyredoxreactionsare so intimately
influence
cycle.The impactof climateon the systemexercisesa profound
ofredoxconditions.
controloftheseasonaldistribution
through
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
169
One generalresultof this investigationhas been to directattentionto the
importanceof (a) processesin the mud, especiallyat the mud surface,and
(b) watermovements,forthe 'metabolism' ofthe lakeas a whole. Both these
aspects of the lake cycle have received some special discussionin previous
sections. In particular,the importanceofthe presenceor absence ofreduction
at the mud surface,discussedin termsof colloid chemistry,was emphasized
especiallyin ?? I and II, while the controllinginfluenceof turbulence,associated withwatermovements,on the transportof dissolvedsubstanceswithin
the lake systemwas demonstratedin ? I. Apart fromsome furtherdiscussion
of water-movements,
this sectiontherefore
will be confinedto a consideration
of some generalimplicationsof the previousfindings.
Biotic influences.It will be noted that the interpretation
of the changes
observedin both naturaland artificialmud-watersystemsin previoussections
has been almost exclusivelyphysico-chemical.Biotic influencesmust not be
ignored,althoughthe closenesswithwhicha relativelysimplephysico-chemical
interpretation
fitsthe facts suggeststhat these influencesexpressthemselves
mainlyalong physico-chemical
lines. Amongsuch influencesmay be included
the relation of bacterial population and its activities to redox conditions
(see Hewitt 1931 for a review of this subject) and the effectof plankton
productionon the rate of additionof organicmatterto the hypolimnionand
mud. The effectof changes in the distributionof physico-chemicalvariables
on organicreactionsshould also be considered. A beginninghas been made
by Kusnetzow & Kusnetzowa (1935), who foundthat the bacterialreduction
offormicacid to methanetookplace mostactivelyin mudsat a redoxpotential
of E7 - O12 V., and that the upper potential limit was between E70 and
+ 0O15V. Active methaneproduction,however,was not found in all muds
below these potential limits. They suggestedthat C and N supply is the
controllingfactor.
The relationof seasonal variationsin redoxconditionsat themud surfaceto
theecologyoftheprofundalbottom
fauna. It appears highlyprobable,but still
remainsto be demonstrated,
that a close relationshipofthiskindexists. Since
the classical work of Thienemannand collaborators,a relationbetween the
profundalbottomfauna, especiallyChironomidae,and degreeof productivity
(trophic condition)in lakes has been established. Hutchinsonet al. (1939)
discusscertaininco4sistenciesthat have been found,suggestthatredoxpotential is an importantdetermining
factor,and demonstratea relationbetween
the Chironomidpopulationin a seriesof lakes and the redox potentialof the
bottom water during thermal stratification.In the absence of potential
measurementsin the muds, they considerthe reducingpower of the mud
only as it affectsthe open water. It should be noted that the potentials
recordedin the presenceof ferrousiron (detectedby ac-c-dipyridyl)are considerably(01-02 V.) higherthan those foundin the presenceof similarFe++
concentrationsin Lake District lakes and artificialmud-watersystems(cf.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
170
Exchangeofdissolvedsubstancesin lakes
previoussectionsand also the discussionof the determination
of Fe++ by
thismethod,Hutchinson
1941). As a resultof a quantitative
studyof the
ecologyof theprofundal
bottomfaunain lakes,Eggleton(1931) concludes:
'Emergenceand egglayingofinsects,variationsin sexualactivityof other
benthictypes,and therateand timeofhatching
ofeggson thelakefloorare
all influenced
by the physical-chemical
seasonalcycleand, in turn,greatly
affectthe qualitative-quantitative
variations
oftheprofundal
benthicpopulation.'
Watermovements
Beforeproceeding
ofthefactorswhichdetermine
to a discussion
whether
ornotreduction
ofthemudsurfaceand associatedphysico-chemical
changes
take place, presentknowledgeof water movementsin the hypolimnion
mustbe considered.The positionis unsatisfactory
in so faras all evidence
of the natureof thesemovements
is indirect.Technicaldifficulties
have so
farprevented
actualmeasurement
of theirvelocityand direction.Although
all suchindirect
evidencefromtherateofchangeofdistribution
ofdissolved
substancesand temperature
agreesin demonstrating
that the hypolimnion
is not stagnant,the viewsso farexpressedon the cause and natureofthe
watermovements
showdisagreement.
The predominant
effectof windin distributing
heat in regionsof lakes
removedfromthe effectof radiationwas originally
recognized
by Murray
(1888,refs.in Murray& Pullar,1910).Thistheoryof wind-distributed
heat
was amplified
by Birge(1916),who,in commonwithSchmidt(1925,1928),
regardedturbulenceassociatedwithwind-generated
currentsas the main
agentin transporting
heat and dissolvedsubstancesthroughout
lakes,includingthehypolimnion.
McEwen(1929)has attempted
to establisha practicallycomplete
andtherefore
complexmathematical
ofthedistribution
theory
oftemperature
and dissolvedsubstances
in naturalwaters,takingradiation,
conduction,
evaporation,
convection
and wind-generated
intoconturbulence
sideration.A generalresultemerging
fromthe applicationofthistheoryto
the distribution
of temperature
in Lake Mendotawas thatthe effect
of all
factors
exceptthelastwasfoundtobepractically
confined
totheepilimnion
and
thethermocline
region.Thistheory
is discussed
indetailbyHutchinson
(1941).
The above authorshave littleto say on the generating
and
mechanism
ofthewatermovements
magnitude
in thehypolimnion.
producing
turbulence
One over-simplified
viewoftenexpressed(cf.Wedderburn,
articlein Murray
& Pullar,1910;alsoWhipple,1927,ref.inWelch,1935),is thatwindproduces
a surfacedriftcompensated
by a returncurrentin the lowerpart of the
whichin turninducesa slowercirculation
epilimnion,
in the hypolimnion.
thata returncurrent
Whippleactuallydemonstrated
mayalso occurin part
belowthe thermocline.
But the markedchemicalstratification
encountered
in the hypolimnion
of manylakes (cf. resultsforEsthwaiteWater)is not
concordant
withtheviewthatthissecondary
circulation
belowthethermo-
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
171
rotationalmotion(overturn)ofthe hypolimnionwater
clineinvolvesa complete
mass of the type figuredby Wedderburn(Murray& Pullar, 1910). This has
been emphasizedby Alsterberg(1927, 1930), who considersthat the primary
circulationin the epilimnioninduces a secondarycirculationin the upper
whichin turninducesa tertiaryone at a lowerlevel, and so on.
hypolimnion,
He envisages a large numberof such circulationsmovingin thin horizontal
laminae, the resultantmotion having a negligiblevertical component. Alit
thoughthis hypothesisexplainsthe preservationof chemicalstratification,
to see how such a complex systemof horizontalstreaming,the
is difficult
directionof whichis reversedat shortdepth intervals,could be set up and
what sourceof energyis available to maintainit.
A discussionof Hutchinson's (1938b) evidence in favour of Alsterberg's
views is relevanthere, as he suggeststhat these views are contradictoryto
thosewhichlay emphasison turbulence. In the opinionof the presentwriter
this disagreementis not a real one. First consideringHutchinson'sevidence,
this is based on a mathematicalanalysis of the verticaldistributionof alkalinityin LinsleyPond (max. depth14*8m., area 0 094 km.2), a smalleutrophic
lake in whichthe rise in alkalinityin the hypolimnionis mainlydue to the
supply of ammonia and ferrousiron from the mud. As pointed out by
Alsterberghimself,one of the deductionsfromhis hypothesisis that a relationshipshouldexistbetweenthe chemicalcharactersof each horizontallayer
of waterand the area of mud surfaceto whichit is exposed at the edges. This
impliesthe unimportanceofverticalturbulenttransportrelativeto horizontal
streaming,i.e. change in concentrationat any one point in the hypolimnion
water-columnresults,not fromtransportfromabove or below, but fromthe
side. Throughoutthe wholeofthe summerHutchinsonfoundthat the vertical
gradientofalkalinitywas considerablyless at two levels,usually
concentration
approximatelyat 8 and 11 m., than at levels just above and below these.
In otherwords,the concentrationincreasedwithdepth,not in a smoothcurve
was respondistributededdy diffusion
of the type to be expectedifuniformly
sible for the vertical transportof alkalinity,but in a series of steps. An
apparentcorrelationexistedbetweenthe formof thislattercurveand a curve
whichrepresentedthe depthdistributionof the relativeareas of mud to which
each horizontallayerof waterwas exposed at its edges. In Hutchinson'sview
thiscorrelationsupportedAlsterberg'shypothesisand excludedthe possibility
of verticalturbulenttransport.
This conclusionis open to question on the followinggeneralgrounds. In
at the(central?)
orderto producethe observedrate ofincreasein concentration
samplingstation,horizontalstreaming,to be effectivein transportover the
distancefromthe side (area of lake is equivalentto a circleof radius 173 m.),
rapid to involve turbulence.
would almost certainlyhave been sufficiently
This argumentwould apply moreforciblyto a largerlake. It is also shown
later in actual examples(Figs. 37, 38, 39 and 41) that isothermsand isopleths
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
172
Exchangeofdissolvedsubstancesin lakes
position.Such displacement
maybe forcedout of theirnormalhorizontal
theory
would disturbpurelyhorizontallaminaryflow. Hydrodynamical
underopen
(Schmidt,1925; Defant,1929)postulatesthatwatermovements
slow
evenat extremely
are associatedwithturbulence
conditions
unstratified
This
to
occur.
ever
hardly
be
expected
velocities.Pure laminaryflowmay
and the
hypothesis
betweenAlsterberg's
beingso, theapparentdisagreement
aspectsofthe
disappears.Bothviewsstressdifferent
hypothesis'
'turbulence
emphasize,
and Hutchinson
It is clearthat,as Alsterberg
samephenomenon.
mustbe mainlyhorizontal;
of watermassesin thehypolimnion
movements
would
associatedwiththesemovements
necessarily
theturbulence
nevertheless
ofsolutes(whichAlsterberg
be sufficient
to accountfortheverticaltransport
diffusion
is morerapidthanwouldbe thecase ifmolecular
has demonstrated
ofchemicalstratification,
and alsoforthemaintenance
alonewereoperative),
eddiesare smallin comparison
of the turbulent
as longas the dimensions
withthehypolimnion.
in moredetail,Hutchinson
watermovements
Discussinghypolimnion
view(1938b),admitsthepresenceofturextreme
his former
(1941)modifies
forthe observed
bulentmixing,but considersit inadequatein accounting
ofLinsley
hypolimnion
lower
in
the
alkalinity
and
oftemperature
distribution
Pond,Lake Quassapaugand Lake Mendota.Data forLake Mendota(area
39 km.2,max. depth23 5 m.) was obtainedfromBirge'scomputedmean
for1895-1915,as used by McEwen(1929).
distribution
weeklytemperature
the phosespeciallythat describing
Muchof Hutchinson'ssubject-matter,
in LinsleyPond,has
ofchemicalstratification
phoruscycleand development
considerable
bearingon mattersdiscussedhere. A moredetailedconsiderawith
apartfroman outlineoftheargument
mustbe deferred,
tion,however,
whichfollows.
regardto watermovements,
ofheatinthewatercolumnduring
If itbe assumedthat(i) thedistribution
fromabove,and
transport
is effected
whollybyturbulent
springand summer
throughout
coefficient
(A) is maintained
that(ii) a constanteddydiffusion
in thecolumnfalls
(d6/dt)
thecolumn,thentherateofchangeoftemperature
withincreasing
depth(z). In theabovelakessucha regionof
exponentially
of
is
confined
to the upperpart of the hypolimnion,
fall
d6/dt
exponential
Departure
whichmayincludepartofthethermocline.
termedclinolimnion,
forms
thebasisofMcEwen's(1929)
fallintheepilimnion
fromtheexponential
cooling,and cannotbe discussedhere. Departurein
theoryof convectional
inwhichd6/dt
tendsto becomeconbathylimnion,
thelowerhypolimnion-or
implies
Thisdeparture
discussion.
stantat all depths-isthesubjectofpresent
coeffiat least,either(a) theeddydiffusion
that,in partofthebathylimnion
heatingmechanism
withdepth,or(b) someothernon-turbulent
cientincreases
is operative. Hutchinsonacceptsthe latteralternativeon the following
grounds.
by McEwen's(1929)
distribution
Mathematical
analysisof temperature
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
173
method(i.e. fittingthe observedverticaltemperaturegradient,d6ldz,to an
arbitraryfunctionwhichcan be simplydifferentiated)
yields mean estimates
ofA fordifferent
levels. These estimatesvarylittlein the clinolimnion
(4-9 m.
in Linsley Pond, 9-16 m. in Mendota) with eitherdepth or 'stability' (i.e.
da/dz,wherea=density). From this,Hutchinsoninfersthat 'the generalizaof turbulenceis minimalin the morestable layersis
tion that the coefficient
clearly erroneousas far as the clinolimnion...is concerned.,Moreover,if as
seems probable,the coefficient
is essentiallyconstantthroughoutthe whole
hypolimnion,the generalizationis essentiallyfalse for all depths below the
thermocline.'In otherwords,he does not expect turbulenceto increasein
the lowerhypolimnionas a result of the decreasedstabilitythere. However,
assumingalternative(a) and the exclusionof (b), and using methodssimilar
to those used to obtain estimatesof A in ? I, Hutchinsondoes in fact arrive
at values which,in the case of Lake Mendota, increase from3 x lo-2 c.g.s.
unitsin the clinolimnionto double this value at 20 m. depth. Nevertheless,
he concludes:'Since, at least in [his]Figure4, the criterionofvalidity[applied
constantA in the clinolimnion]is so clearly
by McEwen 1929, demonstrating
satisfied,it is certainthat these increasingvalues are erroneous.' (Brackets
and italics insertedin above quotationsby presentwriter.)
of this point is important,for,if Hutchinson'sview is correct
Clarification
and of general application,the estimatespresentedin Tables 1 and 2, ? I,
of eddy diffusion.
may not representtruecoefficients
The followingconsiderations,however,preventthe readyacceptance of Hutchinson'sviewsand their
general application withoutfurtherevidence. The 'criterionof validity' in
the figurereferred
to above onlyapplies to a depthof about 15 m., i.e. to the
clinolimnion.Thereis not sufficient
evidenceforthe assumptionthat,because
A varieslittlewithstabilityor depthin the clinolimnion,
thereis no variation
in the bathylimnionand no correlationwithstability. Hutchinsondid in fact
observe a marked decrease in A with increasingstabilityas the season advanced. It appears to the presentwriterthat, pendingfurtherevidence,the
decisionbetweenalternatives(a) and (b) is stillopen, and that,in view of the
in the way of (b), discussedbelow,(a) is the moreprobable.
difficulties
As a non-turbulent
heatingmechanismin the bathylimnion,Hutchinson
suggests'profile-boundchemicaldensitycurrents',combinedwithhorizontal
streamingpresumablyofthe typepostulatedpreviously(1938b). He supposes
that water in contact with the mud, as a result of its increased dissolved
content(1 mg./l.'HCO3 was equivalent to a densityincreaseof 1-8x 10-6 in
Linsley Pond), flowsdown the mud slope to its new densitylevel, carrying
heat withit. This mechanismhas been suggested(Birge et al. 1928) to explain
the warmingof the bottom water of lakes under ice to temperaturesabove
40 C. In discussingthe possible effectiveness
of such a mechanismit should
be rememberedthat in most lakes the mud slope in the deep regionsis very
slight. It is thereforeopen to question whetherthe small densityincrease
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
174
Exchangeofdissolvedsubstancesin lakes
to overcome
the
producedin thewaterin contactwiththemudis sufficient
doesnotdiscussthelocation
friction
offered
bythemudsurface.Hutchinson
resulting
fromsuch 'chemicaldensity
of the compensation
flownecessarily
fortransport
from
streaming
is heldresponsible
currents',
but,as horizontal
the mud slopeto the lake centre,it is possiblethathe envisagesa central
Difficulties
by Alsterberg.
upwardcompensation
flowof thetypesuggested
laminary
flowwerediscussed
in thewayofconception
ofa purelyhorizontal
earlier.
exchangecoefficients
at certainlevelsin the
In ? I a methodofcomputing
hypolimnion
watercolumn,fromthe transportof heat downwardand of
ofthismethod
solutesupwardthrough
theselevels,wasapplied.Examination
showsthatthe estimatesobtainedwereof
and its preliminary
assumptions
on the exchange
and yieldedno information
'virtual'exchangecoefficients
estimates
obtained
is mainlyturbulence,
mechanism.
Nowifthismechanism
ofanyconservative
thelevel,i.e. transproperty
through
fromthetransport
portofheatdownwards
and ofvarioussolutesupwards,shouldbe identical.
On the otherhand,one resultof Hutchinson's
non-turbulent
exchangemeon turbulence,
is a flowof
chanism,
whether
operativealoneor superimposed
and
solutes
the
mud
from
horizontal
streaming,
slope
there,
by
heatand
down
levels of the centralwatercolumn. It followsthat the
to corresponding
at any levelin thiscolumn,computed,as in
'virtual' exchangecoefficient
ofheat,willbe greater
thanthoseestimates
? I, fromthedownward
transport
of solutes. In EsthwaiteWaterand
computedfromthe upwardtransport
Schleinsee
(Table 1) thereversewas foundto be the case,althoughthe estimatescan onlybe regardedas firstapproximations
usinginadequatedata.
estimates
from
ofvarioussoluteswas
between
upwardtransport
Agreement
lowervalues computedfromthe downwardtransport
of heat
satisfactory;
maypossiblybe explainedbyfailureto accountforflowqfheatintothemud.
whentheupwardtransport
ofheatand solutes
Thisdiscrepancy
disappeared
in lakes underice coverwas considered
(EsthwaiteWater,BlelhamTarn,
Table 2).
If,in viewoftheseresults,and in theabsenceofmoredetailedevidence,
is accoefficient,
alternative
(a), i.e. verticalvariationin the eddydiffusion
the
in
of
distribution
of
and
solutes
the
heat
hypoceptedas an explanation
withdepthin LinsleyPond
thenthe'stepwise'increasein alkalinity
limnion,
deter1938b;-cf.also EsthwaiteWater,Figs.7, 11) is primarily
(Hutchinson,
withthe depthdistribution
of mud
mined,notby any apparentcorrelation
thedepth
factorwhichinfluences
area,butby depthvariationofA. Another
and also limitsits applicationas a 'conservative'
of alkalinity,
distribution
in turbulence
is the oxidationofferrous
ironat the
computations,
property
of
the
there-solution
oftheprecipitated
ferric
at
hydroxide
top
hypolimnion,
associatedwiththis. It is ofinterest
lowerlevels,and adsorption
phenomena
etal. (1939)foundthethermocline
in LinsleyPond at 7 m.
thatHutchinson
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
175
depthon 16 September1938,i.e. 1 m. above the upper 'step' in the alkalinity
depth distributioncurve(Hutchinson,1938b).
To summarizethis discussion:resultsto date demonstratethat waterflow
in thehypolimnion
is largelyhorizontal,permittheexpectationthatturbulence
associated with this flowis the main mechanismof heat and chemical exchange in largerlakes, and suggestthat non-turbulent
exchangemechanisms
may become increasinglysignificantin smallerbodies of water. A probable
cause of the horizontalflowis describedbelow.
Suggestedmechanismof inductionof horizontalwater movementsin the
hypolimnion.Murray(1888, refs.in Murray& Pullar, 1910) was the firstto
demonstrate,fromthe studyofverticaldistributionoftemperatureat various
points along an axis of a lake, that a wind blowingin one directionforsome
time across a thermallystratifiedlake may transportwarm surfacewater to
the lee side, resultingin a deepeningof the epilimnionon that side and a
tilt of the isothermsin the thermoclineregion.When the wind
corresponding
drops, this tilt is clearlyunstable. The isothermsswing back to horizontal.
They may swingpast the horizontallevel of equilibriumand set up a seriesof
oscillationsor 'temperatureseiches'. Wedderburn(1911) has shownthat the
theoreticalfrequencyof such oscillationsmay be estimatedfroma consideration of ideal lake systemsin whichthe discontinuity
layerbetweentwo fluids
of different
densityoscillatesin a similarmanner.The theoryhas also been
applied to a stratifiedliquid of varyingdensityin basins of different
shapes.
Close agreementwas obtained betweenthe frequencycomputedfromtheory
and that observed in Loch Earn and in experimentaltanks (Wedderburn,
1912). The appearanceoftemperatureseichesin Loch Earn and in otherlakes
was foundto be related to wind and othermeteorologicalconditions. Correlation between wind and temperatureoscillationswas close in most cases,
but not so completein others. 'Examples of the effectsof winds, both in
startingand in damping oscillationsalready in progress,have been given,
withthe indicationthat even a windof verymoderate
will startoscillastrength
tions, and examples of oscillationsforcedby wind have also been obtained'
(my italics).
It is clear fromthe observationsof Wedderburnand othersthat a tilt of
the thermocline,
i.e. displacementofthe 'isosteres' (surfacesof equal density)
fromthe position of horizontalequilibrium,is a commonoccurrencewhich
mustresultin some displacementof the hypolimnionwatermass. The extent
and path of the resultantmotionis at presentlargelyunknown,but it may
be suggestedfromtheory(Defant, 1925, pp. 24-5, Figs. 4, 5) and fromtatik
experiments(Wedderburn,1911, Pt. I; Wedderburn& Williams,1911; Hutchinson,1938b) that an oscillatorymotionis induced in phase with changes
in declinationof the isosteres,and that in the centralregionof the lake basin
this motionis mainly horizontalor parallel to the contoursof the bottom.
In directattemptsto measureflowin the hypolimnionof Loch Earn it was
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
176
Exchangeof dissolvedsubstancesin lakes
weretoo slowto be detectedwithan Ekmancurrent
foundthatthecurrents
meter,i.e. theywerelessthan1 cm.persec.,below20 m.
by wind-geneIf,as seemsprobable,theflowinducedin thehypolimnion
damped,
ofdiscontinuous,
ofisosteres
has thecharacter
rateddisplacements
ofthe
laminarystreaming
and is nota unidirectional
horizontal
oscillations,
that
Alsterberg
type,thenthisis an additionalreasonforthe expectation
watercolumnis controlled
in a centralhypolimnion
distribution
ofproperties
fromtheseoscillaresulting
due to turbulence
mainlyby verticaltransport
fromthemudslopeto which,ifprojected
tions,and notby lateraltransport
horizontally,
each sliee of the watercolumnis exposedat its edges (cf.
in themechanics
of
thereis nothinginherent
Hutchinson,
1938b). Further,
ofturbulence
is constant
to suggestthatthecoefficient
isosteredisplacement
maybe expected.
at all depths,in factthecontrary
of windin tiltingisotherms
and isoplethsis preEvidenceof the effect
ofhorizontal
sentedin Figs.37, 38, 39 and 41, but thedirectdemonstration
and ofturbulence
associatedwithit has
oscillatory
flowin the hypolimnion
arewind-generated,
therateofspread
stillto be achieved.As themovements
of properties
in the watercolumnmaybe expectedto dependon the work
lengthof'fetch'and
doneby thewind,i.e. on suchfactorsas windvelocity,
articlein Murray
degreeofexposureofthelake. Murray(cf.Wedderburn's
in the abyssalregionsof deep
& Pullar,1910) notedthatthe temperature
lakes increasedduringthe summerin 'fitsand starts',dependingon the
ofwindyspells.
occurrence
ofthe
It can be shownthata relationexistsbetween(a) the dimensions
and
the
mean
to
diffusion
coeffieddy
(b)
lake basin,and its exposure wind,
A windcan exerta greatertotalforceon a larger
cientin thehypolimnion.
withsidesand bottomis less in a
of friction
area, and the dampingeffect
deeperlake. Roughestimatesof a meanvalue ofA, forperiodsof summer
have been made
at certainlevelsin the hypolimnion,
thermalstratification
data by the methodoutlinedin ? I.
fora varietyoflakes,fromtemperature
constants
forthelakes,in Table 4.
withmorphometric
Theseare presented,
has
been
Thisinvolvesan error
into
the
heat
The flowof
neglected.
deposits
forshallowlakes. EstimatesofmeanA forEsthwaite
whichwillbe greatest
Water,obtainedfromotherdata (cf.Table 1), have beenincludedforcomparison. It may be concluded(Fig. 36) that the meanvalue of A in the
to
is roughly
thermalstratification
proportional
duringsummer
hypolimnion
eitherarea,depth,
of the lake. It cannotbe statedwhether
the magnitude
ofA is closestwith
factor.However,correlation
orvolume,is thecontrolling
36
of
station'
at
the
measuring
(Fig. B). Degree exposureto windis
'depth
Thelowvaluein LunzerUnterseein spite
also clearlyofprimary
importance.
ofits depth,forinstance,maybe a resultofshelterin a steep-sided
valley.
isoassociatedwithwind-induced
Chemicalevidenceof watermovements
In thefewstudiesthathave been made of the horizontal
stereoscillations.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
177
Table 4. Comparisonof(i) roughestimates
ofthemeanvalueoftheeddydiffusion
coefficient
(A) in thehypolimnion
ofvariouslakes.duringperiodsofsummer
thermalstratification
with(ii) thedimensionsofthoselakes
Depthat
Roughestimateof
A
measur- .
Max. Mean
At
ing
depth depth station
For
depth
m.
m.
m. A x100
period
m.
295
114
295
310
26. vi -26. ix.
100
1930
503
303
152
285
21. vi -23. x.
100
190
1879
71
195
37
185
53
22 ix.-14.xi.
56
1885
82
67
26
55
39
14 vi.-13.ix.
30
1939
1
67
ix
44
18
30
9
6. vi.-20.
15f
1939
J
39
25 6
12 1
7 15.vi.-15.viii.
23.5
12
mean1900-16
75
27
26
7 17 vii-28. ix
185
1900
14
29
25
5
June-Aug.
15
1926-9*
5
0 68 34
20
32
29.iv.-29.vi.
20
Key
letter Area
Fig.36 km.2
H
121
Lake
Holsfjord
Geneva
(largebasin)
Lomond
(Inversnaid)
Windermere,
NorthBasin
Wmdermere,
SouthBasin
Mendota
M
Maxinkuckee
Ma
Kizakiko
K
Lunz, Untersee
Lu
EsthwaiteWafer
E
10
16
Schleinsee
Sc
015
116
G
L
N
S
5
14
3
Cf.Table 1
12
64
116
2
Cf.Table1
11
ca.
Sourcesofdata
Strom,1932
Forel,1880,1892
Buchanan,1886;
& Pullar,1910
Murray
Taylor,1940
Mortimer
(inprep.VI)
Birgeetal. 1928;
Juday,1914
Evermann& Clark,
1920
1936
Yoshimura,
Muller,1938;
19-12
Gotzinger,
Thispaper,also
Mortimer
(inprepVI)
Einsele& Vetter,1938
* By inspection
in Fig. 6.
ofisotherms
B
A
SG
2
I 05
0-
\~~~~~~~~~~~~f
.2N
0
0
g
0
.s
o01
LU.
*
0*03
002
K
*
Ma
0.1
M
es
M*eMa
Ko *Lu
*EE
.E
Sc
0-1
*N
[Al
02-
0
&05
eG
*Sc
1
10
Area, km.2
100
1000 10
20 30 50 100 200 300
Depth at measuringstation,m.
Fig. 36. A comparisonof (1) the estimatedmean values of the eddy diffusioncoefficient
A ia
the hypolimmaof variouslakes with(ii) the dimensionsof thoselakes.
J. Ecol. 30
12
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
178
Exchangeof dissolvedsubstancesin lakes
lakes
stratified
and chemically
ofchemicalvariablesin thermally
distribution
of the isoplethsfromthe horizontal,
(e.g. Rossolimo,1931),a displacement
dueto windaction,
oftheisotherms
at thesametimeas a similardisplacement
in the Lake Districthave
noted. Some observations
has been frequently
may be producedby quite moderatewinds.
shownthat this phenomenon
sectiononEsthwaiteWaterinFigs.37-39.
longitudinal
for
a
Thisis illustrated
on thislake weresimilar.It willhe notedthatthe
Resultsforcross-sections
tiltas a resultofa moderatewind
exhibita definite
isoplethsand isotherms
blowingat the time. In addition,the oxygenisoplethsin the hypolimnion
werefoundto be depressedat the edges.This mayhave beenthe resultof
withthe bottom)on theseslopesthan
moreintensemixing(due to friction
at thesamelevelsin openwater,causedbythesee-sawmotionoftheisopleths
powerofthemudon
The reducing
withchangesin windforceand direction.
as the adsorbent
of
the
lake,
the slopesmayalso be less thanin the centre
oxidizedsurfacelayerwouldbe givena chanceto formagainif the surface
isopleth
orprolonged
waterbya morepronounced
wasexposedto oxygenated
tiltthanusual.
equilibrium
to horizontal
An exampleofsucha tilt,and itsreadjustment
bychangesobservedat twostations
is illustrated
afterthewindhas dropped,
at interby observations
on BlelhamTarn(Figs.40, 41), and was confirmed
thermowitha reversing
measurements
mediatestations.Aftertemperature
regionby
meter,samplesweretakenat 01 m. intervalsin the thermocline
in? III, waslowered
described
mudsampler,
Thesurface
method.
thefollowing
regionand closed. After
to a selecteddepthin the thermocline
carefully
pouredon to the
raising,the top lid was removedand someliquidparaffin
watersurface.By meansof a specialdevicesampleswerethensiphoned
thetop10 cm.)
fromeach10 cm.depthinthetube(discarding
simultaneously
the
samplefrom
prevent
to
paraffin
liquid
containing
bottles
50
c.c.
into
ofthistechniqueat variouslevels,
comingintocontactwithair. Repetition
causedby
aftermovingtheboat a smalldistanceawayfromthedisturbance
graprevioussampling,enabledthe oscillationof the large concentration
(Fig.41B)
(Fig.41). Thefinallevelofthethermocline
dientto be demonstrated
was a littlelowerthanthemeanlevelduringtheroughspell.Thisrepresents
inducedby the shearingof
workdoneby the wind,appearingas turbulence
whichmusthave occurred
watermassoverthehypolimnion,
the epilimnion
of
the
tilt.
decay
subsequent
and
duringtheformation
Its relation
itsthickness.
control
mudlayer.Factorswhich
Theoxidized
surface
oflakesandlakeevolution
classification
toorganic
production,
here,Grote
inscopefordetailedconsideration
In a book,toocomprehensive
inthispaper.
ofinterest
bearingontheworkdescribed
(1934)raisedmanypoints
ofdiffusion
that,ifthecoefficient
considerations
He deducesfromtheoretical
then
the oxygen
is
to
be
a
mud
assumed
constant,
in
the
ofdissolvedoxygen
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
179
H. MORTIMER
ofwmd-0. .
Direction
4-~~~~~~~~~~ 33
6_ t1
t
|
|
319
1548
15 3
stations'
~~~Samplmng
200
100
15
/
1
,_
500
400
.5
,v
900
800
700
600
Distance in metres
Fig. 37. Estliwaite Water. Distribution of temperature (0 0.) on a longitudinal section,
aIe on this section
shownon the map, Fig. 1, ? I.
19 September1939. Samplingstations
200
100
300
400
500
700
600
Distance in metres
900
800
mecthod)
Fig. 38. Esthwaite Water. Distributionof
disledprtroxyen(ma/ . un odifitudWinkle
I
on
sechsetion
n1 S reptme 1939. hemp,Fg.1
19 Setembe 19
Samlongisttuional
Direction of wmnd
--.-------
3284
83
82
>
-8*
0
I
7~~~~~~~~~~
6
0~~72
~69
~
\
70
71
43
Levelbelowwhich
o 'XTotdlronconcentration>1 mg/I
14-1
100N
69
_
-
_.
~~~
~~~~~~~~~~~~~~~~~~~68-
\
2_
m
95~~~~~~~~~8 82
1
stationls
Samplmng
12
200
300
400}
75
=
a
500
6
600)
'Distancem metres
2
=
1
X//
70()
800
900
Fig. 39. Esthwaite Water. Distributionof electrical conductivity(K18ox 10-6) on a longitudinal section,19 September1939. Also some data foriron.
12-2
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
180
concentrationat the mud surface,divided by the thicknessof the oxidized
layer,roughlyrepresentsthe mean oxygenconcentrationgradientmaintained
in the mud surface,and this must be proportionalto the rate at whichthe
mud absorbs oxygen. The thicknessof the oxidized layer thus representsa
power of the mud, and (b) the
balance between (a) the oxygen-absorbing
oxygen concentrationat the mud surface. If (a), in comparisonwith (b),
exhibitsonlysmall seasonal variation,the thicknessofthe oxidizedlayer,and
whetheror not it disappears,depends only on (b), i.e. the concentrationof
oxygenmaintainedat the mud surface.This will in turn depend on (1) the
available supplyof oxygenin the water mass, with whichthe mud surfaceis
and (2) the degreeof eddy
potentiallyin contact by means of eddy diffusion,
0
__
0.1
04
03
0-2
I.
I
O - 5,
.
10,~~~~~~~/
-2-213 15
05 mile
I
eXX'
Fig. 40. Bathymetricmap of Bleiham Tarn. Contoursfromecho-soundngsurvey
(Mortimer,in prep. VI). * Samplingstations.
in this water mass. (1) also depends to somneextentpn the rate at
diffuxsion
whichreductionprocessesoccur in the water. It is possible to mnakecertain
deductionsfromthis hypothesisand to apply roughchecks with available
data.
Deduction 1: If the mean thicknessof the oxidized layer be comparedin
a seriesof lake muds duringa period when the oxygenconcentrationat the
mud surfaceis maintainedat the same constantlevelin all cases, e.g. during
tnverse relationto the
the wintercirculationperiod,each thicknesswill be in
powerofthe respectivemud. A roughcomparisonhas been
oxygen-absorbing
made, for a series of English Lake District lakes, between (a) the rate of
oxygen absorptionfromthe hypolimnionduringsummerthermalstratification, and (b) the approximatemean thicknessof the oxidized layer during
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
...........o........
181
H. MORTIMER
~~44 ~~~~~~
0
;
-0
0
_.
0
0
r
X
P-0
-~~~~~~~~~~~~~~~~~~4
o
0)
o
-~~~~~~~~~~~~~~~~~
o
o
=
0
00c
QdC)
09l}oW
.M)
~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~o
~
0
Co
bO~~~~~~~~~~~~~~~~~~~~~~~C
H
00
00
0
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
0)
182
Exchangeofdissolvedsubstancesin lakes
Thiscomparison
is ofvalue,notbecausethe
theperiodofwintercirculation.
representative,
data can claimto be completeor morethanapproximately
and indicatesa
generalrelationships
but because it disclosesinteresting
possiblyusefulmethodin regionallimnology.
rate of Esthwaitemudmaybe
oxygenabsorption
(a) The approximate
to theratein four
ofFig. 13,? I. An approximation
by inspection
estimated
of theextent
otherLake Districtlakeshas beenobtainedfroma knowledge
stagnation
at theendofthesummer
in thehypolimnion
ofoxygendepletion
at eachdepthis plotted,
oxygenconcentration
period.In Fig.42 theobserved
underthe
93% saturation
whichrepresents
as wellas at thatconcentration
conditions,
thisbeingthe usual degreeof saturationobsametemperature
was madeforthe height
servedin theselakesduringwinter.No correction
betweenthe observedand the
of the lakes above sea-level.The difference
the 'actual deficit'(see discussionin
93% saturationvalues represents
to Alsterberg's
1938a), and has been employedin preference
Hutchinson,
' absolutedeficit'
andthe100%
concentration
between
observed
(i.e. difference
unsound
saturationvalue at 40 C.), as the use of the latteris theoretically
may possesscertainpracticalad(Grote,1936),althoughits employment
1938a). The total 'actual deficit'in the hypolimnion
vantages(Hutchinson,
fromFig. 42. This,dividedby
planimetrically
of each lake was determined
and 1 May,on which
the numberof days betweenthe date of observation
was assumedto have begun,yieldsa meandaily
date thermalstratification
as gramspersq. m.
forthewholewatercolumn,expressed
oxygendecrement
thanthe' arealhypoof mudsurfaceperdayin Table 5. Thisvalueis higher
(1938a), but is notfarremovedfrom
limneticoxygendeficit'ofHutchinson
for
it. The valuesgivenin Table 5 are simplerto computeand are sufficient
of mudsof widelydiffering
power.
oxygen-absorbing
thisroughcomparison
to thoseofHutchinson
have beencomputedforWinderValuescomparable
data).
mere,Northand SouthBasins 1932,by P. M. Jenkin(unpublished
in 'areal hypolimnetic
Increments
deficit'in bothbasinswas foundto vary
These values are not far
(personalcommunication).
about 0 4 g./m.2/day
different
fromthosefoundin 1938-40.
(b) Estimatesof the mean winterthicknessof the oxidizedlayer,i.e.
depthof the isovoltE7= 0-20V. belowthe mud surface,wereobtainedby
of
winterdistribution
of Fig. 43, whichillustrates
representative
inspection
potentialin coresfromdeepregionsoffivelakesin theEnglishLake District.
Wateris
Theseestimatesare enteredin Table 5. That givenforCrummock
was available. However,
probablytoo low, as onlya summerobservation
positionbetween
thislake has beenincludedas it occupiesan intermediate
later).
Ennerdaleand mesotrophic
Windermere
(definitions
oligotrophic
in anyone
deduction
more
it
is
assumed
If
(i)
that,
precisely:
(1)
Stating
ratesare roughlyproporlake, the summerand winteroxygenabsorption
tional,and (ii) thatin all lakesthewinteroxygenconcentration
(C.) at the
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
*e7--*
Actualconcentration
.-X ---et Equivalent of 93%
saturationat same
temperature
J$"?
11\t
ti7'1~/
20
E
Ig
a)~
~ ~~~~~
o
Ig
E93
=
l
50~
_
E93
N93
= ~~~~Bottom
I
Na
6
7
8
9
10
mg./l.
Oxygen,
of dissolvedoxygenat the
in variouslakes,of (i) the depthdistribution
Fig.42. Comnparison,
temunderthesamne
saturation
that
with
93%
representing
(ii)
endofsummer
stagnation
Water(C), 3 Sepconditions.EnnerdaleWater(E), 17 August1940. Crummrock
perature
NorthBasi-n(N),
SouthBasi-n(S), 4 October1939. Wmdermere,
tember1940. Windermaere,
'93' equals '93%/saturasuffix
a equals 'actual concentration';
11 October1939. Suffix
tionvalue'.
12
11
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
E7 in volts
0*10
-
4
0-20
0*10
l
+
0
l
Reducing
Mud surface
0*40 i
0*30
0'50
0'60
1;
Oxidizing
-\
--
0~~~~~~~~~~0
0
10 .:
2 W
2..
16
X
~
0.10
0610
Lv
*-
, -@
|
......<.
~~~~~~~~~~loo
4,.
-
-x---
j -
X
Es~~~~~X.- Wd.
1
? +
0.60
0150
0. 0
030
0-40
of redox potential(E7 m volts)in the surfacemud coresfrorn
]Fig.43-. Typical winterdistribution
Ennerdale Water (E), 40 m., 15March 1941. Crummnock
lakes.
various
of
the deep regions
Water(C), 40-8m., 3 September1940 (N.B. singlesumrmerobservation). Windermere,
NorthBasin (N), 65 ni. 6 February
South Basin (S), 31 m., 11 February1941. Windermere,
1941. EsthwaiteWater (Es), 14 m., 12 March 1941.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
185
H. MORTIMER
of diffusion
(k) in the mud is of the same
mud surface,and also the coefficient
order,then the followingrelationshipshould be found:
Summeroxygenabsorptionrate (0) oc
(w
z
e
oxidizedlayer(T1')
thickness
Thus if (0) is plottedagainst (T), the pointsshouldlie on a rectangularhyperbola, i.e. iflog (0) is plottedagainstlog (T), the pointsshouldlie on a straight
line. For the data givenin Table 5 thisis foundto be approximatelythe case
(Fig. 44 A).
Table 5. Comparisonof (a) estimatesof theoxygenabsorptionwith(b), winter
thicknessof the oxidized layer, (c) redox potentialat 5 cm. depth,and
(d) organiccontentofmudsfromthedeepregionsofvariouslakes
Lake
.
...
Max. depth,m.*
Ennerdale
Water
(E)
43.9
Windermere
Crummock ,
Water
South Basin NorthBasin
(C)
(S)
(N)
67
43.9
44
Esthwaite
Water
(Es)
16
I. Estimate of (a) mean daily increment(0) of 'actual oxygendeficit',
in hypolimnionwater column(g./sq.m. mud surface)
11. x. 39 Mean May-July
4. x. 39
Date of observation 17. viii. 40
3. ix. 40
cf.Fig. 13
OffLowood
9-14
15-55
Limits of Water
15-39-8
15-40-8
15-31
column,m.
0-65
0-52
009
0-16
0-31
0, g./m.2/day
II. Estimate of (b) winterthickness(T) of oxidized surfacemud layer
and (c) mean winterredox potential(E7) at 5 cm. depth
12. iii. 41
6. ii. 41
Date of collection
5. iii. 41
3. ix. 40t
11. ii. 41
31
14
65:
Water depth,m.
40
40-8
07
1-7
2-2
1.1
4*0
T,cm.
-007
+0-14
+006
-0-05
+0-02?
E7at 5 cm. (V.)
III. (d) Organiccontentof Petersengrab samples (Misra,1938)
40
50
Water depth,m.
12-84
Loss on ignition,
16-84
% drywt.
Total N, % drywt.
0-4506
0-5384
* Othermorphometric
data in Mill (1898).
12
21-34
0-8539
t N.B. summervalue.
$ Only case in this series in which mud samples taken at a point removed fromthat at
which 02 depletionwas estimated.
? Mean of 24 cores; highervalue than indicatedin Fig. 43.
Hutchinson(1938a) has demonstratedthat, in a series of geographically
different
lakes, the incrementof 'areal hyposeparated and morphologically
limneticdeficit'is proportionalto planktonproductionin each lake. He has
suggestedthe limitsH-H (Fig. 44 A) formesotrophiclakes. All lakes with
incrementsabove or below theselimitsare classed as eutrophicor oligotrophic
respectively.Thus, even allowing for the differencebetween Hutchinson's
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeof dissolvedsubstancesin lakes
186
North
wouldclassWindermere,
'areal deficit'and (0) (Table 5), Hutchinson
and
South
Basin,
Windermere,
and
Basinand EsthwaiteWateras eutrophic
as a matterofopinion,
It maybe suggested,
Wateras mesotrophic.
Crummock
in the English
that the limitsL-L (Fig. 44 A) fitthe observedconditions
Waterare conLake Districtbetter.ThusEnnerdaleWaterand Crummock
and EsthwaiteWaterto be eutrophic.
sideredto be oligotrophic
and generallevelofredox
in thedistribution
differences
Fig. 43 illustrates
notonly
are expressed,
potentialin themudsofthelakes.Thesedifferences
oftheoxidizedlayer,but also in thevalueoftheminimum
in thethickness
redoxpotentialin the core,usuallyto be foundat about 5 cm. belowthe
depth
withincreasing
andthegradualriseinpotential
Thisminimum,
surface.
at
decomposition
below5 cm.,mayindicatemoreintenseanaerobicorganic,
4
0-
Oligo-
s
3.0-
L
Meso-
1
Eutrophic
L
L
.0
2-~~~~~~%
+
~~~
0v5<
_
Cvo
XEs
in5
0-5
He
Fig. 43.
vlatlons as in
0
(2I
~
~
~
~
~
I 101610111-4
0-4
060810
o (g./M.2/day)
oVO
~
0
O3
a
05
0
~
~
-
.
~
Es
Fig. 44. Correlations(A) betweenthe rate of oxygenabsorption0 and the wnter thicknessof
the oxidized surfacemud layer T, and (B) betweenthe witer redox potential(E7 in volts)
m muds fromdeepest regionsof various lakes. AbbreoO and
at 5 cm. depth m the mud
viationsas in Fig. 43.
the5 cm.level,i.e. just belowtheoxidizedlayer,and a decreasein intensity
thattheoxygen-absorbing
inolderandlowerdeposit.ZoBell(1937)recognizes
(I) and a capacityfactor(K),
power(0) ofmudsis theproductofan intensity
i.e. 0 = I x K. If redoxpotentialis equatedto I, it is possibleto envisagea
i.e. highintensity
mudoflow potential,
(I), but withlow oxygen-absorbing
vice
and
on
versa.
the
other
hand, I is proportionalto K,
If,
capacity (K),
I will be proportionalto the square root of the oxygen-absorbing
power.This
holds (Fig. 44 B) roughlyforthe muds investigated.
A similar,althoughless detailed,observationofa redoxpotentialminimum
just belowthe mud surfacewas made by Karsinkinetal. (1930). These workers
werethe firstto publishresultgof measurementsof potentialsin muds and to
point out theirrelationto redox conditionsin the water. Since then other
measurementshave been mnadeby the same authors(1931), by lwlew (1937)
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
187
in connexionwitha detailedstudyofseason changesin distributionofvarious
formsof ironin mud and water,and by Misra (1938).
In non-peatymuds it mightbe expectedthat organiccontentis the most
importantfactor determiningthe level of redox potential. Unfortunately,
data forLake Districtmuds are insufficient
to test this. However,if loss on
ignitionand total N values of muds fromthe same localities(Misra,1938) are
comparedwithE7 at 5 cm. (Table 5), the muds are seen to fall into the same
orderif arrangedaccordingto organiccontentor potential.
Typical winterdistributionof electricalconductivityin the surfacemud
in the deepest regionsof the same fivelakes is illustratedin Fig. 45. ComparisonofthiswithFigs. 42 and 43 demonstratesanothercorrelation,namely,
that betweenoxygen-absorbing
powerand electricalconductivity.The highest
conductivityand also the most rapid increaseof conductivitywith depth is
found in the muds with the highestrate of oxygen absorptionand lowest
potential. The depth distributioih
of conductivityis approximatelyexponential. Thus, if the log of the slope of the conductivitycurvesin Fig. 45 is
plotted against depth,the points over a large part of the curve lie approximately on straightlines (Fig. 46 A). Deviations fromthis line at the mud
surfaceindicate adsorptionof ions in the oxidized layer. Other deviations,
usually found at about 12 cm. depth, may indicate changes in the rate of
productionof ions at these levels. A mathematicalanalysis of these and
similarcurveswill be attemptedin a later publication(Mortimer,
in prep. I).
The followingempiricalrelation,however,may be notedhere. The squares of
the slopes (S) of the lines in Fig. 46 A are roughlyproportionalto (0) (see
Fig. 46 B). If we assume with Grote (1934, p. 33) that the rate at which
oxygenis utilizedin decompositionis a measureof the rate at whichmineral
substancesare liberated,and of the rate of lake 'metabolism' as a whole,the
above empiricalrelation suggestsa formulaof the followinggeneral type,
whichgives the conductivity(K) at depth (z) in the mud:
K
KL + (KO-KL) e-ZV(rIc),
wherer is the rate of productionof ions in the mud, c is a constantwhich
includes the coefficient
of diffusionin the mud, KO equals the conductivity
at the mud surface,and KL is the limitingvalue of K whichis approached
withincreasingdepth. Deviations fromthistheoreticaldistributionmay indicate variation in c or (more likely) in r. The above formulais of the same
general type as that which expressesthe distributionof the-steadystate of
temperaturealong a long bar, heated at one end and losingheat by radiation
and conductionall along its surface(Carslaw,1921).
A second deductionmay be made fromthe originalhypothesis(p. 180).
Assumingthe oxygen-absorbing
power of the mud to remain constant,and
the
due
to
slowness
of reductionof oxidized compounds
neglectingany lag
(.e.g. ferrichydroxide),the thicknessof the oxidized layer in any one mud
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
Exchangeofdissolvedsubstancesin lakes
188
at themudsurface.
willbe directly
concentration
to theoxyTgen
proportional
The data areinsufficient
to checkthis.
20
40
60
1
o
t:
!.
tV
|
mm
og
00
80
I
,:..
140
1 W-
Mud surface
minn-
m\m-mm-
2..
120
m---
--
- m
160
180
200
_min
=.v?,
;;]umit
?of
_Lower
oxidizedlae
oflae
t
qLevel
N~E7=+020V.
\
6
208
\,\:6..
"I
"O1tI
Kl8? x 10-
12.
E
14:EcN
of electriLcal
Fig.45. Mean winterdistribution
(K:L8.x 10-6) in the surfacemud
conductivity
coresfromn
deepestregionsof variouslakes. Abbreviations
atnddepthsas in Fig. 43.
*S1gle
summerobservation.
A thirddeduction,
whichhas a bearingon productivity
is as
problems,
follows. In lakes with muds of approximately
equal oxygen-absorbing
whichin mostcasesthe
power,depletionofoxygenin thehypolimnion-for
mudis mainlyresponsible-may
in
appeareitheras a small'volume-deficit'
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
189
H. MORTIMER
a deep lake or as a large 'volume-deficit'in a shallow lake (cf. Hutchinson,
1938a and refs.there).The mud surfacewill onlybecomereducedand exhibit
the acceleratedliberationof ions fromthe mud associated withthis,in lakes
shallow to produce a large enough 'volume-deficit'at the mud
sufficiently
surface. In shallowlakes the volumeofthe hypolimnionis probablythe main
controllingfactor,for,as thismustbe consideredas a partiallyclosed system,
the total available supplyofoxygenis limited. In lakes ofmediumand greater
1
Gradient(dKldz) fromFig. 45 (conductivityunitsper cm.)
2
O I
A
s~~
3
4
I
I
5 6
1 I
8
1520
10
itilnimill
Im I Ii1
XV00
2
0
0
v/
/1'7
.6
07
.
NY~j0/
10
17
3
N*
S2/
(.i.2dy
s~~~~~~~
0
C~~~ *2
4
0
Fig. 46. A. Logarithmsof the gradientsof curves in Fig. 45 (i.e. log dK/dz) plotted against
depth (z). B. Comparisonof the slopes (S) m Fig. 46 A withthe rate of oxygenabsorption
(0) of the mud. Abbreviationsas in Fig. 43. * Single summerobservation.
depthsthe volume of the hypolimnionbecomes of less importancerelativeto
whichapparentlyincreaseswithdepth and other
the degreeof eddy diffusion,
factors(Table 4). If thiswerenot so-i.e. if the degreeof eddy
morphometric
diffusionwere to remainthe same in all lakes, both deep and shallow,with
of oxygen
mudsofthe same oxygenabsorbingpower-the verticaldistribution
than a
more
of
lakes
all
in
be
identical
would
surface
mud
to
the
relative
hypoof
depth
a
greater
exist
whereby
would
certaindepth. No mechanism
in
deep
stratification
of
chemical
A
limnioncould exert its influence. study
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
190
Exchangeofdissolvedsubstancesin lakes
and comparisonofthiswithstratilakes duringsummerthermalstra-tification
may be expectedto be low,
ficationdevelopedunderice, whereeddy diffusion
should yield data to checkthe above conclusions.
Classificationof lakes. Beforeproceedingto discuss the possible effectof
it is necessaryto outline
redox conditionsat the mud surfaceon productivity,
certainambiguitieswhichhave arisenin the classificationof lakes on a productivitybasis. The original and perhaps the clearest definition(refs. in
Naumann, 1932) dependedentirelyon the degreeof plant productionand the
edaphic (geochemical)factorswhich controlthis. Subsequently,other features, often but not necessarilyassociated with oligotrophicor eutrophic
eutrophicor
conditions,have been employedto class lakes into oligotrophic,
categories.Thus a high or low degree of de-oxyintermediate(mesotrophic)
genation in the hypolimnionhas been termed a eutrophicor oligotrophic
conditionrespectively(Thienemann,1928), because in the majorityof cases
these featureshave been foundto be associated with a high or low degreeof
organicproduction.Emphasisis thuslaid moreupon the oxygenconditionspossiblyof greaterinterestto the zoologist-than upon the degree of plant
the same terminologyis employed. Reproduction,althoughunfortunately
cognizingthe influenceof the shape and size of the basin on the distribution
factoras one of
of oxygen,Thienemann(1928) has includedthe morphometric
the most importantin determiningthe trophicconditionof lakes, regarding
it as inseparablefromotherfactors(cf. p. 146). Lundbeck (1934), however,
on the one hand and sedistinguishesbetweenprimary,edcphicoligotrophy
(greatdepth) on the other.The logical conoligotrophy
condarymorphometric
clusionfromthis view has been stated by Hutchinson(1938a), who considers
that the edaphic and morphometricdeterminants'in great measure vary
independently'(my italics), and that the influenceof the latter may be
different
eliminatedin a comparisonof the productivitiesof morphologically
lakes by the employmentof the concept'areal hypolimneticoxygendeficit'.
The limitationsof the latter concept,especiallywhen applied to shallow
lakes (cf. Riley, 1939, cit. Deevey, 1940), should hiotbe ignored.With these
the concept may be applied with profitto the study of
limitationsin mnind,
regional limnologyin areas from which plankton data are not available.
Hutchinsonhas pointed out that the close relation between 'areal deficit'
and planktonproductionbreaks down when considerablequantitiesof allochthonousorganic matter are present. This suggests that a more general
relationis one between (a) areal deficitand (b) reducingpower of the mud.
This may explaina discrepancyobservedbetweenthe Northand South Basins
of Windermere.A study of planktonproductionin these two basins over a
periodof yearshas shownthat phytoplanktonproductionin the South Basin
is at least double that in the North Basin; zooplanktonproductionis also
higherin the former.The mud in the South Basin, however,is
significantly
less reducingthan in the NorthBasin (Fig. 43), and the oxygendeficitin the
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
191
hypolimnion(Fig. 42) in these two basins is correlated,not withthe amount
of planktonproduced in the epilimnion,but with the reducingintensityof
the mud. This is possiblycontrolledby the distributionof decomposingleaf
fragments,
whichare foundin considerablequantitiesin the mud ofthe North
Basin, especiallyin regionsnear the largerinflows,but are relativelyinfrequent in the muds of the South Basin, whichreceivesmost of its inflowfrom
the NorthBasin.
It is of interestto speculate what lightis thrownon the above confusing,
in previous
by the demonstration,
ifnot conflicting,
views oflake classification
sections-,of the acceleration in liberation of ions, including many plant
nutrients,duringreductionof the mud surface. As the resultingincreasein
concentrationof solutes in the water is large, this event may be considered
to have a profoundinfluenceon the degreeof organicproductionin the water.
It has been shown that, in all but exceptionallyreducingmuds, this event
can onlyoccurin relativelyshallowlakes. Extremeoligotrophy,on the other
hand (primaryoligotrophyin Lundbeck's sense), will not be associated with
oxygenexhaustion,even in lakes with the small hypolimnia. A causal connexionmay thereforebe expected,in the higherrangesof productivityonly,
betweendegree of organicproductionand depth of lake. If this connexion
can be demonfstrated
by extended studies of regional limnology,it lends
supportto the generalobservationat the basis of Thienemann'sviews that
highproductionis moreoftenthan not associatedwitha highdegreeofoxygen
depletion in relativelyshallow lakes, and that morphometricand edaphic
determinantsof productionare not entirelyindependent.It was emphasized
earlier that the morphometricdeterminantincludes not only dimensional
factors,but also the influenceof these on water movementsand the degree
whichclearlyalso depends on climate. These speculations
of eddy diffusion,
can onlybe testedby futurework.The presentpositionhas been summedup
by Rawson (1939, cit. Deevey, 1940): 'while the edaphic factorsdetermine
the kindsand amountsof primarynutritivematerials,the morphologyof the
basin and the climatemay to a large extentdeterminethe utilizationof these
materials'.
Lake evolution. It. is also of interestto suggest brieflyhow the above
speculationsmay apply to the conceptof lake evolution. Any change in the
productivityofthe watermay be expectedto producea changein the organic
contentand reducingpower of the mud. If an increasein productivity,not
necessarilyuniformor continuous,is an evolutionarytendency,and the lake
is sufficiently
shallow, a point in time will be reached at which the mud
surfacebecomesreduced.This will have the effect,notedin EsthwaiteWater,
of accelerating(a) oxygendepletionin the hypolimnion,and (b) the release
of ions frommud to water. Thus a primaryphase (I) of slow increasein productivitymay be expectedto be followedby a secondaryphase (II) of accelerated increase,in which,under reducingconditioits,the adsorbinginfluence
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
192
Exchangeof dissolvedsubstancesin lakes
in liberation
and a more
resulting
of oxidizedferriccomplexesis destroyed,
Further
nutrients.
reduction,
resulting
fromthis
utilization
of
plant
complete
of organicmatter,mayinducea tertiary
acceleratedincreasein production
highlyreducedsterilephase (III), in whichin manycases the ironis again
as sulphide.The rateat whichthesechangestakeplace willbe
precipitated
factors.Verydeeplakesand
and morphometric
by geochemical
determined
lakesmayneverpass outofthephaseI, before
all geochemically
oligotrophic
lakesmaypass through
theybecomesiltedup. Shallowand highlyeutrophic
ortheymaybecome
all threestagesin a veryshorttimeaftertheirformation,
in
Linsley
Pond,Hutchinson
arrested
inphasesI orII (cf.'trophicequilibrium'
& Wollack,1940),becausethe 'sterility'of the mud,associatedwiththe
on production
influence
as long as
depressing
phase III, has not sufficient
availablefromthe drainagearea.
suppliesare continuously
amplenutrient
Furtherchangewillbe causedonlyby variation(e.g.cultural)in thisrateof
supply.Thissuggeststhatchangesor lack of changein lakesis determined
oflake basinand drainagearea,as well
mainlyby theindividualcharacters
rateofchangeis probablyat theendofphaseI, and
as climate.The greatest
lakes of
we mayexpectto observethisat the presentday in mesotrophic
arebeingchanged
moderate
depths,orinlakesin whichedaphicdeterminants
class are thoselakesinvestiExamplesoftheformer
by culturalinfluences.
chemicalsurveyofnorth
gatedbyOhle(1933-4),inthecourseofan extensive
has considerably
inthehypolimnion
Germanlakes;in whichoxygendepletion
The bestexampleof the latter
increasedin recentyears('Eutrophierung').
1938),in whichthesuddenacceleraclassis afforded
byLake Zurich(Minder,
as a resultof sewage
and
tion of oxygendepletion
planktonproductivity,
in detailin thedeposits.
is recorded
pollution,
SUMMARY
in lakesis
Thisstudyofphysical-chemical
aspectsoforganicproduction
in thelake
offactorsoperating
concerned
(a), in general,withinvestigation
to the
system(water+ deposits)to controlthe rate of supplyof nutrients
withseasonalchangesin the hypoand (b), in particular,
phytoplankton,
the releaseof
controlling
limnionand bottommud,and withmechanisms
to thewater.The investigation
developedin threestages:(1) study
nutrients
and solutesin a lake subjectto wide
of physicalproperties
of distribution
in redoxconditions;
on mudexperiments
seasonalfluctuations
(2) laboratory
and
lake
of
in
watersystems;(3) correlation, oligoeutrophic types, seasonal
section,'GeneralDiscussion',is added,
changesin waterand mud. A fourth
of chemicalexchangebetweenmudand wateris outin whicha hypothesis
to limnological
theorydiscussed.
lined,and itsapplication
fromApril
weeklyintervals
? I. Sampleswereobtainedat approximately
1939to February1940at 1, 5, 6, 7, 8, 9, 10, 11, 12 and 13 m. depthat a
station(14m. depth)in thedeepestregionofEsthwaiteWater.The
sampling
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
193
CLIFFORD II. MORTIMER
were made on these samples by standardmethods:
followingdeterminations
temperature,02, alkalihity,pll, NH4+, NO2-, NO3-, Si, P, Fe+++, Fe++,
total Fe, and S-- New methods are describedfot the estimationof conductivity,redox potential (correctedto E7, i.e. Eh at pH 7.00),SO4--, turbidityand colour.
Seasonal variation in stratificationof each propertyis illustratedin a
series of 'depth-timediagrams' (Figs. 3-10), whichdemonstratecorrelations
betweenweather(Fig. 2) and thermaland chemicalstratification.
were
Events-in the hypolimnionafterthe onset of thermalstratification
as follows:
Stage I (Juneto mid-July).The rate of oxygendepletionwas greaterwith
depth; the mean rate in the whole hypolimnionwas at firstfairly
increasirrg
in the bottomsample
laterwhenthe concentration
constant,but was retarded,
had fallento 2 mg./l. Increases in alkalinity,conductivity,colour and iron
contentwere observed.
Stage II (mid-Julyto mid-August)was initiatedby a rapid fall in redox
potentialand oxygen concentrationin the bottomsample to E7 0x25V. and
05 mg./l.respectively.This was followed(Fig. 12) by a rapid rise (greater
with increasingdepth) of alkalinity,conductivity,Fe, Si, P, colour and turbidity,accompanied by decrease of NO3- and the appearance of relatively
large amounts of NO2- at certain levels. Increase in-turbidityand colour
resultedmainlyfromthe oxidationand precipitationas Fe(OHl)3 of considerable quantities of Fe++- appearing at the mud surface at this stage. This
accounte-dfor an accelerated decrease in 02 concentration,which at lower
levels became zero (unmodifiedWinklerestimation),by whichtime Fe++ was
detected in the water and the potentialhad fallento E7 0-15V. From this
point onwardsthe Fe contentof the hypolimnionincreasedrapidly and an
increasingproportionconsistedof Fe++.
Rapid ammoniaproduction,at this stage, was of greatermagnitudethan
the equivalent of nitratereduction,which by then was complete at lower
levels (Fig. 13). Nitrogenrelationshipsindicate that, under oxidizingconoccurs imostactively in the oxidized mud surface,and
ditions,nitrification
that, underreducingconditions,the mud is the main sourceof amfmonia.
Stage III (mid-Augustand September)exhibiteda continuedbut slower
rate of rise in concentrationof solutes. The hypolimnionbecame less turbid,
but colourdue to organicmatterpersisted.
intothehypolimnion
The overturn
(5 October),precededbyan encroachment
by a progressivefall in level of the thermocline,resultedin rapid reversalof
the above reductionchanges. An immediaterise in 02 contentwas followed
by a rapid fall in alkalinityconductivity,Fe, Si, P and NH4+. Colourfelloff
less rapidly,and NO3- began to increasesome weeks later.
of the total amount of certain solutes, assumed to
From comhputations
have been derived wholly fromthe mud, which passed upwards through
13
J. Ecol. 30
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
194
Exchangeofdissolvedsubstancesin lakes
watercolumn,and fromthe respective
selectedlevelsin the hypolimnion
roughly
gradientsat thoselevels,it was possibleto estimate'
concentration
(3 x 10-2
forselectedperiods.Theestimates
coefficient
themeaneddydiffusion
20 and 2000 timesthe respective
c.g.s. units,Table 1) are approximately
and chemicaldiffusion.
ofheatconduction
molecularcoefficients
in EsthwaiteWater
During7 weeksundericecover,changeswereobserved
and BlelhamTarn similarto, but slowerthan,thosedescribedforstageI.
of that
coefficient
The eddydiffusion
(Table 2) was estimatedat one-sixth
coefficient,
duringstageI. Even so,it was morethan200timesthemolecular
currents
that convection
preventcompletestagnationunderice.
indicating
matterand a largepart
94 % ofdissolvedsalt content,all humuscolouring
(Table 3).
ofdissolvedgas contentwereremovedfromthewateron freezing
in thewaterimmediately
undertheice.
in concentration
Thisledto increases
seasonalchangesin dissolvedsalt contentofthehypolimnion
Large-scale
to the groupof solutesproducingalkalinity(Fig. 14). Only
wereconfined
part of the alkalinityincreasecouldbe accountedforby increasein NH4+
and Fe. That portiondue to otherbases exhibiteda slow increaseduring
stageI, a rapidincreaseduringstageII, remainedat a constantlevelduring
stageIII (althoughNH4+and Fe continuedto increase),and fellgradually
aftertheoverturn.
mud layerof a fewmillimetres
depth
UntilstageII, a surface-oxidized
ofFe(OH)3and associated
couldbe recognized
bythepresenceofprecipitates
complexes.Muchof this materialwas in colloidalformand possessedadstate. Changes
Fe belowthislayerwas in solubleferrous
sorbentproperties.
II
ofstage suggestthat,belowa limiting
02 conobservedat thebeginning
and redoxpotential,
colloidalferric
in themudsurface
centration
precipitates
in theliberation
of(i) adsorbedbases,and (ii) Fe++.
werereduced,resulting
increasedby thetransition
The rateofspreadofthelatterwas considerably
diffusion
in the mudto turbulent
in the water,acfrommolecular
diffusion
countingforthe acceleratedrate of oxygendepletion.Withthe removalof
barrierconstituted
the adsorbent
by the oxidizedmudsurface,exchangeof
solutesbetweenmud and waterwas relativelyunimpeded(stageIII). The
at theoverturn.Gradualfallin alkalinity
duringsubseprocesswasreversed
quent monthsmay be attributedto,selectiveadsorptionof bases by the
oxidizedmudsurface.
reconstituted
in
Manyofthe e'ventsdescribedin EsthwaiteWaterweredemonstrated
Schleinsee(Fig. 15) usingpublisheddata ofEinsele& Vetter(1938).
designedto testthe above hypothesis,
? II. In laboratoryexperiments
treatments:
artificialmud-water
systemswere subjectedto the following
(1) artificialaeration,(2) watersurfaceexposedto air, (3) watersurface
sealed fromair by liquid and solid paraffin.Equipmentis describedfor
in mud,and
determinations
pH and conductivity
sampling,
CO2 estimation,
of redoxpotentialat 2 mm.depthintervalsabove-andbelow
measurement
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD
H. MORTIMER
195
the mud surface. Measurementsin the mud and estimationsin the water
(those listed in ? I, with CO2 and Mn in addition)wer.emade over a periodof
152 days.
Results are presentedin depth-timediagramsof redox potentialand conductivityin the mud (Fig. 18) and graphsof concentrationof solutes in the
water,uncorrectedforchange of volume on sampling(Figs. 19, 20).
Changesin 'aerated' tanks (1 and 2) were practicallyidentical,although
more rapid in the former.The water retainedthe charactersof oxygenated
lake waterand, apart froma fall in NO3- and alkalinityand a rise in Si and
S04--, littlevariationin concentration
ofothersolutesor in mud conductivity
occurred.The oxidized surfacemud layer,boundedby the isovoltE7 0-24 V.,
graduallyincreasedin thickness.The fall in nitrateand alkalinityis attributed to the high mud/watervolume ratio and the adsorbenj effectof the
oxidized mud surface,respectively.
Changes of much greater magnitude were observed in the 'anaerobic'
tank (3). Aftereffectivesealing fromthe atmosphere,a fall in 02 and NO3and a rise in 002, NO2- and NH4+ concentrationscommenced.The oxidized
surfacemud layer became progressivelythinner,disappearingaftera period
of 40 days, at which time the isovolt E7 0O24V. rose into the water. From
this pointonwards,similarchangesto thosein stage II, ? I, wereobserved,i.e.
considerableincreasesin alkalinity,conductivity,Fe, Mn and turbidity,followed by the appearance of Fe++ and the rapid increaseof Si, P, colour and
mud conductivity,and accelerated decrease in S04 -. By this time only
traces of oxygenremained(Alsterberg'smodificationof Winkler'smethod);
NO3 and NO2- had disappeared. SO4-- became completelyreducedat a later
stage, duringwhicha decreasein Fe contentof the waterand of conductivity
in the mud was attributedto precipitationof ferroussulphide.
A list of approximateredox potential ranges (E7, V.), withinwhich the
fQllowingreductionsproceededactively,is appended. The lower potentialis
the limitbelow whichnone of the oxidized phase could be detected. N03-to NO2--, 045-040; NO2-- to NH4++, 040-035; ferriccomplex to ferrous
complex or Fe++, 030-020; SO47- to S--, 0 10-0 06. The 02 concentrations
associated withthese rangeswere4, 0 4, 01 and zero mg./l.,respectively.
? III. The chemical survey describedin ? I was repeated for a further
annual cycle on Esthwaite Water, also in less detail on Blelham Tarn, and
extended (for comparisonwith lakes in which de-oxygenationof the hypolimniondoes not occur) to Windermere,North and South Basins. At less
frequentoccasionsotherlakes in the EnglishLake Districtwereinvestigated.
The followingestimates-weremade, in addition to those listed in ? I: 02 by
Alsterberg'smodification
ofWinkler'smethod,C02, Mn and Cl. Concurrently,
techniquesdescribedin ? II were applied to the study of the distributionof
redox potential,pH and conductivityin undisturbedcoresof mud, and water
in contact withit, obtainedwitha new type of samplingapparatus (Fig. 22).
13-2
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
196
Exchangeofdissolvedsubstancesin lakes
Resultsfrom(A) EsthwaiteWaterand (B) Windermere,
NorthBasin,
oftwofundamentally
laketypes.
havebeenselectedas representative
different
werealmostidenticalwiththosedescribed
(A) Eventsin thehypolimnion
withchanges
in ? I, whileconcurrent
changesin themudandtheircorrelation
in the watercloselyresembled
thoseobservedin the 'anaerobic'tank,? II.
The oxidizedsurfacemudlayer,boundedby theisovoltE7 0-20V., was progressively
reducedin thicknessfrom7 mm.on 9 May to zero on 12 Jume
(Fig. 28).
Thisinitiated
ratesofoxygendepletion
andincrease
stageJJwith
accelerated
in thewater(Fig.29),
ofalkalinity,
conductivity,
Fe,NH4++,Si andturbidity
at
and risein conductivity
in themud(Fig. 30). Afterthe 02 concentration
the mudsurfacehad fallenbelow1P0mg./l.(18July),theisovoltE7 0-20V
and Fe++ beganto riseintothewater. An explanationofthehighconductivitybelowthemudsurfaceat thistimeis notappareiat.Presenceofsoluble
Mn++saltsin-the
thatmanganic
waterpriortotheappearanceofFe++ indicates
precipitates
in the oxidizedmud surfaceare reducedat a higherpotential
thantheferric
compounds,
of
Stage III exhibited,
as in ? I, a continuedincreasein concentration
certainsolutes,and a steadydecreasein potentialin themudsurfaceand in
the waterjust above, also a steadydecreasein conductivity
in the mud
sulphideprecipitation.
In thewaterS04-surface,
probablydue to ferrous
was onlyreducedto halfits originalconcentration;
the potentialonlyfell
belowthatvalue (E7 010 V.), at whichactiveS04-- reduction
was observed
theoverturi.
in.? II, for2 weekspreceding
ofC02.
Therewas no evidenceofanyconsiderable
anaerobicproduction
in ? I werereChangesobservedin the waterat and afterthe overturn
to spring
peated. The oxidizedsurfacemud layerwas not re-established
a
until
over
month
after
the
and
was
thereafter
subject
overturn,
thickness
to considerable
becomingthinnerduringthe periodunderice
fluctuations,
cover.This suggeststhat accumulatedproductsof reductionin the mud
wereonlyslowlyoxidized.Mudconductivity
fell
surface(e.g.ferrous
sulphide)
somefluctuations
and an increaseunderice.
aftertheoverturn,
exhibiting
of Windermere,
NorthBasin, covered3 months
(B) The investigation
ofsolutesabovethe
beforeand aftertheoverturn.Changesin concentration
weredefinite
but slightcomparedwiththose
mud-(Fig. 31) at theoverturn
ofthe oxidizedsurfacemudlayer,i.e. depth
observedin (A). The thickness
from6 to 12 mm.(Fig.32),and a decrease
ofisovoltE7 020 V., wasincreased
was
also
observed
in mudconductivity
by com(Fig. 33). Thiswas confirmed
in a numberof mud coresfromthe
parison(Figs. 34, 35) of conductivity
deep region,examinedbeforeand afterthe overturn.Seasonal changein
at 1P5cm.belowthesurface,
andwasprobably
wasgreatest
mudconductivity
in the waterjust overthe mud,and the thickness
regulatedby turbulence
and adsorbent
capacityofthesurfaceoxidizedlayer.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
197
The main difference
betweenlakes of Esthwaite (A) and Windermere(B)
type is that, in the latter,the 02 concentrationin the water over the mud is
not sufficiently
depleted duringthermalstratification
to allow the adsorbent
surfaceoxidized layer to be reduced and destroyed. Hence the considerable
increasein rate ofexchangeofsolutesfrommud to water,initiatedin type (A)
by this destruction,is absent in type (B).
? IV. Discussion is devoted in particularto the controllinginfluenceon
lake 'metabolism' of (i) water movementsand (ii) processes in the mud,
especiallyat the mud surface.The relationof (ii) to the ecologyof profundal
mud fauna is brieflydiscussed.
Evidence of (i) in-thehypolimnionis indirect. Chemicalsurveysdemonstrate that flow in the hypolimnionis largely horizontal,and permit the
expectationthat turbujlenceassociated with this flowis the main exchange
of heat and solutes. But, in orderto account forobserveddistrimechanismn
butions of these propertiesin the lower hypolimnion,it must be assumed
that either(a) the eddy diffusioncoefficient
varies with depth, or (b) a nonturbulentexchange mechanismis operative. Examination of Hutchinson's
evidencefor(b) resultedin a provisionalconclusionthat (a) is moreprobable
in large bodjes of water.
It is suggestedthat wind-generateddisplacementsof isosteres(cf. temperatureseiches) can induce horizontaloscillatorywater movementsof sufficient magnitudein the hypolimnionto producethe observeddegreeof turbulence. Evidence ofwind-inducedtiltingofisothermsand isoplethsis presented
(Figs. 37, 38, 39, 41). It is shownforelevenlakes that the degreeofturbulence
in the hypolimnionis proportionalto depth and area (Fig. 36).
Investigatioi of seasonal changes in a centralwater column and underlyingmud in fiveEnglishLakes disclosedrelationships-between
the following:
(i) winter 02 concentration(0w) above the mud surface,(ii) mean winter
thickness(T) of surface-oxidizedmud layer (Fg. 43), (iii) wiater reducing
intensity(I) of mud, measuredby E7 at 5 cm. depth,(iv) winterconductivity
in mud, (v) organiccontentof mud,and (vi) mean summer02 depletionrate
(0) in hypolimnion,expressedper unit area of mud surface. It followsthat
CWIT, i.e. the mean winter02 concentrationgradientmaintainedin the mud
surface,is a measureofthe toducingpowerof the mud. This was proportional
to 0 (Fig. 44A), and may be consideredto be made up of intensity(I) and
capacity factors.These factorswere not found to vary independently,for
(I) was roughlyproportionalto -V/O
(Fig. 44B). (iii), (iv) and (v) exhibited
with depth in the mud was
roughproportionality.Increase in conductivity'
exponential,and an empiricalrelationbetween the exponentand VO was
fo6und
(Fig. 46).
Reduction of the mud surfaceand the associated increase in supply of
solutes to the water may be expected to augmentplanktonproduction.The
occurrenceor non-occurrenceof this event is determinedby the balance
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
198
Exchangeof dissolvedsubstancesin lakes
between(1) thereducingpowerof the mud,and (2) the amountof oxygen
suppliedto the mud surface.(2) dependson (a) the volumeof the hypothere. As (a) and (b) are roughly
limnion,and (b) the degreeof turbulence
proportional
(Fig. 36), it is suggested
that,in all but extremely
oligotrophic
lakes;morphometric
(including
climatic)as wellas edaphicfactorsdetermine
thelevelofproductivity.
or culturalchanges,(1) is inIf, as the resultof natural(evolutionary)
ofthemudsurface,
productivity
may
creasedsufficiently
to effect
reduction
be expectedto increaserelatively
suddenlyto a higherlevel. Examplesare
quoted.
REFERENCES
* Referto publicationsthat are comprehensivein scope or contain
extensivebibliographies.
der Seen. Bot. Notiser,25, 255-74.
Alsterberg, G. (1927). Die Sauerstoffichichtung
Alsterberg, G. (1930). Die thermischenund chemischenAusgleichein den Seen zwischen
Boden- und Wasserkontakt,sowie ihre biologischeBedeutung. Int. Rev. Hydrobiol.24,
290-327.
*American Public Health Association (1936). Standard Methodsfor theExaminationof
Waterand Sewage,8th ed., 309 pp. New York.
Birge, E. A. (1916). The work of the wind in warmingthe lake. Trans. Wis. Acad. Sci. Arts
Lett.18, 341-91.
*Birge, E. A. & Juday, C. (1911). The inland laTkesof Wisconsin.The dissolvedgases of the
water and their biologicalsignificance.Bull. Wis. Geol. Nat. Hist. Surv. No. 222, Scient.
Ser. 7,
Birge, E. A., Juday, C. & March, H. W. (1928). The temperatureof the bottomdeposits
of Lake Mendota. Trans. Wis. Acad. Sci. Arts,Lett.23, 187-231.
Buchanan, J. Y. (1886). On the distributionof temperaturein Loch Lomond duringthe
autumnof 1885. Proc. Roy. Soc. Edinb. 1885-6, pp. 403-28.
to theMathematicalTheoryof theConductionof Beat in
Carslaw, H. S. (1921). Introduction
Solids,268 pp. London.
Coolidge, T. B. (1932). Cytochromeand yeast iron. J. Biol. Chem.98, 755-64.
Cooper, L.-N. H. (1937). Some conditionsgoverningthe solubilityof iron. Proc. Roy. Soc.
B, 124, 299-307.
Cooper, L. N. H. (1938). Qxiaation-reductionpotentialsin sea water. J. Mar. Biol. Ass.
U.K. 22, 167.
to regional
Deevey, E. S. Jr. (1940). LimnologicalstudiesnmConnecticut.V. A contribution
limnology.Am'er.J. Sci. 238, 717-41.
in die Geophysik,
III. Naturwiss.
*Defant, A. (1929). DynamischeOzeanographie. Ernfuhrung
u. Lehrbucher,
9, 222 pp. Berlin.
Monograiphien
Mitteleuropas,
4, 53-160.
*Demoll, R. (1925). Teichdungung.Handb. Binnenftscherei
Eggletong F. E. (1931). A limnologioalstudyof the profundalbottomfauna of certainfreshwaterlakes. Ecol. Monogr.1, 231-332.
BetrachtungeinigerProblele des limnischen
Einsele, W. (1937). Physikalisch-chemische
Mangan-und Eisenkreislaufs.Verh.internat.Vereinig.theor.angew.Lmnologie,8, 69-84.
Einsele, W. (1f938). -Uberchemische und kolloidchemischeVorgange in Eisen-phosphatund limnogeologischen
systemenunterhmnochemischen
Gesichtspunkten.Arch.Hydrobiol.
Plarnkt.
33, 361-87.
derphysikahschen
uberdie EntwiLcklung
Einsele, W. & Vetter, H. (1938). Untersuchungen
und chemischenVerhaltnisseim Jahreszykluas
in einem massig eutrophenSee (Schlemsee
bei Langenargen). Int. Rev. Hpdrobwl.36, 285-324.
Evermann, B. W. & Clark, H. W. (1920). Lake Maxinkuckee. Dept. Conserv.,State of
Indiana, U.S.A. 7.
Forel, F. A. (1880). Recherchessur la temperaturedu lac Leman. Arch. Sc?. phys. nat. 4,
1-33.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFPORD H. MORTIMER
199
1. Lausanne.
Forel, F. A. (1892). Le Le'man. Monographzelimnologique,
derLunzerSeen undihresGebietes.Int. Rev. Hydrobiol.
G6tzinger, G. (1912). Geomorphologie
Hydrogr.Suppl. i Ser.
15, 217 pp. Stuttgart.
der Seen. Bmnnengewasser,
*Grote, A. (1934). Der Sauerstoffhaushalt
im See?
Grote, A. (1936). Ist das absolute Defizitdas Mass des biogen Sauerstoffverbrauchs
Kritische Studien zu den diesbeztglichen Abhandlung Alsterberg's. Arch. Hydrobiol.
Plankt. 29, 410-544.
*Hewitt, L. F. (1931). Oxidation-reductionpotentials in bacteriologyand biochemistry.
L.C.C. Bull. No. 2819. London.
Hju1strOlm, F. (1939). Transportationofdetritusby movingwater. RecentMarine Sediments.
Ass. PetroleumGeologists,
Amner.
TuMla,Oklahoma,pp. 5-31.
*Hutchinson, G. E. (1938 a). On the relationbetweenthe oxygendeficitand the productivity
and typologyof lakes. Int. Rev. Hydrobiol.36, 336-55.
and lake morphology.Proc. Nat. Acad.
Hutchinson, G. E. (1938 b). Chemicalstratification
Sci., Wash.,24, 63-9.
*Hutchinson, G. E. (1941). Limnologicalstudiesin Connecticut.IV. The mechanismsofinterlakes. Ecol. Monogr.11, 21-60.
mediarymetabolismin stratified
Hutchinson, G. E., Deevey, E. S. Jr. & Wollack, A. (1939). The oxidation-reduction
potentialsof lake watersand theirecologicalsignificance.Proc. Nat. Acad. Sci., Wash.,25,
87-90.
Hutchinson, G. E. & Wollack, A. (1940). Studies on Connecticutlake sediments.
II. Chemicalanalyses of a core fromLinsley Pond, North Branford. Amer.J. Sci. 238,
493-517.
Iwlew, W. (1937). Material zum Studium der Stoffbilanzim See. Der Eisenbilanz. [Russian
Moscow,21, 21, summary,pp. 54-9.
withGermanSummary.] Arb. limnol.Sta. Kossi&no,
Jenkin, Penelope M. (in preparation). Seasonal temperatureand dissolvedoxygenchangesin
Windermerein 1931-2.
of the
Juday, C. (1914). The inland lakes of Wisconsm.The hydrographyand morphometry
lakes. Bull. Wis. Geol.Nat. Hist. Surv. no. 27, Sci. Ser. 9.
Karsinkin, G. S., Kusnetzow, S. I. & Kusnetzowa, Z. I. (1930). Zur Aufklarungder
imWasserdes Sees Glubokoje. [RussianwithGerman
UrsachenderDynamikdes Sauerstoffs
Summary.] Arb. Hydrobiol.Sta. Glubokoje,Moscow,6, 9-27, summary,pp. 91-3.
Karsinkin, G. S. & Kusnetzow, S. I. (1931). Neue Methodein der Limnologie. [Russian
with GermanSummary.] Arb. limnol..Sta. Kossino, Moscow, 13-14, 47-62, summary,
pp. 63-8.
Kitto, W. H. (1938). A contributionto water analysis. I. Specificconductivityas a measure
of total dissolvedsolids. Analyst,63, 162.
Kusnetzow, S. I. & Kusnetzowa, Z. I. (1935). Bacteriologicaland chemicalinvestigations
abottomemissionofgases. [RussianwithEnglishSummary.]
on lake mudsin connectionwith
Sta. Kosstno,Moscow,19, 127-42, summary,pp. 1434.
Arb. I,imnol,
Lind, E. M. (1940). Experimentswithpond muds. J. Ecol. 28, 484-90.
Lundbeck, J. (1934). tber den primaroligotrophenSeetypus und den WollingsterSee als
Vertreter.Arch.Hydrobiol.Plankt. 27, 221-250.
dessen mitteleuropaischen
*McEwen, G. F. (1929). A mathematicaltheoryof the verticaldistributionof temperatureand
salinityin water under the action of radiation,conduction,evaporation and mixingdue
2, 197-306.
to resultingconvection. Bull. Scripps Instr. Oceanogr.non-tech.
Mattson, S. (1935). The pH and base saturationof the podzol profile.Trans. 3rdInt. C(ongr.
Soil ScI., Jnt.Comm.papers,pp. 67-70. Oxford.
*Maucha, R. (1932). HydrochemischenMethoden in der Limnologie. Binnengewasser,12,
173 pp.' Stuttgart,
Mill, H. R. (1898). Bathymetricalsurveyof the EnglishLakes. Geogr.J. 6, 46-72, 135-65.
Geol.MeereBinnengewasser,
Minder, L. (1938). Der Zurichseeals Eutrophierungsphanomen.
2, 284-99.
*Misra, R. D. (1938). Edaphic factorsin the distributionof aquatic plantsin theEnglishLakes.
J. Ecol. 26, 411-51.
Moore, E. W. (1939). Graphic determinationof carbon dioxide and the three forms of
Ass. 31.
alkalinity. J. Amer. Waterwks
Mortimer, C. H. (1939). The nitrogenbalance of large bodies of water. Off.Circ., Brit.
Ass. 21, 1-10.
Waterwks
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
200
ExchangeQfdissolvedsubstancesin lakes
Mortimer, C. H. (in preparation). I. Diffusionand eddy diffusion
in lakes. II. Photo-electric
determinationof the transparencyof water samples. III. A portable,direct-reading
electrical conductivitymeter. IV. Conductometricestimationof sulphate in natural waters.
V. Measurementand interpretationof oxidation-reduction
potentialsin lake waters and
muds. VI. Bathymetricsurveys of the English Lakes with echo-soundingapparatus.
Surveyresults.
*Miiller, H. (1938). Beitrage zur Frage der biochemischenSchichtungim Lunzer Ober- und
Untersee. Int. Rev. Hydrobiol.36, 433-500.
Murray, J. & Pullar, L. (1908). Bathymetricalsurveyof the freshwaterlochs of Scotland.
Roy; Geogr.Soc.
Murray, J. & Pullar, L. (1910). Bathymetrical
Survey of the Scottish' FreshwaterLochs.
Vol. 1. Reporton theScientificResults. ChallengerOffice,Edinburgh,785 pp.
*Naumann, E. (1932). Grundzuigeder regionalenLimnologie. Binnengewasser,
11, 176 pp.
Stuttgart.
Niumann, W. (1936). Dier Leitfahigkeitdes Calciumbikarbonatesund die lestimmung der
SulpLate und Gesamthartein naturlichenGewassermitHilfe der elektrischen
Leitfahigkeit.
24, 693.
Naturwissenschaften,
*Ohl, W. (1933-4). Chemischeund physikatischeUntersuchungennorddeutscherSeen. Arch.
IHydrobwol.
Plankt.26, 386-464, 584-658.
Ohle, W. ((1936 a). Zur Vervollkommnung
der hydrochemischen
Analyse. I. Schwefelwasserstoffbestimmung.
Angew.Chem.49, 206-8.
Ohle, W. (1936 b). Zur Vervollkommnung
derhydrochemischen
Analyse. II. Bestimmungdes
im Wasser gelostenSauerstoffes.Angew.Chem.49, 778.
Ohle, W. (1937). Kolloidgele als Nahrstoffregulatoren
der Gewa,sser. NaturwWssenschaften,
25, 471-4.
Pearsall, W. H. & Mortimer, C. H. (1939). Oxidation-reductionpotentials in waterloggedsoils,natural watersand muds. J. Ecol. 27, 483-501.
Rawson, D. S. (1936). Physical and chemical studies in lakes of the Prince Albert Park,
Saskatchewan. J. Biol. Bd. Canada, 2, 227-84.
Rawson, D. S. (1939). Some physicaland chemicalfactorsin the metabolismoflakes. Problems
ofLake Biology(Amer.Ass. Adv. Sci., Publ. 10), pp. 9-26.
Richards, W. T. (1928). The oxygen electrodeas a quasi-quantitativeinstrument.J. Phys.
Chem.32, 990-10Q5.
Riley, G. A. (1939). Limnological studies in Connecticut. I. General limnologicalsurvey.
Ecol. Monogr.9, 53-66.
Roberts, C. H., Grindley, J. & Williams, E. H. (1940). Chemicalmethodsforthe study
of riverpollution. Ministr.Agric.Fish., Fish. Invest.,Series I, IV, no. 2.
Rossolimno, L. (1931). Hydrographische
Studienam PereslawskojeSee. [Russian withGerma.n
Summary.] Arb. limnol.Sta. Kossino, Moscow,13-14, 69-131, summary,p. 119.
Rossolimo, L. & Kusnetzowa, S. I. (1934). DielBoden-Gasauscheidung
als Faktordes Sauerstoffhaushaltes.[Russian with German Summary.] Arb. limnol. Sta. Kossino, Moscow.
17, 87-112, summary,pp. 113-18.
Ruttner, F. (1921). Das elektrolytischeLeitvermogenverdunnterL6sungep unter dem
EinflussesubnierserGewachse. I. BB. Akad. Wiss. Wien,Math. Naturw. KI. 130, 71.
*Schmidt, W. (1925). Der Massenaustauschin freierLuft und verwandte Erscheinungen.
Problemeder kosmischen
Physik,no. 7. Hamburg.
Schmidt, W. (1928). ITberdie Temperatur-und Stabilithtsverhaltnisse
von Seen. Geogr.Ann.,
Stockholm,
10, 143-77.
Stangenberg, M. (1936). Eisenverteilungin den Seen des Sulwalki-Gebieteswahrend des
Sommers. Arch.Hydrobiol.Rybact.,Warsaw, f0, 48-75.
Str0m, K. M. (1932). Tyrifjord.A limnologicalstudy. Skr. Norsk. Vidensk.Akad., Oslo, I,
Math. Naturv. Ki. pp. 1-84.
Taylor, C. 1B. (1940). Bacteriologyof freshwater. I. Distributionof bacteria in English
Lakes. J. Hyg., Camb.,40, 616-40.
Taylor, G. I. (1915). Eddy motionin the atmosphere. Phtlos. Trans. A, 215, 1-26.
*Thienemann, A. (1928). Der Sauerstoffim eutropenund oligotropheiiSee. EimBeitrag zur
Seentypenlehre.Binnengewdsser,
4. Stuttgart.
*Waksman, S. A. (1936). IThmus. Baltimore.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions
CLIFFORD H. MORTIMER
201
Wedderburn, E. M. (1911). The temperatuie seiche. I. Temperatureobservationsin the
Madusee, Pomerania. II. Hydrodynamicaltheory of temperatureoscillations iin lakes.
III. Calculationof the period of the temperatureseiche in the Madusee. Trans. Roy. Soc.
Edinb. 47, 619-36.
Wedderburn, E. M. (1912). Temperatureobservationsin Loch Earn, witha furthercontribution to the hydrodynamicaltheoryof the temperatureseiche. Trans. Roy. Soc. Edinb.
48, 629-95.
Wedderburn, E. M. & Williams, A. M. (1911). The temperatureseiche,.IV. Experimental
verification
of the hydrodynamicaltheoryof temperatureseiches. Trans. Roy. Soc. Edinb.
47, 636-42.
4Welchi P. S. (1935). Limnology,lst ed., 471 pp. New York.
*Wright, C. H. (1939). Soil Analysis; A HandbookofPhysicaland Cheqmical
Methods.276 pp.
London.
of hydrogenion concentrationof
Yoshimura, S. (1932 a). On the dichotomousstratification
some Japaneselake waters. Jap. J. Geol.Geogr.9, 155-85.
Yoshimura, S. (1932 b). Calcium in solutionin the lake watersof Japan. Jap. J. Geol.Geogr.
10, 33-60.
Yoshimura, S. (1933). Rapid eutrophicationwithinrecent years of Lake Haruna, Gunma,
Japan. Jap. J. Geol.Geogr.11, 3-41.
Yoshimura, S. (1936 a). A contributionto the knowledgeof deep watertemperaturesof
JapaneseLakes. Part I. Summertemperature.Jap. J. A8tron.Geophy8.13, 61-120.
Y6shimuxra, S. (1936 b). Contributionto the knowledgeof iron dissolved in the lake waters
of Japan. Second Report. Jap. J. Geol.Geogr.13, 39-56.
ZoBell, C. E. (1937). Oxidation-reduction
conditionsin marine sediments,with particular
referenceto O/R potentialsoxygen deficitand bacteria. A88. Oceanogr.phy8.,Proc-verb.
no, 2, 159-60.
ZoBell, C. E. (1939). Occurrenceand activityof bacteriain marinesediments.RecentMarine
Sediments.Amer.A88. Petroleusm
Geologists,
Tulsa, Oklahoma,pp. 416-27.
This content downloaded on Tue, 5 Mar 2013 12:30:57 PM
All use subject to JSTOR Terms and Conditions