FURTHER RELATIONS
CHLOROPHYLL,
BETWEEN PRIMARY PRODUCTION,
AND PARTICULATE
CARBON
J. H. Steele and I. E. Baird
Marine
Laboratory,
Aberdeen
ABSTRACT
The productivity
of a sea loch, Loch Nevis, on the west of Scotland, is cstimatcd from
nitrate and phosphate data. These results show that even though the nitrate:phosphatc
ratio
in the water is ncvcr more than 10: 1 (by atoms ) and is less than 1: 1 in the euphotic zone in
summer, the assimilation
and regeneration
ratio of these elcmcnts is always close to the
“normal” ratio of 16:l. Chlorophyll
n and particulate organic carbon data are used to study
the possible carbon:chlorophyll
ratios in the plants. During the summer the ratio is calculated to be 74:l and the remaining data suggest lower values for spring and autumn.
For a different area, the northern North Sea, carbon and chlorophyll
samples during the
spring flowering
provide an estimated value of 23: 1 for the carbon:chlorophyll
ratio under
very favorable conditions for growth.
The possible causes of the differences
bctwccn the carbon:chlorophyll
ratios for Loch
Nevis and the northern North Sea are discussed.
ity by more than 2% and usually by much
less. The temperature profiles ( Fig. 1) show
that the temperature of the lower waters
increased continuously throughout the summer and autumn and as a result the oxygen
content near the bottom never fell below 5.0
ml/L.
It is not possible to explain fully the
method of exchange which causes the increased temperatures in the lower waters,
but it is unlikely that there is considerable
lateral transport in the deeper regions since
the loch has a sill depth of 20 m. If it is
assumed that the exchange is equivalent to
vertical mixing, then the effects of vertical
mixing can be calculated from the temperature changes between successive sampling
dates. When these are applied to the nutrient profiles ( Fig. 1) the net losses and gains
in nutrients due to biological activity can be
estimated ( Steele 1956). These calculations
were made for both phosphate and nitrate
for the intervals between sampling from
1 April to 10 August. The results showed a
net decrease in nutrients in the 0 to 20-m
layer and increases in all 10-m layers below
20 m, with one exception when for nitrate,
during the period 14 July to 10 August, there
was a small decrease in the 20 to 30-m layer.
This has been ignored and it is assumed that
the euphotic zone was generally about 20 m
in depth.
Tables 2 and 3 give the results of the calculations. For the intervals from 10 April to
INTRODUCTION
A previous paper ( Steele and Baird 1961)
described the primary productivity
and
especially the possible relations between
chlorophyll and particulate organic carbon
for two areas in the North Sea. In this paper
a further yearly cycle for a sea loch on the
west of Scotland is presented, and also some
data for the spring outburst in the North Sea
which was not adequately sampled in the
previous survey.
METHODS
The only change in method concerned the
filtering of the carbon samples. Instead of
filtering onto a pad composed of equal
weights of SiOZ and Mg0 (Fox, Isaacs, and
Corcoran 1952) the samples were filtered
through a Whatman fine glass paper with
0.02 g MgCOs added at the start of filtration.
A comparison of the two methods, Table 1,
shows little difference.
Loch N&s,
1959-60
Loch Nevis, a sea loch on the west of Scotland, is about 10 miles long and 2 miles wide
at the broadest point. In the center where
the sampling was carried out the depth is 80
to 100 m. During the whole year the salinity
throughout most of the water column was
close to 34s0 ( Fig. 1). The fresh-water
admixture near the surface had a comparatively small effect, never reducing the salin42
PRIMARY
TADLE
4 pairs
1.
PRODUCTION,
CHLOROPHYLL,
The concentration
of carbon (mg/m’) for
of samples using two different
filtering
methods (see text)
SiOz + Mg0
MgCOa
(1)
(2)
(3)
47
53
189
201
432
382
(4)
441
462
10 August, rows (I) and (2) give the calculated changes above and below 20 m. If it is
assumed, firstly, that the latter increase corresponds to the regeneration of nutrients to
inorganic form, and secondly that the same
average rate of regeneration occurs in the
upper 20 m, then row ( 3) gives the values
for regeneration in this layer. The assimilation of nutrients by the plants would then be
composed of the decrease ( 1) plus the
deduced regeneration ( 3 ) , and the addition
of these is given in (5). To estimate the
assimilation for the earlier and later time
intervals the following
calculations were
made. The small observed decreases, mainly
near the surface, between 25 February and
10 April were taken to be the assimilation
values. The usual calculations were not
possible for the last interval since the ther-
AND
PARTICULATE
CARBON
mocline had broken down before 30 October. For the main intervals, however, the
daily regeneration rates (4) were comparatively constant and so it has been assumed
that the rates for the penultimate interval
can bc applied to the last one. When the
observed increases for the whole water
column are subtracted from the total calculated regeneration for the 52 days, the difference is assumed to be the assimilation.
One deduction from these calculations
concerns the relative changes in nitrate and
phosphate. In deeper water and in plankton
the ratio of nitrate:phosphate
is generally
close to 16:l by atoms ( Sverdrup, Johnson,
and Fleming 1942). Yet when nutrients are
depleted by plant uptake this ratio can decrease to 1: 1 or less ( Riley and Conover
1956). It has, however, been pointed out
( Ketchum, Vaccaro, and Corwin 1958) that,
as this depletion occurs, the relative rates of
change can be close to 16:1 until low levels
of nutrients are reached. This suggests that
the plants are assimilating the nutrients in
this ratio down to low concentrations, The
nitrate:phosphate ratios for assimilation and
regeneration in Loch Ncvis confirm this
33
35
0
IO
'\
'.
\
I
,;
i
-7
a@
m/p
FIG.
1.
Environmental
43
data from Loch Ncvis.
i
%o
2°C
44
J. II.
TABLE
~-
-__
~--
2.
AND
-__
--___
April 10
-_
Decrcasc
(O-90 m)
1
[ 1
1
Date
___
_
--.---__-----____
-. Feb. 25
____-_.~.~--
( 1) Decrease
(O-20m)
( 2 ) Increase
( 20-90 m )
( 3 ) Rcgencration
(per20m)
(4) Regn./day
(pcr90m)
( 5 ) Assimilation
( O-20 ) -~
Aug. 10
31
15
10
28
10
3
8
3
0.41
0.57
0.48
19
39
Oct. 31
____~
[0.48]
18
14
.~-
3.
TABI>E
___
July 14
_ -~_-.--___-
16
10 g C/m2, regeneration supplies 18 g C/m’,
but by far the largest portion, 73 g C/m2, is
the result of mixing.
A rough check on these values for production can be obtained by estimating photosynthesis directly from chlorophyll and light
data. A formula similar to that of Ryther
and Yentsch ( 1957), but including
the
effects of light adaptation, will be deduced
in a succeeding paper, The photosynthesis,
P, ( g C/m2/day), in the layer 0 - x, is given
bY
0.24 C,, IO
P=
cxp(-2 e--Lx) - e-2
,
k
for IO > 1.80 g cal/cm”/day.
C, is the average chlorophyll concentration in the layer,
I0 is the seasonal average radiation, and k is
the extinction coefficient. Taking x = 20 m
and k = 0.2 to give the 1% light level at approximately 20 m, then
P = 1.08 C&) .
1
1 The ratio for the first interval is omitted since
the values arc very small. The regcncration
for the
last interval is omitted since it is merely an extrapolation of the value for the previous interval.
-- -- ---
(mg nt./m2)
.-_.
- --_---____.- _.--- - ____
May 12
---____
(Table 4) since they are nearly all close to
16: 1. I Even in August when the nitrate:
phosphate ratio in the surface water is less
than 1: 1, the assimilation ratio has the normal value. This divergence results from the
fact that mixing rather than consumption in
situ is the dominant source of nutrients.
Using the ratios of carbon :nitrogen :phosphorus given by Sverdrup, Johnson, and
Fleming ( 1942), the nitrate and phosphate
assimilation values can be converted to cstimates of net primary production. The histogram in Figure 2 gives the average of these
values and the yearly production derived
from this is 120 g C/m2. To demonstrate the
relative importance of the various sources of
nutrient supply, it has been calculated that
for a total oE 101 g C/m2 during the interval
25 February to 10 August, the observed decrease in the 0 to 20-m layer contributes only
z-r--
I. E. BAIRD
changes in phosphate
~-
Date ._.__........-___--_____ Feb. 25
-_--.
_-~
-~-
( 2 ) Increase
( 20-90 m )
( 3 ) Regeneration
(per20m)
(4) Regn./day
(per 90 m)
( 5 ) Assimilation
(O-20 m)
-.
___-
“Biologicd”
~.
( 1) Dccreasc
(O-20m)
STEELE
_
-
Biological
-
1-z
[ 1
changes in nitrate
__-___----
_--
April 10
---___
Dccrca,sc
(O-90 m)
40
40
__ .-
-
--
May 22
(mg nt./m’)
--
---.-
July 14
520
220
160
470
160
50
130
50
400
650
--
-___-.
Oct. 31
-__
350
9.5
_z=x
Aug. 10
-__.-
6.6
~~
Using radiation data for the north of Scotland (Steele, unpublished)
the points in
7.8
270
17.81
210
-.~
PRIMARY
PRODUCTION,
CHLOROPHYLL,
AND
PARTICULATE
45
CARBON
4. NitratePhosphate ratios for the biological changes deduced in Tables 2 and 3
______-----.--___ --.--TABLE
Date ._____Apr. 10
-----__-
Assimilation
Rcgcncration
____-
FIG.
2. The histogram of production
in Loch
Nevis. Circles (0) indicate photosynthesis
calculatcd from chlorophyll
data ( see text).
Figure 2 are obtained for the dates when I0
> 180. The estimated photosynthesis from
10 April to 10 August is 116 g C/m2 compared with a net production of 100 g C/m2.
The chlorophyll and c,arbon profiles arc
shown in Figure 1. The problem raised by
the carbon data concerns the relative fractions which arc associated with the living
plants and with detrital material. From this
aspect the most interesting profiles arc those
in July and August when there is the largest
range in the chlorophyll values. From the
July 14
May 12
21
16
17
17
--
Aug. 10 Oct. 31
15
15
16
great similarity in the chlorophyll and carbon profiles it would seem intuitively
reasonable to assume that a large part of the
carbon is associated with the chlorophyll
and so with the plants. The statistical rclations between the two can be seen in Figure
3 2 and are not significantly
diffcrcnt; the
carbon:chlorophyll
ratio is 74: 1 and the
“detritus” ( carbon for zero chlorophyll)
is
57 g C/m2. For the other intervals, there is
not sufficient range of values to permit a
statistical estimate of the slope, but it is of
intcrcst to study the possible changes in
chlorophyll: carbon ratios that may occur.
This can be done by assuming that the
2 The graphs include somc supplementary
collcctcd at two adjacent points in the loch.
data
CARBON (mq/m3)
FIG. 3. Relations bctwccn
valid regressions, the da&d
values (see text ).
carbon and chlorophyll
lines arc constructed
in Loch Ncvis. The solid lines indicate statistically
from the averages of the chlorophyll
and c&on
46
J. H. SmE
AND
I. E. BAIRD
I
I
iip
100
/
l
y
5
t
01
CARBON
FIG.
rophyll
i
,
\
,---&e~o
I
&--.I
0
N
0
I
and chlo-
detritus remains at 57 g C/m2 and drawing
the slo~pefrom this point on the carbon axis
through the average of the chlorophyll and
carbon values as shown by the dashed lines
in Figure 3. On this basis it is apparent that
there would be marked changes in the ratio
and these will be considered later in comparison with the North Sea data.
North &~--April
J’F’M’A’M’J’J’A’S
p-0
o---o’
/
FIG. 5.
The possible ratios of carbon to chlorophyll in the phytoplankton
for Loch Nevis (solid
circles) and the Fladcn Ground in the North Sea
( open circles ) .
(mg/m3)
4. The relation bctwccn carbon
in the North Sea, April 1960.
\
/
‘\
\
\
\
I\
1960
The sampling described in the previous
paper (Steele and Baird 1961) unfortunately
did not include data from the peak of the
spring outburst on the Fladen Ground in the
middle of the North Sea. Such data were
collected in the following year a little to the
east of Fladen. The rapid bloom in a shallow
surface layer at the edge of the Norwegian
Deeps has been described elsewhere ( Steele
1961) . Chlorophyll and carbon values collected at this time (31 March to 2 April) are
graphed in Figure 4. The main feature of
these samples is the comparatively
high
carbon: chlorophyll ratio, 23: 1, which they
imply. Or, considered from another point
of view, because of this ratio, the large chlorophyll concentrations do not have such correspondingly
large carbon values. Thus,
although the highest chlorophyll values are
over 5 times as great as the summer maximum in Loch Nevis, the carbon values are
less than twice the corresponding conccntrations.
DISCUSSION
Loch Nevis was chosen as a sampling area
because it had certain physical similarities
with the open North Sea but was expected
to have a different productive cycle. Such
differences were found, since at Fladen
there is a marked spring outburst followed
by a summer minimum in production (Steele
1956 ) , whereas in Loch Nevis the maximum
production is in the summer. The higher
summer production in Loch Nevis is due
to the higher rate of vertical mixing of
nutrients.
These differences in the productive cycles
could be expected to result in associated differences in the physiological condition of the
plants, especially in the summer. In the previous study of Fladen it was suggested that
in very limiting nutrient conditions the chlorophyll content of the plants might be much
lower than under conditions favoring rapid
production.
To illustrate this possible difference, Figure 5 gives the carbon:chlorophyll ratios for the two areas, including the
spring value for 1960.3
Excluding winter, both areas show minima in spring and autumn and maxima in
summer. The maximum at Fladen, however,
is over three times that in Loch Nevis and
this could correspond to the more severe
effects of nutrient limitation at Fladen. A
similar cycle was found for Long Island
Sound ( Harris and Riley 1956). The sam3 For Fladen, the data were grouped into intervals (Stcclc
and Baird 1961).
The first two,
March-early
May, late May-June,
gave significant
For the third group, July-August,
and
rcgrcssions.
also for the data for October and November,
the
ratios have been obtained in the same way as for
Loch Nevis when the regressions were not significant. The January values are omitted since both
the chlorophyll
and carbon values were very low.
PRIMARY
PRODUCTION,
CHLOROPHYLL,
ples were collected in a fine net (75 ,A) after
the water had passed through a coarse net
(415 ,A) and the ratios (taking carbon as
half the weight of organic matter) varied
from 34:l to a summer maximum of 233:l.
The return to high ratios in the winter in
Loch Nevis might be explained as dark
etiolation since the average light available
for the plants is extremely 104 due to the
combined effects of low incident light and
mixing throughout a 90-m water column.
In a further paper an attempt will be made
to produce a theoretical basis for the type
and range of variations dcscribcd here. - RfiFERENCES
Fox,
D. L., J. D. ISAACS, AND E. F. CORCO~XAN.
1952. Marinc Icptopcl, its rccovcry, mcasure;;r116 and distribution.
J. Mar. Rcs., 11:
HARRIS, E., AND G. A. RILEY.
1956.
Oceanogra-
AND
PARTICULATE
CARBON
47
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ChemiBull, Bingcal composition of the plankton.
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KETCIIUM, B. H., R. 17. VACCARO, AND N. COHWIN.
1958. The annual cycle of phosphorus and
nitrogen in New England coastal waters.
J.
Mar. Res., 17: 282-301.
RYTIIER, J. H., AND C. S. YENTSCH. 1957. The
estimation of phytoplankton
production
in the
Limnol.
sea from chlorophyll
and light data.
Oceanogr., 2 : 281-286.
1956. Plant production
on the
STEELE, J. II.
Fladen Ground.
J. Mar. Biol. Ass. U. K., 35:
1-33.
-.
1961. The cnvironmcnt
of a herring
Mar. Rcs. Scot. (in press).
fishcry.
-,
AND I. E. BAIRD. 1961. Relations bctwccn primary
production,
chlorophyll
and
particulate
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Limnol.
Oceanogr., 6 :
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SVERDRUP, H. U., M. W. JOHNSON, AND R. H. FLEMING. 1942. The Oceans; their physics, chemPrentice-Hall,
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istry and gcncral biology.
York.
1087 pp.