IMPACT OF ACID PRECIPITATION ON FRESHWATER
ECOSYSTEMS ON NORWAY1
RICHARD F. WRIGHT, TORSTEIN DALE, EGIL T. GJESSING, GEORGE
R. HENDREY, ARNE HENRIKSEN, MERETE JOHANNESSEN AND IVAR P.
MUNIZ, Norwegian Institute for Water Research, P.O. Box 333,
Blindern, Oslo 3, Norway.
ABSTRACT
Extensive studies of precipitation chemistry during the last
20 years have clearly shown that highly polluted precipitation
falls over large areas of Scandinavia, and that this pollution
is increasing in severity and geographical extent. Precipitation in southern Norway, Sweden, and Finland contains large
amounts of H+, SOZ, and NO; ions, along with heavy metals such
as Cu, Zn, Cd, and Pb, that originate as air pollutants in
the highly industrialized areas of Great Britain and central
Europe and are transported over long distances to Scandinavia,
where they are deposited in precipitation and dry-fallout.
In Norway the acidification of fresh waters and accompanying
decline and disappearance of fish populations was first reported in the 19201s,and since then in S4rlandet (southernmost Norway) the salmon have been eliminated from several
rivers and hundreds of lakes have lost their sport fisheries.
Justifiably, acid precipitation has become Norway's numberone environmental problem, and in 1972 the government launched
a major research project entitled "Acid Precipitation - effects
on forkst and fish", (the SNSF-project). Studies of freshwater ecosystems conducted by the SNSF-project include intensive research at 10 gauged watersheds and lake basins in critical acid-areas of southern Norway, extensive surveys of the
geographical extent and severity of the problem over all of
Norway, and field and laboratory experiments on the effect
of acid waters on the growth and physiology of a variety of
organisms.
Large areas of western, southern, and eastern Norway have been
adversely affected by acid precipitation. The pH of many lakes
'
is below 5.0, and sulfate, rather than bicarbonate, is the
major anion. Lakes in these areas are particularly vulnerable to acid precipitation because their watersheds are
underlain by highly resistant bedrock with low calcrium and
magnesium contents.
Apart from the well-documented decline in fish populations,
relatively little is known about the effects of acid precipitation on the biology of these aquatic ecosystems.
Biological surveys indicate that low pH-values inhibit the
decomposition of allochthonous organic matter, decrease
the species number of phyto- and zooplankton and benthic
invertebrates, and promote the growth of benthic mosses.
Acid precipitation is affecting larger and larger areas of
Norway. The source of the pollutants is industrial Europe,
and the prognosis is a continued increase in fossil,-fuel
consumption. The short-term effects of the increasing
acidity of freshwater ecosystems involve interference at
every trophic level. The long-term impact may be quite
drastic indeed.
INTRODUCTION
Extensive studies of precipitation chemistry during the last 20
years have clearly shown that highly polluted precipitation falls over
large areas of Scandinavia and that this pollution is increasing in
severity and geographical extent (Barrett and Brodin 1955, deBary and
Junge 1963, 0d6n 1968, Bolin et al. 1970, Ottar 1972). Precipitation in
southern Norway, Sweden, and Finland contains large amounts of H+, SO;,
and NOS, ions along with heavy metals such as Cu, Zn, Cd, and Pb, that
originate as air pollutants in the highly industrialized areas of Great
Britain and central Europe and are transported over long distances to
Scandinavia, where they are deposited in precipitation and dry-fallout
(Odgn 1968, Holt-Jensen 1972, Brosset 1973, OECD 1973, ~chlingand
Only a small fraction of the,'H
Tyler 1973, Nard$ 1975, Semb 1975)
SOZ, and NO3 deposited in southern Norway comes from local sources
(Fredriksen 1973, Skogvold 1974, and Fbrland 1973) has firmly established that precipitation falling from air masses that have passed over
industrial Europe has much higher concentrations of these ions than
does precipitation from other air masses.
.
Because much of Norway is underlain by h'ighly resistant granitic
rocks with only a thin cover of unconsolidated glacial till and soil
(Figure 11, the inland waters are characterized by low conductivities
(less than
concentrations of major ions, and extremely low buffer capacities. Thus large areas of Norway are quite
vulnerable to inputs of pollutants from the atmosphere, and the
potential damage to Norway's 300,000 lakes is indeed great.
k'igure 1. A i r view of a mountainous area of
southern Norway sllowi ncj- t h e typical. t h i n s o i l
cover, sparse vegotation and nlally lakes.
Aci.dification of fresh waters and accampanyi.ng cleclixle ancl di.!;ap-pearance of f .i.sh populati-ons was; f i r s t reported i n the 3 920's (Sunclt?
1926, DahS. 1.926), and since then j.11 Sglrlat~dct (suui:herl~most Norway) the
.c;almon have been eliuninatecl from several r i v e r s , ancl hundreds of lakes
have become devoid of f .is h (Jensen and Nnekvik 19'12)
.
J u s t i f i.ab1.y , ac.i.cl precipi.tation has becouz~eNorway's nun9~cr-one envi.rormental. problem, and j.n 1972 the government launched a major ree f f e c t s on f o r e s t ar~clfish",
search p r o j e c t ent5,tied "Acicl preci.pi.tation
(the SNW-proj e c t ) (0verrei.n and Abrahain~ien1975)
Studies of Exeshwater ecosystems concluctcd by the SNSX.'-project include i.ntensj.ve research a t 10 gauged watersheds and lake basins i n c r i t i c a l acid-areas of:'
southern Noxway, ext:ensivc surveys of the geographi.cal. extent and sever-i.ty of the problcm over all. of Norway, and fielcl and l.aboratory exy?eri.ments on the e f f e c t of acid waters on t h c cjrotith rind physi.ol.oc~yof a
v a r i e t y of oryanisrn~ (Table 1)
-
.
.
The impact of acid p r e c i p i t a t i o n on the chcmi.stry and biology of
Norwegian freshwaters i s well i l l u s t r a t e d by the r e s u l t s fro111 a survey
of 155 lakes conducted i n October 1974. T o obtain a s t a t i s t i c a l l y v a l i d
sastlple of lakes i.11 southern Nortray, a 1.0 x 3.0 ksn block was r;el.ected a t
rand on^ from each scluarc of a 50 x 50 krn gri.cl covering Norway south of
63O N l a t i t u d e (E'i.gure 2 ) . Trio small. lakes were chosen from each block
under the conditions t h a t they have minimal 1.ocal sources 06 pollution
and t h a t they be I.arge enough t o pctrrni.t access by I.iyhi: float-plane
(Wri.ght and T,y!;hol~~t1974)
.
Table 1. Research on aquatic ecosystems conducted
by the SNSF-project in 1975.
LAKES
regional
surveys
intensive
stu&s
R IVERS
sediment
studies
regional
surveys
intensive
studies
CHEMISTRY
major ions
nutrients
heavy metals
BIOLOGY
decomposers
bacteria
phytoplankton
benthic algae
macrophytes
zooplankton
benthic fauna
flsh
At each lake water samples were collected, and at 57 lakes the
phyto- and zooplankton, and zoobenthos were sampled. The physiography,
vegetation, and geology of the lake watersheds were described on the
basis of field observations, photographs, and maps. This survey is similar to the study of 50 lakes near the smelter at Sudbury, Ontario
described by Conroy et al. (1974), and to the survey of 400 lakes in
southwest Sweden reported by Almer et al. (1974).
CHEMISTRY
Isopleth maps of the concentrations of various components in the
surface water samples show that the chemistry of Norwegian lakes is
strongly influenced by inputs from the atmosphere. The map for chloride, for example, clearly reflects its seawater source and its deposition in orographic rainfall (Figure 3). The concentrations of sulfate
also reflect a seawater source for this ion (Figure 41, but the high
sulfate concentrations in lakes along the south and southwest coasts are
the result of an atmospheric input of sulfate in excess of that associated with the chloride (Figure 5). The source of this excess sulfate is
most certainly anthropogenic. Air masses moving from industrial Europe
transport sulfur compounds over long distances, and these pollutants
are removed in orographic precipitation along the mountainous coastal
areas of Norway (Nordgf 1975)
.
Reg~onalevannundersokelser hosten 197.4
Regronal Luke Survey Fall 1974
-
".
"
.
:
<'
f2.
Figure 2. Location map of the 10
x 10 km blocks selected at random from each square of the 50 x
50 km grid (from Wright and
Lysholm 1975)
.
The isopleth map of pH thus also reflects the very great impact of
acid precipitation on lakes in large areas of Norway (Figure 6). Whereas unpolluted lakes in granitic basins in central Norway have pH values
above 6.0 and bicarbonate is the major anion, lakes in large areas of
western, southern, and eastern Norway have pH values below 5.5; many
lakes in S6rlandet and southeastern Norway are below 5.0. As a result
of the atmospheric loadings of sulfuric acid, sulfate has replace bicarbonate as the major anion.
The isopleth maps for other components demonstrate additional effects of acid precipitation. For example, the aluminum map (Figure 7)
shows that the acidic, high-sulfate lakes also have unusually high A 1
concentrations, Since precipitation contains very little Al, the A1 in
the lake waters must be supplied from the watersheds, probably due to
the washout of Al by acid precipitation. Because the solubility of A1
is negligible at pH greater than 5.0 (Norton L975), the mobilization of
A 1 indicates that the soil pH has been depressed to levels below 5.
F i g u r e 3 . I s o p l e t h map C 1 (mg/l) i n s u r f a c e - w a t e r
samples (from Wright and Lysholm 1975).
Although t h e washout o f a l k a l i n e e a r t h s (Ca + Mg) by a c i d p r e c i p i t a t i o n
i n Norway h a s been r e p o r t e d ( O v e r r e i n 1972, Henriksen 1 9 7 2 ) , washout of
A1 r e p r e s e n t s t h e n e x t , more s e v e r e s t a g e i n the a l t e r a t i o n of s o i l
c h e m i s t r y (Malmer 1973)
.
0
50
100 km
I
Scale
F I G 3k -
Figure 4. Isopleth map of SO4 (mg/l) in surfacewater samples (from Wright and Lysholm 1975).
BIOLOGY
The altered water chemistry in lakes and rivers of Norway appears
to have affected organisms at every trophic level in these ecosystems.
Experiments underway in the SNSF-project indicate that at low pH levels
bacterial decomposition is retarded while fungal growth increases on
aquatic sediments. The decomposition of cellulose is reduced by 50%
when the pH is lowered from 7.0 to 5.2 (Traaen 1974). Inhibition of decomposition results in an increased accumulation of organic debris and
a decreased rate of nutrient recycling. Organic debris and fungal mats
Figure 5. Isopleth map of excess-SO4 (mg/l) in
surface-water samples.
,"
cover the lake sediments and thereby apparently inhibit nutrient exchange with the overlying water (Grahn et al. 1974). Since the nutrient
recycling rate is an important control of the primary production in many
lakes, reduced recycling in acid lakes would contribute to the "selfaccelerating oligotrophicationt'proposed by Grahn et al. (1974). Hultberg (19751, and Grahn (1975).
Figure 6. Isopleth map of pH in
surface-water samples (from
Wright and Lysholm 1975)
.
Acidification of lake waters alters phytoplankton species-composition and abundances. Analysis of phytoplankton samples from 57 lakes of
the regional survey indicates that lakes with pH less than 6.0 have
fewer species and, in particular, that the Chlorophyceae (green algae)
are affected (Figure 8). Ahner et al. (1974) also found decreased species numbers and altered species-compositions in a survey of 115 lakes
in southwestern Sweden.
The number and type of zooplankton species also are related to pH;
at a low pH fewer species are present (Figure 9). There is also evidence from investigations in Sweden that Daphnia species are absent in
low-pH lakes (Almer et al. 1974, Hanson 1974).
Preliminary results from the regional lake-survey also indicate
that the benthic fauna is sensitive to pH, with again fewer species
present at pH levels below 6. Studies on the distribution of Gammarus
lacustris, another aquatic invertebrate, indicate that this important
food source for fish is rarely found in waters with pH below 6.0
(plkland 1969, 1970). Data from England show that in streams with pH
below 5.7 the insect fauna is greatly impoverished (Sutcliffe and
Carrick 1973).
;
R e g ~ o n a lLoke -Survey 1974
Alumlnurn (mgtrn'l
0
50
100 krn
--Tx--t l l
?'
/
F i g u r e 7. I s o p l e t h map of A 1
(mg/m3 ) i n s u r f ace-water samples.
I n f o r m a t i o n on t h e impact o f a c i d i f i c a t i o n on f r e s h - w a t e r b i o l o g y
i s t h u s m o s t l y of a d e s c r i p t i v e n a t u r e , and a s A l m e r e t a l . (1974)
p o i n t s o u t , v e r y l i t t l e i s known about t h e e f f e c t of low pH on t h e morphology, physiology, and n u t r i t i o n of phyto- and zooplankton.
FISH
A g r e a t d e a l , however, i s known a b o u t f i s h , p r i m a r i l y b e c a u s e of
s i r economic and r e c r e a t i o n a l v a l u e ( c f . EIFAC 1968). Dahl (1926)
I s t r e p o r t e d t h e a d v e r s e e f f e c t s o f a c i d i f i c a t i o n on f i s h in' Norway,
and i n 1959 Dannevig (1959) s u g g e s t e d t h a t a c i d p r e c i p i t a t i o n was t h e
cause of t h e i n c r e a s e d a c i d i t y and a d v e r s e e f f e c t s on f i s h .
*
Salmon-catch r e c o r d s f o r 79 Norwegian r i v e r s r e c o r d e d s i n c e t h e
l a t e 1800's show t h a t t h e c a t c h from 9 r i v e r s i n S $ r l a n d e t d e c l i n e d r a p i d l y between 1885 and 1925 and was e s s e n t i a l l y z e r o by 1968 (Jensen and
Snekvik 1972). The salmon c a t c h f o r t h e e n t i r e c o u n t r y , however, shows
Mean number of Algae species against p H
Mean number
of Algae
Dinophyceae
Cyanophyceae
Figure 8. Mean number of a l g a l s p e c i e s a g a i n s t
p H i n samples from 57 l a k e s of t h e r e g i o n a l
lake-survey
no such d e c r e a s e ( F i g u r e 1 0 ) . These 9 r i v e r s a r e now q u i t e a c i d i c (pH
4.5-5.5), and t h e i r a c i d i t y i s s t i l l i n c r e a s i n g (Henriksen 1972).
There can b e l i t t l e doubt t h a t a c i d p r e c i p i t a t i o n i s t h e cause (Hagen
and Nordby 1967). The dissappearance of salmon from these r i v e r s i s
n o t u s u a l l y marked by massive f i s h k i l l s (although f i s h k i l l s were
r e p o r t e d i n 1911, 1921, 1948 and most r e c e n t l y 1 9 7 5 ) , b u t r a t h e r by t h e
f a i l u r e of r e p r o d u c t i o n and r e c r u i t m e n t (Jensen and Snekvik 1972). Indeed l a b o r a t o r y experiments i n d i c a t e t h a t a c i d water f i r s t a f f e c t s f i s h
eggs and f r y ; t h e lower l i m i t f o r normal r e p r o d u c t i o n i s 5.0-5.5 f o r
salmon, 4.5-5.0 f o r s e a t r o u t , and about 4.5 f o r brown t r o u t (Jensen
and Snekvik 1972)
.
F i s h have a l s o been d i s a p p e a r i n g from l a k e s i n S$rlandet because
Information on t h e f i s h - s t a t u s of
of i n p u t s of a c i d p r e c i p i t a t i o n .
2083 l a k e s i n S d r l a n d e t w a s g a t h e r e d i n 1971 by E. Snekvik and K. W.
Jensen (Norwegian D i r e c t o r a t e f o r Game and Fresh-Water F i s h ) from l o c a l
f i s h e r y a u t h o r i t i e s . O f t h e s e l a k e s , 741 now have no f i s h , and 477
have become devoid of f i s h s i n c e 1940 (Jensen and Snekvik 1972). pH
d a t a for 516 of t h e s e l a k e s show c l e a r l y t h a t a t p H l e v e l s below about
5.5 t h e f i s h a r e e i t h e r e n t i r e l y a b s e n t o r p r e s e n t only i n reduced
numbers (Figure 11).
Percent c o n t r i b u t ~ o n sf r o m 3 classes of z o o p l a n k t o n to total specles number a n d mean
number of z o o p l a n k t o n species, related to pH
Means ore taken tor lakes within intervals of 0 5 p H units.
a
m e a n number ot specles
8
'I. Cladocera, 5 specles
Number
of lakes 2
L.0
9
4.5
1L
5'0
' k C o l a n o t d o , 6 specles
' l a Cyclopoida, 3 species
II
6
60
p H in intervals of 0.5 pH units
II
6.5
3
7'0
7: 7
F / G ?&-5
Figure 9. Percent contributions from 3 classes
of zooplankton to total species number and
mean number of zooplankton species, related
to pH. Data from 57 lakes of the 1974 regional lake-survey.
Acid precipitation has resulted in the decline and loss of fish
populations in other areas of Norway as well. A preliminary survey of
the fish status for lakes over all of southern Norway was conducted
during 1974 as part of the SNSF-project. Lakes w'ith no fish or only
sparse populations occur over large areas of western and east-central
Norway as shown in Figure 12, and these lakes are acid, generally below
pH 5.5 (Muniz 1975)The disappearance of fish from lakes as pH decreases often follows
a characteristic pattern. Long-term increases in acidity apparently
first interfere with reproduction and spawning such that the remaining
adult fish increase in size and age until the only fish left are large
and old. This pattern has been described in Norway (Jensen and Snekvik
1972), in Sweden (Hultberg and Stenson 1970, Almer et al. 1974, Andersson et al. 1971, Almer 1972 a, Almer 1972 b), in Canada (Beamish 19751,
and in the United States (Schofield 1975).
Another mode of fish mortality is caused by large, rapid changes
in pH. Sudden drops in p H cause severe physiological stress that may
produce fish kills at pH levels above those normally toxic to adult
fish. Resistance to such shocks is also species dependent. Sudden
drops in pH are often observed in the early spring when the pollutants
accumulated in the snowpack are released in high concentrations during
the first phases of melting (Hagen and Langeland 1973, Hultberg 1975).
Figure 10. Salmon-catch statistics for 79
Norwegian rivers and for Tovdalselva, an
acidic river in SZrlandet, over the period
1880-1970 (data from Sndkvik 1970)
.
SUMMARY
The precipitation over much of southern Scandinavia contains large
amounts of,'H
SOZ, NO3 that originate as air pollutants in the highly
industrialized areas of Great Britain and central Europe. Because much
of Norway is underlain by highly resistant granitic rocks with only a
thin cover of unconsolidated glacial til,land soil, the inland waters
have extremely low buffer capacities and are thus quite vulnerable to
inputs of atmospheric pollutants.
The continually growing inputs of acidic pollutants have resulted
in major changes in the chemistry of lakes and rivers in southern
Norway. Regression analysis on 10 years of data from several rivers
in Sdrlandet (southernmost Norway) show significant decreases in pH and
increases in conductivity and total hardness, the latter due to the
washout of Ca and Mg from the watersheds. The inputs of sulfate have
resulted in the replacement of bicarbonate by sulfate as the major
anion in many lakes.
High concentrations of aluminum in acid lakes in southernmost
Norway suggest that pH levels in the watershed soils have dropped below
5, resulting in the mobilization and washout of Al.
Group~ng of 516 lakes In southernmost Norway according to fish status and pH
'1. ol takes ~n each pH-class that have var~oust~sh-status
low population
good populorion
over-populated
5,'5
Data lrom Snekvlk 1971 p 50
- 6 -//
.-.-
Figure 11. Grouping of 516 lakes in southernmost Norway according to fish status and pHD
Percent of lakes in each pH-class that have
various fish-status (data from Snekvik 1974).
Information from the survey of 57 lakes in southern Norway indicates that increasing acidity results in a decline in the number of
phytoplankton species, and in particular, a decrease in the abundance
of green algae. The composition of zooplankton and zoobenthos species
are similarily affected. These decreases begin to occur at about pH
6.0.
Data on the annual salmon catch, pH, and success of fish hatching
indicate that acidic precipitation began affecting fish as early as the
1920's. Since then the salmon have been eliminated from many major
rivers, and thousands of lakes have become devoid of fish (Jensen and
Snekvik 1972). Fish are eliminated from lakes and rivers because of
gradual increases in acidity that cause interference with reproduction
and spawning. Sudden drops in pH, especially during snowmelt cause
severe physiological stress and often death in fish. The tolerance of
fish to both long-term and short-term changes in acidity is species
dependent.
Acid precipitation has affected large areas of Norway. These adverse effects are occuring over greater geographical areas with both
increasing frequency and severity. The source of the pollutants is
industrial Europe, and since the prognosis is for a continued increase
in fossil-fuel combustion, the situation will continue to deteriorate.
The short-term effects of the increasing acidity of freshwater ecosystems involve interference at every trophic level. The long-term impacts
may be quite drastic indeed.
F i g u r e 12. F i s h e r i e s s t a t u s i n
l a k e s o f s o u t h e r n Norway showing
a r e a s t h a t have been moderately
and s e v e r e l y a f f e c t e d by a c i d
p r e c i p i t a t i o n (from Muniz 1975).
A l m e r , B.
1972a.
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A l m e r , B.
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1971. Rddingen i
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p8
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