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. Precipita- tion 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 re- ported in the 19201s, and since then in S4rlandet (southern- most 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 number- one 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 fresh- water ecosystems conducted by the SNSF-project include inten- sive research at 10 gauged watersheds and lake basins in cri- tical 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 vulner- able 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 pre- cipitation 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, ~chling and Tyler 1973, Nard$ 1975, Semb 1975) . Only a small fraction of the H', SOZ, and NO3 deposited in southern Norway comes from local sources (Fredriksen 1973, Skogvold 1974, and Fbrland 1973) has firmly estab- lished 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 ex- tremely 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- the typical. t h i n soi 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 ivers , ancl hundreds of lakes have become devoid of f .i s h (Jensen and Nnekvik 19'12) .

Jus t i f i.ab1.y , ac.i.cl precipi.tation has becouz~e Norway's nun9~cr-one en- vi.rormental. problem, and j.n 1972 the government launched a major re- search project ent5,tied "Acicl preci.pi.tation - ef fec ts on fores t ar~cl fish", (the SNW-proj ect) (0verrei.n and Abrahain~ien 1975) . Studies of Exesh- water ecosystems concluctcd by the SNSX.'-project include i.ntensj.ve re- search 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 fec t of acid waters on t h c cjrotith rind physi.ol.oc~y of a variety of oryanisrn~ (Table 1) .

The impact of acid precipitation on the chcmi.stry and biology of Norwegian freshwaters is well i l l u s t r a t ed by the resu l t s fro111 a survey of 155 lakes conducted i n October 1974. To obtain a s t a t i s t i c a l l y valid 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 la t i tude (E'i.gure 2 ) . Trio small. lakes were chosen from each block under the conditions tha t they have minimal 1.ocal sources 06 pollution and tha t they be I.arge enough t o pctrrni.t access by I.iyhi: float-plane (Wri.ght and T,y!;hol~~t 1974) .

Table 1. Research on aquatic ecosystems conducted by the SNSF-project in 1975.

LAKES R IVERS

CHEMISTRY

major ions

nutrients

heavy metals

regional intensive sediment

surveys stu&s studies

BIOLOGY

decomposers

bacteria

phytoplankton

benthic algae

macrophytes

zooplankton

benthic fauna

flsh

regional intensive

surveys studies

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 sim- ilar 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 chlor- ide, for example, clearly reflects its seawater source and its deposi- tion 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 associ- ated 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~onale vannundersokelser hosten 197.4 " . : < ' f 2 . Regronal Luke - Survey Fall 1974 ".

Figure 2. Location map of the 10 x 10 km blocks selected at ran- dom 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). Where- as 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 bi- carbonate as the major anion.

The isopleth maps for other components demonstrate additional ef- fects 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.

Figure 3 . I s o p l e t h map C 1 (mg/l) i n surface-water samples (from Wright and Lysholm 1975).

Although the 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 has been r epor t ed (Overrein 1972, Henriksen 1972) , washout of A1 r e p r e s e n t s t h e nex t , more seve re s t a g e i n the a l t e r a t i o n of s o i l chemistry (Malmer 1973) .

BIOLOGY

0 50 100 km I

Scale

F I G 3k -

Figure 4. Isopleth map of SO4 (mg/l) in surface- water samples (from Wright and Lysholm 1975).

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 de- composition 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 ex- change 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 "self- accelerating oligotrophicationt' proposed by Grahn et al. (1974). Hult- berg (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-composi- tion 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 spe- cies 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 evi- dence 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 l Loke -Survey 1974 Alumlnurn (mgtrn'l

0 50 100 krn

--Tx---

t l l ? ' /

Figure 7. I s o p l e t h map of A1 (mg/m3 ) i n s u r f ace-water samples.

Information on the impact of a c i d i f i c a t i o n on fresh-water b io logy i s thus most ly of a d e s c r i p t i v e na tu re , and a s A l m e r e t a l . (1974) p o i n t s o u t , very 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 mor- phology, 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, is known about f i s h , p r i m a r i l y because of * s i r economic and r e c r e a t i o n a l va lue ( c f . EIFAC 1968). Dahl (1926) I s t r epor t ed t h e adverse 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) suggested 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 increased a c i d i t y and adverse e f f e c t s on f i s h .

Salmon-catch records f o r 79 Norwegian r i v e r s recorded s i n c e t h e la te 1800's show t h a t t h e ca t ch 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 rapid- 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 ca t ch f o r t h e e n t i r e country, 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 spec ies aga ins t p H i n samples from 57 lakes of t h e r eg iona l

lake-survey

no such decrease (Figure 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 increas ing (Henriksen 1972). There can be 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 is no t usua l ly marked by massive f i s h k i l l s (although f i s h k i l l s were repor ted i n 1911, 1921, 1948 and most r ecen t ly 1975), b u t r a t h e r by t h e f a i l u r e of reproduction and recrui tment (Jensen and Snekvik 1972). In- deed labora tory 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 reproduction 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 fo r brown t r o u t (Jensen and Snekvik 1972) .

F i s h have a l s o been disappearing from lakes i n S$rlandet because of inpu t s of a c i d p r e c i p i t a t i o n . Information on t h e f i s h - s t a t u s of 2083 lakes i n Sdrlandetwas gathered i n 1971 by E. Snekvik and K. W. Jensen (Norwegian Di rec to ra te f o r Game and Fresh-Water F ish) 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 hese l akes , 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 these l akes 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 absent o r p resen t only i n reduced numbers (Figure 11).

Percent c o n t r i b u t ~ o n s f r o m 3 classes of zooplankton to total specles number a n d mean number of zooplankton species, related to pH Means ore taken tor lakes within intervals of 0 5 pH units.

mean number ot specles a 'k Colano tdo , 6 specles

8 'I. Cladocera, 5 specles ' l a Cyclopoida, 3 species

Number of lakes 2 9 1L 6 I I I I 3

L.0 4.5 5'0 6 0 6.5 7'0 7: 7 p H in intervals of 0.5 pH units 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 region-

al 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, Anders- son 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,l and 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~ous t~sh-status

low population

good populorion

over-populated

5,'5 Data lrom Snekvlk 1971 p 50 .-.- - 6 -//

Figure 11. Grouping of 516 lakes in southern- most 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 indi- cates 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 ad- verse 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 ecosys- tems involve interference at every trophic level. The long-term impacts may be quite drastic indeed.

Figure 12. F i s h e r i e s s t a t u s i n l akes of southern Norway showing a r e a s t h a t have been moderately and seve re ly 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).

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