Acid deposition and effects in Nordic Europe. Damage to fish populations in Scandinavia continue to apace

Although the decline in fish populations due to acidicwater in Norway started as early as in the 1920's the most rapid losses appeared during the 1960–70's. Until 1978, the populations of Atlantic salmon had disappeared from the southernmost part of Norway, and in these areas, more than half of the brown trout populations had been lost. Today, in spite of no increase in acid depositions, the fishery problems seems to continue at the same speed. Data based on interviews of the local fish authority shows that lakes still holding a fish population in the late 70's, have experienced a 30% loss of brown trout populations and a 12% loss of perch in the period 1978–1983. This trend have been confirmed by testfishing in lake systems having long data series. Salmon rivers on the western coast of Norway have experienced several episodes of fish kills due to rapid changes in water quality. These fish kills have mainly affected smolts of Atlantic salmon. Spawning migrating salmon on entering their acidified home river have also been affected. In Sweden, several salmon populations along the western coast have been lost due to acidification with no positive trends so far in the 1980's. Areas in central Sweden and in some high mountain areas are still experiencing a continuous and increasing acidification with detrimental effects on invertebrates and fish. In Finland, an increase in acidic deposition during the last decades have occurred, leading to acidification in the most sensitive freshwater systems. Although some acidified freshwater lakes are reported to have lost their fish stocks, few data on fish population effects are available.     

Differences in response to liming in a lake-dwelling fish community

The Lake Fjorda water system in southern Norway consists of several lakes which exhibit a gradient in acidification. The system is inhabited by populations of brown trout, Arctic char, whitefish, perch, European minnows and Crucian carp. Populations of Arctic char, whitefish and brown trout were nearly wiped out in some of the locations, as a result of acidification, In 1985, Lake Fjorda was limed in order to improve water quality so the fish community would be recovered. Fish stock assessment by means of gill-net fishing in the epibenthic and pelagic zones was carried out before (1983) and three years after liming (1991–1993). Populations of Arctic char and whitefish have not recovered after eight years of liming. Brown trout are almost extinct and do not seem to be recovering. Perch were less affected by acidification, exhibiting good recruitment also before liming.     

Effects of Acidification Due to Emissions from the Kola Peninsula on Fish Populations in Lakes Near the Russian Border in Northern Norway

In this paper we document the effects of acidification on fish populations in lakes in Sør-Varanger near the Russian border in northern Norway. We used questionnaires in order to assess the current status and distribution of different fish species, and conducted test-fishing to determine relative abundance (CPUE-T) and age structure. Acidification of surface waters in this area is due to emissions of SO₂ from smelters on the Kola Peninsula in Russia (Nikel and Zapoljarnij) between 10 and 30 km from the Norwegian border. Sulphur deposition in Sør-Varanger ranges from 0.6 to 2.0 g S m-² yr-¹, which is similar to levels in the most acidified areas in southern Norway. However, a dominant fraction of the acidic deposition reaches the ground in particulate form during summer and autumn. Coastal areas in Sør-Varanger receive small amounts of precipitation; the annual mean is 580 mm. We obtained fish status from 401 lakes, about 40% of all lakes larger than 3 ha, which were inhabited by 236 and 293 populations of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta), respectively. The extent of fish damage was small as only three populations of Arctic charr were lost, while three populations of Arctic charr and eight populations of brown trout were at various stages of reduction. Damaged and lost fish populations were identified in smaller lakes at relatively high elevations (172–349 m) in six areas in the Jarfjord Mountains, covering a land area of 30.0 km². Most of the damage probably occurred during the 1970s and 1980s. In lakes that supported or had supported Arctic charr and brown trout, we found a significant relationship between CPUE-T, and acid neutralizing capacity (ANC) and pH, and also between alkalinity and the concentration of inorganic Al for brown trout. In both species, the catch of fish in age groups 1+ and 2+ (CPUE-R) increased significantly with CPUE-T. Affected populations typically exhibited irregular age composition, and age-classes were missing, indicating that reductions in fish populations were due to recruitment failure. The limited fish damage is related to relatively good catchment resistance to acidic inputs, small amounts of wet deposition as well as precipitation. These conditions result in low accumulation of acidic compounds, producing less acidic run-off waters and few episodes of unfavourable water quality.     

Fish kills of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in an acidified river of SW Norway

This paper documents population responses of Atlantic salmon and brown trout to fish kills in River Vikedal, an acidified river in SW Norway. The angling statistics show that the adult population of Atlantic salmon in the river has decreased to low numbers during recent years, whereas catches of migrant brown trout have increased in the same period. A total of 659 dead salmon and trout were either collected or observed during spring snowmelt in the years 1982–1985. Parr suffered the highest mortality, and most large specimens. Only a few dead kelts were registered. In the springs of most unfavourable water quality and most severe episods of fish kills (1983 and 1984), salmon parr mortality were significantly higher than that of brown trout. Episodic death of parr in the spring is thought to be an important cause of the reduction in the adult stock of Atlantic salmon in the river during recent years.     

Vertical distribution of brown trout (Salmo Trutta) and perch (Perca Fluviatilis) in an acidified lake

Brown trout (Salmo trutta) and perch (Perca fluviatilis) had different vertical distributions throughout the year in the acidified lake Gjerstadvann. During summer, the brown trout lived in the 0 to 16 m depth interval, whereas the perch lived in the 0 to 8 m interval. In Gjerstadvann, the thermocline lies at 8 to 10 m depth. The epilimnion pH was usually > 5.6, and the thermocline pH was about 5.2. Brown trout and perch in Gjerstadvann, thus experienced different chemical environment during summer-stratification. Two rivers, one of them acidified, the other circum-neutral, were the most important spawning areas for the Gjerstadvann brown trout. Brown trout parr in the acidified river migrated to the lake and matured at younger ages than the brown trout spawning in the non-acidic river. The brown trout stocks were juvenilized because of low survival rate of adult fish (S = 0.15 to 0.19). The short life span was probably dus to low pH and elevated Al. The perch in Gjerstadvann showed fluctuating year class strength but the survival rate of adult perch (S = 0.57) did not seem to be affected by acidification during this investigation. This may due to its vertical distribution during summer.     

Monitoring fish stocks in relation to acidification in Norwegian watersheds

The Norwegian Monitoring Programme for Long-Range Transported Air Pollutants started in 1980. The biological part of this programme includes besides invertebrate studies in streams, (i) fish community status in lakes by means of interviews, test-fishing in lakes by using standard gill-net series, recruitment studies of brown trout in inland streams, and juvenile stock assess and monitoring of fish kills in salmon rivers. Damaged fish stocks are recognized within a land area of 51,500 km² in southern Norway and 30 km² in northern Norway. At least 6,000 lake-dwelling fish stocks have either been lost or are at various stages of reduction. Brown trout (Salmo trutta) is the most widespread and abundant species of fish in Norwegian watersheds, and is also most severe affected by acidification. More recently, there are some indications of an increase in the abundance of brown trout in some areas. However, analysis of age structure in lakes, and fry densities in streams in such areas revealed large annual variations in recruitment rate, which indicates unstable water chemical conditions. Atlantic salmon (Salmo salar) is virtually extinct in 25 rivers in southernmost, southwestern and western Norway.     

WHOLE-CATCHMENT LIMING AT TJØNNSTROND,NORWAY: AN 11-YEAR RECORD

In June 1983 a whole-catchment liming experiment was conducted at Tjønnstrond, southernmost Norway, to test the utility of terrestrial liming as a technique to restore fish populations in remote lakes with short water-retention times. Tjønnstrond consists of 2 small ponds of 3.0 and 1.5 ha in area which drain a 25-ha catchment. The area is located at about 650–700 meters above sea-level in sparse and unproductive forests of spruce, pine and birch with abundant peatlands. A dose of 3 ton/ha of powdered limestone were spread by helicopter to the terrestrial area. No limestone was added to the ponds themselves. The ponds were subsequently stocked with brown and brook trout. Liming caused large and immediate changes in surface water chemistry; pH increased from 4.5 to 7.0, Ca increased from 40 to 200 μeq/L, ANC increased from –30 to +70 μeq/L, and reactive-Al decreased from about 10 to 3 μmol/L. During the subsequent 11 years the chemical composition of runoff has decreased gradually back towards the acidic pre-treatment situation. The major trends in concentrations of runoff Ca, ANC, pH, Al and NO₃ in runoff are all well simulated by the acidification model MAGIC. Neither the measured data nor the MAGIC simulations indicate significant changes in any other major ion as a result of liming. The soils at Tjønnstrond in 1992 contained significantly higher amounts of exchangeable Ca relative to those at the untreated reference catchment Storgama. In 1992 about 75% of the added Ca remains in the soil as exchangeable Ca, 15% has been lost in runoff, and 10% is unaccounted for. The whole-catchment liming experiment at Tjønnstrond clearly demonstrates that this liming technique produces a long-term stable and favourable water quality for fish. Brown trout in both ponds in 1994 have good condition factors, which indicate that the fish are not stressed by marginal water quality due to re-acidification. The water quality is still adequate after 11 years and >20 water renewals. Concentrations of H⁺ and inorganic Al have gradually increased and approach levels toxic to trout, but the toxicity of these are offset by the continued elevated Ca concentrations. Reduced sulphate deposition during the last 4 years (1990–94) has also helped to slow and even reverse the rate of reacidification. The experiment at Tjønnstrond demonstrates that for this type of upland, remote terrain typical of large areas of southern Norway, terrestrial liming offers a suitable mitigation technique for treating acidified surface waters with short retention times.     

Population Density of Brown Trout (Salmo trutta) in Extremely Dilute Water Qualities in Mountain Lakes in Southwestern Norway

We have examined populations of brown trout in low-conductivity mountain lakes (5.0?C13.7 ??S/cm and 0.14?C0.41 mg/l Ca) in southwestern Norway during the period 2000?C2010. Inlets to the lakes were occasionally even more dilute (2007; conductivity?=?2.9?C4.8 ??S/cm and Ca?=?0.06?C0.17 mg/l). The combination of pH and conductivity was the best predictor to fish status (CPUE), indicating that availability of essential ions was the primary restricting factor to fish populations in these extremely diluted water qualities. We suggest that conductivity <5 ??S/cm is detrimental to early life stages of brown trout, and subsequently that there are lakes in these mountains having too low conductivity to support self-reproducing trout populations. Limited significance of alkalinity, Ca, Al, and color suggests that effects of ion deficit apparently overruled the effects of other parameters.     

Long-term changes in fish populations of acid streams and lochs in galloway South West Scotland

During 1978–79, and again in 1984, fish populations were surveyed in 22 lochs and 27 streams in Galloway, southwest Scotland. Chemical analyses of these waters and of bulk precipitation were made over the same period. The study area includes moorland catchments and catchments with young or semi-mature coniferous forest. Trout were not caught in nets set in 5 lochs which were known to contain fish in the past. Angling records also indicated a decline in catches and increased average weight of trout in two other lochs. Evidence for the decline in fish populations suggests that this process has occurred over a period of at least 50 yr. In fishless lochs and streams the levels of acidity and Al were in the range known to be toxic to fish. Stream acidity and sulphate concentrations were significantly higher in catchments with semi-mature coniferous forests. The available evidence for long-term acidification of Galloway lochs and streams is discussed and it is concluded that acid depositions are likely to be the major cause of changes in the status of fisheries in this region.     

Losses and recoveries of fish populations in acidified lakes of southern Finland in the last decade

Acid-induced fish damage in small lakes in southern Finland was studied in a fish status survey of eighty lakes from 1985–1987. Later, twenty of these lakes were selected for further monitoring. A sampling of these lakes from 1988–1989 showed that the decrease in some perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) populations still continued. The results from the same lakes in 1992 showed that successful reproduction had taken place with many of the perch populations that had been close to extinction in 1985. In contrast, no signs of recovery in the roach populations were detected. The explanation for the appearance of new cohorts of perch could have been the decrease in acid deposition but the exceptional hydrological conditions of winters in the early 1990s may also have affected them. The different responses of the perch and roach populations were interpreted as a consequence of the different sensitivity of these two species to acidification. Even a slight improvement in the water quality has resulted in the appearance of strong new year-classes of perch, but not of roach. Therefore, more improvement in water quality is needed until a sensitive species like roach can reproduce again.     

Improved growth in stunted brown trout (Salmo trutta L.) after reliming of Lake Hovvatn,Southern Norway

The chronically acidic Lake Store Hovvatn and the adjoining pond Pollen in southernmost Norway were limed in March 1981. The two locations were stocked with brown trout (Salmo trutta L.) at low and high densities in Hovvatn and Pollen, respectively. After 6 yr of reacidification, the locations were relimed in July 1987. Growth depression during the reacidification process in spite of low fish densities and superabundance of food was observed in Lake Store Hovvatn. Three months after reliming, a substantial growth response was found in trout from Lake Store Hovvatn; Mean annual length increment was 68% higher than that of the preceding year. In Pollen, reliming had no apparent effect on growth. In both populations reliming caused increased swimming activity measured as an increase in CPUE-values. These results show that the growth response to liming depends on population density and food availability. Moreover, the results indicate that the food conversion rate of the trout is negatively affected in acid waters.     

Water quality in guanting reservoir

The concentration of phenol, cyanide, As, Hg, Cr, Cu, Pb, Zn, and F in the Guanting reservoir water has been studied. The analysis shows that the water quality in the reservoir can be divided into three periods, namely 1972–1973, 1974–1978, and 1978–1983. In recent years, the water quality is fairly good. The contents (mg L^?1) of the water behind the dam over a long period of monitoring are: phenol 0.001 to 0.009, cyanide 0.001 to 0.002, As 0.001 to 0.04, Cr 0.001 to 0.01, and Hg 0.0005 to 0.002.     

Changes in the fish community of a limed lake near sudbury,Ontario: Effects of chemical neutralization or reduced atmospheric deposition of acids?

Nelson Lake, a moderately acidic (pH 5.7), metal-contaminated (Cu 22 μg L^?1; Zn 18 ug L^?1) lake, 28 km from the smelters at Sudbury, had a degraded fish community in the early 1970's, with lake trout (Salvelinus namaycush) scarce, smallmouth bass (Micropterus dolomieui) extinct, and the littoral zone dominated by the acid-tolerant yellow perch (Perca flavescens). Liming of the lake in 1975–76 increased pH to 6.4, and decreased metal concentrations. Chemical conditions have remained relatively stable in the 10 yr following base addition. Initially, it appeared that neutralization produced dramatic changes in the resident fish community. Yellow perch abundance declined rapidly after neutralization, lake trout abundance increased to the extent that 3.26 kg ha^?1 were caught in the winter of 1980, and reintroduced smallmouth bass reproduced and established a large population. However, these changes in the fish community can not be directly attributed to liming, as water quality and the sport fisheries of an unlimed nearby lake also improved. Reduced emissions from Sudbury smelters were responsible for improvements in the untreated lake. Recovery of the lake trout population in Nelson Lake appears to have begun prior to liming. Of the lake trout sampled during the 1980 winter fishery, 65.8% were present prior to the chemical treatment. Predation by lake trout was the likely cause of the perch decline. Our results suggest that chemical conditions producing population level responses in fish have abrupt thresholds and that neutralization of lakes above these thresholds may not produce distinguishable effects.     

Relationship between fish populations and pH for lakes in Southermost Norway

Fish status in terms of ‘good, ‘sparse’, ‘lost’, ‘never had fish’, has previously been reported for several thousands of lakes in southermost Norway. In more than a thousand of these lakes pH and conductivity have also been measured. These data have been used to establish a relationship between pH and fish status (brown trout). It is estimated that a uniform pH increase of 0.2 units will result in status changes from category ‘lost’ to ‘sparse’ in 12% of the lakes (27% of the lakes which have lost the fish population). Altogether 21 % of the lakes are predicted to change to a better category. We have used a fixed pH shift in order to make the approach applicable. This is a rather drastic simplification since the lakes will respond very differently to a reduction in S deposition depending on the original acidity and a number of other factors. The limitations of the approach and an alternative method used by Chester (1982) are discussed in detail.     

Reduced Acid Deposition Leads to a New Start for Brown Trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in an Acidified Lake in Southern Norway

Acid deposition has led to acidification and loss of fish populations in thousands of lakes and streams in Norway. Since the peak in the late 1970s, acid deposition has been greatly reduced and acidified surface waters have shown chemical recovery. Biological recovery, in particular fish populations, however, has lagged behind. Long-term monitoring of water chemistry and fish populations in Lake Langtjern, south-eastern Norway, shows that around 2008, chemical recovery had progressed to the point at which natural reproduction of brown trout (Salmo trutta) reoccurred. The stocked brown trout reproduced in the period 2008–2014, probably for the first time since the 1960s, but reproduction and/or early life stage survival was very low. The results indicate that chemical thresholds for reproduction in this lake are approximately pH?=?5.1, Al_i?=?26 μg l^?1, ANC?=?47 μeq l^?1, and ANC_oaa?=?10 μeq l^?1 as annual mean values. These thresholds agree largely with the few other cases of documented recovery of brown trout in sites in Norway, Sweden, and the UK. Occurrence and duration of acidic episodes have decreased considerably since the 1980s but still occur and probably limit reproduction success.     

Interrelationships between mercury levels in yearling yellow perch,fish condition and water quality

Yearling yellow perch were collected from sixteen Muskoka-Haliburton lakes to determine interrelationships between water quality, Hg residues in fish and fish condition. The lakes studied were Precambrian shield lakes with a pH range of 5.6 to 7.3 and total inflection point alkalinities of 0.4 to 16.0 mg L^?1. Mercury residues in yellow perch ranged from 31 to 233 ng g^?1 and were inversely correlated (p < 0.001; r = 0.84) with lakewater pH. Stepwise linear regression analyses selected lakewater pH as the only significant parameter associated with Hg accumulations. Alkalinities, sulphate, Ca and dissolved organic carbon (DOC) were not selected as significant. Likewise, lakewater pH and Hg residues in yellow perch were inversely (p < 0.001) correlated with fish condition. Lakewater pH, accounted for 74% and Hg in fish a further 11% of the variability in fish condition. Terrestrial drainage size/lake volume ratios were also correlated (p < 0.05; r = 0.78) with Hg accumulations in perch from a subset of nine headwater lakes. No temporal trends in Hg residues were evident in yellow perch over a 9 yr interval (1978–1987).     

Reappearance of Highly Acid-Sensitive Invertebrates After Liming of an Alpine Lake Ecosystem

The amphipod Gammarus lacustris was earlier a main food item of brown trout in Lake Svartavatnet at the Hardangervidda mountain plateau in South Norway. In the middle of the 1980's, G. lacustris disappeared from the trout diet due to increased acidification. In order to preserve a unique genetic variant of brown trout living in the area, a liming programme was initiated in 1994. During the first years after liming, G. lacustris was absent both in fish stomachs and in lake littoral samples. In 1999, it reappeared in brown trout stomach samples together with two other strongly sensitive species, the tadpole shrimp Lepidurus arcticus and the freshwater gastropod Lymnaea peregra. Data from monitoring indicate that the water chemical conditions of L. Svartavatnet are still close to the critical limits of these animals. They have probably survived in small refuges of acceptable water quality, either in areas of inflowing groundwater or in the littoral, below the more acidic surface layer. The fact that these sensitive animals have not yet been found in benthic samples emphasise fish diet as an important tool in early registration of the presence/absence of invertebrates with low abundance or patchy distribution.     

Effects of Acidification on Salmonid Spawning Behavior

We studied the effects of acidification on female sexual behavior in brown trout (Salmo trutta) and compared the results with those in hime (land-locked sockeye) salmon (Oncorhynchus nerka) (Kitamura and Ikuta, 2000). The results were similar to those of sockeye salmon. Spawning brown trout were extremely sensitive to the acidity of ambient water, and nest-digging behavior was severely inhibited (p<0.05) by very slight acidification (pH below 6.4). However, there were some differences between the two species. Female trout and salmon showed almost no digging below pH 5.0 and 6.0 (Kitamura and Ikuta, 2000), respectively. When the ambient water was returned to nearly neutral (pH6.6) conditions, digging in hime salmon reappeared in 4 of the 6 fish tested (Kitamura and Ikuta, 2000), whereas digging in brown trout reappeared in all 6 fish tested. The above-mentioned differences in behavioral response between the two species appear to reflect the species difference in terms of vulnerability to acidification (Ikuta et al., 1992). Avoidance of slightly acidic water in selection of spawning site or cessation of spawning behavior in weakly acidic environments may be the most potent cause of the reduction of salmonid populations in the early stages of acidification.     

Recovery of the Perch (Perca Fluviatilis) in an Acidified Lake and Subsequent Responses in Macroinvertebrates and the Goldeneye (Bucephala Clangula)

The perch population of Lake Vähä Valkjärvi, a two hectare clear-water lake in southern Finland, decreased due to acid precipitation during the 1980s. During the early 1990s a decrease in acidic deposition resulted in slight improvement of water quality of the lake. This was followed by recovery of the reproduction of perch starting in 1991. A mark and recapture experiment in spring 1995 indicated a hundred fold increase in the population size of perch in a four year period. A decrease in the abundance of aquatic invertebrates was recorded during 1989–1996. This decrease well coincided with the recovery of the perch population, suggesting that increased predation by fish was responsible for the decrease. The occurrence of goldeneye young also dropped in L. Vähä Valkjärvi since 1993. This was thought to be due to increased food competition with perch.     

Recovery of Young Brown Trout in Some Acidified Streams in Southwestern and Western Norway

Temporal changes in densities of young brown trout (Salmo trutta), mainly of age 0+, and in water quality (pH and alkalinity) were assessed by means of electrofishing in lake tributaries in three acidic, software watercourses in western and southwestern Norway; Gaular and Vikedal (1987–1999) and Bjerkreim (1988–1999). Approximately 74 sites were sampled each year. Most of the streams were acidic with mean annual pH levels between 5.1–5.9. Alkalinity and pH increased significantly in all three areas during the study period. Brown trout fry densities increased significantly during the period in Vikedal and Bjerkreim. Also in Gaular, the density of young brown trout has exhibited a positive trend in recent years. We suggest that the increase in the density of young brown trout is because the study areas have became less acidified during recent years due to reduction in sulphate deposition.