Recovery Pattern from Acidification of Headwater Lakes in Finland

Acid sensitive headwater lakes (n=163) throughout Finland have been monitored during autumn overturn between 1987–1998. Statistically significant decline in sulphate concentration is detected in 60 to 80 percent of the lakes, depending on the region. Median slope estimates are from ?1.1 µeq L^?1 in North Finland to ?3.3 µeq L^?1 in South Finland. The base cation (BC) concentrations are still declining especially in southern Finland (slope ?2.5 µeq L^?1), where every second lake exhibits a significant downward trend. The BC slope is steeper for lakes with less peatlands, more exposed bedrock, longer retention time and southerly location, but these factors are inter correlated. Gran alkalinity slope medians for the three regions range from 1.4 to 1.8 µeq L^?1 yr^?1. No significant negative alkalinity trends were detected. The similarity in the slopes of SO₄, BC and alkalinity in this data compared to seasonal sampling data from Nordic Countries can be regarded as indirect evidence that autumnal sampling is representative for long term monitoring for these ions. There are no indications of increased organic carbon in lakes, as found in some recent trend analyses of similar regional data sets. Although the processes behind the positive development in these lakes have to be revealed with site- specific intensive studies, this data suggests, that the initial recovery from lake acidification in Finland is a regional phenomenon.     

Dose-response relationships for the addition of limestone to lakes and ponds in the Northeastern United States

A titration based model (DeAcid) has been used to predict treatment dose and times for reacidification for CaCO₃-treated lakes in the Living Lakes, Inc. (LLI) aquatic liming program. Water quality constitutents (pH, ANC and Ca) were used to measure the effectiveness of the dosing model and reacidification rates. Data from 22 lakes or ponds in 5 northeast states have been collected since June 1986. With few exceptions, pH and ANC values ranged from 4.5 to 6.5 and ?30 to +65 ueq L^?1, respectively, in untreated sites and 6.5 to 7.8 and 120 to 300 ueq L^?1, respectively, in sites approximately 30 days after treatment. Changes in Ca concentration levels have been used to evaluate the utility of the dose model for treatment of both inland and coastal waters. For coastal, seepage lakes application of a single-box mass transfer model to observed post-liming changes in ANC and Ca adequately simulates lake response.     

Low Success Rate in Re-Establishing European Perch in Some Highly Acidified Lakes in Southernmost Norway

In order to test whether major reductions in acid inputs had improved water quality sufficiently for fish populations to recover, we stocked wild European perch (Perca fluviatilis) in three highly acidified lakes that had previously supported this species, and in one limed lake. The fish, which were introduced from a local lake (donor lake), generally ranged from 12 to 16 cm in total length, and were stocked at densities of 117–177 fish ha^?1. The untreated lakes were highly acid, with minimum pH values and maximum inorganic aluminium concentrations (Al_i) during the spring of 4.6–4.7 and 118–151 µg L^?1 respectively. In the limed lake, the corresponding values for pH and Al_i ranged between 5.8 and 6.6 and 5 and 19 µg L^?1 respectively. Gill-netting in two subsequent years after the introduction yielded only a few recruits (0+) and one adult in one of the three acidified lakes in one year only. However, stocked perch reproduced successfully in both years in the limed lake. There was a significant linear relationship between the catches (CPUE) of juvenile perch (age 0+) in the different lakes in the autumn and the water quality in May (time of hatching), both in terms of Al_i (r ²=0.934, P<0.05) and pH (r ²=0.939, P<0.05). Our data suggest unsuccessful recruitment in waters of pH <5.1 and Al_i>60 µg L^?1.     

Mercury concentrations in an aquatic ecosystem during twenty years following abatement the pollution source

Phenyl Hg was widely used as a slimicide in Finnish pulp industry until the end of 1967. The use of Hg caused a significant increase of Hg levels in fish in several areas. High concentrations were measured in Lake Kirkkojärvi in Hämeenkyrö, SW Finland. Vast amounts of Hg are still present in the lake sediments. Since 1968 uncontaminated fibres have partly covered the contaminated layers. Since 1971 Hg has been monitored in fish, sediments and aquatic plants in the water course downstream from the pulp and paper factory. The Hg concentration of a 1-kg pike (Esox lucius) has decreased from 1.5 µg g^?1 in the years 1971–74 to 0.8 µg g^?1 in 1990.     

Seasonal and long-term temporal patterns in the chemistry of Adirondack lakes

There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO₄ ^2?. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca²⁺, Mg²⁺, K⁺, Na⁺; C_B) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO₃ ^?, while lakes in the central and eastern Adirondacks had lower NO₃ ^? concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 Μeq L^?1 during base flow periods may experience decreases in ANC to near or below 0 Μeq L^?1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO₄ ^2?, consistent with decreases in SO₂ emissions and SO₄ ^2? in precipitation in the eastern U.S. Reductions in SO₄ ^2? have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO₃ ^? that occurred in most of the ALTM drainage lakes.     

Recent trends in the acid-base status of surface waters in Maine,USA

Data from the EPA Long Term Monitoring Program lakes at the Tunk Mountain Watershed, Maine, indicate that decreases of ≤1 Μeq L^?1 yr^?1 in SO₄, and increases of ≤2 Μeq L^?1 yr^?1 in ANC occurred in the 1980s. The sum of base cations also increased. These changes in aquatic chemistry were coincident with decreased concentrations of all solutes in precipitation during the 1980s. Other data on lakes and streams in Maine collected between the 1930s and 1990 generally confirm these trends and further indicate that larger increases in ANC may have occurred in some lowland lakes since 1940. Paleolimnologic studies indicate that decreases of 0.1 to 0.5 pH units occurred in a few small mountain lakes during the past 20 to 70 yr. However, ongoing acidification of lakes is indicated based on available data. Only lakes that were already at least marginally acidic (pH ≤5.8, ANC approximately 0) appear to have acidified.     

Temporal trends in low alkalinity lakes of the Upper Midwest (1983–1989)

The Upper Midwest contains a large concentration of low alkalinity lakes located across a west to east gradient of increasing deposition acidity. We present temporal trends in the chemistry of 28 lakes (4 in Minnesota, 13 in Wisconsin, and 11 in Michigan) representative of the acid-sensitive resource of the region. Lakes were sampled three times per year between 1983 and 1989. Temporal trends in SO₄ ^2? were all negative in direction, consistent with a regional decline in SO₂ emissions and atmospheric SO₄ ^2? deposition. However, these trends occurred predominantly in higher ANC (100 to 225 Μeq L^?1), non-seepage lakes and were associated with increases in ANC and pH in only one of the 8 lakes. ANC decreased in a second group of lakes, usually in concert with decreased [Ca²⁺+Mg²⁺], a response we associate with a severe drought. Disruptions in hydrologic flowpaths caused one lake to acidify rapidly after inputs of ANC-rich groundwater ceased and appeared to cause ANC and [Ca²⁺+Mg²⁺] declines in a second lake by reducing stream-water inflow. Our analysis was thus complicated by hydrochemical effects of climatic variability, which confounded trends related to acidic deposition. Periods longer than 6 yr are needed to transcend climatic signals and verify subtle trends related to atmospheric pollutants.     

Treatment of mercury contaminated fish by selenium addition

Treatment of Hg contaminated fish by addition of Se (the Boliden SRM-method) has been shown to be an effective mean to reduce the Hg concentration of pike and perch. The fullscale tests in eleven lakes in Sweden have confirmed the earlier results in lake Öltertjärn in Sweden. The 1 yr old perch in the treated lakes shows a reduction in the mean Hg concentration. The Hg concentration in tissue varied between 0.04 and 0.29 mg kg in the different lakes before treatment. After treatment the Hg concentration decreased to 0.02 to 0.07 mg kg^?1. The reduction in perch was as much as 60% for the three lakes with lower background concentration in pike (less than 0.7 mg kg^?1) and as high as 85% for eight lakes with higher concentrations. In pike with Hg concentration at or above 1 mg kg^?1it was reduced by 22% after only I yr and by 28% after 2 yr of treatment. Experience gained in these tests verifies the importance of adjusting the dose and addition period to the lake. Good circulation in the lake is essential during addition.     

Measurement of methylmercury and mercury in run-off,lake and rain waters

During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L^?1, 0.04 to 0.8 ng L^?1, and <0.05 to 0.6 ng L^?1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L^?1, 1.35 to 15 ng L^?1, and 7 to 90 ng L^?1, respectively. A Hg-tot level of about 60 ng Hg L^?1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.     

Acidity status of surface waters in Massachusetts

The Massachusetts Acid Rain Monitoring project surveyed 80.5% of the state's 5294 named water bodies between 1983 and 1985. PH and acid neutralizing capacity (ANC) were measured monthly the first 14 mo and semi-annually afterwards. Sample collection and analysis were performed by volunteers. The majority of surface waters in Massachusetts were found to be sensitive to possible long term acidification, with 63% exhibiting ANC less than 200 μeq L^?1 and 22% with ANC less than 40 μeq L^?1. Seasonal patterns in ANC were observed, the median ANC being 384 μeq L^?1 in summer/fall and 134 μeq L^?1 in winter/spring. Geographical differences were also found across the state: the streams and lakes with lowest pH and ANC were located in the southeastern and north-central parts of the state, while the most alkaline surface waters were found in the western-most part of the state, which is the only area of the state with significant limestone deposits.     

Total concentrations of mercury in Wisconsin (USA) lakes and rivers

We analyzed surface waters from 30 Wisconsin lakes and rivers for total mercury ([Hg]_T) and total suspended particulates (TSP) on a state-wide basis with trace-metal ‘ultraclean’ techniques. Mercury concentrations ranged from 0.3 to 2.9 ng L^?1 in lakes and from 0.7 to 8.9 ng L^?1 in rivers. TSP concentrations ranged from 0.9 to 6.6 mg L^?1 in lakes and from 3.1 to 31.4 mg L^?1 in rivers. Spatial trends were weak; however, [Hg] _T was generally higher in the spring than in the autumn of 1991. Total mercury concentration was weakly dependent on TSP with the coefficient of determination (r ²) ranging 0.06 to 0.49 across seasonal and geophysical differences.     

Can Phosphate Help Acidified Lakes to Recover?

Experimental addition of phosphate to enclosures in an acidified lake in Southern Norway was performed to study the effect on nitrate, pH and labile aluminium along a gradient of phosphate from 4–19 µg P L^?1. Nitrate decreased from 180 µg L^?1 to below detection limit after three weeks at P-concentrations > 17 µg L^?1, due to phytoplankton uptake. pH increased from 4.9 to 5.2, corresponding to a 50% decrease of H⁺-equivalents from 12 to 6 µg P L^?1 due to algal uptake of H⁺-ions when assimilating NO₃ ^?-ions. Due to the increased pH and probably also precipitation with phosphate, concentrations of labile aluminium decreased from 150 to 100 µg L^?1 within the P-interval 4–19 µg L^?1. Algal biomass increased from 0.5 to 6 µg chlorophyll a L^?1 along the same P-gradient. The results suggest that moderate P-addition (< 15 µg P L^?1 to avoid eutrophication problems) can improve water quality in moderately acidified lakes, and also increase nitrate retention in strongly acidified lakes. In humic lakes, the treatment will be less efficient due to light limitation of primary production and the presence of organic acids.     

Human exposure to mercury may decrease as acidic deposition increases

It has been hypothesized that human mercury (Hg) exposure via fish consumption will increase with increasing acidic deposition. Specifically, acidic deposition leads to reduced lake pH and alkalinity, and increased sulphate ion concentration ([SO₄ ^2?]), which in turn should cause increased Hg levels in fish, ultimately resulting in increased human Hg exposure via fish consumption. Our empirical test of this hypothesis found it to be false. We specifically examined Hg levels in the hair of Ontario Amerindians, who are known consumers of fish from lakes across the province, and observed a weak negative association with increasing sulphate deposition. An examination of Hg levels in lake trout, northern pike and walleye, three freshwater fish species commonly consumed by Ontario Amerindians, found a similar weak negative association with increasing sulphate deposition. Further analysis of these fish data found that fish [Hg] was most significantly (positively) associated with lake water concentrations of dissolved organic carbon (DOC), not pH, alkalinity or [SO₄ ^2?]. Lake DOC levels are lower in regions of greater acidic deposition. We propose an alternate hypothesis whereby human Hg exposure declines with increasing acidic deposition. In particular, we propose that increasing sulphate deposition leads to reduced lake DOC levels, which in turn leads to lower Hg in fish, ultimately reducing human Hg exposure via fish consumption.     

Trends in the Chemistry of Acidified Bohemian Lakes from 1984 to 1995: I. Major Solutes

Temporal changes in major solute concentrations in six Czech Republic lakes were monitored during the period 1984–1995. Four chronically-acidic lakes had decreasing concentrations of strong-acid anions (C_SA = SO₄ ^2- + NO^{3 -} + Cl^-), at rates of 3.0 to 9.0 μeq L^-1 yr^-1. Decreases in SO₄ ^2-, NO₃ ^-, and Cl^- (at rates up to 5.1 μeq L^-1 yr^-1, 3.2 μeq L^-1 yr^-1, and 0.6 μeq L^-1 yr^-1, respectively) occurred. The response to the decrease in deposition of S was rapid and annual decline of SO₄ ^2- in lake water was directly proportional to SO₄ ^2- concentrations in the acidified lakes. Changes in NO₃ ^- concentrations were modified by biological consumption within the lakes. The decline in C^SA was accompanied in the four most acidic lakes by decreases in Al_T, increases in pH at rates of 0.011 to 0.016 pH yr^{- 1}, and decreases of Ca²⁺ and Mg²⁺ (but not Na⁺) in three lakes. The acid neutralizing capacity (ANC) increased significantly in all six lakes. Increases in base cation concentrations (CB = Ca²⁺ + Na⁺ + Mg²⁺ + K⁺) were the principal contributing factor to ANC increases in the two lakes with positive ANC, whereas decrease in C_SA was the major factor in ANC increases in the four chronically-acidic lakes. The continued chemical recovery of these lakes depends on the uncertain trends in N deposition, the cycling of N in the lakes and their catchments, and the magnitude of the future decrease in S deposition.     

Chemistry differences in two streams entering an acidic lake in the Adirondack Mountains,New York (U.S.A.)

Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H⁺, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L^?1 of H⁺ and sulfate-S, μmol L^?1 Al, μeq L^?1 total base cations and μmol L^?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L^?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L^?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L^?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed.     

Extreme acidification of a lake in southern Norway caused by weathering of sulphide-containing bedrock

In 1986 Lake Langedalstjenn in southern Norway was a weakly acidified lake with a pH of 5.2–5.6, and an average concentration of SO₄ of 330 μeq L^?1. The total Al concentration varied between 10 and 20 μeq L^?1 (expressed as Al³⁺). The lake supported populations of brown trout and perch and had supplied about 100 people with drinking water until the late 1980's. During 1986–1989, a dramatic change in the water chemistry occurred because of blasting of and weathering of sulphidic gneisses in the watershed. The oxidation of sulphide to sulphate (sulphuric acid) caused an increase in the SO₄ concentration of the draining stream of up to ≈ 4800 μeq L^?1. Weathering and/or cation exchange of Ca and Mg neutralized approximately 52% of the protons from the sulphuric acid production, while about 46% were consumed by mobilization of aluminium and iron. Nevertheless, about 2% of the hydrogen ions from the sulfuric acid were still present, which resulted in a stream pH of 4.0. In the lake, the pH was 4.4, and the concentrations of all major cations and anions were significantly lower than in the heavily affected stream. Mixing of the stream water with lake water, formation of aluminium-sulphate complexes and coprecipitation of Ca may explain the resulting concentrations of major ions in the lake.     

Chemistry of soft-water seepage lakes in the upper midwest: Lacustrine alkalinity production in summer

A total of 26 soft-water, seepage lakes in the Northern Highlands (NH) of Wisconsin (N =16) and the Upper Peninsula (UP) of Michigan (N=10) were sampled four times between early May and mid October 1984 as part of the ‘PIRLA’ Project (Paleolimnological Investigations of Recent Lake Acidification). Because of low antecedent recharge of the local water-table, this ‘summer’ interval likely featured minimal groundwater inputs (<2 cm over lake surface) to most of these seepage lakes. Based on this hydrogeologic relationship, and on regional deposition data, I evaluated short-term net epilimnetic (June–August) and whole-lake (May–October) sediment-water exchange of ANC, base cations, acid oxy-anions, Al, DOC and silicic acid in these lakes using a simplified mass balance algorithm. Silica, nitrate and ammonium were all efficiently retained in these seepage lakes. The assimilation of NO₃ ^? (19±4 meq m^?2) slightly exceeded assimilation of NH₄ ⁺ (16±4), resulting in a net internal ANC production of only +3 meq m^?2 over 161 d between early May and mid October 1984. Over this same interval ANC production resulting from lacustrine S retention averaged +35±8 meq m^?2 in the NH, but was too variable to be statistically significant (+21±21 meq m^?2) in the UP. Epilimnetic S retentions in mid summer were more comparable (21±4 in NH; 14±5 meq m^?2 in UP). McNearney Lake (UP) illustrates how high sulfate, linked to low alkalinity, high Al, low P, and low productivity, can become a negative correlate of lacustrine S retention. Temporal changes in base cations in the 26 lakes were generally small and erratic compared with uncertainties in deposition inputs and analytical errors, rendering estimates of related ANC production inconclusive. Even small analytical biases can be critical when designing and interpreting lake monitoring studies.     

Response to a smelter closure in Cascade mountain lakes

A statistically significant decrease in sulfate was observed in high elevation Cascade lakes during 1983 through 1988. The total decrease averaged 2.2 μeq L^?1 in two slow-flush lakes and 4.2 μeq L^?1 in three fast-flush lakes for 1983–1985 vs 1986–1988, respectively. Coincident with these changes in sulfate concentrations were a sharp decrease of SO₂ emissions from the ASARCO smelter (100 km SE of the lakes), from 87 to 70 kt yr^?1 during 1983–1984 to 12 in 1985, the year of its closure, and a gradual change in SO₂ emissions from Mt. St. Helens, from 39 to 27 during 1983–1984 to 5 in 1988. The sharpest decreases occurred in non-marine sulfate in fast-flush lakes from 1984 to 1985 (about 2 μeq L^?1) and in slow-flush lakes from 1985 to 1986 (1 μeq L^?1, which point to the ASARCO closure as the sole cause. However, some of the more gradual decline in non-marine sulfate observed during 1983 through the 1988 sampling periods may have been due to a slow washout of sulfate enriched ash from the 1980 Mt. St. Helens' eruption. Sulfate concentrations in precipitation also declined significantly by about 2 μeq L^?1, but changes in volume-weighted sulfate content were not significant. Lake alkalinity did not show a consistent increase in response to decreased sulfate. This was probably due to either watershed neutralization of acidic deposition or the greater variability in alkalinity measurements caused by small changes in acidic deposition making it difficult to detect changes.     

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.