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.     

Climate confounds detection of chemical trends related to acid deposition in upper Midwest lakes in the USA

Between 1983–94, as acid deposition rates declined, SO₄ ^2? concentrations decreased in 18 of 28 lakes monitored by the upper Midwest LTM program. The expected recovery of ANC and pH was less common, however. Differences in climate may account for divergent trend patterns across the region. Only in Minnesota, where climatic shifts were less pronounced, did we observe a general pattern of increasing lake ANC and pH accompanying declines in SO₄ ^2?. In contrast, the widespread negative trends in lake SO₄ ^2? in the upper Michigan lakes were generally not associated with recovery of ANC and pH, but with decreases in Ca+Mg. These cation decreases may be linked to decreased groundwater inputs during the drier climatic conditions characterizing the study period and decreases in Ca+Mg in atmospheric deposition. In many of the Wisconsin lakes, an overall decline in SO₄ ^2? was precluded by SO₄ ^2? increases during a 4-year drought midway through the study period. During the drought, declining lake water level and volume caused evaporative concentration of solutes, and may have decreased the areal extent of sulfate reduction. Despite controls on sulfur emissions across the region, recovery of pH and ANC has been hindered by climatic shifts and concurrent decreases in atmospheric deposition of cations.     

The influence of organic acidity on the acid-base chemistry of surface waters in Maine,USA

Results from surveys of low-ANC lakes (high elevation, and seepage lakes), and of surface waters in dystrophic, acidic bogs, indicate that acidic precipitation and organic acidity are each generally necessary, but not solely sufficient, for chronically acidic status in Maine lakes. Acidic, low DOC (ANC < 0; DOC < 5 mg L^-1) lakes of all hydrologic types are acidic due largely to acidic deposition; high DOC (DOC > 30 mg L^-1) acidic seepage lakes are acidic due largely to organic acidity, and high DOC drainage lakes are acidic due to a combination of both factors. No low DOC drainage lakes are known with pH less than about 5.0, suggesting that organic acidity is necessary to depress lake pH values to below 5 in Maine at current deposition loadings,The dominant anion of low DOC, acidic waters is sulfate. Acidic waters with intermediate concentrations of DOC (5 to 30 mg L^-1), may be dominated by S04 and/or organic acidity. Seepage-input lakes were the only group to include both organically-dominated (37% of the acidic lakes) and S0₄-dominated members (63% of the acidic lakes). High DOC systems are typically low pH bogs, and are all organic acid-dominated.     

Trends and patterns in lake acidification in the State of Vermont: Evidence from the Long-Term Monitoring Project

Twenty-four low acid neutralizing capacity (ANC) lakes in Vermont have been monitored since 1980 to characterize their chemical variability, and to determine if they exhibit temporal trends in acid/base chemistry. Many of the lakes exhibit significant decreasing trends in SO₄ ^2? and base cation (C_B) concentrations, but few exhibit significant changes in pH or ANC. An examination of all trend results (significant and insignificant) suggests a tendency for ANC and pH values in these lakes to be increasing, but either the changes are too small, or the number of observations too small, for these trends to be significant. Data from these lakes suggest that the primary responses of surface waters in this region to declining rates of SO₄ ^2? deposition are decreases in SO₄ ^2? concentrations and rates of cation leaching from watershed soils. Decreasing rates of c_b deposition may combine with lower rates of cation leaching to produce declines in c_B that are very similar to measured declines in SO₄ ^2? concentration. Vermont lakes exhibit their lowest ANC values in spring, attributable, for the most part, to dilution of c_B concentrations during spring snow melt. Concentrations of SO₄ ^2? are also more dilute in the spring, but c_B decreases are greater, and the net effect is a lowering of ANC. One quarter of the Vermont lakes monitored exhibit strong seasonality in NO₃ ^? concentrations, with peak concentrations near 70 Μeq L^?1. In these lakes, spring increases in NO₃ ^? concentrations are more important than C_B dilution in producing minimal spring ANC values.     

recent lake acidification and recovery trends in southern quebec,canada

A total of 51 lakes in southern Quebec, Canada, were sampled between 1985 and 1993 to study changes in water chemistry following reductions in SO₂ emissions (main precursor of acid precipitation). Time series analysis of precipitation chemistry revealed significant reductions in concentrations and deposition of SO₄ ^2- from 1981 to 1992 in southern Quebec as well as reductions in concentrations and deposition of base cations (Ca²⁺, Mg²⁺), NO₃ ^- and H⁺ in the western section of the study area. Reductions in atmospheric inputs of SO₄ ^2- have resulted in decreased lakewater SO₄ ^2- concentrations in the majority of the lakes in our study, although only a small fraction (9 of 37 lakes used in the temporal analysis) have improved significantly in terms of acidity status (pH, acid neutralizing capacity – ANC). The main response of the lakes to decreased SO₄ ^2- is a decrease in base cations (Ca²⁺+Mg²⁺), which was observed in 17 of 37 lakes. Seventeen lakes also showed significant increases in dissolved organic carbon (DOC) over the period of study. The resulting increases in organic acidity as well as the decrease in base cations could both play a role in delaying the recovery of our lakes.     

Long-term trends in the chemistry of precipitation and lake water in the Adirondack Region of New York,USA

Long-term changes in the chemistry of precipitation (1978–94) and 16 lakes (1982–94) were investigated in the Adirondack region of New York, USA. Time-series analysis showed that concentrations of SO₄ ^2–, NO₃ ^–, NH₄ ⁺ and basic cations have decreased in precipitation, resulting in increases in pH. A relatively uniform rate of decline in SO₄ ^2– concentrations in lakes across the region (1.81±0.35 eq L^–1 yr^–1) suggests that this change was due to decreases in atmospheric deposition. The decrease in lake SO₄ ^2– was considerably less than the rate of decline anticipated from atmospheric deposition. This discrepancy may be due to release of previously deposited SO₄ ^2– from soil, thereby delaying the recovery of lake water acidity. Despite the marked declines in concentrations of SO₄ ^2– in Adirondack lakes, there has been no systematic increase in pH and ANC. The decline in SO₄ ^2– has corresponded with a near stoichiometric decrease in concentrations of basic cations in low ANC lakes. A pattern of increasing NO₃ ^– concentrations that was evident in lakes across the region during the 1980's has been followed by a period of lower concentrations. Currently there are no significant trends in NO₃ ^– concentrations in Adirondack lakes.     

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.     

Soil geochemistry in relation to water chemistry and sensitivity to acid deposition in Finnish Lapland

Ecosystems in Finnish Lapland are threatened by heavy metal pollution and acid deposition derived from emissions of Cu-Ni smelters in Kola Peninsula and to varying extent to pollution from southern Fennoscandian and Central European sources. Extensive chemical analyses of small lake waters collected in Finnish Lapland have demonstrated that a significant number of lakes are acidified (ANC < 0μcq/l) or their buffering capacity is critical (ANC = 0–50μe/l). The relative abundance of mafic, ultramafic and carbonate rock components in the catchment were the chief factors controlling ANC and the main base cation (Ca²⁺, Mg²⁺) concentrations of lake waters. Both humic and clearwater lakes with low buffering capacity (ANC < 50μeq/l) were mainly located in the catchment areas identified as sensitive to acidification on the basis of low content of base cations (Ca²⁺ +Mg²⁺ +K⁺ < 500 meq/kg) in till. The ratio of the catchment area to the lake area was distinctly smaller for acidic lakes than for the well-buffered lakes, indicating the importance of catchment processes in determining the ANC and main base cations. The high sulphur concentrations (median 60μeq/1) of acidic lakes in northeastern Lapland, near the Finnish-Norwegian border, were strongly correlated with the highest deposition of sulphur derived from smelters of Kola Peninsula. The anomalously high concentrations of sulphur of well-buffered lakes in the western part of Lapland were due to sulphide minerals of soil and bedrock. The acidity of humic lakes in southern Lapland was in large part due to the organic acidity derived from peatlands.     

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.     

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.     

Metal concentration in the gill,gastrointestinal tract,and carcass of white suckers (Catostomus commersoni) in relation to lake acidity

Adult white suckers were collected from four lakes in Maine that ranged in pH from 7.0 to 5.4. The gastrointestinal tract and remainder of the carcass of fishes of similar age and size from each lake, and gills from additional fishes of similar size, were analyzed for Al, Cd, Pb, and Zn. Carcasses were also analyzed for Hg. Concentrations of Al, Cd, and Pb were highest in the gastrointestinal tract and lowest in the carcass; Zn concentration was highest in the gill. For carcass, all metals except Al differed significantly among lakes, for gill tissue Cd and Pb differed, and for gastrointestinal tract, only Cd differed among lakes. Where differences were significant, patterns among lakes were similar in each tissue analyzed. Concentrations of Cd, Hg, and Pb were negatively correlated with lake water pH, acid neutralizing capacity (ANC), Ca, and lake:watershed area, and positively correlated with lake water SO₄, indicating that concentrations were higher in fish from more acidic lakes. Zinc concentrations in gills were unrelated to lake acidity, and carcass concentrations were higher in the less acidic lakes, which is the opposite of the pattern for the other metals studied. Zinc in gastrointestinal tract did not differ among lakes. Although the lakes we studied were located in undisturbed watersheds and did not receive any point source discharges, fish metal concentrations were comparable to or higher than those reported from waters receiving industrial discharges.     

Episodic acidification during snowmelt of high elevation lakes in the Sierra Nevada mountains of California

Atmospheric loads to dilute lakes in the Sierra Nevada mountains of California are very low, and fall almost entirely as snow. When acidic anions preferentially elute from melting snow, these low loads may nontheless be enough to acidify low ANC lakes. Two of the ten lakes included in the Sierra Episodes Study are discussed here: High Lake, the only lake in the study to become acidic during snowmelt; and Treasure Lake, typical of the remainder of the lakes. All lakes exhibited increases in NO₃ ^? concentrations during early snowmelt; these were accompanied by increases in base cations, primarily Ca²⁺. In the first few days of snowmelt, NO₃ ^? concentrations at High Lake increased more rapidly than concentrations of base cations, resulting in ANC values below zero. Export of both NO₃ ^? and SO₄ ^2? from the watersheds exceeded the inputs from the snowpack, suggesting that other sources (e.g., watershed minerals, stored inputs from the previous summer, transformations of other inputs) of these anions are important.     

Trends in Water Chemistry of Acidified Bohemian Lakes from 1984 to 1995: II. Trace Elements and Aluminum

The concentrations of Al, Be, Cd, Cu, F, Fe, Mn, Pb, and Zn were monitored in five glacial lakes and one man-made lake in the southwestern part of the Czech Republic. The lakes had median pHs of 4.4 to 6.5 during 1984 to 1995. Decreases in the concentrations of Mn and Pb occurred in five acidified lakes. The concentrations of Al_T, Be, Cd, and F decreased in the four chronically acidified lakes, Zn decreased in two lakes. Concentrations of Cu and Fe remained unchanged. The decreases in Be, Mn, and Zn concentrations were proportional to the decrease in C_SA (C_SA = SO₄ ^2- + NO₃ ^-+ Cl^-); decreases in Al_T, Cd, and Pb concentrations were proportionately higher, while F was lower. The greater decrease in the Pb concentrations (61 to 79%, at a rate up to 0.15 μg L^-1yr^-1) was caused by pronounced decreases in deposition of Pb derived from mobile sources. The decrease of Al_T concentrations was dominated by a decrease in Al³⁺, whose concentration decreased by 51 to 86%. The concentrations of complexes Al(OH)²⁺, Al(OH)₂ ⁺, AlF²⁺, and AlH₃SiO₄ ²⁺ also decreased. The decrease in the concentrations of inorganic forms of Al (Al_i) compensated 65% of the decrease in C_SA. The Cd concentrations were highly variable in the years 1986 to 1988 because of variable amounts of accumulation on particles.     

Perch mercury content is related to acidity and color of 26 Russian lakes

We determined mercury in fish (perch Perca fluviatilis) from 26 Russian lakes in three regions over four years. The lakes ranged in size from 2 to 395,000 ha, in pH from 4.5 to 10.0, and in color from 3 to 190 hazen. Sixteen lakes were drainage lakes, with permanent outlets, and 10 were seepage lakes, with no permanent inlets or outlets. The lakes were generally located in forested regions with little or no human habitation in the watershed. The three regions were geologically distinct: Precambrian Shield granitic bedrock covered with thin soil; Triassic bedrock covered with thick glacial tills; and Triassic bedrock covered with thin sediments. At each lake water samples were collected and analyzed for pH, add neutralizing capacity (ANC), major cations, and anions. Dissolved mercury species were estimated with a thermodynamic equilibrium model (MINTEQA2). Mercury content of dorsal muscle varied from 0.04 to 1.0 g/g wet weight, and was linearly related to calculated HgCH₃Cl (r²0.68, p<0.001). lake=">₃Cl, in turn, was related to lake pH (r²=0.86, p<0.001). stepwise=" multiple=" regression=" selected=" lake=">₃Cl and color as the factors most highly related to fish mercury content, with the model accounting for 75% of the variation.     

Sudbury Sediments Revisited: Evaluating Limnological Recovery in a Multiple-Stressor Environment

Paleolimnological techniques were utilized to determine whether diatom and scaled chrysophyte assemblages in Daisy, Swan, and Tilton lakes (Sudbury, Ontario) have recovered toward their preimpact conditions as a result of reduced inputs of anthropogenic pollutants (SO ₄ ^2? and metals) or whether other environmental stressors have affected recovery trajectories. In addition, geochemical analysis was used to track trends in sedimentary nickel and copper concentrations through time. Preindustrial algal assemblages were primarily dominated by circumneutral to alkaline and pH-indifferent taxa. However, with the onset of open-pit roasting and smelting operations, there was a stratigraphic shift toward acid-tolerant species. With wide-scale smelter emission reductions commencing in the 1970s, scaled chrysophyte assemblages in Swan and Daisy lakes have started to show signs of biological recovery in ～1984 and ～1991, respectively. Although the scaled chrysophyte assemblage in Tilton Lake has not recovered toward the predisturbance assemblage, the decline in acidophilic taxa and increase in circumneutral taxa in recently deposited lake sediments indicate that the community is responding to increased lake water pH. Conversely, diatom assemblages within each of the study lakes have not begun to recover, despite well-documented chemical recovery. It is suspected that biological recovery in Sudbury area lakes may be impeded by other environmental stressors such as climate warming. Copper and nickel concentrations in lake sediments increased with the onset of mining activities and subsequently declined with emission controls. However, metal concentrations in lake sediments remain elevated compared to preindustrial concentrations. Together, biological and geochemical evidence demonstrates the clear environmental benefits associated with smelter emission controls.     

Decrease in Acid Deposition - Recovery in Norwegian Waters

Concentrations of sulphate in precipitation in southern Norway have decreased by 50–60% from 1980–1999. This has caused a decrease in sulphate concentrations in lakes of 30–40% from 1986–1999. Nitrogen in precipitation has decreased slightly over the last 10-years. In lakewater there has also been a significant but slight decrease. Concentrations of non-marine base cations in precipitation have decreased by 40% from 1980–1999. In lakewater, non-marine base cation concentrations have been at about the same level the last 10 years. This indicates that acid deposition has decreased sufficiently such that the pool of exchangeable base cations in the soil is now being replenished. The acidification situation in lakes in Norway has thus shown a clear improvement over the last 8–10 years. pH, alkalinity and ANC (acid neutralising capacity) have all increased. Concentrations of inorganic (toxic) aluminium species have decreased. The trends in H⁺ and Alⁿ⁺ do not follow the relation expected if Alⁿ⁺ concentrations were governed solely by a single solid phase of Al(OH)₃.     

Acid neutralizing capacity of lakes in the North Cascades area of Washington State

Thirty three lakes were surveyed in 1983 in the North Cascades area of Washington State and 27 additional lakes were surveyed in 1984 to characterize lake chemistry in the area. Lakewater ANC was less than 100 ueq 1^?1 for 37% of the lakes and less than 200 ueq 1^?1 for 68% of the lakes. The North Cascades are very similar to unimpacted sensitive areas of North America and Northern Europe in mean alkalinity and (Ca + Mg). Bedrock geology appears to have a significant influence on surface water ANC with lakes on granitic and metamorphic bedrocks having the lowest ANC.     

The chemical responses of acidic Woods Lake,NY to two different treatments with calcium carbonate

A study was conducted to compare and contrast two approaches to neutralize an acidic lake by CaCO₃ addition (Woods Lake, Adirondack Mountains, New York, U.S.A.; 42°52′ N, 71°58′ W); direct water column treatment and treatment of both the water column and sediment. The latter treatment strategy was designed to release a slow, diffusive Ca²⁺. flux across the sediment/water interface and thereby delay the rate of reacidification. Both applications satisfactorily increased the acid neutralizing capacity (ANC) and Ca²⁺ of the lake, temporarily buffering the water column pH against acidic inputs from the watershed. The water column/sediment application involved a greater (50% more) dose in order to accomplish sediment treatment and resulted in a prolonged period of positive ANC in the water column. However, both treatments neutralized approximately the same quantity of runoff and equivalence of acidic inputs. Water column/sediment treatment may be an effective approach to help delay reacidification in shallow lakes of moderate hydraulic retention times. Unfortunately, many acidic Adirondack lakes have very short hydraulic retention times (<0.5 yr) and may not be neutralized for adequate durations by either water column or water column/sediment CaCO₃ treatments.