Role of precipitation chemistry versus other watershed properties in Wisconsin lake acidification

Data for over 100 watershed properties, including aspects of topography, hydrology, geology, soils, vegetation, lake morphometry and input precipitation chemistry, have been developed since 1980 for 316 watersheds in northern Wisconsin. The hypothesis being evaluated for this lake population is that the observed water chemistry, can be accounted for as a function of antecedent water and chemical inputs, after considering exchange processes in the lake and watershed and the lake/groundwater interactions. The variables found by regression analysis to explain observed variability in color, sulfate, and acid neutralizing capacity (ANC) levels in Wisconsin lakes are: for color, vegetative characteristics, mean depth, and water renewal times; for sulfate, precipitation concentration of sulfur, evaporative concentration, and lake water renewal time; ANC appears to be controlled by the size of the watershed, lake depth or water renewal time, and the intensity of anthropogenic inputs and cultural developments in the watershed. These results differ from previous studies in Wisconsin and nearby areas of Michigan and Minnesota by indicating that in some lakes acidity may not be in equilibrium with current precipitation chemistry.     

Regional chemical characteristics of lakes in North America Part II: Eastern United States

A survey of 1592 lakes ( >4 ha and ≤ 2,000 ha) was conducted in Fall, 1984. The study area was three regions of the eastern United States (Northeast, Upper Midwest, and Southeast) expected to contain the most lakes with acid neutralizing capacity (ANC) ≤400 μeq/L. The design of the survey provides statistically reliable estimates of the number, location and chemical characteristics of lakes in the study area. Frequency distribution statistics are presented for pH, ANC, sulfate and organic anion. The highest percentages and numbers of acidic lakes occurred in Florida, the Adirondaks, and the Upper Peninsula of Michigan. The highest percentages and numbers of lakes with high sulfate concentrations occurred in the Poconos/Catskills, Southern New England and Florida. The highest percentages and numbers of lakes with high organic anion concentrations occurred in Northeastern Minnesota, the Upper Great Lakes Area and Florida. The percentage of acidic lakes by sulfate concentration class revealed no discernable pattern across subregions. In contrast, the acidic lakes occur with the highest frequency in the lowest organic anion concentration class. The complex distribution of low ANC lakes cannot be explained simply by sulfate concentrations or organic acids.     

Effects of sulfate deposition on pore water dissolved organic carbon,nutrients, and microbial enzyme activities in a northern peatland

Export of dissolved organic carbon from lakes and streams has increased throughout Europe and North America over the past several decades. One possible cause is altered deposition chemistry; specifically, decreasing sulfate inputs leading to changes in ionic strength and dissolved organic carbon solubility. To further investigate the relationship between deposition chemistry and dissolved organic carbon export in peatlands, a field experiment was conducted to compare the pore water chemistry and peat microbial enzyme activity of mesocosms receiving sulfate amendments to mesocosms receiving no additions. To consider how peatlands respond during recovery from increased inputs of sulfate, samples were also analyzed from an area of the same peatland that was previously amended with sulfate. Current additions of sulfate decreased dissolved organic carbon concentration and increased dissolved organic carbon aromaticity. Total dissolved phosphorus decreased in response to current sulfate amendments but was elevated in the area of the peatland recovering from sulfate amendment. The total dissolved phosphorus increase, which was reflected in microbial enzyme activity, may have shifted the system from P limitation to N limitation. This shift could have important consequences for ecosystem processes related to plant and microbial communities. It also suggests that the recovery from previous sulfate amendments may take longer than may be expected.     

The Effect of Climate Warming on the Hydrochemistry of Alpine Lakes

The hydrochemistry of mountain lakes is highly conditioned by the chemicalcomposition of atmospheric deposition and by climate characteristics. Consequently these ecosystems have proved to be sensitive to long-term changes in both factors. Climate warming seems to be particularly pronounced in the Alpine region. A reduction of snow cover in space and time, due to less precipitation and higher temperatures, means a greater exposure of rocks and soils in the watersheds, which enhances weathering processes. In this paper we aim to evaluate the possible effect of these processes on long-term changes in the chemistry of alpine lakes. Recent climate changes affecting the study area were investigated through a data series referring to temperature, precipitation, snow depth and duration at some stations in the Ossola Valley. Chemical data of 35 lakes located in the Ossola and Sesia Valleys (Central Alps) were used. Lakes were sampled both in the late summer of 2000 and 2001 in the framework of two European Projects and the results compared with previous data (1984–1987). Two lakes (Boden Superiore and Inferiore, 2343 and 2334 m a.s.l., respectively), located in the northern part of the study area, have been sampled more or less continuously since the late 70s, enabling us to evaluate the trends of the main chemical variables. For lakes lying in catchments with highly soluble rocks, a comparison between the two data sets shows an increase of solute contents in the last few years. This result could be attributed to increased weathering rates due to climate warming.     

Changes in soil chemistry accompanying acidification over more than 100 years under woodland and grass at Rothamsted Experimental Station, UK

We have examined the effect that acid deposition and other sources of acidity have had over the last 110–140 years on soil under woodland (Broadbalk and Geescroft Wildernesses) and grassland (Park Grass) comprising some of the Classical Experiments at Rothamsted Experimental Station. Changes in soil chemistry have been followed by analysing some of the unique archive of stored samples for pH, water-soluble and exchangeable base cations, aluminium, iron and manganese, exchangeable acidity, cation exchange capacity (CEC) and soluble anions. Proton balances and historical data show the importance of acid deposition to acidification and concomitant changes in the chemistry of the soil. The pH of the surface soil of Geescroft Wilderness has fallen from 6.2 to 3.8 since 1883. The decrease in the pH of the unlimed, unfertilized plot on Park Grass was less over a similar period (from pH 5.2 to 4.2), illustrating the significant effect of the woodland canopy on the interception of acidifying pollutants. The effect of increasing acidity on the soil chemistry of Geescroft Wilderness is seen in its decreasing base saturation and CEC, with base cations moving down the soil profile. Clay minerals are being irreversibly weathered, and Mn and Al progressively mobilized, so that today Al occupies 70% of the exchange complex in the surface soil. Even with present reductions in sulphur deposition critical loads for sulphur, nitrogen and acidity are still exceeded. Such semi-natural ecosystems are unsustainable under the current climate of pollution.     

Natural variance in pH As a complication in detecting acidification of lakes

Natural variance in the pH of three dilute lakes in the Flat Tops Wilderness Area, Colorado, complicates the detection of acidification. Variations in pH during July–September of 1983 were: 0.95 (Ned Wilson Lake), 1.36 (Upper Island Lake), and 1.53 (Oyster Lake). Mean diurnal variations in pH during 1983 were: 0.37 (Ned Wilson Lake), 0.54 (Upper Island Lake), and 0.39 (Oyster Lake). Replicate pH measurements indicate that pH can be measured with a mean variance due to measurement error of ± 0.005. Regression analysis indicates that samples collected on the same day of different years may differ because of time of day and percentage of cloud cover. Differences in wind duration and intensity and primary productivity also may cause the pH to differ between years. Such differences can be either random or systematic. Comparisons of pH among 3 yr of data from Ned Wilson Lake indicate that natural variations in pH are much larger than variations in Colorado Lakes previously attributed to acidification by precipitation.     

Changes in water quality in the Laflamme Lake Watershed Area,Canada

The Laflamme Lake Watershed Area is located in a sensitive region on the Canadian Shield and is subjected to wet atmospheric loading between 17 and 25 kg ha^?1 yr^?1. From 1981 to 1988, the level and fluctuations of the atmospheric deposition of acidifying substances has led to various responses in the water chemistry of headwater lakes in the area. The general trend in atmospheric inputs is a gradual increase of acidifying substances from 1981 to 1985 followed by a 2 yr decrease then a return to previous values. In the two lakes with almost no alkalinity acidification has occured throughout the 1983 to 1988 period. In the four lakes with slightly higher alkalinity values, a reversal in acidification is seen when atmospheric loading decreased in 1986. Along with the interannual trends, seasonal variability to acidification occurs with sensitivity of surface waters being highest during spring melt. Sensitivity to acidification can also be altered by watershed processes and in the Laflamme Lake Watershed, soil processes are effective in altering the acidity of precipitation before it reached the lake. In this watershed, wet atmospheric inputs of H⁺ and NO₃ ^? are larger than surface water outputs while the reverse occurs for Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^? and SO₄ ^2?.     

Laboratory and field testing of a dose calculation model for neutralization of Adirondack acidic lakes

A deterministic lake dose calculation model has been applied to estimate the quantity of Ca carbonate-based material needed to achieve a desired initial water chemistry in a whole lake treatment of two Adirondack acid lakes. The study lakes were treated with calcite during May 30–31, 1985. The model accurately simulated laboratory column water chemistry profiles (spatially and temporally) and dissolution efficiencies; however, the model predicted conservative efficiencies for the study lakes. Time-series water chemistry profiles of the lakes suggest that epilimnetic mixing extended suspension time of fine calcite particles, and that atmospheric carbon dioxide intrusion rate was greater than expected. The combination of these factors enhanced dissolution efficiency.     

Organochlorine residues in brook trout from remote lakes in the Northeastern United States

Organochlorine residues were analyzed in brook trout (Salvelinus fontinalis) collected from six undisturbed lakes in Maine, New Hampshire and Vermont. The residues (whole body) were compared among age groups of fish and were correlated by regression analyses with water chemistry factors that might be affected by acid precipitation. There were significant differences in the organochlorine content of fish from different lakes but not among age groups of fish within each lake or among all lakes. There were no significant correlations between the water chemistry values measured and organochlorine content of the fish. Inasmuch as no organochlorine pesticides have been used within the lake watersheds, the compounds must have reached these lakes by atmospheric transport.     

A Comparison of the Temporally Integrated Monitoring of Ecosystems and Adirondack Long-Term Monitoring Programs in the Adirondack Mountain Region of New York

This paper compares lake chemistry in the Adirondack region of New York measured by the Temporally Integrated Monitoring of Ecosystems (TIME) and Adirondack Long-Term Monitoring (ALTM) programs by examining the data from six lakes common to both programs. Both programs were initiated in the early 1990s to track the efficacy of emission reduction policies and to assess the full impacts of acid deposition on surface water chemistry. They now serve to inform on the emerging chemical recovery of these waters. The Adirondack TIME program utilizes a probability-based approach to assess chronic acidification in a population of lakes using one summer sample per year. The ALTM attempts to track changes in both chronic and episodic acidification across a gradient of lake types using monthly samples. The ALTM project has two important attributes that contrast with the TIME program in the Adirondacks: higher temporal resolution (monthly versus once during the summer or fall) and speciation of aluminum. In particular, the ALTM program provides inorganic monomeric aluminum (Al_IM), the fraction of Al that is most toxic. The monthly sampling of the ALTM program includes the spring snowmelt period when acid-neutralizing capacity and pH are near their lowest and Al levels are near their highest. We compare chemistry trends (1992?C2008) for sulfate, nitrate, base cations, dissolved organic carbon, hydrogen ion, acid neutralizing capacity, and Al for the six lakes common to both programs. We also compare relatively high springtime Al_IM concentrations from the ALTM with relatively low summertime total Al concentrations from the TIME, showing that the ALTM program provides a more biologically relevant indicator of the effects of acid deposition, illustrating the value of the complementary monitoring efforts in the Adirondack region.     

Remote mountain lakes as indicators of diffuse acidic and organic pollution in the Iberian peninsula (AL:PE 2 studies)

In the framework of the AL:PE 2 project, studies on acidification and organic pollution in mountain lakes have been conducted in several ranges in the Iberian peninsula: Pyrenees (Northeastern Spain), Sierra de Gredos (Central Spain), Sierra Nevada (Southern Spain) and Serra da Estrela (Central Portugal). These studies focused on water and sediment chemistry and organisms (benthic diatoms, Zooplankton, aquatic macroinvertebrates, and fish) as indicators of acidification. Organic micropollutants (PAH, PCB, DDE, hexachlorobenzene and others) in lake sediments and fish have been studied as tracers of atmospheric pollution. The Iberian peninsula lakes do not show severe anthropogenic acidification. pH values are in the range of sensitive lakes, but the levels of acidic pollutants are low. The status of the organisms surveyed agreed with this diagnosis. Pyrenean lakes showed the highest fluxes of organic pollutants related to fossil fuel combustion., higher pollutioninduced versus natural acidity ratios, and modeled alkalinity and pH declines.     

Current and historical inputs of mercury to high-latitude lakes in Canada and to Hudson Bay

Sediment cores collected from several lakes in northern Canada have been analyzed for mercury and several other chemical contaminants. Sites ranged from the Experimental Lakes Area of northwestern Ontario, north to Cornwallis Island, and west to the southern Yukon. Cores were sliced at sites of collection and individual slices were freeze dried and analyzed for Pb-210 and Cs-137 to estimate average time intervals of deposition. The earliest date estimated by Pb-210 was about 1850, and mercury concentrations in some lakes were clearly increasing before then, assuming no vertical movements of mercury within the sediments. Extrapolation of dates downward to deeper slices, assuming a constant sedimentation rate, indicated that in some lakes mercury inputs increased slowly even in the 1500's, more rapidly after 1750, and more rapidly yet over the current century. These increases are interpreted as increased fluxes of mercury to the lakes as a result of long-range transport of atmospheric mercury, since there are no local industrial sources of mercury. Slices taken near the bottom of a core are taken to estimate the geological component while elevations in excess of that in surface slices are taken to represent contamination from fallout. This partitioning suggests that sediments in the eastern Northwest Territories are dominated by pollution, while those from the western Northwest Territories are influenced more by their geological settings. Two cores from Hudson Bay suggest that mercury is increasing there too, but has not yet exceeded geological sources. Mercury shows little or no tendency to decline in the most recent slices; indicating that inputs of mercury remain at or near their historical maxima. Given relatively high and continuing inputs of mercury to northern lakes it seems likely that some portion of that mercury may find its way into the food chain, hence the long-term prospect is for increasing levels of mercury in northern fish.     

Organic and inorganic sulfur constituents of the Sediments in three New York lakes: Effect of site,sediment depth and season

Water and sediment parameters, with emphasis on S constituents, were compared among lakes (Oneida, South, Deer), seasons, sites and sediment depths. The three lakes differed in size, morphometry, productivity and acid neutralizing capacity and none of the lakes had anoxia in the water column. Redox potentials (Eh) were higher for oligotrophic South and mesotrophic Deer than cutrophic Oneida within the sediment. In the water column, the only S constituent measured was sulfate which was higher in nutrient rich Onieda (110 to 490 μmol I^?1) than South (30 to 70 μmol I^?1) or Deer (10 to 60 μmol ^?1) Total S in sediment was higher for South than for either Deer or Oneida. For Deer and South sediment, total S was greatest in the 5 to 15 cm layer, and this was likely due to historical changes in anthropogenic inputs through atmospheric deposition. The high S concentration in South sediment can be accounted for by particulate deposition of S through the water column. Organic S constituents constituted major forms of S in the sediments of the three lakes. Non-HI reducible S, of which carbon-bonded S was a dominant constituent, comprised a major portion of total S in Oneida, South and Deer. Ester sulfate was the next largest S constituent in South and Deer. As a percent of total S, sulfide (HCL digestion) and sulfate was higher in Oneida than South or Deer. There was an inverse relationship between sediment Eh and sulfide. Pyritic S was measured on bulk samples and constituted 37, 12, and 6% of total S in Oneida, South and Deer. Both inorganic and organic S forms showed seasonal variation and the transformation and translocation of these forms play an important role in the S dynamics of lakes.     

Comparison of paleolimnological with magic model reconstructions of water acidification

In sensitive areas receiving acidic deposition, paleolimnolgical data indicate changes in lake pH over 1 to 3 decades during the past century. Estimates of deposition of SOx and NOx over this same period suggest that deposition rates changed (1) earlier and (2) more slowly than did changes in lake chemistry. Clearly chemical and biological processes in the terrestrial catchment damp, delay, and moderate the response of surface water pH to deposition of acidifying compounds. This response is controlled by key terrestrial processes that include chemical weathering, sulfate adsorption, cation exchange, dissolution and precipitation of Al compounds, and dissolution and dissociation of inorganic C. MAGIC (Model of Acidifcation of Groundwater In Catchments) provides a tool by which these processes can be simultaneously and quantitatively linked to examine the impact of acid deposition on surface water chemistry. We have applied MAGIC to 4 lakes from which paleolimnological reconstructions are available — Big Moose Lake in the Adirondacks, Loch Grannoch in Scotland, Lake Gårdsjøn in Sweden, and Lake Hovvatn in Norway. The results indicate that the processes linked in MAGIC can account for temporal trends in pH and alkalinity such as those obtained from paleolimnological data.     

Seasonal,annual and long-term variability in the water chemistry of a remote high mountain lake: Acid rain versus natural changes

Seasonal fluctuations as well as long-term trends in water chemistry were studied in Schwarzsee ob Sölden (Tyrol, Austria), an oligotrophic softwater lake situated at 2796 m a.s.l. The catchement is composed of granite, plagioclase and micaschists containing considerable amounts of sulphur, with little soil cover. The lake is ice covered for about nine months, during this time the deepest layers (>16m) become anoxic. During summer overturn, alkalinity (ALK) is lowest (?8 μeq l^?1) in the whole water column, whereas pH reaches its minimum (4.88) at the surface during snowmelt. A decrease of pH from 5.8 to 5.4 during winter is caused by CO₂ oversaturation, but deep water ALK increases to up to 130 μeq l^?1 due to in-lake ALK generation by reductive processes and base cation (BC) release. The seasonal pattern of ALK in SOS is driven by in-lake processes in winter, the snowmelting in spring and watershed processes and precipitation during summer. Since 1989 summer sulfate concentrations in SOS, originating mainly from the catchment, show a tendency to increase presumably caused by enhanced weathering. In contrast, SO₄ ^2? concentrations in other high mountain lakes which are dominated by atmospheric depositions show a decreasing trend. SOS is a good example for the complexity of interactions between catchment and in-lake processes which act at different time scales and depend on climate changes and atmospheric inputs.     

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.     

Response of limed lakes to episodic acid events in Southwestern Sweden

Occurrence of stratified acidic water is described for five forest lakes situated in the westcoast region of Sweden. Differentiation between two types of acid events is made related to origin; one is caused by heavy rains and the other associated with snowmelt during winter and spring. Acid events are due to incomplete mixing between lake and inflow water. Both mixing forces like wind and density differences are important factors regulating the actual stratification. As observed in the lakes studied, stratification therefore occurs during periods of ice-cover when wind-induced mixing is impeded and generally results in an acidic surface water of varying depth. However, in this study we also describe the stratification of acidic inflow water at the sediment-water interface. This type of inlayering is presumably less frequent as a complex set of conditions must be satisfied for its occurrence. Our study shows that acid events may cause temporal and spatial water chemistry changes even in lakes and streams with relatively high pH and buffer capacity. Thus, early biotic damages can be expected in neutral and limed (soft water) lakes.     

Defoliation and Atmospheric Deposition Influences on Spring Baseflow Chemistry in 56 Pennsylvania Mixed Land-Use Watersheds

Using samples of spring baseflow chemistry on 56Pennsylvania watersheds with predominantly forested to mixedland-uses and widely varying geology/physiography, weattempted to determine spatial patterns in stream chemistrydue to insect defoliation and atmospheric deposition. Landuse and land form relations to stream chemistry wereexamined as well. Defoliation effects on stream chemistrydue to repeated, and sometimes intense, insect defoliationover the past several years were seen as reduced streamnitrate concentrations in a watershed data set (n = 11) thatincluded 100% forested lands only. Basins in regions withhigher atmospheric sulfate deposition loads had higherstream concentrations of sulfate in 100% forested basins.Significant positive correlations of stream nitrogen andpotassium with agricultural land use indicated possiblecontamination of stream waters by excess fertilizers and/oranimal wastes. Weak positive correlations were also foundwith many of the stream chemistry parameters and percentageurban/barren land use. Ridge-top versus valley bottomwatersheds also showed differences in baseflow chemistry dueto changing surficial geology and/or land use. Overall, thestudy showed that agricultural, urban, geologic, andphysiographic influences on spring baseflow chemistry maskthe effects of insect defoliation and atmospheric depositionon mixed land-use basins (<100% forest). Regionaldifferences in atmospheric deposition on 100% forestedbasins were directly reflected in spring baseflow SO₄concentrations. When restricted to 100% forested basinswith relatively uniform geology, insect defoliation appearedto reduce stream nitrogen concentrations in the long term.This is believed to be due in part to nitrogen bound invegetative growth and a dilution of nitrogen from increasedflows as a result of defoliation and tree mortality bringingabout reduced evapotranspiration.     

Sulphate in Sudbury, Ontario, Canada, Lakes: Recent Trends and Status

Sulphur emissions from the Sudbury, Ontario, metal smelting industry have affected thousands of lakes in Ontario, Canada. Reductions in these emissions during the 1970's resulted in reduced lakewater SO₄ concentrations and other water quality changes in the 1970's and 1980's. Further declines in lakewater SO₄ concentrations have accompanied additional recent S emission reductions achieved by 1994. Recent (1997) SO₄ concentrations are still related to distance from the Sudbury smelters. A strong inverse relationship with distance is evident to about 45 km, and is most pronounced in lakes within about 20 km. In lakes beyond 45 km, dissolved organic carbon (DOC), which was correlated with hydrological response time and total phosphorus concentrations, was the best correlate with recent SO₄ concentrations, indicating that some slowly-flushing, oligotrophic lakes still exhibit a "Sudbury" effect. Most lakes beyond 45 km, however, showed SO₄ declines and recent SO₄ concentrations comparable to lakes around Dorset, ～200 km from Sudbury, suggesting that these lakes are now most affected by the long-range atmospheric transport of S.     

Vegetational changes associated with recreational use and fire suppression in the Eagle Cap Wilderness, Oregon: Some management implications

Construction and use of trails and campsites, grazing by recreational packstock, and suppression of fires have altered the vegetation of the Eagle Cap Wilderness Area in northeastern Oregon, USA. The amount and type of alteration has varied among vegetation types and with the kind of activity. Changes attributed to intensive recreational use are localised but severe, particularly in more densely forested areas. Suppression of fires has produced subtle but widespread changes. Current attempts to minimise these changes are often inadequate due to the lack of ecological information and the difficulties of implementing regulations. Management suggestions are offered.