Lake Acid Neutralizing Capacity Research Articles

Factors influencing critical and target loads for the acidification of lake–watersheds in the Adirondack region of New York

Critical loads (CLs) and target loads (TLs) are tools used to guide air emissions control strategies for recovery of forest and aquatic ecosystems impacted by elevated atmospheric deposition. We use the dynamic hydrochemical model-PnET-BGC (photosynthesis evapotranspiration biogeochemical) to evaluate biophysical factors that affect CLs and TLs of acidity for the Constable Pond watershed, as an example of a chronically acidic drainage lake in the Adirondack region of New York, USA. These factors included a range of future scenarios of decreases in atmospheric nitrate, ammonium and sulfate deposition from present to 2200; historical forest harvesting; supply of naturally occurring organic acids; and variations in lake hydraulic residence time. Simulations show that decreases in sulfate deposition were more effective in increasing lake acid neutralizing capacity (ANC) than equivalent decreases in nitrate deposition, 4.6 times greater in 2040–2050 but decreasing to 2 times greater by 2200. Future lake ANC is anticipated to increase to a greater extent when the watershed experiences past forest cutting compared to a scenario without historical land disturbance. Under higher rates of watershed supply of naturally occurring dissolved organic carbon (DOC ~1000 µmol C/L), ANC is lower than under relatively low DOC supply (~100 µmol C/L) due to strongly acidic functional groups associated with dissolved organic matter. Lakes with longer hydrologic residence time exhibit less historical acidification and can achieve a greater ANC from recovery than lakes with shorter hydrologic residence times due to in-lake production of ANC. This study improves understanding of how biogeochemical processes at the landscape level can influence the rate and extent of recovery of lake–watersheds in response to decreases in atmospheric deposition.

Responses of 20 lake-watersheds in the Adirondack region of New York to historical and potential future acidic deposition

Critical loads (CLs) and dynamic critical loads (DCLs) are important tools to guide the protection of ecosystems from air pollution. In order to quantify decreases in acidic deposition necessary to protect sensitive aquatic species, we calculated CLs and DCLs of sulfate (SO42−)+nitrate (NO3−) for 20 lake-watersheds from the Adirondack region of New York using the dynamic model, PnET-BGC. We evaluated lake water chemistry and fish and total zooplankton species richness in response to historical acidic deposition and under future deposition scenarios. The model performed well in simulating measured chemistry of Adirondack lakes. Current deposition of SO42−+NO3−, calcium (Ca2+) weathering rate and lake acid neutralizing capacity (ANC) in 1850 were related to the extent of historical acidification (1850–2008). Changes in lake Al3+ concentrations since the onset of acidic deposition were also related to Ca2+ weathering rate and ANC in 1850. Lake ANC and fish and total zooplankton species richness were projected to increase under hypothetical decreases in future deposition. However, model projections suggest that lake ecosystems will not achieve complete chemical and biological recovery in the future.

Development of a total maximum daily load (TMDL) for acid-impaired lakes in the Adirondack region of New York

Acidic deposition has impaired acid-sensitive surface waters in the Adirondack region of New York by decreasing pH and acid neutralizing capacity (ANC). In spite of air quality programs over past decades, 128 lakes in the Adirondacks were classified as “impaired” under Section 303(d) of the Clean Water Act in 2010 due to elevated acidity. The biogeochemical model, PnET-BGC, was used to relate decreases in atmospheric sulfur (S) and nitrogen (N) deposition to changes in lake water chemistry. The model was calibrated and confirmed using observed soil and lake water chemistry data and then was applied to calculate the maximum atmospheric deposition that the impaired lakes can receive while still achieving ANC targets. Two targets of ANC were used to characterize the recovery of acid-impaired lakes: 11 and 20 μeq L−1. Of the 128 acid-impaired lakes, 97 currently have ANC values below the target value of 20 μeq L−1 and 83 are below 11 μeq L−1. This study indicates that a moderate control scenario (i.e., 60% decrease from the current atmospheric S load) is projected to recover the ANC of lakes at a mean rate of 0.18 and 0.05 μeq L−1 yr−1 during the periods 2022–2050 and 2050–2200, respectively. The total maximum daily load (TMDL) of acidity corresponding to this moderate control scenario was estimated to be 7.9 meq S m−2 yr−1 which includes a 10% margin of safety.

Lake/watershed sulfur budgets and their response to decreases in atmospheric sulfur deposition: watershed and climate controls

AbstractAtmospheric sulfur (S) emissions peaked in North America in the early 1970s followed by declines in S deposition and sulfate (SO42−) concentrations in surface waters. Changes in S biogeochemistry affect the mobilization of toxic (Al+3, H+) and nutrient (Ca2+, Mg2+, K+) cations, and the acid–base status of ecosystems. We focused on lake/watersheds in the Adirondack Mountains of New York, USA, one of the most acid‐sensitive and acid‐impacted regions in North America. We used 16 of the 17 original Adirondack Long‐Term Monitoring Lakes from 1984 through 2010 and found significant declines (−2.14 µmolc l−1 year−1) in SO42− concentrations. There were significant declines (−0.28 kg S ha−1 year−1) in total S deposition for all lake/watersheds. We constructed S mass balances for 14 lakes/watersheds from wet and dry S deposition and SO42− loss from drainage and found a comparable decline (−0.26 kg S ha−1 year−1) in lake SO42− export. There was a discrepancy (mean 2.34 kg S ha−1 year−1) between atmospheric S deposition and watershed S loss due to internal S sources. Using major solute chemistry including dissolved silica and watershed characteristics, it was evident that the watershed S budget discrepancy increased with thickness of surficial deposits. The annual discrepancies in S mass balances were strongly linked with annual watershed discharge. These results suggest that internal S sources are becoming increasingly important as atmospheric S inputs have declined. The internal SO42− supply of watersheds decreased concomitantly with lake acid neutralizing capacity (ANC). These findings suggest that the limited contributions from internal sources of SO42− will facilitate the recovery of ANC from those lake/watersheds with the lowest ANC. With long‐term decreases in atmospheric S deposition, the effects of climate, especially increases in precipitation, will play an increasingly important role in regulating S budgets and the amount of SO42− mobilized from internal watershed sources. Copyright © 2012 John Wiley & Sons, Ltd.

Target loads of atmospheric sulfur and nitrogen deposition for protection of acid sensitive aquatic resources in the Adirondack Mountains, New York

The dynamic watershed acid‐base chemistry model of acidification of groundwater in catchments (MAGIC) was used to calculate target loads (TLs) of atmospheric sulfur and nitrogen deposition expected to be protective of aquatic health in lakes in the Adirondack ecoregion of New York. The TLs were calculated for two future dates (2050 and 2100) and three levels of protection against lake acidification (acid neutralizing capacity (ANC) of 0, 20, and 50 μeq L−1). Regional sulfur and nitrogen deposition estimates were combined with TLs to calculate exceedances. Target load results, and associated exceedances, were extrapolated to the regional population of Adirondack lakes. About 30% of Adirondack lakes had simulated TL of sulfur deposition less than 50 meq m−2 yr to protect lake ANC to 50 μeq L−1. About 600 Adirondack lakes receive ambient sulfur deposition that is above this TL, in some cases by more than a factor of 2. Some critical criteria threshold values were simulated to be unobtainable in some lakes even if sulfur deposition was to be decreased to zero and held at zero until the specified endpoint year. We also summarize important lessons for the use of target loads in the management of acid‐impacted aquatic ecosystems, such as those in North America, Europe, and Asia.

Seasonal Dynamics of CO2 Flux Across the Surface of Shallow Temperate Lakes

We used data collected from 1989 to 2009 from 151 shallow (mean depth < 3 m) temperate lakes in Denmark to explore the influence of lake trophic status, surface area and catchment size on the seasonal dynamics of the air–water flux of CO2. Monthly CO2 fluxes were derived from measurements of acid neutralizing capacity (ANC), pH, ionic strength, temperature, and wind speed. CO2 fluxes exhibited large seasonal variability, in particular in oligo-mesotrophic lakes. Most of the lakes emitted CO2 during winter (median rates ranging 300–1,900 mg C m−2 day−1), and less CO2 during summer or, in the case of some of the highly eutrophic lakes, retained CO2 during summer. We found that seasonal CO2 fluxes were strongly negatively correlated with pH (r = −0.65, P < 0.01), which in turn was correlated with chlorophyll a concentrations (r = 0.48, P < 0.01). Our analysis suggests that lake trophic status (a proxy for pelagic production) interacts with the lake ANC to drive the seasonal dynamics of CO2 fluxes, largely by changing pH and thereby the equilibrium of the free CO2 and bicarbonate relation. Long-term observations from four lakes, which have all undergone a period of oligotrophication during the past two decades, provide further evidence that CO2 efflux generally increases as trophic status decreases, as a consequence of decreased pH. Across these four lakes, the annual average CO2 emission has increased by 32% during the past two decades, thus, demonstrating the strong link between lake trophic status and CO2 flux.

Application of the PnET-BGC – An integrated biogeochemical model – To assess the surface water ANC recovery in the Adirondack region of New York under three multi-pollutant proposals

We applied an integrated biogeochemical model PnET-BGC to predict the response of acid neutralizing capacity (ANC) in lakes – a measure of the ability of water to neutralize inputs of strong acid – from 2001 to 2050 in the Adirondack region of New York, USA under three multi-pollutant proposal scenarios. Through model predictions, we assessed the impacts of these proposals on ecosystem recovery for research and policy initiatives. Our analysis indicated that the predicted recovery rates of surface water ANC obtained from the PnET-BGC model show low spatial autocorrelation. Predicted recovery rates are also closely related with the percentage of watershed areas of coniferous vegetation and deciduous vegetation, elevation and lake area, which turn out not to be significantly different from each other over the entire period of future scenarios (2001–2050). We applied a Geographic Weighted Regression model (GWR) to study the spatial patterns of predicted lake ANC in the Adirondacks through 2050 due to its high spatial autocorrelation. These results showed that lake depth and square of elevation can explain 40% of variation in the predicted ANC, which is 26% more variation than explained by the non-spatial Ordinary Least-Squares Regression (OLS). Our calculations also suggest that even under the Carper Bill, the most aggressive air pollutant control scenario considered, not all Adirondack lakes will recover (i.e., ANC > 50 μeq/L) from elevated acidic deposition by 2050. The research provides a basis for more informed emission controls and land use/land cover (LULC) policy-making in the north-eastern USA and elsewhere.

Base cation reservoirs in soil control the buffering capacity of lakes in forested catchments

The acidification of forest soils and surface waters and their relatively poor recovery record following reductions in atmospheric sulphur emissions is a major ongoing environmental problem, particularly in northeastern North America. The slow recovery of surface water is widely hypothesized to result from depletion of reservoirs of base cations in soil. This is concordant with the theory that the acid-neutralizing capacity (ANC) of lakes is likely proportional to the size of the exchangeable base cation reservoirs present in surrounding watershed soils. However, data describing these linkages are still nonexistent in the literature. Here we show that lake ANC is highly predictable (r2 = 0.75) based on the size of the exchangeable Ca2+ reservoir in soil in 21 catchments representative of soil and lake conditions encountered in northeastern North America. This finding indirectly supports the hypothesis that the poor recovery of surface water from acidification is governed by the size of base cation reservoirs present in catchment soils. The size of the base cation reservoir in soil is thus a strong indicator of the acid–base status of both soils and surface waters.

A Screening Procedure for Identifying Acid-Sensitive Lakes from Catchment Characteristics

Monitoring of Wilderness lakes for potential acidification requires information on lake sensitivity to acidification. Catchment properties can be used to estimate the acid neutralizing capacity (ANC) of lakes. Conceptual and general linear models were developed to predict the ANC of lakes in high-elevation (> or = 2170 m) Wilderness Areas in California's Sierra Nevada mountains. Catchment-to-lake area ratio, lake perimeter-to-area ratio, bedrock lithology, vegetation cover, and lake headwater location are significant variables explaining ANC. The general linear models were validated against independently collected water chemistry data and were used as part of a first stage screen to identify Wilderness lakes with low ANC. Expanded monitoring of atmospheric deposition is essential for improving the predictability of lake ANC.

Factors Affecting Acid Neutralizing Capacity in the Adirondack Region of New York: a Solute Mass Balance Approach

High rates of acidic deposition in the Adirondack region of New York have accelerated acidification of soils and surface waters. Annual input-output budgets for major solutes and acid-neutralizing capacity (ANC) were estimated for 43 drainage lake-watersheds in the Adirondacks from 1998 to 2000. Sulfate was the predominant anion on an equivalent basis in both precipitation and drainage export. Calcium ion had the largest cation drainage export, followed by Mg2+. While these watersheds showed net nitrogen (N) retention, the drainage losses of SO4(2-), Cl-, base cations, and ANC exceeded their respective inputs from precipitation. Land cover (forest type and wetlands) affected the export of SO4(2-), N solutes, and dissolved organic carbon (DOC). The relationships of solute export with elevation (negative for base cations and Cl-, positive for NO3- and H+) suggest the importance of the concomitant changes of biotic and abiotic watershed characteristics associated with elevational gradients. The surface water ANC increased with the sum of base cations and was greatest in the lakes with watersheds characterized by thick deposits of glacial till. The surface water ANC was also higher in the lake-watersheds with lower DOC export. Some variation in lake ANC was associated with variability in acidic deposition. Using a classification system previously developed for Adirondack lakes on the basis primarily of surficial geology, lake-watersheds were grouped into five classes. The calculated ANC fluxes based on the major sinks and sources of ANC were comparable with measured ANC for the thick-till (I) and the medium-till lake-watersheds with low DOC (II). The calculated ANC was overestimated for the medium-till with high DOC (III) and the thin-till with high DOC (V) lake-watersheds, suggesting the importance of naturally occurring organic acids as an ANC sink, which was not included in the calculations. The lower calculated estimates than the measured ANC for the thin-till lake-watersheds with low DOC (IV) were probably due to the mobilization of Al as an ANC source in these watersheds that were highly sensitive to strong acid inputs. Our analysis of various drainage lakes across the Adirondacks on the basis of solute mass balances, coupled with the use of a lake classification system and GIS data, demonstrates that the lake-watersheds characterized by shallow deposits of glacial till are highly sensitive to acidic deposition not only in the southwestern Adirondack region where previous field-based studies were intensively conducted but also across the entire Adirondack region. Moreover, the supply of organic acids and Al mobilization substantially modify the acid-base status of surface waters.

Modelling regional response of lakewater chemistry to changes in acidic deposition: the MAGIC model applied to lake surveys in southernmost Norway 1974-1986-1995

Abstract. Two methods for modelling regional responses of lake water quality to changes in acidic deposition in southernmost Norway were examined. Both methods are based upon the MAGIC model but differ in mode of regional application; one uses site-specific while the other uses Monte-Carlo methods for model calibration. The simulations of regional responses from both methods were compared with observed responses based on data from three lake surveys in southernmost Norway conducted in 1974, 1986 and 1995. The regional responses of the two modelling approaches were quite similar and agreed well with the observed regional distributions of lakewater chemistry variables. From 1974 to 1986 the observed data indicated that despite a decline of approximately 10% in sulphate (SO4) deposition, the mean acid neutralizing capacity (ANC) of lakes in southernmost Norway declined by approximately 6 μeq l-1. Both modelling approaches simulated no change or a very small decline in mean ANC for that period. From 1986 to 1995 the observed data indicated that, in response to an approximate 40% decline in SO4 deposition, the mean ANC of lakes in southernmost Norway increased by 11-16 μeq l-1. The modelling approaches simulated increases of 9-10 μeq l-1 in mean ANC for the same period. Both simulations and observations indicate that &gt; 65% of lakes in southernmost Norway were acidic in 1974 and 1995. Both simulation methods predict that &gt;65% of the lakes in southernmost Norway will have positive ANC values within 10 years of reductions of SO4 deposition to 20% of 1974 levels. Of the two regionalization methods the site-specific method appears preferable, because whereas the Monte-Carlo method gives results for a region as a whole, the site-specific method also reveals patterns within the region. The maintenance of a one-to-one correspondence between simulated and observed systems means that simulation results can be mapped for a geographically explicit presentation of model results. The ability to examine geographic patterns of response is becoming increasingly important in regional assessments.

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 SO42−. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca2+, Mg2+, K+, Na+; CB) 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 SO42−, consistent with decreases in SO2 emissions and SO42− in precipitation in the eastern U.S. Reductions in SO42− 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.

The predicted effect of SO2 emission controls on the water quality of eastern Canadian lakes

Changes in SO inf4 (sup2-) deposition predicted to occur in response to implementation of announced SO2 emission control programs in Canada and the U.S.A. have been used as input to water chemistry models thereby giving an estimate of the changes in lake acid neutralizing capacity (ANC) and pH that can be expected from these programs. Eastern Canada has been divided into 22 subregions for the purpose of this analysis. Relative to the current level (1982-86) of SO inf4 (sup2-) deposition (Scenario 1), the effect of the Canadian SO2 emission control program alone (Scenario 2) is compared to that obtained when controls are implemented throughout North America (Scenarios 3 and 4). SO2 emission reduction will effect a shrinkage of the high wet SO inf4 (sup2-) deposition field in NE North America such that under Scenario 4 conditions, almost no area will remain in Canada that receives >20 kg ha(-1) yr(-1). The greatest decrease in deposition and resulting change in lake chemistry occurs in southern Ontario and southwestern Quebec. ANC distributions shift to higher concentrations and the percentage of lakes having pH<6 decreases in these areas. The Atlantic Provinces will obtain only a minor benefit from the control programs, i.e. experiencing only a small decrease in deposition and improvement in water quality. High sensitivity of the terrain in many parts of Atlantic Canada means that large numbers of lakes will remain acidic (i.e. ANC<0) and/or have pH<6 (an important biological threshold) even after full implementation of the current plans for SO2 control in Canada and the U.S.

Modeling Lake-Chemistry Distributions: Approximate Bayesian Methods for Estimating a Finite-Mixture Model

A modification of the Laplace method is presented and applied to estimation of posterior functions in a Bayesian analysis of finite-mixture distributions. The technique is nonsequential yet relatively fast and provides estimates of mixture-model parameters and classification probabilities. The method is applied to a regional distribution of lake-chemistry data for north central Wisconsin. A mixture density of two lognormal populations is estimated for the acid-neutralizing capacity of lakes in the region, using several other lake characteristics as explanatory variables for classification into lake subpopulations. The fitted mixture model provides a good representation of the observed distribution. Separation into subpopulations based solely on the other lake characteristics matches the mixture-model classification relatively well.

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

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