Long-Term Changes in Boreal Lake and Stream Chemistry: Recovery From Acid Deposition and the Role of Climate (original) (raw)
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Hydrology and Earth System Sciences, 2003
Sulphate deposition in south-central Ontario declined between 1976 and 2000 by more than 50%, whereas lake sulphate (SO 4 2 ) concentrations decreased by, on average, only half as much. To investigate the factors that controlled this slower than expected response, the temporal patterns in lake SO 4 2 concentrations were compared with patterns in both deposition and climate, since climate has a major influence on the hydrological cycle in this part of the continent. To do this, the temporal coherence in SO 4 2 concentrations between 9 lake basins was estimated using the intraclass correlation from a repeated-measures analysis of variance and two subsets of lakes were found (six in one group, four in the other), each with lakes having synchronous patterns. One subset (4 lakes) included the 3 with the longest water replenishment times (>3.4 yr) which are expected to respond to decreases in SO 4 2 deposition more slowly. However, the average pattern reflecting the temporal changes of each of the two subsets was very similar. The response of both subsets of lakes to the decreasing SO 4 2 deposition over two decades was independent of the degree of acidification or sensitivity to acidification of the lakes. In a determination of which factors best predicted each of those two subsets SO 4 2 time series, good predictive models were produced by regional/global-scale climate indices, specifically the Southern Oscillation Index (SOI) describing the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation Index (NAOI), as well as by SO 4 2 deposition indices. When the predictor variables were combined, models which described the long-term changes in lake SO 4 2 concentration best included the SOI, the NAOI and SO 4 2 deposition. Thus, large-scale climate factors play a major role in determining the response of aquatic systems to changes in SO 4 2 deposition, perhaps through their influence on lake and/or catchment processes that effectively delay recovery.
Hydrological Processes, 2013
Atmospheric sulfur (S) emissions peaked in North America in the early 1970s followed by declines in S deposition and sulfate (SO 4 2À ) concentrations in surface waters. Changes in S biogeochemistry affect the mobilization of toxic (Al +3 , H + ) and nutrient (Ca 2+ , Mg 2+ , 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 (À2.14 mmol c l À1 year À1 ) in SO 4 2À concentrations. There were significant declines (À0.28 kg S ha À1 year À1 ) in total S deposition for all lake/watersheds. We constructed S mass balances for 14 lakes/watersheds from wet and dry S deposition and SO 4 2À loss from drainage and found a comparable decline (À0.26 kg S ha À1 year À1 ) in lake SO 4 2À export. There was a discrepancy (mean 2.34 kg S ha À1 year À1 ) 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 SO 4 2À supply of watersheds decreased concomitantly with lake acid neutralizing capacity (ANC). These findings suggest that the limited contributions from internal sources of SO 4 2À 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 SO 4 2À mobilized from internal watershed sources.
Environmental monitoring and assessment
The lakes in Killarney Provincial Park, located 40-60 km southwest of Sudbury, Ontario, were some of the first lakes in North America to be acidified by atmospheric pollutants. Acidification affected thousands of fish and invertebrate populations in dozens of lakes. Since the 1970's, water quality has improved in response to atmospheric pollution reductions and some lakes have already recovered to approximately their pre-industrial pH levels, as inferred from diatom microfossils in lake sediments. Since the 1970's, fish species richness has not changed substantially, but zooplankton species richness has increased in acidified lakes. The critical sulphur load, the amount of SO2-derived acid deposition that can occur while still maintaining suitable water quality, was estimated to be exceeded in 38% of the park area in 1997. Depending on which of four possible North American emission control scenarios (CLR = currently legislated reduction; CLR + 25%; CLR + 50%; CLR + 75%) is a...
Changes in the chemistry of lakes near Subury, Ontario following reductions of SO 2 emissi
Water Air Soil Pollut, 1986
Emissions of SO 2 in the Sudbury area declined from an estimated average of 1. 4 1 X 106 tonne yr-~ in 1973-78 to 0.68 X 106 tonne yr-I in 1979-85. As a result, SO 4 concentrations of lakes in the area have decreased, and the pH of each of the acidic lakes that was studied has increased. Aluminum, Cu, Ni and Zn concentrations have also decreased; however, the latter three metals have probably declined because of reductions in emissions of metals from the smelters rather than because of the pH changes in the lakes.
Monitoring the results of Canada/U.S.A. acid rain control programs: some lake responses
Environmental monitoring and assessment
Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from the extensive research and monitoring programs, a sequence of issue assessments demonstrated the necessity of reducing the anthropogenic emissions of acidifying pollutants, particularly sulphur dioxide (SO2). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO2 emissions by approximately 40% relative to 1980 levels by 2010, and at present, both countries have reduced emissions beyond their AQA commitment. In response to reduced SO2 emissions, atmospheric deposition of sulphate (SO4(2-)) and SO4(2-) concentrations in many lakes have declined, particularly in south-central Ontario and southern Québec. Sulphate deposition still exceeds aquatic critical loads throughout southeastern Canada however. Increasing pH or alkalinity (commonly deemed 'recovery') has been observed in only som...
Biogeochemical Investigations at Watershed, Landscape, and Regional Scales
A simple mass flux model was developed to simulate the response of SO/ concentrations in surface waters to past and anticipated future changes in atmospheric deposition of SO/". Values of bulk (or wet) SO/" deposition and dry deposition ofS determined from measured air concentrations and a deposition velocity were insufficient to balance watershed SO/ export at the Hubbard Brook Experimental Forest, NH and for a regional survey of watersheds in the northeastern U.S. We propose two explanations for the unmeasured S source: I) a significant underestimation of dryS deposition, and/or 2) internal watershedS sources, such as weathering and/or mineralization of soil organicS. Model simulations based on these two mechanisms agreed closely with measured stream SO.'" concentrations at Hubbard Brook. Close agreement between measured and model predicted results precluded identification of which of the two mechanisms controlled long-term trends in stream SO/. Model simulations indicated that soil adsorption reactions significantly delayed the response of stream water to declines in SO/ inputs since 1970, but could not explain the discrepancy in watershedS budgets. Extrapolation of model predictions into the future demonstrates that uncertainty in the source of the S imbalance in watersheds has important implications for assessments of the recovery of surface water acid neutralizing capacity in response to anticipated future reductions in so2 emissions.
Journal of Paleolimnology, 2006
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (>$20 cm) was approximately constant in all lakes, and indicated a preindustrial d 34 S value between +4.0 and +5.3&, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment were relatively low (1.9-5 mg S g À1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in d 34 S at a depth corresponding to the beginning of industrialization in the Great Lakes region ($1900), resulting in a generally reciprocal depth pattern between total S concentration and d 34 S ratios. While initial shifts in total S and d 34 S were likely due to enhanced SO 4 reduction of newly available anthropogenic SO 4 , both the magnitude and pattern of up-core S enrichment and shifts in d 34 S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and d 34 S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake characteristic. This work indicates that sediment cores do not provide consistent records of changes in postindustrial S deposition in this region, likely due to redox-related mobility of S in upper sediment.