Probable changes in lake chemistry in Canada’s Atlantic Provinces under proposed North American emission reductions (original) (raw)
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Past and future changes to acidified eastern Canadian lakes: A geochemical modeling approach
Applied Geochemistry, 2007
As SO 2 emissions are being reduced in North America, it has become important to know how rapidly the surface water chemistry of aquatic systems will recover. The authors applied the model of acidification of groundwater in catchments (MAGIC) to 410 acid-sensitive lakes located in a 3000 km east-west gradient in eastern Canada. The goal was to estimate the water chemistry from pre-acidification times, under worst case conditions (mid 1970s) and what it should be in the year 2030 after proposed acid emission reduction levels agreed-to or planned by Canada and the United States are in place. In eastern Canada, large decreases in pH and ANC are shown between pre-acidification and 1975, the year of greatest historical deposition. Current-day conditions are much improved from 1975. Under the most likely future acid deposition reduction scenarios, an improvement of pH and ANC is shown in all the regions from current-day levels, but not to pre-acidification levels. Dissolved Ca levels were considerably higher at the height of acidification than under pristine conditions, but will return to pre-acidification levels at most of the sites by the year 2030. The results also show that under proposed control programs, a large number of sites in eastern Canada will not return to ANC values >40 leq L À1 , thought to be suitable for healthy aquatic communities. Crown
Hydrology and Earth System Sciences, 2003
The dynamic model MAGIC was applied to 25 lakes in south-central Ontario, Canada using a regional modelling methodology. Soil and lake water chemistry for each lake catchment was simulated for the period 18502050. Sulphate (SO 4 2 ) deposition forecasts were derived from recently proposed emission reductions, which correspond roughly to a 50% reduction in SO 4 2 deposition by 2010 from the 2000 baseline. Changes in SO 4 2 deposition had a significant impact on lake chemistry. Simulated lake water chemistry showed a recovery potential under the current deposition scenario; by 2050 concentration levels recovered to values predicted for the early 1900s. Moreover, simulated future lake water chemistry showed significant recovery compared to 1975 levels. However, although regional simulations predict that base cation losses have decreased in recent years, soils in the region will continue to acidify with Ca 2+ losses dominating depletion of the exchangeable pool. Base cation losses from the exchangeable pool are currently buffering lakes against the impacts of acid deposition; ultimately base cation inputs into the lakes will decrease as exchangeable base cation pools become depleted. Further emission reductions are necessary to ensure continued recovery from acidification.
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...
Acid Sensitivity of Lakes in Nova Scotia, Canada: Assessment of Lakes at Risk
Ecosystems, 2011
The sensitivity of surface waters to acidic deposition is governed by the interaction of catchment geology, soils, topography, land use, climate and atmospheric deposition. Accordingly at the landscape scale, catchment attributes may be used to predict lake chemistry (for example, acid neutralising capacity (ANC), pH, calcium (Ca 2+) and dissolved organic carbon (DOC)). Empirical (multiple linear regression) models based on average measured chemistry (2000-2006) for 204 lakes in Nova Scotia (NS) Canada, and their catchment attributes, were used to predict chemistry for all lakes in NS (n = 6104). Damage to aquatic biota, such as loss of species and/or reduced biodiversity has been widely evaluated using critical chemical thresholds commonly based on pH, ANC and Ca 2+. The proportion of sensitive lakes in NS (that is, the stock at risk) was estimated as lakes with ANC less than 20 leq l-1 , pH below 6, and Ca 2+ less than 75 leq l-1 (13, 73 and 74%, respectively). Many lakes in NS are characterized by high DOC (>7 mg l-1); in these lakes organic acids contribute to total acidity, making anthropogenic influences difficult to discern. To account for the potential contribution of organic acidity, all lakes with pH below 6 (and DOC < 7 mg l-1) and lakes below a threshold for ANC adjusted for organic acids were quantified; 63% of the lakes fell below either of these thresholds. Despite substantial reductions in sulphur emissions in North America since the 1980s, many lakes in NS remain at risk to acidic deposition.
Changes in Freshwater Acidification Trends in Canada's Atlantic Provinces: 1983–1997
Water Air and Soil Pollution, 2002
Sixty-three lakes were sampled semi-annually for acid precipitation – related variables in Canada's Atlantic Provinces,Nova Scotia and Newfoundland from 1983 to 1997. A further 31 sites were sampled beginning in 1989 in Nova Scotia. We analyzedthe water chemistry data for trends in pH, acid neutralization capacity, sulfate and base cations using the whole data set for the original 63 sites and the most recent eight years' data for all sites. We also analyzed acid deposition at two CAPMoN precipitation chemistry sites located at the two extremes of thesampling region for trends. We found that hydrogen deposition decreased by 20% in Newfoundland and 30% in Nova Scotia, and sulfate decreased by 36 and 34%, respectively. Sulfate and basecations in lake waters showed decreases as expected, though lakeacidity and acid neutralization capacity did not show improvements. The conflicting trends in chemical variables suggest that though anthropogenically-induced weathering is diminishing in this region, conditions have not returned to `natural' background conditions.
Hydrobiologia, 2008
In contrast to other lakes studied in Cape Breton Highlands National Park (Nova Scotia, Canada), our paleolimnological results indicated that Glasgow Lake has been impacted by acidic deposition starting in the early 1900s. Based on analysis of diatom assemblages, the lake experienced a decrease in diatom-inferred lakewater pH from a pre-industrial pH of *5.8 to a current pH of 5.3 (2000-2002 measured mean pH = 5.0) as well as a decrease in diatom-inferred Gran-alkalinity. In this study, diatombased paleolimnological techniques were used in conjunction with a dynamic biogeochemical model (MAGIC) to assess both the timing and extent of the acidification trend, as well as determine a probable explanation as to why this lake, and none of the other 15 Cape Breton Highlands lakes studied for paleolimnology thus far, acidified under a peak nonmarine sulphate deposition load of 43.6 mmol c m-2 year-1 in the mid-1970s. Steady-state models estimate that Glasgow Lake had the lowest buffering capacity of six study lakes and estimated critical sulphate loading of\1 mmol c m-2 year-1. MAGIC also estimated a loss of charge balance alkalinity from a pre-1850 value of 38 lmol c l-1 to a low of 12 lmol c l-1. While no evidence of biological recovery has been recorded, MAGIC estimates an increase in charge balance alkalinity to 27 lmol c l-1 in 2002 in response to decreased SO 2 emissions. Of the five other lakes that were modelled, all showed trends towards more acidic states and subsequent increases in charge balance alkalinity; however, the empirical paleo-diatom approach applied to these lakes showed no evidence of acidification. Thus, Glasgow Lake has the lowest buffering capacity among the Cape Breton Highland study lakes and serves as a sentinel of potential acidification trends and recovery in this region.
Estimation of Critical Loads of Acidity for Lakes in Northeastern United States and Eastern Canada
Environmental Monitoring and Assessment, 2005
The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Plan in June 1998, and issued a series of action items to support its work toward a reduction of sulfur dioxide (SO 2 ) and nitrogen oxide (NO x ) emissions in northeastern North America. One of these action items was the preparation of an updated critical load map using data from lakes in the NEG/ECP area. Critical load maps provide a more complete index of the surface water sensitivity to acidification. Combined sulfur and nitrogen critical loads and deposition exceedances were computed using Henriksen's Steady-State Water Chemistry (SSWC) model. Results show that 28% of all 2053 lakes studied have a critical load of 20 kg/ha/year or less, making them vulnerable to acid deposition. Emission reductions, and more specifically SO 2 emission reductions have proven beneficial because critical loads were exceeded in 2002 for 12.3% of all studied lakes. Those lakes are located in the more sensitive areas where geology is carbonate-poor. Of these lakes, 2.9% will never recover even with a complete removal of SO 4 deposition. Recovery from acidification for the remaining 9.4% of the lakes will require additional emission SO 2 reductions.
Canadian Journal of Fisheries and Aquatic Sciences, 1991
1990. Assessing the potential extent of damage to inland lakes in eastern Canada due to acidic deposition. I!. Application of the regional model. Can. J. In this, the second of two papers can the development and application of a regional model of surface water acidification, we present the results of initial applications of the model to sensitive regions of eastern Canada. Data used for regional application of the model were obtained from a variety of sources, including acidic sulphate deposition monitoring data and regional lake water chemistry surveys. While these data do not provide a random sample of eastern Canadian lakes, we argue that there are no a priori reasons for expecting highly misleading biases in the data. Results of model applications are presented for observed 19863 sulphate deposition levels and for three alternative emission scenarios. The emission scenarios were simulated using a transfer matrix derived from the AES-BRTAP model. The results suggest that substantial additional damage (declines in surface water alkalinity and pH) is expected in some regions (e.g. northeastern Ontario), even at current deposition levels. The consequences of simple emission reduction strategies differ significantly among regions, suggesting that more complex strategies may be required to produce eqaritable benefits. To assist interpretation of a complex array of results, we propse an integrated representation of regional impacts that uses quantile-quantile plots of regional distributions of lake chemistry. Finally, we argue that while the results presented are highly uncertain, there are reasons to believe that, if anything, our damage estimates are conservative.