Acid Sensitivity of Lakes in Nova Scotia,Canada: Assessment of Lakes at Risk |
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Authors: | Marta B Wolniewicz Julian Aherne Peter J Dillon |
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Institution: | (1) Environmental and Resource Studies, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada |
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Abstract: | 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 (Ca2+) 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 Ca2+. The proportion of sensitive lakes in NS (that is, the stock at risk) was estimated as lakes with ANC less than 20 μeq l−1, pH below 6, and Ca2+ less than 75 μeq 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. |
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