Paleolimnological proxies reveal continued eutrophication issues in the St. Lawrence River Area of Concern |
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Authors: | Katherine E. Moir M. Brian C. Hickey Peter R. Leavitt Jeffrey J. Ridal Brian F. Cumming |
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Affiliation: | 1. School of Environmental Studies, Queen''s University, Kingston, K7L 3J9, Ontario, Canada;2. St. Lawrence River Institute of Environmental Sciences, Cornwall, K6H 4Z1, Ontario, Canada;3. Limnology Laboratory, Department of Biology, University of Regina, Regina, S4S 0A2, Saskatchewan, Canada;4. Institute of Environmental Change and Society, University of Regina, Regina, S4S 0A2, Saskatchewan, Canada;5. Paleoecological Environmental Assessment and Research Laboratory, Department of Biology, Queen''s University, Kingston, K7L 3N6, Ontario, Canada |
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Abstract: | Recent surface-water surveys suggest that high nutrient concentrations and nuisance algae remain issues in the St. Lawrence River Area of Concern (AOC) at Cornwall, Ontario, specifically in the tributaries and nearshore zones of Lake St. Francis (LSF). In particular, it is unclear whether management actions designed to reduce nutrient inputs, first implemented in the 1990s as part of the Remedial Action Plan for the AOC, have reduced algal production or influenced assemblage composition. To address this issue, a paleolimnological approach was used to provide a historical context for the present-day nutrient concentrations and to quantify the extent of change in water quality in LSF since the early 1990s. A sediment core was collected near the north shore of LSF and was examined for changes in the concentrations and compositions of fossil diatoms and pigments, as well as stable isotope (δ15N and δ13C) values. Analyses of diatom and pigment concentrations indicated that overall algal abundance has risen in the last few decades, including trends of increasing occurrences of potentially toxic cyanobacteria, despite ongoing remediation efforts. Temporal patterns of stable isotope signatures in the core suggest a steady increase in nutrient influx since the mid-20th century, with the post-1990 increase in algal production likely attributable to recent inputs associated with land-use changes in local contributing watersheds. These patterns suggest that the AOC delisting goals for the LSF tributaries will not be reached without a drastic change in land management practices. |
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Keywords: | Eutrophication Paleolimnology St. Lawrence River Pigments Diatoms Stable isotopes |
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