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  • Title: Spatio-temporal variation of nitrate sources to Lake Winnipeg using N and O isotope (δ15N, δ18O) analyses.
    Author: Soto DX, Koehler G, Wassenaar LI, Hobson KA.
    Journal: Sci Total Environ; 2019 Jan 10; 647():486-493. PubMed ID: 30086500.
    Abstract:
    Anthropogenic nitrogen inputs into Lake Winnipeg, Canada, from watershed sources have increased during the last decades, contributing to eutrophication. These nutrient N inputs include loadings from agriculture (inorganic fertilizer and animal waste) and urban sources (wastewater discharge from sewage treatment plants). The aim of this study was to evaluate the sources and seasonal patterns of dissolved nitrates in two major contributors to Lake Winnipeg; the Assiniboine and Red rivers. The relative contribution of nitrate sources was estimated using Bayesian isotope mixing models incorporating δ15N and δ18O values of dissolved nitrate. Overall, δ15N values of nitrate in the rivers ranged from -2 ‰ to +20 ‰, and δ18O values ranged from -20 ‰ to +20 ‰, which indicated variable contribution of nitrate sources, depending on the river reach and seasonal period of sampling. The results indicated that nitrate in the Assiniboine River originated up to 62 % from waste or municipal sources (i.e. manure and/or waste water discharge), whereas ca. 40 % of nitrate in the Red River originated predominantly from inorganic agricultural fertilizers. These different source contributions were temporally variable, with a decrease in fertilizer loading following spring snowmelt. We found higher proportions of inorganic fertilizers in the Assiniboine River watershed during flooding, which has relevant implications for water nutrient management in response to stochastic flooding events.
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