Aquatic Sciences Meeting, Albuquerque 2001

SS33 Human Impacts and Activities on Riverine Ecosystems (Science and Society Connections)

Date: Thursday, February 15, 2001, Time: 10:45:00 AM

Location: Galisteo

Leavitt, P, R, University of Regina, Regina, Canada, Peter.Leavitt@uregina.ca

Graham, M, D, University of Regina, Regina, Canada, Mark.Graham@uregina.ca

Wang, D, , University of Regina, Regina, Canada, Dunling.Wang@uregina.ca

LANDSCAPE IMPACTS OF SEWAGE POLLUTION REVEALED BY STABLE ISOTOPE ANALYSIS OF LAKE SEDIMENTS

The Qu'Appelle Valley includes seven sequential lakes which supply water to 1/3 the population of the Canadian Great Plains. While over 95% of the catchment is used for agriculture, multivariate analyses suggest that urban sources of N may be more important than land-use practices as controls of water quality. We tested this hypothesis by analyzing fossil pigments and stable isotopes of N (del15N) and C (del13C) in sediments from each lake (1800-present). At Pasqua Lake, sedimentary del15N (but not del13C) values were significantly correlated (r2 = 0.84; P < 0.0001) with the mass of N from urban sewage (1875-1995) and rose to 14 o/oo from background levels of 6.3 +/- 0.3 o/oo. In contrast, sedimentary del15N in reference Last Mountain Lake declined 1.2 +/- 0.1 o/oo over the same period, reflecting regional increases in abundance of N-fixing cyanobacteria (0 o/oo). Sewage signals were rapidly attenuated in lakes downstream from Pasqua Lake, but remained 1.8 o/oo above background even after four intervening depositional basins. Comparison of source-sink del15N values suggested that denitrification during transportation was the main cause of elevated sedimentary del15N signals.

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Aquatic Sciences Meeting, Albuquerque 2001

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