Elevated mercury levels in biota along an agricultural land use gradient in the Oldman River basin, Alberta

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Brinkmann, Lars, Rasmussen, Joseph B.
• Other Authors: Kidd, Karen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2012
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Canada; Catostomus catostomus
• Online Access: http://dx.doi.org/10.1139/f2012-056; http://www.nrcresearchpress.com/doi/full-xml/10.1139/f2012-056; http://www.nrcresearchpress.com/doi/pdf/10.1139/f2012-056

This study examines relationships between anthropogenic influence and mercury concentrations in biota along an elevational river gradient with intensifying agricultural and urban land use in the Oldman River basin, Alberta, Canada. We use nitrogen stable isotope signatures (δ 15 N) indicative of anthropogenic sources of N to indicate the extent of land use influence on the river ecosystem. δ 15 N values in biota increased by 4.2‰ along the river gradient, consistent with increasing nitrogen sources from sewage and manure. Mercury concentrations in longnose dace ( Rhinichthys cataractae ), suckers ( Catostomus catostomus , Catostomus commersonii ), and net-spinning caddisfly larvae, the most abundant macroinvertebrates, all increased downstream; dace ranged from 0.023 ppm total mercury below the Oldman reservoir to 0.10 ppm total mercury downstream of Lethbridge. Dace consumed mostly insect larvae, and no increase in trophic position (as estimated by δ 15 N) was observed along the gradient. Fish directly exposed to agricultural and urban effluents had significantly lower mercury levels, or showed no difference, relative to reference sites, which suggests that these effluents play no significant role in elevating mercury levels in river food webs.