M11 AM Using Stable Isotopes in Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 343-344

(CAM-1117-764050) Assessing biomagnification of mercury in food webs using stable isotopes: A global perspective.

Campbell, LM¹, Dixon, DG², Evans, M³, Hecky, RE², Gerwutz, S⁴, Kendall, C⁵, Kidd, K⁶, Lockhart, L⁷, Muir, DG⁸, ¹ School of Environmental Studies, Queen's University, Kingston, ON, Canada² Department of Biology, University of Waterloo, Waterloo, ON, Canada³ National Water Research Institute, Environment Canada, Saskatoon, SK, Canada⁴ Department of Geography, University of Toronto, Toronto, ON, Canada⁵ United States Geological Survey, Menlo Park, CA, USA⁶ Department of Biology, University of New Brunswick, St. John, NB, Canada⁷ Freshwater Institute, Department of Fisheries & Oceans, Winnipeg, MB, Canada⁸ National Water Research Institute, Environment Canada, Burlington, ON, Canada

ABSTRACT- For the past decade, stable isotopes of nitrogen and carbon have been used as an effective tool to assess food web structure in freshwater and marine ecosystems globally. Stable nitrogen isotope ratios (¹⁵N) have been used as a trophic position indicator, while stable carbon isotope ratios (¹³C) have been used to assess carbon sources to biota. The ability of mercury (Hg), particularly methylmercury (MeHg) to biomagnify through food webs is well known. As such, biomagnification factors (BMFs) can be obtained for an ecosystem using the slope of the regression of Hg concentrations in biota from an ecosystem against their trophic position, as indicated by ¹⁵N values. The importance of BMF to Hg burdens in food webs can be compared with other factors such as food chain length, latitude and lake trophic status. Databases for lakes ranging over a wide gradient of sizes and trophic status in tropical, temperate and arctic latitudes have been assembled over the last 10 years. In addition, a review of other mercury biomagnification studies that incorporated stable isotope analyses is included. This provides an opportunity to compare Hg biomagnification and trophodynamics across latitudes, lake sizes and climate regimes. Regression slopes of log Hg vs ¹⁵N were found to range from 0.16 to 0.29 across systems, with most slope values around 0.20. Food chain length, as estimated from lower trophic species to top trophic predators were calculated, and were found to be a more significant predictor of Hg concentrations in top predators. Despite similar biomagnification factors and longer food chain lengths in many African lakes, Hg concentrations in tropical pisivorous fish are lower than those in North American lakes. This suggests that while Hg BMF's are relatively consistent, the bioavailability of Hg may be different in tropical and temperate lakes.

Key words: mercury, stable nitrogen isotopes, stable carbon isotopes, latitudual gradients