416 - Modeling Methylmercury and Selenium Biomagnification in Lake Food Webs Using Cysteine

Diet-borne contaminants like methylmercury (MeHg) and selenium (Se) vary and biomagnify through aquatic food webs for reasons not fully understood. Mercury cycling and storage is inherently linked to sulfur, including to thiol groups within proteins of organisms. Previous research showed that the cysteine content of aquatic invertebrate families was a significant predictor of their MeHg concentration, and cysteine and relative trophic level (measured as delta15N) were positively correlated through food webs. Therefore, we predict that cysteine content may be used to model biomagnification through lake food webs. In 2013, food web taxa (biofilm, benthic invertebrates, zooplankton, and fishes) were collected from six lakes within Kejimkujik National Park, Nova Scotia, Canada. Food web models of both MeHg and Se concentrations versus cysteine content were contrasted against relationships developed using delta15N. MeHg and Se levels varied among taxa, but only MeHg increased from lower to higher trophic levels in these lakes. There were no correlations between log-transformed MeHg and total Se in tissues when all taxa were pooled (r = 0.17, p = 0.064, n = 125) or within each of the four lakes (r = 0.04-0.29, p = 0.09-0.82, n = 29-34). Across all six lakes, MeHg was significantly and positively related to both cysteine (R2 = 0.65-0.80, p < 0.001) and delta15N (R2 = 0.88-0.94, p < 0.001), with no among-system differences in these slopes. In contrast, Se was significantly related to cysteine in two lakes R2=0.20 & 0.37, p=0.014 &

Authors: Jennifer Thera, Karen Kidd, Robin Stewart, Robert Bertolo, Nelson O’Driscoll