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Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of zooplankton are potentially good indicators of energy and nutrient fluxes, and trophic interactions in lake food‐webs, yet, are poorly understood.Based on a synoptic survey of 233 boreal lakes, we evaluated the relationships of water chemistry, hydromorphological, and land cover variables (lake/catchment‐specific factors), and the spatial position of lakes in the landscape (representing potential regional factors) with the δ13C and δ15N of nine meso‐zooplankton taxa.The δ13C variation of most taxa was negatively related to water chemistry variables associated with allochthonous inputs (colour/dissolved organic carbon), and positively correlated with nutrient concentrations (together explaining 12–69% of variation). Most of the δ13C variation explained by significant hydromorphological and land cover variables (% peat area, drainage basin area:lake area, shoreline development index, and lake area, explaining 26–47% of variation) was shared by significant water chemistry variables. Together, this suggests that δ13C variation of zooplankton reflects different environmental influences on δ13C of lake primary producers.The δ15N variation of most taxa was significantly related to pH, total phosphorous concentration (water chemistry variables, explaining 8–64% of variation), and water retention time (hydromorphological variable, explaining 13–87% of variation). These relationships are probably reflective of the association of zooplankton δ15N with terrestrial organic matter flux, environmentally‐induced biogeochemical nitrogen transformations and phytoplankton 15N fractionation.Specific water chemistry, hydromorphological, and land cover predictors of δ13C and δ15N and the direction of their effects (i.e. positive or negative) were largely similar among taxa. However, their degree of importance varied among taxa particularly for δ13C, probably due to contrasting feeding selectivity and resulting differences in allochthony. This suggests that δ13C of different taxa may respond differently to changes in limnological gradients due to environmental perturbations affecting boreal regions.The lake/catchment‐specific factors were more important than regional factors (lithology, soil properties and atmospheric nitrogen deposition; which are represented by the spatial position of lakes) in explaining δ13C and δ15N variation of zooplankton. Hence, before inferring regional effects in stable isotope studies, the influence of lake/catchment‐specific factors needs to be explicitly quantified. [ABSTRACT FROM AUTHOR]

Mercury bioaccumulation models developed for fish provide insight into the sources and transfer of Hg within ecosystems. Mercury concentrations were assessed for 16 fish species of the western reach of Lake Diefenbaker, Saskatchewan, Canada. For top predators (northern pike, Esox Lucius; walleye, Sander vitreum), Hg concentrations were positively correlated to δ(15)N, and δ(15)N to fish age, suggesting that throughout life these fish fed on organisms with increasingly higher trophic values and Hg concentrations. However, fish mass and/or age were the principal parameters related to Hg concentrations for most species. For 9 common species combined, individual variation in Hg concentration was explained in declining order of importance by fish mass, trophic position (δ(15)N), and fish age. Delta (15)N value was not the leading variable related to Hg concentration for the assemblage, probably because of the longevity of lower--trophic-level species (3 species ≥ 20 yr), substantial overlap in Hg concentration and δ(15)N values for large-bodied fish up to 3000 g, and complex relationships between Hg concentration and δ(15)N among species. These results suggest that the quantity of food (and Hg) consumed each year and converted to fish mass, the quantity of Hg bioaccumulated over years and decades, and trophic position were significant determinants of Hg concentration in Lake Diefenbaker fish., (© 2015 SETAC.)