Biomass size spectrum and environmental parameters in relation to fish mercury levels in Ontario lakes, Canada

Background/Question/Methods

Mercury in fish can be bioaccumulated through food web and harm the central nervous system of human.  Understanding what factors are strongly related to fish mercury levels in Ontario lakes is important for the health of aquatic ecosystems and human in Ontario.  Mercury bioaccumulation in fish is related to species metabolism and the flux of energy and matter in aquatic ecosystems.  These relationships could be considered by using size spectrum approach based on the size distributions of individual organisms within each ecosystem.  Size spectrum slope can indicate how quickly species density declines as size increases, energy transfer efficiency, and the size ratio between prey and predators.  In this study, we examine the relationships between fish mercury levels in Ontario lakes and fish biomass size spectrum when accounting for lake environmental and order parameters.  We use fish biomass size spectrum slope, lake environmental and order information, and mercury concentrations in walleye, northern pike, lake trout, and smallmouth bass from Ontario lakes.  Principal component analysis and generalized linear model are used to examine whether fish mercury levels in Ontario lakes are strongly related to the physical, chemical, or biological characteristics of aquatic ecosystems.

Results/Conclusions

Our results indicate that mercury concentrations in walleye, northern pike, lake trout, and smallmouth bass are strongly related to dissolved organic carbon, pH, sulphate, and fish biomass size spectrum slope.  Mercury levels in the four fish species are more likely to be higher in lakes that have lower pH and sulphate concentration, and higher values of dissolved organic carbon and fish biomass size spectrum slope.  This may be because that pH and sulphate concentration could affect mercury methylation process and the generation of methylmercury.  Dissolved organic carbon may be related to primary productivity from which mercury accumulates through food web, and the fish biomass size spectrum slope of a lake could indicate the biomass ratio between small-size fish and large-size fish which have different magnitudes of mercury bioaccumulation.