Assessment of lake trout (Salvelinus namaycush) mercury concentration across a gradient of food web complexity and environmental variables

Abstract

Exposure to mercury has been linked to health risks in both people and wildlife. In Ontario, mercury pollution is to blame for 85% of the consumption restrictions on fish from inland lakes. Heavy metals like mercury accumulate up the food chain. Different rates of contaminant accumulation may be caused by variations in feeding and food web biomagnification. To assess the role of food web biomagnification in an apex predator, four distinct classes of lake trout (Salvelinus namaycush) prey with increasing food chain lengths were compared to determine whether differences in food chain length could account for the differences in muscle tissue mercury concentration. The analysis for this study included fish, water chemistry, and mercury concentrations that were collected from the IISD-Experimental Lakes Area (1973-2019) and the Ontario Ministry of Natural Resources and Forestry’s Broad-scale Monitoring Program where the Ministry of Environment and Climate Change analyzed the fish tissue. Accounting for variation in fish body size, lake trout mercury concentration cannot be explained by food chain length as predicted, although a significant interaction between body size and lake class suggests there is a positive relationship with body size that varies based on food web class. In attempt to contextualize this result, I examined the possibility that environmental factors, such as lake chemistry (dissolved organic carbon, pH, total dissolved phosphorus), and lake morphometry (i.e. maximum lake depth, surface area) are also associated with variation mercury concentration. All environmental variables examined show a positive correlation with mercury concentration; amongst the variables assessed, dissolved organic carbon (DOC) had the strongest association with fish mercury concentrations. Understanding the biotic and abiotic factors that influence mercury accumulation can help make decisions on fish consumption guidelines and can help further research opportunities.