Food Matters: Using Stable Isotopes to Establish the Dominant Biological Pathways of Contaminant Accumulation in Trout-Stocked Mountain Lake Food Webs

High elevation mountain lakes serve as early-warning indicators of ecological stress. They have simple food webs, and are relatively isolated compared to other ecosystems.  These qualities make mountain lakes an ideal place to conduct research on the interaction between human activities and the environment. Our study explores the interactions of trout stocking and bioaccumulation of compounds such as PCBs and mercury, which are atmospherically deposited in these historically fishless, high elevation systems. In 2014, fish were collected from North Cascades Lakes, and consequently analyzed for PCBs, total mercury, methylmercury, and stable carbon and nitrogen isotopes. By modeling the interactions of elevation and lake size, as well as size, age, lipid content, trophic status, and food source, we illuminate the potential for predicting contaminant concentrations in the primary consumer food web. When corrected for elevation, size, and age, the level of contaminants in fish are influenced both by lipid content, and by food source. This suggests the potential for identifying the dominant biological pathways of contaminant accumulation in top predators. Future work will apply this model to compare contaminant concentrations in food-webs of fishless versus fish-stocked lakes as a means of understanding the mechanisms of accumulation in these systems.