Correlates of mercury in fish from lakes near Clyde Forks, Ontario, Canada

Subsurface soils near Clyde Forks, Ontario, Canada, can have naturally high concentrations of mercury (Hg) from local geological sources. To investigate Hg in local aquatic food webs, Hg was measured in fish dorsal muscle (mainly yellow perch [YP] and pumpkinseed sunfish [PS]) and surface sediments from 10 regional lakes. Water chemistry, along with fork length, weight, and stable isotopes (δ15N, δ13C, δ34S) in fish were also measured. No lake sediments had elevated (>0.3 μg/g dw) Hg, and average Hg concentrations in fish were not sufficiently high (<1 μg/g dw) to be of concern for fish-eating wildlife. Variance in fish Hg was best explained by dietary carbon source (δ13C), and certain lake variables (e.g., pH for YP). PS with more pelagic feeding habits had higher δ34S and Hg than those with more littoral feeding habits. Potential biological linkages between fish Hg and δ34S, a parameter that may be related to the lake sulphate-reducing bacteria activity, requires further investigation.