Organochlorine transfer in the food web of subalpine Bow Lake, Banff National Park

Lake trout (Salvelinus namaycush) from subalpine Bow Lake, near the Contine ntal Divide in Banff National Park, have been reported to have higher conce ntrations of toxaphene than other lake trout populations of the Rocky Mount ains. Our original hypothesis was that unusually high biomagnification via a long food chain was responsible for elevated levels of toxaphene and othe r persistent organochlorines in the lake trout. This hypothesis was refuted by the analyses of stable carbon (delta(13)C) and nitrogen (delta(15)N) is otope ratios in lake biota. Stable nitrogen isotope analyses demonstrated t hat the food chain length in Bow Lake was short. The sources of carbon (pel agic or benthic), as indicated by stable carbon isotope values, were highly correlated with organochlorine concentrations in the food web. Lake trout with more pelagic carbon signatures had higher organochlorine concentration s than littoral-feeding mountain whitefish (Prosopium williamsoni) and lake trout. The pelagic copepod Hesperodiaptomus arcticus had higher organochlo rine concentrations (wet weight basis) than any other organism, including t he fish. This was attributed to the high lipid content of copepods and poss ibly their ingestion of suspended solids, including glacial silt or direct absorption from solution in glacial inflows.