Duration and extent of elevated mercury levels in downstream fish following reservoir creation
Anderson, M. Robin
While mercury accumulation in reservoir fish following impoundment is a well known phenomenon, consequences for downstream populations are less understood. In particular, the effects on downstream estuarine populations have only rarely been studied. This study examined data from a Northern Canadian reservoir system to demonstrate that elevated mercury levels can be seen in fish downstream for a distance of over 300 km and into the estuary for some species. The Smallwood Reservoir in Labrador, Canada, created in the mid 1970's, drains into the Churchill River and hence into Lake Melville, a large estuarine fjord. Mercury levels in most species in the Churchill River were elevated immediately following impoundment and have since declined as have the levels in several estuarine species. Return times for downstream fish were similar to those in the reservoir and depended on trophic position and habitat use. Lake whitefish, longnose suckers and northern pike showed evidence of a shift in trophic position below the Churchill Falls tailrace.