PREDICTING FISH MERCURY LEVELS FROM PHYSICAL CHARACTERISTICS OF BOREAL RESERVOIRS

Reservoir formation has often resulted in increased fish mercury levels. Predicting the potential for increase prior to impoundment would be useful in future environmental impact assessment. We developed several linear models relating mercury burdens of northern pike (Esox lucius), walleye (Stizostedion vitreum), and lake whitefish (Coregonus clupeaformis) to physical characteristics of 21 lakes and reservoirs in the Churchill River diversion region of northern Manitoba. Ratios of flooded terrestrial area to water volume of the reservoir itself (within-lake effects) and of inflowing waters (upstream effects) were able to explain 76-84% of the variation in mean mercury burden. Upstream effects consistently accounted for more variation than within-lake effects. We tested these models using data from 18 Canadian lakes and reservoirs. Manitoba reservoirs generally fit the models well. The largest deviations of observed mercury levels from predicted mercury levels were for reservoirs of northern Quebec and Labrador. We attribute this to differences in the relative contributions of within-lake effects and upstream effects between reservoirs of this region and those used to build the models. Future models should refine the relative contributions of these two components for individual reservoirs.