SS3.17 Global Mercury Cycling: From Natural to Anthropogenic Sources
Date: Tuesday, June 11, 2002
Time: 4:45:00 PM
Location: Carson C
 
SchetagneR, Hydro-Quebec, Montreal, Canada, schetagne.roger@hydro.qc.ca
 
DURATION OF POST-IMPOUNDMENT INCREASES IN FISH MERCURY LEVELS AT THE LA GRANDE HYDROELECTRIC COMPLEX, QUÉBEC, CANADA
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At the La Grande hydroelectric complex, mercury concentrations were measured in over 25 000 fish from natural and modified aquatic systems as part of an ongoing environmental effects monitoring program, over a 20 year period. Total mercury concentrations were measured by standard cold vapour atomic absorption spectrophotometry. In reservoirs, concentrations in all species increased rapidly after impoundment, peaking after 5 to 9 years in non-piscivorous fishes, and after 10 to 13 years in piscivorous species, then significantly and gradually declined. Peak concentrations reached levels 3 to 7 times those measured in surrounding natural lakes. Concentrations in the non-piscivorous species have returned to levels typical of natural lakes 10 to 19 years after flooding. In the piscivorous northern pike and walleye the rate of decline, which begins after 15 years, strongly suggests that natural concentrations are reached between 20 to 30 years after flooding. Data show that, along a series of large reservoirs emptying one into the other, the effect of an upstream reservoir on fish mercury levels is limited to the first downstream reservoir.