TOTAL DISSOLVED MERCURY IN THE WATER COLUMN OF SEVERAL NATURAL AND ARTIFICIAL AQUATIC SYSTEMS OF NORTHERN QUEBEC (CANADA)

Total dissolved mercury concentrations in the water column of the La G rande-2 and Laforge-1 hydroelectric reservoirs and four neighbouring l akes near James Bay, northern Quebec, were measured to establish the i mpacts of extensive flooding of terrestrial environments on this poten tial vector of contamination to the aquatic biota. During three field visits between June and October 1993, while the sites were free from i ce cover and the water column was not strongly stratified, filtered wa ter samples were collected from multiple depths at various locations w ithin both reservoirs and the four lakes. To, compare the diverse sube nvironments within the reservoir systems, sampling sites were selected to represent differences in (i) type of flooded soil, (ii) impoundmen t history, and (iii) water depth. At all stations total dissolved merc ury concentrations were nearly constant, with an average value of 2.30 ng L(-1), and a standard error of 0.04 ng . L(-1). Furthermore, reser voir concentrations were not statistically different from those of the lakes. Hence, we propose that the dissolved component in the water co lumn does not play a significant role in the transfer of inorganic mer cury to the aquatic food chain in recently developed hydroelectric res ervoirs.