DIFFERENT FACTORS RELATED TO MERCURY CONCENTRATION IN SEDIMENTS AND ZOOPLANKTON OF 73 CANADIAN LAKES

Surficial sediments were sampled with a light-weight gravity corer at 175 sites in 73 Ontario and Quebec lakes and zooplankton was collected with a 225 mu m mesh size net in 24 lakes. Hg concentrations in surfi cial sediments (0-2 cm) ranged from 3 to 267 ng g(-1) dry weight with a mean of 80 ng g(-1) dry weight for all sites. A regression model inc luding organic content of sediments and the ratio of the catchment are a / lake surface explained 60% of the variation in sediments Hg concen trations. Hg in zooplankton ranged from about 25 to 377 ng g(-1) dw wi th a mean of 108 ng g(-1) dw and was weakly correlated with catchment area, primary productivity and TOC. Our data indicate that an importan t fraction of Hg originates from the catchments, but do not show a cle ar west-east regional gradient for Kg concentrations in surficial sedi ments or in zooplankton.