MERCURY IN MACROINVERTEBRATES FROM SWEDISH FOREST LAKES - INFLUENCE OF LAKE TYPE, HABITAT, LIFE-CYCLE, AND FOOD QUALITY

Mercury concentrations in lacustrine macroinvertebrates were concurrently studied in eight remote Swedish forest lakes of differing dystrophy, acidity, and eutrophy. The aim was to assess the influence of ecological factors (taxon, habitat, and feeding habits), chemical factors (characterizing different types of lakes), and regional and climatic factors (Hg deposition and mean temperature) on the accumulation of Hg. Concentrations varied from <50 to >5000 ng Hg.g dry weight-1. A large part of this high variability could be ascribed to differences in water and sediment chemistry, ecological niches, and species-specific seasonalities. Both taxonomic composition and Hg concentrations were highly dependent on the type of lake. Concentrations were highest in acidic dystrophic lakes and lowest in oligotrophic lakes. Mean Hg concentrations in the examined taxa within a lake differed 100-fold. Contrary to widely held views on biomagnification, the lowest concentrations among profundal chironomids were found in predators whereas the highest concentrations occurred in detritivores. Seasonal variations were negligible in some taxa but considerable in others and appeared in some taxa to be related to the life cycle. We conclude that Hg accumulation in macroinvertebrates is largely determined by feeding behaviour and food quality.