INFLUENCE OF NUTRIENT ADDITIONS ON CADMIUM BIOACCUMULATION BY AQUATICINVERTEBRATES IN LITTORAL ENCLOSURES

Cadmium distribution and bioaccumulation were examined over a 2-year p eriod (1991-1992) in two nutrient-enriched and two control littoral en closures and in the littoral zone in Lake 382 (L382). Lake 382, a smal l oligotrophic lake, is located within the Experimental Lakes Area in northwestern Ontario, Canada, and received experimental Cd additions f rom 1987 to 1992. In the second year of this study, chlorophyll a and suspended C concentrations in the nutrient-enriched enclosures increas ed by 6.6 and 3.4 times, respectively, compared to the controls. As a result of increased particulate produced by the nutrient additions, Cd concentrations in water from the nutrient-enriched enclosures were hi gher (46-114 ng/L) compared to the controls (23-84 ng/L). Estimated Cd /C concentrations in water were lower in the nutrient-enriched enclosu res relative to the controls because of higher particle concentrations . Effects on Cd bioaccumulation were limited even though mesotrophic t o eutrophic conditions were reached in the nutrient-enriched enclosure s. Trends for lower Cd concentrations in mussels and crayfish from the nutrient-enriched enclosures compared to the controls were observed; however, significant differences were rarely detected. Zooplankton and immature Chironomidae from the nutrient-enriched enclosures had consi stently higher Cd concentrations compared to the controls, but signifi cant differences were not detected. Enhanced accumulation of Cd-rich p articulate matter by these organisms may account for this trend. Musse ls and crayfish accumulated significantly more Cd when exposed in the lake compared to the enclosures. This observation is due to elevated C d water concentrations in the lake compared to the enclosures because of continued Cd additions to the lake. These results suggest that the water route of exposure is an important pathway for Cd accumulation by these organisms.