Influence of ecological processes on the accumulation of persistent organochlorines in aquatic ecosystems

摘要

Several ecological problems influences the fate, transport, and accumulation of persistent organochlorines (OCs) in aquatic ecosystems. In this thesis, I have focused on two processes, namely (i) the food chain bioaccumulation of OCs, and (ii) the trophic status of the aquatic system. To test the biomagnification theory, I investigated PCB concentrations in planktonic food chains in lakes. The concentrations of PCB on a lipid basis did not increase with increasing trophic level. In another study, I investigated the relationship between OC concentrations and trophic level, measured as (delta) N-15, in a specific predatory fish population. The dry weight OC concentrations and (delta) N-15 were related, indicating effects of prey choice on the OC accumulation. However, here also, lipid content explained the major part of the variation in OC concentrations, independent of trophic level (e. g. (delta) N-15). I investigated the effects of trophic status, measured as Tot-P concentration in water, on the concentrations of OCs in water, planktonic food chains and sediment in lakes. The dry weight concentrations of PCBs in phytoplankton were negatively related to the trophic status of the lakes. However, this relationship was explained by the decreasing lipid content of phytoplankton with lake trophic status. In lotic ecosystems, I found a positive correlation between the OC concentrations in fish and the Tot-P concentrations in the stream water. I suggest that this may be a result of one or several processes differing between lotic and lentic systems, none of which are mutually exclusive. Processes likely to cause the observed correlation are; increased periphyton biomass in eutrophic streams (e. g. decreased spiralling length), the shift from heterotrophy to autotrophy in eutrophic streams, and an increased load of OCs from the catchment area of eutrophic streams, due to different land use (e.g. agricultural land use). 133 refs, 13 figs