Seasonal Variations of DDT Compounds and PCB in a Eutrophic and an Oligotrophic Lake in Relation to Algal Biomass

Interactions between eutrophication and organic pollutants (PCB, DDTs and γ-HCH) were investigated during 1996-1997 in two lakes, one eutrophic (Lake E) and one oligotrophic (Lake O) but with otherwise similar morphometry and water chemistry. Soil samples from the watersheds indicated similar atmospheric exposure of the lakes. No biomass dilution was observed in Lake E compared to Lake O. Lake E had higher levels of PCB based on organic carbon and lipid mass in sedimenting matter (1.5×), surface sediment (1.4×) and perch (Perca fluviatilis) (2.4×), and also higher settling fluxes of particulate matter and PCB measured in sediment traps and in surface sediment. Phytoplankton was responsible for most of the PCB transport to the sediment in Lake E. Higher DDD/DDE ratios seemed to correlate to a high load of p,p′-DDT more than to that of anaerobic conditions. A high DDD/DDE ratio was recorded in the deep sediment core from Lake O together with high levels of sDDT and was also highest in the sediment traps during periods with, probably, the highest runoff of parental DDT from the watershed.