The effect of lake trophy on lipid content and PCB concentrations in planktonic food webs

We investigated the influence of trophic status on the lipid content and polychlorinated biphenyl (PCB) concentrations in planktonic food webs from 19 lakes in southern Sweden. The lipid content in phytoplankton (10-45 mum), microzooplankton (45-150 mum) and large macrozooplankton (>500 mum) was negatively related to the total phosphorus (Tot-P) concentration in lakes. The lipid content in macrozooplankton (>150 Gem) and young-of-the-year roach (Rutilus rutilus) was not related to Tot-P in lakes. On a dry mass basis (ng/g dry mass), the sum of PCB concentrations in phytoplankton and microzooplankton was negatively related to Tot-P in lakes. Thus, the PCB concentrations in phytoplankton and microzooplankton were explained by the decreasing lipid content of these fractions with increasing trophic status of lakes; and when normalized to lipid content (ng/g extractable lipid) we found no differences in PCB concentrations among lakes. We conclude that the lipid content of phytoplankton increased with increased nutrient stress, explaining the negative relationship between lake trophy and phytoplankton organochlorine (OC) concentrations on a dry mass basis. The relationship found between lipids and lake trophy in producers was not transferred in the food chain.