TRACE METAL DISTRIBUTION IN PHYTOPLANKTON- AND MACROPHYTE-DOMINATED ZONES OF A LARGE, EUTROPHIC FRESHWATER LAKE, TAIHU

Phytoplankton and macrophytes are major primary producers and play important roles in driving the biogeochemical cycling of trace metals in aquatic ecosystems. In this study, we examined the distribution of trace metals in lake water and sediments of different lake zones (phytoplankton- and macrophyte-dominated) in a large, shallow, eutrophic freshwater lake in summer. The labile metal concentrations in lake water were determined with diffusive gradients in thin films (DGT) technique. Metal concentrations in bloom assemblages and macrophyte materials were measured. The results demonstrated that dissolved metal concentrations exhibited dramatically different distribution patterns in different lake zones, whereas metal concentrations in sediments were less influenced. Cadmium (Cd) was highly accumulated by Microcystis (cyanobacteria) bloom assemblages, suggesting that the decay and deposition of Microcystis-bloom detritus may contribute to the enriched Cd in the phytoplankton-dominated lake zone. The dissolved and labile copper (Cu) and zinc (Zn) concentrations were quite low in macrophyte-dominated zone, which may be attributed to the bioaccumulation of metals by aquatic macrophytes. Concentrations of labile chromium (Cr) and lead (Pb) in lake water were less influenced by environmental factors, which could be attributed to the higher affinity of these two metals with the sediment particles. Overall, the results of this study implied that different ecological types might have different influences on the transportation and fate of trace metals in aquatic environments, and different metals were characterized with dissimilar cycling behaviors.