UPTAKE, TRANSFORMATION, AND IMPACT OF SELENIUM IN FRESH-WATER PHYTOPLANKTON AND BACTERIOPLANKTON COMMUNITIES

The uptake, transformation and effects of selenium on natural plankton communities from a freshwater reservoir with a history of selenium co ntamination were examined. The majority of uptake occurred by particle s >0.8 mu m, reflecting the dominance of biomass by phytoplankton. Sel enium uptake was proportional to plankton biomass and selenium concent ration. Short-term uptake (0 to 24 h) of selenite was approximately 4 to 5 times faster than that of selenate. In long-term cultures, the re lative rates of selenate uptake by size classes varied with the distri bution of biomass among size classes. The only transformation of selen ium observed was an increase in selenite in long-term cultures enriche d with selenate. Selenate concentrations of 127 nM caused a significan t reduction in phytoplankton growth rates and biomass, suggesting that natural communities may be more sensitive than cultured algae.