Uptake, transformation, and impact of selenium in freshwater phytoplankton and bacterioplankton communities

The uptake, transformation and effects of selenium on natural plankton communities from a freshwater reservoir with a history of selenium contamination were examined. The majority of uptake occurred by particles >0.8 pm, reflecting the dominance of biomass by phytoplankton. Selenium uptake was proportional to plankton biomass and selenium concentration. Short-term uptake (0 to 24 h) of selenite was approximately 4 to S times faster than that of selenate. In long-term cultures, the relative rates of selenate uptake by size classes varied with the distribution of biomass among size classes. The only transformation of selenium observed was an increase in selenite in long-term cultures enriched with selenate. Selenate concentrations of 127 nM caused a significant reduction in phytoplankton growth rates and biomass, suggesting that natural communities may be more sensitive than cultured algae.