The use of enclosed ecosystems for the study of cycling and impact of trace elements

Phytoplankton play an important role in the biogeochemistry of many trace elements, through incorporation within the cell and direct or indirect chemical transformation. We report on studies carried out in large-volume, continuous cultures maintained outdoors under ambient conditions of light and temperature in which we examined the role natural phytoplankton populations play in the availability and speciation of two toxic trace elements. Silver was readily taken up by phytoplankton, with uptake inversely proportional to salinity. Uptake and incorporation reduced silver availability to other estuarine organisms. Arsenic is modified either by reduction or methylation. These transformations relieve toxicity to phytoplankton, but may serve to increase the toxicity of arsenic to estuarine fauna. It is important that we understand how physico-chemical controls of trace element speciation, algal incorporation, transformation and release are coupled in productive estuaries before we can predict the impact of anthropogenic inputs of trace elements