Temporal variations in dissolved selenium in a coastal ecosystem

Abstract

In oceanic environments biological processes are now known to have a central role in establishing the redox state and spatial distribution of certain dissolved trace elements. Biological effects on the natural cycles of Cr, As, Se, Cd, Ni and Al are inferred from the existence of thermodynamically unfavourable species, from non-conservative vertical profiles or because trace element levels in planktonic debris are such that the subsequent regeneration of material could produce the observed profiles1–7. In cases where biological activity has been implicated as a determinant of either redox state or spatial distribution in the oceans no field investigations have yet been made into the relationships between rapid fluctuations of biological parameters and trace element levels and speciation. We now present a temporal study of the response of selenium levels and redox state to pulses of primary productivity in a coastal ecosystem. The sampling time series demonstrated selective assimilation of the lower oxidation state, selenite [Se(IV)]. Ratios of particulate selenium to particulate organic carbon (Se:C) allowed an estimation of the selenium levels in a natural phytoplankton population and the flux of selenium from surface ocean water to deep water.