Very low salinity regions of estuaries: important sites for chemical and biological reactions

Abstract

THE importance of biogeochemical interactions in estuaries is widely recognised1,2,4–6; in particular, theoretical models of estuarine speciation of trace metals7 and of the pH–carbonate system8 predict that sharp changes of thermodynamic equilibrium conditions should occur at very low salinities (<1‰). However, because of the limitations of conventional sampling strategies12, the chemical properties of this freshwater–seawater interphase (FSI) have not been adequately characterised. Instead, the expected variability has usually been represented by a scatter of spatially and temporally unresolved data points1,3,5,6. Over the past two years, we have carried out periodic detailed investigations of the immediate mixing of the fresh and brackish water in the Tamar Estuary, South West England and we present data here for 11 determinands which point to the FSI as being an important site for chemical and biological processes in estuaries.