The biogeochemical behaviour of Cd, Cu, Pb and Zn in the Scheldt estuary: results of the 1995 surveys

Concentrations of dissolved and particulated fractions of cadmium, copper, lead and zinc in samples obtained from the Scheldt estuary during 1995 were determined by analysis, with special emphasis on quality assurance in respect of all major steps in the analytical process, including sample handling, preconcentration and quantitative estimation. Longitudinal profiles were also obtained for dissolved oxygen, turbidity and chlorophyll-a concentrations at different times of the year. The results indicated that desorption and redox processes effectively controlled the dissolved copper and cadmium profiles, while mobilization of zinc was small and confined to an area of low salinity in the late spring. Dissolved lead exhibited the clearest influence of dilution while parameters such as dissolved oxygen and salinity correlated satisfactorily with the profiles for the particulate metal fractions. In addition there was evidence for an effect due to phytoplankton activity (chlorophyll-a levels) on both the dissolved and particulate metal profiles which exhibited some seasonal variations.