COMPLEX-FORMATION AND THE CHEMISTRY OF SELECTED TRACE-ELEMENTS IN ESTUARIES

The estuarine chemistry of several metals and anion-forming elements is compared. Differences in the estuarine behaviour of nickel and copper appear to be caused by differences in the stability and reaction rates of organic complexes of these metals. Nickel occurs partially in very stable organic complexes that have an estuarine pathway different from the electrochemically labile (weakly complexed) fraction as the two fractions are not in equilibrium on the estuarine time scale; whereas, the complexes of copper in the estuary are in equilibrium with each other. Titanium occurs largely in a nonlabile form and is subject to removal at low salinities; it is released again at intermediate salinities (25 practical salinity units) and behaves conservatively at higher salinities. Comparison of several anion-forming elements reveals differences; uranium, antimony, and molybdenum show nonconservative behaviour and selenium shows conservative behavior. Voltammetric measurements of the chemical speciation of molybdenum in estuarine waters indicated the unexpected presence of a nonlabile species for this element.