PROCESSES AFFECTING TRACE-ELEMENT SPECIATION IN ESTUARIES - A REVIEW

Estuaries encompass the river/ocean interface, a physically and chemic ally dynamic region where biogeochemical processes radically modify th e composition of river waters. Pronounced chemical reactivity results from the mixing of fresh water and sea-water, which gives rise to shar p gradients in the estuarine master variables of salinity, temperature , dissolved O-2, pH and the type and concentration of particles in sus pension. The rapidly changing reaction conditions induce sorption, flo cculation and redox cycling of trace metals and because particle-water interactions are time-dependent, trace elements are transported in a complex manner. A knowledge of the kinetics, mechanisms and equilibria associated with particle-water interactions is essential in the devel opment of biogeochemical models capable of accurately predicting the f ate of trace elements, particularly toxic metals from anthropogenic so urces. This critical review examines the key processes controlling the speciation of trace metals based on field observations, controlled la boratory experiments and biogeochemical models, using European estuari es as exemplars.