Trace element dynamics in estuaries

Estuarine processes play a key role in global trace element biogeochemical cycles by mediating the magnitude and chemical form of land-ocean trace element fluxes. This chapter reviews the estuarine dynamics of selected trace elements (Fe, Al, Cu, Zn, Ba, Ni, Co, Mn, Pb and Cd) that serve as examples of key micronutrients, toxins, and tracers of environmental processes. Key processes for controlling estuarine trace element dynamics, including colloidal flocculation, adsorption-desorption reactions, and benthic exchange, are explained in context of estuarine physicochemical gradients. The magnitude and variability of these processes is explored using data from 68 estuaries. The implications for constraining global trace element biogeochemical cycles and their sensitivity to environmental change are discussed.