28. Influence of Groundwater Discharge Through a Coastal Sandy Barrier in Southern Brazil on Seawater Metal Chemistry

Sandy barriers developed during the Holocene transgressing sea are common features of many coastal regions throughout the world. We present here the results of the study of groundwater-surface water interactions associated with a 600-km barrier which created the Mirim-Patos Lagoon system, the largest in South America. Results show that the composition of the groundwater discharge to the ocean from these permeable sands differs significantly in metal concentrations from those of surface freshwater-seawater mixtures, primarily as a result of redox processes. Estimates of the volume of freshwater transport and seawater cycling through the sands, and metal concentrations in surface waters and in groundwaters, were used to estimate metal fluxes between compartments of this system and indicate that iron, manganese, cobalt and perhaps vanadium, cadmium, copper and zinc are being enriched in adjacent coastal waters, whereas uranium and perhaps molybdenum are being depleted.