Isotopic studies of groundwater-seawater interactions in the Ubatuba coastal area, Brazil

Abstract

Stable isotopes and nutrients data collected during 2002 and 2003 campaigns offshore Ubatuba are presented and discussed. The isotopic composition (δD, δ18O) of submarine waters is characterised by significant variability and heavy isotope enrichment, indicating that a contribution of groundwater in submarine waters may vary up to 20%, depending on the location and the tide level. The nutrient data showed scaterred distributions with offshore distance and salinity, what implies that in the complex coast with many small bays and islands the mixing patterns have been very complex. The sources of nutrients observed in the visited bays are both due to transport of pollutants by local currents and due to contributions of submarine groundwater. Submarine groundwater discharge in Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region.