Nutrient distributions in the Ria de Aveiro, Portugal. Preliminary Results

The Aveiro Lagoon is a bar-built estuary dynamics situated in northern Portugal, with a single mouth to the Atlantic Ocean. The distribution of nutrients (nitrate, nitrite, ammonium, phosphate and silicate) was studied together with water mass tracers (salinity, temperature) and with indicators of biological activity (dissolved oxygen, inorganic carbon and chlorophyll a). During diel cycles, nutrient variations are mostly induced by tidal mixing which hide variations due to biological activity. While the phytoplankton growth. Two trends emerge for the nutrient distribution in the Ria: agriculture in the south, inducing high nitrate and phosphate concentrations; and industry and urban activity in the north, a source of ammonium, nitrate and phosphate. Eutrophication seem to be limited to areas of relatively stagnant water and/or close to industrial effluents.