Seasonal variation of atmospheric and terrestrial nutrients and their influence on primary production in an oligotrophic coastal system-southeastern Brazil

. Abstract: In an oligotrophic coastal zone, land drainage and atmospheric precipitation can temporarily modify the concentrations of specific dissolved compounds in local surface waters, mainly nutrient salts, setting up conditions for "new" primary production of phytoplankton. The Ubatuba region (23°30'S 45°06'W) is considered an oligo-mesotrophic region subject to a high average annual precipitation (2,000 mm). The small rivers flowing into Palmas' Inlet present outtlow patterns linked to the precipitation cycle. Rain and river waters show nitrate, nitrite, ammonium, phosphate and silicate concentrations that are very variable often higher than in surface seawater. When one considers the total nutrient inventory ofPalmas' Inlet (total volume) in each sampling period, the relative contribution of nutrients from rain water presents the following seasonal variations: DIN (0.1-21.0 %), nitrate (0.06 15.86 %), phosphate (0.01 2.75 %), silicate (0.01 0.50 %); and the contribution from river waters varies within the following limits: DIN (0.02 0.36 %); nitrate (0.01 0.88 %); phosphate (0.01