Itajai-acu river estuary (Santa Catarina, Brazil): Preliminary budget for dissolved inorganic nutrients

The purpose of this work was to determine a preliminary budget of inorganic dissolved nutrients and to evaluate their variability in the ltajai-acu River estuary. The estuary is the main estuary of Santa Catarina State, Southern Brazil. The ltajai-acu River flows through the most economically important region of the state, the Itajai Valley. Its land use is characterized by intensive agricultural uses, with industrial zones and important cities. The biggest fisheries harbor of Brazil also is located in the lower Itajai Estuary. The nutrients (NH4+, NO2-, NO3-, and PO43-) were sampled at 5 stations along the estuary, from Indaial (located 90 km upstream the the river mouth) to Itajai city, at the estuarine mouth, collected at weekly basis from July 2000 to July 2001. The nutrients concentrations were determined according to classical colorimetric methods and the budgets were calculated according to methodology proposed by LOICZ. The budgets were calculated for two river discharges classes: below 200 m(3).s(-1) and between 200 and 800 m(3).s(-1). The results of concentration monitoring suggest the estuary presents a net metabolism heterotrophic. The budgets showed that the estuary behavior as a sink for phosphor-us and as a source for amonium. Similar conclusion was found for the Camboriu estuary, situated about 10 km south. The budgets also showed residual transport of DIN and DIP to the coastal zone. Along the estuary The ammonium presented higher concentration at the estuarine head, probably by the anthropogenic influence.