Spatial changes in the water quality of Itajai-Acu Fluvial-Estuarine System, Santa Catarina, Brazil

This study was carried out with the aim of evaluating the spatial variation of the water quality in the Itajai-Acu River estuary. Seven stations along the estuary were monitored on a weekly basis, from October 2003 to December 2004, plus two stations in tributaries (Itajai-Mirim River, the main tributary, and one reference station). This monitoring included measurements of salinity, pH, dissolved oxygen, temperature, nutrients (NH4+, NO2-, NO3-, PO43-, H4SiO4), Biochemical Oxygen Demand (BOD), total phosphorous and dissolved organic phosphorus (TP and DOP), particulate organic carbon (POC), suspended particulate matter (SPM) and chlorophyll-a (Cla). Multivariate analyses demonstrated the compartmentalization of the system based on the deterioration in water quality and marine influence. Urban development was the main factor responsible for the spatial variation of the monitored variables, resulting in increases in the indicators for organic matter and a progressive decrease in O-2. Despite the effect of dilution by marine influence, there was an increase in ammonium, attributed to the influence of the municipal districts of Itajai and Navegantes, close to the river mouth.