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The aim of this study was to understand how a stream ecosystem that flows from its fountainhead to its mouth inside a city, changes from a water resource to a point pollution source. A multidisciplinary descriptive approach was adopted, including the short-term temporal and spatial determination of physical, chemical, biological and ecotoxicological variables. Results showed that water quality rapidly decreases with increasing urbanization, leading the system to acquire raw sewage attributes even in the first hundred meters after the fountainheads. Despite the tidal circulation near the stream mouth being restricted by shallowness, some improvement of the water quality was detected in this area. The multidisciplinary evaluation showed to be useful for obtaining a more realistic understanding of the stream degradation process, and to forecast restoration and mitigation measures.

The region of fluvial influence (ROFI) of Itajaí-Açu River was assessed through fourteen surveys covering thirty sampling stations in a radial shape with origin in the estuarine inlet. The total sampled area was of 100 km 2 , with depth ranging from 6 to 25 m, and until 10 Km offshore. The surveys were nearly monthly, from October 2002 to December 2003. The variables collected were salinity, temperature, suspended particulate matter, dissolved oxygen, chlorophyll a, picoplankton (autothrophic and heterothrophic) and zooplankton. River discharge and meteorological data were also obtained to help in the general characterization. The results indicated that in terms of averaged values of each variable, the sampling area is poorly related with the river discharge, or in other words, the sampling area is wider than the ROFI. Only salinity showed reasonably agreement with river discharge, although during the winter the region is affected by the Plata estuarine front. Further analysis on the data gathered must cope with spatial variability, either horizontal, e.g., plume dispersion, as vertical, e.g., plume buoyancy flow.

This study was carried out with the aim of evaluating the spatial variation of the water quality in the Itajaí-Açú River estuary. Seven stations along the estuary were monitored on a weekly basis, from October 2003 to December 2004, plus two stations in tributaries (Itajaí-Mirim River, the main tributary, and one reference station). This monitoring included measurements of salinity, pH, dissolved oxygen, temperature, nutrients (NH , 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 Itajaí and Navegantes, close to the river mouth.

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