Biotemas (Mar 2010)
Nutrient variations and coastal water quality of Santa Catarina Island, Brazil
Abstract
In the present study, seasonal variations of nutrient concentration and water quality of two coastal areas of Santa Catarina Island (SCI) were investigated from August 2006 to February 2008. Water samples were analyzed for temperature, salinity, pH, dissolved oxygen, suspended particulate matter (SPM), chlorophyll-a, dissolved inorganic nitrogen (DIN) (nitrite + nitrate + ammonium), phosphate, silicate, total nitrogen (TN) and total phosphorus (TP). The results showed that water temperature and salinity in the North Bay present greater variation than in Pantano do Sul. The average values of temperature and salinity of 17.6oC and 34.8 in the winter, 18.1oC and 34.6 in the spring, and the highest nitrate concentrations of 4.12μM (in the spring), are strongly related to the signatures of Subtropical Shelf Water (STSW) and South Atlantic Central Water (SACW) respectively. The low N:P (DIN:phosphate) and high Si:N (silicate:DIN) ratios indicate that nitrogen is the limiting nutrient in the area. In addition, dissolved inorganic nutrient concentrations are lower than in other urbanized coastal areas in the Southeastern Brazilian Bight (SBB). The trophic state evaluation showed that SCI coastal waters can be classified in general as mesotrophic, reaching eutrophic conditions during some periods of the year.
