Temporal and spatial dynamics of nutrients and particulate suspended matter in Paranaguá Bay, PR, Brazil

Résumé

In order to assess the seasonal and spatial variations on the trophic structure in the estuarine region of Bay of Paranaguá, 12 monthly sampling cruises were carried out between July/1994 - June/1995, at 9 selected stations along the major axis of the bay. Dissolved inorganic nutrients (nitrate, nitrite, ammonium, phosphate and silicate), dissolved oxygen, pH, transparency, temperature, salinity, seston, chlorophyll-a (Chl-a) and particulate organic carbon (POC) in both surface and bottom waters were evaluated. The bay exhibited a striking spatial and seasonal pattern for most of the studied parameters and, except for silicate, all nutrients showed a non-conservative behavior. This is probably due to the interactions between hydrodynamic processes and different mechanisms of loss and supply of these constituents, such as biological uptake, fresh-water input associated with the rainfall regime, sediment-water interactions and sewage discharge from the city of Paranaguá. In spite of the great spatial variability observed in nutrient and chlorophyll-a levels along the salinity gradient, acute eutrophication was not detected. As expected, dissolved inorganic nitrogen: phosphate ratios demonstrate that nitrogen is potentially more limiting for the pelagic production. Marked variations of POC:Chl.-a indicate the occurrence of temporal changes in the source of organic detritus for the pelagic system of the Bay of Paranaguá, with a greater contribution from detritus derived from the phytoplankton in summer.