MICROALGAE OF THE PATOS LAGON ESTUARY: SEDIMENT-WATER COLUMN INTERACTION

Abstract

The water column and sediment of a fixed station at the shallow (?0.5 m) region of the Patos Lagoon estuary, were sampled weekly between April 1990 and April 1991. Microalgae abundance, biovolume, species composition as well as the concentration of chlorophyll-a (Chl-a), particulate organic carbon (POC) and abiotic factors were measured in both systems. Chl-a and POC concentrations in the sediment were three orders of magnitude higher than in the water column. No seasonal pattern was observed for POC in the water column, whereas for Chl-a, high values occurred during the austral spring-summer of 1991, and low values were observed in autumn-winter of 1990. In the sediment both variables showed high values in the winter and lower in the spring of 1900. The variation of phytoplankton biovolume in the water column was similar to Chl-a, while in the sediment high values were measured during winter and spring of 1990. A statistically significant relationship was observed between POC concentration in the water column and south-southwesdt-, and westerly winds, indicating resuspension, for the southeast-, easterly winds this relationship was not so direct, probably due to the geographic position of the sampling station which is protected from these winds. The results suggest that the interaction between sediment and water column occur in two different ways: (1) during low salinity and low light intensity conditions, both the water column and sediment function as a single system with the presence of benthic euryhaline species in both compartments; (2) under both high salinity and light intensity, the sediment and water column function in a more independent way, with high cellular abundance and biomass of neritic species found in the column.