Long-term phytoplankton studies in the Bahía Blanca estuary, Argentina

Abstract

Phytoplankton composition and abundance in the Bah a Blanca estuary, Argentina, have been studied from 1978 to 1993; also water temperature, salinity, transparency, and nutrient concentrations. The pattern of seasonal distribution showed a winter/ early spring bloom of diatoms, dominated by Thalassiosira spp., as the most important event in the annual cycle. Annual means of temperature and salinity showed relatively minor variations. Nutrient concentrations (nitrate, silicate, and phosphate) exhibited a positive trend with time. Chlorophyll a showed marked seasonal variations, with maximum values (up to 42 g l 1 ) during the winter-early spring diatom bloom. The relationship between phytoplankton and environmental factors was investigated using multiple regression analysis. Chl a concentrations and total phytoplankton cell abundance were significantly negatively correlated with temperature, suggesting that temperature was the major source of temporal variability in phytoplankton in the area. Among the nutrients, the highest coefficient was for phosphate concentrations, indicating that this nutrient was more affected by phytoplankton uptake than were silicate and nitrate concentrations.