Hydrobiological parameters during an annual cycle in the Arcachon Basin

Abstract

Temperature, salinity, nutrients and phytoplankton biomass were monitored on a weekly to bimonthly frequency at six stations in the Bay of Arcachon from July 1984 to July 1985. This particular period appears to have differed from the last ten years in displaying higher amplitudes of both temperature and salinity (1.5° to 24.5°C and 20 to 34.5‰) at high tide. However, although in spring both temperature and salinity were normal (14°C, 28‰), an important phytoplankton spring bloom occurred, with maximum chlorophyll levels reaching 15 μg l^-1 in April. Utilization of nutrients was high, particularly for nitrate and silicate, the concentrations of which decreased, respectively, from 10–15 to 0.1–2 μM and 10–20 to 0.25–3 μM from February to May. Exhaustion of nitrate was observed in May, except in areas subjected to river input. In contrast, silicate increased throughout the study area from May to July.