Short-term environmental variability and phytoplankton abundance in a shallow tidal estuary. II. Spring and fall

In spring, the estuary was in transition from riverine to lagoonal condition. Temperatures rose steadily (22 to 28°C), salinities (23 to 35‰) and chl a biomass (22 μg l-1) were high, and dissolved inorganic nitrogen (DIN) low (0.13 μM). Growth-limiting N was supplied as NH4+ by biological remineralization, rising (0.2 to 3.0 μM) on 11 of 14 nights, then declining each following day to below detection. Diet tidal height variations and daily wind stress changes accounted for about half the daily two-fold oscillation in chl a; the remainder was driven by daytime phytoplankton growth followed by nighttime grazing losses. In fall, the estuary was more riverine (20 to 32‰) and temperatures variable (12 to 20°C). Chl a biomass was low (4 μg l-1) and DIN high (2.0 μM). Chl a varied at the tidal and interday periods. Interday changes were correlated with water temperature changes, in turn coupled to the passage of atmospheric fronts at 3-4 d intervals. In both spring and fall periodic ecological processes operating on time scales equivalent to phytoplankton cell division times were important in contolling chl a biomass changes -from Authors

Duke Scholars

Author Joseph S. Ramus Marine Science and Conservation