CAN PHYTOPLANKTON MAINTAIN A POSITIVE CARBON BALANCE IN A TURBID, FRESH-WATER, TIDAL ESTUARY

An analysis of phytoplankton primary production in the tidal freshwater portion of the Hudson River estuary suggests that net primary production is strongly limited by light and mixing regime. In this turbid, well-mixed system, cells-spend from 18 to 22 h d-1 below the 1% light level. Autotrophic dark respiration, conservatively estimated at 5% of P(b)max, is of sufficient magnitude to make positive algal growth impossible over much of the river and much of the year. It is particularly difficult to explain the observed increase in algal biomass during blooms in spring and summer. We hypothesize that such blooms can occur only in a small fraction of the river where depth is less than or similar to 4 m.