Plankton productivity and biomass in a tributary of the upper Chesapeake Bay. I. Importance of size-fractionated phytoplankton productivity, biomass and species composition in carbon export

Abstract

Phytoplankton productivity, community composition and biomass were determined over a nine-month period in brackish waters of the lower Gunpowder River, a tributary of Chesapeake Bay. Primary productivity followed expected seasonal magnitudes for temperate estuaries with rates exceeding 142·4 mg C m −3 h −1 in July through September 1979 and minimum rates of 1·6 mg C m −3 h −1 in February 1980. Annual primary production was estimated at 45·5 gC m −2. Cell numbers were highest in August, September and November with cyanophytes dominating the planktonic algae. Primary productivity, chlorophyll concentrations and cell densities were dominated by nanoplanktonic forms (< 10 μm) through-out the study. Phytoplankton carbon calculated from cells volumes exceeded nutritional requirements of the pelagic herbivores in all months suggesting a mean daily export (to the bay or sediments) of 1607 mg C m −3 d −1.