Plankton studies in Buzzards Bay, Massaschusetts, USA. II. Nutrients, chlorophyll a and phaeopigments, 1987 to 1990

Abstract

Ammonium comprised up to 99.79% (mean 75.79%) of total dissolved inorganic nitrogen, due to nutrient loading at one station from a sewage outfall, and to resuspension of benthic nutrients due to shallow depth and frequent mixing throughout the entire bay. Nitrate levels were maximal in winter. Those of orthophosphate were higher during warmer months. Silicate exhibited sustained bay-wide summer increases followed by precipitous declines in autumn. Inverse relationships between silicate and diatoms during 1987 to 1988 suggest that silicate fluctuations were biologically related, in that the summer increase was a rebound from heavy utilization during the spring diatom bloom, and the autumn silicate decline was due to utilization by fall diatom bloom. Chlorophyll a levels were comparatively high (>5.0 mg l-1) and relatively uniform throughout the bay except for higher concentrations near the sewage outfall, or within an enclosed harbor. Buzzards Bay is a habitat favourable to high phytoplankton production because shallow depth and frequent mixing results in a water column that is holomictic and euphotic throughout most of the year, and the sediments act as a nutrient pump injecting ammonium and other remineralized nutrients into the water column. (See also 94L/10329). -from Authors