Chesapeake Bay nutrient and plankton dynamics. 1. Bacterial biomass and production during spring tidal destratification in the York River, Virginia, estuary1,2

Bacterial abundance, biomass, and I”H]thymidine incorporation rates were studied during spring tidal destratification of the York River, Virginia, estuary. Monthly high spring tides cause salinity destratification in the modcratcly stratified estuary, which oscillates between stratified (top-to-bottom salinity difference >1%0) and vertically homogeneous (salinity difference <1%0) conditions on a time scale of l-10 days. Bacterial abundance and carbon biomass ranged from 1 to 8 x 10R cells * liter-’ and 20 to 100 pg C * liter-‘. Thymidine incorporation into cold TCA-insoluble fractions ranged from 1 to 10 x lop9 mol.litcr ‘*de’; bacterial carbon production rates and specific growth rates were estimated at 7-75 pg C*liter-‘*d-l and 0.21.1. d-l. Biomass increased steadily during the destratification process while production remained constant. Production then increased twofold to threefold in 12 h during the period of maximum water-column homogeneity. Increased vertical mixing and possibly stimulation of phytoplankton production are suggested as the major causes of this bacterial response to destratification.

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