AME 30:135-148 (2003)  -  doi:10.3354/ame030135

ABSTRACT: Bacterial community dynamics were investigated over seasonal and basin scales within the York River estuary, Virginia. Variables describing bacterioplankton dynamics were measured at 6 stations spanning the entire salinity gradient (0 to ca. 20 psu over 60 km). Samples were collected monthly from June 1996 through May 1997 and every other month from June 1997 through May 1998. Bacterial abundance and production were high throughout the estuary. Bacterial abundance ranged from 4.4 x 10⁸ to 1.3 x 10¹⁰ cells l^-1. Incorporation of ³H thymidine ranged from 10 to 863 pmol^-1 h^-1 while ³H leucine incorporation rates ranged from 25 to 1963 pmol l^-1 h^-1. A strong relationship between bacterial properties and temperature was found with clear seasonal trends. On a basin scale, bacterial properties were strongly related to changes in salinity, suggesting that freshwater inputs and estuarine circulation controlled the distribution of bacterial abundance and activity in the river. Although there was a great deal of variability from month to month, 2 opposing trends were consistently found: bacterial abundance increased from freshwater to the mouth of the river, while incorporation rates decreased from freshwater to the mouth. These patterns imply a strong landward gradient in specific growth rates, and thus a close match between production and removal near the freshwater endmember and throughout the estuary.

KEY WORDS: Bacterioplankton · Estuary · Environmental controls · Spatial patterns · Temporal patterns