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

Bacterioplankton dynamics in the York River estuary: primary influence of temperature and freshwater inputs

Gary E. Schultz Jr.1,*, Edward D. White III2, Hugh W. Ducklow3

1Texas A & M University-Galveston, 5007 Avenue U, Galveston, Texas 77551, USA
2Department of Mathematics and Statistics, Air Force Institute of Technology, Building 640, 2950 P Street, Wright-Patterson Air Force Base, Ohio 45433-7765, USA
3School of Marine Science, College of William and Mary, PO Box 1346, Gloucester Point, Virginia 23062, USA

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

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