Distribution and activity of bacteria in the headwaters of the Rhode River Estuary, Maryland, USA

Biology Department Whitman College 99362 Walla Walla WA USA; Marine Biological Laboratory Ecosystems Center 02543 Woods Hole MA USA
Microbial Ecology (Impact Factor: 3.28). 08/1984; 10(3):243-255. DOI: 10.1007/BF02010938

ABSTRACT A transect along the axis of the headwaters of a tidal estuary was sampled for microbial, nutrient, and physical parameters. Chlorophylla averaged 42g 1–1 and phytoplankton comprised an estimated 80% of the total microbial biomass as determined by adenosine triphosphate (ATP). Bacterial concentrations ranged from 0.3–53.9106 cells ml–1 and comprised about 4% of the total living microbial biomass. Bacterial production, determined by3H-methyl-thymidine incorporation was about 0.05–2.09 109 cells 1–1 h–1, with specific growth rates of 0.26–1.69 d–1. Most bacterial production was retained on 0.2m pore size filters, but passed through 1.0m filters. Significant positive correlations were found between all biomass measures and most nutrient measures with the exception of dissolved inorganic nitrogen nutrients where correlations were negative. Seasonal variability was evident in all parameters and variability among the stations was evident in most. The results suggest that bacterial production requires a significant carbon input, likely derived from autotrophic production, and that microbial trophic interactions are important.

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    ABSTRACT: Samples were collected at stations located in the mesohaline, oligohaline, and tidal fresh regions of the Potomac River, Maryland, between April 1998 and December 1999 to evaluate the seasonal distribution of bacterioplankton and microbially labile organic carbon (MLOC) in relation to hydrodynamic parameters (dissolved oxygen, salinity, and temperature). Bacterioplankton abundance (BA) averaged 13 × 106 cells ml−1 at all stations, a value that is higher than the average observed in many other temperate estuaries around the world, and were almost exclusively free-living. During the summer of 1998, BA often exceeded 30 × 106 cells ml−1 in the mesohaline region during periods of anoxia in subpycnocline waters. Dissolved MLOC typically accounted for 40% of total MLOC and on some occasions during summer and autumn accounted for 80%. A significant positive relationship between dissolved MLOC and BA was evident in the mesohaline Potomac River, the region where anoxia occurs each summer, but the regressions of particulate MLOC and chla on BA were not significant at this location. In the mesohaline Potomac River, BA regressed negatively and significantly on dissolved oxygen (r2=0.50, p<0.001). BA may be an important indicator of ecosystem health in this and other eutrophied estuaries, because of the relationships between BA, dissolved MLOC, and dissolved oxygen in the salinity stratified Potomac River and because free-living BA was elevated along the length of the river.
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