Abstract
Bacterial particle association has important consequences for water-quality monitoring and modeling. Particle association can change vertical and horizontal transport of bacterial cells, as well as patterns of persistence and production. In this study, the abundance and particle association of total bacteria and the fecal-indicator, Enterococcus, were quantified between June and October 2008 in the lower Hudson River Estuary (HRE). Twelve sites were sampled, including mid-channel, near shore, and tributary habitats, plus a sewage outfall. Total bacterial cell counts averaged 9.2 × 109 ± 6.4 × 109 cell l–1 (1 standard deviation), comparable to previous sampling in the HRE. Unlike earlier studies, bacterial abundance did not change consistently along the north/south estuarine salinity gradient. Enterococcus concentrations were highly variable, but mid-channel stations had significantly lower values than other habitat categories. Counts of total bacteria and Enterococcus were both correlated with turbidity, which was also significantly lower at mid-channel stations. A larger fraction of Enterococci were associated with particles (52.9 ± 20.9%, 1 standard deviation) than in the pool of total bacteria (23.8 ± 15.0%). This high frequency of particle association, relative to total bacteria, could cause Enterococcus to be preferentially retained near input sources because of enhanced deposition to bottom sediments, where they would be available for later resuspension. In turn, retention and resuspension in nearshore environments may explain the observed cross-channel variability of turbidity and Enterococcus. Assessments and predictive models of estuarine water quality may be improved by incorporating cross-channel variability and the effects of particle association on key indicators.
Highlights
Association with particles can be a key aspect of the ecology of aquatic bacteria, including both naturallypresent cells, and allochthonously-introduced pathogens [1]
This high frequency of particle association, relative to total bacteria, could cause Enterococci to be preferentially retained near input sources because of enhanced deposition to bottom sediments, where they would be available for later resuspension
Particle association is relevant to the management of bacterial contamination of ambient water by sewage
Summary
Association with particles can be a key aspect of the ecology of aquatic bacteria, including both naturallypresent cells, and allochthonously-introduced pathogens [1]. Particle-associated bacteria can have higher production rates [6,7] and different susceptibility to predation than freeliving cells [8,9]. For these reasons, particles can be viewed as islands of favorable microbial habitat suspended within the less favorable water phase [1]. Particle-associated bacteria may be shielded from disinfection by UV light and chemicals [9]. Another consideration is that bacteria associated with particles are likely to sink faster than free-living cells [10,11].
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