Terrestrial Sources Homogenize Bacterial Water Quality During Rainfall in Two Urbanized Watersheds in Santa Barbara, CA
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Microbiological contamination from runoff is a human health concern in urbanized coastal environments, but the contamination sources are often unknown. This study quantified fecal indicator bacteria and compared the distributions of human-specific genetic markers and bacterial community composition during dry and wet weather in urban creeks draining two neighboring watersheds in Santa Barbara, CA. In a prior study conducted during exclusively dry weather, the creeks were contaminated with human waste as indicated by elevated numbers of the human-specific Bacteroidales marker HF183 (Sercu et al. in Environ Sci Technol 43:293–298, 2009). During the storm, fecal indicator bacterial numbers and loads increased orders of magnitude above dry weather conditions. Moreover, bacterial community composition drastically changed during rainfall and differed from dry weather flow by (1) increased bacterial diversity, (2) reduced spatial heterogeneity within and between watersheds, and (3) clone library sequences more related to terrestrial than freshwater taxa. Finally, the spatial patterns of human-associated genetic markers (HF183 and Methanobrevibacter smithii nifH gene) changed during wet weather, and the contribution of surface soils to M. smithii nifH gene detection was suspected. The increased fecal indicator bacteria numbers during wet weather were likely associated with terrestrial sources, instead of human waste sources that dominated during dry weather flow.
KeywordsTerminal Restriction Fragment Length Polymorphism Bacterial Community Composition nifH Gene Fecal Indicator Bacterium Terminal Restriction Fragment Length Polymorphism Analysis
This research was supported by the City of Santa Barbara through Measure B funding and by the Switzer Foundation through a Leadership Grant to the City. Flow data were provided through the NSF-funded Santa Barbara Long Term Ecological Research project (NSF OCE 9982105 and OCE 0620276) with assistance from Scott Coombs, Blair Goodridge, and John Melack. Additional assistance at UCSB was from Shurong Xiang, Allison Horst and John Priester (for sampling and sample processing), and Noah Fierer (clone library analysis). Additional assistance from the City of Santa Barbara was from Tim Burgess, Jill Zachary, Harry Slicker, Steve Mack, and Rebecca Bjork.
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