Urban street runoff influences on water quality of an adjacent waterway

Background/Question/Methods

Urban areas commonly rely on combined sewer systems to transport sewage and surface runoff. The capacity of these systems is frequently exceeded during rain events, subsequently leading to the bypass of municipal sewage treatment and discharge directly into local waterways. Prior studies have demonstrated that fecal indictor bacteria (FIB) and antibiotic resistant bacterial (ARB) concentrations increase in urban waterways of New York City following precipitation, leading to growing concern about impacts on aquatic ecology and public health. Using culture-based assays for FIB and ARB we evaluated the extent to which urban street runoff, as opposed to sewage, may influence microbial assemblages in urban waterways. The goals of this study are to: 1) compare FIB concentrations in urban street runoff and CSO-impacted waterways; 2) examine ARB abundance and taxonomic diversity in urban street runoff; and 3) to characterize the microbial community composition in urban stormwater. We hypothesized that FIB and ARB would be detected in urban street runoff at high concentrations relative to urban surface water, and that the microbial community composition in urban street runoff would include taxa found to increase in waterways following rain events.  

Results/Conclusions

High concentrations of FIB were found in all urban storm water samples collected, in all cases exceeding EPA guidelines for beach closure by an order of magnitude. These FIB values were significantly greater than dry weather concentrations in an adjacent CSO-impacted waterway (p<0.01). Similarly, ampicillin and tetracycline resistant bacterial concentrations in urban runoff were found to exceed dry weather background concentrations (p<0.01 in both cases), with tetracycline resistant abundances exceeding even wet weather background concentrations in the adjacent waterway (p<0.01). Sulfamethoxazole and ampicillin resistant bacteria were consistently more abundant than tetracycline resistant bacteria in urban street runoff. Thus, it appears that urban stormwater, not just sewage discharge, represents a significant, and poorly managed, input of FIB and ARB to the waterways surrounding New York City.  Given the elevated FIB and ARB concentrations observed in urban street runoff, and the number of individuals encountering stormwater during a typical rain event, as opposed to urban waterways, it would be valuable to better understand the public health risk associated with this exposure.