Drivers of Stormwater Runoff Characteristics from Non-Point Source Urban Pollution

As human populations continue to increase, so does the demand for drinking water and infrastructure. In urban areas, continued construction of impervious surfaces, such as rooftops and roadways, have the ability to generate considerable amounts of runoff; however associated runoff has been found to be heavily contaminated. The presence and resilience of fecal indicator bacteria in urban runoff could pose a threat to public health, as most non-point source runoff is not treated.Through investigations of rooftop and roadway runoff, microbial communities and fecal indicator bacteria presence was consistent between storm events and over the course of storms, respectively. Runoff quality characteristics were found to be highly dependent on total precipitation, antecedent dry period, and runoff intensity. Further experiments using Escherichia coli (E. coli) isolated from rooftops revealed that the environmental E. coli was capable of attaching to and surviving on glass surfaces. The ability of the E. coli to survive was impacted by temperature, as a lower temperature slowed attachment but prolonged cell longevity.Preliminary rooftop runoff experiments exhibited the consistency of runoff quality over the duration of a storm. With this discovery, rooftop runoff was collected and analyzed using random grab samples from housing developments in both the United States and China. Automatic flow-weighted samples were collected from the roadway and analyzed using 16S rRNA Sequencing technologies. Attachment and survival was analyzed using a modified acridine orange dye count method which paired epifluorescence microscopy with spatial analysis tools in ArcGIS to determine cell coverage on the glass surfaces.Geographic location and storm characteristics seem to have a strong impact on non-bacterial quality from urban impervious surfaces. Roadway microbial populations were consistent between storm events, and E. coli concentrations were constant within a storm event in rooftop runoff. Environmentally isolated strains of E. coli have now been shown to be capable in surviving in environments which mimic roadway and rooftop conditions. This further supports the idea that E. coli is not a suitable choice for measuring fecal contamination, and that first flush diversion will not prevent bacterial contamination of cisterns; creating a need for new designs for runoff collection.

Portions of this documents were previously published in the Journal of Environmental Quality