Identifying and Assessing Bacterial Contamination in Stormwater Runoff and Receiving Streams

Stormwater runoff has been recognized as a significant non-point source of pollution responsible for serious ecological impacts. Microbial pollutants represent one of the major contaminants of concern in stormwater runoff and the receiving streams. Traditionally, fecal indicator bacteria (FIB) have been used extensively to assess the microbial quality of water, particularly the extent of fecal contamination in water. However, the application of FIB as indicators of microbial contamination bears known disadvantages of cultivation-dependent techniques, such as the inability to identify the majority of microbial populations that are not amenable to cultivation under laboratory conditions. The effectiveness of a cultivation-independent sequencing technique targeting the 16S rRNA genes was evaluated by comparison with FIB enumeration. Tested with samples from various environmental matrices, including stream water, stormwater runoff, sewage, and stream sediments, the efficacy of the sequencing techniques was validated with the ability to profile the microbial community present in stormwater runoff and stream water. Comparison of microbial contamination in stormwater and receiving streams indicates that roadway traffic characteristics and seasonal effects had considerable impacts on the extent of microbial contamination in stormwater runoff and subsequently the receiving streams.

The survival of E. coli strains isolated from pavement runoff, as representatives of microbial contaminants of concern, was investigated under relevant environmental conditions, showing that these microorganisms exhibited limited persistence on asphalt pavement and polystyrene plastic surfaces with the maximum T₉₀ averaging 0.25 days. However, the presence of moisture was shown to significantly prolong the viability of these strains, suggesting the potential persistence of these microbial populations in the stormwater runoff and stream water.

Natural variations of the bacterioplankton communities in the streams were evaluated. The results showed while spatial and temporal variations were observed, the stream sizes and characteristics were larger drivers for stream microbial community. Further, the impact of stormwater runoff onto microbial communities in receiving streams was investigated. In stream wetflow, the microbes sourced from the stormwater runoff were determined, as well as the overall contributions that stormwater runoff had on the microbial water quality of streams. Findings in this study could be helpful for developing stormwater runoff control measures.