Variability of Intra-event Statistics for Multiple Fecal Indicator Bacteria in Urban Stormwater

Pathogens in surface waters continue to be a worldwide concern. The potential presence of pathogens is often identified through the use of fecal indicator bacteria such as fecal coliform, E. coli, and enterococci, each of which are still utilized worldwide depending on local regulations. Urban stormwater runoff has been shown to convey fecal indicator bacteria to surface waters; however, the fate and transport dynamics of these microbes in urban stormwater are not well established. This is particularly the case for intra-event (within event) processes. The intra-event characteristics of total suspended solids and three types of fecal indicator bacteria (FIB), fecal coliform, E. coli, and enterococci, were analysed for a watershed in Raleigh, NC, USA. FIB showed higher variability than TSS among intra-event characteristics such as normalized peak concentration, rate of change, and normalized concentration in the first 3 mm of rainfall (C-3mm), but similar variability in concentrations throughout each storm. FIB intra-event statistics appear to be influenced by climate variables whereas total suspended sediments statistics are most influenced by hydrologic variables. Changes in intra-event total suspended concentrations were consistently well described by rainfall intensity, while FIB correlations with rainfall intensity were weaker and inconsistent between events. This study showed similar patterns of variability among the intra-event FIB statistics and comparable correlations to climatic and hydrologic variables between fecal coliform, E. coli, and enterococci. Thus, similar processes appear to influence the variability of all three indicator bacteria, suggesting that microbial models may be adaptable amongst various types of FIB.