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In this paper we present a quantitative sanitary survey of the Middle Santa Ana River, in southern California, utilizing a variety of source tracking tools, including traditional culture-dependent fecal markers (Enterococcus and Escherichia coli by IDEXX), speciation of enterococci isolates, culture-independent fecal markers (human-specific HF183 Bacteroides and Enterococcus by quantitative polymerase chain reaction, qPCR), and chemical markers of sewage and wastewater (nutrients, enantiomeric fraction (EF) of propranolol and ethylenediaminetetraacetic acid). To facilitate comparison of these different methods, data are interpreted in a loading (i.e., mass per time) framework that enables a quantitative apportionment of fecal markers and nutrients to specific source waters in the Middle Santa Ana River. Multiple lines of evidence support the hypothesis that Enterococcus in the Middle Santa Ana River originates primarily from in situ growth in streambed sediments, not from significant and persistent sources of untreated human waste. The EF of propranolol of tertiary treated wastewater effluent is in the range (0.42 to 0.71) previously reported for raw sewage, making EF of propranolol an unsuitable marker for fecal pollution, at least at this site. The human fecal marker HF183 Bacteroides was detected at a few sites, although not in a source of disinfected and tertiary treated wastewater effluent. Based on the results presented here and prior experience at other sites in southern California, HF183 Bacteroides would appear to be a candidate marker of fecal contamination for inland waters, although more qPCR measurements in disinfected wastewater effluent are needed to account for variations due to treatment plant performance and other factors. More generally, our results support the notion that regrowth of fecal indicator bacteria (FIB) in river sediments may lead to a decoupling between FIB and pathogen concentrations in the water column and thus limit the utility of FIB as an indicator of recreational waterborne illness in inland waters.

The contribution of freshwater discharge to fecal indicator bacteria (FIB) impairment of an estuarine environment can be approximated from simple, two end-member mixing models using salinity as a tracer. We conducted a yearlong time series investigation of Newport Bay, a regionally important estuarine embayment in southern California, assessing the concentrations of FIB, specifically Escherichia coli and enterococci bacteria, and salinity. In total, eight within-bay stations and one offshore control site were sampled nearly once per week and the three tributaries draining into Newport Bay were sampled approximately daily. Using salinity as a conservative tracer for water mass mixing and determining the end-member values of FIB in both the creek sites and the offshore site, we created a linear, two end-member mixing model of FIB within Newport Bay. Deviations from the mixing model suggest either an additional source of FIB to the bay (e.g. bird feces, storm drain discharge) or regrowth and/or die-off of FIB within the bay. Our results indicate that salinity mixing models can be useful in predicting changes in FIB concentrations in the estuarine environments and can help narrow the search for sources of FIB to the bay and enhance our understanding of the fate of FIB within the bay.

Field studies were conducted to characterize the concentration vs streamflow relationships (or "flow fingerprints") of fecal pollution and suspended solids in stormwater runoff from the Santa Ana River watershed, the largest watershed in southern California. The concentrations of fecal indicator bacteria and F+ coliphages (viruses infecting E. coli) exhibit little-to-no dependence on streamflow rates, whereas the concentrations of total suspended solids (TSS) exhibit a very strong (power-law) dependence on streamflow rates. The different flow fingerprints observed for fecal pollutants, on one hand, and TSS, on the other hand, reflect different sources and transport pathways for these stormwater constituents. The flow-independent nature of fecal indicator bacteria and F+ coliphages is consistent with the idea that these contaminants are ubiquitously present on the surface of the urban landscape and rapidly partition into the surface water as the landscape is wetted by rainfall. The flow-dependent nature of TSS, on the other hand, is usually ascribed to the shear-induced erosion of channel bed sediments and/or the expansion of drainage area contributing to runoff. The apparent ubiquity of fecal indicator bacteria and F+ coliphages, together with the very high storm-loading rates of fecal indicator bacteria and the low detection frequency of human adenovirus and human enterovirus, suggest that fecal pollution in stormwater runoff from the Santa Ana River watershed is primarily of nonhuman waste origin.