Ecological Control of Fecal Indicator Bacteria in an Urban Stream

Abstract

Fecal indicator bacteria (FIB) have long been used as a marker of fecal pollution in surface waters subject to point source and non-point source discharges of treated or untreated human waste. In this paper, we set out to determine the source(s) of elevated FIB concentrations in Cucamonga Creek, a concrete-lined urban stream in southern California. Flow in the creek consists primarily of treated and disinfected wastewater effluent, mixed with relatively smaller but variable flow of runoff from the surrounding urban landscape. Dry and wet weather runoff contributes nearly 100% of FIB loading to Cucamonga Creek, while treated wastewater contributes significant loading of nutrients, including dissolved organic carbon (DOC), phosphorus, nitrate, and ammonium. FIB concentrations are strongly positively correlated with DOC concentration in runoff (Spearman's rho >or= 0.66, P <or= 0.037), and microcosm studies reveal that the survival of Escherichia coli and enterococci bacteria in runoff is strongly dependent on the concentration of both DOC and phosphorus. Below threshold concentrations of 7 and 0.07 mg/L, respectively, FIB die off exponentially (die-off rate 0.09 h(-1)). Above these thresholds, FIB either grow exponentially (growth rate 0.3 h(-1)) or exhibit a periodic steady-state in which bacterial concentrations fluctuate around some mean value. The periodic steady-state pattern is consistent with a Lotka-Volterra predator-prey oscillation model, and the clearance rate (20 microL predator(-1) h(-1)) obtained by fitting the model to our data is consistent with the hypothesis that predacious protozoa regulate FIB concentrations in runoff at high DOC concentrations. Collectively, these results indicate that FIB impairment of Cucamonga Creek is best viewed as an ecological phenomenon characterized by both bottom-up and top-down control.

Indigenous Microbiota and Habitat Influence Escherichia coli Survival More than Sunlight in Simulated Aquatic Environments

“…This observation indicates that, within the confines of our experimental design, the effect of indigenous microbiota on E. coli survival in the water column is influenced by the water type. While protozoan bacterivory is a recognized contributor to the decline of bacterial populations in aquatic environments (29,(59)(60)(61)(62)(63), the relative magnitudes of impact of protozoan presence on E. coli survival in sunlight-exposed freshwater and seawater systems have not been previously described. Interestingly, in the seawater mesocosms, the matrix (water/ sediment) had a greater effect on the persistence of E. coli than the presence of indigenous microbiota.…”

Enterococci in the Environment

“…Notably, lower rates of grazing were observed for Gram-positive organisms (including E. faecalis) than for E. coli (75,126,169,170,253). Nonetheless, several experiments conducted in mesocosms and environmental chambers documented decreases in concentrations of enterococci in marine (29,75,146,229) and freshwater (75,229,317) environments in the presence of protozoa ( Table 2).…”

Indicator and Pathogen Removal by Low Impact Development Best Management Practices

“…Many abiotic and biotic conditions such as sunlight/Ultraviolet (UV) radiation, temperature, osmotic stress, moisture content, nutrient availability, and biotic competition can affect persistence of microbes in the environment [11,18,19]. Sunlight/UV exposure and moisture content were found to be important for E. coli survival in biofilter surface layers, while temperature and the presence of indigenous microbial communities greatly affected E. coli at all biofilter depths [20].…”