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Abstract

Two watersheds in northwestern Indiana were selected for detailed monitoring of bacterially contaminated discharges (Escherichia coli) into Lake Michigan. A large watershed that drains an urbanized area with treatment plants that release raw sewage during storms discharges into Lake Michigan at the outlet of Burns Ditch. A small watershed drains part of the Great Marsh, a wetland complex that has been disrupted by ditching and limited residential development, at the outlet of Derby Ditch. Monitoring at the outlet of Burns Ditch in 1999 and 2000 indicated that E. coli concentrations vary over two orders of magnitude during storms. During one storm, sewage overflows caused concentrations to increase to more than 10,000 cfu/100 mL for several hours. Monitoring at Derby Ditch from 1997 to 2000 also indicated that E. coli concentrations increase during storms with the highest concentrations generally occurring during rising streamflow. Multiple regression analysis indicated that 60% of the variability in measured outflows of E. coli from Derby Ditch (n = 88) could be accounted for by a model that utilizes continuously measured rainfall, stream discharge, soil temperature and depth to water table in the Great Marsh. A similar analysis indicated that 90% of the variability in measured E. coli concentrations at the outlet of Burns Ditch (n = 43) during storms could be accounted for by a combination of continuously measured water-quality variables including nitrate and ammonium. These models, which utilize data that can be collected on a real-time basis, could form part of an Early Warning System for predicting beach closures.

Bacteria in Beach Sands: An Emerging Challenge in Protecting Coastal Water Quality and Bather Health

“…For example, based on flow conditions and standard hydrologic relations in a river, one can estimate how frequently sediments near a sewage outfall that are enriched in bacteria would be resuspended into the water (98). Models of sediment and sand resuspension at beaches (eg., 99, 61) can further help to understand when these bacteria may impact water quality and may even contribute to “early warning” models (101). …”

“…Likewise, as rapid molecular methods of FIB detection are standardized for water quality regulators, these methods will need to be optimized for the detection of FIB in beach sands. If qPCR is used, important questions for moving forward with sand samples will include basic issues related to PCR (see 101, 102, for detailed review), as well as how much sample needs to be used for DNA extraction, how is the recovery of sample DNA from the extraction protocol estimated and whether to correct for this in the final cell estimation, how is inhibition of PCR (which may be highly variable among samples) handled, and what primer sets and standards should be used for the PCR assay. As with water quality samples, it will be important to determine how DNA-based estimates of cells correspond to risk-based analyses that have been based on culturable FIB in epidemiological studies.…”

Predicting E. coli concentrations using limited qPCR deployments at Chicago beaches

“…The defining characteristic of prior-day nowcast models is using FIB levels from the previous day (t−1) to predict bacteria levels for the current day ( t ). Models will also incorporate covariates or predictors to improve the accuracy of models, such as precipitation (Ackerman and Weisberg, 2003; Morrison et al., 2003), sunlight (Whitman et al., 2004), wind (Smith et al., 1999; Olyphant and Whitman, 2004), wave and tidal levels (Le Fevre and Lewis, 2003; Crowther et al., 2001), lake levels (Francy et al., 2009), turbidity (Olyphant et al., 2003), and density of humans and animals (Boehm et al., 2003; Reeves et al., 2004).…”

Meeting Report: Knowledge and Gaps in Developing Microbial Criteria for Inland Recreational Waters

“…The sites for land-based contamination of IW are many, because waterborne pollutants enter IW from multiple sites as it flows downstream. Because the volumes of water in many IW sites are relatively small and land-based pollutants are often close to these sites, the dilution of pollutants is more limited in streams than in coastal settings (Olyphant et al 2003). Parameters such as flow and turbulence vary substantially within the category of IWs and could account for more variability in FIB levels in IWs than in CWs.…”