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Beach Closures: Using Maps, Modeling, and Economic Policy Analyses to Assess Swim Closure Effectiveness at Fresh Water and Marine Beaches
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| Interpolated map of fecal indicator bacteria (FIB) density shows that some portions of a swim area have FIB densities that exceed a level considered safe (E. coli > 235 coliform-forming units per 100mL) while most of the area does not. This situation is problematic for both monitoring and swim closures decisionmaking |
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Fecal contamination of natural water bodies used for swimming is a significant public health concern worldwide. Most beach monitoring programs use fecal indicator bacteria (FIB) such as Escherichia coli and enterococci as "indicators" for the level of risk to human health. Implicit in the policies driving monitoring programs is the assumption of a strong relationship between FIB measurements taken one day and the public health risk on the following day. Recent microbiologic studies suggest, however, that FIB levels may vary over space and time in ways that may reduce the effectiveness of existing monitoring and closure strategies. As local, State and Federal regulatory agencies struggle to understand, address, and remediate local recreational water-quality problems, simple but realistic methods are needed to assess which monitoring approaches and public-health policies will produce the greatest safety with the least amount of cost and lost recreation access.
In our research, we assert that the FIB status of a beach can be modeled effectively for the purpose of evaluating water-quality monitoring efforts. The probabilities of a swim area transitioning from exceeding or not exceeding a recommended health standard can be computed from existing datasets and used in combination with risk and value estimates to predict the economic, health, and recreational impacts of various swim closure policies. Rabinovici and others (2004) describe this approach and its application to a beach in Indiana on Lake Michigan. The research showed that swim closures on average failed to produce net economic benefit for swimmers.
Policy-analysis methods help decisionmakers analyze risk by using the best available science in the context of economic trade-offs
Future work will quantify and compare the effectiveness of closure policies at fresh water beaches at Lake Michigan and marine beaches in Southern California. We are improving our policy-analysis method by applying it to multiple beach sites and including a model of visitor-behavior responses to closures (such as going to a nearby beach or delaying beach trips). We will also apply the method to investigate the performance of alternative closure policies on the basis of other factors such as lunar cycles or remotely sensed sea surface temperature. The contrasting environments of a fresh water and marine beach provide opportunities to evaluate the importance of physical and biological processes (such as dilution and inactivation of FIB) on policy performance.
Point of Contact: Sharyl Rabinovici
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