Rapid, highly accurate water-quality predictions can help better prevent recreationalists from getting sick at Great Lakes beaches, according to a new U.S. Geological Survey report.
USGS scientists and partners tested the performance of near-real-time water-quality assessments known as nowcasts at 42 Great Lakes beaches in 2012. According to the new report, the nowcasts perform better than the current method of predicting beach water-quality because they work faster and are more accurate. Managers can use nowcast information to make educated beach closure and advisory decisions, which benefit public health and the local economies that rely on beach recreation.
"Informed decisions can prevent beachgoers from coming into contact with contaminated water or beaches from being closed unnecessarily," said Donna Francy, USGS scientist and lead author of the report. "Like weather forecasts, nowcasts provide the percent chance that water bacteria will reach unsafe levels at Great Lakes beaches."
Managers issue water-quality advisories or beach closings in the U.S. when concentrations of indicator organisms, such as E. coli, exceed state-designated safety standards. Indicator organisms are present in sewage and waste, and signify the possible presence of pathogens, or disease-causing organisms.
Current methods to determine levels, or concentrations, of E. coli take at least 18 hours to complete because they involve culturing the organisms. During this period, E. coli concentrations in water can change dramatically. This means that a beach site may be closed unnecessarily, or an advisory may not be posted on a day when the risk of pathogen exposure is high.
Nowcasts are different because they use environmental and water-quality variables that are easily and quickly measured in near-real-time through mathematical models, rather than relying on the previous day’s E. coli concentrations. The U.S. Environmental Protection Agency developed a software program, available free to the public called "Virtual Beach," that can be used by those with little modeling or statistical knowledge to develop these mathematical models for beaches.
The USGS has cooperated with local agencies on the Ohio Nowcast project since 2006, and has been involved in past nowcast systems in Wisconsin and Indiana. During the USGS study, nowcast systems were added to beaches in Illinois and Pennsylvania.
"We found that nowcasts were effective at the majority of beaches we tested," said Francy. "The USGS will continue to collaborate with local agencies to expand nowcasting to more beaches around the Great Lakes."
For more information on nowcasts, please visit the USGS Ohio Water Science Center website on beach monitoring research.