Environmental factors influencing the abundance of enterococci in Gulf Coast beach waters

摘要

Enterococci concentrations in seawater samples collected in 2010 at a Gulf Coast beach in the afternoon were significantly lower (12 MPN/100 mL) compared with morning samples (172 MPN/100 mL). The factors affecting temporal differences of enterococci concentration in beach waters were studied through five laboratory experiments analyzing beach sands, solar radiation, salinity, and turbidity. Enterococci were found in beach sands at a geometric mean of 43 MPN per 100 g of sand, demonstrated the ability to persist for extended periods of time, and increased when incubated (geometric mean of 54 MPN per 100 g sand). Solar radiation inactivated large enterococci concentrations (≥24,196 MPN/100 mL) in as little as four hours in salinities ranging from 0 to 25 parts per thousand (ppt). Increased turbidity (70 and 140 NTU) hindered the effect of solar radiation, suggesting that near-shore turbidity may promote higher enterococci concentrations. The results indicate that enterococci replenishment along Gulf coastal waters is not due to reactivation as found in other areas. This work illustrates that beach sands, solar radiation, salinity, and turbidity impact enterococci concentrations in Gulf Coast beach waters.