Fate and Transport of Enterococcus spp. at a Tropical Sandy Beach

Most of Puerto Rico’s beaches are affected by episodes of fecal contamination due to water inflow from polluted streams, waste discharge or stormwater runoff. The current operational strategy to assess swimming conditions consists of taking in-situ samples every other week through a process which requires at least 18 hours of incubation. Fecal bacteria concentration in coastal waters might change in a short timeframe, meaning once the results are obtained, they may no longer represent the actual state of the beach. When fecal bacteria are discharged at the sea, the conditions they encounter inhibit their growth and increase their mortality rate. To this end, a 48-hour sampling campaign was conducted at Rincón Public Beach in October 2016 to better understand the presence of Enterococcus spp. along the coastline during average metocean conditions. Hourly in-situ water samples were taken at eight stations along the beach, including two freshwater streams. Results show that 1) instances of high stream flow are consistent with high Enterococci concentration; 2) high bacteria concentration remain at the beach for 12 hours after a significant rainfall event; and 3) transport of bacteria is consistent with the dominating currents resolved by an ADCP. Water quality simulations are currently under development using Delft3D to predict the dispersion and decay of Enterococcus spp. at the site. Once validated and fine-tuned with the above-mentioned data set, this model will be used to simulate fate and transport of Enterococcus spp. for additional metocean conditions.