Beach advisories are issued at recreational beaches when the water quality exceeds regulatory limits for the indicator organism, enterococci. Elevated levels of enterococci have been observed at Hobie Cat Beach, the study marine beach site, located on Virginia Key, Florida. The study site represents a classic non-point source sub/tropical marine recreational beach area with high human and animal use, representative of many beaches worldwide in sub/tropical areas. The dissertation consisted of two separate but related studies: the first to identify environmental and geographic factors, and the second to evaluate the impact of known animal sources of enterococci. The first efforts were made to identify the geographic location of the source of enterococci to the beach waters and to assess the environmental factors that impact the variation in concentrations observed at the site. These environmental factors and conditions include: proximity to shoreline, tidal changes, impacts of runoff, and sunlight intensity. Enterococci were enumerated by traditional membrane filtration or the chromogenic substrate method. Overall, results showed that the source of enterococci to the study beach was geographically located within the inter-tidal zone. These results suggest that the wash-in of sediments and accompanying pore waters (where the pore water is the water filling the spaces between grains of sediment) from the inter-tidal zone play a major role in controlling enterococci levels within the water column. Wash-in occurs through both tidal fluctuations and runoff. The second effort evaluated non-point sources, including animals, which are known to contribute to elevated levels of enterococci in recreational marine beach waters. Specifically, feces from dogs, birds, and shrimp mounds were collected from the beach; additional bird fecal samples were collected from both a local zoo and bird rehabilitation center. Fecal samples were weighed gravimetrically, and enumerated for enterococci using traditional membrane filtration method. The total numbers of animals which frequented the site were obtained through camera image analysis and in-field visual counting surveys. The highest enterococci concentrations were observed in dog feces (avg. 7.4 x 10^6 CFU/g dry feces), then birds (avg. 3.3 x 10^5 CFU/g dry feces) and the lowest measured levels of enterococci were observed in shrimp fecal mounds (2.0 CFU/g dry feces on average). A comparison of the microbial load (CFU per fecal event) showed that 1 dog fecal event was equivalent to 6,940 bird fecal events or 3.2 x 10^8 shrimp fecal events. Given the abundance of animals observed on the beach, these study results suggest that dogs are the largest contributing source of enterococci to the beach site (6.3 x 10^11 CFU per day during weekends and 2.9 x 10^11 CFU per day during weekdays), with humans (4.6 x 10^9 CFU per day during weekends and 4.8 x 10^8 CFU per day during weekdays) and birds (2.7 x 10^8 CFU per day) serving as secondary contributors. Shrimp served as an insignificant source (1.9 x 10^4 CFU per day). When maximum daily contributions were considered, dogs contributed the highest proportion of enterococci (99.2%) compared to humans (0.72%), birds (0.04%), and shrimp (<0.04%). Beach management efforts at the study site should thus focus on requiring dog owners to properly dispose of dog feces deposited at the beach.

Enterococci levels are measured to assess water safety in recreational beaches through a state surveillance program. This surveillance informs the public of beach safety, yet the sampling methodology is limited to only making an advisory posting one sample at a time. This methodology poses a challenge for managers such as: 24 hour advisory waiting period, untested days and extreme variability of enterococci levels in the environment. Therefore, there is a need to integrate adaptive management methodologies that can assist managers to proactively assess beach water safety. This study explored the utility of a historical analysis and logistic regression modeling as a method and as an advisory tool. The analysis utilized 10 years of enterococci surveillance data (7,422 samples) from 15 sub-tropical beaches in Miami-Dade County, Florida. It was determined that Miami beaches have historical low enterococci exceedance counts (3% of total data), that there are some beaches that are more propense to higher exceedance counts than others and that the wet season overall did not readily appear to affect exceedances counts. The logistic regression model utilized an exceedance/ non-exceedance dichotomy and spatial, temporal and annual variables. The model indicated that the overall range of probability of having an exceedance for the sampled beaches under each variable was less than 10%. The ability to use this model and get probability results showed that logistic regression is an accurate statistical tool that provides the historical probabilities of an exceedance on a beach and can complement a random sampling methodology. Furthermore it’s a simple and inexpensive methodology that provides the ability to categorize and recognize patterns estimating the surveillance-managed sample sites probabilities that provides foresight as to where to focus resources in order to reduce risk and facilitating beach management. Through the use of a historical analysis and a logistic regression model, it is possible to address dynamic recreational beach environments with a large-scale view and in a historically comprehensive manner, instead of only making management choices sample by sample.