Publication Date

2008-01-01

Availability

Open access

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil, Architectural and Environmental Engineering (Engineering)

Date of Defense

2008-04-08

First Committee Member

Dr. Helena Solo-Gabriele - Committee Chair

Second Committee Member

Dr. Junko Kazumi - Committee Co-Chair

Third Committee Member

Dr. Lora E. Fleming - Committee Co-Chair

Abstract

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.

Keywords

Enterococci; Indicator Microbes; Sources; Recreational Beaches; Water Quality

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