Development of a water quality model which incorporates non-point microbial sources

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Civil and Architectural Engineering

First Committee Member

Helena Solo-Gabriele - Committee Chair


Traditionally monitoring the sanitation of recreational coastal waters has been regulated by measuring concentrations of fecal indicator bacteria (E. coli, fecal coliforms, and enterococci). The bacteria utilized are those typically found in human feces in high concentrations. Recently the use of fecal indicator bacteria to monitor and regulate the recreational use of coastal waters has come into question, particularly in the tropical and sub-tropical marine environment (e.g., Hawaii, Guam, Puerto Rico, and South Florida) where the non-point sources (i.e. beach sand and/or sediment, animals, run-off water, and bathers) are the dominant fecal bacteria input source. In addition, little work has been done in the area of recreational water quality modeling, especially water quality models that incorporate non-point sources of fecal bacteria indicators to predict the bacterial loading in the water column.The primary objective of this dissertation was to characterize and quantify non-point sources of enterococci at a marine beach, Hobie Cat Beach, located in Miami-Dade County, Florida. This information will be incorporated into a water quality model to evaluate the relative importance of each of the non-point sources of enterococci. In order to achieve this objective, two main tasks were completed and discussed.The first task focused on estimating the concentrations of enterococci and Staphylococcus aureus shed directly off the skin of bathers and the amount of beach sand and the corresponding concentration of enterococci that can be transported by bathers into the water column. Enterococci, a common fecal indicator, and Staphylococcus aureus, a common skin pathogen, can be shed by bathers affecting the quality of recreational waters and resulting in possible human health impacts. Two sets of field studies were conducted at Hobie Cat Beach. The first study, referred to as the "Large Pool" study, involved 10 volunteers who immersed their bodies in a 4700 liter inflatable plastic pool filled with off-shore marine water during four 15 minute cycles with exposure to beach sand in cycles 3 and 4. The second study, referred to as the "Small Pool" study involved 10 volunteers who were exposed to beach sand for 30 minutes before they individually entered a small tub. After each individual was rinsed with offshore marine water, sand and rinse water were collected and analyzed for enterococci. Results from the "Large Pool" study showed that bathers shed concentrations of enterococci and S. aureus on the order of 6x105 and 6x106 colony forming units per person in the first 15 minute exposure period, respectively. Significant reductions in the bacteria shed per bather (50% reductions for S. aureus and 40% for enterococci) were observed in the subsequent bathing cycles. The "Small Pool" study results indicated that the enterococci contribution from sand adhered to skin was small (about 2% of the total) in comparison with the amount shed directly from the bodies of the volunteers.The second task focused on developing the algorithms for simulating non-point sources of enterococci specific to the study site including sand, dogs, birds, water runoff, and bathers, and the application of the developed algorithms to quantify the enterococci loads associated with each one of the sources. The five dominant non-point sources of enterococci were described and expressed as mathematical equations along with their variables. Estimates for all variables were defined and computed using the most recent literature, studies and direct field measurements values. The task showed that water runoff is the most significant non-point source contributing enterococci into the water column followed by dogs, sand, birds, and bathers respectively.Overall this dissertation suggests that non-point sources of fecal bacteria indicators contribute significant amounts of enterococci into the water column and they should thus be considered when designing water quality models. Regulatory beach monitoring programs should include site specific predictive water quality models in order to assess the sanitation of coastal recreational water bodies.


Biology, Microbiology; Engineering, Civil; Health Sciences, Public Health; Engineering, Environmental

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