Theses and Dissertations

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Defense Date

2003

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Andrew Rogerson

Second Advisor

Donald McCorquodale

Third Advisor

Scott Schatz

Abstract

Analysis of samples collected bimonthly between summer 2001 and spring 2002 showed that the numbers of enterococci on three South Florida beaches were significantly higher in 'dry' sand compared to wet sand. Moreover, the wet and dry sand samples showed higher levels of fecal organisms than present in seawater. Other fecal bacteria (E. coli and total coliforms) showed similar trends. These interesting results suggest that the sand is acting as a filter and is concentrating fecal bacteria from the water column. This idea was supported by quantitative laboratory and field experiments showing that sand does actively filter fecal organisms out of the water column. However, this does not satisfactorily explain how high numbers of fecal bacteria are being amassed in the upper beach sand (='dry' sand), which is above the high water mark. The possibility that high numbers of fecal organisms were being transported in the air was tested using an Anderson Type impactor air sampler. A total of 45,000 liters of air were filtered but no airborne enterococci were detected. A more likely explanation is that there W8 increased survival of sand-trapped enteric bacteria in beach sand although the degree of survival

must fluctuate given the wide range of different physical and chemical parameters from the water line to the top of the beach. Mesocosm experiments were conducted in a controlled laboratory environment, using sterile seawater and sterile beach sand seeded with a known number of E. coli and enterococci. Parameters of interest included temperature, moisture content, salinity, particle size, and nutrient status. Generally, these mesocosm experiments showed that fecal bacteria can grow (and reproduce) in sand but slowly die in seawater alone. Additional mesocosm experiments conducted using natural seawater and beach sand containing indigenous microbiota suggested that predation had a dramatic effect on the fate of fecal bacteria in the beach environment. A series of palatability studies added additional information by showing that micropredators were capable of consuming fecal indicator bacteria in the beach environment.

Comments

Funding provided by the USEPA, awarded to A. Rogerson (R828830).

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