ABSTRACTEnterococci, recommended at the U.S. federal level for monitoring water quality at marine recreational beaches, have been found to reside and grow within beach sands. However, the environmental and ecological factors affecting enterococcal persistence remain poorly understood, making it difficult to determine levels of fecal pollution and assess human health risks. Here we document the presence of enterococci associated with beach sediment biofilms at eight south Florida recreational beaches. Enterococcal levels were highest in supratidal sands, where they displayed a nonlinear, unimodal relationship with extracellular polymeric secretions (EPS), the primary component of biofilms. Enterococcal levels peaked at intermediate levels of EPS, suggesting that biofilms may promote the survival of enterococci but also inhibit enterococci as the biofilm develops within beach sands. Analysis of bacterial community profiles determined by terminal restriction fragment length polymorphisms showed the bacterial communities of supratidal sediments to be significantly different from intertidal and subtidal communities; however, no differences were observed in bacterial community compositions associated with different EPS concentrations. Our results suggest that supratidal sands are a microbiologically unique environment favorable for the incorporation and persistence of enterococci within beach sediment biofilms.
Synopsis
Between Stirling and Fintry the beds between the Lower Old Red Sandstone and the Clyde Plateau Lavas fall naturally into four lithological formations named, from below upwards, the Gargunnock Sandstones, the Cornstone Beds, the Ballagan Beds and the Downie’s Loup Sandstones. All of these formations except the Ballagan Beds consist dominantly of sandstone and are thought to be fluvial deposits. The Ballagan Beds are alternating thin dolomites and mud-stones and are not dealt with in this paper.
The Gargunnock Sandstones rest unconformably upon the Lower Old Red Sandstone. Apart from the basal conglomerates they are uniform, brick-red sandstones with few argillaceous beds and may possibly be the deposits of braided streams which carried detritus from a source area of wind blown sand. The Cornstone Beds and Downie’s Loup Sandstones closely resemble each other despite their being separated by a considerable thickness of Ballagan Beds. Both formations comprise a series of ‘fining-upwards’ cycles, each with a lower sandstone member which is commonly white and an upper siltstone or mudstone member which is commonly red and contains caliche-like cornstones. It is thought that these formations were deposited by meandering streams. Cross-strata dip samples from each formation show that all three were laid down by currents flowing dominantly from the north and west. Statistical tests—chi-squared and Steinmetz’s (1962) method—show that only the sample s from the lower two formations are likely to belong to a single population.
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