The influence of rainfall on the incidence of microbial faecal indicators and the dominant sources of faecal pollution in a Florida river.

ABSTRACT

AIMS: An assessment of microbial densities in an urbanized Florida watershed was performed during a period of changing rainfall patterns to investigate the role of climate coupled with urbanization in declining water quality. METHODS AND RESULTS: Concentrations of traditional and alternative faecal indicators were assessed by standard methods over 24 months. Sources of faecal contamination were determined by antibiotic resistance analysis (ARA) of faecal coliform (FC) bacteria. Composite indices of indicator organisms based on a suite of microbial measurements were used to quantify pollution impacts in the river. ARA results found that FC from wild animal sources dominated during the drought, and the relative frequency of FC from human sources increased after cumulative rainfall increased to near-normal levels. CONCLUSIONS: Changes observed in faecal indicator densities and in FC sources during changing rainfall patterns strongly suggest a role of precipitation on the sources and extent of microbial pollution in urbanized coastal watersheds. SIGNIFICANCE AND IMPACT OF THE STUDY Bacterial source tracking coupled with a composite index of microbial contamination resulted in a more complete picture of microbial pollution within the river, as opposed to the general practice of reliance on one indicator organism. Improved land use decisions in urban areas are necessary to insure maintenance of coastal environmental health under changing climate patterns and population density.