Affiliation:
1. Department of Civil, Architectural and Environmental Engineering, University of Miami, Coral Gables,1 and
2. Nova Southeastern University, Fort Lauderdale,2 Florida
Abstract
ABSTRACT
Sources of
Escherichia coli
in a coastal waterway located in Ft. Lauderdale, Fla., were evaluated. The study consisted of an extensive program of field measurements designed to capture spatial and temporal variations in
E. coli
concentrations as well as experiments conducted under laboratory-controlled conditions.
E. coli
from environmental samples was enumerated by using a defined substrate technology (Colilert-18). Field sampling tasks included sampling the length of the North Fork to identify the river reach contributing high
E. coli
levels, autosampler experiments at two locations, and spatially intense sampling efforts at hot spots. Laboratory experiments were designed to simulate tidal conditions within the riverbank soils. The results showed that
E. coli
entered the river in a large pulse during storm conditions. After the storm,
E. coli
levels returned to baseline levels and varied in a cyclical pattern which correlated with tidal cycles. The highest concentrations were observed during high tide, whereas the lowest were observed at low tide. This peculiar pattern of
E. coli
concentrations between storm events was caused by the growth of
E. coli
within riverbank soils which were subsequently washed in during high tide. Laboratory analysis of soil collected from the riverbanks showed increases of several orders of magnitude in soil
E. coli
concentrations. The ability of
E. coli
to multiply in the soil was found to be a function of soil moisture content, presumably due to the ability of
E. coli
to outcompete predators in relatively dry soil. The importance of soil moisture in regulating the multiplication of
E. coli
was found to be critical in tidally influenced areas due to periodic wetting and drying of soils in contact with water bodies. Given the potential for growth in such systems,
E. coli
concentrations can be artificially elevated above that expected from fecal impacts alone. Such results challenge the use of
E. coli
as a suitable indicator of water quality in tidally influenced areas located within tropical and subtropical environments.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
372 articles.
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