Contamination by high concentrations of fecal indicator bacteria has been identified as one of the most common causes of surface water quality impairment in the United States; however, there is currently very little quantitative data available for use in designing watershed restoration plans that detail microbial transport in receiving waters. In this study, association with settleable particles (“partitioning”), a behavior frequently neglected in water quality models that can affect in-stream fate and transport, is more thoroughly characterized through the analysis of samples from several watersheds.
Results suggest that while intermittent, stormwater flows contribute the majority of indicator organism inputs to receiving waters, as cumulative storm loadings can be equal to several years' worth of equivalent background loadings. Loadings of microorganisms associated with settleable particles appear to be largely transported in the initial “first flush” of storm events. Observations of particle association by fecal indicator bacteria appear to be a reasonable approximation of the partitioning behavior of Salmonella; however, Salmonella bacteria, as well as the protozoan pathogens Cryptosporidium and Giardia , were readily recoverable from samples meeting current water quality standards.
Monitoring data from two suburban detention basins suggest that settleable indicator organisms and Salmonella are removed at a higher rate than their free-phase counterparts, indicating that sedimentation may be an important microbial removal mechanism in stormwater treatment structures. However, despite mean removals by one pond near the USEPA's typical rate of 65%, effluent concentrations remained several orders of magnitude greater than recommended levels.
Comparisons of free phase and settleable E. coli concentrations as measured by a culture-based technique and the quantitative polymerase chain reaction (qPCR) may support previous studies suggesting that particle association reduces cell die-off in addition to accelerating sedimentation in the water column, although further investigation of potential inhibition of the PCR reaction is required. Despite significant differences between enumeration techniques in free phase E. coli concentrations, measures of total concentration were equivalent and produced similar conclusions regarding water body impairment. Regardless of detection method or indicator organism used in assessment, compiled data indicate that all four study watersheds will be in violation of recommended standards following storm events.
|Advisor:||Characklis, Gregory W.|
|Commitee:||Noble, Rachel T., Singer, Philip C., Sobsey, Mark D., Stamm, Lola V.|
|School:||The University of North Carolina at Chapel Hill|
|Department:||Environmental Sciences & Engineering|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 70/07, Dissertation Abstracts International|
|Keywords:||Indicator organisms, Nonpoint source pollution, Stormwater, TDML program, Waterborne pathogens|
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