Abstract
Fecal indicator bacteria, such as total coliforms and E. coli, are a challenge to control in urban and rural stormwater runoff. To assess the challenges of improving bacterial water quality standards in surface waters, microcosm experiments were conducted to assess how decay rates of total coliforms and E. coli are affected by sediments and associated organic matter. Samples were collected at a lake embayment to create laboratory microcosms consisting of different combinations of unsterilized and sterilized water and sediment. Calculated first-order decay rate constants ranged from 0.021 to 0.047 h-1 for total coliforms and 0.017 and 0.037 h-1 for E. coli, depending on how each microcosm was prepared. It is evident that sediment in contact with the water column decreases bacteria decay rate, showing that care should be taken when designing stormwater treatment measures. In addition, high organic carbon content in the sediment temporarily increased bacteria concentrations in the water column. The results demonstrate that stormwater treatment measures, such as extended detention basins and constructed wetlands, must hold water for several days to allow for reduction of bacterial concentrations to acceptable levels. In addition, to troubleshoot detention basins and constructed wetlands for causes of high effluent bacterial concentrations, analyses of sediment, organic carbon, and water column depth should be conducted.
Highlights
The presence of fecal indicator bacteria (FIB) in surface waters can have detrimental consequences to human and economic health
The results demonstrate that stormwater treatment measures, such as extended detention basins and constructed wetlands, must hold water for several days to allow for reduction of bacterial concentrations to acceptable levels
The microcosms were created according to assumptions that sediment and its associated nutrients, together with nutrients in water, would prolong the survival of FIB in the water column
Summary
The presence of fecal indicator bacteria (FIB) in surface waters can have detrimental consequences to human and economic health. The denotation of “pathogens” includes known pathogenic organisms but, more commonly, FIB, such as total coliforms, fecal coliforms, Escherichia coli (E. coli), and enterococci bacteria. Solutions to controlling pollution to surface waters from stormwater runoff are called Best Management Practices (BMPs), known as Stormwater Control Measures (SCMs), and include a range of strategies from educating the public to cleaning animal feces from paved surfaces to constructing stormwater treatment detention basins and wetlands. Current efforts to reduce concentrations of FIB using stormwater BMPs have yielded inconsistent results. Some monitoring efforts of the same type of BMP but in different locations yield opposite results [7], and some BMPs perform well in all seasons except summer [8]
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