The Role Of Roadside Ditches As Conduits Of Fecal Indicator Organisms And Sediment To Downstream Drinking Water Supply Systems

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Bacterial and sediment pollution is widespread in US waters, contributing to increases in human disease as well as aquatic ecosystem degradation. Identifying pathways of pollutants from source to stream may help improve water quality management. Few studies have examined the impacts of roadside ditch networks on water resources, though ditches are ubiquitous. The goal of this study was to determine if roadside ditches are conduits for fecal indicator organisms and sediment and if land use, specifically manure amendment, affects these concentrations and loadings. Seven roadside ditches were monitored for Escherichia coli (E. coli) using ISCO(TM) automated water samplers and the Idexx Colilert(TM) system, as well as total suspended solids, pH, conductivity and flow for one year in central New York. Ditches were either adjacent to manure amended agricultural fields or predominately forested land. E. coli concentrations in ditch water samples following storms ranged from undetectable to [GREATER THAN] 241,960 MPN/100mL and frequently exceeded NYS DEC and US EPA recommendations. Overall, ditches adjacent to manure amended fields had significantly higher concentrations and loads of E. coli than forested sites, though this was dependent on the season. The concentrations were also unexpectedly high in the forested sites, with possible sources including wildlife, pets, septic wastes and livestock. Peak concentrations were observed in both summers following manure spreading with declining levels thereafter, but viable organisms were detected throughout the year. Viable E. coli were also present in ditch sediment between storm events and therefore were available for resuspension and transport. Total suspended solids concentrations reached as high as 52.2 g L-1 and were overall significantly higher for agricultural sites as compared to forest sites. There was a complex association between total suspended solids and E. coli concentrations. These findings gain significance when placed in the broader framework that roadside drainage networks are acting to rapidly shunt stormwater runoff to downstream drinking water supplies. As a result, recommendations to reduce pathogen transport and improve water quality should focus on reducing farm runoff, using buffer strips or constructed wetlands and improving roadside ditch management.

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