Modeling potential future changes in microbial water quality and the effectiveness of management responses.
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Most commonly occurring waterborne pathogens (e.g., pathogenic Escherichia coli and Cryptosporidium) in the United States are linked to fecal sources (e.g., humans, livestock, wildlife). Potential future increases in temperature and changing precipitation patterns could alter survival and transport to waterbodies, presenting a threat to human health through drinking water and recreational use. Understanding responses is complicated because transport depends on uncertain future changes in hydrology, driven largely by variability in projected future precipitation, together with changes in air and water temperature, which affect survival. Human activities affecting sources on land, including urban development and agriculture, are also key factors affecting fate and transport. Managing the risk of future microbial impairment requires a better understanding of future changes, and the effectiveness of management responses in different regional and watershed settings. This study assesses potential changes in microbial water quality and management responses in 2 small agricultural basins – the Chippewa watershed, Minnesota and the Tye watershed, Virginia. The Hydrologic Simulation Program in FORTRAN (HSPF) is used to: (a) simulate fecal indicator bacteria (FIB: indicate the potential presence of pathogenic organisms) responses to a range of mid-century climate realizations; and (b) evaluate the effectiveness of commonly applied best management practices at mitigating impacts. Results suggest that hotter and drier conditions will reduce survival and in-stream loads; however, more violations of concentration-based microbial water quality standards could occur due to lower flow volumes which reduce in-stream dilution of point source discharges. Increases in FIB load are associated with greater transport from nonpoint sources in response to wetter and slightly warmer future conditions. The results of this work can help characterize future risk and inform decision makers about potential management responses needed to meet existing microbial water quality standards under a range of plausible but uncertain future conditions. Disclaimer: The views expressed in this abstract are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency.