Quantifying Pathogen Sources in Streams by Hydrograph Separation

A new technique for quantifying pathogen sources to streams is proposed and demonstrated. Hydrograph separation is used to partition measured streamflow into surface runoff and base flow, and characteristic pathogen concentrations are assigned to each flow component along with a background source flux. The maximum-likelihood characteristic concentrations and background flux are determined from measured instream pathogen concentrations. This approach is shown to yield comparable to superior performance in predicting instream pathogen concentrations compared with much more complex terrestrial fate and transport models. Application of the proposed approach to six catchments yields Nash-Sutcliffe efficiencies of the log-transformed fecal-coliform concentrations in the range of 0.21 to 0.48. The characteristic fecal-coliform concentrations in surface runoff are in the range of 200-700 cfu/dL and the base-flow characteristic concentrations are in the range of 20-100 cfu/dL. It is shown that the frequency distribution of bacteria concentrations derived from sample measurements can sometimes differ significantly from their long-term frequency distribution. DOI: 10.1061/(ASCE)EE.1943-7870.0000394. (C) 2011 American Society of Civil Engineers.