Rainfall-induced release of microbes from manure: model development, parameter estimation, and uncertainty evaluation on small plots Keewook Kim, Gene Whelan, Marirosa Molina, S. Thomas Purucker, Yakov Pachepsky, Andrey Guber, Michael J. Cyterski, Dorcas H. Franklin and Ryan A. Blaustein ABSTRACT A series of simulated rainfall-runoff experiments with applications of different manure types (cattle solid pats, poultry dry litter, swine slurry) was conducted across four seasons on a field containing 36 plots (0.75 × 2 m each), resulting in 144 rainfall-runoff events. Simulating time-varying release of Escherichia coli, enterococci, and fecal coliforms from manures applied at typical agronomic rates evaluated the efficacy of the Bradford–Schijven model modified by adding terms for release efficiency and transportation loss. Two complementary, parallel approaches were used to calibrate the model and estimate microbial release parameters. The first was a four-step sequential procedure using the inverse model PEST, which provides appropriate initial parameter values. The second utilized a PEST/bootstrap procedure to estimate average parameters across plots, manure age, and microbe, and to provide parameter distributions. The experiment determined that manure age, microbe, and season had no clear relationship to the release curve. Cattle solid pats released microbes at a different, slower rate than did poultry dry litter or swine slurry, which had very similar release patterns. These findings were consistent with other published results for both bench- and field-scale, suggesting the modified Bradford–Schijven model can be applied to microbial release from manure. Keewook Kim (corresponding author) Oak Ridge Institute for Science and Education, US Department of Energy, Oak Ridge, TN 37830, USA and Idaho Falls Center for Higher Education, University of Idaho, Idaho Falls, ID 83402, USA E-mail: kkeewook@uidaho.edu Keewook Kim Gene Whelan Marirosa Molina S. Thomas Purucker Michael J. Cyterski National Exposure Research Laboratory, Ecosystem Research Division, US Environmental Protection Agency, Athens, GA 30605, USA Yakov Pachepsky Environmental Microbial and Food Safety Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705, USA Andrey Guber Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lancing, MI 48824, USA Dorcas H. Franklin Agricultural Research Service, US Department of Agriculture, Watkinsville, GA 30677, USA and Department of Crop and Soil Sciences, University of Georgia, Athens, GA 30602, USA Ryan A. Blaustein Department of Environmental Science and Technology, University of Maryland at College Park, College Park, MD 20742, USA Key words | bootstrap, Bradford–Schijven release model, manure, microbe, PEST, quantitative microbial risk assessment (QMRA) 443 © IWA Publishing 2016 Journal of Water and Health | 14.3 | 2016 doi: 10.2166/wh.2016.239 Downloaded from https://iwaponline.com/jwh/article-pdf/14/3/443/394336/jwh0140443.pdf by guest on 01 May 2019