title: Modeling the interannual variability of microbial quality metrics of irrigation water in a Pennsylvania stream.
abstract: Knowledge of the microbial quality of irrigation waters is extremely limited. For this reason, the US FDA has promulgated the Produce Rule, mandating the testing of irrigation water sources for many farms. The rule requires the collection and analysis of at least 20 water samples over two to four years to adequately evaluate the quality of water intended for produce irrigation. The objective of this work was to evaluate the effect of interannual weather variability on surface water microbial quality. We used the Soil and Water Assessment Tool model to simulate E. coli concentrations in the Little Cove Creek; this is a perennial creek located in an agricultural watershed in south-eastern Pennsylvania. The model performance was evaluated using the US FDA regulatory microbial water quality metrics of geometric mean (GM) and the statistical threshold value (STV). Using the 90-year time series of weather observations, we simulated and randomly sampled the time series of E. coli concentrations. We found that weather conditions of a specific year may strongly affect the evaluation of microbial quality and that the long-term assessment of microbial water quality may be quite different from the evaluation based on short-term observations. The variations in microbial concentrations and water quality metrics were affected by location, wetness of the hydrological years, and seasonality, with 15.7-70.1% of samples exceeding the regulatory threshold. The results of this work demonstrate the value of using modeling to design and evaluate monitoring protocols to assess the microbial quality of water used for produce irrigation.
authors.affiliation: USDA-ARS, Environmental Microbial and Food Safety Lab, 10300 Baltimore Avenue, BARC-East Bldg. 173, Beltsville, MD 20705, USA; Oak Ridge Institute of Science and Engineering, ARS Research Participation Program, MS 36 P.O. Box 117, Oak Ridge, TN 37831, USA. Electronic address: Eunmi.Hong@ars.usda.gov.
authors.forename: Eun-Mi
authors.initials: EM
authors.lastname: Hong
authors.affiliation: USDA-ARS, Environmental Microbial and Food Safety Lab, 10300 Baltimore Avenue, BARC-East Bldg. 173, Beltsville, MD 20705, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Shelton
authors.affiliation: USDA-ARS, Environmental Microbial and Food Safety Lab, 10300 Baltimore Avenue, BARC-East Bldg. 173, Beltsville, MD 20705, USA.
authors.forename: Yakov A
authors.initials: YA
authors.lastname: Pachepsky
authors.affiliation: Department of Bioresources and Rural Systems Engineering, Hankyong National University, Anseong, Gyeonggi 17579, Republic of Korea.
authors.forename: Won-Ho
authors.initials: WH
authors.lastname: Nam
authors.affiliation: USDA-ARS, Environmental Microbial and Food Safety Lab, 10300 Baltimore Avenue, BARC-East Bldg. 173, Beltsville, MD 20705, USA.
authors.forename: Cary
authors.initials: C
authors.lastname: Coppock
authors.affiliation: Farm Systems & Environment, AgResearch Ltd, Invermay Research Centre, Private Bag 50034, Mosgiel 9053, New Zealand.
authors.forename: Richard
authors.initials: R
authors.lastname: Muirhead
mesh_terms: D057914:Agricultural Irrigation; D000383:Agriculture; D002138:Calibration; D003198:Computer Simulation; D004926:Escherichia coli; D059022:Food Safety; D010414:Pennsylvania; D011336:Probability; D045483:Rivers; D012621:Seasons; D012987:Soil; D012988:Soil Microbiology; D013997:Time Factors; D014871:Water Microbiology; D060753:Water Quality; D014887:Weather
chemical_list: D012987:Soil
keywords: Food Safety Modernization Act; Irrigation water; Microbial quality; Water quality metrics