Model of Fecal Coliform Overland Transport From Agricultural Lands Fertilized with Animal Manure.

Assessment of the potential for manure applications to cause surface water contamination after application requires developing microbial transport models. The objectives of this work were: (i) to develop and calibrate an event-based model describing bacterial transport with runoff water at field scale; and (ii) to characterize the associated uncertainties both in model inputs and model predictions. Experiments were carried out at the USDA ARS Beltsville watershed site in Maryland. Bovine manure was broadcast at the 60 ton/ha application rate on a 3.6-ha experimental field. Fecal coliform (FC) contents were measured in applied manure at 20 locations selected randomly on the field. Both runoff volume and FC concentrations in runoff water were monitored using a flume equipped with a refrigerated sampler. Precipitation data were measured within 70 m of the experimental field. A total of 6 runoff events were recorded from May 2 through July 8, 2004. The FC concentrations were highest in the runoff water collected 7 days after the manure application and then declined over time. No clear relationship between FC content and runoff flow rates was observed. A bacteria transport add-on module was developed for the event-based kinematic runoff and erosion model (KINEROS2). The bacteria transport module described convective-dispersive overland transport and accounted for bacteria release from manure, reversible attachment-detachment to soil, and surface straining of infiltrating bacteria. The model was calibrated with the experimental runoff data and adequately described the FC transport with runoff water. Uncertainty in model predictions was evaluated that stemmed from the uncertainty in the spatial distribution of FC contents in applied manure and from the uncertainty in the probability distribution of FC in manure related to the number of manure samples taken to characterize the highly skewed distribution of FC contents in applied manure.