Estimation of KINEROS Parameters with Pedotransfer Functions and Associated Uncertainty in Modeling of Fecal Coliform Overland Transport.

Assessment of the potential for manure applications to cause surface water contamination requires developing microbial transport models and estimation of the model parameters. The objectives of this work were: (i) to develop and calibrate an event-based model describing bacterial transport with runoff water at field scale; (ii) to estimate the soil hydraulic parameters of the model using different pedotransfer functions (PTFs), and (iii) evaluate uncertainty in fecal coliform overland transport associated with spatial variability of soil texture and PTFs. 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 in 70 m from the experimental field. The FC concentrations were highest in the runoff water collected 7 days after the manure application and then declined over time. Soil texture was measured in 34 samples taken randomly from the field at depth of 10 cm. Nine PTFs were used to estimate soil hydraulic properties. 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. Both spatial variability in soil texture and PTFs caused uncertainty in predictions of FC transported with runoff water. More uncertainty was associated with PTFs than with spatial variation in soil properties