Monday, November 13, 2006 - 2:30 PM
90-5
Runoff Transport of Manure-Borne Fecal Coliforms and Chloride: Fied Plot Experiment and Modeling.
Andrey Guber1, D.R. Shelton2, Y.A. Pachepsky2, and K.A. Sefton3. (1) Dept of Earth and Environmental Sci, Univ of California, A135 Bourns Hall, Riverside, CA 92521, (2) USDA-ARS-BA-ANRI-EMSL, Bldg. 173, Rm. 203, BARC-EAST, Powder Mill Road, Beltsville, MD 20705, (3) USDA-ARS-BARC-EQL, 10300 Baltimore Av, Bldg.007, Beltsville, MD 20705
Fecal coliform (FC) and chloride (Cl) transport from dissolving manure applied on hillslopes was studied in the field plot scale and simulated. Two-by-six meters runoff plots were set in triplicate on vegetated and bare 20% slopes with sandy loam and clay loam soils in the ARS BARC. Fresh bovine manure was applied at the top 30-cm wide strip of runoff plots. Rainfall (ca. 6 cm per hour) was simulated for 1-1.5 hours. Runoff was collected from troughs at the edge of runoff plots at five-min intervals and analyzed for Cl and FC content. The volume of runoff, Cl and FC recovery was smaller from vegetated than from bare plots, and from sandy loam than from clay loam plots. The Bradford-Schijven model was employed to simulate Cl and FC release from manure, advective-dispersion equation (ADE) for modeling of Cl and FC transport with runoff. Kinematic wave equation simulated runoff. Parameters of water infiltration and ADE were calibrated with the experimental data. An acceptable fit to the experimental data was obtained for vegetated plots. Fitted parameters were different for Cl and FC. Release rate from manure was less for FC, than for CL at all plots. Despite the difference in release rate, Cl and FC appeared simultaneously in relatively high concentrations in the first runoff water sample at bare plots. The advective-dispersion equation failed to simulate high Cl and FC content at the earliest runoff stage. The model tended to overestimate Cl and FC content right after the runoff started and to underestimate Cl and FC content at late runoff stage. Overall, the preferential flow model should be considered to simulate fast Cl and FC transport with runoff from the bare slopes whereas the regular ADE appears to be applicable to simulate this transport at the vegetated slopes.