HR: 1340h
AN: H33B-0472    [Abstracts]
TI: Assessment of Long-term Nitrate Transport to Groundwater in a Deep Alluvial Unsaturated Zone
AU: * Onsoy, Y S
EM: yonsoy@ucdavis.edu
AF: University of California, Davis Department of Land, Air, and Water Resources, One Shields Avenue, Davis, CA 95616
AU: Harter, T
EM: thharter@ucdavis.edu
AF: University of California, Davis Department of Land, Air, and Water Resources, One Shields Avenue, Davis, CA 95616
AU: Ginn, T R
EM: trginn@ucdavis.edu
AF: University of California, Davis Department of Civil and Environmental Engineering, One Shields Avenue, Davis, CA 95616
AU: Hopmans, J W
EM: jwhopmans@ucdavis.edu
AF: University of California, Davis Department of Land, Air, and Water Resources, One Shields Avenue, Davis, CA 95616
AB: As part of a comprehensive assessment of the fate and transport of applied nitrate in the vadose zone under an orchard, detailed numerical modeling was conducted to simulate transient, two-dimensional flow and nitrate transport over a seven year period to estimate potential for N leaching to groundwater. Simulations reflect two alternative N management practices with respective fertilizer application rates of 110 and 365 kg N/ha/yr, with realistic, temporally varying site boundary conditions for flow and nitrate transport utilizing data obtained from a 12-year fertilizer experiment (1982-1995) conducted at Kearney Research Site in Fresno, California. Subsurface sampling shows the presence of eight non-horizontal lithofacies based on soil color, texture, and cementation. Each lithofacies is conceptualized as a homogenous unit with soil hydraulic parameters that are defined in the form of van Genuchten model. Nitrate is treated as a tracer in the deep vadose zone based on the data interpretation of the measured biochemical properties. The results indicate that despite of the presence of the deep vadose zone, there is a profound effect of atmospheric boundary conditions on water flux to groundwater. Temporal changes in the mean pressure head both in the root zone and in the deep vadose zone are primarily controlled by irrigation wetting regimes. The results further suggest that irrigation management practices are not well integrated with the site climate conditions and crop water requirements. A substantial amount of nitrate is carried through the root zone primarily by irrigation water applications that took place after the fall fertilizer application and to a lesser extent by winter precipitation. The results indicate the need for a rigorous examination of current fertilizer application strategies, especially in light of worldwide vulnerability of shallow groundwater resources to nitrate contamination.
DE: 5104 Fracture and flow
DE: 5139 Transport properties
DE: 3210 Modeling
DE: 3260 Inverse theory
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting