The characterization of contaminant transport on a central Texas research facility

Abstract

Non point source (NPS) pollution is a growing concern in the United States and the world. Sediment, nitrogen, phosphorous and pesticides are the major contributors to the non-point source pollution problem in the United States (U.S. EPA, 1983; Mostaghimi et al., 1988). The purpose of this study was to monitor the fate of certain agricultural chemicals and sediment on a research plot located in a river floodplain in central Texas. The site provided the unique opportunity to measure the quantity and quality of runoff from an actual river floodplain. A 0.89-ha agricultural research plot located on the Brazos River floodplain was instrumented for surface water runoff studies. The chemicals applied, pre-emergent, were atrazine, bromide, and a granular fertilizer which contained ammonium and nitrate. Bromide was applied as a non-reactive tracer. The field was planted in corn and during the four month growing season surface water runoff samples were analyzed for these four chemicals and total solids. The site is located on the Texas A&M research farm approximately 10 miles west of the main campus in College Station, Texas. The soil surface layer is a Ships Clay, which has high shrink/swell properties. The GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model was used to simulate runoff events, chemical and sediment losses (Leonard et al., 1987). The study measured little atrazine in the runoff (0. 15 % of applied). The bromide and nitrate losses were 4.0 % and 4.6 I/o, respectively, with ammonium losses of 0.13 %. The lower percentage of ammonium can be attributed to volatilization and its oxidation to nitrate (Padgett and Leonard, 1993; Ashraf and Borah, 1992). The amount of atrazine lost from the field due to sediment transport was estimated as 1.0 % of the initial amount applied using a fraction of organic carbon of 1.0 %. Model simulation results included surface runoff and atrazine, bromide, nitrate, ammonium, and sediment losses. The correlation coefficients for simulated versus measured characteristics ranged from 0.35 to 0.83, indicating poor agreement between the measured results and the simulated results.