Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/18/1999
Publication Date: N/A
Citation: Zhang, X.C., Norton, L.D., Lei, T., Nearing, M.A. 1999. Coupling mixing zone concept with cde to model chemical transport from soilsolution to surface runoff. Transactions of the ASAE. 42(4):987-994. Interpretive Summary: Use of agricultural chemicals such as pesticides and fertilizers has substantially increased crop productivity, but it has also degraded our environmental quality, especially surface water quality. Development of a predictive tool which can be used to estimate contamination potentials by agricultural chemicals is important for preserving our precious water resources. Based on our experimental study, we have developed a new approach or method which can be used to predict pesticide and fertilizer losses in surface water runoff from farm lands. This study further evaluated our method by comparing predicted chemical concentration or loss with measured data. Results showed that our method worked well in estimating chemical losses in surface water runoff. This research provides useful information to predictive tool or model developers to develop better tools for use in predicting chemical loss in water runoff. These tools will help environment conservationists to select the best management plans for preserving our environments.
Technical Abstract: Modeling chemical transfer from soil to surface runoff is essential for developing a surface water quality model which can be used to assess pollution potentials of agricultural chemicals. Chemical transport to runoff can be modeled as a two-rate process. A fast rate subprocess, which prevails at early stages of rainfall, causes an exponential depletion of chemicals from the mixing zone. A slow rate subprocess, which becomes significant under poorly drained conditions, transports chemicals into the mixing zone from the soil below. The two-rate process can be described by coupling the mixing zone concept with the convection diffusion equation (CDE). We evaluated this coupling approach by comparing predicted results with measured bromide concentration data. A finite element scheme was developed to solve the CDE in conjunction with a near-surface boundary condition derived from the mixing concept. Overall results showed the coupling approach satisfactorily predicted bromide concentrations in both surface runoff and soil solution. The coupling approach, while allowing for direct use of the mixing concept under free infiltration conditions, refines the mixing concept for use under poorly drained conditions.