Quantification of Chemical Transport Processes from Soil to Surface Runoff.

Although there is a conceptual understanding on processes governing chemical transport from soil to surface runoff, there are little literature and research results actually quantifying these individual processes. We developed a laboratory flow cell and experimental procedures to quantify chemical transport from soil to runoff water by each of the individual processes: i.e., 1) erosion; 2) convection under a vertical hydraulic gradient; 3) convection from surface flow or the Bernoulli effect; and 4) diffusion. We imposed different vertical hydraulic gradients by setting the flow cell to different seepage or drainage conditions. Our data confirmed the general form of the convection-diffusion equation, nevertheless, we now have additional quantitative data describing the contribution from each individual chemical loading processes under different surface runoff and soil hydrologic conditions. The results will be used to improve the water quality modeling.