ESTIMATING TRANSPORT OF CHEMICALS FROM SOIL TO PONDING WATER

We simulate the accumulation of a chemical transported from soil to pe nding water. We consider one-dimensional convective-diffusive solute t ransport in water and soil, The results are compared with those of mod els which simulate an instantaneous mixing in the surface water layer and the surface solute flux dependent on the difference in solute conc entrations between soil and water. Numerical inversion of Laplace tran sforms is used to obtain the simulation results for all models. Result s of this work show that the relative effect of diffusion on the accum ulation of a solute in pending water may be significant at infiltratio n rates that are not uncommon in agriculture practice. The results als o imply that locations with low infiltration rates within fields may h ave a large effect on the overland accumulation of chemicals. (C) 1998 Elsevier Science B.V. All rights reserved.