A parameter estimation tool for nonlinear transport and degradation processes of xenobiotics in soil

The environmental fate of xenobiotics in soil is influenced by a number of processes including leaching, degradation, sorption and volatilization. Mat hematical modelling of these processes usually leads to instationary partia l differential equations coupled with nonlinear ordinary differential equat ions. In these models typically unknown parameters have to be identified fr om measurements. Here, we present new, efficient numerical methods for inve rse modelling, in particular for parameter estimation in one-dimensional mu ltispecies transport-reaction systems. Partial differential equations are transformed into systems of ordinary dif ferential equations using the method of lines. Finite differences are emplo yed for spatial discretization. Discretization in time is done by multiple shooting. Result is a large scale, finite dimensional, nonlinear constraine d least-squares problem which can be efficiently solved by a reduced genera lized Gauss-Newton method. These methods have been implemented in the new p arameter estimation tool ECOFIT. Several practical applications of ECOFIT are presented. Based on column or field experimental data of matric potentials/water contents and pesticide c oncentrations transport parameters (hydraulic parameters of the water trans port model, hydrodynamic dispersion coefficients etc.) and environmental fa te parameters of xenobiotics (sorption constants, degradation rates etc.) c an be estimated. A statistical analysis of the solution is given.