Stochastic analysis of water flow and pesticides transport in a field experiment

Analysis of water flow and transport of one conservative (Bromide) and two reactive [Bromacil (BMC) and Terbuthylazine (TBA)] solutes in a field experiment at Bet Dagan site, Israel is carried out. The study is based on the early developed column model of flow and transport in unsaturated soil which is expanded here to incorporate the redistribution stage. The transport of reactive solute is modeled by assuming three mechanisms: advection by water flow, equilibrium sorption and linear decay. The solutions of flow and transport equations are derived for a infiltration–redistribution cycle and averaged further by regarding the soil properties (saturated conductivity, saturated and residual water contents) and the rate of water application by irrigation on the soil surface as independent random values. The most extensive experimental data are concentration measurements in 20 vertical profiles at a few depths and times. These data are used in order to evaluate the spatially averaged concentration as function of time and depth. Flow parameters are identified by a best fit between the model and measured mean concentration of the conservative solute. The same procedure is used to identify the reactive properties (partition coefficient, half life) of the reactive solutes.