Modeling nitrogen dynamics in unsaturated soils for evaluating nitrate contamination of the Mnasra groundwater

Groundwater pollution by nitrates is one of the most significant environmental problems in the agricultural fields of the Mnasra area. Evaluation of the nitrate contamination of the groundwater requires knowledge of the nitrogen dynamics in the vadose zone environment. This study aims, through modeling and field experimental data, to evaluate the nitrate contamination of the groundwater. An unsaturated zone model is developed to describe nitrogen dynamics in the field. The model was kept simple and uses parameters that can be found in the literature or calculated from commonly measured physical and chemical soil properties. The simulation model proved that it is a valuable tool for assessing water and nitrate fluxes leaching from the unsaturated zone of the Mnasra agricultural soils. When the dilution of the leached nitrate in groundwater was not substantial, the temporal integration of these fluxes was satisfactory; the model qualitatively simulated seasonal nitrate concentrations sampled at different observation wells within a large area. However, it would be necessary to couple the actual unsaturated zone model with a saturated zone one when significant lateral groundwater fluxes could carry high nitrate concentrations from outside the study area towards the Atlantic Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.