First Attempts for Predicting Seasonal Nitrate Concentration Variations at Mnasra Aquifer (Morocco)

Abstract

We have developed a simple mechanistic simulation model for predicting in-situ unsaturated water and nitrogen transfers in a large area (7760 ha) located at Mnasra zone. A new physically-based approach was used for determining accurate soil hydraulic properties. It can be applied for surveying large areas using the easily measured soil textural and structural data. The mean hydraulic parameters were used for solving unsaturated water and nitrogen transfer equations. Errors resulting from omitting groundwater flow modelling and spatial variability of the saturated hydraulic conductivity were negligible. Comparison between observed and calculated seasonal groundwater nitrate concentrations, during the expedition of 1992/93 and 1993/94, proved the simulation model performance and that the application rate of 120 kg N ha−1 per annum at agricultural soils should be reduced. The major risk of groundwater contamination were observed during winter which coincided with heavy rainfall and the absence of vegetation cover.