First attempts for predicting seasonal nitrate concentration variations atMnasra aquifer (Morocco)

We have developed a simple mechanistic simulation model for predicting in-s itu unsaturated water and nitrogen transfers in a large area (7760 ha) loca ted at Mnasra zone. A new physically-based approach was used for determinin g accurate soil hydraulic properties. It can be applied for surveying large areas using the easily measured soil textural and structural data. The mea n hydraulic parameters were used for solving unsaturated water and nitrogen transfer equations. Errors resulting from omitting groundwater flow modell ing and spatial variability of the saturated hydraulic conductivity were ne gligible. Comparison between observed and calculated seasonal groundwater n itrate 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 o f groundwater contamination were observed during winter which coincided wit h heavy rainfall and the absence of vegetation cover.