Impact of agricultural practices on groundwater quality in intensive irrigated area of Chtouka-Massa, Morocco.

The Plio-Quaternary aquifer of Chtouka is located in Southwestern of Morocco. The intensive agricultural activity in Chtouka basin requires the mobilization of 94% of fresh water resources for irrigation. This overexploitation, along with the succession of drought years, sea water intrusion and various sources of pollution, affected the quality and availability of groundwater resources. Several sampling campaigns were carried out in different sites of the study area in order to investigate the spatial variation of groundwater quality. The temporal evolution of groundwater level shows that the water table was subjected to a gradual decline during the last decade, indicating an intensive exploitation mainly in irrigated areas. In the Southern part around Belfaa and the irrigated area along Massa River, nitrate concentrations exceed 50mg/L, which is the threshold set by the World Health Organization, while in the northern part around Biougra and Ait Amira, the nitrate concentration is mostly below 50mg/L indicating a relative good groundwater quality. This finding can be explained by the improvement of agricultural practices, particularly the conversion of flood and sprinkler irrigation to drip irrigation (80% of the total irrigated area) in most of the developed farms in this part of the study area. Moreover, the exploitation of groundwater from the deep aquifer, due to the increasing water demand in the region, can also explain the low chemical concentrations since the deep aquifer is not affected by anthropogenic pollutants or marine intrusion. Stable isotopes (18 O and2 H) highlight the different origins of groundwater, indicating the complexity of the aquifer system path flows, which is attributable to the intensive exploitation and irrigation water return.