Nitrate contamination of alluvial groundwater in the Ziz basin, southeastern Morocco

Abstract

Nitrate pollution usually originates from diffused sources, like intensive agriculture and unsewered sanitation or point sources, such as septic tanks and human and animal wastes. This study aims to investigate the degree of the influence of nitrate contaminants sources on groundwater. The groundwater in the Ziz basin has been polluted by municipal wastewater, and agricultural activities. The nitrate concentrations at fifty seven sampling points within the basin, ranged from 0 mg/L to 315.6 mg/L. In comparison to the Moroccan drinking water standards based on World Health Organization (WHO) standards of 50mg/L, 25% of water samples showed higher nitrate concentrations above 50 mg/L and 36 % samples exceed the recommended limit of 25 mg/L, while, nitrates concentrations of 64% water samples were low than 25 mg/L. The analysis of nitrates variations suggests a contribution of the irrigation return flow containing nitrogenous compounds which can migrate downward from the unsaturated zone to groundwater, and transferring contaminants, and the high level of nitrates around the population agglomerations, which are not served by sewage systems, constitutes an additional source of nitrate pollution due to widespread and common use of septic tanks for domestic waste water. The nitrate pollution of groundwater in the Ziz Basin has negative effects on water quality, mainly, for the population that depends extensively on groundwater for drinking and other domestic needs. Thus, all agricultural and groundwater management measures should be applied to secure a sufficient water quality.