Assessment of water quality and nitrate source in the Massa catchment (Morocco) using δ 15N and δ 18O tracers.

The Massa basin in Morocco suffers from water scarcity and water quality degradation largely due to salinity and nitrate contamination. In this study, a multi-tracer approach, was used that integrated water chemistry, stable isotopes of water (δ18O, δ2H) and stable isotopes of nitrate (δ15N, δ18O), to investigate mineralization and nitrate contamination in the Massa catchment. The main objective was to identify, for the first time in the area, water pollution sources, with an emphasis on nitrate-originated contamination using the δ15N isotope. Water samples were collected from rivers, dams, wells, boreholes and springs, from different parts of the area (irrigated farms, along Massa River, Anti-Atlas Mountains and coastal areas). The results show a large variability of water mineralization in space indicating rock-water interaction, sea-water intrusion and anthropogenic influence. The lowest mineralization value is measured in spring water located in the Anti-Atlas Mountains while the highest one is measured in Massa River. The results also show a large variability of NO 3 with high contents in many sites. Some domestic wells showed the highest NO 3 concentrations. The field investigation reveals a practise where domestic wastewater is being poured directly into traditional septic tanks. 15N results indicate mixing origins of nitrate related to sea-water intrusion, NH 4 fertilizers and manure septic which constitute the main issue. Our results will be an essential recommendation for decision-makers for the implementation of wastewater treatment systems before they are discharged into the environment. Improving individual septic systems is also a necessary condition. • Stable isotopes of water show that surface waters are impacted by evaporation due to the aridity of climate and that recharge area of the aquifer is located in local high elevations. • Water quality is impacted by nitrate contamination. • δ15N values, used for the first time in this area, indicate that the main sources of nitrate are septic and manure. • Results indicate rock-water interaction, sea-water intrusion and anthropogenic influence. [ABSTRACT FROM AUTHOR]