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 (delta O-18, delta H-2) and stable isotopes of nitrate (delta N-15, delta O-18), 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 delta N-15 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 NO3 with high contents in many sites. Some domestic wells showed the highest NO3 concentrations. The field investigation reveals a practise where domestic wastewater is being poured directly into traditional septic tanks. N-15 results indicate mixing origins of nitrate related to sea-water intrusion, NH4 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.