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

Saadou Oumarou Danni; Lhoussaine Bouchaou; Ahmed Elmouden; Yassine Ait Brahim; Baudelaire N'da

doi:10.1016/j.apradiso.2019.108859

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

Appl Radiat Isot. 2019 Dec:154:108859. doi: 10.1016/j.apradiso.2019.108859. Epub 2019 Aug 13.

Authors

Saadou Oumarou Danni¹, Lhoussaine Bouchaou², Ahmed Elmouden², Yassine Ait Brahim³, Baudelaire N'da²

Affiliations

¹ Applied Geology and Geo-Environment Laboratory, Faculty of Sciences, Ibn Zohr University, BP 8106, Agadir, Morocco. Electronic address: saadou.danni@uiz.ac.ma.
² Applied Geology and Geo-Environment Laboratory, Faculty of Sciences, Ibn Zohr University, BP 8106, Agadir, Morocco.
³ Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, Shaanxi, China.

PMID: 31539708
DOI: 10.1016/j.apradiso.2019.108859

Abstract

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 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. ¹⁵N 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.

Keywords: Contamination; Nitrogen; Quality; Stable isotopes; Water scarcity.