ISONITRATE - Improved management of nitrate pollution in water using isotopic monitoring

Research shows that there is significant added value in using isotopic measurements (nitrogen and oxygen isotopes of nitrate, and boron isotopes) to precisely identify nitrate pollution sources (urban or agricultural), trace them in water and quantify their respective contributions. This is because the N and O isotopic ratios of nitrate from different sources (atmospheric, mineral fertilizer, urban or industrial wastewater, animal manure, soil organic matter) are most often significantly distinct. The project’s main aim was to demonstrate to policy makers the technical and economical feasibility of integrating the isotope approach as part of characterising water bodies and analysing pressure and impact of nitrate pollution, for a more effective implementation of environmental management measures on river basins.

Four sampling sites were studied in the aquifer of Alsace in north-eastern France. Different cases of nitrate concentration and nitrate sources (animal manure, mineral fertilisers and wastewater) were analysed. These four scenarios confirmed that the multi-isotope approach usually brings non-equivocal constraints on the main NO3 contamination sources in water. This results in the contamination-source-specific isotope signatures found in the different types of NO3 sources. One case study estimated the cost-benefit of the isotope approach: it showed that the benefit of investing in isotope monitoring reduced the environmental return (expressed as monetary value of additional information via avoided environmental damage) of reducing nitrate management pollution by over €7 000 per monitoring campaign - suggesting a marginal rate of return of 62%.