Improving understanding of nitrate sources in connected river and groundwater systems through linking nitrate isotopes and contaminants of emerging concern

Nitrate contamination makes water unconsumable hence, reducing access to drinking water - a key factor of well-being as recognized in the Sustainable Development Goals (SDG 6). While nitrate source identification remains challenging using hydrochemical measurements, the analysis of stable isotopes in nitrate opens the possibility to track nitrate sources and processes. However, nitrate isotopes are not suitable to differentiate closely related sources of nitrate contamination with overlapping isotopic signatures, such as sewage and manure, as well as treated versus raw sewage inputs. One solution is to use isotopic techniques in conjunction with compounds of emerging concern (CECs). CECs are ideal chemical markers of faecal contamination (sewage or manure) as they are usually linked to a specific source, are ubiquitous in that source and are persistent and present at detectable concentrations in contaminated environmental samples but not in clean water. Their high solubility in water and low volatility facilitates their use as tracers for water-soluble components originating in sewage and manure. The CRP puts forward this innovative approach of combining stable isotopes of nitrate with CECs in surface and groundwater in order improve nitrogen source tracking and source delineation, understanding hydrological and hydrochemical behavior of anthropized water systems, and more precise quantification of groundwater/surface water interaction and rapid infiltration rates.