Présentations Colloques

Oral Presentation
7.03
Session 7.03: Agricultural and sanitation contaminants and implications for water services and health
Aunay Bertrand
A robust hydrochemical and isotopic method for urban and agricultural origins of nitrate in groundwater
The ever increasing human population and the resultant increase in anthropogenic activities have led to a gradual decline in groundwater quality across many regions of the world. Amongst the many contaminants, nitrates are currently considered as one of the major causes of groundwater pollution mainly due to their high solubility in water. Frequently attributed to agricultural activities, nitrates can also come from other sources from urban and suburban areas, particularly due to the presence of on-site sanitation systems.**To reclaim groundwater quality by acting on the most significant and dominant sources, it is necessary to precisely determine the origin of nitrates.**A robust approach based on the combined use of multiple environmental tracers was implemented on two watersheds characterized by mixed pollution sources (on-site sanitation and agricultural activities). These two watersheds are located in Reunion Island (Indian Ocean), where on-site sanitation dominates, with a significant non-compliance rate- it is estimated that in Reunion Island the on-site sanitation is found in 60% of houses, with a non-compliance rate close to 80%.**The hydrochemical analysis coupled with the spatial analysis of land use land cover helped us to characterize the different groundwater facies. Water isotope ratios (delta 18O and delta 2H) were used to determine the average recharge altitude, while the rare earths, pharmaceutical compounds, nitrate isotopic ratios (delta 15N and delta 18O), boron isotopes 10B and 11B allowed us discriminate between the agricultural and urban sources of nitrates in groundwater. The relative contribution of pollution from on-site sanitation and agricultural activities was determined.**Finally, CFC's and SF6 were used to calculate the apparent ages of water and identify the temporal effectiveness of measures implemented in the watershed, characterized by mixed pollution sources.
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