Use of isotopes techniques to reveal the origin of water salinity in an arid region of Central-Western Argentina

Abstract

Groundwater is a strategic and vital resource for agriculture and oil production in the arid region of Carrizal sub-basin (CSB) in Argentina. Increasing groundwater salinity in some areas has created legal conflicts between water users over the source of the salinity. A multidisciplinary approach using hydrogeological, chemical and isotope tools were used to evaluate the source of groundwater salinity in CSB. The Mendoza River is the main source of recharge to the CSB aquifer. Groundwater and surface water from the recharge area near the Mendoza River to the discharge area of the CSB were analyzed for the study. The groundwater salinity varies between ~1000 μS/cm in the north (recharge area) to ~4000 μS/cm in the central region. There is a clear correlation between high level of nitrate and the high salinity spots in the aquifer. These data and the stable isotopes data suggests the source of groundwater salinity is associated with irrigation return flows from the agriculture areas. This is fully supported by the carbon isotopes data that showed clearly the input of carbon from the irrigated agriculture areas in the aquifer. No evidence was found about the role of the oil industry in the salinization of groundwater in the study area. However, a groundwater of different origin than the recharge from the Mendoza River was found down-gradient of the oil field which needs further investigation. The results of this study have implications for improving water management in agriculture areas in arid environments where water resources are under significant pressure due to more demand by an increase in population and agriculture activities under a scenario of a cycle of droughts and climate change.