Identifying the seasonal variability in source of groundwater salinization using deuterium excess- a case study from Mewat, Haryana, India

[Display omitted] •Identified groundwater salinisation sources using d- excess & salinity relationship.•Mineral dissolution contributes 76–97 % in average salinity.•Increase in initial salinity contribution in monsoon & post monsoon seasons. Mewat (renamed as Nuh) district of Haryana, India having geographical area of 1507 km2, comes under semi arid climatic conditions and Aravali hill ranges separates it from Rajasthan state. Groundwater salinization is an emerging threat to water management. Understanding the sources of salinization, and their relative contributions by different sources and seasonal variability has become priority for planning best practices in water management and suggesting remedial measures. For identifying the sources of salinization, the direct application of the relationship between δ18O and δD is limited as it depends upon initial isotopic composition showing no isotopic variation in the mineral dissolution process. The present study advocates the use of deuterium excess which is independent of initial isotopic composition and extends this concept for identifying the relative contribution of different sources towards seasonal variability in salinization. The district showed an average salinity of 6.7 g/L in pre-monsoon; 7.3 g/L in monsoon and 7.4 g/L in post-monsoon season thus a variability of 0.7 g/L observed. The area affected by the salinization (>2 g/L) also registers an increase from 86 % (pre-monsoon) to 99 % (post-monsoon) period. Mineral dissolution is found to be responsible for overall groundwater salinization with contribution of 97 %, declined to 86 % in post monsoon. In post monsoon season, contributions from initial salinity and evapoconcentration towards salinization increased by 8% and 3%, respectively.