Characterization of Mechanisms and Processes Controlling Groundwater Recharge and its Quality in Drought-Prone Region of Central India (Buldhana,Maharashtra) Using Isotope Hydrochemical and End-Member Mixing Modeling

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO₃ facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ²H, δ¹⁸O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

     

Tracer-based estimation of temporal variation of water sources: an insight from supra- and subglacial environments

ABSTRACT

The temporal variations in electrical conductivity and the stable isotopes of water, δD and δ¹⁸O, were examined at Chhota Shigri Glacier, India, to understand water sources and flow paths to discharge. Discharge is highly influenced by supraglacially derived meltwater during peak ablation, and subglacial meltwaters are more prominent at the end of the melt season. The slope of the best fit linear regression line for δD versus δ¹⁸O, for both supraglacial and runoff water, is lower than that for precipitation (snow and rain) and surface ice, indicating strong isotopic fractionation associated with the melting processes. The slope of the local meteoric water line (LMWL) is close to that of the global meteoric water line (GMWL), reflecting that the moisture source is predominantly oceanic. The d-excess variation in rainwater confirms that the southwest monsoon is the main contributor during summer while the remainder including winter is mostly influenced by westerlies.     

Geochemical characterization of groundwater from an arid region in India

A study on the geochemical processes in arid region of western India (Kachchh district) was carried out using major, minor, trace metal data and isotopic composition (δ²H, δ¹⁸O) of groundwaters. Results indicate that the distribution of chemical species in groundwater of this district is controlled by leaching of marine sediments, dissolution of salts in root zone and incongruent dissolution of carbonate minerals. Common inorganic contaminants such as fluoride, nitrate and phosphate are within drinking water permissible limits. However, most of the samples analyzed contain total dissolved salts more than desirable limits and fall in doubtful to unsuitable category with regard to irrigational purpose. Trace metal data indicates no contamination from toxic elements such as arsenic and lead. An increased salt content is observed in groundwater at shallower depths indicating mixing with surface water sources. The chemical characteristics of the groundwater have found to be strongly dependent on the local lithological composition. Environmental isotopic data indicates that the groundwater is of meteoric origin and has undergone limited modification before its recharge. The processes responsible for observed brackishness are identified using chemical and isotope indicators, which are in agreement with subsurface lithology and hydrochemistry. These data though represent hydrochemical scenario of 2001 can still be used for understanding the long-term fluctuations in water chemistry and would be quite useful for the planners in validating groundwater quality models.