Satya Narayan Sethy

Relentless extraction of groundwater has led to falling water levels and widespread concerns over the long-term sustainability of extensive groundwater-based irrigated agriculture in India. Hence, effective water management strategies must be developed with a thorough understanding of groundwater recharge. Here, we assess the source, recharge mechanism, and hydrogeochemical evolution of groundwater in the Nalanda-Rajgir region of eastern India using stable isotopes, physico-chemical parameters, and multivariate statistics. Based on major ion chemistry, ~ 40% of the groundwater samples are categorized as Ca2+-Mg2+-HCO3− type, characteristic of active recharge zones. Therefore, groundwater in these regions has short residence time and hence limited water–rock interactions. The other major group (~ 45%) of groundwater samples is of Na+-HCO3− type, which indicates the dominance of ion-exchange processes. The distribution of δ18O in groundwater ranges from − 10 to − 6.9 ‰ and that of δ2H from − 57.9 to − 40.4 ‰. While the hot spring sample is characteristically depleted in heavier isotopes, the remaining samples have been categorized into two groups based on their isotopic composition. Group I samples have a slope similar to that of the Global Meteoric Water Line (GMWL) and signify rapid recharge of rainwater. In contrast, group II samples with evidence of extensive evaporation due to prolonged exposure to the atmosphere represent water retained from irrigation return flow in agricultural fields. Hierarchical cluster analysis further corroborates that the association of major ions and isotopes in different clusters primarily indicates a largely meteoric source of groundwater that has been significantly influenced by human intervention.

A comprehensive assessment of groundwater is carried out in parts of the Southern Gangetic Plain to identify the hydrogeochemical processes influencing groundwater geochemistry and to ascertain the suitability of groundwater for drinking and irrigational uses. Results of detailed chemical analysis reveal that groundwater of the study area is slightly acidic (pH values from 6.2 to 7.37) during post-monsoon, with dominant concentrations of Na+ and Ca2+ cations and HCO3− and Cl− anions. Groundwater chemistry is largely controlled by rock-weathering and ion-exchange processes with secondary contribution from anthropogenic sources. In particular, values of EC, total hardness and concentrations of Na+ and HCO3− exceed the prescribed limits of Indian and WHO water quality standards. Suitability of groundwater for irrigation purposes are evaluated on the basis of sodium adsorption ratio, sodium percent (%Na+), magnesium hazard, residual sodium carbonate and Kelley’s index. In this regard, nearly 40–50 % of the groundwater in the study area is found to be of excellent to good quality. In addition, principal component analysis, performed to identify the dominant geochemical processes, shows that the first three components are together account for 80.84 and 78.85 % of the total variance in the dataset for post-monsoon and pre-monsoon periods, respectively. This analysis also reveals key contributions from hydrogeochemical processes like mineral dissolution, silicate and carbonate weathering alongside anthropogenic activities like leaching of fertilizers from agricultural lands.

Relentless extraction of groundwater has led to falling water levels and widespread concerns over the long-term sustainability of extensive groundwater-based irrigated agriculture in India. Hence, effective water management strategies must be developed with a thorough understanding of groundwater recharge. Here, we assess the source, recharge mechanism, and hydrogeochemical evolution of groundwater in the Nalanda-Rajgir region of eastern India using stable isotopes, physico-chemical parameters, and multivariate statistics. Based on major ion chemistry, ~ 40% of the groundwater samples are categorized as Ca2+-Mg2+-HCO3− type, characteristic of active recharge zones. Therefore, groundwater in these regions has short residence time and hence limited water–rock interactions. The other major group (~ 45%) of groundwater samples is of Na+-HCO3− type, which indicates the dominance of ion-exchange processes. The distribution of δ18O in groundwater ranges from − 10 to − 6.9 ‰ and that of δ2H from − 57.9 to − 40.4 ‰. While the hot spring sample is characteristically depleted in heavier isotopes, the remaining samples have been categorized into two groups based on their isotopic composition. Group I samples have a slope similar to that of the Global Meteoric Water Line (GMWL) and signify rapid recharge of rainwater. In contrast, group II samples with evidence of extensive evaporation due to prolonged exposure to the atmosphere represent water retained from irrigation return flow in agricultural fields. Hierarchical cluster analysis further corroborates that the association of major ions and isotopes in different clusters primarily indicates a largely meteoric source of groundwater that has been significantly influenced by human intervention.

In India, persistent dependence on groundwater for intensively irrigated agriculture, industrial use and domestic activities imposes substantial threat to the quality and quantity of groundwater. This study assesses the suitability of groundwater for drinking purposes in parts of the Southern Gangetic Plain based on samples collected from 33 dug wells. In this scope, two robust indices are utilized, namely Groundwater Quality Index (GQI) and the Canadian Council of Ministers of the Environment (CCME) Water Quality Index (CCME_WQI), to assess the overall quality of groundwater by integrating observed water quality determinants like pH, TDS and major ion concentration. The concentration of major anions and cations is observed to be in the order of HCO3− > Cl− > SO42− > NO3− and Na+ > Ca2+ > Mg2+ > K+, respectively. The pH values of the analyzed samples vary between 6.2 and 7.37 during the post-monsoon (POM) period and between 6.6 and 7.9 during the pre-monsoon (PRM) ...

A comprehensive assessment of groundwater is carried out in parts of the Southern Gangetic Plain to identify the hydrogeochemical processes influencing groundwater geochemistry and to ascertain the suitability of groundwater for drinking and irrigational uses. Results of detailed chemical analysis reveal that groundwater of the study area is slightly acidic (pH values from 6.2 to 7.37) during post-monsoon, with dominant concentrations of Na ? and Ca 2? cations and HCO 3-and Cl-anions. Groundwater chemistry is largely controlled by rock-weathering and ion-exchange processes with secondary contribution from anthropogenic sources. In particular, values of EC, total hardness and concentrations of Na ? and HCO 3-exceed the prescribed limits of Indian and WHO water quality standards. Suitability of groundwater for irrigation purposes are evaluated on the basis of sodium adsorption ratio, sodium percent (%Na ?), magnesium hazard, residual sodium carbonate and Kelley's index. In this regard, nearly 40–50 % of the groundwater in the study area is found to be of excellent to good quality. In addition, principal component analysis, performed to identify the dominant geochemical processes, shows that the first three components are together account for 80.84 and 78.85 % of the total variance in the dataset for post-monsoon and pre-monsoon periods, respectively. This analysis also reveals key contributions from hydrogeochemical processes like mineral dissolution, silicate and carbonate weathering alongside anthropogenic activities like leaching of fertilizers from agricultural lands.