The spatiotemporal variation of groundwater chemistry across the fastest developing urban agglomerate is of utmost importance. It is important to identify sources of contaminants, recharge sources, so that suitability can be ascertained. Hydrochemistry and isotopic analysis were done in parts of National Capital Region to establish spatiotemporal variation in hydrochemistry, isotopic ratios and their suitability for drinking and irrigation purposes. A total of 115 samples were collected and analyzed for hydrogeochemistry and 70 samples were collected and analysed for stable isotopic ratios (δ18O and δD) during pre-monsoon (May) and post-monsoon (November) seasons of 2017, respectively. Ca2+ >Mg2+ >Na+>K+ is the order of cation abundance (mg/l) and HCO3− >Cl− >SO42− >CO2− >F− in anion abundance in both seasons. Approximately 50% of groundwater samples in the pre-monsoon season and 35% in the post-monsoon season exhibited a dominant Ca-Mg-HCO3 hydrochemical facies. Significant seasonal variation was observed in the concentrations of Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, Cl⁻, and SO₄²⁻. pH has shown significant temporal variations (p value < 0.05) between both seasons. However, significant spatial variation in the concentration of pH, EC, TDS, Hardness, Ca2+, Mg2+, Na+, HCO3−, SO42−, Cl− and F− have been analyzed by using ANOVA. No significant spatial differences have been observed in K+, CO2− and NO3− in alluvium and quartzite formation. Principal Component analysis signifies that all groundwater samples are influenced by 4 components i.e. dissolution and cation exchange process, extensive application of fertilizer, ion exchange process, and geo-genic salinity hazard. The Water Quality Index (WQI) indicates that, during the pre-monsoon and post-monsoon seasons, 67% and 74% of groundwater samples fell into the excellent category, 23% and 16% into the good category, 7% and 4% into the poor category, and 5% in both seasons were classified as very poor. Groundwater in the study area is generally characterized by higher hardness levels. Based on Residual Sodium Carbonate and Sodium Absorption Ratio, 97% and 98% of the groundwater samples were found to be suitable for irrigation. However, due to naturally occurring salinity, many samples, particularly in the western regions, exhibited potential salinity hazards. The isotopic composition of groundwater reveals distinct seasonal shifts, with pre-monsoon δ¹⁸O values showing enrichment due to extensive evaporation, while post-monsoon samples exhibit depletion, indicating direct infiltration of monsoonal precipitation. The pre-monsoon d-excess varies heterogeneously between 5 to -5‰, reflecting significant evaporative losses before recharge. In contrast, the increased d-excess in the post-monsoon season suggests the dominance of fresh rainfall infiltration with minimal evaporation effects. The seasonal isotopic variations highlight the critical role of monsoonal recharge in sustaining groundwater resources while also exposing the aquifer system to contamination risks from anthropogenic activities such as landfill leachate and agricultural runoff. These findings emphasize the need for sustainable groundwater management strategies, including the protection of recharge zones and the implementation of artificial recharge techniques to mitigate seasonal water quality deterioration.

Spatio-temporal variation in hydrochemistry, environmental isotopes and its suitability for drinking and irrigation, National Capital Region, Delhi

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发表日期：

2025年10月21日

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Shilpi Gupta,
Janardhana Raju Nandimandalam,
Amit Pandey

摘要

The spatiotemporal variation of groundwater chemistry across the fastest developing urban agglomerate is of utmost importance. It is important to identify sources of contaminants, recharge sources, so that suitability can be ascertained. Hydrochemistry and isotopic analysis were done in parts of National Capital Region to establish spatiotemporal variation in hydrochemistry, isotopic ratios and their suitability for drinking and irrigation purposes. A total of 115 samples were collected and analyzed for hydrogeochemistry and 70 samples were collected and analysed for stable isotopic ratios (δ¹⁸O and δD) during pre-monsoon (May) and post-monsoon (November) seasons of 2017, respectively. Ca²⁺ >Mg²⁺ >Na⁺>K⁺ is the order of cation abundance (mg/l) and HCO₃⁻ >Cl⁻ >SO₄²⁻ >CO₂⁻ >F⁻ in anion abundance in both seasons. Approximately 50% of groundwater samples in the pre-monsoon season and 35% in the post-monsoon season exhibited a dominant Ca-Mg-HCO3 hydrochemical facies. Significant seasonal variation was observed in the concentrations of Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, Cl⁻, and SO₄²⁻. pH has shown significant temporal variations (p value < 0.05) between both seasons. However, significant spatial variation in the concentration of pH, EC, TDS, Hardness, Ca²⁺, Mg²⁺, Na⁺, HCO₃⁻, SO₄²⁻, Cl⁻ and F⁻ have been analyzed by using ANOVA. No significant spatial differences have been observed in K⁺, CO₂⁻ and NO₃⁻ in alluvium and quartzite formation. Principal Component analysis signifies that all groundwater samples are influenced by 4 components i.e. dissolution and cation exchange process, extensive application of fertilizer, ion exchange process, and geo-genic salinity hazard. The Water Quality Index (WQI) indicates that, during the pre-monsoon and post-monsoon seasons, 67% and 74% of groundwater samples fell into the excellent category, 23% and 16% into the good category, 7% and 4% into the poor category, and 5% in both seasons were classified as very poor. Groundwater in the study area is generally characterized by higher hardness levels. Based on Residual Sodium Carbonate and Sodium Absorption Ratio, 97% and 98% of the groundwater samples were found to be suitable for irrigation. However, due to naturally occurring salinity, many samples, particularly in the western regions, exhibited potential salinity hazards. The isotopic composition of groundwater reveals distinct seasonal shifts, with pre-monsoon δ¹⁸O values showing enrichment due to extensive evaporation, while post-monsoon samples exhibit depletion, indicating direct infiltration of monsoonal precipitation. The pre-monsoon d-excess varies heterogeneously between 5 to -5‰, reflecting significant evaporative losses before recharge. In contrast, the increased d-excess in the post-monsoon season suggests the dominance of fresh rainfall infiltration with minimal evaporation effects. The seasonal isotopic variations highlight the critical role of monsoonal recharge in sustaining groundwater resources while also exposing the aquifer system to contamination risks from anthropogenic activities such as landfill leachate and agricultural runoff. These findings emphasize the need for sustainable groundwater management strategies, including the protection of recharge zones and the implementation of artificial recharge techniques to mitigate seasonal water quality deterioration.