The Indo-Gangetic Basin is home to a vital groundwater resource that sustains intensive agriculture across South Asia. However, this alluvial aquifer system faces significant pressure from overuse and pollution. Declining groundwater levels and increasing contamination threaten the long-term sustainability of this critical water source.
Previous research has identified various sources of groundwater recharge within the Indo-Gangetic Basin, including rainfall, river and canal leakage, and irrigation return flow. While isotopic studies have provided insights into the origin of recharge water, their influence on the quality of groundwater remains poorly understood. This study by FJG van Broekhoven et al. “Linking recharge water sources to groundwater composition in the Hindon subbasin of the Ganges River, India“ aims to better understand how different recharge sources affect the hydrochemical and isotope composition of groundwater.
Groundwater quality could be linked to both recharge from irrigation canal water as well as recharge from polluted river water of the Hindon and its tributaries. This study aims to address this knowledge gap by investigating the relationship between recharge sources and groundwater quality within the Hindon subbasin, a region within the Indo-Gangetic Basin heavily impacted by human activities. By combining isotopic and hydrochemical data, researchers traced the origin and impact of different recharge sources on groundwater composition along Hindon River.
The study area encompasses the ~7000 km² Hindon River subbasin in western Uttar Pradesh. This subbasin, part of the Ganges Basin, lies in the humid subtropical region with a monsoon climate. The flat terrain is characterised by the Indo-Gangetic Basin alluvial aquifer, comprising thick, permeable sediments.
The Hindon River, originating in the Shivalik Hills, experiences seasonal flow, drying up outside the monsoon season due to increased water demand for irrigation and the impact of the green revolution. This has led to significant groundwater depletion and severe water quality degradation in the river.
Land use within the subbasin is dominated by agriculture, with significant urbanisation and industrialisation near Delhi. The study area faces challenges from declining groundwater levels, increasing water demand, and significant water quality issues arising from pollution.
Groundwater quality in the Hindon subbasin is influenced by a variety of recharge sources:
Rainfall infiltration: A significant portion of rainfall infiltrates directly, contributing relatively low solute concentrations to groundwater, particularly during the monsoon season.
Irrigation water infiltration: Irrigation water, often with higher solute concentrations due to evaporation and fertilizer application, infiltrates throughout the year, potentially contributing to nutrient and pesticide contamination.
Irrigation canal water infiltration: Canal water, originating from the Himalayas, generally has lower solute concentrations and a distinct isotopic signature.
Municipal wastewater infiltration: Untreated municipal wastewater, rich in organic matter and nutrients, infiltrates through ponds, septic systems, and drainage networks.
Industrial wastewater infiltration: Industrial effluent, containing high levels of organic matter, suspended solids, and heavy metals, can directly infiltrate the aquifer through leakage and spills.
River water infiltration: Declining groundwater levels have increased river water infiltration, particularly in the dry season. However, the Hindon River is heavily polluted with heavy metals, nutrients, and pesticides, impacting groundwater quality.
These diverse recharge sources, with varying chemical and isotopic compositions, significantly influence the overall quality of groundwater within the Hindon subbasin.
The study involved sampling 53 water sources along a 50-kilometer transect within the Hindon River subbasin. This included surface water (canals and ponds), shallow (<40 m), and deep groundwater (40-80 m). Samples were collected from diverse locations to capture the influence of various recharge sources, such as rainfall, irrigation water, canal water, municipal and industrial wastewater, and river water infiltration.
Field measurements (EC, pH, temperature) and GPS coordinates were recorded. Water quality analysis included major ions, trace elements, stable isotopes, and other parameters. Data quality was rigorously assessed, and statistical methods like Factor Analysis and Hierarchical Cluster Analysis were employed to group groundwater samples based on their chemical composition.
Results of the hydrochemical analysis of recharge sources and groundwater clusters within the Hindon subbasin
Recharge sources
Canals: Low solute concentrations, except for NH4, Al, and A
Rainfall: Low EC and solute concentrations, with high Pb.
Ponds: High concentrations of EC, COD, Cl, Na, NH4, and Co.
Rivers: High trace metal concentrations (Cd, Cr, Cu, Fe, Ni, Pb) and high concentrations of COD, Na, and Cl.
Groundwater clusters
Cluster 1: High concentrations of most components, including major ions, nutrients, and several metals.
Cluster 2: Low or average concentrations for most variables, with high As concentrations.
Cluster 3: Low nutrient concentrations and high metal concentrations (Ni, Cu, Zn, Cd, Pb).
Cluster 4: Low nutrient concentrations and high metal concentrations, with higher V and U compared to Cluster 3.
Spatial distribution of clusters
Cluster 1: Primarily located below the Hindon and Kali rivers, near villages, and in shallow depths.
Cluster 2: Mainly found below irrigation canals in shallow depths.
Cluster 3: Spatially distributed, predominantly in deeper groundwater.
Cluster 4: Located exclusively in deeper groundwater.
Stable isotope analysis
Isotopic data showed a general trend consistent with the LMWL, with variations among clusters. Canal water exhibited the most negative isotopic values, while pond water and Cluster 1 samples had the least negative values. Spatial distribution of δ18O values indicated potential canal water recharge zones. These findings provide insights into the hydrochemical characteristics of recharge sources and groundwater clusters within the Hindon subbasin, highlighting the influence of various factors on groundwater quality.
Linkages between recharge sources and groundwater composition within the Hindon subbasin
Irrigation canal recharge (Cluster 2): Hydrochemical and isotopic signatures strongly suggest that Cluster 2 groundwater originates from irrigation canal water. Canal water, sourced from the Himalayas, has a distinct isotopic signature and low solute concentrations. Groundwater in Cluster 2 exhibits similar characteristics, with depleted isotopic values and low solute concentrations, albeit with some differences (higher K, silica, Fe, F, V, Mn, Zn).
Anthropogenic polluted recharge (Cluster 1): High concentrations of major ions and nutrients in Cluster 1 suggest significant anthropogenic influence. Similarities in composition with village ponds and polluted river water indicate that municipal wastewater and polluted river water are major recharge sources. Isotopic enrichment in Cluster 1 groundwater suggests the influence of evaporation, likely from irrigation return flow and evaporation in village ponds. High NO3 concentrations in Cluster 1 groundwater likely result from nitrification processes in the unsaturated zone.
Geogenically influenced rainfall recharge (Clusters 3 and 4): Deeper groundwater in Clusters 3 and 4 shows lower levels of anthropogenic pollution, likely due to older recharge periods with less intensive land use. Elevated concentrations of certain metals (e.g., U) in these clusters may be attributed to geogenic sources and hydrogeochemical processes. Isotopic values in these clusters suggest local rainfall recharge with minimal evaporation.
Conceptual model of groundwater system evolution: Pre-pumping conditions: Dominated by rainfall and canal recharge, with pristine groundwater quality.
Present-day conditions: Intensive groundwater pumping, increased irrigation, and urbanization have led to declining groundwater levels and significant pollution. Anthropogenic pollution (Cluster 1) is widespread, particularly in shallow groundwater. Canal recharge (Cluster 2) remains significant. Deeper groundwater (Clusters 3 and 4) exhibits lower pollution levels, likely due to older recharge periods and geogenic influences.
This conceptual model provides a comprehensive understanding of the complex interplay between recharge sources, groundwater quality, and human activities within the Hindon subbasin and has broader implications for groundwater management in the Indo-Gangetic Basin.
This study demonstrates significant groundwater pollution in the Hindon subbasin, extending to depths of at least 80 meters. Shallow groundwater exhibits strong anthropogenic influence from agriculture, municipal, and industrial wastewater. Deeper groundwater, while less polluted, still shows signs of contamination.
The study revealed several key findings regarding groundwater dynamics and pollution in the Hindon subbasin. Firstly, irrigation canals contribute significantly to groundwater recharge, providing a source of relatively clean water. Secondly, the polluted Hindon River and its tributaries are now infiltrating into the aquifer, posing a significant risk to groundwater quality. Thirdly, intensive groundwater pumping has likely enhanced vertical flow within the aquifer, increasing the vulnerability of deeper groundwater to contamination.
These findings underscore the urgent need for several critical actions. Firstly, mitigating groundwater pollution is crucial. This involves implementing measures to reduce pollution from agriculture, industry, and municipal sources. Secondly, improving river water quality is essential. Implementing proper treatment facilities for municipal and industrial wastewater is vital to reduce river pollution and its subsequent impact on groundwater. Finally, it is crucial to consider the potential impact of canal lining. While lining canals can potentially improve water use efficiency, it may also reduce canal recharge, negatively impacting groundwater levels and quality.