Stressed aquifers, water quality deteriorations and the critical role of lateral flows; Insights from India

In last a few decades, intensive groundwater extraction for irrigation in India has severely depleted aquifers at several stretches of the country. This study evaluates the impacts of over-pumping on groundwater quality by integrating depth-to-water levels (DTWs) and water quality with stage of groundwater extraction (SoGE) and annual groundwater recharge (GWR) from Central Ground Water Board (CGWB) assessments. About 75% of deeper DTWs (>20 m bgl) and 42-60% of poor-quality samples (exceeding BIS limits) occur in over-exploited, critical, or semi-critical (OCS) zones. Rising SoGE corresponds with falling DTWs, higher pH, and declining water quality, with stronger negative pH-GWR correlations in alluvium (ALV) (r = -0.50) than in hard-rock (HR) aquifers (r = -0.35). Between SoGE ranges of ~60-140% (ALV) and ~50-160% (HR), solutes such as Na, Cl, SO₄, NO₃, HCO₃, F, and TDS increase in groundwater with stronger revelation in HR. Fluoride and nitrate enrichment, linked to irrigation returns, peaks within these ranges but reduces beyond critical thresholds. While most states show rising TDS with increasing SoGE, some (e.g., Punjab, Haryana, Uttar Pradesh, Delhi, Tamil Nadu) exhibit declining TDS at higher exploitation levels, sustained by lateral groundwater flows from uplands, foothills, and river valleys, often through palaeochannels. These flows help buffer aquifers against quality deterioration, highlighting their critical role in groundwater management under stress.