Impact of environment and LULC changes on groundwater resources in the Soan Basin, western Himalaya

The present study assesses the environmental and Land Use Landcover (LULC) changes in the Soan Basin, western Himalaya between 1999 and 2015 and their impacts on groundwater quality and static water level (SWL). An increase in the area of agricultural land (19%), settlement (~ 300%), and dense forest (25%) at the expense of open forest and waste cum grazing land was observed subsequently since the year 1999. SWL was lowered in the basin between 1999 and 2013 due to less groundwater recharge with decreased permeable surfaces and decreased rainfall, except in a few locations in the valley fill region plausibly due to the secondary recharge through seepages, infiltration of irrigational wastewater, and waterlogging in the agricultural fields. A continuous lowering of SWL after 2015, even after increasing the rain amount significantly, indicates overexploitation of groundwater in the region. Enhanced use of fertilizers has resulted in an increased concentration of Na⁺ and Cl^- ions in groundwater. The results are further substantiated by comparing the hydrochemical data for the years 1999 and 2015, which again indicate the high concentration of Na⁺ and Cl^- ions due to waterlogging. From 1999 to 2015, nitrate (average 12.8 mg/l to 16 mg/l) and fluoride concentration (average 0.3 to 0.9) have also increased because of the excessive use of fertilizers in the agricultural fields. The increasing trend of nitrate concentrations in water in successive years since 1994 supports the changes observed in an agricultural pattern in LULC maps for the years 1999, 2009, and 2015. The results divulge that the groundwater quality of the basin has been deteriorating due to an increase in agricultural practices and demands for appropriate water management practices.