Hydrogeochemical and stable isotopic evidence to different water origins of karst springs in the western Himalayas, India

摘要

Karst aquifers provide tremendous benefits to the people in the Indian subcontinent, but their studies are limited due to scanty observational data.This study examines the ionic and stable isotopic composition of water samples (n = 233 collected between 2012 and 2014) from karst springs in the western Himalayas to determine geogenic and anthropogenic solute sources and karst aquifers recharge. A principal component analysis suggests that karst springs acquire Ca2+, Mg2+, HCO3-, Na+, K+, and SO4- through natural processes, including carbonate and silicate dissolution. With a pollution index of 38%, about 50-88% of the NO3-, F- and Cl- contributing to karst springs have an anthropogenic origin. Karst springs are under-saturated with respect to calcite and dolomite, have higher pCO2, and electrical conductivity is inversely related to discharge, suggesting potential of recharging waters to dissolve the host rocks along flow paths. The springs display a distinct seasonal pattern in isotope characteristics with lower values from March to May and from August to October, reflecting the recharge from the snowmelt. Occasional higher isotopic values in February, June, and July suggest episodic rainfall events. The lower values of slope (6.9 +/- 0.4) and intercept (9.8 +/- 1.4) along with higher d-excess ( 16 parts per thousand) of the karst springs provide strong evidence of winter snow as the primary source of recharge. Based on the karst index, the karst springs were classified as moderately to well karstified in the Liddar and Bringi catchments while slightly karstified in the Kuthar catchment. The study increases the understanding of karst aquifer sensitivity, which is necessary for implementing water supply protection schemes within the region.