Delineation of the recharge areas and distinguishing the sources of karst springs in bringi watershed, kashmir himalayas using hydrochemistry and environmental isotopes

Abstract

Water samples were collected from precipitation, streams and karst springs of the mountainous Bringi catchment of Kashmir Himalayas for major ions, stable isotopes (δ18O and δD) and 3H analysis. The main objective is to identify the potential recharge area for karst springs. The water in the Triassic limestone aquifer of the Bringi watershed is characterized by low levels of mineralization with TDS of the spring water samples ranging between 99 and 222 mg/l except the Kongamnag spring, which contained TDS up to 425 mg/l. As expected in an area with dominant carbonate lithology, Ca–HCO3 and Ca– Mg–HCO3 hydrochemical facies were found. Based on the amount weighed monthly averages (n = 6), the local meteoric water line (LMWL) for Bringi watershed is δD = 7.7 × δ18O + 11.1 (r2 = 0.99). The isotopic signature of winter precipitation is reflected in stream and spring water in late spring and is therefore, a representative of snow melting. The spring waters in September bear the δ2H and δ18O enriched isotopic signatures of summer rainfall. With the help of the local vertical isotopic gradient of precipitation (δ18O = −0.27‰ per 100 m increase in elevation), the mean elevation of precipitation that recharged the aquifer is estimated and ranges about 2500–2900 m amsl. There is a very strong correlation (r2 = 0.97) between the seasonal isotope composition of streams and springs, indicating that streams and springs either share similar catchments or the springs are recharged by the streams.