Investigation of Stable isotope systematics and geochemical signatures of surface water from the Satluj River Basin (SRB), Himalayas, India.

The present study explores the signature of stable isotopes (δ¹⁸O and δD) and major inorganic solute ion concentrations of Satluj river water and its tributaries to gain insight into the dominant hydrogeochemical process that controls the water chemistry in the Satluj River Basin (SRB), Himalayas, India. In isotopic and geochemical terms, the surface water of SRB is poorly characterized for its whole length; their potential variability has yet to be widely used as an aid in hydrological research. The δ¹⁸O values in the SRB range from – 14.50‰ to – 7.35‰ and δD from – 100.30‰ to − 44.70‰, showing general enrichment from Khaab to downstream Harike barrage. The upper reaches of Satluj River and its major upstream tributaries like Spiti and other small streams contributing to the Satluj are relatively depleted in δ¹⁸O and δD, possibly indicative of precipitation originating at higher elevations and/ or recharge from snow/glacial meltwater. While lower reaches are relatively enriched in δ¹⁸O and δD. The local water line for the SRB was found to be δD = 8.12 × δ¹⁸O + 18.89. The higher slope and higher intercept as compared to GMWL indicate a system recharged by snow/glacier meltwater and recycled moisture derived from continental sources in addition to monsoonal climates. In addition, a higher intercept indicates that the moisture source of precipitation (snow/rainfall) in this region originates from the Western Disturbance (WD). The Deuterium excess (d-excess) in the SRB varies between 12.50‰ and 25.81‰ with an average of 17.40‰, which is mostly higher than the long-term average for the Indian summer monsoon (~ 8‰). The higher d-excess value is because of the contribution of moisture from Mid-latitude westerlies. A significant negative correlation of Satluj river water δ¹⁸O with elevation was observed with a vertical lapse rate of 0.15‰/100 m. Geochemical analysis showed that the solute concentrations show spatial heterogeneity with decreasing elevation in the SRB. This is related to the complex lithologic compositions and different water sources from different elevations that contribute to the Satluj river. This study also established a relationship between total cation abundance (∑Cat*, corrected for cyclic components) and δ¹⁸O in waters of the Satluj mainstream. The variation in δ¹⁸O and ∑Cat* along the course of the Satluj is brought about by independent processes, the intensity of chemical weathering in the catchments and associated sub-catchments (tributaries), and altitude effect. ∑Cat* is higher at higher altitudes because of intense weathering, and δ¹⁸O is more depleted because the source waters are from depleted snow/glacial melt and cloud that is depleted in ¹⁸O because of previous rainouts during its ascent. The relationship between total cation abundance (∑Cat*) and δ¹⁸O suggests that ∑Cat* would increase by a factor of 0.93 for every 1‰ increase in δ¹⁸O.