Application of environmental isotopes and hydrochemistry in the identification of source of seepage and likely connection with lake water in Lesser Himalaya, Uttarakhand, India

Oxygen ( $${\updelta }^{18}\hbox {O}$$ ) and hydrogen ( $${\updelta }^{2}\hbox {H}$$ and $$^{3}\hbox {H}$$ ) isotopes of water, along with their hydrochemistry, were used to identify the source of a newly emerged seepage water in the downstream of Lake Nainital, located in the Lesser Himalayan region of Uttarakhand, India. A total of 57 samples of water from 19 different sites, in and around the seepage site, were collected. Samples were analysed for chemical tracers like $$\hbox {Ca}^{++}$$ , $$\hbox {Mg}^{++}$$ , $$\hbox {Na}^{+}$$ , $$\hbox {K}^{+}$$ , $${\hbox {SO}_{4}}^{--}$$ and $$\hbox {Cl}^{-}$$ using an Ion Chromatograph (Dionex IC-5000). A Dual Inlet Isotope Ratio Mass Spectrometer (DIIRMS) and an Ultra-Low Level Liquid Scintillation Counter (ULLSC), were used in measurements of stable isotopes ( $${\updelta }^{2}\hbox {H}$$ and $${\updelta }^{18}\hbox {O}$$ ) and a radioisotope ( $$^{3}\hbox {H}$$ ), respectively. Results obtained in this study repudiate the possibility of any likely connection between seepage water and the lake water, and indicate that the source of seepage water is mainly due to locally recharged groundwater. The study suggests that environmental isotopes ( $${\updelta }^{2}\hbox {H}$$ , $${\updelta }^{18}\hbox {O}$$ and $$^{3}\hbox {H}$$ ) can effectively be used as ‘tracers’ in the detection of the source of seepage water in conjunction with other hydrochemical tracers, and can help in water resource management and planning.