Abstract:
In the present paper, results of isotopic investigations of two Western Himalayas lakes i.e., Nainital (located in Uttarakhand) and Mansar lake (located in Jammu and Kashmir) are discussed. The d180 and dD composition of the local precipitation, springs, hand pumps and lakes are used to study the hydrological behaviour of lakes. The slope of Local Meteoric Water Lines (LMWL) in both the study area is found very close to that of the Global Meteoric Water Line. In case of Nainital Lake, isotopic signatures of all the samples fall on the LMWL while Mansar Lakes' samples fall below the LMWL. Therefore, Mansar Lake isotopic signatures show considerable evaporative enrichment of lake water. However, samples from epilimnion zone of Nainital Lake show the evaporation trend but evaporative enrichment is insignificant because all the samples from Mesolimnion and hypolimnion fall on LMWL. This is due to substantial subsurface inflow and shorter retention time of the lake. In contrast, Mansar Lake bears isotopic signatures of evaporated water from epilimnion to hypolimnion which clearly indicate that subsurface inflow to lake is very poor and water retention period is comparatively higher. The change of composition of oxygen and hydrogen isotope from epilimnion to hypolimnion region in a lake reveals the status of interaction of lake water with groundwater regime in the lake catchment and water retention period, which is very useful to know the status of hydrological conditions of the lake.
