INFLUENCE OF GLACIAL MELTWATER ON WATER BALANCE PROCESSES OF TWO TIBETAN LAKES INDICATED BY ä18O

δ¹⁸O measurements based on systematic sampling and isotopic modeling have been adopted to study the affects of glacial meltwater in two lake basins (Lakes Yamdrok-tso and Puma Yum-tso) at two different elevations on the southern Tibetan Plateau. Temporally, δ¹⁸O values in precipitation and lake water display a seasonal fluctuation in both lakes. Spatially, δ¹⁸O values in the two lake basins increase by 10‰ from the termini of glaciers to the lake shores, by about 1‰ from the lakeshores to the lake center, by 0.4‰ from the water surface to depth in these lakes. The obvious annual δ¹⁸O variations indicate that lake water mixes sufficiently in a short time. Model results show that glacial meltwater is an important factor on lake water balance process. Equilibrium δ¹⁸O values decrease 0.8‰ for Yamdrok-tso Lake and 0.6‰ for Puma Yum-tso Lake when contributions of glacial meltwater to these lakes shrink by 60%. δ¹⁸O ratios increase rapidly during the initial stages and take a relatively longer time to approach the equilibrium value. The modeled results also show that the surface lake water temperature has a minimal impact on this process.