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δ18O measurements based on systematic sampling and isotopic modeling have been adopted to study the controls of stable isotopes in lakewater in two lake basins (lakes Yamdrok-tso and Puma Yumtso) at two different elevations on the southern Tibetan Plateau. Temporally, d18O 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 ~1% from the lake shores to the lake center and by 0.4% from the water surface to depth in these lakes. The clear annual δ18O variations indicate that lake water mixes sufficiently in a short time. Model results show that glacial meltwater and surface lake-water temperature are not the dominant factors in the balance process of stable isotopes in lake water. Equilibrium d18O values decrease by 0.8%for Yamdrok-tso lake and 0.6% for Puma Yum-tso lake when glacial meltwater contributions to these lakes shrink by 60%. δ18O ratios increase rapidly during the initial stages and take a longer time to approach the equilibrium value. [ABSTRACT FROM AUTHOR]

Stable isotope variability and fractionation associated with transformation of precipitation/accumulation to firn to glacial river water is critical in a variety of climatic, hydrological and paleoenvironmental studies. This paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central Tibetan Plateau. Isotopic changes are observed by sampling firnpack profiles, glacier surface snow/ice, meltwater on the glacier surface and catchment river water at different times during a melt season. Results show the isotopic fractionation effects associated with glacier melt processes. The slope of the δD-δ18O regression line and the deuterium excess values decreased from the initial precipitation to the melt-impacted firnpack (slope from 9.3 to 8.5 and average d-excess from 13.4‰ to 7.4‰). The slope of the δD-δ18O line further decreased to 7.6 for the glacier runoff water. The glacier surface snow/ice from different locations, which produces the main runoff, had the same δD-δ18O line slope but lower deuterium excess (by 3.9‰) compared to values observed in the firnpack profile during the melt season. The δD-δ18O regression line for the river water exhibited a lower slope compared to the surface snow/ice samples, although they were closely located on the δD-δ18O plot. Isotope values for the river and glacier surface meltwater showed little scatter around the δD-δ18O regression line, although the samples were from different glaciers and were collected on different days. Results indicate a high consistency of isotopic fractionation in the δD-δ18O relationships, as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fully physics-based, process-level, distributed fluid flow and reactive transport hydrological models are rarely used in practice until recent years. These models are useful tools to help understand the fundamental physical, chemical, and biological processes that take place in nature. In this study, sensitivity analyses based on a mountain area river basin modelling study are performed to investigate the effect of river channel geometric characteristics on downstream water flow. Numerical experiments show that reduction in the river channel geometric measurement interval may not significantly affect the downstream water stage simulation as long as measurement accuracy at special nodes is guaranteed. The special upstream nodes include but are not limited to 1) nodes located close to the observation station, 2) nodes near the borders of different land covers with considerable riverbed roughness changes, 3) nodes at entering points of tributaries causing discharge jump and 4) nodes with a narrow cross-section width that may control the flow conditions. This information provides guidelines for field investigation to efficiently obtain necessary geometric data for physics-based hydrological modelling. It is especially useful in alpine areas such as the Tibetan Plateau where field investigation capability is limited under severe topography and climate condition. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] First detailed long-term water balance observations on a large Tibetan lake. [•] Two catchment runoff coefficients and two glacial runoff depths were obtained. [•] First solid result demonstrating the existence of Tibetan lake water seepage. [•] Results significantly affect environmental studies on Tibet and the surrounding areas. [Copyright &y& Elsevier]