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During the observation period, the volume-weighted mean values of δ18O for streamflow at the catchment outlet, for the precipitation at the two sample sites, and for glacial meltwater were −11.9‰, −11.3‰, and −15.6‰, respectively. Calculations using the isotope hydrograph separation method, Equation (4), show that the contribution of glacial melt runoff to total runoff was 15.0%. Uncertainty results for hydrograph separation were shown in Table 1. Calculated by Equation (7), the uncertainty of the separation was ± 3.7% at the confidence level of 95%. Therefore, the contribution of glacial melt runoff was 15.0 ± 3.7% (the confidence level of 95%) at the Gaerqu River catchment. As the total runoff during the observation period was 2.55 × 108 m3, the glacial melt runoff can be calculated as (0.38 ± 0.09) × 108 m3.

Table 1

Statistics of the δ18O values and uncertainty results for hydrograph separation

SamplesNumber of samplesWeighted mean δ18O (‰)Standard deviationt (95%)Uncertainty (95%)
Precipitation 12 −11.3 8.3 2.201 18.246 
Glacier 42 −15.6 4.8 2.020 1.436 
Streamflow 24 −11.9 0.7 2.069 9.740 
SamplesNumber of samplesWeighted mean δ18O (‰)Standard deviationt (95%)Uncertainty (95%)
Precipitation 12 −11.3 8.3 2.201 18.246 
Glacier 42 −15.6 4.8 2.020 1.436 
Streamflow 24 −11.9 0.7 2.069 9.740 

Note: 95% represents the confidence level.

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