The researchers investigated the moisture origin and contribution of different water sources to surface runoff entering the headwaters of the Heihe River basin on the basis of NECP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research) re-analysis data and variations in the stable hydrogen and oxygen isotope ratios(δD and δ¹⁸O) of precipitation,spring,river,and melt water. The similar seasonality in precipitation δ¹⁸O at different sites reveals the same moisture origin for water entering the headwaters of the Heihe River basin. The similarity in the seasonality of δ¹⁸O and d-excess for precipitation at Yeniugou and Urumchi,which showed more positive δ¹⁸O and lower d-excess values in summer and more negative δ¹⁸O and higher d-excess values in winter,indicates a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter. Higher d-excess values throughout the year for Yeniugou suggest that in arid inland areas of northwestern China,water is intensively recycled. Temporal changes in δ¹⁸O,δD,and d-excess reveal distinct contributions of different bodies of water to surface runoff. For example,there were similar trends for δD,δ¹⁸O,and d-excess of precipitation and river water from June to September,similar δ¹⁸O trends for river and spring water from December to February,and similar trends for precipitation and runoff volumes. However,there were significant differences in δ¹⁸O between melt water and river water in September. Our results show that the recharge of surface runoff by precipitation occurred mainly from June to mid-September,whereas the supply of surface runoff in winter was from base flow(as spring water) ,mostly with a lower runoff amount.

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