Abstract
We 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 (δ D 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 δ D, 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.
Highlights
Precipitation is a primary input for the water cycle
We 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 (δ D and δ 18O) of precipitation, spring, river, and melt water
3.1 Isotopic evidence for the origins of moisture entering the headwaters of the Heihe River basin (i) Variation in precipitation δ D and δ 18O. δ D and δ 18O
Summary
Precipitation is a primary input for the water cycle. Spatial and temporal variations in stable hydrogen and oxygen isotope ratios (δ D and δ 18O) in precipitation can provide important clues to the origins of water and the climatic conditions under which it formed [1,2,3,4]. In the headwaters of the Heihe River basin, the primary mountain runoff is generated in the drainage of the western part of the main stream because precipitation tends to decrease from the southeast to the northwest [30]. Observation data from 40 stations within the basin, operated by the Hydrological Bureau of Gansu Province, revealed that sites recording precipitation of more than 300 mm were all located near the western part of the main stream. Based on this data, the drainage area in the western part of the main stream is the primary catchment in the Heihe River basin. The meteorological data recorded by the Dayekou station gave a highest July temperature of
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