Characteristics of Water Isotopes and Water Source Identification During the Wet Season in Naqu River Basin, Qinghai–Tibet Plateau

Abstract

Climate change is affecting the discharge of headstreams from mountainous areas on the Qinghai–Tibet Plateau. To constrain future changes in discharge, it is important to understand the present-day formation mechanism and components of runoff in the basin. Here we explore the sources of runoff and spatial variations in discharge through measurements of δ2H and δ18O in the Naqu River, at the source of the Nu River, on the Qinghai–Tibet plateau, during the month of August from 2016 to 2018. We established thirteen sampling sites on the main stream and tributaries, and collected 39 samples from the river. We examined all the water samples and analyzed them for isotopes. We find a significant spatial variation trend based on one-way analysis of variance (ANOVA) (p < 0.05) between Main stream-2 and tributaries. The local meteoric water-line (LMWL) can be described as: δ2H = 7.9δ18O + 6.29. Isotopic evaporative fractionation in water and mixing of different water sources are responsible for the spatial difference in isotopic values between Main stream-2 and tributaries. Based on isotopic hydrograph separation, the proportion of snowmelt in runoff components ranges from 15% to 47%, and the proportion of rainwater ranges from 3% to 35%. Thus, the main components of runoff in the Naqu River are snowmelt and groundwater.

Characteristics of hydrogen and oxygen isotopes and their differences of different water bodies in the subalpine shrubland of the eastern Qilian Mountains in China

“…In general, mainstream and tributary river water have similar seasonal differences (Li et al 2016b). However, the isotopic values of the mainstream and tributary river water were different in study area, which may be related to the evaporative fractionation and the recharge source of river water (Chen et al 2019). In spring, the main recharged sources of tributary river water were snow and permafrost meltwater, resulting in isotope values of river water lower.…”

Water use strategies of Nitraria tangutorum in the lake-basin region of the Badain Jaran Desert

“…As scarce local rainfall inputs cannot offset for the water loss ( Ma et al., 2014 ; Dong et al., 2016 ), another recharge source is essential. There are conflicting opinions regarding the regional water cycle ( Chen et al., 2014 ; Zhan et al., 2018 ; Wang et al., 2021 ). Some researchers have concluded that local rainfall does not contribute substantially to the regional water systems ( Chen et al., 2005 ; Dong et al., 2016 ; Jin et al., 2018 ).…”

“…The vertical profile of the soil water isotope composition integrates the processes involved in rainfall replenishment, groundwater recharge, blending with pre-existing water, and evaporation ( Tang and Feng, 2001 ; Brooks et al., 2015 ; Wang J. et al., 2019 ). Isotopic enrichment of the surface soil ( Figures 4 , 5 ) was influenced by evaporation ( Zhou et al., 2019 ), as well as evaporative water vapor condensation ( Chen et al., 2014 ), of which strong evaporation resulted in a lower SWC in this layer ( Figure 2 ). In comparison, the deeper soil water contains less heavy isotopes than the shallower layers, primarily attributable to the fact that deep soil layers were less influenced by evaporation and more affected by capillary upward recharge of groundwater containing light isotopes ( Wu et al., 2018 ; Zhou et al., 2019 ).…”

The Chemical Weathering of Rocks and Its Carbon Sink Effect in the Naqu River Basin of the Nujiang River Source Area, Southwest China

“…The Naqu River, which is 460 km long, covers 16,350 km 2 of total drainage area [20]. The Naqu River is composed of four main tributaries, which are, Chengqu, Mugequ, Gongqu, and Luoqu from north to south [21]. Most of the Naqu River basin is located in a plateau subfrigid monsoon semi-humid climate zone, with intensive solar radiation and thin air.…”