Stable isotopic variations (δD and δ¹⁸O) in a mountainous river with rapidly changing altitude: Insight into the hydrological processes and rainout in the basin

Abstract

Hydrological processes play an important role in stable isotopic compositional variations of the river water. The present study includes spatial distributions of stable hydrogen and oxygen isotopes (δD and δ18O) of a Himalayan River (the Teesta) to trace various hydrological processes and their associated roles on isotopic fractionation of river water. The δ18O compositions of the water samples varies between −12.2‰ and −5.4‰ (mean: −8.01‰ ± 1.81‰) and that of δD between −95.1‰ and −38.5‰ (mean: −57.6‰ ± 15.6‰). The observed compositional variation in δ18O, δD and d values of river water is mainly governed through snowmelt input, evaporation, and recycled moisture contribution. The variation of δ18O and δD values point towards an early melting of snow in the basin and a significant contribution of snowmelt to the river water. The orographic induced precipitation front appears to control the hydrological regimes in a distinct manner as reflected in the trend between d values and elevation. The rain shadow affected northern reaches of the basin are characterized with dry & arid climate triggering evaporation whereas, the windward southern side witness temperature influenced evaporation. The study suggests that the differential degree of recycled moisture contribution to the local precipitation is also a key component in bringing the stable isotopic variation in the river water. This varied magnitude of moisture recycling could result from uneven distribution of evapotranspiration and surface water evaporation. Results found that a rapid change in the altitude of a river basin can give rise to different hydrometeorological conditions, thereby resulting in simultaneous operation of almost all the major hydrological processes and a complex isotopic compositional variation in the river water. Also, the rainout percentage in the Teesta basin is found to be higher owing to this rapid rate of elevation increase.

Seasonal variation and influence factors of river water isotopes in the East Asian monsoon region: a case study in the Xiangjiang River basin spanning 13 hydrological years

“…For instance, the river water stable isotopes primarily reflect the characteristics of precipitation, as precipitation input acts as the primary water source (Sprenger et al, 2022;. Moreover, due to varying degrees of evaporative enrichment and mixing processes experienced by different water bodies within a basin, the river water isotopes markedly differ from those of the precipitation input and exhibit distinct seasonality (Jiang et al, 2021;Sun et al, 2021;Das and Rai, 2022). This disparity forms the basis for employing stable isotope techniques to investigate river water generation processes in basins, while the stable isotope techniques were widely used to indicate the water cycle processes (Boral et al, 2019;Xiao et al, 2020;Wu et al, 2021) and find extensive application in hydrometeorology modeling and diagnosis (e.g., Aggarwal et al, 2016;Sinha and Chakraborty, 2019;Zhiña et al, 2022) as well as in paleoclimate reconstruction (e.g., Steinman et al, 2010;Jiménez-Iñiguez et al, 2022;Emmanouilidis et al, 2022).…”

“…Extensive efforts have been made to investigate the extent of variations in river water isotopes and to examine the relationship between stable isotopes in river water and specific environmental factors (e.g., Yang et al, 2020;Das and Rai, 2022;Ren et al, 2023). Linear regression is an effective tool to build the empirical relationships between hydrometeorological factors and river water isotopes, while numerous empirical formulas have been developed and used for paleoclimate reconstruction and interpretation based on these empirical relationships (Kendall and Coplen, 2001;Nan et al, 2019).…”

“…Moreover, extreme-precipitation and drought events have become more frequent against the background of global climate changes, as evidenced in numerous regions worldwide (Nkemelang et al, 2018;Cook et al, 2018;Grillakis, 2019;Marengo et al, 2020;Cardoso et al, 2020). Furthermore, the scale effect and spatial heterogeneity have always been a problem in hydrological model research (Seyfried and Wilcox, 1995;Blöschl, 2006;Pechlivanidis et al, 2011;Devia et al, 2015), e.g., the representation of the observations at limited sampling sites on the whole basin scale with a large area. These introduce additional complexities and uncertainties in identifying the seasonal variation and influence factors of river water isotopes on a basin scale, and thus the interpretation of the extreme isotopic signals and the variations in river water isotopes and the representation of the site observation based on the spatial correlation analysis become nec-essary (Uchiyama et al, 2017;Boutt et al, 2019;Saranya et al, 2020).…”

Seasonal variation and influence factors of river water isotopes in the East Asian monsoon region: A case study in Xiangjiang River basin spanning 13 hydrological years

“…For instance, the stable river water isotopes primarily reflect the characteristics of precipitation, as precipitation input acts as the primary water source (Sprenger et al, 2022;Wang et al, 2023). Moreover, due to varying degrees of evaporation enrichment and mixing processes experienced by different water bodies within a basin, the river water isotopes markedly differ from that of the precipitation input and exhibit distinct seasonality (Jiang et al, 2021;Sun et al, 2021;Das and Rai, 2022). This disparity forms the basis for employing stable isotope techniques to investigate runoff generation processes in basins.…”

“…River water is commonly recognized as a natural integrator of basin hydrological processes, offering insights into the effects of hydrometeorological factors like air temperature, evaporation, precipitation input, and runoff discharge/water level (Yang et al, 2020;von Freyberg et al, 2022). Extensive efforts have been made to investigate the extent of variations in river water isotopes and examine the relationship between stable isotopes in river water and specific environmental factors (e.g., Yang et al, 2020;Das and Rai, 2022;Ren et al, 2023). However, in regions where new water mixes thoroughly with old water, the river water isotopes exhibit dampened signals, indicating that old water dominates the composition of stream water and that the response of river water isotopes to hydrometeorological factors is sluggish (Munoz-Villers and McDonnell, 2012;Streletskiy et al, 2015).…”