Spatial and temporal variability of stable isotopes (δ18O and δ2H) in surface waters of arid, mountainous Central Asia

Characterization of spatial and temporal variability of stable isotopes (delta O-18 and delta H-2) of surface waters is essential to interpret hydrological processes and establish modern isotope-elevation gradients across mountainous terrains. Here, we present stable isotope data for river waters across Kyrgyzstan. River water isotopes exhibit substantial spatial heterogeneity among different watersheds in Kyrgyzstan. Higher river water isotope values were found mainly in the Issyk-Kul Lake watershed, whereas waters in the Son-Kul Lake watershed display lower values. Results show a close delta O-18-delta H-2 relation between river water and the local meteoric water line, implying that river water experiences little evaporative enrichment. River water from the high-elevation regions (e.g., Naryn and Son-Kul Lake watershed) had the most negative isotope values, implying that river water is dominated by snowmelt. Higher deuterium excess (average d = 13.9 parts per thousand) in river water probably represents the isotopic signature of combined contributions from direct precipitation and glacier melt in stream discharge across Kyrgyzstan. A significant relationship between river water delta O-18 and elevation was observed with a vertical lapse rate of 0.13 parts per thousand/100 m. These findings provide crucial information about hydrological processes across Kyrgyzstan and contribute to a better understanding of the paleoclimate/elevation reconstruction of this region.