The altitude effect of δ18O in precipitation and river water in a Permafrost-Underlain headwater Basin, Northeastern Tibetan Plateau, China

Abstract

The altitude effect of stable isotopes in precipitation and river water is crucial for understanding hydrological cycles and reconstructing paleo-altitudes. In this study, we collected precipitation and river water samples along an altitude transect in the Binggou Basin, Northeastern Tibetan Plateau, and investigated the topographical and meteorological factors influencing δ¹⁸O in precipitation and river water (δ¹⁸O_P and δ¹⁸O_R). Our findings indicate that the δ¹⁸O_P lapse rate is − 0.25 ‰ per 100 m, closely matching the global average of − 0.28 ‰ per 100 m. The δ¹⁸O_R lapse rates, determined through linear fitting considering average, lowest, and highest basin altitudes, were − 0.29 ‰, −0.10 ‰, and 0.04 ‰ per 100 m, respectively. Notably, the linear fitting, multiple linear regressions, and boosted regression trees confirmed that average basin altitude significantly influences the δ¹⁸O_R, supporting the feasibility of paleo-altitude reconstruction in this region. Analyzing δ¹⁸O_R using the sampling site altitude, which is the lowest basin altitude, may result in lower lapse rates. For comparability between studies and the reasonableness of data analysis, we recommend using the average basin altitude for such altitude effect analyses. We observed higher spring δ¹⁸O_R lapse rates compared to summer, with altitude having a lesser impact on the summer δ¹⁸O_R, likely due to the freeze–thaw cycle and seasonal shift in river water sources. Our study highlights that δ¹⁸O_R lapse rates exhibit strong seasonality and variability, influenced by the seasonal runoff generation processes.