Differential isotopic characteristics of eco‐hydrologic processes in a subtropical watershed, China

Abstract

AbstractIn order to better understand isotopic characteristics of eco‐hydrologic processes in subtropical zones, this study selected a typical subtropical watershed in China to investigate and determine the complex differential mechanisms inherent to this water body type. Results showed that stable isotopes in precipitation within a Local Meteoric Water Line in the Xiangxi River basin (where δD = (8.23 ± 0.27)δ18O + (17.97 ± 1.65); R2 = 0.94) weighted δD and δ18O average precipitation values were −22.11‰ and −5.23‰, respectively. Furthermore, enrichment trends in river water δ18O (−4.21‰ to −6.91‰) and δD (−25.11‰ to −38.13‰) and soil solution δ18O (−6.30‰ to −11.21‰) and δD (−11.21‰ to −34.57‰) were greater compared with precipitation δ18O (−0.23‰ to −12.06‰) and δD (0.54‰ to −98.52‰) and throughfall δ18O (−1.11‰ to −4.72‰) and δD (−2.11‰ to −24.95‰). This study found obvious seasonality and higher deuterium excess (d‐excess) values in precipitation during the dry season and lower values during the rainy season. Moreover, the orchard was more enriched and the coniferous and broad‐leaved mixed forest was more depleted in δD and δ18O compared with other land cover types. Precipitation was an important climate variable in subtropical watersheds under the influence of monsoon systems. According to results from the isotopic mixture model, precipitation input fractions were greater than 88% in the soil solution and greater than 21% in river water.