In this study, we analyzed the stable hydrogen and oxygen isotopes of precipitation and three different land use patterns (cultivated land, grass land, and forest land) at 0-15 cm and 15-45 cm in a karst ridge-trough area (Zhongliang Mountain, Beibei District, Chongqing) in May 2017 and September 2017 to investigate the spatial and temporal variation of stable isotopes in different soil profiles using the isotope tracer technique. The results show that:① The average values of the soil water δD and δ18O are -50.0‰±33.6‰ and -7.9‰±4.3‰, respectively, and all plot around the local meteoric water line (LMWL), indicating that precipitation is the main source of the soil water supply in this area. ② The seasonal variations of δD and δ18O of the soil water are significant in different months of the rainy season, May (-19.4‰±6.8‰ and -4.1‰±1.0‰)>September (-82.2 ‰±14.0‰ and -11.9‰±2.2‰). ③ However, there is no significant difference in the soil water δD and δ18O under different land use patterns. ④ The soil water δD and δ18O change with soil depth gradients, which decrease along the depth in vertical direction for all types of soil land use in May but mainly increase/decrease in the cultivated land and woodland/grassland in September, respectively.
Keywords: different land use patterns; hydrogen and oxygen isotopes; karst ridge-trough area; soil water; temporal and spatial variation.