Stable isotopes in precipitation in Xilin River Basin, northern China and their implications

Abstract

Under the increasing pressure of water shortage and steppe degradation, information on the hydrological cycle in steppe region in Inner Mongolia, China is urgently needed. An intensive investigation of the temporal variations of δD and δ18O in precipitation was conducted in 2007–2008 in the Xilin River Basin, Inner Mongolia in the northern China. The δD and δ18O values for 54 precipitation samples range from +1.1‰ to −34.7‰ and −3.0‰ to −269‰, respectively. This wide range indicates that stable isotopes in precipitation are primarily controlled by different condensation mechanisms as a function of air temperature and varying sources of vapor. The relationship between δD and δ18O defined a well constrained line given by δD = 7.89 δ18O + 9.5, which is nearly identical to the Meteoric Water Line in the northern China. The temperature effect is clearly displayed in this area. The results of backward trajectory of each precipitation day show that the vapor of the precipitation in cold season (October to March) mainly originates from the west while the moisture source is more complicated in warm season (April to September). A light precipitation amount effect existes at the precipitation event scale in this area. The vapor source of precipitation with higher d-excesses are mainly from the west wind or neighboring inland area and precipitation with lower d-excesses from a monsoon source from the southeastern China.