The hydrogen and oxygen isotopic compositions of precipitation in a forested watershed of the South Qinling Mts., China

The stable isotopic compositions (delta D and delta O-18) of precipitation were firstly investigated from May 2012 to November 2013 in the Jinshui River basin of the South Qinling Mts., China. The local meteoric water lines (LMWLs) based on all daily and monthly precipitation-weighted data were defined as delta D = 8.32 delta O-18 + 12.57 (r (2) = 0.957, n = 47, p < 0.001) and delta D = 8.11 delta O-18 + 11.59 (r (2) = 0.946, n = 15, p < 0.001), respectively. The fluctuations of daily deuterium excess (d-excess) values indicated the mixing moisture sources from the monsoon circulation during the rainy season and the local moisture recycling during the dry season in the river basin. The monthly precipitation-weighted values of d-excess confirmed the moisture sources and determined the temporal variations in moisture supply for the river basin. The precipitation amount and temperature effects were found to be significant, with amount gradient of - 0.06 parts per thousand/mm for daily delta O-18 variability and temperature gradients of - 1.51 and - 0.44 parts per thousand/degrees C for daily delta D and d-excess variability, respectively. However, the isotopes of local precipitation during precipitation events were almost unaffected by relative humidity due to overwhelming recycled moisture at relative humidity > 85%. The results of this research provide an effective method for tracing the local water hydrologic cycle in the South Qinling Mts., China.