Temporal variations of atmospheric water vapor δD and δ18O above an arid artificial oasis cropland in the Heihe River Basin

The high temporal resolution measurements of delta D, delta O-18, and deuterium excess (d) of atmospheric water vapor provide an improved understanding of atmospheric and ecohydrological processes at ecosystem to global scales. In this study, delta D, delta O-18, and d of water vapor and their flux ratios were continuously measured from May to September 2012 using an in situ technique above an arid artificial oasis in the Heihe River Basin, which has a typical continental arid climate. The monthly delta D and delta O-18 increased slowly and then decreased, whereas the monthly d showed a steady decrease. delta D, delta O-18, and d exhibited a marked diurnal cycle, indicating the influence of the entrainment, local evapotranspiration (ET), and dewfall. The departures of delta D, delta O-18, and d from equilibrium prediction were significantly correlated with rain amount, relative humidity (RH), and air temperature (T). The "amount effect" was observed during one precipitation event. delta D and delta O-18 were log linear dependent on water vapor mixing ratio with respective R-2 of 17% and 14%, whereas d was significantly correlated with local RH and T, suggesting the less influence of air mass advection and more important contribution of the local source of moisture to atmospheric water vapor. Throughout the experiment, the local ET acted to increase delta D and delta O-18, with isofluxes of 102.5 and 23.50mmol m(-2) s(-1) parts per thousand, respectively. However, the dominated effect of entrainment still decreased delta D and delta O-18 by 10.1 and 2.24 parts per thousand, respectively. Both of the local ET and entrainment exerted a positive forcing on the diurnal variability in d.