2.2 Sampling and laboratory analysis
From April 2015 to October 2017, the researchers conducted monthly multi-water bodies sampling work in the Xiying River Basin (Fig.1; Table1). The 655 precipitation, reservoir water and river water were collected for this research (Fig.1; Table1).
For reservoir water sampling, the bottles were first flushed with runoff water 3 times, then each bottle was placed under the water surface until three quarters of the volume of the bottle was filled. The two sampling bottles were continuously collected by means of the above method. Before the experiment, all the collected samples were stored in the freezer (-5℃). The researchers installed a precipitation collection device to collect samples from the collection device at 20.00 (Beijing time). If the precipitation was snow, it was filled into the vial after it had naturally melted at room temperature indoors in the laboratory. All the samples were analyzed using a liquid water isotope analyzer DLT-100 (Los Gatos Research, Inc.) in the Stable Isotope Laboratory, College of Geography and Environmental Science, Northwest Normal University. The precision of measurement is ±0.6% for δ D and ±0.2% forδ 18O, respectively. The isotope ratio of the samples was expressed as parts per mil (&) relative to the Vienna Standard Mean Ocean Water (V-SMOW): δ (‰) = (R S/R V-SMOW-1) ×1000.
Table 1 Date for sampling station