Abstract
The stable isotopic study of the mechanism of runoff replenishment in the Qinghai-Tibet Plateau is a time-consuming and complicated process requiring complex monitoring data and scientific evaluation methods. Based on the data of water stable isotopes (18O and 2H) in the Naqu River basin, the present paper developed a framework of the variable fuzzy evaluation model (VFEM) to provide a method to classify stable isotopes and generalize the source identification of water replenishment by rainfall or snowmelt in the Naqu River basin. The grade eigenvalues of tributaries were ranked from low to high as follows: 1, 1.005, 1.089, 1.151, 1.264, 1.455 and 2.624. Three sets of tributaries were distinguished. The grade eigenvalues of the Najinqu, Bazongqu, Mumuqu, Chengqu and Gongqu Rivers were small, indicating that these tributaries were strongly supplemented by precipitation and snowmelt; the grade eigenvalue of the Zongqingqu River was in the medium range (1.455); the third group included the Mugequ River with a high status value (2.624). This study mainly highlighted the combination of the classification of stable isotopes and plots of δ2H vs. δ18O in the source identification of water replenishment, which will be helpful for studying runoff replenishment and the evolution mechanism in the Qinghai-Tibet Plateau.
Highlights
The study of water cycle evolution to solve water resource and related environmental issues has become a significant task for hydrological observation processes
This paper presents a set of criteria using variable fuzzy evaluation model (VFEM) to determine the classification of stable isotopes for the identification of water replenishment in the Naqu River basin
A VFEM based on variable fuzzy sets was proposed to identify the classification of stable isotopes in the Naqu River basin, and the theory and methodology of the proposed model is presented here
Summary
The study of water cycle evolution to solve water resource and related environmental issues has become a significant task for hydrological observation processes. Variations in the stable isotopes of water, such as 18 O and 2 H, are widely used as environmental tracers in studying hydrological processes [2,3,4,5,6]. Isotopes of particular interest for hydrological studies include the stable isotopes of water (18 O, 2 H), which are incorporated within the water molecule (H2 18 O, 1 H2 H16 O), and exhibit systematic spatial and temporal variations as a result of isotope fractionations that accompany water-cycle phase changes and diffusion [8]. Stable- and radio-isotope tracers have been widely applied in Earth systems studies, including hydrological and climatological research, for their ability to provide a sharper focus on some of the underlying processes
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