A rapid groundwater recharge and circulation system has developed in Qaidam Basin, China. Stable H and O isotopes were monthly sampled in both river water and groundwater, and water table fluctuations were monitored over a complete seasonal cycle from dry-season to wet-season conditions in the Nalenggele River catchment in Qaidam Basin. The main goals are to demonstrate and explain rapid circulation in the groundwater system. A distinct seasonal fluctuation of the water table with associated stable isotopic variations can be observed in the alluvial-fluvial fan of the Nalenggele River catchment. During the wet season, replenishment of the aquifer results in a rising water table rises. The recharge mechanism appears to be related to the coincidence of several favorable hydrological conditions: an abundant recharge water source from summer precipitation and glacial-snow melt in the high Kunlun mountains, large-scale active faults, a volcanic crater and other macro-structures that act as favorable recharge conduits, the large hydraulic head from recharge areas to the alluvial-fluvial fan, and the presence of over 100 m of unconsolidated sand and gravel acting as the main aquifer. Warming climate is expected to increase precipitation and to accelerate melting of glaciers in the Kunlun Mountains, increasing recharge and leading to rapid rise in the water table in the alluvial-fluvial fan. Increased recharge in the future will provide water of improved quality to the Qaidam Basin, and will allow management of land in ways that reduce soil salinity and alkalinity.

The stability and safety of water environment are the foundation of agricultural development. The possibility of salinization and desertification in the oasis agricultural area is much higher than that in other areas, for the population density, lack of water resources and high salinity. Therefore, it is necessary to study the water environment of irrigation water in this area, so as to make a reasonable water resource utilization and protection plan. In the agricultural irrigation period (from Apr. to Sep.) and non-irrigation period (from Oct. to Mar. of the next year), there were 9 sampling points set up from the source area to the oasis of the middle and lower reaches in Shiyang River Basin. Evaluating the irrigation water quality of surface water by ion concentration, SAR and end-member mixing diagram. The results shown: (1) the dilution effect of precipitation has a decisive influence on the ion concentration of surface water in the watershed. Due to the overlapping of irrigation period and rainy season, rainfall dilution makes irrigation water quality better. (2) There are spatial differences in hydrochemical types. The upstream hydrochemical type is mainly Ca-HCO3 type. The hydrochemical type of the middle and lower reaches is Ca (Na) - HCO3 mixed type. The upstream surface water is very suitable for agricultural irrigation, and the middle and downstream oasis area is suitable. (3) Surface rock weathering and evaporation crystallization are the main factors affecting the hydrochemical characteristics of surface water. Due to changes in the underlying surface environment in a short time, it is unlikely that the water quality will deteriorate. (4) In recent years, with the increase in precipitation caused by climate change and the strict environmental protection policies, the risk of deterioration of irrigation water quality is greatly reduced, surface water may be more suitable for agricultural irrigation.

The dissolved organic carbon(DOC) content of rivers is the most active part of the carbon cycle migration in the basin under consideration, and it is the basis for a comprehensive understanding of the regional carbon cycle. In this study, we periodically took samples from four monitoring stations in the Xiying River Basin of the Qilian Mountains in the northern Qinghai-Tibet Plateau. We calculated the fluxes of organic carbon in the rivers within the study area and will discuss the influencing factors of Dissolved Organic Carbon concentration in these rivers in this paper. Our results showed that: (1) The DOC concentration and output flux in the inland river runoff area are basically the same as those in the Heihe River Basin, but far lower than those in the low-latitude monsoon climate zone and most of the basins in the Eurasian Arctic region. This is mainly due to the small river runoff and low DOC concentration in the area. (2) The Dissolved Organic Carbon concentration and transport flux of the rivers show significant seasonal changes, with the Dissolved Organic Carbon content in summer and autumn being higher than in winter and spring. (3) The larger runoff causes higher concentrations of dissolved organic carbon in rivers. Runoff is the primary means of carbon migration in the Inland River Basin. There are significant carbon migrations from the upstream to the middle and downstream sections of the Inland River Basin.