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Precipitation plays an important role in global water cycle, and the stable hydrogen and oxygen isotopes of precipitation provide useful information in hydrological processes. To evaluate the controlling factors on stable isotopes of precipitation in the northwesternmost Tibetan Plateau (NWTP), the spatial-temporal variation of δ18O and δ2H in precipitation was investigated based on 120 event-based precipitation samples collected from 3 stations (Jiangka, Shaman and Xihexiu) during 2011–2014 and 45 monthly average precipitation data of Hetian station (GNIP) and 23 individual precipitation events of Shiquanhe station during 2001. The values of δ18O and δ2H in precipitation are more positive in the summer (June to July) and negative in the winter (November to March). The seasonal d-excess pattern observed in the NWTP is remarkably different from that in adjacent regions. The local meteoric water line (LMWL) was calculated as δ2H = 8.22 δ18O + 12.41 (R2 = 0.98, n = 194) based on the event-based samples. Temperature and altitude effects show significant influence on the precipitation δ18O in the study area. Sub-cloud evaporation and recycling moisture also are important controlling factors during the precipitation process. The sub-cloud evaporation decreased d-excess between 1.7% and 45.8%, and the d-excess decreased linearly with increasing sub-cloud evaporation at about 1.15‰ per 1% change of sub-cloud evaporation. The recycled moisture has an important influence on the precipitation on the Xihexiu, Shaman and Jiangka stations. The result of this study is helpful to the understanding of regional water cycling and optimal water resource management during water shortages.

The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China (ARNC). Water shortages also affect the stability of the region’s oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources (including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that: (1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains; (2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains; (3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and (4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.

Soil erosion is a critical environmental problem of the Chinese Loess Plateau (CLP). The effects of vegetation cover on soil erosion reduction under different rainfall types are not well understood especially in the eastern Chinese Loess Plateau (ECLP). In this study, we monitored runoff and sediment yield at the Fengjiagou water and soil conservation station with five types of vegetation cover (arbor trees (ARC), shrubs (SHC), arable (ABC), natural vegetation (NVC), and artificial grass (APC)) and three slope gradients (10°, 15°, and 20°) in the ECLP. Based on long-term monitoring data, five rainfall types were classified by the maximum 30 min rainfall intensity (I30). We also quantitatively revealed the interactive effects of different types precipitation, vegetation cover and slope gradients on regional soil erosion. The results showed that (1) The RII (13 times) and RIII (eight times) type are the most threatening erosive rainfall in this region. (2) The ARC and SHC type were most beneficial for soil and water conservation in the ECLP; The APC and ABC are not conductive to the prevention of regional soil erosion. (3) Runoff and sediment yields increased with the slope gradient. The farmland is vulnerable to soil erosion when the slope gradient exceeds 10°. The results of this study can improve the understanding of regional soil erosion processes on the ECLP and provide useful information for managing regional water and land resources.

Potential evapotranspiration (ET0) is an integral component of the hydrological cycle and the global energy balance, and its long-term variation is of much concern in climate change studies. The Loess Plateau is an important area of agricultural civilization and water resources research. This study analyzed the spatial and temporal evolution processes and influential parameters of ET0 at 70 stations in different topographical areas of the Chinese Loess Plateau (CLP). Using the Mann−Kendall trend, Cross wavelet transform, and the ArcGIS platform, the ET0 of each station was quantified using the Penman−Monteith equation, and the effects of climatic factors on ET0 were assessed by analyzing the correlation coefficients and contribution rates of the climatic factors. The results showed that: (1) the overall trend of the ET0 in different terrains of the Loess Plateau is consistent, however, the ET0 values differ; the hill region (HR) has the highest ET0, followed by the valley region (VR), and the mountain region (MR) has the lowest, and ET0 changes differ between seasons. (2) Spatial distribution characteristics of multiyear mean ET0 in the study are as follows: the ET0 values in mountain and hilly areas are decreasing from west to east, and the higher mean annual ET0 value in the VR is mainly concentrated in the eastern CLP. (3) In the past 58 years, the annual mean and the seasonal ET0 of the region showed increasing trends, however, differences in different terrains were obvious. (4) ET0 has significant correlations with El Niño−Southern Oscillation (ENSO), Pacific−North American teleconnection (PNA), and Atlantic Multidecadal Oscillation (AMO). The resonance period of ET0 and ENSO was 3−6 a, mainly in 1976−1985. The mean coherence phase angle was close to 360°, indicating that ET0 lags behind PNA by approximately 2−6 a; ET0 has a very strong positive correlation with AMO. (5) Relative humidity (RH) is the main influencing factor of ET0 change in the Loess Plateau. Temperature (T) variation has the highest contribution rate (42%) to the regional ET0 variation in the entire CLP. We should pay more attention to the variation of evaporation under future climate change, especially temperature change.

Soil NO3− in the South China Plain has recently received considerable attention because it is closely related to soil leaching. Elevated atmospheric O3 influences soil N through altered rhizosphere C allocation. Little is known about how elevated O3 (eO3) concentrations affect the availability of soil NO3−. Here, we used structural equation modeling (SEM) to investigate the direct and indirect influence of eO3 on soil NO3− in the rhizosphere of Yannong 19 (O3-sensitive) and Yangmai 16 (O3-tolerant) wheat (Triticum aestivum L.) cultivar. Compared with ambient O3 (aO3), eO3 led to a significant decrease in soil pH, soil moisture (SM), nitrification enzymes and protease and an increase in soil NH4+ and NO3−. SEM showed direct and indirect connections between eO3 and increased NO3− through nitrification enzymes, Protestant and total nitrogen. Additionally, based on redundancy analysis (RDA), O3 is the main element among the selected environmental factors, including soil pH, soil moisture (SM), total nitrogen, NH4+ and NO3−, that affects nitrification enzymes and Protestant. In conclusion, in the jointing stage in wheat, enzymes play an important role in determining the direct and indirect influence of eO3 on soil NO3− concentration.

By using 233 isotope samples, we investigated the spatial and temporal variations of δ(18)O and δ(2)H in precipitation and surface water, and the contribution of different water sources in the rivers within the Tarim River Basin (TRB), which receives snow/glacier meltwater, groundwater, and rainfall. Our study revealed a similar seasonal pattern of precipitation δ(18)O and δ(2)H at both the north and south edges of the basin, indicating the dominant effect of westerly air masses in the summer and the combined influence of westerly and polar air masses during the winter, although the southern part showed more complex precipitation processes in the summer. River water in the basin has relatively large temporal variations in both δ(18)O and δ(2)H showing a distinct seasonal pattern with lower isotope values in May than in September. Higher d-excess values throughout the year in the Aksu river and the Tizinafu river suggest that water may be intensively recycled in the mountains of the TRB. Based on isotopic hydrograph separation, we found that groundwater is the main water source that discharges the entire basin although individual rivers vary.