Effects of season and slope orientation on stable isotopes of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains in China.

The subalpine shrub zone of the Qilian Mountains is an important water-retaining area, and it is crucial to clarify the processes of its hydrological cycle. Therefore, based on the stable isotope values of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, the characteristics of δD and δ18O of different water bodies and their hydraulic relationships with each other were studied. The results showed that the stable isotope values of precipitation exhibited the largest fluctuations, while they were the most stable for groundwater. Plant transpiration was stronger than the evaporation of other water bodies. The stable isotope of precipitation was enriched in high temperature and low humidity environments. Isotopic values of plant and soil water were higher and more stable on the semi-sunny slope than on the semi-shady slope. According to the stable isotopes, there was a strong hydraulic relationship between the different water bodies in the study area, and precipitation was the ultimate source of all of them. Precipitation replenished soil water through infiltration. Part of the soil water was absorbed by plants, while the rest continued to infiltrate to replenish groundwater. Groundwater and precipitation replenished the river water.

The competitive relationship of scrub plants for water use in the subalpine zone of the Qilian Mountains in China.

Samples of scrub plants and soil were collected from May to October 2019 in the subalpine scrub zone of the Qilian Mountains. Based on measured oxygen isotope values (δ18O) in plant xylem water and soil water, the multivariate linear mixed model (IsoSource) and the proportional similarity index (PS index) were used to analyze the using proportion for each potential water source and the competition relationship for water use of scrub plants in different growing periods and habitats. The results showed that the soil water content gradually decreased with increasing depth of the soil layer, with the maximum value in the soil layer of 0-10 cm. Most of the scrub plants mainly used soil water in the soil layer of 0-30 cm during the different periods of growing season, but Salix sclerophylla Anderss. and Salix oritrepha Schneid. on the semi-sunny slope habitat mainly used soil water in the soil layer of 40-80 cm during the middle period of growing season (July-August), with the proportion of 59.5% and 52.1%, respectively; and Potentilla fruticosa Linn. and Salix cupularis Rehd. on the semi-shady slope habitat mainly used soil water in the soil layer of 30-60 cm during the early period of growing season (May-June), with the proportion of 61.1% and 49.7%, respectively. The competition relationships of scrub plants for water use varied during different periods of growing season (P < 0.05). On the semi-sunny slope habitat, they were fiercest for Salix cupularis Rehd. and Rhododendron thymifolium Maxim., Potentilla fruticosa Linn., and Salix sclerophylla Anderss. during the early period of growing season; Salix cupularis Rehd. and Rhododendron thymifolium Maxim. during the middle period of growing season, and Salix sclerophylla Anderss. and Salix oritrepha Schneid. during the end period of growing season (September-October). On the semi-shady slope habitat, they were fiercest for Salix oritrepha Schneid. and Caragana jubata (Pall.) Poir. during the early period of growing season; Rhododendron przewalskii Maxim. and Rhododendron thymifolium Maxim. during the middle period of growing season; and Salix cupularis Rehd. and Salix oritrepha Schneid. during the end period of growing season. This study reveals the competitive relationship of scrub plants for water use in the subalpine zone and their response to environmental changes, so as to provide theoretical references for the ecological conservation in the ecologically fragile areas of the Qilian Mountains.

Contribution of recycled moisture to precipitation and its influencing factors in the subalpine zone of Qilian Mountains.

Recycled moisture, the part of precipitating vapor that comes from surface evapotranspiration, plays an important role in the hydrological process and the feedback of the land surface-atmosphere system. In this study, we use the δ2H and δ18O data of precipitation, plant water, and surface water systematically collected in the subalpine area of the Qilian Mountains from May to October, 2019, and assess the contribution of recycled moisture to precipitation based on the three-component isotopic mixing model. The results indicated that the main source of precipitating vapor comes from the advected vapor, and its contribution reaches up to 87.8 ± 1.6%. The contribution of local recycled moisture is 12.2 ± 1.6%, in which the proportion of transpiration and evaporation are 8.9 ± 0.6% and 3.3 ± 1.0%, respectively. In terms of the correlation between recycled moisture and its influencing factors, the temperature has a positive effect on evapotranspiration and promotes moisture recycling, while precipitation and humidity have a certain inhibition effect on evapotranspiration and reduce the contribution of recycled moisture.

[Stable Isotope Characteristics and Vapor Source of Precipitation in the South and North Slopes of Wushaoling Mountain].

We analyze the stable isotope characteristics and vapor source of precipitation in a monsoon marginal area in the southern and northern slopes of Wushaoling Mountain, northwestern China, using 97 precipitation samples collected from October 2016 to October 2017. Correlation analysis and HYSPLIT model are used to study the characteristics of stable isotopes in precipitation, local meteoric water line equation, temperature and precipitation effects, and vapor source. The study found the following results. ① The slope and intercept of the southern slope local meteoric water line were lower than of those of the northern slope and global averages. ② Although the isotope temperature effects and seasonal effects of both slopes were obvious, the temperature effect of the northern slope was more obvious than of that of the southern slope. ③ The stable isotopes of precipitation during the summer on the northern slope and the precipitation on the southern slope<5 mm revealed that the precipitation effect was weak. There was no obvious precipitation effect in other seasons or in other precipitation levels on both slopes. ④ Vapor from the northwest and north accounted for>90% of the total. The northern slope was rarely affected by monsoon vapor, but the southern slope was affected by the southeast monsoon during the summer. Local water vapor recycling contributed to water vapor in the southern and northern slopes of Wushaoling Mountain. This study could improve the cognition of precipitation isotopic evolution in alpine regions, and lays a foundation for further research on isotope hydrology in cold and arid regions.

[Hydrochemical Characteristics and Sources of Ions in Precipitation at the East Qilian Mountains].

Precipitation of the northwest China is different from that in other regions of China. The vapor reaches this region after long distance transportation with little precipitation, and the ratio of precipitation variation is large. Wushaoling at the east Qilian Mountains is an important divided line of climate in China. The east region of it is affected by South Asia and East Asia monsoon, while the west region of it is influenced by Westerly circulation. So ion combinations in precipitation are complex for the trajectories of water vapor transportation, the natural environments and the development levels of social and economy in different regions. Precipitation samples were collected at Heisongyi located at the east Qilian Mountains. Hydrochemical characteristics and sources of ions were analyzed by factor analysis, Enrichment factor analysis and back trajectory analysis. EC values in precipitation ranged from 29.20 to 892.00 µS·cm-1, which were controlled by alkaline element. The precipitation was weak alkaline with pH values ranging from 7.02 to 8.89. EC values in precipitation were higher in autumn and winter than in spring and summer, opposite to pH values. The type of precipitation was SO42--Ca2+ for the cation concentrations following the order of Ca2+ >Mg2+ >Na+ >NH4+ >K+ and the anion concentrations following the order of SO42- >Cl- >NO3-. The concentrations of K+, Mg2+, Ca2+, NH4+, Cl-, NO3- and SO42- were the highest in autumn, but the peak value of Na+ concentration appeared in winter. As a whole, ion concentrations were higher in autumn and winter than in spring and summer. Enrichment factor indicated that Na+and Cl- mainly came from marine source but Na+ partly originated from crust source in winter and Cl- partly originated from anthropogenic source in winter, and that K+, Mg2+ and Ca2+ mainly came from crust source except that Mg2+ partly originated from anthropogenic source in winter, and that NO3- and SO42- mainly came from anthropogenic source. The trajectories of water vapor transportation from directions of northwest, north, north with southeast, northwest with southeast, northwest with southwest, northwest with north and southeast were ion original sources in precipitation, and the major trajectory came from northwest direction. Among these trajectories of water vapor transportation, that from northwest, north and north with southeast appeared in each season, but that from northwest with southeast appeared in spring and summer, that from northwest with southwest and northwest and north with southeast appeared in summer. Though ions originated from marine transport by Westerly and monsoon, from crust provided by desert and Gobi in central Asia, Xingjiang and Mongolian plateau, and from humanity activity related to cities pollution and industrial and agriculture production of oasis at all trajectories, the concentrations of ions in precipitation were effected by the strong and weak variations of different weather systems.

[Analysis on chemical compositions of rainwater in summer, Lijiang City, China].

Rainwater samples were colleted from Lijiang City, China, in 23 May-2 July, 2006. Rainwater chemical compositions and sources were studied, using HYSPLIT model, ions tracer techniques, correlation and trend analysis. Total ionic concentration was dominated by SO4(2-) and Ca2+, which account for 65.5% and 15.6% respectively. Sort order of ions concentration is SO4(2-) > Ca2+ > Cl(-) > NO3(-) > Na+ > K+ > Mg2+. Total anions concentration is higher than total cations concentration in 13 rainwater events. The ratio of SO4(2-) to NO3(-) varies from 7.2 to 37.1 and average value is 15.7, it reflected SO4(2-) made great contribution to rainwater acidity in Lijiang City. The correlation among ions is significant due to the atmospheric chemical process and similar ionic sources, and correlation coefficient between SO4(2-) and NO3(-) is 0.74. And what's more, the negative correlation of ionic concentration, precipitation and the average wind speed is also outstanding. The source of NO3(-), SO4(2-), K+ and Ca2+ is mainly land dust, and the non-marine source percent of NO3(-), SO4(2-), K+, Ca2+, Mg2+ and Cl(-) is 100%, 98.8%, 96%, 99.3%, 46.7% and 50.3%, respectively. The main reason of atmospheric environmental variation in Lijing City is pollution caused by economic actions. The pollutants from surrounding industrial parks input into Lijiang City by local circulation, and from industrial regions of Southern Asia, Southeastern Asia and Southeastern China input into Lijiang City by monsoonal circulation.