[Spatial Distribution Characteristics and Influencing Factors of Soil Organic Carbon Density in Yellow River Basin Based on MGWR Model].

As the largest terrestrial carbon pool, the spatial distribution characteristics and influencing factors of soil organic carbon have important implications for global carbon cycle processes. Soil organic carbon density (SOCD) and influencing factors were predicted in the Yellow River basin using a mixed geographically weighted regression (MGWR) model based on soil organic carbon density data and environmental factors. The results showed that:① the SOCD ranged from 0-14.82 kg·m-2 and 0-32.39 kg·m-2 for the soil depths of 0-20 cm and 0-100 cm, with mean values of 3.48 kg·m-2 and 8.07 kg·m-2 and reserves of 2.76 Pg and 6.48 Pg, respectively. The high SOCD value areas were mainly located in the southern part of the Qinghai-Tibet Plateau and Loess Plateau, and the low value areas were located in the eastern part of the upper Yellow River and the inland flow area. ②Among the ecosystem types, the SOCD of soil depth in 0-20 cm was in the descending order of:forest>water body and wetland>other>grassland>farmland>settlement>desert, with mean values of 4.52, 4.31, 3.84, 3.73, 2.89, 2.78, and 2.22 kg·m-2, respectively, and the SOCD of the 0-100 cm soil depth was in the descending order of:water bodies and wetlands>forest>other>grassland>farmland>settlement>desert, with mean values of 9.58, 9.58, 8.85, 8.66, 7.07, 6.81, and 5.29 kg·m-2, respectively. The SOCR in descending order was:grassland>farmland>forest>desert>water bodies and wetlands>settlement>others, with 1.40, 0.60, 0.47, 0.11, 0.07, 0.06, and 0.05 Pg at a soil depth of 0-20 cm and 3.31, 1.49, 0.99, 0.26, 0.17, 0.14, and 0.12 Pg at a soil depth of 0-100 cm, respectively. ③ The main factors affecting the SOCD distribution were intercept, profile curvature, NDVI, and precipitation; in addition, curvature and silt also had important effects on the deep SOCD distribution in the Yellow River basin. Among the ecosystem types, precipitation and NDVI were the main factors affecting the SOCD distribution. The intercept also had important effects on the SOCD distribution in the all ecosystems except forests, whereas curvature and silt only had important effects on deserts and other ecosystems. These results revealed the spatial distribution of SOCD, influencing factors, and SOCR in the Yellow River basin and can provide a scientific basis for carbon balance, soil quality evaluation, and ecological management restoration and consolidation in the region.

Transformation mechanism of ions on different waters in alpine region.

The study investigates transformation mechanism of ions on different waters in Alpine region through analyzed the hydrochemical characteristics of the major ions of precipitation, glacier and snow meltwater, supra-permafrost water and river water in permafrost regions in the Tibetan Plateau under climate warming. The results showed that, The relation between recharge and discharge was the major ways for ionic transformation of each water body. Precipitation and glacier and snow meltwater are the main input sources for ionic transformation, and river water is the final output source. Different water bodies had different ionic concentrations and different hydrochemical types. However, different water bodies in different months (from June to September) also had different hydrochemical types. The water - rock interaction, reactions for ions, dilution effect and other effect for ions played an important role in the process of ion transformation. The increasing of temperature would lead to the accelerated melting of glaciers, permafrost and snow in the alpine regions, so the amount of supra-permafrost water and glacier and snow meltwater will increase, which leads to the increase of runoff. Meanwhile, the increase of temperature makes evaporation stronger. The strong of evaporation will accelerate the transformation of liquid water to gaseous water. Moreover, ion translation and water conversion are synchronous. Accordingly, ions are also accelerating transformation in the process of accelerated transformation of water body. Climate change is not only the main driving force for multiphase water transformation, but also the main driving force for the ion transformation of various water bodies.

The sources of supra-permafrost water and its hydrological effect based on stable isotopes in the third pole region.

The sources of supra-permafrost water and its hydrological effects were studied, based on the presence of stable isotopes in 562 samples collected in different ablation periods from the source regions of the Yangtze River. The δ18O (δD and d-excess) values for the initial ablation, ablation, and end ablation periods were -10.18‰ (-71.39‰ and 10.08‰), -12.14‰ (-85.58‰ and 11.51‰) and -11.50‰ (-78.75‰ and 13.23‰), respectively. The order of the slopes for the supra-permafrost water evaporation lines from the different ablation periods was initial ablation (IA) > ablation (A) > end ablation (EA). An anti-altitude effect is documented here, for a specific altitude range, in what is believed to be the first record of such an occurrence. Outside of that range, clear altitude effects were apparent. We have been able to show that supra-permafrost water was mainly recharged by atmospheric precipitation, ground ice, and glacier and snow meltwater, in the initial ablation and end ablation periods, and contributions from glacier and snow meltwater were mainly concentrated in higher altitude regions. In contrast, in the ablation period, supra-permafrost water was mainly recharged by atmospheric precipitation and ground ice. The contributions of precipitation to supra-permafrost water were 78.79%, 85.47%, and 82.99% in the initial ablation, ablation, and end ablation periods, respectively. The contributions of ground ice to the supra-permafrost water were 14.05%, 14.53%, and 11.94%, respectively, while contributions of glacier and snow meltwater were 7.15% and 5.07% in the initial and end ablation period. For the initial ablation, ablation, and end ablation periods, contributions from atmospheric precipitation to the supra-permafrost water were 85.47%, 86.86%, and 86.84%, while contributions from ground ice were 14.53%, 13.14% and 13.16%, respectively.

Response mode of hydrochemical types of river water to altitude gradient in alpine regions.

The study investigates the hydrochemical type and characteristics of river water in permafrost regions in the Tibetan Plateau by analyzing 532 samples collected from the source region of the Yangtze River. The hydrochemical type of the river water was Cl--Na+-SO42-, and its hydrochemical characteristics were primarily influenced by the soil sources, though the influence of the sea sources and anthropogenic factors could not be ignored. Significant negative correlations were found between temperature and NO3-, SO42-, Mg2+, Ca2+, and between precipitation, relative humidity, and SO42- and Mg2+ in the river water. River water in the higher altitudes of over 5000 m above sea level was mainly recharged from glacier snowmelt water and by the supra-permafrost water and precipitation at the altitudes between 3500 and 5000 m above sea level. The controlled sources of hydrochemical characteristics of glacier snowmelt water were different for different ablation rates in the area with elevations of over 5000 m above sea level. Different hydrochemical types in different ablation rates implied the hydrochemical type was extremely sensitive to ablation periods in areas with elevation of over 5000 m above sea level. However, hydrochemical type was not sensitive to ablation periods from 3500 to 5000 m above sea level. The ionic concentration of glacier snowmelt water was mainly controlled by pollutants in glaciers and snow. Melting rates of glacier snowmelt water also had a certain effect on ionic concentration. Meanwhile, the stability of the hydrochemical type implied river water mainly controlled the hydrochemical type from 3500 to 5000 m above sea level. Hydrochemical type had no effect on elevation in end ablation.

[Space-time Characteristics and Environmental Significance of Stable Isotopes in Precipitation at an Arid Inland River Basin].

This study was based on one complete hydrological year sampling of precipitation and meteorological data of the Shiyang River Basin in the Wuwei Station (1531 m a.s.l.), Minqin Station (1389 m a.s.l.), and Xidahe Station(2897 m a.s.l.) from July 2013 to July 2014. This paper aims to analyze temporal and spatial variation of stable isotopes in local precipitation, and discuss the impact of environmental factors during precipitation. The stable isotope evolution correlation with temperature, humidity, precipitation, vapor pressure, and average relative humidity is analyzed. The results show that:①During the study period, the stable isotope of precipitation showed significant seasonal changes, lower in the winter and spring, higher in the summer and autumn;②The monthly average D-excess of Wuwei Station is lower than that of Xidahe Station. In addition to the possibility of different water vapor sources, the high-altitude mountain areas are more affected by local recirculating water vapor, and the secondary evaporation under the clouds in low-altitude plain areas is stronger;③The stable isotope of precipitation in the basin shows a significant temperature effect, and the precipitation effect is reflected on the weather scale, which may be affected by leaching or monsoon circulation;④The δ18O value of precipitation is negatively correlated with the average relative humidity. It may be that the secondary evaporation under the cloud is weakened by the increase of precipitation and humidity.

[Characteristics of Stable Isotopes and Analysis of Water Vapor Sources of Precipitation at the Northern Slope of the Qilian Mountains].

This study is based on precipitation samples from eight sites at the northern slope of the Qilian Mountains, combined with meteorological factors over the same period. Precipitation isotope characteristics, influence factors and the vapor sources of precipitation were analyzed, and the results show that:① The stable isotopes of precipitation in the study area show obvious seasonal changes, which are characterized by enrichment in the summer half-year and depletion in the winter half-year. The spatial precipitation δ18O value shows a significant downward trend with increasing altitude, and the altitude effect of the annual precipitation δ18O is -0.19‰/100 m, respectively;② At all stations, the slope and intercept of local meteoric water lines show an increasing trend from low altitude to high altitude. The high-altitude mountains above 2000 m are affected by local water vapor recirculation;③ The temperature effect is more significant and the temperature effect of δ18O is 0.64‰, and there is only a weak precipitation effect in summer;④ The results indicate that sub-cloud evaporation has a great influence on the δ18O of precipitation; the average raindrop evaporation rate of δ18O is 23%, 11%, 12%, and 16%,and the δ18O composition has been enriched by 46%, 27%, 38%, and 32% in May, June, July, and August from cloud base to ground, respectively.⑤ Under the condition of continuous rainfall in summer, the vapor sources of precipitation mainly come from the west and are affected by local evaporation of water vapor. The study enhances knowledge of isotopic evolution of precipitation and provides a basis for further study of isotopic hydrology in arid regions.

[Stable isotopes characteristics of precipitation over Shaanxi-Gansu-Ningxia and its water vapor sources.] / é™•ç”˜å®åœ°åŒºé™æ°´ç¨³å®šåŒä½ç´ ç‰¹å¾åŠæ°´æ±½æ¥æº.

Based on hydrogen and oxygen stable isotopes in precipitation and meteorological data over Shaanxi-Gansu-Ningxia provided by the Global Network of Isotopes in Precipitation (GNIP) and in previous literature, the spatial and temporal variations of oxygen stable isotopes in precipitation and their driving factors were analyzed, the local meteoric water line (LMWL) functions were established. The results showed that the slope and intercept of the LMWL changed in the order of Gansu

[Space-Time Characteristics and Environmental Significance of the Stable Isotopes in Precipitation in the Gulang River Basin].

Based on the precipitation samples and meteorological data simultaneously collected during individual precipitation events at the Gulang (2085 m a.s.l.) and Anyuan stations (2700 m a.s.l.) in Gulang, this article analyzes the temporal variation and local meteroic water lines and discusses the relationship between precipitation stable isotopes and temperature and precipitation and relative humidity. The results show that:① Gulang and Anyuan have higher δ18O values in summer and autumn and lower δ18O values in spring and winter, respectively; ② The vaule of δ18O decreases with increasing altitude, while the value of the d-excess increases, reflecting the gradual depletion of stable isotopes of precipitation when the air mass is rising along the slope; ③ The slope and intercept of the local meteroic water lines deviate from that of the global meteroic water lines, showing that they may also be affected by local water vapor recirculation, except for the dry environment and strong evaporation effect; and ④ The temperature effect of Gulang in the low-altitude area is more significant than that of the Anyuan station and the Gulang River Basin does not show a precipitation effect. It has been proven that precipitation is not the fundamental factor determining the δ18O of the precipitation in arid areas. The results of this study are helpful to further understand the water circulation mechanism in the Gulang River Basin.

[Influence of below-cloud secondary evaporation on stable isotope composition in precipitation in Northwest China.] / è¥¿åŒ—åœ°åŒºé™æ°´ç¨³å®šåŒä½ç´ çš„äº‘ä¸‹äºŒæ¬¡è’¸å‘æ•ˆåº”.

The precipitation isotope data and meteorological data of eight stations provided by GNIP (Global Network for Isotopes in Precipitation) and two stations from the present study, combined with HYSPLIT model and water droplet evaporation model were used to examine the spatial and temporal distribution of precipitation δ18O and d values in Northwest China. The secondary evaporative effect of existence was evaluated and then quantitatively discussed, with the sensitive factors of secondary evaporative effect being considered. The results showed that during the summer monsoon, the δ18O and d values decreased from south to north in Xinjiang, while the δ18O value increased but d values decreased from south to north and from east to west of Shaanxi-Gansu-Ningxia region. During the winter monsoon, the δ18O value decreased from east to west in whole Northwest region, while the d value increased from south to north in Xinjiang, decreased from south to north and increased slightly from east to west in Shanxi-Gansu-Ningxia. The slope and intercept (6.80, -0.07) of the atmospheric precipitation line in the summer monsoon period was significantly lower than that of annual mean (7.27, 3.37) and winter monsoon period (7.46, 6.07), indicating that the secondary evaporation was stronger during the summer monsoon. The evaporation ratio in the summer monsoon was 4.49%, which was higher than 3.65% in the winter monsoon. However, the evaporation ratio of the winter monsoon was higher than the summer monsoon around of Loess Plateau, which might closely relate to the increasing drought of the Loess Plateau in recent years. Finally, the intensity of secondary evaporation decreased with increasing relative humidity, precipitation and vapor pressure but increased with increasing temperature (greater than 0 ℃). The influences of those factors (humidity, precipitation, temperature and vapor pressure) on the secondary evaporation were dependent on the differences of ranges.

[Environmental Significance of the Stable Isotopes in Precipitation at Different Altitudes in the Tuolai River Basin].

Precipitation samples and meteorological data were collected simultaneously during individual precipitation events at Tuole station (3367 m a.s.l.) and Jiayuguan station (1658 m a.s.l.) in the Tuolai River Basin. A study of temporal variation, Local Meteoric Water Lines, and altitude change on precipitation stable isotopes was conducted. The relationships between precipitation stable isotopes and temperature, precipitation, average vapor pressure, and relative humidity were determined in order to explore the environmental significance of the stable isotopes at different altitudes in the middle reaches of the Qilian Mountains. The analysis indicated that the stable isotopes of the precipitation in Tuole and Jiayuguan station were characterized by pronounced seasonal variation, with Tuole having higher δ18O values in summer and autumn and lower δ18O values in spring and winter, while Jiayuguan displays higher δ18O values in spring and lower in other seasons. The d-excess was correlated negatively with δ18O, and the correlation coefficients between δ18O and d-excess decreased with increasing altitude due to weakening sub-cloud evaporation. The slope and intercept of the Local Meteoric Water Lines from Jiayuguan to Tuole rose significantly, showing an increasing trend from low altitude to high altitude. For the precipitation events above 10℃, δ18O of Tuole was positively correlated with the temperature, but the Jiayuguan results indicated the opposite. Sub-cloud evaporation weakened with high precipitation events in Jiayuguan. δ18O and d-excess were positively correlated with the average vapor pressure, which declined from Tuole to Jiayuguan. Since the water vapor pressure and saturated water vapor pressure increased, it was difficult to form precipitation with decreasing altitude. The local strong sub-cloud evaporation caused δ18O and δD was positive at low altitude, while the effect of moisture recycling is obvious, such that δ18O and δD are negative in high altitude areas. There is no significant positive correlation between the δ18O and the relative humidity of the precipitation in Jiayuguan, while Tuole displays an opposite pattern. The results of the study will provide a scientific basis for further study of precipitation isotopes in the Tuolai River basin.

[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.

[Environmental significance of wet deposition composition in the central Qilian Mountains, China].

A total of 90 precipitation samples were collected from individual precipitation events at the Qilian Alpine Ecology & Hydrology Research Station (Hulugou Station, 30 degrees 47'N, 90 degrees 58'E; 3 260 m a. s. l) located in the central Qilian Mountains from August 2012 to November 2013. All samples were analyzed for major cations (Na, K+, Ca2+ and Mg2+), anions (Cl- , NO3- and SO4(2-)) and conductivity. Precipitation EC values ranged from 2.26 to 482 µS x cm(-1) with an average value of 41.9 µS x cm(-1). The precipitation was of SO4(2-) -Mg(2+) -Ca2+ type, which contributed > 70% to the total ionic concentration. The same as the precipitation alkalinity, precipitation events occurred around summer showed lower concentrations, while it had higher concentrations in winter and spring with little precipitation and larger wind speed. Enrichment factor (EF), correlation and factor analysis indicated that regional crustal aerosols and species from central Asian and northwestern China arid regions brought by the westerly circulation were the major sources for these ions, some dust from human pollution were the secondary sources, and the contribution of sea salt was the least due to the long distance transport. These characteristics could be also confirmed by the correlation between ionic concentrations and metrological data in the study region. It is also interesting that the precipitation chemistry was different under the different atmospheric circulation: the monsoon precipitation, the interaction precipitation events ( influenced both by monsoon and westerly) and the westerly precipitation.

[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.