Comprehensive analysis of relationship between vegetation attributes and soil erosion on hillslopes in the Loess Plateau of China

In soil and water conservation research, vegetation is considered to be a primary factor affecting soil erosion. Many studies focus on the relationship between soil erosion and a given attribute of vegetation. Few studies have attempted a comprehensive analysis of vegetation attributes. Thus, the aim of this study is to explain the relationship between vegetation and soil erosion in detail. We studied 104 vegetation plots and 104 soil samples in the Yangjuangou catchment, Loess Plateau, Shaanxi Province, China. According to a correlation analysis of the vegetation attributes and soil ¹³⁷Cs inventories, vegetation cover exerts a positive effect on soil erosion. In addition, vegetation aggregation increases with increasing soil loss. During this period of study, plant diversity can have different relationships with soil erosion according to the vegetation pattern. When vegetation distribution is relatively homogeneous, plant cover decreases with increasing diversity, and the soil loss increases. When vegetation pattern distributes between homogeneous and heterogeneous, the relationship between vegetation diversity and soil erosion is not obvious. When vegetation distribution is in a heterogeneous pattern, cover increases with increasing diversity, and soil loss decreases.     

The variation of soil temperature and water content of seasonal frozen soil with different vegetation coverage in the headwater region of the Yellow River, China

The variation and distribution of temperature and water moisture in the seasonal frozen soil is an important factor in the study of both the soil water cycle and heat balance within the source region of the Yellow River, especially under the different conditions of vegetation coverage. In this study, the impact of various degrees of vegetation coverage on soil water content and temperature was assessed. Soil moisture (θ _v) and soil temperature (T _s) were monitored on a daily basis. Measurements were made under different vegetation coverage (95, 70–80, 40–50 and 10%) and on both thawed and frozen soils. Contour charts of T _s and θ _v as well as a θ _v–T _s coupling model were developed in order to account for the influence of vegetation cover and the interaction between T _s and θ _v. It was observed that soil water content affected both the overall range and trend in the soil temperature. The regression analysis of θ _v versus T _s plots indicated that the soil freezing and thawing processes were significantly affected by vegetation cover changes. Vegetation coverage changes also caused variations in the θ _v–T _s interaction. The effect of soil water content on soil temperature during the freezing period was larger than during the thawing period. Moreover, the soil with higher vegetation coverage retained more water than that with lower coverage. In the process of freezing, the higher vegetation coverage reduced the rate of the reduction in the soil temperature because the thermal capacity of water is higher than that of soil. Areas with higher vegetation coverage also functioned better for the purpose of heat-insulating. This phenomenon may thus play an important role in the environmental protection and effective uses of frozen soil.     

Definition of the Quaternary Qiangtang Paleolake in Qinghai-Tibetan Plateau, China

Since the Quaternary, many lakes have been present in the Qinghai-Tibetan Plateau. As peculiar geological processes in the evolution of the uplifting of Qinghai-Tibetan Plateau, the distributions and evolutions of the Quaternary paleolakes in the Qinghai-Tibetan Plateau have been the focus of interest among the international geosciences circle. Comparisons of the newly obtained and existing data from field surveys, remote sensing images, characteristics of tectonic landforms and distribution of the lacustrine strata, the author have, for the first time, defined a large-sized Quaternary Qiangtang Paleolake. The paleolake starts from the east-westerly direction at Rutog in western Tibet, passing through Gêrzê, and finally ends at Nagqu in eastern Tibet. Its length is approximately 1,200 km; it is about 420 km at its widest point (north-southerly). The Paleolake forms an E-W (or NWW) ellipsoid with an estimated area of 354920 km2. The Paleolake is bordered by the Mts. Gangdisê and Nyainqêntanglha to the south and the Karakorum Pass-Tozê Kangri-Zangbagangri- Tanggula Pass to the north. It generally appears as a basinal landform with low mountains and valleys in the central part (altitudes of 4400 m) and higher altitudes (5000 m) in the peripheries. The formation and development of the Paleolake was controlled by the nearly E-W trending structures.     

Potential Oil and Gas-Bearing Basins of the Qinghai-Tibetan Plateau,China

A number of composite sedimentary basins are present on the Qinghai-Tibet (Tibetan) Plateau. Some of these basins are filled with marine sediments, whereas others are fault-bounded continental depressions. Mixed source-rock types are present, of variable organic matter content; source rocks are mainly carbonates and secondarily mudstones. Vitrinite reflectance and biomarker analyses show that Mesozoic and Cenozoic source rocks have reached the peak stages of oil generation; older source rocks may have generated natural gas. The hydrocarbon reserves of these basins are believed to total ～37.2 billion barrels. The Qiangtang-Qamdo basin probably has the greatest potential for oil exploration.     

青藏高原拉萨地块新生代超钾质岩与南北向地堑成因关系

青藏高原拉萨地块广泛分布有新生代超钾质岩,岩石地球化学和Sr-Nd-Pb同位素特征表明这些超钾质岩来源于与古俯冲环境有着密切联系的含金云母的富集地幔源区,它们主要喷发于25~10 Ma。同时在拉萨地块分布有多条南北向地堑(裂谷),且它们的切割深度可能到达下地壳的深部甚至岩石圈地幔,它们主要形成于23~8 Ma。拉萨地块大多数超钾质岩沿着新生代的南北向地堑(裂谷)分布,并且它们在形成时代和空间分布上存在着明显的耦合性,结合沿着印度-雅鲁藏布江缝合带分布的中新世埃达克质岩,笔者认为这些超钾质岩很可能与中新世早期北向俯冲的印度岩石圈沿着印度-雅鲁藏布江缝合带附近发生断离,以及由此而引起拉萨地块东西向伸展构造活动产生的南北向地堑(裂谷)系统有关。     

青藏高原土壤碳排放研究进展

青藏高原土壤碳排放研究是评估国家区域碳排放量和预测气候变化所可能导致影响的关键. 首先对青藏高原土壤碳排放的关键性影响因子进行探讨, 并分析了土壤碳排放的时空分布格局变化. 目前青藏高原土壤碳排放研究主要是针对高寒草甸及高寒草地生态系统, 较少涉及高寒荒漠, 研究区域较为分散; 土壤碳排放受到气候环境因素、生物因素及人为因素等多重因素的影响, 其中温度、土壤湿度、土壤区系生物、人为因素及多年冻土退化是最关键的影响因素; 土壤碳排放具有明显的时空变异性, 空间变异性在生物群丛、景观、区域和生物群系四个尺度体现, 时间变异性在日、季、年上体现. 总体而言, 青藏高原土壤碳排放的研究较少, 尤其关于大尺度、长时间序列的研究以及土壤碳排放的机理等方面的研究十分缺乏, 有待于后续加强研究.     

Assessment of eco-environment vulnerability in the northeastern margin of the Qinghai-Tibetan Plateau,China

The northeastern margin of the Qinghai-Tibetan Plateau is typically a vulnerable eco-environment where an overload of alpine meadows and serious soil degeneration have led to vulnerability to natural disasters. Consequently, this vulnerable eco-environment does not allow for rapid socioeconomic development, resulting in weak potential for sustainable development. The northeastern margin of the Qinghai-Tibetan Plateau in China is used for this case study, which sets up 17 impact factors of eco-environment vulnerability (EEV) to assess the indexes, including natural impact factors, economic impact factors and social impact factors. Subsequently, the study uses an analytic hierarchy process to endow index weights and proposes an assessment model of ^n P_i W_i /( _i = 1^n P_i W_i + _i = 1^n P_i W_i ) G = 1 - \sum\nolimits_{i = 1}^{n} {{{P_{i} \cdot W_{i} } /{( {\max \sum\nolimits_{i = 1}^{n} {P_{i} \cdot W_{i} } + \min \sum\nolimits_{i = 1}^{n} {P_{i} \cdot W_{i} } } )}}} to analyze and assess the dynamic changes in the EEV of the study area from 1987–2008. Finally, the correlation of the EEV and 17 impact factors is analyzed.     

青藏高原湖泊水化学与盐度的相关性初步研究

本文综合分析了青藏高原地区400多个湖泊的水化学成分(Mg2+、Ca2+、Sr2+、Sr/Ca和Mg/Ca)与湖水盐度的相关关系,以及这种关系随着湖水变化(不同采样时间和采样点以及蒸发实验)而产生的变化规律。认为:在青藏高原湖泊中,Mg2+与盐度具有较为稳定的正相关关系,而Ca2+、Sr2+、Sr/Ca以及Mg/Ca与盐度的相关性较弱且不稳定。而在特定的水化学类型的湖泊中,碳酸盐型湖泊的Mg2+、Ca2+以及Mg/Ca与盐度均没有明显的相关性。硫酸盐型湖泊中Mg2+和盐度呈现较高的正相关关系,而Ca2+以及Mg/Ca与盐度的相关性仍很弱。而在氯化物型湖泊中,Mg2+与盐度呈更强的正相关关系,Ca2+与盐度也呈一定的正相关关系,而Mg/Ca与盐度的相关性依然很弱。在特定的单个湖泊中,Ca2+以及Mg/Ca与盐度的相关性仍然不稳定或很弱,而Mg2+与盐度仍然保持明显的正相关关系。在青藏高原利用湖相沉积恢复特定湖区古环境演化序列的时候,Mg2+浓度是湖水古盐度一个较好的转换指标,而在应用Mg/Ca这一指标时应谨慎。     

Effects of vegetation restoration on soil physical properties of abandoned farmland on the Loess Plateau,China

To improve the ecological environment in China, the Chinese government implemented a country-wide ecological protection and reforestation project (namely the “Grain for Green Project”) in 1999 to return cultivated land with slopes of 25° or more to perennial vegetation. Vegetation restoration reduces soil erosion mainly by changing the soil physical properties. Different vegetation restoration methods might produce different impacts on soil physical properties. In this study, two vegetation restoration methods (i.e., natural restoration and artificial restoration) were compared on abandoned farmland in the typically hilly and gullied areas of the Loess Plateau of Northwest China. In the natural restoration method, the farmland was abandoned to natural vegetation succession without irrigation, fertilization or other artificial disturbances. In the artificial restoration method, the farmland was planted with black locust (Robinia pseudoacacia L.) and watered and cultivated for the first two years. Three soil physical properties (i.e., soil moisture, bulk density and aggregation) were investigated under the two vegetation restoration methods. The results showed that the soil moisture and soil bulk density were higher under artificial restoration than under natural restoration within the first three years of vegetation restoration. By the fourth year, the soil moisture and soil bulk density were higher under natural restoration than under artificial restoration. For the stability of soil aggregates?>?0.25 mm, the soil aggregates in the 0-20 cm soil layer were more stable under artificial restoration than under natural restoration, while the results were the opposite for the 40-60 cm soil layer. Overall, the soil physical properties were continuously improved during the restoration of vegetation on abandoned farmland. In choosing between vegetation restoration methods, natural restoration is preferable to artificial restoration, but artificial intervention is needed during the first three years.     

Investigating soil thermodynamic parameters of the active layer on the northern Qinghai-Tibetan Plateau

The soil thermodynamic parameters, including thermal conductivity, diffusivity and volumetric capacity within the active layer on the northern Tibetan Plateau, were calculated using the measured data of soil temperature gradient, heat flux, and moisture at four stations from October 2003 to September 2004. The results showed that the soil thermodynamic parameters exhibited clear seasonal fluctuation. The thermal conductivity and diffusivity in summer and autumn at Beiluhe, Kexinling, and Tongtianhe were larger than those in winter. The volumetric thermal capacity causes an opposite change; it was larger in autumn and winter than in summer. In spring, the soil thermal conductivity at the Kekexili station was larger than that in summer. Generally, fine-grained soils and lower saturation degrees in the topsoil might be a reason for the lower soil thermal conductivity in winter. For a given soil, soil moisture was the main factor influencing the thermodynamic parameters. The unfrozen water content that existed in frozen soils greatly affected the soil thermal conductivity, whose contribution rate was estimated to be 55 %. The thermodynamic parameters of frozen soils could be expressed as a function of soil temperature, volumetric ice content and soil salinity, while for the unfrozen ground the soil moisture content is the dominant factor for those thermal parameters. As for the soil thermal diffusivity, there exists a critical value of soil moisture content. When the soil moisture content becomes less than a critical value, the soil thermal diffusivity increases as the soil moisture content rises.     

Influence of vegetation factors on biological soil crust cover on rehabilitated grassland in the hilly Loess Plateau, China

Biological soil crusts (BSCs) perform essential ecosystem functions in arid and semi-arid ecosystems worldwide. The formation, development, and distribution of BSCs are influenced by changes in multiple environmental factors, including changes in the vascular plant community. The influence of changes in vegetation factors on BSC cover in 8-, 12-, and 16-year-old rehabilitated grasslands were studied in the hilly area of the Chinese Loess Plateau. The rate of degradation of BSCs underneath litter (P < 0.01) and the degradation cover of BSCs (P < 0.05) differed significantly between the 8- and 16-year-old successions. Stepwise multiple linear regression analysis showed that the main vegetation factors influencing the dynamics of BSC cover differed among the 8-, 12-, and 16-year-old rehabilitated grasslands. Basal cover, phytomass, and litter cover were the main vegetation factors influencing the dynamics of BSC cover on 8-year-old rehabilitated grassland. Phytomass, litter thickness, and litter cover were the main factors influencing the dynamics of BSC cover on 12-year-old rehabilitated grassland. On 16-year-old rehabilitated grassland, Pielou evenness index, litter thickness, and litter biomass were the main vegetation factors influencing degradation of BSC cover underneath litter, whereas basal cover, litter thickness, and litter biomass were the main vegetation factors influencing the degradation cover of BSCs. At particular stages of herbaceous succession, vegetation factors can have a large influence on changes in the community’s basal cover and litter, which are key factors influencing changes in BSC cover. The degradation of BSCs underneath litter may be a result of complicated eco-physiological processes.     

Winter and summer monsoonal evolution in northeastern Qinghai-Tibetan Plateau during the Holocene period

Climate change especially moisture condition in the northeastern Qinghai-Tibetan in China are mainly controlled by the strength and variability of Asian winter and summer monsoon. In this paper, we presented the climate record and related winter and summer monsoonal history in Gonghe Basin, northeastern Qinghai-Tibetan Plateau, based on the geochemical indicators (geochemical elements content, i.e., Fe₂O₃, CaO, Zr and Sr content, and geochemical parameters, i.e., the chemical index of alteration (CIA), Zr/Rb, Rb/Sr, CaO/MgO, SiO₂/TiO₂ and SiO₂/(Al₂O₃ + Fe₂O₃) ratio) of the peat deposits and ¹⁴C and OSL technologies. The regional temperature and humidity gradually increased in 10.0–8.5 cal ka BP, accompanied by enhanced summer monsoonal strength and decreased winter monsoonal strength. But climate became cold and dry between 8.5 cal ka BP and 7.6 cal ka BP owing to the stronger winter monsoon. During the 7.6–3.8 cal ka BP, stronger summer monsoon and weaker winter monsoon led to an optimal warm and humid condition, although it had several cold phases. From 3.8 cal ka BP to 0.5 cal ka BP, the regional climate tended to be cold and dry, with increasing winter monsoonal strength and decreasing summer monsoonal strength. Thereafter, the relatively warm and humid climate appeared again, due to the stronger summer monsoon. That is to say, the regional climate conditions are mainly related to the winter and summer monsoonal changes. These changes are consistent with palaeoclimatic records (monsoonal model) from the region influenced by the Asian monsoon in eastern China. In addition, nine cold events were recorded: 8.5–7.8 cal ka BP, 6.1–5.6 cal ka BP, 5.2–4.8 cal ka BP, 4.7–4.3 cal ka BP, 4.1–4.0 cal ka BP, 3.8–3.4 cal ka BP, 3.0–2.3 cal ka BP, 1.4–1.3 cal ka BP, and 1.0–0.5 cal ka BP, which are coincident with cold fluctuations in the high and low latitudes of the Northern Hemisphere on a millennial scale, as recorded by lakes, peat sediments, and ice cores in the Qinghai-Tibetan Plateau. In conclusion, Holocene millennial-scale climatic changes in Gonghe Basin were controlled by the dual function of Asian monsoonal changes and global cold fluctuations.     

Spatio-temporal variability in remotely sensed surface soil moisture and its relationship with precipitation and evapotranspiration during the growing season in the Loess Plateau,China

The distribution and variability of surface soil moisture at regional scales is still poorly understood in the Loess Plateau of China. Spatial and temporal dynamics of surface soil moisture is important due to its impact on vegetation growth and its potential feedback to atmospheric and hydrologic processes. In this study, we analyzed surface soil moisture dynamics and the impacts of precipitation and evapotranspiration on surface soil moisture using remote sensing data during the growing season in 2011 for the Loess Plateau, which contain surface soil moisture, precipitation, vegetation index and evapotranspiration. Results indicate that the areas with low surface soil moisture are mainly located in the semi-arid region. Under dry surface soil moisture, evapotranspiration temporal persistence has a higher positive correlation (0.537) with surface soil moisture temporal persistence, and evapotranspiration is very sensitive to surface soil moisture. But under wet surface soil moisture regime, surface soil moisture temporal persistence has a higher negative correlation (?0.621) with evapotranspiration temporal persistence. Correlation of surface soil moisture and monthly precipitation, evapotranspiration and vegetation index illustrated that precipitation was a significant factor influencing surface soil moisture spatial variance. The correlation coefficients between monthly surface soil moisture and precipitation was varied in different climatic regions, which was 0.304 in arid, 0.364 in semi-arid, 0.490 in transitional and 0.300 in semi-humid regions. Surface soil moisture is more sensitive to precipitation, evapotranspiration, in transitional regions between dry and wet climates.     

近百年来青藏高原冰川的进退变化

近百年来, 青藏高原的冰川虽然出现过两次退缩速率减缓或相对稳定甚至小的前进阶段, 但总的过程仍然呈明显的波动退缩趋势. 随着全球气候的波动变暖, 特别是进入20世纪80年代以来的快速增温, 使高原冰川末端在近几十年间出现了快速退缩. 以高原东部和南部边缘山地的冰川变化幅度最大, 而高原中北部山区和羌塘地区的冰川变化幅度较小, 相对比较稳定. 显示出青藏高原冰川对气候变化响应的敏感性在边缘山区较中腹地区更为敏感.     

Variations in soil properties and their effect on subsurface biomass distribution in four alpine meadows of the hinterland of the Tibetan Plateau of China

To understand and predict the role of soils in changes in alpine meadow ecosystems during climate warming, soil monoliths, extending from the surface to the deepest roots, were collected from Carex moorcroftii, Kobresia humilis, mixed grass, and Kobresia pygmaea alpine meadows in the hinterland of the Tibetan Plateau, China. The monoliths were used to measure the distribution with depth of biomass, soil grain size, soil nutrient levels, and soil moisture. With the exception of the K. pygmaea meadow, the percentages of gravel and coarse sand in the soils were high, ranging from 37.7 to 57.8% for gravel, and from 18.7 to 27.9% for coarse sand. The texture was finest in the upper 10 cm soil layer, and generally became coarser with increasing depth. Soil nutrients were concentrated in the top 15 cm soil layer, especially in the top 10 cm. Soil water content was low, ranging from 3 to 28.4%. Most of the subsurface biomass was in the top 10 cm, with concentrations of 79.8% in the K. humilis meadow, 77.6% in the mixed grass meadow, and 62.3% in the C. moorcroftii meadow. Owing to deeper root penetration, the concentration of subsurface biomass in the upper 10 cm of K. pygmaea soil was only 41.7%. The subsurface biomass content decreased exponentially with depth; this is attributed to the increase in grain size and decrease in soil nutrient levels with depth. Soil water is not a primary factor influencing the vertical and spatial distribution of subsurface biomass in the study area. The lack of fine material and of soil nutrients resulted in low surficial and subsurface biomass everywhere.     

青藏高原东北部15万年来的多年冻土演化

青藏高原东北部最近１５万年中至少存在４次多年冻土强烈扩展时期。第一次发生在１４０ｋａＢＰ的倒数第二次冰期，各地广泛发育冰楔；第二次发生在末次冰期早期（８０～５３ｋａＢＰ），若尔盖盆地发育融冻扰曲；第三次发生在２７～２３ｋａＢＰ，高原东北缘出现冰楔；第四次发生在２１～１０ｋａＢＰ，巴颜喀拉山以南地区和若尔盖盆地发育冰楔，黄河源、共和及青海湖周围出现原生砂楔。不考虑构造上升，上述冻土扩展时期多年冻土带下界高度较现代低１７００～１８００ｍ     

青藏高原拉萨地块松多榴辉岩的岩相学特征和变质演化过程

松多榴辉岩出露于拉萨地块的石英片岩中,主要由较为基性的金红石榴辉岩和较为酸性的石英榴辉岩组成。榴辉岩相矿物组合为石榴子石 绿辉石 绿帘石±多硅白云母±石英±金红石。岩石发生了较强烈的退变质作用,退变质矿物有角闪石、绿帘石、石英、钠长石及绿泥石。石榴子石变斑晶具有生长环带结构,变斑晶和基质石榴子石主要落入C类榴辉岩区,少数石榴子石变斑晶边部和基质石榴子石落入B类榴辉岩区;单斜辉石主要为绿辉石,少数Ⅰ世代和Ⅲ世代为普通辉石;角闪石均为钙质角闪石。根据石榴子石-绿辉石-多硅白云母矿物温压计计算,获得的温压范围为630～777℃和2.58～2.70GPa,峰期变质条件接近于石英-柯石英转变线。榴辉岩的原岩经历了从高绿片岩相、角闪岩相、榴辉岩相、角闪岩相到高绿片岩相的变质过程,这反映了与古特提斯洋闭合有关的俯冲进变质作用和随后的折返退变质作用。     

Microbial Succession in Response to Salinity in the Sediments of Lakes on the Northeastern Qinghai-Tibetan Plateau,China

正Salinity is an important factor controlling the microbial distribution in lakes.However little is known about how microbial communities evolve in response to salinity variation.In this study,we investigated the microbial     

Salinity control on long-chain alkenone distributions in lake surface waters and sediments of the northern Qinghai-Tibetan Plateau, China

Long-chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions, and have been found in many different types of lakes around the globe. A wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems. Lake environmental conditions, such as temperature (in particular) and salinity, are among the key factors controlling alkenone distributions in lacustrine settings. Here we investigated alkenone distribution patterns in lakes of the northern Qinghai-Tibetan Plateau, China, and their possible relationship with environmental conditions, by analyzing paired samples of suspended particulate matter in surface waters and surface sediments. Salinity of investigated lake waters ranges from almost 0 to ∼100 g/L, while temperature variation among the lakes is minimal, effectively eliminating temperature effects on the alkenone distribution patterns observed here. We show that (1) alkenone concentrations vary substantially between the lakes, yet controlling mechanisms remain elusive; (2) C₃₇/C₃₈ ratios are substantially lower in the lakes of the Qaidam Basin than in the Lake Qinghai region, probably indicating different alkenone producers in the two regions; and (3) large variations in %C_37:4 (the percentage of the C_37:4 alkenone), determined from both surface waters and sediments, are negatively correlated with salinity. We suggest that the %C_37:4 index could be used as a salinity indicator at least on a regional scale, with careful considerations of other potentially complicating factors. However, potential reasons for why salinity could significantly affect %C_37:4 values need further investigation.     

柴达木盆地中的砂楔及其意义

冰楔假形和原生砂楔是指示古冻土发育的重要证据。两者虽然具有相似的外观形态,但形成过程不同,在反映古气候、古环境和古冻土演化等方面具有不同的指示意义。在利用地层中的楔形构造推测古环境时,确定其类型是正确解读其环境意义的前提。本文讨论了柴达木盆地发现的楔形构造,通过楔形围岩和充填物中的一些微结构判断其属于原生砂楔,进而探讨了这些砂楔代表的环境意义和多年冻土发育状况。柴达木盆地中的砂楔主要形成在末次冰消期的Heinrich 1（H1）和Younger Drays两次降温事件期间。这表明,末次冰消期,柴达木盆地地表几乎全部被风沙覆盖,处于极端干旱的沙漠环境,年平均气温较现在降低6℃左右,多年冻土下界较现在下降了约1000 m。然而,多年冻土并没有占据整个盆地,在盆地中部和南部保留着大片融区,据此推测,即使末次冰期时期,柴达木盆地仍然保留一定面积的融区。末次冰期以来,青藏高原主体和祁连山两大现代多年冻土区并没有通过柴达木盆地连成一片。