Northeast Tibetan Plateau Research Articles

Satellite-based simulation of soil freezing/thawing processes in the northeast Tibetan Plateau

Accurate quantification of the distribution and characteristics of frozen soil is critical for evaluating the impacts of climate change on the ecological and hydrological systems in high-latitude and -altitude regions, such as the Tibetan Plateau (TP). However, field observations have been limited by the harsh climate and complex terrain on the plateau, which greatly restricts our ability to predict the existence of and variations in frozen soils, especially at the regional scale. Here, we present a study relying solely on satellite data to drive process-based simulation of soil freeze-thaw processes. Modifications are made to an existing process-based model (Geomorphology-Based Eco-Hydrological Model, GBEHM) such that the model is fully adaptable to remote sensing inputs. The developed model fed with a combination of MODIS, TRMM and AIRX3STD satellite products is applied in the upper Yellow River Basin (coverage of ~2.54 × 105 km2) in the northeast TP and validated against field observations of freezing and thawing front depths (Dft) and soil temperature (Tsoil) at 54 China Meteorological Administration (CMA) stations, as well as frozen-ground types at 22 boreholes. Results indicate that the developed model performs reasonably well in simulating Dft (R2 = 0.69; mean bias = −0.03 m) and Tsoil (station averaged R2 and mean bias range between 0.90–0.96 and −0.51~−0.14 °C at eight observational depths, respectively), and outperforms the original GBEHM forced with ground-measured meteorological variables. The frozen-ground types are also (in general) accurately identified by the satellite-based approach, except for a few permafrost boreholes located near the permafrost boundary regions. Additionally, we also demonstrate the importance of considering dynamic soil water content in frozen soil simulation: We find that a static-soil-moisture assumption (as used in previous studies) would lead to biased soil temperature estimates by >0.5 °C. Our study demonstrates the value of using satellite data in frozen-soil simulation over complex landscapes, potentially leading to a greater understanding of soil freeze-thaw processes at the regional scale.

Centennial-scale process activity in a complex landslide body in the Qilian Mountains, northeast Tibetan Plateau, China

Mass movements in China typically encompass landslides, rockfalls, and debris flows, and these processes affect almost 70% of all mountain areas of China. An improved understanding of geomorphic process dynamics and their drivers and process histories are important prerequisites for a proper assessment and a sustainable management of mountain hazards. Tree rings have on varied occasions proven to be a reliable tool for the acquisition of data on past mountain hazards. Here we present the first reconstruction of past landslide activity on a slope in the Qilian Mountains, northeast Tibetan Plateau, China. To this end, a total of 543 Qilian juniper (Sabina przewalskii Kom.) samples were selected from 239 trees growing on or next to a complex landslide body, with the aim to reconstruct past landslide histories at the site. The dataset of disturbed trees was complemented with 174 increment cores from 84 reference Qilian juniper trees growing on three adjacent, yet undisturbed sites. Based on the dating of the samples and the interpretation of growth disturbances (GD) in the tree-ring series of affected trees, we provide the first reconstruction of past landslides as retrieved from a dendrogeomorphic record covering more than a millennium (956–2011 CE). Results show that the first detectable GD occurred as early as in 1042 CE, followed by seven major landslide reccurrences in 1703, 1816, 1848, 1863, 1913, 1970, and 1982. Comparison between our landslide record and a dendroclimatic precipitation reconstruction points to the crucial role of major, longer-term wet precipitation anomalies on landslide occurrence.

Hf-Nd-Sr isotopic fingerprinting for aeolian dust deposited on glaciers in the northeastern Tibetan Plateau region

Abstract This study investigated the isotopic compositions of Hf, Nd, and Sr in aeolian dust deposited in several glacier basins of the northeast Tibetan Plateau in order to trace the source and provenance of long-range transported (LRT) dust in the region. Transmission electron microscope (TEM) and energy dispersive X-ray spectrometer (EDX) measurements and dust size distributions both indicated that LRT dust was dominant in glacier cryoconite and snowpacks. Isotopes of Hf-Nd-Sr exhibited a generally heterogeneous geographic distribution that varied from north to south. The northern sites (e.g. Miaoergou Glacier) in the Tianshan Mountains showed much higher eNd and eHf values, whereas the southern sites (e.g. Yuzhufeng Glacier) in the Kunlun Mountains had lower eNd, with the Hf isotope exhibiting two parts: one positive eHf section and one negative eHf section. Lower 87Sr/86Sr ratios were apparent in the Miaoergou Glacier compared to other locations. In general, the Miaoergou Glacier had similar Hf-Nd-Sr isotopic compositions to those of southern Mongolian Gobi and Taklimakan Deserts. By contrast, Qilian Mountain locations exhibited similar Hf, Nd, and Sr isotopic compositions to those of the north Tibetan Plateau soil crust and Chinese Gobi Deserts. However, the Yuzhufeng Glacier, located in the hinterland of the Tibetan Plateau, had LRT dust that was derived predominantly from the north Tibetan Plateau desert and surface crust, but also partly from the Taklimakan desert. Compared with Nd Sr isotopes, Hf Nd isotopes provided new evidence for LRT dust transport. For example, the Yuzhufeng and Miaoergou Glaciers had similar Hf Nd isotopes to those of the Taklimakan Desert and Mongolian Gobi, respectively, implying the potential LRT dust source and atmospheric transport routes. The marked spatial differences in LRT dust source were mainly caused by large-scale atmospheric circulation interactions (e.g. the Mongolian High and Westerlies) during spring and summer. Wind stream analysis and MODIS AOD also demonstrated the potential differences in the sources of dust and the routes taken between northern and southern locations. This work provides new evidence and a more complete view of aeolian transport over the northeast Tibetan Plateau region under the current climate.

Understanding changes in the water budget driven by climate change in cryospheric‐dominated watershed of the northeast Tibetan Plateau, China

AbstractGlacial retreat and the thawing of permafrost due to climate warming have altered the hydrological cycle in cryospheric‐dominated watersheds. In this study, we analysed the impacts of climate change on the water budget for the upstream of the Shule River Basin on the northeast Tibetan Plateau. The results showed that temperature and precipitation increased significantly during 1957–2010 in the study area. The hydrological cycle in the study area has intensified and accelerated under recent climate change. The average increasing rate of discharge in the upstream of the Shule River Basin was 7.9 × 106 m3/year during 1957–2010. As the mean annual glacier mass balance lost −62.4 mm/year, the impact of glacier discharge on river flow has increased, especially after the 2000s. The contribution of glacier melt to discharge was approximately 187.99 × 108 m3 or 33.4% of the total discharge over the study period. The results suggested that the impact of warming overcome the effect of precipitation increase on run‐off increase during the study period. The evapotranspiration (ET) increased during 1957–2010 with a rate of 13.4 mm/10 years. On the basis of water balance and the Gravity Recovery and Climate Experiment and the Global Land Data Assimilation System data, the total water storage change showed a decreasing trend, whereas groundwater increased dramatically after 2006. As permafrost has degraded under climate warming, surface water can infiltrate deep into the ground, thus changing both the watershed storage and the mechanisms of discharge generation. Both the change in terrestrial water storage and changes in groundwater have had a strong control on surface discharge in the upstream of the Shule River Basin. Future trends in run‐off are forecasted based on climate scenarios. It is suggested that the impact of warming will overcome the effect of precipitation increase on run‐off in the study area. Further studies such as this will improve understanding of water balance in cold high‐elevation regions.

Tomographic imaging of the 2017 Ms7.0 Jiuzhaigou earthquake source region and its implications on material extrusion in the northeast Tibetan plateau

Due to the heavy damages caused by the 2017 Ms 7.0 Jiuzhaigou earthquake that occurred in a complex tectonic environment, investigations on the seismogenic structure and tectonic environment are very important for understanding the geodynamic mechanism and mitigating earthquake hazards in the region. In this work, we present a high-resolution 3-D crustal seismic model for the source region of the Jiuzhaigou earthquake by exploiting the arrival times of aftershocks based on double difference tomography. Our results revealed that zones of Jiuzhaigou's rupture fault and aftershocks predominantly coincide with the high-velocity anomalies that are surrounded by the low-velocity anomalies, from the western territory to the aftershock zone. An area with a high Poisson's ratio ~0.28 is primarily the cradle for most of the aftershocks, and the lithology is interpreted as consisting of mafic and calcium-rich rocks. In the mid-crust, tomographic images exhibit a low-velocity zone in and around the source region. This low-velocity zone originates from the interior of the Tibetan Plateau, extends across the thrust faults (the Longriba fault and the Minjiang fault and the Jiuzhaigou's causative fault) and then finally encounters the strike-slip faults (the Tazang fault and East Kunlun fault). The counter belt of both the Tazang fault and East Kunlun fault features high-velocity anomalies. The mid-crust low anomalous zone is characterized by a high Poisson's ratio and low shear wave velocity, which indicates a weaker crust that easily flows and deforms. Therefore, we propose that this low velocity is a crustal channel flow in the vicinity of seismic sources, which causes the transformation from thrusting to strike-slip motion in the study area.

Spatial variability, mixing states and composition of various haze particles in atmosphere during winter and summertime in northwest China

Pollutants, which are usually transported from urban cities to remote glacier basins, and aerosol impurities affect the earth's temperature and climate by altering the radiative properties of the atmosphere. This work focused on the physicochemical properties of atmospheric pollutants across the urban and remote background sites in northwest China. Information on individual particles was obtained using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). Particle size and age-dependent mixing structures of individual particles in clean and polluted air were investigated. Aerosols were classified into eight components: mineral dust, black carbon (soot)/fly ash, sulfates, nitrates, NaCl salt, ammonium, organic matter, and metals. Marked spatial and seasonal changes in individual particle components were observed in the study area. Aerosol particles were generally found to be in the mixing state. For example, salt-coated particles in summer accounted for 31.2–44.8% of the total particles in urban sites and 37.5–74.5% of the total particles in background sites, while in winter, almost all urban sites comprised >50%, which implies a significant effect on the radiative forcing in the study area. We found that in PM2.5 section, the internally mixed black carbon/organic matter particles clearly increased with diameter. Moreover, urban cities were characterized by atmospheric particles sourced from anthropogenic activities, whereas background locations exhibited much lower aerosol concentrations and increased particle density, originating from natural crustal sources (e.g., mineral dust and NaCl salt), which, together with air mass trajectory analysis, indicates a potential spatial transport process and routes of atmospheric transport from urban cities to background locations. Thus, this work is of importance in evaluating atmospheric conditions in northwest China and northeast Tibetan Plateau regions, to discover the transport processes and facilitate improvements in climatic patterns concerning atmospheric impurities.

Tracing the Provenance of Long-Range Transported Dust Deposition in Cryospheric Basins of the Northeast Tibetan Plateau: REEs and Trace Element Evidences

Based on cryoconite and snow dust samples collected from various glaciers and snowpacks in northeast Tibetan Plateau (NETP) margin and surrounding areas, this study investigated the rare earth element (REE) and trace element composition of long-range transported (LRT) dust in glacier surfaces at the NETP locations, in order to trace its source areas and the transport over the region. Results showed that the deposited dust in NETP mainly originated from the adjacent Qaidam Basin, Badain Jaran and Taklimakan Deserts based on the similarity in (La/Sm)N, Th/YbN and Nb/YbN ratios. However, most samples collected at Miaoergou Glacier (MG) located in the Tianshan Mountains showed very different rare earth elements (REEs) ratios from the above locations attributed to the dominant contribution of LRT dust emitted by the southern Gobi Deserts. We found that large central Asian deserts rarely contributed LRT dust to Yuzhufeng (YG) in the hinterland Tibetan Plateau (TP). Taking the region as a whole, it was found that most of the glacier and snowpacks showed mixed dust sources and inputs from different parts of surrounding central Asian deserts that are characterized by different mineralogical settings. Geochemical data indicated that the NETP region acts as an important channel for aeolian transport from large Asian deserts into Loess Plateau and eastern regions, with atmospheric circulations bringing plenty of dust particles deposition to the high-altitude glacier surface in NETP margin. This work is of great importance in providing a new complete view of LRT aeolian emission and transport over the NETP region.

Parametric study of the production performance of an enhanced geothermal system: A case study at the Qiabuqia geothermal area, northeast Tibetan plateau

Abstract Enhanced Geothermal System (EGS) is an essential approach to entrap heat from deep hot dry rock (HDR), a low-carbon and renewable energy. Understanding the long-term productivity performance of the EGS and its sensitivity to different reservoir parameters can help to achieve efficiently the optimized exploitation of a designated reservoir. The Qiabuqia geothermal area, located in the northeastern margin of the Gonghe basin, Tibetan Plateau, is one of the areas that have the greatest HDR geothermal resources exploration and development potential in China so far. Based on the geological data of the GR1 borehole at the Qiabuqia geothermal area, northeast Tibetan plateau, a 3D thermo-hydraulic coupled numerical model is established in this study with the method of finite element to assess the heat production potential. The mathematical model presented in this study is validated by the analytical solution of a single fracture model. By varying several key reservoir parameters (e.g. thermal conductivity, permeability, porosity, injection mass flow rate, injection fluid temperature, and lateral well spacing), the sensitivity analysis of the long-term production temperature and electric power rate evolution is implemented. The simulation results indicate that in the basal granitic reservoir with a depth of 2900 m–3400 m and a corresponding initial temperature of 160 °C–180 °C, the temperature produced and effective electric power can maintain at 173.4 °C and 2.48 MW for the first 7 years of simulation under the combination of 50 kg/s of injection flow rate, 60 °C of the injection fluid temperature and a 300 m of lateral well spacing. At the end of the 40-year operation period, the outlet temperature decrease to 162.8 °C, as well as a drop of 9.7% in the electric power. Sensitivity analysis with the method of ‘One Factor At a time’ suggests that the permeability is the parameter that affects the production temperature and energy extraction the most compared with the thermal conductivity and porosity. For a specified geothermal field with a known distribution of permeability, thermal conductivity and porosity, the injection mass flow rate has the most significant effect on the electric power output, followed by the injection temperature and the lateral well spacing. The results from the complete factorial experimental design simulation suggest the electric power performance of the reservoir can be increased by a reasonable multi-parameter combination. For a doublet well extraction system, based on the Qiabuqia geothermal area, a combination of 70 kg/s injection flow rate, 60 °C injection temperature, and 500 m lateral well spacing can attain an effective electric power output of 3.47–3.50 MW. Thus, this study compares the different heat mining performance potential under various reservoir parameters and their combinations through the aforementioned sensitivity analysis and can greatly promote the establishment and development of EGS program in the Qiabuqia geothermal area in the future.

Differentiation of spatial morphology of rural settlements from an ethnic cultural perspective on the Northeast Tibetan Plateau, China

Rural settlements are carriers of ethnic culture, and their spatial morphology is restricted by the natural environment and ethnic culture, especially in areas where ethnic consciousness is strong. In this study, we selected multi-ethic communities in northwest China to analyze spatial morphology of rural settlements, and we described the relationship between ethnic culture and spatial morphology from the perspective of different ethnicities, leading industries, religious beliefs, and modern education. There were obvious geographical clustering characteristics and gradient variations in morphological structure of rural settlements in Qinghai Province, China. Spatial morphology of rural settlements in different multi-ethnic communities highlighted the ethnic characteristics of this unique nation, and it had an obvious relationship with their leading industries, modern education, and religious beliefs. The relationship between the spatial morphology of rural settlements and the leading economic activity revealed regular change in characteristics, from farming towns (F) to farming and animal husbandry towns (F-AH) to animal husbandry and farming towns (AH-F), and finally to animal husbandry towns (AH). The spatial morphology of other industrial towns (OI) did not show the coordinated regulation as did the other four categories, which showed the particularity of spatial morphology. All ethnic rural settlements had a significantly higher dependence on primary education than on religious beliefs. We concluded that educational resources will become an important factor in the future for optimizing the spatial pattern of rural settlements of multi-ethnic settlements in Northwest China.

Insight Into Radio‐Isotope 129I Deposition in Fresh Snow at a Remote Glacier Basin of Northeast Tibetan Plateau, China

AbstractWe present data of 129I deposition in fresh snow in the Laohugou glacier basin, northeast Tibetan Plateau, in summer 2016 and 2017, and trace its source and elevational distribution in the troposphere. Our results show that the 129I/127I atomic ratios in the fresh snow on the glacier surface are about 2 orders of magnitude larger than those in the Antarctic fresh snow and 4 orders the prenuclear level, indicating a predominantly anthropogenic source of the 129I in the mountain glacier environment of northeast Tibetan Plateau. The 129I level in the Laohugou glacier basin is 1–2 orders of magnitude lower than at representative European locations, and not significantly higher than that observed at other sites in Asia. The 129I/127I atomic ratio and 129I level show clear increases with elevation from 4,300 to 5,100 m above sea level. The 129I in the Laohugou glacier basin is probably deposited from the upper troposphere where there exists a local maximum of 129I. A conceptual model for interpretation of the observed 129I concentration and profile in Laohugou is provided. Thus, this work is of importance in providing a more complete view on the transport, dispersion, and removal of 129I in the atmosphere.

Three-dimensional magnetotelluric imaging of the geothermal system beneath the Gonghe Basin, Northeast Tibetan Plateau

To explore the geothermal system in the Gonghe basin located between Kunlun and Qinlin Orogen in northeast Tibetan Plateau, 310 Magnetotelluric (MT) sites were deployed in the basin. The MT sites have an average spacing of 1∼2 km and almost cover the whole basin with an area of ∼100 km by 100 km. We first analyzed the MT data using phase tensor analysis to qualitatively estimate the dimensionality of the subsurface resistivity structure and the resistivity anomalies. We then determined a 3D resistivity model from the surface to the depth of ∼50 km through a 3D MT inversion of MT data at the 272 sites with relatively higher quality. Overall, the inverted resistivity model fits the MT data very well. Our 3D resistivity model reveals significantly conductive anomalies at depths above ∼3 km, which are interpreted as widespread hot dry rocks or hydrothermal reservoirs. Furthermore, the 3D resistivity model shows pronounced low resistivity zones in the middle crust (∼15-35 km). These anomalies trend a NW-SE direction, consistent with the Kunlun Fault strike. Between the near-surface conductive zone and the middle crust conductive zone, lie several vertical narrow conductive zones, which are generally associated with hidden faults identified in the basin. Synthetic tests are used to validate the resolution of large low resistivity anomalies in the middle crust and the vertically elongated low resistivity anomalies in the model. These faults may serve as the channels for transporting heat from the heat source in the middle crust to the shallow zone around the depth of 3 km. Our 3D MT imaging results characterize for the first time the 3D distribution of the geothermal system in the Gonghe Basin.

Comparison of seasonal surface temperature trend, spatial variability, and elevation dependency from satellite-derived products and numerical simulations over the Tibetan Plateau from 2003 to 2011

ABSTRACTLand surface temperature (LST) and near-surface air temperature products have been commonly used in the studies of global climate change. In this work, we compare satellite-observed LST from Advanced Along-Track Scanning Radiometer (AATSR) and surface skin temperature and 2 m air temperature (T2) simulated from High Asian Refined analysis (HAR) to provide an independent overview of the surface/air temperature trend over Tibetan Plateau (TP) region in 2003–2011. We investigate the seasonal trend, spatial variability, and the elevation dependency of LST and air temperature over TP for the last decade. Linear regression method is applied to all data sets to illustrate the warming and cooling trends and variability of temperature over the study area. Our analysis shows that an overall warming slope is 0.04 K year–1 in the day trend and 0.05 K year–1 in the night and the trend slope is stronger in the simulated HAR data sets than that in the AATSR LST, especially for the night air temperature. However, in regions with elevation above 4000 m, the proportion of areas with the warming trend is less than 50% except in autumn from HAR data sets. The Namco and Qomolangma sites show an apparent trend of warming and cooling, respectively. The results from both satellite observations and numerical outputs show that warming trend over the entire TP was not obvious during last decade and the cooling trend was even found in the northeast TP.

Unraveling the influence of throw and stratigraphy in controlling subseismic fault architecture of fold-thrust belts: An example from the Qaidam Basin, northeast Tibetan Plateau

Understanding the detailed fault architecture of reverse faulting is critical for understanding the processes involved in fold-thrust belts as well as predicting the degree of fault compartmentalization, the relationship between folds and faults, the distribution of strain, and subseismic faulting deformation. The Lenghu5 fold-thrust belt provides an exceptionally well-exposed outcrop example of a reverse fault-related fold. Detailed stratigraphic logging coupled with high-resolution cross sections provides a unique insight into the three-dimensional geometry of a thrust fault at both basin and outcrop scale. In this study, we observe that 85%–90% of the estimated throw is accommodated on the main fault zone, which has sufficient throw to be imaged on a seismic profile, whereas 15%–20% of the throw is accommodated on smaller-scale folds and faults that are beyond seismic resolution. The plan-view mapping of the structure reveals that there is significant variation in how strain is accommodated along the structure, which is associated with the throw variations in the main fault. In addition, by coupling the structural observations within a stratigraphic context, we can demonstrate that although the main fault controls the overall strain in the system, the local stratigraphy plays a critical role in how the strain is accommodated and whether it is partitioned into single faults, multiple-fault splays, or folding. By demonstrating the remarkable geometric similarity between the outcrop observations with a comparable structure in the subsurface (Niger Delta), the study provides an insight into the potential subseismic fault-zone geometry present in poorly imaged fold-thrust systems.

Distribution and controlling factors of soil organic carbon storage in the northeast Tibetan shrublands

Although large amounts of soil organic carbon (SOC) stored in the shrublands, information about SOC storage was little on the Tibetan Plateau. This study aims to evaluate the spatial patterns and storage of SOC in the shrublands and the relationships of climatic variables and soil pH on the Tibetan Plateau. We used 177 profiles of soil samples obtained from 59 shrubland sites on the northeast Tibetan Plateau from 2011 to 2013. Ordinary least squares regressions, curve estimation, and multiple linear regressions were used to evaluate controlling factors on SOC stock. Kriging interpolation was used to upscale sit-level measurements to the whole study area. We found that SOC storage in the northeast Tibetan shrublands was 1.36 Pg C in the top 1 m with an average SOC stock of 12.38 kg m−2. SOC stock decreased from east to west and south to north but generally increased significantly with the mean annual temperature (MAT) and the mean annual precipitation (MAP), and tended to decrease with soil pH. Although similar relationships were also observed in alpine shrublands, the trends among SOC stock, MAP, and MAT were not observed in desert shrublands. Our results indicate that a reduction in soil pH accelerates the C sequestration potential. Furthermore, global warming contributed to C sequestration in alpine shrublands, specifically, SOC stock increased 8.44 kg m−2 with an increased unit of MAT in alpine shrublands just considering temperature effects. Meanwhile, the C sequestration was different among different regions due to the uneven increases in precipitation. However, in desert shrublands, MAP and MAT did not significantly affect SOC stock. The results indicate that though a reduction in soil pH could contribute to C sequestration, MAT and MAP have different effects on SOC stock in different Tibetan Plateau shrublands. Increased MAT and MAP were 0.05 °C and 1.67 mm every year on the Tibetan Plateau, which will increase C sequestration in alpine shrublands, but might have limited impacts on desert shrublands, which help us comprehend soil C cycling in the global climate change scenario.

Hebei loess section in the Anyemaqen Mountains, northeast Tibetan Plateau: a high‐resolution luminescence chronology

The extensive aeolian deposits of the Tibetan Plateau (TP) represent important environmental archives, recording information about the past interplay between the Asian monsoon and Westerlies and the link between dust accumulation and Quaternary glaciations. In the northeast TP, mantles of sandy loess form a distinct belt lying between 3500 and 4500 m a.s.l. on the east‐facing slopes of the Anyemaqen Mountains. However, there is little chronological information about the loess deposits in this region. This study provides a detailed chronology for loess formation in the region using luminescence dating. A total of 29 samples were collected from an 8‐m‐thick homogeneous loess section at Hebei (HB) in order to date sand‐sized (63–90 μm) quartz and K‐feldspar fractions using optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL and pIRIR) signals, respectively. The resulting quartz and feldspar ages are in good agreement over the last 40 ka; beyond this (i.e. De >120 Gy), the quartz age is underestimated, and the pIRIR170 feldspar ages are considered more reliable. The HB loess section records continuous environmental information from c. 50 to c. 30 ka, i.e. throughout Marine Isotope Stage (MIS) 3. Mass accumulation rates (MARs) varied considerably over this period with increased dust accumulation around c. 38 ka and after c. 32 ka; in between, and at the beginning of MIS 3 (50–40 ka), the dust accumulation rate was ~50% lower. Finally, the HB section also records a MIS 2 hiatus of c. 17 ka duration, probably resulting from deflation. This study implies that loess deposition on the TP is predominantly an interglacial/interstadial phenomenon and the TP may be deflating at the same time as the Chinese Loess Plateau is accumulating, at least during MIS 2.

Anthropogenic-management could mitigate declines in growth and survival of Qinghai spruce (Picea crassifolia) in the east Qilian Mountains, northeast Tibetan Plateau

Ongoing climate changes posed significant threats to forest growth, structure and ecological functions. However, in our field survey in the east Qilian Mountains, we found that growth condition of Qinghai spruce under climate changes was better in anthropogenic management forest than disturbance-free stands. Accordingly, we suggested a hypothesis that the environmental change induced suppression in Qinghai spruce growth could be mitigated by anthropogenic management. Such a hypothesis was tested by comparing Qinghai spruce growth and population dynamic patterns between anthropogenic-managed forests and disturbance-free ones. We found that Qinghai spruce radial growth persistently declined since the late 1950s in the disturbance-free forests, while the radial growth of anthropogenic-managed trees almost kept steady-going trends since the 1970s in which anthropogenic-management appeared. Besides, some anomalous growth-declining years occurred in disturbance-free forests did not appear in anthropogenic-managed forests in the same year after anthropogenic-management emerged. Moreover, missing ring and tree mortality took place in disturbance-free stands and became increasingly frequent after the mid-1980s. The frequencies and proportions of missing rings and tree die-off were much lower in anthropogenic-managed forests than disturbance-free ones. Additionally, the occurrence of Qinghai spruce radial growth decline and increased mortality in recent time in our disturbance-free forests could be well explained by global-change-type drought in conjunction with elevated temperature and warming-related pest outbreaks. These results would be of fundamental significance for the further understanding of the changing forests, which could provide new clues for forest management and conservation in the future.

Hydrochemical characteristics and water quality assessment of surface water in the northeast Tibetan Plateau of China

Abstract The Tibetan Plateau is very important as it provides water resources for about 40% of the world's population and the runoff-yield area of the Yellow rivers. In this paper, the water quality in Xiahe County, located in the northeast Tibetan Plateau, was investigated. Six parameters (chloride, chemical oxygen demand, ammonia nitrogen, nitrate, fluoride, sulfate) were selected to assess the quality and health status of surface water in Xiahe County. The main types of hydrochemical in the surface water were considered to be Mg2+-Ca2+-HCO3−-Cl− and Mg2+-Ca2+-HCO3−. The cations and anions were mainly from weathering and dissolution of carbonate rock. Fuzzy comprehensive evaluation (FCE) results showed that the water quality in all 69 sampling sites was all class I. The integrated health status was higher than 0.95 and the health rate was 100%. Although ammonia nitrogen was recognized as the main contaminant, it had little effect on the entire body of water. Overall, the surface water qualities of most samples in Xiahe County were found to be in good condition.

Spatiotemporal evolution of prehistoric Neolithic-Bronze Age settlements and influencing factors in the Guanting Basin, northeast Tibetan Plateau

For almost two decades, the relationship between prehistoric natural disasters that struck the Guanting Basin in northeast Tibetan Plateau and the destruction of Lajia, an archeological site, has attracted scholarly attention and been widely discussed. Whereas most studies have focused on the impacts of disasters on a single site within the Guanting Basin, few have examined patterns of spatiotemporal evolution of human settlements from the Neolithic to the Bronze Age. Consequently, there is a lack of clarity on the processes and mechanisms underlying the evolution of prehistoric human-land relationships in the Guanting Basin. We therefore examined spatiotemporal variations in settlements in the Guanting Basin during the period, based on the locations, altitudes, and areas of archaeological sites. We found that four sites were located on the third terrace of the Yellow River during the late Yangshao period (5500–5000 cal yr BP) and distributed within a small area. During the period between the Majiayao and Qijia cultures (5300–3600 cal yr BP), the number of sites evidently increased and the scale and distribution of settlements expanded, with settlements generally shifting toward the lower elevation areas of the Guanting Basin. During the Xindian period (3400–2700 cal yr BP), the number and scale of sites showed a downward trend and the distribution of settlements contracted. The Xindian settlement underwent altitude-based spatial differentiation, with some groups moving to areas at higher altitudes and others remained in lower altitude areas. Moreover, we found that the number, scale, and distribution range of Neolithic and Bronze Age sites in the Guanting Basin were closely related to the evolution and distribution patterns of prehistoric cultures in the regions of Gansu and Qinghai, which were further affected by climate change and agricultural development. Furthermore, there is no evidence that the altitudinal distribution pattern of Neolithic and Bronze Age settlements in the Guanting Basin was influenced by paleofloods rather it was primarily influenced by changes in subsistence strategies.

Impacts of the spatial extent of pollen-climate calibration-set on the absolute values, range and trends of reconstructed Holocene precipitation

Pollen-based quantitative reconstructions of past climate variables is a standard palaeoclimatic approach. Despite knowing that the spatial extent of the calibration-set affects the reconstruction result, guidance is lacking as to how to determine a suitable spatial extent of the pollen-climate calibration-set. In this study, past mean annual precipitation (Pann) during the Holocene (since 11.5 cal ka BP) is reconstructed repeatedly for pollen records from Qinghai Lake (36.7°N, 100.5°E; north-east Tibetan Plateau), Gonghai Lake (38.9°N, 112.2°E; north China) and Sihailongwan Lake (42.3°N, 126.6°E; north-east China) using calibration-sets of varying spatial extents extracted from the modern pollen dataset of China and Mongolia (2559 sampling sites and 168 pollen taxa in total). Results indicate that the spatial extent of the calibration-set has a strong impact on model performance, analogue quality and reconstruction diagnostics (absolute value, range, trend, optimum). Generally, these effects are stronger with the modern analogue technique (MAT) than with weighted averaging partial least squares (WA-PLS). With respect to fossil spectra from northern China, the spatial extent of calibration-sets should be restricted to radii between ca. 1000 and 1500 km because small-scale calibration-sets (<800 km radius) will likely fail to include enough spatial variation in the modern pollen assemblages to reflect the temporal range shifts during the Holocene, while too broad a scale calibration-set (>1500 km radius) will include taxa with very different pollen-climate relationships.

Soil Nitrogen Storage, Distribution, and Associated Controlling Factors in the Northeast Tibetan Plateau Shrublands

Although the soils in the Tibetan Plateau shrublands store large amounts of total nitrogen (N), the estimated values remain uncertain because of spatial heterogeneity and a lack of field observations. In this study, we quantified the regional soil N storage, spatial and vertical density distributions, and related climatic controls using 183 soil profiles sampled from 61 sites across the Northeast Tibetan Plateau shrublands during the period of 2011–2013. Our analysis revealed a soil N storage value of 132.40 Tg at a depth of 100 cm, with an average density of 1.21 kg m−2. Soil N density was distributed at greater levels in alpine shrublands, compared with desert shrublands. Spatially, soil N densities decreased from south to north and from east to west, and, vertically, the soil N in the upper 30 and 50 cm accounted for 42% and 64% of the total soil N stocks in the Tibetan Plateau. However, compared with desert shrublands, the surface layers in alpine shrublands exhibited a larger distribution of soil N stocks. Overall, the soil N density in the top 30 cm increased significantly with the mean annual precipitation (MAP) and tended to decrease with the mean annual temperature (MAT), although the dominant climatic controls differed among shrubland types. Specifically, MAP in alpine shrublands, and MAT in desert shrubland, had a weak effect on N density. Soil pH can significant affect soil N density in the Tibetan Plateau shrublands. In conclusion, changes in soil N density should be monitored over the long term to provide accurate information about the effects of climatic factors.