Revealing the Ground Deformation and Its Mechanism in the Heihe River Basin by Interferometric Synthetic Aperture Radar and Optical Images

The Heihe River Basin (HRB), located on the northeast margin of the Qilian Mountains, is China's second largest inland river basin. It is a typical oasis-type agricultural area in northwest China's arid and semiarid areas. It is important to monitor and investigate the spatiotemporal distribution characteristics and mechanisms of surface deformation in HRB for the ecology of inland river basins. In recent years, research on HRB has mainly focused on hydrology, meteorology, geology, or biology. Few studies have conducted wide-area monitoring and mechanism analysis of the surface stability of HRB. In this study, an improved interferometric point target analysis InSAR (IPTA-InSAR) technique is used to process 101 Sentinel-1 SAR images from two adjacent track frames covering the HRB from 2019 to 2020. The wide-area deformation of the HRB is obtained first for this period. The results show that most of the surface around the HRB is relatively stable. There are six areas with an extensive deformation range and magnitude in the plain oasis area. The maximum deformation rate is more than 50 mm/year. The maximum seasonal subsidence and uplift along the satellites' line-of-sight (LOS) direction can be up to -70 mm and 60 mm, respectively. Moreover, we use the Google Earth Engine platform to process the multisource optical images and analyze the deformation areas. The remote sensing indicators of the deformation areas, such as the normalized difference vegetation index (NDVI), soil moisture (SMMI), and precipitation, are obtained during the InSAR monitoring period. We combine these integrated remote sensing results with soil type and precipitation to analyze the surface deformations of the HRB. The spatiotemporal relationships between soil moisture, vegetation cover, and surface deformation of the HRB are revealed. The results will provide data support and reference for the healthy and sustainable development of the inland river basin economic zone.

Environmental significance of atmospheric nitrogen deposition in the transition zone between the Tibetan Plateau and arid region

The ecological effect of atmospheric N deposition has become a hot research point along with intensive human activities and global climatic change. As the transition zone between the Tibetan Plateau and the arid region, the Qilian Mountains are important ecological barriers and source regions of inland rivers in northwest China. However, the quantification of N deposition in the transition zone between the Tibetan Plateau (TP) and the arid region remains unclear, primarily due to the lack of in situ measurements. Hence, an observational study was conducted on the Qilian Mountains, and precipitation data were collected. Approximately 1382 samples were collected and analyzed regarding their characteristics and environmental effects of the atmospheric N wet deposition. The annual wet deposition of atmospheric N was 10.05 kg/hm², and showed a decreasing trend from the south to the north of the Qilian Mountains. NO₃^--N deposition was the main form of wet deposition of atmospheric N on the Qilian Mountains, accounting for 73.83% of the DIN deposition. Additionally, altitude, meteorological factors, and ecosystem types were found to influence the wet deposition of atmospheric N. The contribution of NO₃^--N to the wet deposition of atmospheric N in meadows, forests, grasslands, farmlands, and towns was 48.38%, 71.55%, 77.54%, 69.61%, and 82.84%, respectively. This study provides a scientific basis for the effective management and sustainable development of environmental protection in the transition zone between the TP and the arid region. The results showed that relevant policies, as well as scientific and governmental measures, could contribute to reducing N deposition effectively. However, the further mitigation measures should be proposed and strictly enforced.

Effects of Ecological Restoration on the Distribution of Soil Particles and Organic Carbon in Alpine Regions

This study discusses the impact of two different ecological restoration approaches on the distribution of soil particle size and organic carbon, expecting to provide references for research on the effects of ecological restoration on the soil carbon pool in alpine regions. By replacing the method of time sampling with spatial sampling, grasslands enclosed only in the growing season and woodlands enclosed all year round were respectively selected as the research objects. Through centrifugation, the soil samples were classified by grain size into sand (50–2000 μm), silt (2–50 μm), and clay (<2 μm) to analyze the distribution of organic carbon in soil particles of different sizes. The major findings were as follows. First, sand accounted for the largest proportion of all the soil components in the grasslands and woodlands that had been restored for different years, followed by silt and clay. Second, most of the organic carbon in the grasslands and woodlands was from sand and silt. As the restoration years increased, the proportion of organic carbon in clay grew in fluctuation. In short, both ecological restoration approaches have improved the soil structure and raised the content of soil organic carbon (SOC). Specifically, the restoration scheme of the woodlands exerted a more significant influence on the soil components and the distribution of organic carbon than that of the grasslands.

Effectiveness of the Qilian Mountain Nature Reserve of China in Reducing Human Impacts

The management effectiveness of protected areas plays a key role in biodiversity and ecosystem services conservation. We evaluated the effectiveness of Qilian Mountain Nature Reserve (QMNR) in reducing human footprint (HF). Four dominant human activity factors, including population density, land use, road distribution, and night light, were incorporated for HF mapping. Comparisons of the HF value between inside and outside QMNR and its four functional zones were conducted. The results show that both the HF inside and outside of QMNR were increasing, but the difference between them was increasing, indicating partial management effectiveness. The north part of the central reserve has a good effect in reducing human impacts, while the effectiveness was poor at both ends of the reserve. The HF value of the most strictly managed core and buffer zones increased by 10.50 and 6.68%, respectively, for 2010–2020. The QMNR was effective in controlling population density and land use, but ineffective in reducing road construction, mining, and construction of hydropower facilities.

Dynamic Monitoring of Laohugou Glacier No. 12 with a Drone, West Qilian Mountains, West China

Laohugou glacier No. 12 (LHG12), located in the northeast of the Qinghai–Tibet Plateau, is the largest valley glacier in the Qilian mountains. Since 1957, LHG12 has shrunk significantly. Due to the limitations of in situ observations, simulations and investigations of LHG12 have higher levels of uncertainty. In this study, consumer-level, low-altitude microdrones were used to conduct repeated photogrammetry at the lower part of LHG12, and a digital orthophoto map (DOM) and a digital surface model (DSM) with a resolution at the centimeter scale were generated, from 2017 to 2021. The dynamic parameters of the glacier were detected by artificial and automatic extraction methods. Using a combination of GNSS and drone-based data, the dynamic process of LHG12 was analyzed. The results show that the terminus of LHG12 has retreated by 194.35 m in total and by 19.44 m a−1 on average during 2008–2021. The differential ablation leading to terminus retreat distance markedly increased during the study period. In 2019–2021, the maximum annual surface velocity was 6.50 cm day−1, and during ablation season, the maximum surface velocity was 13.59 cm day−1, 52.17% higher than it is annually. The surface parameters, motion, and mass balance characteristics of the glacier had significant differences between the west and east branches. The movement in the west branch is faster than it is in the east branch. Because of the extrusion of the two ice flows, there is a region with a faster surface velocity at the ablation area. The ice thickness of LHG12 is decreasing due to intensified ablation, leading to a deceleration in the surface velocity. In large glaciers, this phenomenon is more obvious than it is in small glaciers in the Qilian mountains.

Influence of Open-Pit Coal Mining on Ground Surface Deformation of Permafrost in the Muli Region in the Qinghai-Tibet Plateau, China

The Qinghai-Tibet Plateau (QTP) is the largest mid-to low latitude and high-altitude permafrost. Open-pit coal mining and other activities have caused serious damage to the alpine ecological environment and have accelerated the degradation of permafrost on the QTP. In this study, the influence of open-pit coal mining on the time series ground surface deformation of the permafrost in the Muli region of the QTP was analyzed from 19 January 2018 to 22 December 2020 based on Landsat, Gaofen, and Sentinel remote sensing data. The primary methods include human-computer interactive visual interpretation and the small baseline subsets interferometric synthetic aperture radar (SBAS-InSAR) method. The results showed that the spatial distribution of displacement velocity exhibits a considerably different pattern in the Muli region. Alpine meadow is the main land use/land cover (LULC) in the Muli region, and the surface displacement was mainly subsidence. The surface subsidence trend in alpine marsh meadows was obvious, with a subsidence displacement velocity of 10–30 mm/a. Under the influence of changes in temperature, the permafrost surface displacement was characteristics of regular thaw subsidence and freeze uplift. Surface deformation of the mining area is relatively severe, with maximum uplift displacement velocity of 74.31 mm/a and maximum subsidence displacement velocity of 167.51 mm/a. Open-pit coal mining had resulted in the destruction of 48.73 km2 of natural landscape in the Muli region. Mining development in the Muli region had increased the soil moisture of the alpine marsh meadow around the mining area, resulting in considerable cumulative displacement near the mining area and the acceleration of permafrost degradation.

Spatiotemporal Dynamics of Land Surface Albedo and Its Influencing Factors in the Qilian Mountains, Northeastern Tibetan Plateau

Land surface albedo directly determines the distribution of radiant energy between the surface and the atmosphere, and it is a key parameter affecting the energy balance on the land surface. However, the spatiotemporal dynamics of land surface albedo and associated influencing factors in the Qilian Mountains (QM) have been rarely reported. By using the long-time series data products of MODIS shortwave albedo, normalized difference vegetation index (NDVI), and snow cover with a spatial resolution of 0.05° from 2001 to 2020, this paper analyzes the temporal and spatial variations of land surface albedo in the QM over the past 20 years and its influencing factors. The analysis results show that the multi-year average surface albedo in the QM has obvious differences in spatial distribution: it increases with the altitude, and it is high in the west (at the west of 98° E) and low in the east. Meanwhile, the surface albedo has different distribution characteristics in different seasons: the spatial distribution of surface albedo is similar in spring and autumn; the areas with a high surface albedo in summer are significantly fewer than those in other seasons. Besides, in the past 20 years, the annual average surface albedo has shown a weak growth trend in the QM, with a change rate of 5 × 10−3/10a, and the minimum and maximum values were reached in 2001 and 2019, respectively. In addition, the annual variation of the surface albedo in the QM showed a “U” shape, with the largest variation in January and the smallest variation in August. The annual variation of surface albedo is significantly positively correlated with snow cover (r = 0.96) and significantly negatively correlated with NDVI (r = −0.91). Moreover, the interannual variation of the surface albedo in the QM is closely related to land surface cover and is greatly affected by snow cover. Spatially, the annual variation of surface albedo in most areas of the QM is dominated by the change of snow cover, and the increase of surface albedo in the middle area is consistent with the increase of snow cover, while the decrease of albedo in the edge area is related to the improvement of vegetation cover. The results of this study provide a scientific basis for studying the climate and environmental changes caused by changes in the surface of the QM and making ecological environment restoration strategies.

Permafrost Degradation and Its Hydrogeological Impacts

Under a warming climate, permafrost degradation has resulted in profound hydrogeological consequences. Here, we mainly review 240 recent relevant papers. Permafrost degradation has boosted groundwater storage and discharge to surface runoffs through improving hydraulic connectivity and reactivation of groundwater flow systems, resulting in reduced summer peaks, delayed autumn flow peaks, flattened annual hydrographs, and deepening and elongating flow paths. As a result of permafrost degradation, lowlands underlain by more continuous, colder, and thicker permafrost are getting wetter and uplands and mountain slopes, drier. However, additional contribution of melting ground ice to groundwater and stream-flows seems limited in most permafrost basins. As a result of permafrost degradation, the permafrost table and supra-permafrost water table are lowering; subaerial supra-permafrost taliks are forming; taliks are connecting and expanding; thermokarst activities are intensifying. These processes may profoundly impact on ecosystem structures and functions, terrestrial processes, surface and subsurface coupled flow systems, engineered infrastructures, and socioeconomic development. During the last 20 years, substantial and rapid progress has been made in many aspects in cryo-hydrogeology. However, these studies are still inadequate in desired spatiotemporal resolutions, multi-source data assimilation and integration, as well as cryo-hydrogeological modeling, particularly over rugged terrains in ice-rich, warm (>−1 °C) permafrost zones. Future research should be prioritized to the following aspects. First, we should better understand the concordant changes in processes, mechanisms, and trends for terrestrial processes, hydrometeorology, geocryology, hydrogeology, and ecohydrology in warm and thin permafrost regions. Second, we should aim towards revealing the physical and chemical mechanisms for the coupled processes of heat transfer and moisture migration in the vadose zone and expanding supra-permafrost taliks, towards the coupling of the hydrothermal dynamics of supra-, intra- and sub-permafrost waters, as well as that of water-resource changes and of hydrochemical and biogeochemical mechanisms for the coupled movements of solutes and pollutants in surface and subsurface waters as induced by warming and thawing permafrost. Third, we urgently need to establish and improve coupled predictive distributed cryo-hydrogeology models with optimized parameterization. In addition, we should also emphasize automatically, intelligently, and systematically monitoring, predicting, evaluating, and adapting to hydrogeological impacts from degrading permafrost at desired spatiotemporal scales. Systematic, in-depth, and predictive studies on and abilities for the hydrogeological impacts from degrading permafrost can greatly advance geocryology, cryo-hydrogeology, and cryo-ecohydrology and help better manage water, ecosystems, and land resources in permafrost regions in an adaptive and sustainable manner.

Mapping and Evaluating Human Pressure Changes in the Qilian Mountains

Human activities have dramatically changed ecosystems. As an irreplaceable ecological barrier in western China, the Qilian Mountains (QLM) provide various ecosystem services for humans. To evaluate the changes in the intensity of human activities in the QLM and their impact on the ecosystem, the human footprint (HF) method was used to conduct a spatial dataset of human activity intensity. In our study, the NDVI was used to characterize the growth of vegetation, and six categories of human pressures were employed to create the HF map in the QLM for 2000–2015 at a 1-km scale. The results showed that the mean NDVI during the growing season showed a significant increasing trend over the entire QLM in the period 2000–2015, while the NDVI showed a significant declining trend of more than 70% concentrated in Qinghai. Human pressure throughout the QLM occurred at a low level during 2000–2015, being greater in the eastern region than the western region, while the Qinghai area had greater human pressure than the Gansu area. Due to the improvement in traffic facilities, tourism, overgrazing, and other illegal activities, grasslands, shrublands, forests, wetlands, and bare land were the vegetation types most affected by human activities (in decreasing order). As the core area of the QLM, the Qilian Mountains National Nature Reserve (NR) has effectively reduced the impact of human activities. However, due to the existence of many ecological historical debts caused by unreasonable management in the past, the national park established in 2017 is facing great challenges to achieve its goals. These data and results will provide reference and guidance for future protection and restoration of the QLM ecosystem.

Mapping Frozen Ground in the Qilian Mountains in 2004–2019 Using Google Earth Engine Cloud Computing

The permafrost in the Qilian Mountains (QLMs), the northeastern margin of the Qinghai–Tibet Plateau, changed dramatically in the context of climate warming and increasing anthropogenic activities, which poses significant influences on the stability of the ecosystem, water resources, and greenhouse gas cycles. Yet, the characteristics of the frozen ground in the QLMs are largely unclear regarding the spatial distribution of active layer thickness (ALT), the maximum frozen soil depth (MFSD), and the temperature at the top of the permafrost or the bottom of the MFSD (TTOP). In this study, we simulated the dynamics of the ALT, TTOP, and MFSD in the QLMs in 2004–2019 in the Google Earth Engine (GEE) platform. The widely-adopted Stefan Equation and TTOP model were modified to integrate with the moderate-resolution imaging spectroradiometer (MODIS) land surface temperature (LST) in GEE. The N-factors, the ratio of near-surface air to ground surface freezing and thawing indices, were assigned to the freezing and thawing indices derived with MODIS LST in considerations of the fractional vegetation cover derived from MODIS normalized difference vegetation index (NDVI). The results showed that the GEE platform and remote sensing imagery stored in Google cloud could be quickly and effectively applied to obtain the spatial and temporal variation of permafrost distribution. The area with TTOP < 0 °C is 8.4 × 104 km2 (excluding glaciers and lakes) and accounts for 46.6% of the whole QLMs, the regional mean ALT is 2.43 ± 0.44 m, while the regional mean MFSD is 2.54 ± 0.45 m. The TTOP and ALT increase with the decrease of elevation from the sources of the sub-watersheds to middle and lower reaches. There is a strong correlation between TTOP and elevation (slope = −1.76 °C km−1, p < 0.001). During 2004–2019, the area of permafrost decreased by 20% at an average rate of 0.074 × 104 km2·yr−1. The regional mean MFSD decreased by 0.1 m at a rate of 0.63 cm·yr−1, while the regional mean ALT showed an exception of a decreasing trend from 2.61 ± 0.45 m during 2004–2005 to 2.49 ± 0.4 m during 2011–2015. Permafrost loss in the QLMs in 2004–2019 was accelerated in comparison with that in the past several decades. Compared with published permafrost maps, this study shows better calculation results of frozen ground in the QLMs.