Soil parameters form the foundation of hydrogeological research and are crucial for studying engineering construction and maintenance, climate change, and ecological environment effects in cold regions. However, the soil properties in the permafrost region of the Qinghai-Tibet Plateau (QTP) remain unclear. Hence, in this study, soil temperature (Ts), volumetric specific heat capacity (C), thermal conductivity (K), thermal diffusivity (D), soil water content (SWC), electric conductivity (EC), vertical (Kv) and horizontal (Kh) saturated hydraulic conductivity, bulk density (rho b), and soil texture near the Qinghai-Tibet Railway were measured, and their effects on the freeze-thaw process were evaluated. The results revealed a predominantly sandy loam soil texture, with Kh and Kv showing strong spatial variability, while the other parameters presented moderate spatial variability. Thermokarst lake had a limited influence on D, C, K, and rho b but significantly reduced Kh and Kv. Groundwater affected SWC, Ts, and EC. The model results showed that all parameters indicated small sensitivities to the maximum thawing depth (MTD), with MTD positively responding to all parameters except for Kv and porosity (rho p). Except for Kh and Kv, all parameters showed high sensitivities to the time from starting to complete freezing (TSCF). TSCF responded positively to C, rho p, and density (rho d) and negatively to K and Kh. This study expanded the quantification of soil properties in the QTP, which can help improve the accuracy of cryohydrogeologic models, thus guiding the construction and maintenance of infrastructure engineering.

Ice-rich permafrost thaws in response to rapid Arctic warming, and ground subsidence facilitates the formation of thermokarst lakes. Thermokarst lakes transform the surface energy balance of permafrost, affecting geo-morphology, hydrology, ecology, and infrastructure stability, which can further contribute to greenhouse gas emissions. Currently, the spatial distribution of thermokarst lakes at large scales remains a challenging task. Based on multiple high-resolution environmental factors and thermokarst lake inventories, we used machine learning methods to estimate the spatial distributions of present and future thermokarst lake susceptibility (TLS) maps. We also identified key environmental factors of the TLS map. At 1.8 x 106 km2, high and very high susceptible regions were estimated to cover about 10.4 % of the region poleward of 60 degrees N, which were mainly distributed in permafrost-dominated lowland regions. At least 23.9 % of the area of TLS maps was projected to disappear under representative concentration pathway scenarios (RCPs), with increased susceptibility levels in northern Canada. The slope was the key conditioning factor for the occurrence of thermokarst lakes in Arctic permafrost regions. Compared with similar studies, the reliability of the TLS map was further evaluated using probability calibration curve and coefficient of variation (CV). Our results provide a means for assessing the spatial distribution of thermokarst lakes at the circum-Arctic scale but also improve the understanding of their dynamics in response to the climate system.

Thermokarst lake development significantly affects hydrologic systems, infrastructure stability and biogeo-chemical processes, while the spatial and temporal changes in thermokarst lakes remain largely unknown. Here, we created a thermokarst lake dataset on the Qinghai-Tibet Plateau (QTP) using a threshold-based mapping method based on Google Earth Engine (GEE) data associated with visual inspection. The dataset includes a thermokarst lake inventory on the QTP at a 10 m resolution produced from Sentinel-2A images and a multi-temporal inventory along the Qinghai-Tibet Highway (QTH) from Landsat and Sentinel-2A images. We analyzed the temporal and spatial changes in thermokarst lake area and their relationships to environmental factors. Our results showed that thermokarst lakes on the QTP permafrost region covered a total area of 1572 +/- 184 km(2), with most of the thermokarst lakes <10,000 m(2) in area. The spatial distributions of thermokarst lakes are affected by the ground thermal stability, active layer thickness, vegetation type, and ground ice content. Over the past 30 years, the number and surface area of thermokarst lakes along the QTH have increased by 58.8 % and 83.1 %, respectively, with the increase in lakes likely caused by climate warming and precipitation increasing. This study provides deep insight in the long-term interannual variations and its driving factors in thermokarst lakes along the QTH.

s The rapidly warming climate on the Qinghai-Tibet Plateau (QTP) leads to permafrost degradation, and the thawing of ice-rich permafrost induces land subsidence to facilitate the development of thermokarst lakes. Thermokarst lakes exacerbate the instability of permafrost, which significantly alters regional geomorphology and hydrology, affecting biogeochemical cycles. However, the spatial distribution and future changes in thermokarst lakes have rarely been assessed at large scales. In this study, we combined various conditioning factors and an inventory of thermokarst lakes to assess the spatial distribution of susceptibility maps using machine-learning algorithms. The results showed that the extremely randomized trees (EXT) performed the best in the susceptibility modeling process, followed by random forest (RF) and logistic regression (LR). According to the assessment based on EXT, the high- and very high-susceptibility area of the present (2000-2016) susceptibility map was 196,222 km(2), covering 19.67% of the permafrost region of the QTP. In the future (the 2070s), the area of the susceptibility map was predicted to shrink significantly under various representative concentration pathway scenarios (RCPs). The susceptibility map area would be reduced to 37.06% of the present area in RCP 8.5. This paper also performed correlation and importance analysis on the conditioning factors and thermokarst lakes, which indicated that thermokarst lakes tended to form in areas with flat topography and high soil moisture. The uncertainty of the susceptibility map was further assessed by the coefficient of variation (CV). Our results demonstrate a way to study the spatial distribution of thermokarst lakes at the QTP scale and provide a scientific basis for understanding thermokarst processes in response to climate change.

One of the most significant environmental changes across the Tibetan Plateau (TP) is the rapid lake expansion. The expansion of thermokarst lakes affects the global biogeochemical cycles and local climate regulation by rising levels, expanding area, and increasing water volumes. Meanwhile, microbial activity contributes greatly to the biogeochemical cycle of carbon in the thermokarst lakes, including organic matter decomposition, soil formation, and mineralization. However, the impact of lake expansion on distribution patterns of microbial communities and methane cycling, especially those of water and sediment under ice, remain unknown. This hinders our ability to assess the true impact of lake expansion on ecosystem services and our ability to accurately investigate greenhouse gas emissions and consumption in thermokarst lakes. Here, we explored the patterns of microorganisms and methane cycling by investigating sediment and water samples at an oriented direction of expansion occurred from four points under ice of a mature-developed thermokarst lake on TP. In addition, the methane concentration of each water layer was examined. Microbial diversity and network complexity were different in our shallow points (MS, SH) and deep points (CE, SH). There are differences of microbial community composition among four points, resulting in the decreased relative abundances of dominant phyla, such as Firmicutes in sediment, Proteobacteria in water, Thermoplasmatota in sediment and water, and increased relative abundance of Actinobacteriota with MS and SH points. Microbial community composition involved in methane cycling also shifted, such as increases in USC gamma, Methylomonas, and Methylobacter, with higher relative abundance consistent with low dissolved methane concentration in MS and SH points. There was a strong correlation between changes in microbiota characteristics and changes in water and sediment environmental factors. Together, these results show that lake expansion has an important impact on microbial diversity and methane cycling.

With the gradual increase of global temperature, thermokarst lakes are widely developed and become major environmental disasters in the Tundra Plateau which have impacted the stability of the project such as the Qinghai-Tibetan highway. In this study, some typical thermokarst lakes in the Qinghai-Tibet Plateau (QTP) were selected as the research object. And four samples were taken from different freezing-thawing processes of the lakes in 2019 to analyze the hydrogeochemical process of the thermokarst lake in the context of climate change. Results show that the main hydrogeochemical types of the lake water in the northern part of the study area were HCO3 center dot Cl - Na center dot Ca center dot Mg or Cl center dot HCO3 - Na center dot Mg, whereas in the central and southern parts were mainly Cl - Na center dot Mg. The variations of hydrogeochemical concentration in thermokarst lake water are mainly affected by evaporation concentration, rock differentiation, freezing desalination in the active layer, and plant photosynthesis, which are mainly due to temperature changes. Furthermore, the results of the saturation index (SI) show that dolomite and calcite leaching control the hydrogeochemical composition in thermokarst lakes. In addition, the evaporation-to-inflow (E/I) ratios of the lake reach the maximum in the middle and later periods of the active layer thawing. On the contrary, the E/I values of the lakes decrease during the initial thawing or freezing periods of the active layer.

As a result of global warming induced permafrost degradation in recent decades, thermokarst lakes in the Qinghai-Tibet plateau (QTP) have been regulating local hydrological and ecological processes. Simulations with coupled moisture-heat numerical models in the Beiluhe basin (located in the hinterland of permafrost regions on the QTP) have provided insights into the interaction between groundwater flow and the freeze-thaw process. A total of 30 modified SUTRA scenarios were established to examine the effects of hydrodynamic forces, permeability, and climate on thermokarst lakes. The results indicate that the hydrodynamic condition variables regulate the permafrost degradation around the lakes. In case groundwater recharges to the lake, a low-temperature groundwater flow stimulates the expansion of the surrounding thawing regions through thermal convection. The thawing rate of the permafrost underlying the lake intensifies when groundwater is discharged from the lake. Under different permeability conditions, spatiotemporal variations in the active layer thickness significantly influence the occurrence of an open talik at the lake bottom. A warmer and wetter climate will inevitably lead to a sharp decrease in the upper limit of the surrounding permafrost, with a continual decrease in the duration of open talik events. Overall, our results underscore that comprehensive consideration of the relevant hydrologic processes is critical for improving the understanding of environmental and ecological changes in cold environments.

Despite the importance of soil and surface waters freezing in permafrost landscapes, the behaviour of dissolved organic carbon (DOC), nutrients and metals during periodic freeze-thaw cycles (FTC) remains poorly known. The on-going climate warming is likely to increase the frequency of FTC in continental aquatic settings, which could modify the chemical composition of waters. In this study, we conducted 9 repetitive cycles of overnight freezing (similar to 20 degrees C) and 5 h thawing (4 degrees C) in the laboratory using representative 0.22 mu m-filtered waters from NE European permafrost peatland: leachates of vegetation and soil, and natural surface waters (depression, thermokarst lake and river). Only minor (10%). The leachates and the depression water were enriched in trace elements, whereas the thermokarst lake and the river demonstrated a decrease in concentration of Fe (similar to 39 and similar to 94%, respectively), Al (similar to 9 and similar to 85%), and Mn (similar to 10 and similar to 79%) during FTC. Overall, the observations demonstrated an increase in aliphatic low molecular weight organic matter (OM), and the precipitation of Fe, Al hydroxides and organo-mineral particles. Therefore, enhanced of frequency of FTC can favour the release of metals and toxicants from acidic OM-rich surface waters and maintain stable OM-metalscolloids in large lakes and rivers, thus regulating aquatic transport of DOC and metals from soils to the Arctic Ocean. (C) 2021 Elsevier Ltd. All rights reserved.

Permafrost regions at high latitudes and altitudes store about half of the Earth's soil organic carbon (SOC). These areas are also some of the most intensely affected by anthropogenic climate change. The Tibetan Plateau or Third Pole (TP) contains most of the world's alpine permafrost, yet there remains substantial uncertainty about the role of this region in regulating the overall permafrost climate feedback. Here, we review the thermal and biogeochemical status of permafrost on the TP, with a particular focus on SOC stocks and vulnerability in the face of climate warming. SOC storage in permafrost-affected regions of the TP is estimated to be 19.0 +/- 6.6 Pg to a depth of 2 m. The distribution of this SOC on the TP is strongly associated with active layer thickness, soil moisture, soil texture, topographic position, and thickness of weathered parent material. The mean temperature sensitivity coefficient (Q(10)) of SOC decomposition is 9.2 +/- 7.1 across different soil depths and under different land-cover types, suggesting that carbon on the TP is very vulnerable to climate change. While the TP ecosystem currently is a net carbon sink, climate change will likely increase ecosystem respiration and may weaken or reverse the sink function of this region in the future. Although the TP has less ground ice than high latitude permafrost regions, the rugged topography makes it vulnerable to widespread permafrost collapse and thermoerosion (thermokarst), which accelerates carbon losses. To reduce uncertainty about SOC quantities and sensitivity to warming, future studies are needed that explain variation in Q(10) (e.g. based on SOC source or depositional position) and quantify the role of nutrient availability in regulating SOC dynamics and ecosystem recovery following disturbance. Additionally, as for the high latitude permafrost region, soil moisture and thermokarst formation remain major challenges to predicting the permafrost climate feedback on the TP. We present a conceptual model for of greenhouse gas release from the TP and outline the empirical observations and modeling approaches needed to test it.

Thermokarst lakes form following the thaw of ice-rich permafrost and drain after a few decades to millennia. Drained thermokarst lake basins (DTLBs) become epicenters for peat accumulation and re-aggradation of ice-rich permafrost. This re-aggradation of permafrost may be interrupted by subsequent thermokarst lake formation with sufficient disturbance. Thermokarst lakes and DTLBs are abundant near Old Crow, Yukon, Canada, but little is known about their evolution through the Holocene. In this study, we investigate the hydrology and drainage histories of seven DTLBs from the Old Crow Flats on the basis of cryostratigraphy, radiocarbon dating, and pore-ice delta O-18 and delta H-2 records. Cryostratigraphic evidence implies only one of the seven studied DTLBs underwent multiple thermokarst cycles. Radiocarbon age-depth models demonstrate a slowdown in the rate of post-drainage peat accumulation with time. Pore-ice isotope analyses reveal a spectrum of possible post-drainage isotopic histories resulting from spatial variability in permafrost, vegetation, and hydrology. Unlike lacustrine silt, post-drainage peat contains relatively constant pore-ice isotope trends. In light of our findings, we propose that syngenetic peat permafrost in DTLBs preserve a warm-season sampling of local meteoric waters. These pore-ice delta O-18 and delta H-2 records may aid millennial-scale paleoclimate investigations, as we demonstrate through our reconstruction of Holocene climate change in northern Yukon.