Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming.

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η). Here, we analyzed η values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in η for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on η over the past 27 y. Soil moisture was found to modulate the sensitivity of η to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback.

High carbon emissions from thermokarst lakes and their determinants in the Tibet Plateau.

Thermokarst lakes are potentially important sources of methane (CH4 ) and carbon dioxide (CO2 ). However, considerable uncertainty exists regarding carbon emissions from thermokarst lakes owing to a limited understanding of their patterns and motivators. In this study, we measured CH4 and CO2 diffusive fluxes in 163 thermokarst lakes in the Qinghai-Tibet Plateau (QTP) over 3 years from May to October. The median carbon emissions from the QTP thermokarst lakes were 1440 mg CO2 m-2 day-1 and 60 mg CH4 m-2 day-1 , respectively. The diffusive rates of CO2 and CH4 are related to the catchment land cover type. Sediment microbial abundance and hydrochemistry explain 51.9% and 38.3% of the total variance in CH4 diffusive emissions, respectively, while CO2 emissions show no significant relationship with environmental factors. When upscaling carbon emissions from the QTP thermokarst lakes, the annual average CH4 release per lake area is equal to that of the pan-Arctic region. Our findings highlight the importance of incorporating in situ observation data with different emission pathways for different land cover types in predicting carbon emissions from thermokarst lakes in the future.

Vertical distribution characteristics of soil mercury and its formation mechanism in permafrost regions: A case study of the Qinghai-Tibetan Plateau.

Continuing permafrost degradation is increasing the risk of mercury (Hg) exposure in the permafrost regions on the Qinghai-Tibetan Plateau (QTP), but related studies are still limited, especially the ones on the detailed Hg migration processes in permafrost. The vertical distribution characteristics of soil Hg were investigated in three ecosystems in the Beiluhe area on the QTP, and its influencing factors and formation mechanism were investigated. The results indicate that the total soil mercury (THg) concentration in the Beiluhe area remains at an extremely low level (6.33 ± 2.45 ng/g). In the vertical profile, the THg concentration of the shallow soil layer (0-50 cm) (5.96 ± 2.22 ng/g) is significantly lower than that of the deep layer (50-400 cm) (7.44 ± 2.71 ng/g) (p < 0.05). Within the upper 50 cm, the THg concentration decreases with soil depth, and the peak THg concentration occurs at 100-300 cm on the entire profile. Although the THg concentration is slightly affected by the organic matter in the shallow soil layer, in general, the soil parent material is the dominant factor affecting the THg concentration. Intense weathering results in a low THg concentration in the shallow soil layer because the soil Hg is carried downward with the soil moisture. To a certain depth, the impermeable frozen soil layer intercepts the flow of the soil Hg, and it forms a Hg enrichment layer. This paper presents the distinctive pattern of the soil Hg distribution in the permafrost regions of the QTP.

Comparison of safety, efficacy and serum immune indexes of Clostridium butyricum Enterococcus triple viable vs Bifidobacterium triple viable in the treatment of bronchial asthma in children.

The principal objective of our study was to investigate the safety and efficacy of Clostridium butyricum enterococci triple viable vs Bifidobacterium triple viable in the cure of bronchial asthma in children, and to compare the serum immune indexes. We retrospectively investigated 180 children with BA treated in Lianshui County People's Hospital from June 2019 to June 2021. These children were divided into three groups in accordance with the cure methods: The control group (group A) gave consent to routine drug treatment, the children in the Clostridium butyricum enterococci triple viable group (group B) received routine treatment, combined with Clostridium butyricum enterococci triple viable tablets and the children in the Bifidobacterium Lactobacillus triple viable group (group C) received routine treatment, combined with Bifidobacterium Lactobacillus triple viable powder. Combined with the treatment results, the effect of combined probiotics on BA in children is more significant than that of routine treatment, which can effectively enhance the immune function, lung function and inflammation of children. The effect of Clostridium butyricum enterococci triple viable bacteria is better than that of Bifidobacterium triple viable bacteria.

Characterization of the prokaryotic diversity through a stratigraphic permafrost core profile from the Qinghai-Tibet Plateau.

Permafrost on the Qinghai-Tibet Plateau is one of the most sensitive regions to climate warming, thus characterizing its microbial diversity and community composition may be important for understanding their potential responses to climate changes. Here, we investigated the prokaryotic diversity in a 10-m-long permafrost core from the Qinghai-Tibet Plateau by restriction fragment length polymorphism analysis targeting the 16S rRNA gene. We detected 191 and 17 bacterial and archaeal phylotypes representing 14 and 2 distinct phyla, respectively. Proteobacteria was the dominant bacterial phylum, while archaeal communities were characterized by a preponderance of Thaumarchaeota. Some of prokaryotic phylotypes were closely related to characterized species involved in carbon and nitrogen cycles, including nitrogen fixation, methane oxidation and nitrification. However, the majority of the phylotypes were only distantly related to known taxa at order or species level, suggesting the potential of novel diversity. Additionally, both bacterial α diversity and community composition changed significantly with sampling depth, where these communities mainly distributed according to core horizons. Arthrobacter-related phylotypes presented at high relative abundance in two active layer soils, while the deeper permafrost soils were dominated by Psychrobacter-related clones. Changes in bacterial community composition were correlated with most measured soil variables, such as carbon and nitrogen contents, pH, and conductivity.

Diversity and community structure of fungi through a permafrost core profile from the Qinghai-Tibet Plateau of China.

While a vast number of studies have addressed the prokaryotic diversity in permafrost, characterized by subzero temperatures, low water activity, and extremely low rates of nutrient and metabolite transfer, fungal patterns have received surprisingly limited attention. Here, the fungal diversity and community structure were investigated by culture-dependent technique combined with cloning-restriction fragment length polymorphism (RFLP) analysis of sediments in a 10-m-long permafrost core from the Qinghai-Tibet Plateau of China. A total of 62 fungal phylotypes related to 10 distinct classes representing three phyla were recovered from 5031 clones generated in 13 environmental gene libraries. A large proportion of the phylotypes (25/62) that were distantly related to described fungal species appeared to be novel diversity. Ascomycota was the predominant group of fungi, with respect to both clone and phylotype number. Our results suggested there was the existence of cosmopolitan psychrophilic or psychrotolerant fungi in permafrost sediments, the community composition of fungi varied with increasing depth, while these communities largely distributed according to core layers.

Formation processes of shallow ground ice in permafrost in the Northeastern Qinghai-Tibet Plateau: A stable isotope perspective.

The Source Area of the Yellow River (SAYR) on the Northeastern Qinghai-Tibet Plateau (QTP) stores substantial amounts of ground ice, which plays a significant role in understanding the hydrological processes and past permafrost evolution on the QTP. However, little is known about the initial sources and controlling factors of the ground ice in the SAYR. In this study, for the first time, ground ice stable isotope data (δ18O, δD, and d-excess) are presented, along with cryostratigraphic information for nine sites is integrated into three cryostratigraphic units (palsa, thermo-gully, and lake-affected sites) in the central SAYR. The ground ice in the nine sites exhibited diverse structures, ice contents, and stable isotopes due to differences in the initial water sources, ice formation mechanisms, soil types, and climate conditions. All of the freezing lines of ground ice are below those of the precipitation, streams, and lakes in most cases, suggesting the freezing of liquid water. The near-surface ground ice (NSGI) originated from precipitation, active layer water, and precipitation-fed springs. The NSGI was formed by quick freezing at the thermo-gully site (TG-1). In contrast, the formation of the NSGI at the palsa site (Palsa-1) experienced a slow segregation process during the permafrost aggradation. The NSGI was formed by quick freezing at the lake-affected sites under colder climate conditions. Conversely, the deep-layer ground ice (DLGI) at the lake-affected sites was fed by isotopically negative water and lake water occurred during a colder climate period. The DLGI at the TG-1 and Palsa-1 formed via similarly slow segregation of supra-permafrost water (mixed with precipitation), but had opposite water migration directions. The stable isotope compositions of the DLGI at the lake-affected sites became gradually more positive with decreasing distance from WL Lake, emphasizing the large influence of the lake changes on the growth of ice. The two end-member mixing model estimated that the contributions of paleo-lake water to the DLGI ranged from 9.8 % to 63.4 % towards the lake at the lake-affected sites, while the meltwater from past permafrost/ground ice contributed 36.6-90.2 % of the total input. A conceptual diagram of the δ18O trajectories of ground ice was constructed, the water migration patterns and ground ice formation processes between the palsa, thermo-gully, and lake-affected sites were clarified. The results of this study emphasize the influence of lake changes and past permafrost evolution on ground ice growth and improve our understanding of permafrost changes on the QTP.

Effect of permafrost degradation on carbon sequestration of alpine ecosystems.

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg‧ha-1‧a-1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Degraded frozen soil and reduced frost heave in China due to climate warming.

Frost heave hazard is the uneven uplift of the ground surface due to the freezing of water and the expansion of ice bodies in soil, especially in seasonally frozen soil. First, this study quantified temporal and spatial variations of frozen soil, the active layer and frost heave in China in the 2010s. Subsequently, the study predicted the changes in the frozen soil, active layer, and frost heave for the 2030s and 2050s under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 climate scenarios. The permafrost will have degraded to seasonally frozen soil, and the seasonally frozen soil will have a reduced depth or even become non-frozen. By the 2050s, the area of permafrost and seasonally frozen soil will have degraded by 17.6-59.2 % and 4.8-13.5 %, respectively. There is a 19.7-37.2 % reduction in area for seasonally frozen soil when the maximum depth of the seasonally freezing layer (MDSF) < 1.0 m, 8.8-18.5 % when 2.0 < MDSF <3.0 m, and an increase up to 13 % when 1.0 < MDSF <2.0 m. The area with a frost heaving <1.5 cm, 1.5-3.0 cm, 3.0-5.0 cm will have been reduced by 16.6-27.2 %, 18.0-24.4 %, and -8.0-17.1 % in the 2050s, respectively. Areas where permafrost degrades to seasonally frozen soil require attention when managing frost heave hazards. This study will help guide engineering and environmental practices in cold regions.

Permafrost degradation alters the environmental signals recorded in tree-ring lignin methoxy group δ2H in northeastern China.

Climate warming has profoundly altered the status of permafrost and has caused extensive permafrost degradation in the Northern Hemisphere. However, long-term observations investigating the hydrological dynamics of permafrost and its ecological effects on plant growth are lacking. Previous studies have reported tree-ring stable hydrogen isotope ratios of lignin methoxy groups (δ2HLM) as an archive of hydrological signals. This study sampled tree-ring cores from a Larix gmelinii forest in Nanwenghe Forest Park, Northeastern China, and separately measured the tree-ring δ2HLM for earlywood and latewood from 1900 to 2020. Earlywood and latewood δ2HLM values, as well as the difference between them, showed no significant long-term trend from 1900 to 1987; however, they both exhibited significant increasing trends since 1988 at rates of 2.6 ‰ and 4.9 ‰ per decade, respectively. This variance changes the magnitude of the difference between the two chronologies and can be explained by the shift in source water δ2H values during tree growth. Based on a structural equation model analysis, when the influence of permafrost melting weakened due to permafrost degradation, the growing season temperature was better recorded in latewood δ2HLM through the effects of precipitation δ2H from July to September. Based on the environmental response of tree-ring δ2HLM in the permafrost region, permafrost degradation influences the source water δ2H values of trees, thereby affecting the expression of temperature signals in tree-ring δ2HLM. The novel results in this study provide a new perspective on permafrost degradation based on the dynamic responses of tree-ring δ2HLM to source water δ2H during permafrost degradation.

Convergence and divergence emerging in climatic controls of polynomial trends for northern ecosystem productivity over 2000-2018.

Recent rapid warming has caused uneven impacts on the composition, structure, and functioning of northern ecosystems. It remains unknown how climatic drivers control linear and non-linear trends in ecosystem productivity. Based on a plant phenology index (PPI) product at a spatial resolution of 0.05° over 2000-2018, we used an automated polynomial fitting scheme to detect and characterize trend types (i.e., polynomial trends and no-trends) in the yearly-integrated PPI (PPIINT) for northern (> 30°N) ecosystems and their dependence on climatic drivers and ecosystem types. The averaged slope for the linear trends (p < 0.05) of PPIINT was positive across all the ecosystems, among which deciduous broadleaved forests and evergreen needle-leaved forests (ENF) showed the highest and lowest mean slopes, respectively. More than 50% of the pixels in ENF, arctic and boreal shrublands, and permanent wetlands (PW) had linear trends. A large fraction of PW also showed quadratic and cubic trends. These trend patterns agreed well with estimates of global vegetation productivity based on solar-induced chlorophyll fluorescence. Across all the biomes, PPIINT in pixels with linear trends showed lower mean values and higher partial correlation coefficients with temperature or precipitation than in pixels without linear trends. Overall, our study revealed the emergence of latitudinal convergence and divergence in climatic controls on the linear and non-linear trends of PPIINT, implying that northern shifts of vegetation and climate change may potentially increase the non-linear nature of climatic controls on ecosystem productivity. These results can improve our understanding and prediction of climate-induced changes in plant phenology and productivity and facilitate sustainable management of ecosystems by accounting for their resilience and vulnerability to future climate change.

Deep-sequencing transcriptome analysis of chilling tolerance mechanisms of a subnival alpine plant, Chorispora bungeana.

BACKGROUND: The plant tolerance mechanisms to low temperature have been studied extensively in the model plant Arabidopsis at the transcriptional level. However, few studies were carried out in plants with strong inherited cold tolerance. Chorispora bungeana is a subnival alpine plant possessing strong cold tolerance mechanisms. To get a deeper insight into its cold tolerance mechanisms, the transcriptome profiles of chilling-treated C. bungeana seedlings were analyzed by Illumina deep-sequencing and compared with Arabidopsis. RESULTS: Two cDNA libraries constructed from mRNAs of control and chilling-treated seedlings were sequenced by Illumina technology. A total of 54,870 unigenes were obtained by de novo assembly, and 3,484 chilling up-regulated and 4,571 down-regulated unigenes were identified. The expressions of 18 out of top 20 up-regulated unigenes were confirmed by qPCR analysis. Functional network analysis of the up-regulated genes revealed some common biological processes, including cold responses, and molecular functions in C. bungeana and Arabidopsis responding to chilling. Karrikins were found as new plant growth regulators involved in chilling responses of C. bungeana and Arabidopsis. However, genes involved in cold acclimation were enriched in chilling up-regulated genes in Arabidopsis but not in C. bungeana. In addition, although transcription activations were stimulated in both C. bungeana and Arabidopsis, no CBF putative ortholog was up-regulated in C. bungeana while CBF2 and CBF3 were chilling up-regulated in Arabidopsis. On the other hand, up-regulated genes related to protein phosphorylation and auto-ubiquitination processes were over-represented in C. bungeana but not in Arabidopsis. CONCLUSIONS: We conducted the first deep-sequencing transcriptome profiling and chilling stress regulatory network analysis of C. bungeana, a subnival alpine plant with inherited cold tolerance. Comparative transcriptome analysis suggests that cold acclimation is not a major chilling tolerance mechanism of C. bungeana. Activation of protein phosphorylation and ubiquitination may confer chilling tolerance to C. bungeana in a more rapid and flexible way than cold acclimation. Such differences may have contributed to the differences in cold tolerance between C. bungeana and Arabidopsis. The results presented in this paper will be informative for gene discovery and the molecular mechanisms related to plant cold tolerance.

Research Priorities and Trends on Bioenergy: Insights from Bibliometric Analysis.

Replacing fossil fuels with bioenergy is crucial to achieving sustainable development and carbon neutrality. To determine the priorities and developing trends of bioenergy technology, related publications from 2000 to 2020 were analyzed using bibliometric method. Results demonstrated that the number of publications on bioenergy increased rapidly since 2005, and the average growth rate from 2005 to 2011 reached a maximum of 20% per year. In terms of publication quantity, impact, and international collaboration, the USA had been leading the research of bioenergy technology, followed by China and European countries. Co-occurrence analysis using author keywords identified six clusters about this topic, which are "biodiesel and transesterification", "biogas and anaerobic digestion", "bioethanol and fermentation", "bio-oil and pyrolysis", "microalgae and lipid", and "biohydrogen and gasification or dark fermentation". Among the six clusters, three of them relate to liquid biofuel, attributing that the liquid products of biomass are exceptional alternatives to fossil fuels for heavy transportation and aviation. Lignocellulose and microalgae were identified as the most promising raw materials, and pretreating technologies and efficient catalysts have received special attention. The sharp increase of "pyrolysis" and "gasification" from 2011 to 2020 suggested that those technologies about thermochemical conversion have been well studied in recent years. Some new research trends, such as applying nanoparticles in transesterification, and hydrothermal liquefaction in producing bio-oil from microalgae, will get a breakthrough in the coming years.

Spatial state distribution and phase transition of non-uniform water in soils: Implications for engineering and environmental sciences.

The physical behaviors of water in the interface are the fundamental to discovering the engineering properties and environmental effects of aqueous porous media (e.g., soils). The pore water pressure (PWP) is a key parameter to characterize the pore water state (PWS) and its phase transition in the micro interface. Traditionally, the water in the interface is frequently believed to be uniform, negative in pressure and tensile based on macroscopic tests and Gibbs interface model. However, the water in the interface is a non-uniform and compressible fluid (part of tensile and part of compressed), forming a spatial profile of density and PWP depending on its distance from the substrate interface. Herein, we introduced the static and dynamic theory methods of non-uniform water based on diffuse interface model to analyze non-uniform water state dynamics and water density and PWP. Based on the theory of non-uniform water, we gave a clear stress analysis on soil water and developed the concepts of PWS, PWP and matric potential in classical soil mechanics. In addition, the phase transition theory of non-uniform water is also examined. In nature, the generalized Clausius-Clapeyron equation (GCCE) is consistent with Clapeyron equation. Therefore, a unified interpretation is proposed to justify the use of GCCE to represent frozen soil water dynamics. Furthermore, the PWP description of non-uniform water can be well verified by some experiments focusing on property variations in the interface area, including the spatial water density profile and unfrozen water content variations with decreasing temperature and other factors. In turn, PWP spatial distribution of non-uniform water and its states can well explain some key phenomena on phase transition during ice or hydrate formation, including the discrepancies of phase transition under a wide range of conditions.

Holocene monsoon dynamics at Kunlun Pass on the northeastern Qinghai-Tibet Plateau.

Various proxy records have been used for the understanding of environmental and climate variations during the Holocene. Here, for the first time, we use meteoric 10Be isotope measurements performed on sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate hydroclimate changes during the Holocene. The 10Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the 10Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These 10Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the 10Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase is indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Ground ice at depths in the Tianshuihai Lake basin on the western Qinghai-Tibet Plateau: An indication of permafrost evolution.

The stable-isotope data of ground ice from a deep borehole (~46 m) at the Tianshuihai (TSH) lake basin on the northwestern Qinghai-Tibet Plateau (QTP) are presented together with cryolithological information. Remarkable variations in the stable isotope composition of ground ice at depths allow a division of five clearly delineated stages. The remarkable deviations in stable isotopes of ground ice during each stage underline different initial source water and formation processes, indicating considerable fluctuations in paleo-lake conditions and multiple patterns of climatic-induced permafrost evolutions. In combination with the ground ice isotopes for two deep boreholes on the interior QTP, the position of the present permafrost table is found at 2-3 m. Two possible positions of paleo-permafrost tables at depths of 7-8 and 15-16 m are identified based on the ice isotopic composition of wellbores in combination with those from the other two deep boreholes on the interior QTP. The high uniformity in stable isotopic composition of ground ice below the depth of 16 m may have reflected the consistent regional climate transitions and the resultant permafrost evolution on the QTP. This study provides some new insights on the ground ice as an indicator for permafrost evolution on the QTP.

The effect of desertification on frozen soil on the Qinghai-Tibet plateau.

Under the influences of climate change and human activities, desertification has become widespread on the Qinghai-Tibet Plateau (QTP). However, the effect of desertification on frozen soil is still debated. Here, soil temperatures are observed through 14 boreholes at Honglianghe River Basin on the QTP to study the relationship between desertification and frozen soil. The results showed soil temperatures change with the thickness of sand cover. With increasing sand thickness, maximum soil temperatures at shallow depths (0.05-6.00 m) increase by 0.25-1.57 °C, but minimum temperatures decrease by 0.21-1.49 °C, on average. Temperatures at deep depth (≥6.00 m) exhibit a rising trend that temperatures increase by 0.01-0.05 °C on average with each increment of 10 cm in sand thickness. Furthermore, aeolian sand enhances seasonal thawing processes, resulting in an increase of 7.70-9.50 cm in active layer thickness with each increment of 10 cm in sand thickness. Meanwhile, aeolian sand weakens seasonal freezing processes, resulting in a decrease of 1.07-13.00 cm in seasonal freezing depth with each increment of 10 cm in sand thickness. Moisture contents of aeolian sand and vegetation coverages on the sand cover surface influence energy state and thermal regime of frozen soil. Annual heat budgets of soil under aeolian sand increase from -57.97 MJ m-2 to -26.28 MJ m-2 as water content of sand layer decreases from 13.42% to 3.61%. Annual range of ground temperatures of soil at shallow depths (0.05-1.60 m) increase by 2.19-6.17 °C on average as vegetation coverage increases from 5% to 20%. Due to the effects of aeolian sand on frozen soil, desertification accelerates, and can even cause, the degradation of frozen soil on the QTP. Our study provides an important reference for future research about the interaction between desertification and frozen soil in other regions.

Experimental Study of the Formation Rate and Distribution of Methane Hydrate in Layered Sand.

The geological structure and gas hydrate occurrence are stratification-dependent in the vertical direction. It is necessary to explore the formation processes and distribution characteristics of methane hydrate in layered porous media. The sand sample consists of two equal parts in a testing cylinder. The upper part is 0.5-1 mm sand in particle diameter, and the lower parts are 0.075∼0.5, 0.5∼1, and 1∼2 mm. The experimental results show that the formation rate of methane hydrate gradually decreases as the reaction goes on, and it is higher in layered sand than in nonlayered sand in the beginning. With the increase of the sand size in the lower part, saturation of methane hydrate gradually decreases in the upper part and increases in the lower part. In the layered sand, saturation of methane hydrate is higher in the sand layer whose particle size is bigger. The abovementioned results can be used to predict the favorable area where methane hydrate may appear in different stratigraphic structures in nature.

Permafrost degradation enhances the risk of mercury release on Qinghai-Tibetan Plateau.

Permafrost on the Qinghai-Tibetan Plateau (QTP) has been degrading in the past decades. While the degradation may mobilize previously protected material from the permafrost profile, little is known about the stocks and stability of mercury (Hg) in the QTP permafrost. Here we measured total soil Hg in 265 samples from 15 permafrost cores ranging from 3 to 18 m depth, and 45 active layer (AL) soil samples from different land cover types on the QTP. Approximately 21.7 Gg of Hg was stored in surficial permafrost (0-3 m), with 16.58 Gg of Hg was stored in the active layer. Results from six permafrost collapse areas showed that much of the thawed Hg is mobile, with decreases in total Hg mass of 17.6-30.9% for the AL (top 30 cm) in comparison with non-thermokarst surfaces. We conclude that the QTP permafrost region has a large mercury pool, and the stored mercury is sensitive to permafrost degradation.

Carbon and mercury export from the Arctic rivers and response to permafrost degradation.

Arctic rivers export a large amount of organic carbon (OC) and mercury (Hg) to Arctic oceans. Because there are only a few direct calculations of OC and Hg exports from these large rivers, very little is known about their response to changes in the active layer in northern permafrost-dominated areas. In this study, multiyear data sets from the Arctic Great Rivers Observatory (ArcticGRO) are used to estimate the export of dissolved organic carbon (DOC), particulate organic carbon (POC), total mercury (THg) and methylmercury (MeHg) from the six largest rivers (Yenisey, Lena, Ob, Mackenzie, Yukon and Kolyma) draining to the Arctic Ocean. From 2003 to 2017, annual DOC and POC export to the Arctic Ocean was approximately 21612 Gg and 2728 Gg, and the exports of Hg and MeHg to the Arctic Ocean were approximately 20090 kg and 110 kg (0.002% of the total Hg stored in the northern hemisphere active layer). There were great variations in seasonal OC and Hg concentrations and chemical characteristics, with higher fluxes in spring and lower fluxes in winter (baseline). DOC and Hg concentrations are significantly positively correlated to discharge, as discharge continues to increase in response to a deepening active layer thickness during recent past decades. This study shows that previous results likely underestimated DOC exports from rivers in the circum-Arctic regions, and both OC and Hg exports will increase under predicted climate warming scenarios.