Permafrost thickness under identical climates in cold regions can vary significantly because it is severely affected by climate change, topography, soil physical and thermal properties, and geothermal conditions. This...Permafrost thickness under identical climates in cold regions can vary significantly because it is severely affected by climate change, topography, soil physical and thermal properties, and geothermal conditions. This study numerically in- vestigates the response of ground thermal regime and talik development processes to permafrost with different thicknesses under a thermokarst lake on the Qinghai-Tibet Plateau. On the basis of observed data and information from a representative monitored lake in the Beiluhe Basin, we used a heat transfer model with phase change under a cylindrical coordinate system to conduct three simulation cases with permafrost thicknesses of 45 m, 60 m, and 75 m, respectively. The simulated results indicate that increases in permafrost thickness not only strongly retarded the open talik formation time, but also delayed the permafrost lateral thaw process after the formation of open talik. Increasing the permafrost thickness by 33.3% and 66.7% led to open talik formation time increases of 83.66% and 207.43%, respectively, and resulted in increases in the lateral thaw duration of permafrost under the modeled thermokarst lake by 28.86% and 46.54%, respectively, after the formation of the open taliks.展开更多
As significant evidence of permafrost degradation,thermokarst lakes play an important role in the permafrost regions by regulating hydrology,ecology,and biogeochemistry.In the Sources Area of the Yellow River(SAYR),pe...As significant evidence of permafrost degradation,thermokarst lakes play an important role in the permafrost regions by regulating hydrology,ecology,and biogeochemistry.In the Sources Area of the Yellow River(SAYR),permafrost degradation has accelerated since the 1980s,and numerous thermokarst lakes have been discovered.In this paper,we use Sentinel-2 images to extract thermokarst lake boundaries and perform a regional-scale study on their geometry across the permafrost region in the SAYR.We also explored the spatiotemporal variations and potential drivers from the perspectives of the permafrost,climate,terrain and vegetation conditions.The results showed that there were 47,518 thermokarst lakes in 2021 with a total area of 190.22×106 m^(2),with an average size of 4,003.3 m^(2).The 44,928 ponds(≤10,000 m^(2))predominated the whole lake number(94.1%)but contributed to a small portion of the total lake area(28.8%).With 2,590 features(5.9%),small-sized(10,000 to 100,000 m^(2))and large-sized lakes(>100,000 m^(2))constituted up to 71.2%of the total lake area.Thermokarst lakes developed more significantly in warm permafrost regions than in cold permafrost areas;74.1%of lakes with a total area of 119.6×106 m^(2)(62.9%),were distributed in warm permafrost regions.Most thermokarst lakes were likely to develop within the elevation range of 4,500~4,800 m,on flat terrain(slope<10°),on SE and S aspects and in alpine meadow areas.The thermokarst lakes in the study region experienced significant shrinkage between 1990 and 2021,characterized by obvious lake drainage;the lake numbers decreased by 5418(56.1%),with a decreasing area of 58.63×106 m^(2)(49.0%).This shrinkage of the thermokarst lake area was attributable mainly to the intensified degradation of rich-ice permafrost thawing arising from continued climate warming,despite the wetting climatic trend.展开更多
Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain...Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain their age.We obtained lake-bottom samples of 50 cm length from lake BLH-A and 25 cm length from lake BLH-B.Environmental 137 Cs and 210 Pb and radiocarbon age dating techniques were applied to the 50 cm and 25 cm samples,respectively.The results indicate that the initiation of BLH-A is about 800-900 a B.P.,and approximately 1,450±30 a B.P.to 2,230±30 a B.P.for BLH-B.These results will provide scientific bases for sedimentological study and thermokarst activity in Beiluhe Basin.展开更多
A thermokarst lake is defined as a lake occupying a closed depression formed by ground settlement following thawing of ice-rich permafrost or the melting of massive ice. As it is the most visible morphologic landscape...A thermokarst lake is defined as a lake occupying a closed depression formed by ground settlement following thawing of ice-rich permafrost or the melting of massive ice. As it is the most visible morphologic landscape developed during the process of permafrost degradation, we reviewed recent literature on thermokarst studies, and summarized the main study topics as： development and temporal evolution, carbon release, and ecological and engineering influence of thermokarst lakes. The climate warming, forest fires, surface water pooling, geotectonic fault and anthropogenic activity are the main influencing factors that cause an increase of ground temperatures and melting of ice-rich permafrost, resulting in thermokarst lake formation. Normally a thermokarst lake develops in 3–5 stages from initiation to permafrost recovery. Geo-rectified aerial photographs and remote sensing images show that thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance in most regions of the Arctic, while both lake numbers and areas on the Qinghai-Tibet Plateau have increased. Field studies and modeling indicates that carbon release from thermokarst lakes can feedback significantly to global warming, thus enhancing our understanding of the influences of thermokarst lakes on the ecological environment, and on regional groundwater through drainage. Based on field monitoring and numerical simulations, infrastructure stability can be affected by thermal erosion of nearby thermokarst lakes. This review was undertaken to enhance our understanding of thermokarst lakes, and providing references for future comprehensive studies on thermokarst lakes.展开更多
This study presents thermokarst lake changes at seven different sites in the continuous and isolated permafrost zones in Mongolia. Lakes larger than 0.1 ha were analyzed using Corona KH-4, KH-4A and KH-4B (1962-1968),...This study presents thermokarst lake changes at seven different sites in the continuous and isolated permafrost zones in Mongolia. Lakes larger than 0.1 ha were analyzed using Corona KH-4, KH-4A and KH-4B (1962-1968), Landsat ETM + (1999-2001), and ALOS/AVNIR-2 (2006-2007) satellite imagery. Between 1962 and 2007, the total number and area of lakes increased by +21% (347 to 420), and +7% (3680 ha to 3936 ha) in the continuous permafrost zone, respectively. These changes correspond to the appearance of 85 new lakes (166 ha) during the last 45 years. In contrast, lakes in the isolated permafrost zone have decreased by –42% (118 to 68) in number and –12% (422 ha to 371 ha) in area from 1962 to 2007. The changes in lake area and number are likely attributed to shifts in climate regimes and local permafrost conditions. Since 1962, the mean annual air temperature and potential evapotranspiration have increased significantly in the northern continuous permafrost zone compared to the southern isolated permafrost zone. Due to ongoing atmospheric warming without any significant trend in annual precipitation, patches of ice-rich subsurface have thawed, and the number and area of lakes have accordingly developed in the continuous permafrost zone. Shrinking of thermokarst lakes in the isolated permafrost zone may be due to disappearing permafrost, deepening of the active layer, and increased water loss through surface evaporation and subsurface drainage.展开更多
Viruses,the most diverse of all biological entities,are ubiquitous and can influence nearly all life forms on Earth[1].The preliminary pathway through which viruses affect microbialmetabolism and evolution is viral in...Viruses,the most diverse of all biological entities,are ubiquitous and can influence nearly all life forms on Earth[1].The preliminary pathway through which viruses affect microbialmetabolism and evolution is viral infection[2].There are two distinct infection modes for viruses interacting with prokaryotes,namely temperate and virulent lifestyles[3].Virulent viruses trigger their hosts’death by lysis once they invade the host cells[2],whereas temperate viruses can replicate alongside their host inthe lysogenic cycle until a lytic cycle is induced[2,3].It has beenreported that viral lifestyles are key determinants of virusencoded auxiliary metabolic genes(AMGs)that are crucial toolboxes for viruses to reprogram host metabolisms[4].An in-depthinvestigation of virus-microbe infection modes over a broad geographical scale is thus vital for understanding the potential effectsof viruses on the microbial community and biogeochemical cycles.展开更多
This work presents changes of thermokarst lakes from Beilu River Basin on the Qinghai-Tibet Plateau over the past four decades （1969-2010） using aerial and satellite image interpretation. The results indicated that ...This work presents changes of thermokarst lakes from Beilu River Basin on the Qinghai-Tibet Plateau over the past four decades （1969-2010） using aerial and satellite image interpretation. The results indicated that thermokarst lake activity had generally increased rapidly between 1969 and 2010. The number of thermokarst lakes had increased by approximately 534, and their coverage expanded by about 410 ha. The two main changes observed were an increase in the number of small lakes and the expansion of larger lakes. These changes are likely the result of persistent climate warming and a gradually increasing imbalance between precipitation and evapotranspiration （PET）. However, some non-climatic factors, such as the lake-bottom substrate and local engineering activities, have also influenced the lake changes. If air temperature and P-ET continue to rise, the number of thermokarst lakes and the area they cover may continue to increase in the future.展开更多
Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typical...Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and, with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10 and 20 cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacity in the area of the thermokarst lake.展开更多
作为多年冻土退化的重要标志,热融湖对其热状态、水文过程、生态环境及冻土工程稳定性具有重要影响。然而,现有的热融湖识别研究受青藏高原复杂地形和下垫面、广泛存在的云雾与冰雪,以及识别方法和影像分辨率本身的制约,导致青藏高原小...作为多年冻土退化的重要标志,热融湖对其热状态、水文过程、生态环境及冻土工程稳定性具有重要影响。然而,现有的热融湖识别研究受青藏高原复杂地形和下垫面、广泛存在的云雾与冰雪,以及识别方法和影像分辨率本身的制约,导致青藏高原小型热融湖存在严重漏提问题。本文基于Sentinel-2影像,提取细小水体边界区分度高的植被红边水体指数(vegetation red edge based water index,RWI),辅以人工目视剔除河流与积雪,实现了青藏高原热融湖的准确识别。在此基础上,应用频率比法评估了环境因子与热融湖发育的相关性。通过叠加各环境因子频率比值的权重积,建立了热融湖的易发性分区。结果表明,RWI在热融湖提取中总体精度为98.97%、制图精度为85.52%、用户精度为83.12%、Kappa系数为0.8118,体现出较高的识别精度。在青藏高原共识别出182668个热融湖,总面积为2456.13 km^(2),总体呈现出“小型热融湖数量多面积占比小,大型热融湖数量少面积占比大”的特征。各环境因子对热融湖影响程度依次排序为坡度>高程>活动层厚度>归一化植被指数>地下冰含量>降水量>年平均地温。热融湖易发性分区显示,低易发区面积占比最大(31.01%),但仅包含4.04%的热融湖,密度为2.01个⋅(100km^(2))^(-1);高与极高易发区面积占比之和仅为25.19%,却集中了84.30%的热融湖,极高易发区热融湖点密度达77.92个⋅(100km^(2))^(-1),是低易发区的38.76倍。展开更多
Climate warming rates in the Arctic are far greater than the global average,exerting stronger impacts on permafrost degradation and thermokarst landform development.Thermokarst lakes and ponds(TLPs),which are widely d...Climate warming rates in the Arctic are far greater than the global average,exerting stronger impacts on permafrost degradation and thermokarst landform development.Thermokarst lakes and ponds(TLPs),which are widely distributed in the Lena Basin in the Russian Arctic,play a vital role in altering local ecosystem.However,the detailed distribution of TLPs in the Lena Basin still remains poorly known.In this study,we built the first 10 m resolution TLP dataset for the Lena Basin in the 2020 thawing season by utilizing 4902 Sentinel-2 images.A robust mapping workflow was developed and implemented in the Google Earth Engine(GEE)platform.The accu-racy assessment demonstrates a satisfactory accuracy(93.63%),and our results exhibit a better consistency with real TLPs than global water body products.A total of 380,477 TLPs(~0.53%of the total surface area of the Lena Basin)were identified,showing an uneven distribution in the five sub-basins.The TLPs were found to be mainly located within plain areas,with an active layer thickness in the range of 80-100 cm.The higher ground ice content and mean annual ground temperature were favorable for TLP development.This dataset will be valuable for investigating the complex interac-tion between TLPs and permafrost.It will also serve as a baseline product for better incorporating thermokarst processes into perma-frostclimate models.展开更多
Mapping and monitoring the spatial–temporal evolution of thermokarst lakes on the Tibetan Plateau can significantly contribute to the estimation of climate change impacts on permafrost degradation.Remote sensing-base...Mapping and monitoring the spatial–temporal evolution of thermokarst lakes on the Tibetan Plateau can significantly contribute to the estimation of climate change impacts on permafrost degradation.Remote sensing-based methods have been developed to monitor the interannual changes of thermokarst lakes.However,the seasonal changes,which are vital for understanding thermokarst lake dynamics,are commonly overlooked.This paper developed automatic methods which integrated the normalized difference water index(NDWI),modified normalized difference water index(MNDWI),principal component analysis(PCA),and independent component analysis(ICA)with Markov random field(MRF)for rapid mapping of thermokarst lakes in different physical states characterized by season changes.To validate the effectiveness,the proposed methods were applied to map thermokarst lakes on the central Tibetan Plateau,using four Sentinel-2 images representing different evolutionary states.Specifically,the areato-point regression kriging(ATPRK)method was employed to downscale the 20-m short-wave infrared(SWIR)band to 10 m.Using manually digitized lakes as a reference,the proposed methods achieved an average Kappa coefficient of 0.79,significantly outperforming the water index thresholding method that merely attained 0.44.The results corroborate that the proposed methods can be robustly applied in mapping thermokarst lake dynamics with both interannual and seasonal trends on the Tibetan Plateau.展开更多
This study examines the Carolina Bays and Nebraska Rainwater Basins,using high-resolution LiDAR elevation models to analyze their unique shapes.The research reveals that well-preserved Bays exhibit precise elliptical ...This study examines the Carolina Bays and Nebraska Rainwater Basins,using high-resolution LiDAR elevation models to analyze their unique shapes.The research reveals that well-preserved Bays exhibit precise elliptical geometry,distinguishing them from various oriented lakes they are often compared to.While the timing of their formation is discussed,the primary goal of this paper is to establish a repeatable method for quantifying the elliptical nature of these dominant geomorphic landforms.By applying the least squares method to points selected along the perimeters of these extraordinary basins,the study confirms their elliptical geometry with an error margin of less than 3%.This rigorous mathematical approach sets a high standard for any hypothesis attempting to explain the origin of these depressions using natural environmental conditions.Notably,the long axes of these elliptical basins converge near the Great Lakes region,and since ellipses can be described as conic sections,this finding supports the plausibility of a cosmic impact origin.The study suggests that these basins may be secondary impact features formed during a past glacial cycle of the Laurentide Ice Sheet.This research establishes a strong mathematical foundation to support future studies on the possible impact origin of the Carolina Bays and Nebraska Rainwater Basins.展开更多
基金supported by the National Natural Science Foundation of China (NSFC) (No.41271076)the National Key Basic Research Program of China (No.2010CB951402)the Open Fund Project of the Institute of Plateau Meteorology, China Meteorological Administration (No.LPM2008019)
文摘Permafrost thickness under identical climates in cold regions can vary significantly because it is severely affected by climate change, topography, soil physical and thermal properties, and geothermal conditions. This study numerically in- vestigates the response of ground thermal regime and talik development processes to permafrost with different thicknesses under a thermokarst lake on the Qinghai-Tibet Plateau. On the basis of observed data and information from a representative monitored lake in the Beiluhe Basin, we used a heat transfer model with phase change under a cylindrical coordinate system to conduct three simulation cases with permafrost thicknesses of 45 m, 60 m, and 75 m, respectively. The simulated results indicate that increases in permafrost thickness not only strongly retarded the open talik formation time, but also delayed the permafrost lateral thaw process after the formation of open talik. Increasing the permafrost thickness by 33.3% and 66.7% led to open talik formation time increases of 83.66% and 207.43%, respectively, and resulted in increases in the lateral thaw duration of permafrost under the modeled thermokarst lake by 28.86% and 46.54%, respectively, after the formation of the open taliks.
基金supported by the Natural Science Foundation of Qinghai Province,China(No.2021-ZJ940Q)the Open Project of State Key Laboratory of Plateau Ecology and Agriculture,Qinghai University(No.2022-ZZ-02)。
文摘As significant evidence of permafrost degradation,thermokarst lakes play an important role in the permafrost regions by regulating hydrology,ecology,and biogeochemistry.In the Sources Area of the Yellow River(SAYR),permafrost degradation has accelerated since the 1980s,and numerous thermokarst lakes have been discovered.In this paper,we use Sentinel-2 images to extract thermokarst lake boundaries and perform a regional-scale study on their geometry across the permafrost region in the SAYR.We also explored the spatiotemporal variations and potential drivers from the perspectives of the permafrost,climate,terrain and vegetation conditions.The results showed that there were 47,518 thermokarst lakes in 2021 with a total area of 190.22×106 m^(2),with an average size of 4,003.3 m^(2).The 44,928 ponds(≤10,000 m^(2))predominated the whole lake number(94.1%)but contributed to a small portion of the total lake area(28.8%).With 2,590 features(5.9%),small-sized(10,000 to 100,000 m^(2))and large-sized lakes(>100,000 m^(2))constituted up to 71.2%of the total lake area.Thermokarst lakes developed more significantly in warm permafrost regions than in cold permafrost areas;74.1%of lakes with a total area of 119.6×106 m^(2)(62.9%),were distributed in warm permafrost regions.Most thermokarst lakes were likely to develop within the elevation range of 4,500~4,800 m,on flat terrain(slope<10°),on SE and S aspects and in alpine meadow areas.The thermokarst lakes in the study region experienced significant shrinkage between 1990 and 2021,characterized by obvious lake drainage;the lake numbers decreased by 5418(56.1%),with a decreasing area of 58.63×106 m^(2)(49.0%).This shrinkage of the thermokarst lake area was attributable mainly to the intensified degradation of rich-ice permafrost thawing arising from continued climate warming,despite the wetting climatic trend.
基金supported by the State Key Development Program of Basic Research of China (973 Plan,2012CB026101)the Open Foundation of Key Laboratory of Highway Construction & Maintenance Technology in Permafrost Region,CCCC First Highway Consultants Co.Ltd.the Independent Project of State Key Laboratory of Frozen Soil Engineering,CAS (Grant No.SKLFSE-ZY-14)
文摘Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain their age.We obtained lake-bottom samples of 50 cm length from lake BLH-A and 25 cm length from lake BLH-B.Environmental 137 Cs and 210 Pb and radiocarbon age dating techniques were applied to the 50 cm and 25 cm samples,respectively.The results indicate that the initiation of BLH-A is about 800-900 a B.P.,and approximately 1,450±30 a B.P.to 2,230±30 a B.P.for BLH-B.These results will provide scientific bases for sedimentological study and thermokarst activity in Beiluhe Basin.
基金support from the State Key Development Program of Basic Research of China(973 Plan,2012CB026101)the Western Project Program of theChinese Academy of Sciences(KZCX2-XB3-19)+1 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(GrantNo.41121061)the National Sci-Tech Support Plan(2014BAG05B05)
文摘A thermokarst lake is defined as a lake occupying a closed depression formed by ground settlement following thawing of ice-rich permafrost or the melting of massive ice. As it is the most visible morphologic landscape developed during the process of permafrost degradation, we reviewed recent literature on thermokarst studies, and summarized the main study topics as： development and temporal evolution, carbon release, and ecological and engineering influence of thermokarst lakes. The climate warming, forest fires, surface water pooling, geotectonic fault and anthropogenic activity are the main influencing factors that cause an increase of ground temperatures and melting of ice-rich permafrost, resulting in thermokarst lake formation. Normally a thermokarst lake develops in 3–5 stages from initiation to permafrost recovery. Geo-rectified aerial photographs and remote sensing images show that thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance in most regions of the Arctic, while both lake numbers and areas on the Qinghai-Tibet Plateau have increased. Field studies and modeling indicates that carbon release from thermokarst lakes can feedback significantly to global warming, thus enhancing our understanding of the influences of thermokarst lakes on the ecological environment, and on regional groundwater through drainage. Based on field monitoring and numerical simulations, infrastructure stability can be affected by thermal erosion of nearby thermokarst lakes. This review was undertaken to enhance our understanding of thermokarst lakes, and providing references for future comprehensive studies on thermokarst lakes.
文摘This study presents thermokarst lake changes at seven different sites in the continuous and isolated permafrost zones in Mongolia. Lakes larger than 0.1 ha were analyzed using Corona KH-4, KH-4A and KH-4B (1962-1968), Landsat ETM + (1999-2001), and ALOS/AVNIR-2 (2006-2007) satellite imagery. Between 1962 and 2007, the total number and area of lakes increased by +21% (347 to 420), and +7% (3680 ha to 3936 ha) in the continuous permafrost zone, respectively. These changes correspond to the appearance of 85 new lakes (166 ha) during the last 45 years. In contrast, lakes in the isolated permafrost zone have decreased by –42% (118 to 68) in number and –12% (422 ha to 371 ha) in area from 1962 to 2007. The changes in lake area and number are likely attributed to shifts in climate regimes and local permafrost conditions. Since 1962, the mean annual air temperature and potential evapotranspiration have increased significantly in the northern continuous permafrost zone compared to the southern isolated permafrost zone. Due to ongoing atmospheric warming without any significant trend in annual precipitation, patches of ice-rich subsurface have thawed, and the number and area of lakes have accordingly developed in the continuous permafrost zone. Shrinking of thermokarst lakes in the isolated permafrost zone may be due to disappearing permafrost, deepening of the active layer, and increased water loss through surface evaporation and subsurface drainage.
基金supported by the National Key Research and Development Program of China(2022YFF0801901 and 2022YFF0801903)the National Natural Science Foundation of China(32425004)the New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Viruses,the most diverse of all biological entities,are ubiquitous and can influence nearly all life forms on Earth[1].The preliminary pathway through which viruses affect microbialmetabolism and evolution is viral infection[2].There are two distinct infection modes for viruses interacting with prokaryotes,namely temperate and virulent lifestyles[3].Virulent viruses trigger their hosts’death by lysis once they invade the host cells[2],whereas temperate viruses can replicate alongside their host inthe lysogenic cycle until a lytic cycle is induced[2,3].It has beenreported that viral lifestyles are key determinants of virusencoded auxiliary metabolic genes(AMGs)that are crucial toolboxes for viruses to reprogram host metabolisms[4].An in-depthinvestigation of virus-microbe infection modes over a broad geographical scale is thus vital for understanding the potential effectsof viruses on the microbial community and biogeochemical cycles.
基金supported by the National Basic Research Program of China (2012CB026101)the Western Project Program of the Chinese Academy of Sciences (KZCX2-XB3-19)the National Sci-Tech Support Plan (2014BAG05B01)
文摘This work presents changes of thermokarst lakes from Beilu River Basin on the Qinghai-Tibet Plateau over the past four decades （1969-2010） using aerial and satellite image interpretation. The results indicated that thermokarst lake activity had generally increased rapidly between 1969 and 2010. The number of thermokarst lakes had increased by approximately 534, and their coverage expanded by about 410 ha. The two main changes observed were an increase in the number of small lakes and the expansion of larger lakes. These changes are likely the result of persistent climate warming and a gradually increasing imbalance between precipitation and evapotranspiration （PET）. However, some non-climatic factors, such as the lake-bottom substrate and local engineering activities, have also influenced the lake changes. If air temperature and P-ET continue to rise, the number of thermokarst lakes and the area they cover may continue to increase in the future.
基金supported by the National Natural Science Foundation of China(Grant No.41271092)the National Basic Research Program of China(Grant Nos.2010CB951402,2012CB026101)the Key Project of the National Natural Science Foundation of China(Grant No.D010102-91125010)
文摘Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and, with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10 and 20 cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacity in the area of the thermokarst lake.
文摘作为多年冻土退化的重要标志,热融湖对其热状态、水文过程、生态环境及冻土工程稳定性具有重要影响。然而,现有的热融湖识别研究受青藏高原复杂地形和下垫面、广泛存在的云雾与冰雪,以及识别方法和影像分辨率本身的制约,导致青藏高原小型热融湖存在严重漏提问题。本文基于Sentinel-2影像,提取细小水体边界区分度高的植被红边水体指数(vegetation red edge based water index,RWI),辅以人工目视剔除河流与积雪,实现了青藏高原热融湖的准确识别。在此基础上,应用频率比法评估了环境因子与热融湖发育的相关性。通过叠加各环境因子频率比值的权重积,建立了热融湖的易发性分区。结果表明,RWI在热融湖提取中总体精度为98.97%、制图精度为85.52%、用户精度为83.12%、Kappa系数为0.8118,体现出较高的识别精度。在青藏高原共识别出182668个热融湖,总面积为2456.13 km^(2),总体呈现出“小型热融湖数量多面积占比小,大型热融湖数量少面积占比大”的特征。各环境因子对热融湖影响程度依次排序为坡度>高程>活动层厚度>归一化植被指数>地下冰含量>降水量>年平均地温。热融湖易发性分区显示,低易发区面积占比最大(31.01%),但仅包含4.04%的热融湖,密度为2.01个⋅(100km^(2))^(-1);高与极高易发区面积占比之和仅为25.19%,却集中了84.30%的热融湖,极高易发区热融湖点密度达77.92个⋅(100km^(2))^(-1),是低易发区的38.76倍。
基金supported by the National Science Fund for Distinguished Young Scholars[41925027].
文摘Climate warming rates in the Arctic are far greater than the global average,exerting stronger impacts on permafrost degradation and thermokarst landform development.Thermokarst lakes and ponds(TLPs),which are widely distributed in the Lena Basin in the Russian Arctic,play a vital role in altering local ecosystem.However,the detailed distribution of TLPs in the Lena Basin still remains poorly known.In this study,we built the first 10 m resolution TLP dataset for the Lena Basin in the 2020 thawing season by utilizing 4902 Sentinel-2 images.A robust mapping workflow was developed and implemented in the Google Earth Engine(GEE)platform.The accu-racy assessment demonstrates a satisfactory accuracy(93.63%),and our results exhibit a better consistency with real TLPs than global water body products.A total of 380,477 TLPs(~0.53%of the total surface area of the Lena Basin)were identified,showing an uneven distribution in the five sub-basins.The TLPs were found to be mainly located within plain areas,with an active layer thickness in the range of 80-100 cm.The higher ground ice content and mean annual ground temperature were favorable for TLP development.This dataset will be valuable for investigating the complex interac-tion between TLPs and permafrost.It will also serve as a baseline product for better incorporating thermokarst processes into perma-frostclimate models.
基金supported by Second Tibetan Plateau Scientific Expedition and Research Program(STEP)[grant number 2019QZKK0207-02]National Natural Science Foundation of China[grant number 42171343]。
文摘Mapping and monitoring the spatial–temporal evolution of thermokarst lakes on the Tibetan Plateau can significantly contribute to the estimation of climate change impacts on permafrost degradation.Remote sensing-based methods have been developed to monitor the interannual changes of thermokarst lakes.However,the seasonal changes,which are vital for understanding thermokarst lake dynamics,are commonly overlooked.This paper developed automatic methods which integrated the normalized difference water index(NDWI),modified normalized difference water index(MNDWI),principal component analysis(PCA),and independent component analysis(ICA)with Markov random field(MRF)for rapid mapping of thermokarst lakes in different physical states characterized by season changes.To validate the effectiveness,the proposed methods were applied to map thermokarst lakes on the central Tibetan Plateau,using four Sentinel-2 images representing different evolutionary states.Specifically,the areato-point regression kriging(ATPRK)method was employed to downscale the 20-m short-wave infrared(SWIR)band to 10 m.Using manually digitized lakes as a reference,the proposed methods achieved an average Kappa coefficient of 0.79,significantly outperforming the water index thresholding method that merely attained 0.44.The results corroborate that the proposed methods can be robustly applied in mapping thermokarst lake dynamics with both interannual and seasonal trends on the Tibetan Plateau.
文摘This study examines the Carolina Bays and Nebraska Rainwater Basins,using high-resolution LiDAR elevation models to analyze their unique shapes.The research reveals that well-preserved Bays exhibit precise elliptical geometry,distinguishing them from various oriented lakes they are often compared to.While the timing of their formation is discussed,the primary goal of this paper is to establish a repeatable method for quantifying the elliptical nature of these dominant geomorphic landforms.By applying the least squares method to points selected along the perimeters of these extraordinary basins,the study confirms their elliptical geometry with an error margin of less than 3%.This rigorous mathematical approach sets a high standard for any hypothesis attempting to explain the origin of these depressions using natural environmental conditions.Notably,the long axes of these elliptical basins converge near the Great Lakes region,and since ellipses can be described as conic sections,this finding supports the plausibility of a cosmic impact origin.The study suggests that these basins may be secondary impact features formed during a past glacial cycle of the Laurentide Ice Sheet.This research establishes a strong mathematical foundation to support future studies on the possible impact origin of the Carolina Bays and Nebraska Rainwater Basins.
