Oil spills have become a serious problem in cold environments with the ever-increasing resource exploitation, transportation, storage, and accidental leakage of oil. Several techniques, including physical, chemical, a...Oil spills have become a serious problem in cold environments with the ever-increasing resource exploitation, transportation, storage, and accidental leakage of oil. Several techniques, including physical, chemical, and biological methods, are used to recover spilled oil from the environment. Bioremediation is a promising option for remediation since it is effective and economic in removing oil with less undue environmental damages. However, it is a relatively slow process in cold regions and the degree of success depends on a number of factors, including the properties and fate of oil spilled in cold environments, and the major microbial and environmental limitations of bioremediation. The microbial factors include bioavailability of hydrocarbons, mass transfer through the cell membrane, and metabolic limitations. As for the environmental limitations in the cold regions, the emphasis is on soil temperatures, freeze-thaw processes, oxygen and nutrients availability, toxicity, and electron acceptors. There have been several cases of success in the polar regions, particularly in the Arctic and sub-Arctic regions. However, the challenges and constraints for bioremediation in cold environments remain large.展开更多
Many observations in and model simulations for northern basins have confirmed an increased streamflow from degrading permafrost,while the streamflow has declined in the source area of the Yellow River(SAYR,above the T...Many observations in and model simulations for northern basins have confirmed an increased streamflow from degrading permafrost,while the streamflow has declined in the source area of the Yellow River(SAYR,above the Tanag hydrological station)on the northeastern Qinghai-Tibet Plateau,West China.How and to what extent does the degrading permafrost change the flow in the SAYR?According to seasonal regimes of hydrological processes,the SAYR is divided intofour sub-basins with varied permafrost extents to detect impacts of permafrost degradation on the Yellow River streamflow.Results show that permafrost degradation may have released appreciable meltwater for recharging groundwater.The potential release rate of ground-ice melt-water in the Sub-basin 1(the headwater area of the Yellow River(HAYR),above the Huangheyan hydrological station)is the highest(5.6 mm per year),contributing to 14.4%of the annual Yellow River streamflow at Huangheyan.Seasonal/intra-and annual shifts of streamflow,a possible signal for the marked alteration of hydrological processes by permafrost degradation,is observed in the HAYR,but the shifts are minor in other sub-basins in the SAYR.Improved hydraulic connectivity is expected to occur during and after certain degrees of permafrost degradation.Direct impacts of permafrost degradation on the annual Yellow River streamflow in the SAYR at Tanag,i.e.,from the meltwater of ground-ice,is estimated at 4.9%that of the annual Yellow River discharge at Tanag,yet with a high uncertainty,due to neglecting of the improved hydraulic connections from permafrost degradation and the flow generation conditions for the ground-ice meltwater.Enhanced evapotranspiration,substantial weakening of the Southwest China Autumn Rain,and anthropogenic disturbances may largely account for the declined streamflow in the SAYR.展开更多
On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafros...On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions.Significant thaw subsidence of ground surfaces along the ChinaRussia Crude Oil Pipeline(CRCOP) from Mo'he to Daqing,Heilongjiang Province,Northeast China have been observed at some segments underlain by ice-rich warm(>1.0°C) permafrost since the official operation in January 2011.Recent monitoring results of the thermal states of foundation soils at the kilometer post(KP) 304 site along the CRCOP are presented in this paper.The results indicate that during the period from 2012 to 2014,shallow soils(at the depths from0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 maway from the pipeline axis,and deeper permafrost(such as at the depth of 15 m,or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis,and 0.07°C per year 5 m away from the pipeline axis.The results indicate an all-season talik has developed around and along the CRCOP.The thaw bulb,with a faster lateral expansion(compared with the vertical growth),enlarges in summer and shrinks in winter.This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design,construction,operation and maintenance of pipelines in permafrost regions.展开更多
Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical ...Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical simulations and statistical regressions were applied for analyzing the recovery processes of the backfill and its major influencing factors for the thermal equilibrium in recently backfilled open pits at the Gulian strip coalmine in Mo'he, Northeast China. Results show that the thermal recovery time of backfilled areas is positively correlated to the backfill depth(BD) of the soils, the backfilled soil temperature(BST), and the mean annual ground surface temperature(MAGST); meanwhile, climate warming can impact on thermal regimes of the backfill area. The impact of climate warming on ground temperature of the backfill will show up significantly in about 50 years afterbackfilling(BD at 10.0 and 20.0 m, BST at 20.0°C) under the climate warming scenario(CWS) of 0.025°C·year ^(-1). Grey-relation analyses show that the sensitivity of the backfill recovery time declines in the order of the BD, BST and MAGST. On the basis of the abovementioned studies, the layer-by-layer backfilling in cold seasons is advised for more effective and more rapid recovery of thermal regimes of the backfilled open-pits in cold regions.展开更多
To understand the variations in surface water associated with changes in air temperature,precipitation,and permafrost in the Headwater Area of the Yellow River(HAYR),we studied the dynamics of alpine lakes larger than...To understand the variations in surface water associated with changes in air temperature,precipitation,and permafrost in the Headwater Area of the Yellow River(HAYR),we studied the dynamics of alpine lakes larger than 0.01 km^2 during 1986-2019 using Google Earth Engine(GEE)platform.The surface areas of water bodies in the HAYR were processed using mass remote sensing images consisting of Landsat TM/ETM-H/OLI,Sentinel-2A,and MODIS based on automatic extraction of water indices under GEE.Besides,the lake ice phenology of the Sister Lakes(the Gyaring Lake and the Ngoring Lake)was derived by threshold segmenting of water/ice area ratio.Results demonstrate that the change of surface areas experienced four stages:decreasing during 1986-2004,increasing during 2004-2012,decreasing again during 2012-2017,and increasing again during 2017-2019.Correspondingly,the number of small lakes decreased(-26.5 per year),increased(139.5 per year),again decreased(-109.0 per year),and again increased(433.0 per year).Eight lakes larger than 1 km^2 disappeared in 2004 but restored afterward.The overall trends in the area of small lakes(0.01-1 km^2),large lakes(>1 km^2),and all lakes during 1986-2019 were 0.4,3.1,and 3.4 km^2 per year,respectively.Although the onsets of freezing,freeze-up,breaking and the break-up of the Sister Lakes varied from year to year,there is no obvious trend regarding the lake ice phenology.Tendencies of lake variations in the HAYR are primarily related to the increased net precipitation and the declined aridity,followed by the construction of hydropower station around the outlet of the Ngoring Lake,as well as permafrost degradation.展开更多
The Nanwenghe Wetlands Reserve in the Yile'huli Mountains is a representative region of the Xing'an permafrost.The response of permafrost to climate change remains unclear due to limited field investigations.T...The Nanwenghe Wetlands Reserve in the Yile'huli Mountains is a representative region of the Xing'an permafrost.The response of permafrost to climate change remains unclear due to limited field investigations.Thus,longer-term responses of the ground thermal state to climate change since 2011 have been monitored at four sites with varied surface characteristics:Carex tato wetland(P1)and shrub-C.tato wetland(P2)with a multi-year average temperatures at the depth of zero annual amplitude(T_(ZAA))of−0.52 and−1.19℃,respectively;Betula platyphylla-Larix gmelinii(Rupr.)Kuzen mixed forest(P3)with T_(ZAA) of 0.17℃,and;the forest of L.gmelinii(Rupr.)Kuzen(P4)with T_(ZAA) of 1.65℃.Continuous observations demonstrate that the ecosystem-protected Xing'an permafrost experienced a cooling under a warming climate.The temperature at the top of permafrost(TTOP)rose(1.8℃ per decade)but the TZAA declined(−0.14℃ per decade),while the active layer thickness(ALT)thinned from 0.9 m in 2012 to 0.8 m in 2014 at P1.Both the TTOP and TZAA increased(0.89 and 0.06℃ per decade,respectively),but the ALT thinned from 1.4 m in 2012 to 0.7 m in 2016 at P2.Vertically detached permafrost at P3 disappeared in summer 2012,with warming rates of+0.42 and+0.17℃ per decade for TTOP and T_(ZAA),respectively.However,up to date,the ground thermal state has remained stable at P4.We conclude that the thermal offset is crucial for the preservation and persistence of the Xing'an permafrost at the southern fringe.展开更多
In boreal and arctic regions,forest fires exert great influences on biogeochemical processes,hydrothermal dynamics of the active layer and near-surface permafrost,and subsequent nutrient cycles.In this article,the stu...In boreal and arctic regions,forest fires exert great influences on biogeochemical processes,hydrothermal dynamics of the active layer and near-surface permafrost,and subsequent nutrient cycles.In this article,the studies on impacts of forest fires on the permafrost environment are reviewed.These studies indicate that forest fires could result in an irreversible degradation of permafrost,successions of boreal forests,rapid losses of soil carbon stock,and increased hazardous periglacial landforms.After forest fires,soil temperatures rise;active layer thickens;the release of soil carbon and nitrogen enhances,and;vegetation changes from coniferous forests to broad-leaved forests,shrublands or grasslands.It may take decades or even centuries for the fire-disturbed ecosystems and permafrost environment to return to pre-fire conditions,if ever possible.In boreal forest,the thickness of organic layer has a key influence on changes in permafrost and vegetation.In addition,climate warming,change of vegetation,shortening of fire return intervals,and extent of fire range and increasing of fire severity may all modify the change trajectory of the fire-impacted permafrost environment.However,the observations and research on the relationships and interactive mechanisms among the forest fires,vegetation,carbon cycle and permafrost under a changing climate are still inadequate for a systematic impact evaluation.Using the chronosequence approach of evaluating the temporal changes by measuring changes in the permafrost environment at different stages at various sites(possibly representing varied stages of permafrost degradation and modes),multi-source data assimilation and model predictions and simulations should be integrated with the results from long-and short-term field investigations,geophysical investigations and airborne surveys,laboratory testing and remote sensing.Future studies may enable quantitatively assess and predict the feed-back relationship and influence mechanism among organic layer,permafrost and active layer processes,vegetation and soil carbon under a warming climate at desired spatial and temporal scales.The irreversible changes in the boreal and artic forest ecosystem and their ecological and hydrothermal thresholds,such as those induced by forest fires,should be better and systematically studied.展开更多
1.Introduction Permafrost is present extensively in polar,high-plateau,alpine,and mountainous regions,with a model-estimated total extent of permafrost regions at 22.79 million km^(2)(Gruber,2012).However,among ever i...1.Introduction Permafrost is present extensively in polar,high-plateau,alpine,and mountainous regions,with a model-estimated total extent of permafrost regions at 22.79 million km^(2)(Gruber,2012).However,among ever increasing modeling results,these estimates are based on applications of different permafrost models of various validity,but with a large range of uncertainty.Permafrost affects terrestrial ecosystems and ground hydrothermal dynamics,biogeochemical cycles,engineered infrastructures,and socioeconomic development to varied extents.Under a warming climate,permafrost has been degrading extensively.Permafrost studies have been flourishing due to increasing concerns on the climatic feedbacks of permafrost carbon,ecological impacts from degrading permafrost,sustainable water supplies,and engineering ramifications.展开更多
基金Project supported by the 100 Talents Program of the Chinese Academy of Sciences (No.2004407).
文摘Oil spills have become a serious problem in cold environments with the ever-increasing resource exploitation, transportation, storage, and accidental leakage of oil. Several techniques, including physical, chemical, and biological methods, are used to recover spilled oil from the environment. Bioremediation is a promising option for remediation since it is effective and economic in removing oil with less undue environmental damages. However, it is a relatively slow process in cold regions and the degree of success depends on a number of factors, including the properties and fate of oil spilled in cold environments, and the major microbial and environmental limitations of bioremediation. The microbial factors include bioavailability of hydrocarbons, mass transfer through the cell membrane, and metabolic limitations. As for the environmental limitations in the cold regions, the emphasis is on soil temperatures, freeze-thaw processes, oxygen and nutrients availability, toxicity, and electron acceptors. There have been several cases of success in the polar regions, particularly in the Arctic and sub-Arctic regions. However, the challenges and constraints for bioremediation in cold environments remain large.
基金the Chinese Academy of Sciences Strategic Priority Research Program(XDA20100103)Ministry of Science and Technology of China Key R&D Program(2017YFC0405704)CAS Overseas Professorships of Victor F Bense and Sergey S Marchenko at the former Cold and Arid Regions Environmental and Engineering Research Institute(now renamed to Northwest Institute of Eco-Environment and Resources),CAS during 2013-2016.
文摘Many observations in and model simulations for northern basins have confirmed an increased streamflow from degrading permafrost,while the streamflow has declined in the source area of the Yellow River(SAYR,above the Tanag hydrological station)on the northeastern Qinghai-Tibet Plateau,West China.How and to what extent does the degrading permafrost change the flow in the SAYR?According to seasonal regimes of hydrological processes,the SAYR is divided intofour sub-basins with varied permafrost extents to detect impacts of permafrost degradation on the Yellow River streamflow.Results show that permafrost degradation may have released appreciable meltwater for recharging groundwater.The potential release rate of ground-ice melt-water in the Sub-basin 1(the headwater area of the Yellow River(HAYR),above the Huangheyan hydrological station)is the highest(5.6 mm per year),contributing to 14.4%of the annual Yellow River streamflow at Huangheyan.Seasonal/intra-and annual shifts of streamflow,a possible signal for the marked alteration of hydrological processes by permafrost degradation,is observed in the HAYR,but the shifts are minor in other sub-basins in the SAYR.Improved hydraulic connectivity is expected to occur during and after certain degrees of permafrost degradation.Direct impacts of permafrost degradation on the annual Yellow River streamflow in the SAYR at Tanag,i.e.,from the meltwater of ground-ice,is estimated at 4.9%that of the annual Yellow River discharge at Tanag,yet with a high uncertainty,due to neglecting of the improved hydraulic connections from permafrost degradation and the flow generation conditions for the ground-ice meltwater.Enhanced evapotranspiration,substantial weakening of the Southwest China Autumn Rain,and anthropogenic disturbances may largely account for the declined streamflow in the SAYR.
基金supported by the National Natural Science Foundation Program of China on"Formation mechanisms and mitigative measures for thaw settlement of foundation soils of the China-Russia Crude Oil Pipeline"(Grant No.41171055)the State Key Laboratory of Frozen Soils Engineering Research Projects of China on"Monitoring on thaw settlement of permafrost around the China-Russia Crude Oil Pipeline"(Grant No.SKLFSE-ZY-11)and"Research on isotope tracing and radar detection of permafrost along the China-Russia Crude Oil Pipeline route"(Grant No.SKLFSE-201302)
文摘On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions.Significant thaw subsidence of ground surfaces along the ChinaRussia Crude Oil Pipeline(CRCOP) from Mo'he to Daqing,Heilongjiang Province,Northeast China have been observed at some segments underlain by ice-rich warm(>1.0°C) permafrost since the official operation in January 2011.Recent monitoring results of the thermal states of foundation soils at the kilometer post(KP) 304 site along the CRCOP are presented in this paper.The results indicate that during the period from 2012 to 2014,shallow soils(at the depths from0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 maway from the pipeline axis,and deeper permafrost(such as at the depth of 15 m,or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis,and 0.07°C per year 5 m away from the pipeline axis.The results indicate an all-season talik has developed around and along the CRCOP.The thaw bulb,with a faster lateral expansion(compared with the vertical growth),enlarges in summer and shrinks in winter.This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design,construction,operation and maintenance of pipelines in permafrost regions.
基金supported by the research projects of the National Natural Science Foundation of China (Grant No. 41401081) "Thermal impacts of organic matter on properties of permafrost soils in the Da Xing'anling (Hinggan) Mountains"the State Key Laboratory of Frozen Soils Engineering, Ministry of Science and Technology, China "Impacts of human activities on the hydrothermal processes of permafrost in the Da Xing'anling (Hinggan) Mountains – a case study from the Gulian strip coal mine" (Grant No. SKLFSE-ZT-41)
文摘Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical simulations and statistical regressions were applied for analyzing the recovery processes of the backfill and its major influencing factors for the thermal equilibrium in recently backfilled open pits at the Gulian strip coalmine in Mo'he, Northeast China. Results show that the thermal recovery time of backfilled areas is positively correlated to the backfill depth(BD) of the soils, the backfilled soil temperature(BST), and the mean annual ground surface temperature(MAGST); meanwhile, climate warming can impact on thermal regimes of the backfill area. The impact of climate warming on ground temperature of the backfill will show up significantly in about 50 years afterbackfilling(BD at 10.0 and 20.0 m, BST at 20.0°C) under the climate warming scenario(CWS) of 0.025°C·year ^(-1). Grey-relation analyses show that the sensitivity of the backfill recovery time declines in the order of the BD, BST and MAGST. On the basis of the abovementioned studies, the layer-by-layer backfilling in cold seasons is advised for more effective and more rapid recovery of thermal regimes of the backfilled open-pits in cold regions.
基金National Key Research and Development Program of China(2017YFC0405701)the National Natural Science Foundation(NSF)of China(41671060).
文摘To understand the variations in surface water associated with changes in air temperature,precipitation,and permafrost in the Headwater Area of the Yellow River(HAYR),we studied the dynamics of alpine lakes larger than 0.01 km^2 during 1986-2019 using Google Earth Engine(GEE)platform.The surface areas of water bodies in the HAYR were processed using mass remote sensing images consisting of Landsat TM/ETM-H/OLI,Sentinel-2A,and MODIS based on automatic extraction of water indices under GEE.Besides,the lake ice phenology of the Sister Lakes(the Gyaring Lake and the Ngoring Lake)was derived by threshold segmenting of water/ice area ratio.Results demonstrate that the change of surface areas experienced four stages:decreasing during 1986-2004,increasing during 2004-2012,decreasing again during 2012-2017,and increasing again during 2017-2019.Correspondingly,the number of small lakes decreased(-26.5 per year),increased(139.5 per year),again decreased(-109.0 per year),and again increased(433.0 per year).Eight lakes larger than 1 km^2 disappeared in 2004 but restored afterward.The overall trends in the area of small lakes(0.01-1 km^2),large lakes(>1 km^2),and all lakes during 1986-2019 were 0.4,3.1,and 3.4 km^2 per year,respectively.Although the onsets of freezing,freeze-up,breaking and the break-up of the Sister Lakes varied from year to year,there is no obvious trend regarding the lake ice phenology.Tendencies of lake variations in the HAYR are primarily related to the increased net precipitation and the declined aridity,followed by the construction of hydropower station around the outlet of the Ngoring Lake,as well as permafrost degradation.
基金This study is financially supported by the program of National Natural Science Foundation of China(41401081,41871052,41771074)Joint Key Program of NSFC‒Heilongjiang Province for Regional Development(U20A2082)the Research Project of the State Key Laboratory of Frozen Soil Engineering(SKLFSE-ZT-41,SKLFSE-ZY-20).
文摘The Nanwenghe Wetlands Reserve in the Yile'huli Mountains is a representative region of the Xing'an permafrost.The response of permafrost to climate change remains unclear due to limited field investigations.Thus,longer-term responses of the ground thermal state to climate change since 2011 have been monitored at four sites with varied surface characteristics:Carex tato wetland(P1)and shrub-C.tato wetland(P2)with a multi-year average temperatures at the depth of zero annual amplitude(T_(ZAA))of−0.52 and−1.19℃,respectively;Betula platyphylla-Larix gmelinii(Rupr.)Kuzen mixed forest(P3)with T_(ZAA) of 0.17℃,and;the forest of L.gmelinii(Rupr.)Kuzen(P4)with T_(ZAA) of 1.65℃.Continuous observations demonstrate that the ecosystem-protected Xing'an permafrost experienced a cooling under a warming climate.The temperature at the top of permafrost(TTOP)rose(1.8℃ per decade)but the TZAA declined(−0.14℃ per decade),while the active layer thickness(ALT)thinned from 0.9 m in 2012 to 0.8 m in 2014 at P1.Both the TTOP and TZAA increased(0.89 and 0.06℃ per decade,respectively),but the ALT thinned from 1.4 m in 2012 to 0.7 m in 2016 at P2.Vertically detached permafrost at P3 disappeared in summer 2012,with warming rates of+0.42 and+0.17℃ per decade for TTOP and T_(ZAA),respectively.However,up to date,the ground thermal state has remained stable at P4.We conclude that the thermal offset is crucial for the preservation and persistence of the Xing'an permafrost at the southern fringe.
基金supported by the Natural Science Foundation of China Program(42001052)Startup Research Funding of Northeast Forest University for Chengdong Leadership(LJ2020-01)+3 种基金Outstanding Young Scholar(YQ2020-10)Natural Science Foundation of China Program(41871052),Joint Key Program of National Natural Science Foundation of China(NSFC)-Heilongjiang Province Joint Foundation for Regional Development(U20A2082)the State Key Laboratory of Frozen Soils Engineering Open Fund Project(SKLFSE201811)Russian Foundation for Basic Research(18-05-00990).
文摘In boreal and arctic regions,forest fires exert great influences on biogeochemical processes,hydrothermal dynamics of the active layer and near-surface permafrost,and subsequent nutrient cycles.In this article,the studies on impacts of forest fires on the permafrost environment are reviewed.These studies indicate that forest fires could result in an irreversible degradation of permafrost,successions of boreal forests,rapid losses of soil carbon stock,and increased hazardous periglacial landforms.After forest fires,soil temperatures rise;active layer thickens;the release of soil carbon and nitrogen enhances,and;vegetation changes from coniferous forests to broad-leaved forests,shrublands or grasslands.It may take decades or even centuries for the fire-disturbed ecosystems and permafrost environment to return to pre-fire conditions,if ever possible.In boreal forest,the thickness of organic layer has a key influence on changes in permafrost and vegetation.In addition,climate warming,change of vegetation,shortening of fire return intervals,and extent of fire range and increasing of fire severity may all modify the change trajectory of the fire-impacted permafrost environment.However,the observations and research on the relationships and interactive mechanisms among the forest fires,vegetation,carbon cycle and permafrost under a changing climate are still inadequate for a systematic impact evaluation.Using the chronosequence approach of evaluating the temporal changes by measuring changes in the permafrost environment at different stages at various sites(possibly representing varied stages of permafrost degradation and modes),multi-source data assimilation and model predictions and simulations should be integrated with the results from long-and short-term field investigations,geophysical investigations and airborne surveys,laboratory testing and remote sensing.Future studies may enable quantitatively assess and predict the feed-back relationship and influence mechanism among organic layer,permafrost and active layer processes,vegetation and soil carbon under a warming climate at desired spatial and temporal scales.The irreversible changes in the boreal and artic forest ecosystem and their ecological and hydrothermal thresholds,such as those induced by forest fires,should be better and systematically studied.
基金supported by the Chinese Academy of Sciences(CAS)Strategic Priority Research Program(XDA20100103)Ministry of Science and Technology of China Key R&D Program(2017YFC0405704)the National Natural Science Foundation of China(41871052,41690144).
文摘1.Introduction Permafrost is present extensively in polar,high-plateau,alpine,and mountainous regions,with a model-estimated total extent of permafrost regions at 22.79 million km^(2)(Gruber,2012).However,among ever increasing modeling results,these estimates are based on applications of different permafrost models of various validity,but with a large range of uncertainty.Permafrost affects terrestrial ecosystems and ground hydrothermal dynamics,biogeochemical cycles,engineered infrastructures,and socioeconomic development to varied extents.Under a warming climate,permafrost has been degrading extensively.Permafrost studies have been flourishing due to increasing concerns on the climatic feedbacks of permafrost carbon,ecological impacts from degrading permafrost,sustainable water supplies,and engineering ramifications.
