Continuous Permafrost Region Research Articles

Occurrence and distribution of emerging contaminants in mine-impacted lake water and potential use as co-tracers of anthropogenic activity in the subarctic region, Northwest Territories, Canada

The emerging contaminant (EC) perchlorate (ClO4−), a blasting agent widely used in mining and refining operations, has been used as a practical indicator of mining activities. Widespread occurrence of ECs, such as pharmaceutical compounds, artificial sweeteners, and perfluoroalkyl substances, and their use as co-tracers of wastewater associated with anthropogenic activities in the urban and Arctic environments have been previously investigated. However, limited studies have reported the occurrence of these ECs and the feasibility of their use as co-tracers of anthropogenic activities in pristine waterbodies (e.g., continuous permafrost region) that receive effluent from mine sites. In this study, water samples were collected from the surface of 10 lakes within the Coppermine and Lockhart Watersheds in the continuous permafrost region in the Northwest Territories, Canada during the open water seasons of 2016, 2017, and 2018. Concentrations of 16 ECs were determined to delineate the spatial and temporal distribution of these compounds in waterbodies receiving effluent from mine sites. Slightly elevated concentrations of ClO4− (100–700 ng L−1), caffeine (0.2–5.9 ng L−1), acesulfame-K (0.5–1.5 ng L−1), perfluorooctanoic acid (PFOA; 5–34 ng L−1), perfluorooctane sulfonic acid (PFOS; 11–40 ng L−1), chloride (1.5–2.3 mg L−1), and sulfate (1.0–3.6 mg L−1) were observed across the two investigated watersheds, especially downstream of the mining sites. The concurrence of elevated concentrations of these target ECs combined with other dissolved constituents (chloride and sulfate) may indicate the influence of mining activity on the receiving waterbodies and the potential use of these compounds as co-indicators of anthropogenic activity. Results from this study provide novel information on the distribution of 16 ECs in pristine waterbodies that receive effluents from mining sites in the Canadian subarctic in advance of more expansive human development and increased warming and melting of mine sites, including mine wastes.

Groundwater Flow Through Continuous Permafrost Along Geological Boundary Revealed by Electrical Resistivity Tomography

AbstractIn continuous permafrost regions, pathways for transport of sub‐permafrost groundwater to the surface sometimes perforate the frozen ground and result in the formation of a pingo. Explanations offered for the locations of such pathways have so far included hydraulically conductive geological units and faults. On Svalbard, several pingos locate at valley flanks where these controls are apparently lacking. Intrigued by this observation, we elucidated the geological setting around such a pingo with electrical resistivity tomography. The inverted resistivity models showed a considerable contrast between the uphill and valley‐sides of the pingo. We conclude that this contrast reflects a geological boundary between low‐permeable marine sediments and consolidated strata. Groundwater presumably flows toward the pingo spring through glacially induced fractures in the strata immediately below the marine sediments. Our finding suggests that flanks of uplifted Arctic valleys deserve attention as possible discharge locations for deep groundwater and greenhouse gases to the surface.

Remote Sensing-Based Statistical Approach for Defining Drained Lake Basins in a Continuous Permafrost Region, North Slope of Alaska

Lake formation and drainage are pervasive phenomena in permafrost regions. Drained lake basins (DLBs) are often the most common landforms in lowland permafrost regions in the Arctic (50% to 75% of the landscape). However, detailed assessments of DLB distribution and abundance are limited. In this study, we present a novel and scalable remote sensing-based approach to identifying DLBs in lowland permafrost regions, using the North Slope of Alaska as a case study. We validated this first North Slope-wide DLB data product against several previously published sub-regional scale datasets and manually classified points. The study area covered >71,000 km2, including a >39,000 km2 area not previously covered in existing DLB datasets. Our approach used Landsat-8 multispectral imagery and ArcticDEM data to derive a pixel-by-pixel statistical assessment of likelihood of DLB occurrence in sub-regions with different permafrost and periglacial landscape conditions, as well as to quantify aerial coverage of DLBs on the North Slope of Alaska. The results were consistent with previously published regional DLB datasets (up to 87% agreement) and showed high agreement with manually classified random points (64.4–95.5% for DLB and 83.2–95.4% for non-DLB areas). Validation of the remote sensing-based statistical approach on the North Slope of Alaska indicated that it may be possible to extend this methodology to conduct a comprehensive assessment of DLBs in pan-Arctic lowland permafrost regions. Better resolution of the spatial distribution of DLBs in lowland permafrost regions is important for quantitative studies on landscape diversity, wildlife habitat, permafrost, hydrology, geotechnical conditions, and high-latitude carbon cycling.

Spatiotemporal variations and regional differences in air temperature in the permafrost regions in the Northern Hemisphere during 1980–2018

Surface air temperature is an important factor for the permafrost thermal state in the Northern Hemisphere. It is therefore necessary to understand the variations and regional differences in air temperature to determine the interactions between permafrost degradation and climate change. In this study, we used observational data from the National Centers for Environmental Information, the China Meteorological Administration, and the World Data Centre for Meteorology to quantitatively analyze the variations and regional differences in air temperature from 1980 to 2018. The results demonstrated that the annual mean air temperatures were low in continuous permafrost regions and high in sporadic and isolated permafrost regions, with a significant warming rate of 0.371 ± 0.086 °C/decade. Air temperatures warmed the slowest during the winter and fastest during the spring, and no “warming hiatus” was observed in the permafrost regions of the Northern Hemisphere. The spatial patterns of freezing degree-days (FDDs) and thawing degree-days (TDDs) had different spatial characteristics. The decreasing rate of FDDs was −6.97 °C·days/year, while the increasing rate of TDDs was 6.4 °C·days/year. The air temperatures and warming trends had largely regional differences with respect to high latitude, transitional, and high altitude permafrost regions. Air temperature and its warming trend was the highest in high altitude regions. In addition, air temperature warming trends gradually decreased from the continuous permafrost zone to the island permafrost zone. The FDDs had a significant decreasing trend from the continuous permafrost zone to the island permafrost zone, whereas TDDs exhibited the opposite trend. The results indicate that the air temperature warming rate in the permafrost regions was approximately 2.0 times that of the global warming rate, and 1.3 times the global land warming rate from 1980 to 2018. These findings offer a perspective on the differences in permafrost and its thermal state across different regions under climate change.

Soil Enzyme Activities and Their Relationships With Soil C, N, and P in Peatlands From Different Types of Permafrost Regions, Northeast China

Peatland is a key component of terrestrial ecosystems in permafrost regions and have important effects on climate warming. Soil enzymes are involved in biogeochemical cycle of soil carbon (C), nitrogen (N) and phosphorus (P), which can be used as early sensitive indicators of soil nutrient changes caused by climate change. To predict the possible effects of permafrost degradation on soil enzymes in peatlands, ten peatlands from three types of permafrost regions along the permafrost degradation sequence (predominantly continuous permafrost region-predominantly continuous and island permafrost region-sparsely island permafrost region) in northeast China were selected to examine the activities of soil invertase, β-glucosidase, urease and acid phosphatase and their relationships with soil physicochemical properties. The results demonstrated that permafrost type had significant effect on soil enzyme activities. Soil enzyme activities in predominantly continuous and island permafrost region were significantly higher than those in sparsely island permafrost region and predominantly continuous permafrost region. The activities of four soil enzymes were higher in 0–15 cm than 15–30 cm soil layer. Soil enzymes activities were positively correlated with soil ammonia nitrogen (NH4+-N), soil moisture content (SMC), total phosphorus (TP) and total nitrogen (TN), but negatively correlated with soil nitrate nitrogen (NO3−-N). Soil inorganic nitrogen and moisture contents were the main factors affecting soil enzyme activities, with NH4+-N accounted for 41.6% of the variance, SMC 29.6%, and NO3−-N 11.0%. These results suggested that permafrost degradation may change soil enzyme activities by changing soil physicochemical properties. In this study, only 0–30 cm peat soil in permafrost regions was collected during the complete thawing period of permafrost active layer, further studies should be placed on the change of soil enzyme activities in active layer and permafrost layer during freezing and thawing process in the southernmost location of northeast China in the Eurasia permafrost body and boreal forest belt.

Geochemical Assessment of Desulphurized Tailings as Cover Material in Cold Climates

It is essential to develop effective mine waste management approaches and mine site reclamation techniques to curtail the adverse effects of mining processes on the natural environment. This study focuses on the use of partially desulphurized tailings as a moisture-retaining layer in an insulation cover with capillary barrier effects (ICCBE). Tailings were obtained from a nickel ultramafic ore processing plant at a mining company located in a continuous permafrost region of northern Québec, Canada. The geochemical response of tailings at two different sulphur contents (0.4 and 0.8 wt%), with and without ICCBEs, was tested by applying eight freeze-thaw and wetting cycles. Desulphurization of the tailings allowed to reduce the content of sulphide minerals by about 90%, from ~22 wt% to around 1.2–2.2 wt%. Column kinetic geochemical tests showed that Ni leaching was significantly reduced to concentrations ranging between 0.01–0.22 mg L−1 compared to 0.63–1.92 mg L−1 from the raw tailings (thanks to the desulphurization process). Zinc release was maintained around 0.04–1.72 mg L−1 compared to 0.4–3.69 mg L−1 from the raw tailing. Although all the columns produced leachates displaying circumneutral to slightly alkaline pH, the columns with ICCBE are expected to prevent acid mine drainage generation longer than the other columns due to reduced sulphide content and a constantly high degree of saturation maintained by capillary barrier effects.

Geophysical Observations of Taliks Below Drained Lake Basins on the Arctic Coastal Plain of Alaska

AbstractLakes and drained lake basins (DLBs) together cover up to ∼80% of the western Arctic Coastal Plain of Alaska. The formation and drainage of lakes in this continuous permafrost region drive spatial and temporal landscape dynamics. Postdrainage processes including vegetation succession and permafrost aggradation have implications for hydrology, carbon cycling, and landscape evolution. Here, we used surface nuclear magnetic resonance (NMR) and transient electromagnetic (TEM) measurements in conjunction with thermal modeling to investigate permafrost aggradation beneath eight DLBs on the western Arctic Coastal Plain of Alaska. We also surveyed two primary surface sites that served as nonlake affected control sites. Approximate timing of lake drainage was estimated based on historical aerial imagery. We interpreted the presence of taliks based on either unfrozen water estimated with surface NMR and/or TEM resistivities in DLBs compared to measurements on primary surface sites and borehole resistivity logs. Our results show evidence of taliks below several DLBs that drained before and after 1949 (oldest imagery). We observed depths to the top of taliks between 9 and 45 m. Thermal modeling and geophysical observations agree about the presence and extent of taliks at sites that drained after 1949. Lake drainage events will likely become more frequent in the future due to climate change and our modeling results suggest that warmer and wetter conditions will limit permafrost aggradation in DLBs. Our observations provide useful information to predict future evolution of permafrost in DLBs and its implications for the water and carbon cycles in the Arctic.

Evaluation of damage probability of railway embankments in permafrost regions in Qinghai–Tibet Plateau

The Qinghai–Tibet Railway (QTR) has been operating since 2006. It crosses continuous permafrost regions in the Qinghai–Tibet Plateau. Half of these regions are characterized by high ground temperature and ice content, and slight changes in the permafrost may cause embankment damage. In this study, the deformed embankment data of the QTR collected from 2010 to 2018 were analyzed. The analysis results showed that the total length of deformed embankments of the QTR in the permafrost regions was 22.97 km, and the damage rate since its completion in 2006 was approximately 5.4%. The results also indicated that the embankments stabilized over time. In 2010, the deformed embankments that were reinforced consisted of 26 sites and were 7.64-km long, whereas in 2018, only a 0.48-km long site was reinforced. In this study, a damage probability model of the embankments is developed. The damage probability of the embankments along the QTR in permafrost regions was classified into five grades: slight, low, moderate, high, and extremely-high damage probability levels. The total lengths of embankment sections with slight, low, moderate, high, and extremely-high levels of damage probability are 190.38, 161.42, 61.72, 13.51, and 2.99 km, respectively. It is suggested that damage-free embankment sections with high and extremely-high levels of damage probability should be monitored more closely during railway embankment maintenance. This study provides a reference for the application of the logistic regression model to establish the damage probability model of railway embankments in permafrost regions. • Statistically analysis of ten years’ worth of monitoring and reinforcement data of QTR embankments. • Distribution of deformed QTR embankments and embankment damage rate in permafrost regions. • Causes of embankment deformation, case records of reinforcement and maintenance measures. • Model to evaluate the damage probability of QTR embankments in permafrost regions.

增温对冻土区泥炭沼泽土壤孔隙水甲烷关联微生物和溶解性有机碳的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 增温对冻土区泥炭沼泽土壤孔隙水甲烷关联微生物和溶解性有机碳的影响 DOI: 10.5846/stxb201911142421 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41671105，41871090，41571089，41971143） Effects of warming on abundances of methane-related microorganisms and concentration of dissolved organic carbon in soil pore water of permafrost peat swamp in Daxing'anling Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:多年冻土区泥炭沼泽土壤孔隙水甲烷关联微生物及底物的研究有助于深入理解气候变化背景下寒区湿地生态系统甲烷循环过程。选取大兴安岭连续多年冻土区柴桦-泥炭藓和狭叶杜香-泥炭藓两种典型植被群落泥炭沼泽，设置开顶箱（Open Top Chamber，OTC）增温实验。于生长季（6月、7月、8月和9月）采集土壤孔隙水样品，对比分析OTC内外土壤孔隙水中产甲烷菌数量、甲烷氧化菌数量及溶解性有机碳（Dissolved Organic Carbon，DOC）浓度的动态变化特征，并探究土壤孔隙水甲烷关联微生物与DOC浓度的关系。结果表明：增温提高了生长季大兴安岭多年冻土区土壤孔隙水中产甲烷菌数量和DOC浓度，而对甲烷氧化菌数量的影响因月份而异。生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量的平均增加幅度分别为54.52%和44.97%，DOC浓度的平均增加幅度分别为34.16%和28.33%。增温使得生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中甲烷氧化菌平均数量分别降低了46.20%和31.42%。一元线性回归分析结果表明，土壤孔隙水中DOC浓度可分别解释柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量变化的29.00%和24.10%（P<0.01），而对两种植被群落下土壤孔隙水中甲烷氧化菌数量的影响并不显著（P>0.05）。 Abstract:Study of methane related microorganisms and substrates in soil pore water of peat swamp in permafrost regions is helpful to understand the methane cycle process of wetland ecosystem in cold regions under the background of climate change. In this study, the open top chamber (OTC) experiments were set up in two typical vegetation communities of Betula fruticosa-sphagnum and Ledum palustre-sphagnum peat swamp in continuous permafrost region of Daxing'anling. The abundances of methanogens, methane oxidizing bacteria and the concentration of dissolved organic carbon (DOC) in soil pore water inside and outside the OTC were compared and analyzed. The relationship between methane-related microorganisms and DOC in soil pore water was also explored. The results showed that warming increased the abundances of methanogens and the content of DOC in soil pore water in this region during the growing season, while the effect on the abundances of methane oxidizing bacteria varied with month. The average increase of the abundances of methanogens in soil pore water of Betula fruticosa-sphagnum and Ledum palustre-sphagnum peat swamp was 54.52% and 44.97%, and the average increase of DOC content was 34.16% and 28.33%, respectively. Warming reduced the average abundances of methane oxidizing bacteria in soil pore water of growing season of Betula fruticosa-sphagnum and Ledum palustre-sphagnum peat swamp by 46.20% and 31.42%, respectively. The results of one-variable linear regression analysis showed that the DOC content in soil pore water could explain 29.00% and 24.10% of the changes of methanogens in the Betula fruticosa-sphagnum and Ledum palustre-sphagnum peat swamp (P<0.01). However, there was no significant effect on the abundances of methane oxidizing bacteria in soil pore water under two vegetation communities (P>0.05). 参考文献 相似文献 引证文献

Aufeis fields as novel groundwater‐dependent ecosystems in the arctic cryosphere

AbstractRiver aufeis (ow′ fīse) are widespread features of the arctic cryosphere. They form when river channels become locally restricted by ice, resulting in cycles of water overflow and freezing and the accumulation of ice, with some aufeis attaining areas of ~ 25 + km2 and thicknesses of 6+ m. During winter, unfrozen sediments beneath the insulating ice layer provide perennial groundwater‐habitat that is otherwise restricted in regions of continuous permafrost. Our goal was to assess whether aufeis facilitate the occurrence of groundwater invertebrate communities in the Arctic. We focused on a single aufeis ecosystem (~ 5 km2 by late winter) along the Kuparuk River in arctic Alaska. Subsurface invertebrates were sampled during June and August 2017 from 50 3.5‐cm diameter PVC wells arranged in a 5 × 10 array covering ~ 40 ha. Surface invertebrates were sampled using a quadrat approach. We documented a rich assemblage of groundwater invertebrates (49 [43–54] taxa, [95% confidence limits]) that was distributed below the sediment surface to a mean depth of ~ 69 ± 2 cm (± 1 SE) throughout the entire well array. Although community structure differed significantly between groundwater and surface habitats, the taxa richness from wells and surface sediments (43 [35–48] taxa) did not differ significantly, which was surprising given lower richness in subsurface habitats of large, riverine gravel‐aquifer systems shown elsewhere. This is the first demonstration of a rich and spatially extensive groundwater fauna in a region of continuous permafrost. Given the geographic extent of aufeis fields, localized groundwater‐dependent ecosystems may be widespread in the Arctic.

Microbial abundance as an indicator of soil carbon and nitrogen nutrient in permafrost peatlands

Abstract Soil microbial abundance, which is related to soil characteristics and process rates, is an early indicator of changes in soil health and quality. However, microbial functional groups in permafrost peatland soils have rarely been studied. These soils are important C and N stores and possibly vulnerable to climate warming. We randomly gathered surface soils (0–15 cm and 15–30 cm soil layers) from 10 peatlands in sporadic island, discontinuous island, and continuous permafrost regions in Northeast China. The aim was to clarify the soil microbial abundance distribution in different types of permafrost peatlands. Results revealed different effects of permafrost types on different soil C- and N-cycling microbial abundances in peatlands. The bacteria, amoA, and nirK gene abundances in the two soil layers were the highest in discontinuous island permafrost peatlands. Soil mcrA and pmoA gene abundances in 0–15 cm soil were high in continuous and discontinuous island permafrost peatlands, respectively. The amoA gene abundance in both soil layers and nirS gene abundance in 15–30 cm soil were high in discontinuous island permafrost peatlands. The average nirK gene abundance in both soil layers was in the order: discontinuous island permafrost peatlands > continuous permafrost peatlands > sporadic island permafrost peatlands. No significant differences in archaeal abundance were observed in both soil layers among the different types of permafrost peatlands. Moreover, 42.5%, 15.9%, and 15.3% of the variation in soil microbial abundances could be explained by soil ammonia-N, pH, and total C, respectively. Our results imply that soil microbial abundance can be utilized as effective soil N availability, C pool, and pH indicators in permafrost peatlands.

Soil conditions required for reaction wood formation of drunken trees in a continuous permafrost region

ABSTRACT Black spruce trees lean to form “drunken” forest on degrading permafrost; however, the causes of tree leaning on continuous permafrost remain unclear. Leaning events are recorded by reaction wood formation in tree rings, and it remains unclear what soil conditions are required for reaction wood formation of drunken trees. Tree disk morphology and soil hummock properties were examined for fifty tree–mound combinations in Northwest Territories, Canada. Spruce trees growing on mound edges form reaction wood on the downslope sides of their trunks. Reaction wood formation in mature trees was greatest in stem tissues between ground level and 30 cm aboveground. Reaction wood formation occurred only in trees growing on mound edges. The extent of reaction wood formation was higher in trees growing in clayey soils than in trees on sandy soils. For trees growing on clayey mound edges, the extent of reaction wood formation decreased with increasing permafrost table depth. Black spruce tree rings formed between ground level and 30 cm aboveground could record movement of clayey soil hummocks over shallow, underlying permafrost tables. A combination of clayey soil texture and shallow permafrost table is likely required for development of hummocks and drunken forests on the continuous permafrost region studied.

Responses of N2O emissions to spring thaw period in a typical continuous permafrost region of the Daxing'an Mountains, northeast China

In the context of global climate warming, spring thaw period had been changed in the permafrost regions, which significantly affect heat and water dynamics, along with soil microbial community structure and diversity, and microbially-mediated nitrogen cycle changes. However, in-situ N2O emission research is scarce in the permafrost regions and the drivers of N2O emission during spring thaw period remain unclear. We selected three type of swamp forests in the permafrost region to investigate the N2O emissions during spring thaw period from 17 March to 23 May 2017. We found that N2O emission ranged from −35.75 to 74.17 μg m−2 h−1 in the permafrost region during spring thaw period, and there was no significant large burst of N2O emissions as observed in other ecosystems. The N2O emission during spring thaw period were lower than those from growing season, which were significant affected by soil temperature. During spring thaw period, swamp forest types had no significantly influence on N2O emissions, which mainly limited by NO3−-N content. Stepwise multiple linear regression indicated that the air temperature, thawing depth, soil temperature, soil moisture, pH, NH4+-N, NO3−-N, TOC, TN, and C/N ratio were the environmental factors which significant effecting the N2O emissions. In the field campaign, cumulative N2O emissions were mainly controlled by thawing depth, soil moisture, pH, NH4+-N, NO3−-N and TN during spring thaw period. Overall, the results demonstrate that in the permafrost ecosystems spring thaw period is an important source of N2O emissions.

Warmer Winter Ground Temperatures Trigger Rapid Growth of Dahurian Larch in the Permafrost Forests of Northeast China

AbstractPermafrost degradation due to rapid increase in ground surface temperature (GST) in recent years may strongly affect boreal forest ecosystems. However, comparatively few studies have explored how changes in permafrost affect tree growth dynamics in boreal forest. Here, we used a tree ring network of 12 Dahurian larch (Larix gmelinii) sites across permafrost regions in northeast China. We observed an increase in L. gmelinii growth over the past decade, seemingly linked to a shift in their climatic limitations, where winter GST has become the most strongly limiting factor for L. gmelinii growth. The recent increase in growth was particularly strong in older trees (&gt;300 years), which could be related to older trees having a more developed root system. GST was the main limiting factor for tree growth. While summer GST had a somewhat consistently positive correlation with tree growth, winter GST has shifted from a negative to a strongly positive correlation with growth in the last decade, coincidental with a sharp increase in winter GST since 2004. Winter GST is also strongly correlated with the rapidly thawing permafrost dynamics. Overall, our results suggest a link between recent changes in the permafrost and shifts in climate‐growth correlations for one of the main boreal tree species. As a result, L. gmelinii has experienced an important increase in radial growth that may indicate that, unlike what has been reported for other boreal species, it may temporally benefit from warming climate in the continuous permafrost region of the Asian boreal forests.

The microbial diversity of a sulfur-rich and saline cold pool in the Canadian high Arctic

Currently, the surface of Mars cannot sustain liquid water, but there is evidence suggesting that water was present in the Noachian. Although water might exist in the subsurface of Mars, it could not sustain in the present day unless it was highly saline. Thus, saline springs in polar desert environments are analogues with which to investigate martian conditions. An example of this is Axel Heiberg Island, located in a region of continuous permafrost in the Canadian High Arctic, which hosts sulfidic and highly saline springs. In this study, cultivation-dependant and independent techniques were used to investigate the microbial diversity of a sediment sample collected from a saline cold (3–8 °C) pool at Colour Peak Springs on Axel Heiberg. Both DNA and RNA were extracted from the samples, and the microbial community was characterised using the 16S rRNA gene from the extracted nucleic acids. The metabolic profile was characterised by screening DNA and cDNA for functional genes relating to the cycling of carbon (coxL, xoxF, cbbL), nitrogen (nifH, nosZ, nod) and sulfur (dsrB, soxB). The community profiles were used to inform enrichment strategies, allowing for the isolation and characterisation of several halophilic isolates including strains of Marinobacter, Halomonas, Halanaerobium and Loktanella. Through this work we have been able to develop an in-depth characterisation of the metabolic and phylogenetic diversity that is present and viable within this analogue site. This allows us to start building an understanding of the underlying mechanisms and strategies that enable organisms to persist in these environments.

Estimating Surface Soil Heat Flux in Permafrost Regions Using Remote Sensing-Based Models on the Northern Qinghai-Tibetan Plateau under Clear-Sky Conditions

The ground surface soil heat flux (G0) quantifies the energy transfer between the atmosphere and the ground through the land surface. However; it is difficult to obtain the spatial distribution of G0 in permafrost regions because of the limitation of in situ observation and complication of ground surface conditions. This study aims at developing an improved G0 parameterization scheme applicable to permafrost regions of the Qinghai-Tibet Plateau under clear-sky conditions. We validated several existing remote sensing-based models to estimate G0 by analyzing in situ measurement data. Based on the validation of previous models on G0; we added the solar time angle to the G0 parameterization scheme; which considered the phase difference problem. The maximum values of RMSE and MAE between “measured G0” and simulated G0 using the improved parameterization scheme and in situ data were calculated to be 6.102 W/m2 and 5.382 W/m2; respectively. When the error of the remotely sensed land surface temperature is less than 1 K and the surface albedo measured is less than 0.02; the accuracy of estimates based on remote sensing data for G0 will be less than 5%. MODIS data (surface reflectance; land surface temperature; and emissivity) were used to calculate G0 in a 10 x 10 km region around Tanggula site; which is located in the continuous permafrost region with long-term records of meteorological and permafrost parameters. The results obtained by the improved scheme and MODIS data were consistent with the observation. This study enhances our understanding of the impacts of climate change on the ground thermal regime of permafrost and the land surface processes between atmosphere and ground surface in cold regions.

Evidence for ecosystem state shifts in Alaskan continuous permafrost peatlands in response to recent warming

Peatlands in continuous permafrost regions represent a globally-important store of organic carbon, the stability of which is thought to be at risk under future climatic warming. To better understand how these ecosystems may change in a warmer future, we use a palaeoenvironmental approach to reconstruct changes in two peatlands near Toolik Lake on Alaska's North Slope (TFS1 and TFS2). We present the first testate amoeba-based reconstructions from peatlands in continuous permafrost, which we use to infer changes in water-table depth and porewater electrical conductivity during the past two millennia. TFS1 likely initiated during a warm period between 0 and 300 CE. Throughout the late-Holocene, both peatlands were minerotrophic fens with low carbon accumulation rates (means of 18.4 and 14.2 g C m−2 yr−1 for cores TFS1 and TFS2 respectively). However, since the end of the Little Ice Age, both fens have undergone a rapid transition towards oligotrophic peatlands, with deeper water tables and increased carbon accumulation rates (means of 59.5 and 48.2 g C m−2 yr−1 for TFS1 and TFS2 respectively). We identify that recent warming has led to these two Alaskan rich fens to transition into poor fens, with greatly enhanced carbon accumulation rates. Our work demonstrates that some Arctic peatlands may become more productive with future regional warming, subsequently increasing their ability to sequester carbon.

Remote sensing quantifies widespread abundance of permafrost region disturbances across the Arctic and Subarctic

Local observations indicate that climate change and shifting disturbance regimes are causing permafrost degradation. However, the occurrence and distribution of permafrost region disturbances (PRDs) remain poorly resolved across the Arctic and Subarctic. Here we quantify the abundance and distribution of three primary PRDs using time-series analysis of 30-m resolution Landsat imagery from 1999 to 2014. Our dataset spans four continental-scale transects in North America and Eurasia, covering ~10% of the permafrost region. Lake area loss (−1.45%) dominated the study domain with enhanced losses occurring at the boundary between discontinuous and continuous permafrost regions. Fires were the most extensive PRD across boreal regions (6.59%), but in tundra regions (0.63%) limited to Alaska. Retrogressive thaw slumps were abundant but highly localized (<10−5%). Our analysis synergizes the global-scale importance of PRDs. The findings highlight the need to include PRDs in next-generation land surface models to project the permafrost carbon feedback.

The impact of wildfire on microbial C:N:P stoichiometry and the fungal-to-bacterial ratio in permafrost soil

Wildfires thaw near-surface permafrost soils in the boreal forest, making previously frozen organic matter available to microbes. The short-term microbial stoichiometric dynamics following a wildfire are critical to understanding the soil element variations in thawing permafrost. Thus, we selected a boreal wildfire chronosequence in a region of continuous permafrost, where the last wildfire occurred 3, 25, 46, and > 100 years ago (set as the control) to explore the impact of wildfire on the soil chemistry, soil microbial stoichiometry, and the fungal-to-bacterial gene ratio (F:B ratio). We observed the microbial biomass C:N:P ratio remained constant in distinct age classes indicating that microbes are homeostatic in relation to stoichiometric ratios. The microbial C:N ratios were independent of the shifts in the fungal-to-bacterial ratio when C:N exceeded 12. Wildfire-induced reduction in vegetation biomass positively affected the fungal, but not the bacterial, gene copy number. The decline in microbial biomass C, N, and P following a fire, primarily resulted from a lack of soil available C and nutrients. Wildfire affected neither the microbial biomass nor the F:B ratios at a soil depth of 30 cm. We conclude that microbial stoichiometry does not always respond to changes in the fungal-to-bacterial ratio and that wildfire-induced permafrost thawing does not accelerate microbial respiration.

Emissions of nitrous oxide from continuous permafrost region in the Daxing'an Mountains, Northeast China

Permafrost ecosystems play an important role in global climate change, and climate warming would result in permafrost thawing and changing microbial mediated N cycles. Emissions of nitrous oxide (N2O) are an important component of N budgets in high-latitude permafrost ecosystems, especially in the context of global climate change. However, few studies have investigated the emissions of N2O from a swamp forest in a permafrost ecosystem. In this paper, we investigated the N2O emissions rates and cumulative budget from continuous permafrost region in the Daxing'an Mountains, northeast China, and identified the key environmental factors affecting N2O emissions from three swamp forests in the growing season. A bootstrapping model estimated that average N2O fluxes during the growing season were 40.76 ± 6.13, 29.56 ± 3.21 and 38.27 ± 8.46 μg m−2 h−1 from three swamp forests consisting of Larix gmelinii - Ledum palustre var. dilatatum (LL), Larix gmelinii - Carex appendiculata (LC) and Betula fruticose - Carex schmidtii (BC), respectively. The types of swamp forests had no statistically significant impact on N2O emissions (P > 0.05). The cumulative N2O emissions were estimated to be 1.07 ± 0.09 (LL), 0.79 ± 0.18 (LC) and 1.05 ± 0.11 kg ha−1 (BC) in the swamp forests, indicating that the permafrost region of the Daxing'an Mountains might be a potential N2O source during the growing season. The N2O emissions were mainly controlled by soil temperature, water table level, pH, ammonium nitrogen, nitrate nitrogen, total organic carbon and the carbon-to-nitrogen ratio. N2O emission showed significant negative correlation with nitrate nitrogen in the three swamp forests; thus, the low nitrate would limit the rate of N2O emissions in the permafrost region. In addition, we found that denitrification could be the potential source of N2O fluxes in the permafrost region of Daxing'an Mountains. Our results indicated that permafrost swamp forests were significant source for N2O emissions, and N2O emissions were controlled by multiple environmental factors.