Seasonal Thaw Layer Research Articles

The main results of monitoring the power of the active layer at CALM sites of the Nadymsky object

Monitoring of the thickness of the active layer within the lake-marsh type of terrain in the northern taiga was carried out at three sites organized in 1997, 2013 and 2022. In these areas, two types of tracts are distinguished: frozen peat bogs and swampy runoff hollows with a lowered roof of permafrost (the cross-section of the sites is the same type, the only difference is in the thickness of the peat). The work methodology complied with the unified protocol of the international CALM program. Additionally, the surface settlement was assessed (based on leveling from a local benchmark), geophysical studies were carried out and the temperature of the active layer rocks was measured at different gullies. In swampy runoff hollows, hollows with open water and on specific mineral spots within peat bogs, the depth of the permafrost roof is 3–10 m. At the boundaries of peat bogs and in swampy runoff hollows, the thawing depth exceeds 2 m, and on peat bogs it varies from 0.8 to 1.6 m depending on the thickness of the organic layer and the condition of the ground cover. On peatlands with an organic layer more than 1 m thick and a continuous ground cover, the depth of the seasonal thawing layer in some places does not exceed 0.4 m. These peatlands respond poorly to climate change. The depth of the permafrost roof within thin peat bogs (less than 0.5 m of peat) with oppressed vegetation cover is currently more than 2 m, marking the beginning of the replacement of the seasonally thawed layer with seasonally frozen and the formation of areas with a lowered permafrost roof. Monitoring of soil temperatures in such areas has showed that a random combination of climatic factors in individual years can lead to short-term (two years) new formation of permafrost or the merging of seasonal permafrost with permafrost. Thus, the formation of non-merging permafrost is of a reciprocating nature.

Geochemical Characteristics of the Vertical Distribution of Heavy Metals in the Hummocky Peatlands of the Cryolithozone.

One of the main reservoirs depositing various classes of pollutants in high latitude regions are wetland ecosystems. Climate warming trends result in the degradation of permafrost in cryolitic peatlands, which exposes the hydrological network to risks of heavy metal (HM) ingress and its subsequent migration to the Arctic Ocean basin. The objectives included: (1) carrying out a quantitative analysis of the content of HMs and As across the profile of Histosols in background and technogenic landscapes of the Subarctic region, (2) evaluating the contribution of the anthropogenic impact to the accumulation of trace elements in the seasonally thawed layer (STL) of peat deposits, (3) discovering the effect of biogeochemical barriers on the vertical distribution of HMs and As. The analyses of elements were conducted by atom emission spectroscopy with inductively coupled plasma, atomic absorption spectroscopy and scanning electron microscopy with an energy-dispersive X-ray detecting. The study focused on the characteristics of the layer-by-layer accumulation of HMs and As in hummocky peatlands of the extreme northern taiga. It revealed the upper level of microelement accumulation to be associated with the STL as a result of aerogenic pollution. Specifically composed spheroidal microparticles found in the upper layer of peat may serve as indicators of the area polluted by power plants. The accumulation of water-soluble forms of most of the pollutants studied on the upper boundary of the permafrost layer (PL) is explained by the high mobility of elements in an acidic environment. In the STL, humic acids act as a significant sorption geochemical barrier for elements with a high stability constant value. In the PL, the accumulation of pollutants is associated with their sorption on aluminum-iron complexes and interaction with the sulfide barrier. A significant contribution of biogenic element accumulation was shown by statistical analysis.

Express-Diagnostics of the Water Sources of a Small Arctic River by the Results of Short-Time Hydrological Survey, Chaunskaya Lowland, Chukotka

The article gives the results of generalization of a short-time expedition hydrological–hydrochemical survey in an arctic river basin in the northeastern part of Chaunskaya Lowland in the northern Chukotka, carried out in July 2020. At a scale of a small Yanranaivaam River basin, the structure of water masses was analyzed, and the catchments of individual tributaries with intense development of cryogenic processes were identified; these processes have an effect on water chemistry, in particular, in a higher concentration of hydrocarbonate ions, dissolved ferrum, and dissolved organic carbon. Two-tracer mixing model was used to identify and evaluate the contributions of water sources and their spatial relationships at the moment of survey. The main river water sources are atmospheric waters (mostly snowmelt water), slope soil water of the seasonally thawed layer (STL), and melt water of bald-mountain ice. The dominating water source in the catchments of the middle and upper parts of the basin is atmospheric water (67–78%), and that in the catchments of the lower part of the basin is STL soil water (59–64%). River recharge by meltwater of bald-mountain ice is typical of the entire basin, and at the moment of survey it accounted for 10–14% of the total.

Geology, Structure, Ground Temperature and Groundwater Level in Aquifer Taliks in the Shestakovka River Basin, Eastern Siberia

The objective of this study was to evaluate subaerial taliks’ geology, configuration, ground temperature and groundwater level in the continuous permafrost environment of Central Yakutia (Eastern Siberia). The study included geophysical surveys, borehole drilling and measurements of ground temperature and groundwater level variation in a talik aquifer in the Shestakovka research watershed. The talik occupies a gentle, sandy slope covered by a sparse pine forest. Its thickness varies from 3 to 17 m. The talik has several water-conducting branches along its slope. The seasonal thaw layer outside the talik and the talik itself form a single aquifer at the end of the summer. Water-saturated deposits in the talik have a temperature of about 0 °C throughout the year and do not freeze because of the constant filtration of water through the pores and convective heat transfer. Although the groundwater level is relatively close to the land surface, at a depth of just 1–3 m, it has very weak response to snowmelt and precipitation events. The maximum groundwater level occurs in February under cryogenic pressure due to deep seasonal ground freezing above the talik aquifer. Complicated relations between the landscape and the groundwater in the given geological conditions lead to the long-term existence of talik aquifers in the continuous permafrost environment.

Temporal Changes in the Content of Polyarenes in Samples of the Seasonally Thawed Layer from Tundra Peatlands during a Model Experiment

Temporal Changes in the Content of Polyarenes in Samples of the Seasonally Thawed Layer from Tundra Peatlands during a Model Experiment

Influence of the Thickness of the Seasonally Thawed Layer of Permafrost in the Eastern Siberia Catchments on the Content of Organic Matter in River Waters

In the context of global climate change, a significant increase in the active layer thickness (ALT) of permafrost is expected in the current century. This process has been observed by researchers over the past few decades. If the current climate trend continues, an increase in ALT may have a significant impact on the concentration of organic matter in Arctic river waters. The relationship between the thickness of the seasonally thawed layer of permafrost and the concentration of dissolved organic matter in river waters has been explored using clustering, one-way ANOVA, and cross-tabulation analysis. The data set for analysis included original details on the content of organic matter in the rivers of Eastern Siberia (in terms of COD, BOD5, and the color of the water), phytoplankton abundance and biomass, and data on the permafrost active layer thickness (ALT) in the catchments. It was revealed that in the areas of catchments where the ALT is deeper, the content of organic matter in the rivers is lower than in areas with a shallow, seasonally thawed permafrost. Our results are consistent with the existing conceptual model of the influence of ALT on the chemistry of river waters in the cryolithozone. This knowledge is important for predicting the chemical composition of the Arctic rivers, eutrophication, and the rate of inflow of dissolved solids into the Arctic Ocean under the current conditions of ALT deepening.

СОВРЕМЕННОЕ СОСТОЯНИЕ МЕЛИОРИРОВАННЫХ ЗЕМЕЛЬ В АРКТИЧЕСКОЙ ЗОНЕ ЯКУТИИ В УСЛОВИЯХ МЕНЯЮЩЕГОСЯ КЛИМАТА

On the example of the estuary irrigation system «Bolshaya Polyana» of the Verkhoyansk region, the current state of reclaimed lands in the Arctic zone of Yakutia in a changing climate is considered. Research methods included reconnaissance and topographic surveys of the study area, analysis and processing of research materials previously obtained by the author. An analysis of natural and climatic conditions showed that due to climate change, there is a reduction in the cold winter period, catastrophic amounts of winter precipitation, abnormal heat in summer periods and an increase in the average annual temperature over the past 15 years by 1.2°С, which affected the shift in the start date of irrigation of estuary meadows for early periods up to 9 days. The heterogeneity of the relief of estuary meadows and the overgrowth (cluttering) of irrigation canals were revealed, in connection with which the irrigation period reaches 25-30 days, as a result of which waterlogging of the soil occurs. Agrochemical studies determined the type of soils, frozen peat-gley soil in the hay area of estuary irrigation and frozen humus-gley soil in the natural area. Measurements of the seasonal thaw layer in the natural area show deeper thawing of soils than in the hayfi elds of the estuary irrigation system. Also, measurements at different flood depths show that the greater the flood depth, the smaller the thawing layer. These phenomena, in our opinion, are due to the type of soils and may be associated with the influence of the layer of irrigated waters on the thawing of soils. The results of the studies carried out require further measures and studies to create an optimal irrigation regime, improve the water-physical properties of soils, for which it is proposed to improve irrigation methods by building a double-regulation reclamation network and subsequent study of its effect on the thermal and moisture conditions of irrigated haylands and agrochemical indicators of soils.

Assessment of Mercury Concentrations and Fluxes Deposited from the Atmosphere on the Territory of the Yamal-Nenets Autonomous Area

The problem of mercury input and its further distribution in the Arctic environment is actively debated, especially in recent times, due to the observed processes of permafrost thawing causing the enhanced release of mercury into the Arctic atmosphere and further distribution in the terrestrial and aquatic ecosystem. The atmospheric mercury deposition occurs via dry deposition and wet scavenging by precipitation events. Here we present a study of Hg in wet precipitation on the remote territory of the Russian Arctic; the data were obtained at the monitoring stations Nadym and Salekhard in 2016–2018. Mercury pollution of the Salekhard atmosphere in cold time is mainly determined by regional and local sources, while in Nadym, long-range transport of mercury and local fuel combustion are the main sources of pollutants in the cold season, while internal regional sources have a greater impact on the warm season. Total mercury concentrations in wet precipitation in Nadym varied from <0.5 to 63.3 ng/L. The highest Hg concentrations in the springtime were most likely attributed to atmospheric mercury depletion events (AMDE). The contributions of wet atmospheric precipitation during the AMDE period to the annual Hg deposition were 16.7% and 9.8% in 2016/2017 and 2017/2018, respectively. The average annual volume-weighted Hg concentration (VWC) in the atmospheric precipitation in Nadym is notably higher than the values reported for the remote regions in the Arctic and comparable with the values obtained for the other urbanized regions of the world. Annual Hg fluxes in Nadym are nevertheless close to the average annual fluxes for remote territories of the Arctic zone and significantly lower than the annual fluxes reported for unpolluted sites of continental-scale monitoring networks of the different parts of the world (USA, Europe, and China). The increase of Hg deposition flux with wet precipitation in Nadym in 2018 might be caused by regional emissions of gas and oil combustion, wildfires, and Hg re-emission from soils due to the rising air temperature. The 37 cm increase of the seasonally thawed layer (STL) in 2018 compared to the 10-year average reflects that the climatic changes in the Nadym region might increase Hg(0) evasion, considering a great pool of Hg is contained in permafrost.

Effects of a long‐term anoxic warming scenario on microbial community structure and functional potential of permafrost‐affected soil

AbstractPermafrost (PF)‐affected soils are widespread in the Arctic and store about half the global soil organic carbon. This large carbon pool becomes vulnerable to microbial decomposition through PF warming and deepening of the seasonal thaw layer (active layer [AL]). Here we combined greenhouse gas (GHG) production rate measurements with a metagenome‐based assessment of the microbial taxonomic and metabolic potential before and after 5 years of incubation under anoxic conditions at a constant temperature of 4°C in the AL, PF transition layer, and intact PF. Warming led to a rapid initial release of CO2 and, to a lesser extent, CH4 in all layers. After the initial pulse, especially in CO2 production, GHG production rates declined and conditions became more methanogenic. Functional gene‐based analyses indicated a decrease in carbon‐ and nitrogen‐cycling genes and a community shift to the degradation of less‐labile organic matter. This study reveals low but continuous GHG production in long‐term warming scenarios, which coincides with a decrease in the relative abundance of major metabolic pathway genes and an increase in carbohydrate‐active enzyme classes.

The Effect of Post-Fire Disturbances on a Seasonally Thawed Layer in the Permafrost Larch Forests of Central Siberia

We examined and simulated the consequences of the degradation of the litter and the moss–lichen layer after fire impact, which could affect the seasonal temperature of the soil and the depth of the seasonally thawed layer (STL) in the permafrost zone. According to the analysis of satellite imagery for 2000 to 2019, the fire-disturbed area in the region of interest amounted to 20%. The main aims of the study included quantitative evaluation of the variation range of summer temperature anomalies at fire-damaged plots, summarizing the statistical norm of the STL depending on natural conditions, and numerical simulation of the response of the STL. Using Terra and Aqua/MODIS imagery, we analyzed surface temperature (in bands of λ = 10.780–11.280 and 11.770–12.270 μm) coupled with the normalized difference vegetation index (NDVI) for non-disturbed and fire-damaged sites under the same natural conditions of larch forests in Central Siberia. Heat transfer, freezing and thawing processes were numerically simulated for two extreme cases of soil conditions: dry soil and water-saturated soil. The model was also applied to soil with non-homogeneous water content. As input parameters, we used data on the properties of cryogenic soils collected in larch forests (Larix gmelinii) in the flat-mountainous taiga region of the Evenkia (Central Siberia). For post-fire plots, surface temperature anomalies observed during summer months remained significant for more than 15–20 years after fire impact, while the NDVI values were restored to the statistical norm within 7–10 years of the fire. According to the results of numerical simulation, the thickness of the STL could show a 30–50% increase compared to the statistical norm. In the first approximation, we showed the annual soil temperature dynamics at various depths in disturbed and non-disturbed plots.

Methods for assessing territory pollution by oil or petroleum product spills

During the development of oil and gas fields and transportation of hydrocarbons, the ecology of regions is subject to various negative impacts. The most severe consequences for the environment are caused by accidental spills of oil or petroleum products, which occur due to through damage to pipelines. Polluted territories are subject to mandatory reclamation in accordance with government regulations and industry regulations. However, despite the measures taken by the administrations of the northern regions to increase the rate of reclamation of damaged territories in recent years, there has been a trend of growth of areas contaminated with hydrocarbons.Various remediation technologies that have been tested in warm and temperate climates are not very effective in regions with permafrost. Pollution of the daytime surface with oil or petroleum products leads to an increase in the absorption of the sun's radiant energy, the growth of the seasonal thaw layer and the development of destructive processes for the territory. To achieve a positive effect as a result of rehabilitation measures, it is necessary to take into account the individual characteristics of the territory and the extent of its pollution.

Structural and textural features of genetic types of the massive and ice wedges, and the conditions of their formation in the lower reaches of the Gyda River

In the structure of the frozen thickness of the 2nd lake-alluvial terrace of the Gyda River were detected polygonal-wedge, lens massive and lensoid ice were. A detailed analysis of structural and textural peculiarities in the layers was carried out for the first time for these morphological types of underground ice. Based on the cryolithological structure of host rocks and structural-textural features of ice, the main mechanisms of deposit formation – polygonal-wedge, infiltration-segregational, and congelation were determined. The development of polygonal-wedge ice occurred in an alluvial floodplain setting of sedimentation accompanied by the climate fluctuations in the end of the Late Pleistocene and Holocene. The growth of ice wedge in the second half of the Sartan Period was interrupted under the reservoirs with shallow talik waters, after freezing of which there formed infiltration-segregational lensoid formation ices. The structure of frozen thickness was complicated by the lenses of congelation ice formed in thermoerosive niches in the Holocene optimum of about 6.5 thousand years ago. At the present time is possible the formation of similar types of ice on various sections of the relief. The established peculiarities of cryogenic structure are important for the creation of paleogeographic reconstructions and forecasting the dynamics of permafrost-facies environments accompanied by the modern changes in the depth of the seasonal thaw layer and the development of thermokarst.

Seasonal Thawing Local Changes Indicators for UAV-Based Cryolithozone Mapping

Remote sensing methods make it possible to evaluate the reaction of the cryolithozone and tundra landscapes in hard-to-reach Arctic areas based on the indicators of modern climate changes. In 2016–2019, numerous organic frost boils were discovered on the peatland surfaces of drained lakes in the southern tundra of the Pur-Taz interfluve in the northern part of West Siberia and studied. It is established that the formation of frost boils caused by organic mass injections occurs in the summertime and that they indicate local deepening of seasonal thawing. Frost boils emerging at peatlands in summertime was identified after analysis of UAV survey in 2019. Local deepening of seasonal thaw layer on polygonal peatlands is evidence of permafrost reaction to global warming.

Influence of soil properties on active layer thermal propagation along the western Antarctic Peninsula

AbstractThe rate of energy transfer through soils is an important factor governing the active layer (seasonal thaw layer) in polar regions. Energy is transferred through conductive and convective means, which are primarily influenced by the bulk density and water content of soils. With global temperatures changing, it becomes important to understand how soil properties influence heat transfer and active layer depths in climatically sensitive regions, such as the Antarctic Peninsula. In this study we analyzed conductive energy transfer through several soil types on Amsler Island and Cierva Point in the central region of the western Antarctic Peninsula. Active layer temperatures on Amsler Island were monitored every three hours using iButton thermistors installed at regular depth intervals down to 2 m. Soil textures were loamy to sandy with water contents between 5 and 27%. Freezing and thawing transmission rates for all soils ranged from 1.4 to 6.9 cm/day. Thermal transmission rates were fastest in sandy soils with low water contents, indicating that the large, interconnected pores of the sandy soils facilitated the quick movement of heat with water flow through the soil profile. Snow accumulation differences also played a significant role on winter thermal propagation by providing a thermal barrier between the ground surface and atmosphere. Although there was a wide range in thermal transmission among the soils, active layer depths had little variation (7.8–9.7 m). This consistency derives from the greater dependence of very thick active layers on long‐term climatic conditions rather than on soil properties. The presence of thick moss significantly slowed thermal transmission and decreased active layer thicknesses. These effects primarily are due to the high heat capacity of water and air retained within the moss, slowing thermal transmission rates, acting as a thermal buffer between atmospheric conditions and the underlying soils. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of trees on the burning of organic layers on permafrost terrain

We collected data to estimate depth of the remaining (residual) organic layer as well as data to estimate total pre-fire organic layer depth in 99 plots located in mature black spruce (Picea mariana (Mill.) BSP) forests in interior Alaska that burned during the large fire seasons of 2004 and 2005. These data were collected immediately adjacent to trees as well as from throughout the plot along with tree stand characteristics (density and basal diameter), and used to assess if trees influenced depth of burning. While other studies have found residual organic layer depths to be shallower under trees than at randomly located points within a given area, our results showed that mean and median residual organic layer depth, as well as the frequency of depths <3cm, did not differ at a plot scale versus adjacent to trees. Regardless of proximity to trees, residual organic layer depths were affected by drainage and timing of the fire, with deeper organic layers occurring in poorly drained plots and in plots that burned early in the growing season. The amount of foliar biomass was a significant but weak predictor of residual organic layer depth. There was no interaction between drainage class and mean tree basal diameter, basal area, or foliar biomass in explaining variation in organic layer depths following fires. Since the depth of the organic layer in this region regulates ground temperature, degree of permafrost formation, and site drainage, we hypothesize that the seasonal thaw layer impedes drainage in Alaskan black spruce forests, resulting in a horizontal redistribution of moisture just above frozen soil in plots with permafrost. This reduces the impacts of tree canopies (such as canopy interception of precipitation) on variability in depth of burning of the surface organic layer.

Organic matter composition and potential trace gas production of permafrost soils in the forest tundra in northern Siberia

The amount, quality and bioavailability of organic matter stored in permafrost soils are important factors determining the response of high-latitude soils to climate warming. In this study, we investigated the storage and composition (isotopic composition, lignin, pyrogenic carbon) of organic matter in mineral soils which are differently affected by permafrost, and we determined the potential CO 2 emission, CH 4 exchange and N 2O emission of these soils at different temperature (5 °C and 15 °C) and moisture (60% of the maximum water-holding capacity [WHC] and completely water saturated) in a laboratory incubation experiment. Soil samples were collected in the summer of 2002 and 2003 from the mineral soils of the Grawijka Creek catchment in the Siberian forest tundra and for comparison, from a fertilized grassland in Germany. The depth of the seasonal thaw layer of the Siberian soils ranged from 15 cm to > 90 cm and was greater in soils located on slopes than in soils of plane areas where drainage was poor and soils showed gleyic properties. The soil organic carbon (SOC) concentration ranged from 14 to 74 g kg − 1 in the upper 20 cm and from 5 to 128 g kg − 1 in the subsoil. The total SOC and N accumulation in the upper 30–40 cm were larger in soils with a seasonal thaw layer < 40 cm (up to 23 kg C m − 2 and 1.3 kg N m − 2) than in soils without permafrost in the upper 90 cm (approximately 8 kg C m − 2 and 0.6 kg N m − 2). The concentration of lignin-derived CuO oxidation products in soil OC were larger in a soil without permafrost than in the permafrost soils in which lignin oxidation appears to be more advanced. All soil samples from the forest tundra contained considerable amounts of black carbon (up to 57 g C kg − 1 SOC), which indicates the importance of fire in this ecosystem. Water logging in the permafrost soils seems to restrain the decomposition of black carbon. Soil organic carbon mineralization in the gleyic permafrost soils increased by a factor of approximately 4 if soil temperature was raised from 5 to 15 °C and soil moisture reduced from complete water saturation to 60% WHC. Emission of N 2O was negligible from all Siberian soils but very high from the fertilized grassland soil at complete water saturation. At 60% WHC, all forest tundra soils were a net-sink for atmospheric methane with significantly larger CH 4 uptake in the A horizon of the soil without permafrost (∼ 0.1 ng CH 4–C h − 1 g − 1) than in the A horizon of the permafrost soils (< 0.02 ng CH 4–C h − 1 g − 1). The results show that permafrost distribution is an important factor determining storage and composition of SOC in the Grawijka Creek area and that permafrost distribution may considerably affect current and future net fluxes of the greenhouse gases CO 2 and CH 4 in this region.

Predicting Carbon Storage in Tundra Soils of Arctic Alaska

The distribution of soil organic carbon (SOC) was determined in 60 pedons from northern Alaska by horizon, within the seasonal thaw layer, and to a depth of 1 m. Concentration of SOC, bulk density, and SOC density were remarkably uniform for a given genetic horizon and had low standard errors. With increasing degree of decomposition, the bulk density increased, the concentration of SOC decreased, and the soil horizon C density increased in organic horizons. For mineral horizons, gleying is accompanied by an increase in C density, which is due to the effect of saturation on limiting decomposition of organic matter. Cryoturbation of organic or mineral minerals into the subsoil results in an increase in C density primarily from an increase in bulk density because of compaction from the overlying layers and more closely packed soil particles from frost churning. Estimated SOC storage for individual horizons and for the seasonal thaw layer were highly correlated (p < 0.01) with measured values from an independent data set for the same region published by other investigators. Equations relating C density to percentage of visible ice enable prediction of SOC in the near-surface permafrost. The equations generated by this study will be useful in preparing a detailed soil C map of the arctic regions.

Contaminant migration through the permafrost active layer, Mackenzie Delta area, Northwest Territories, Canada

AbstractBuried pits (sumps), used for the disposal of drilling muds in the Mackenzie Delta area of Arctic Canada, provide an opportunity for assessing the effectiveness of ice-bonded permafrost sediments as a containment for industrial wastes. Potassium chloride (KCI) added to drilling muds as a freezing-point depressant provides a suitable tracer, because it is easily identified and natural concentrations in sediment pore water are typically low (less than 0.02 g l−1; potassium). Muds with KCI concentrations of up to 10% by weight (100 g l−1) have been used. In the vicinity of sumps, potassium is found at elevated concentrations of up to several g l−1 in the seasonal thaw layer (active layer) at distances well beyond what would be expected from diffusive transport alone. Within the level alluvial silts of the modern Mackenzie Delta, KCI has moved up to 50 m laterally from sump edges. On surrounding tundra uplands, KCI has migrated several hundred metres downslope within the active layer.Although ice-rich permafrost sediments appear to form an effective barrier against downward movement of solutes, thawing ice lenses and veins within the active layer greatly increase the lateral hydraulic conductivity in this zone during the thaw season. Compared with unfrozen silty sediments, the large pores left by thawed ice fabric in the same sediment after a freeze–thaw cycle have been shown to increase the hydraulic conductivity up to four orders of magnitude. This phenomenon is probably common in thawing, ice-rich sediments and presumably favours accelerated downhill movement of solutes. On level ground, it is anticipated that KCI movement is promoted by fluid densities approaching that of sea water. Laboratory experiments with thawed sand and both unfrozen and thawing Mackenzie Delta silt confirm the existence of density-driven solute movement and the importance of thawing ice fabric in promoting solute movement. The thawed ice fabric of active-layer sediments and the presence of a frost table promote lateral movement of fluids when a density or elevation gradient is present. These tendencies widen the area potentially affected by contaminant migration from abandoned waste sites and they may also promote the movement of contaminants that escape from future containments.

Temporal variation in methane emission from tundra wetlands in a permafrost area, northeastern Siberia

Summer variations in net methane flux and environmental variables were investigated in a Siberian permafrost area during the summers of 1993 and 1995. In each region, the measurements were made at two fixed sites: waterlogged wetlands and relatively dry grasslands. Methane flux from the waterlogged site at Tiksi (71.5°N, 130.0°E) averaged 46.3 mg CH 4 m −2 d −1. Flux from the waterlogged site at Chersky (68.5°N, 161.4°E) was approximately one order of magnitude greater than that at Tiksi and averaged 281.1 mg CH 4 m −2 d −1. Fluxes from the relatively dry sites were near zero and frequently negative in both regions. The emissions from the waterlogged sites showed diurnal and intraseasonal variation, while no significant variation in flux was observed at the dry sites. Our results suggest that temporal variation in methane flux from waterlogged sites in permafrost areas was controlled by the thermal regime of a seasonal thaw layer. The diurnal variation in the flux was correlated with ground temperature at a depth of 10–30 cm. For summer-season variation, the correlation between flux and centimeter–degrees, which is the product of ground temperature and thaw depth, was quite strong. The parameter, centimeter–degrees, is expected to be a good predictive indicator of methane emission from wetlands in permafrost areas.