Soil Thawing Research Articles

Impacts of seepage flow and soil thaw depth on hillslope snowmelt erosion in Chinese Mollisol region

Snowmelt erosion is an important way of soil loss in Chinese Mollisol region. However, little is known about the effects of seepage flow and soil thaw depth on hillslope snowmelt runoff erosion. An indoor simulated experiment was conducted to analyze the impacts of seepage flow and soil thaw depth on hillslope snowmelt erosion. There were two snowmelt flow rates (1 and 4 L·min-1), two soil thaw depths (5 and 10 cm), and two near-surface hydrological conditions (with and without seepage flow). The results showed that hillslope runoff depth and soil erosion amount in the treatment with seepage flow were 1.1 to 1.2 times and 1.3 to 1.9 times of those in the treatment without seepage flow, respectively. Under two snowmelt flow rates, when soil thaw depth increased from 5 cm to 10 cm, hillslope runoff depth and soil erosion amount increased by 10.0% to 13.5% and 15.4% to 37.1% in the treatment without seepage flow, respectively. In the treatment with seepage flow, when soil thaw depth shifted from 5 cm to 10 cm, hillslope runoff depth increased by 6.5% to 8.5%, and soil erosion amount remained stable. Moreover, hillslope rill development was comprehensively influenced by seepage flow, soil thaw depth, and snowmelt flow rate, with rill erosion amount occupying more than 72% of hillslope snowmelt erosion amount. Compared with the treatment without seepage flow, flow velocity and shear stress under the treatment with seepage flow increased by 20.3% to 23.2% and 37.0% to 51.3%, respectively; but Darcy-Weisbach friction coefficient reduced by 9.0% to 21.4%, which caused an increase of hillslope snowmelt erosion. In addition, seepage flow enhanced rill development, which caused rill erosion amount to increase by 43.6% to 69.9% compared with the treatment without seepage flow, and it further resulted in the increase of hillslope snowmelt erosion amount. The main reason for soil thaw depth enhancing hillslope snowmelt erosion amount under the treatment without seepage flow was that both sloping runoff erosivity and erodible materials increased with increasing soil thaw depth. Furthermore, soil thaw depth had a significant impact on hillslope rill morphology development under the treatment with seepage flow. Rill widening process was dominated when soil thaw depth was 5 cm, whereas rill incision process was dominant when soil thaw depth was 10 cm. This study could improve the understanding of hillslope snowmelt erosion mechanism in Chinese Mollisol region and provide theoretical guidance for the development of water erosion model.

Temperature sensitivity of Antarctic soil-humic substance degradation by cold-adapted bacteria.

Heteropolymer humic substances (HS) are the largest constituents of soil organic matter and are key components that affect plant and microbial growth in maritime Antarctic tundra. We investigated HS decomposition in Antarctic tundra soils from distinct sites by incubating samples at 5°C or 8°C (within a natural soil thawing temperature range of -3.8°C to 9.6°C) for 90 days (average Antarctic summer period). This continuous 3-month artificial incubation maintained a higher total soil temperature than that in natural conditions. The long-term warming effects rapidly decreased HS content during the initial incubation, with no significant difference between 5°C and 8°C. In the presence of Antarctic tundra soil heterogeneity, the relative abundance of Proteobacteria (one of the major bacterial phyla in cold soil environments) increased during HS decomposition, which was more significant at 8°C than at 5°C. Contrasting this, the relative abundance of Actinobacteria (another major group) did not exhibit any significant variation. This microcosm study indicates that higher temperatures or prolonged thawing periods affect the relative abundance of cold-adapted bacterial communities, thereby promoting the rate of microbial HS decomposition. The resulting increase in HS-derived small metabolites will possibly accelerate warming-induced changes in the Antarctic tundra ecosystem.

Modeling the Process of Thawing of Tailings Dam Base Soils by Technological Waters

The storage of wastes from mining and mineral processing plants in the tailing dumps in regions with cold climates has a number of environmental consequences. Interactions of water with tailings in cold climates often lead to the thawing of permafrost soils, formation of technogenic thawing zones, and leakage of drainage waters. In the case of fault zones development in these areas, technogenic solutions are often filtered outside the tailing dump, promoting further development of filtration channels. In order to prevent leakage of solution from tailing dumps over time, it is necessary to determine the thawing zones and prevent the formation of filtration channels. In the case of the formation of a filtration channel, it is necessary to know what rate of rock thawing occurred near the formed filtration channel. In this study, for the tailing dump of a diamond mining factory, we calculated two exothermic effects: (1) due to physical heating of dump rock by filtering industrial water with temperatures from 2 to 15 °C through the rock; and (2) due to the chemical interaction of industrial water with the dam base rock. The amount of energy transferred by the water to the frozen and thawed rock over 10 years was calculated using thermophysical modeling and was 207.8 GJ and 8.39 GJ respectively. The amount of energy that the rock received during the ten-year period due to dissolution of the limestones and equilibration of solutions was calculated using thermodynamic modeling and was 0.37 GJ, which is 4.4% of the average amount of energy, expended on heating the thawed rock (8.39 GJ).

Efficiency of forest planting in the spring and autumn periods in the conditions of the Republic of Kalmykia

The Republic of Kalmykia is the driest region in the south of the European part of Russia. The purpose of the study is to find a new approach to reforestation and breeding in the republic, which will ensure the increase in the survival rate of forest crops, and subsequently increase the forest cover of the region. The article analyzes data for a ten-year period in a zonal section on the survival rate of tree and shrub species cultivated in the forestry of the Republic of Kalmykia. It is concluded that carrying out forest cultivation works in the autumn period has no advantages in survival rate over the spring period and they should be carried out either in early spring (in late March and early April) on thawing soil, or in autumn, before the onset of persistent cold weather. The main factor of successful afforestation in the dry steppe and semi-desert is the correct selection of the forest area, the accuracy and quality of forest planting, agrotechnical and forestry care. Special attention should be paid to the control of locust pests, which in the conditions of Kalmykia in some years can cause significant damage to the planting of young forest crops.

Linkage between anomalies of pre-summer thawing of frozen soil over the Tibetan Plateau and summer precipitation in East Asia

The Tibetan Plateau (TP) is sensitive to climate change in the land–atmosphere coupling mechanism due to its complex topographic features and unique geographic location. This study explored the teleconnection between pre-summer thawing of frozen soil over the TP and summer precipitation in East Asia in the Meiyu–Baiu rainy season (June, July) from 1981 to 2019 using maximum covariance analysis (MCA). The precipitation fields forced by thawing of frozen soil were calculated by the coupled manifold technique. The variations in East Asian precipitation are significantly impacted by thawing of frozen soil over the TP, with a variance explained ratio in the surrounding middle and lower reaches of Yangtze River (MLYR) of around 10%–20%. The MCA analysis also revealed that the thickness of pre-summer frozen soil thawing had a positive relationship with summer precipitation in the MLYR and southern Japan (fraction = 0.59, correlation ≈ 0.99). To find out the possible mechanism, composite analyses were conducted on atmospheric and surface components with reanalysis products. The analysis results suggested that more (less) frozen soil thawing would increase (decrease) the sensible heat and land surface temperature with enhanced (weakened) surface diabatic heating over the TP. Then, the positive (negative) surface diabatic heating would result in an enhanced (weakened) South Asia High extending eastward followed by stronger (weaker) upper troposphere (200 hPa) westerlies, as well as the West North Pacific Subtropical High extending westward. As a result, the northeastward movement of the integrated vapor transport intensified (weakened) with the westward extension (eastward retreat) of the Meiyu–Baiu rain belt, leading to more (less) precipitation in the MLYR and southern Japan. It is thus suggested that pre-summer thawing of frozen soil over the TP could play a vital role in regulating East Asian summer precipitation and movement of the Meiyu–Baiu rain belt.

Building Stability On Permafrost In Vorkuta, Russia

The Infrastructure stability on permafrost is currently an important topic as the Arctic countries are developing climate change adaptation and mitigation programs. Assessing the sustainability of infrastructure facilities (especially in urban environments) is a difficult task as it depends on many parameters. This article discusses the city of Vorkuta, which is located in the northwest of Russia. This city differs from many others built on permafrost because most of buildings were built according to Principle II (The Active Method) of construction on permafrost with thawing soil prior to construction. Assessments of the engineering and geocryological conditions, basic principles of construction in the city, and reasons for building failures, were carried out within this study. The research is based on publications, open data about buildings, and visual observations in Vorkuta. About 800 buildings are in use in Vorkuta in 2020 (43% of what it was 50 years ago). According to the analysis, about 800 houses have been demolished or disconnected from utility lines over the past 50 years (about 250 of these are still standing, pending demolition). Since 1994, the construction of new residential buildings has almost stopped. Therefore, buildings that have been in use for over 50 years will account for 90% of the total residential housing stock by 2040. The effects of climate change in the city will depend primarily on the principle of construction employed and on the geocryological conditions of the district. Buildings constructed according to Principle I (The Passive Method) were found to be more vulnerable due to a decrease in permafrost bearing capacity. The impact of increasing air temperature on some of the buildings built on bedrock (the central part of the city) and some built on thawing soil will be minimal, as other factors are more significant.

Nutrient Inputs Stimulate Mercury Methylation by Syntrophs in a Subarctic Peatland

Climate change dramatically impacts Arctic and subarctic regions, inducing shifts in wetland nutrient regimes as a consequence of thawing permafrost. Altered hydrological regimes may drive changes in the dynamics of microbial mercury (Hg) methylation and bioavailability. Important knowledge gaps remain on the contribution of specific microbial groups to methylmercury (MeHg) production in wetlands of various trophic status. Here, we measured aqueous chemistry, potential methylation rates (kmeth), volatile fatty acid (VFA) dynamics in peat-soil incubations, and genetic potential for Hg methylation across a groundwater-driven nutrient gradient in an interior Alaskan fen. We tested the hypotheses that (1) nutrient inputs will result in increased methylation potentials, and (2) syntrophic interactions contribute to methylation in subarctic wetlands. We observed that concentrations of nutrients, total Hg, and MeHg, abundance of hgcA genes, and rates of methylation in peat incubations (kmeth) were highest near the groundwater input and declined downgradient. hgcA sequences near the input were closely related to those from sulfate-reducing bacteria (SRB), methanogens, and syntrophs. Hg methylation in peat incubations collected near the input source (FPF2) were impacted by the addition of sulfate and some metabolic inhibitors while those down-gradient (FPF5) were not. Sulfate amendment to FPF2 incubations had higher kmeth relative to unamended controls despite no effect on kmeth from addition of the sulfate reduction inhibitor molybdate. The addition of the methanogenic inhibitor BES (25 mM) led to the accumulation of VFAs, but unlike molybdate, it did not affect Hg methylation rates. Rather, the concurrent additions of BES and molybdate significantly decreased kmeth, suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in kmeth with combined addition of BES and molybdate, and accumulation of VFA in peat incubations containing BES, and a high abundance of syntroph-related hgcA sequences in peat metagenomes provide evidence for MeHg production by microorganisms growing in syntrophy. Collectively the results suggest that wetland nutrient regimes influence the activity of Hg methylating microorganisms and, consequently, Hg methylation rates. Our results provide key information about microbial Hg methylation and methylating communities under nutrient conditions that are expected to become more common as permafrost soils thaw.

Soil temperature field and dynamics of freezing-thawing processes in the south of the Vitim Plateau (Transbaikal region)

The results of geographic and stationary studies of temperature, water and permafrost regimes and soil properties in the south of the Vitim Plateau (Transbaikal region) are discussed. Instrumental data on soil temperature regimes indicate the dynamics of soil freezing–thawing processes and attest to changes in the thawing depth of permafrost-affected soils. The revealed spatiotemporal patterns of soil freezing/thawing reflect the distribution of heat and cold (permafrost) in the soils of the studied cryoarid landscapes. Seasonal, annual and long-term differences in the soil temperature field cause a great heterogeneity of soil toposequences with contrasting soils on the north– and south–facing slopes. An increase in the soil thawing depth has been observed over the past 50 years. In the relatively wet and cold 1970–1990 years, its rate varied from 1.0 to 1.5 cm/year with higher values typical for Haplic Chernozems under meadow-steppe vegetation, and lower values for Phaeozems under forest vegetation. Over the recent 25 years, the rate of the increase in the soil thawing depth for the same soils has intensified by 2.5– 3.0 times in relation to aridization and climate warming.

Thermal regime of Cryosols and underlying permafrost in North Yakutia in the context of global climate change

The warming and an increase in the amount of solid precipitation, which became apparent in North Yakutia on the threshold of the 21st century, have led to an increase of soil temperature in winter season and of the permafrost. The heat fluxes measured in the taiga soil on the Kolyma Lowland reveal an imbalance in the annual heat gain and loss in the cryogenic ecosystem amounting to 26.3–56.1% of the incoming energy. An increase in the summer air temperatures of the 2000th caused a universal increase in the depth of seasonal soil thawing. After the drop in high summer temperatures, the active layer thickness (ALT) either continued to grow or stabilized at higher levels in the watershed ecosystems of the Kolyma Lowland; however, ALT returned to its initial values in the tundra of the Yana-Indigirka Lowland. As for the floodplain landscapes, ALT increased near-linearly over the 24 years of monitoring. The waterlogged tundra and taiga soils as well as the upland gleyzem of the Bykovsky Peninsula differed only by a temporary increase in the thawing depth. The degree of the soil and permafrost thermal regime transformation tends to increase from west to east, fitting the heterogeneity of climate changes.

Preforming floral primordia converge on a narrow range of stages at dormancy despite multiple effects of temperature on development.

Phenological studies often focus on relationships between flowering date and temperature or other environmental variables. Yet in species that preform flowers, anthesis is one stage of a lengthy developmental process, and effects of temperature on flower development in the year(s) before flowering are largely unknown. We investigated the effects of temperature during preformation on flower development in Vaccinium vitis-idaea. Using scanning electron microscopy, we established scores for developing primordia and examined effects of air temperature, depth of soil thaw, time of year and previous stage on development. Onset of flower initiation depends on soil thaw, and developmental change is greatest at early stages and during the warmest months. Regardless of temperature and time during the season, all basal floral primordia pause development at the same stage before whole-plant dormancy. Once primordia are initiated, development does not appear to be influenced by air temperature differences within the range of variation among our sites. There may be strong endogenous flower-level controls over development, particularly the stage at which morphogenesis ceases before dormancy. However, the strength of such internal controls in the face of continuing temperature extremes under a changing climate is unclear.

The use of quicklime for soil thawing in pile foundation setting

Due to the fact that in the winter period, which in the Northern regions of the Republic of Kazakhstan lasts up to 6 months, and in the Southern regions – up to 4 months, construction companies are forced to suspend construction and installation works on the foundations. As a result, the total duration of construction of facilities increases, which leads to additional financial expenses. Therefore, new technological solutions are needed for the construction of foundations in winter, to ensure the continuity of construction and installation work. The purpose of the study is to develop a formula of chemical reagents for thawing and protection from the freezing of seasonally frozen soil in places where pile foundations are driven in winter conditions. For the study, a three-component mixture of chemical reagents of the following composition, wt.%, was selected: quick lime (CaO) – 75, calcium chloride (CaCl) – 20, sodium chloride (NaCl) – 5. The choice of the specified composition is determined by taking into account their specific chemical properties and special reactions when interacting with water and frozen soil. The active components of quick lime (CaO) are converted to Ca(OH)2 when interacting with a wet environment or water. This process is accompanied by spontaneous heat release. In the course of the study, a new composition of a chemical reagent based on quick lime was developed for local thawing and protection from the freezing of seasonally frozen clay soil in the areas of driving pile foundations. This composition has advantages in terms of reducing energy costs for thawing seasonally frozen soil, since when interacting with water, the proposed chemical reagent spontaneously releases heat (t = 100oC) and does not cool down for a long time despite the negative ambient temperature of the air.

Effect of Simulated Tibetan Sheep and Yak Trampling at Different Periods on the Reproductive Characteristics, Underground Morphology, and Carbohydrate Content of Kobresia humilis

Studying the effects of trampling at different stages on plant reproduction is necessary to provide the basis for grassland management. However, the changes in forage growth characteristics are still unclear under the action of livestock trampling from soil thawing to regreening stage of alpine meadows.We studied the changes of growth, reproduction, and storage characteristics of Kobresia humilis in the alpine meadow of Tianzhu, Gansu Province, after 2 yr of simulated Tibetan sheep and yak trampling at five periods (prophase, initial, and middle period of thawing, initial regreening, and regreening period).Trampling period had the highest influence on K. humilis phenotypic traits, followed by livestock species. Considering the same trampling period, the negative effects of Tibetan sheep trampling on the sexual reproduction, different modular biomass, and root growth of K. humilis were lower than those of yak trampling. Sexual reproduction effort and storage growth effort were higher in Tibetan sheep trampling conditions, and vegetative reproductive effort was lower in sheep compared with yak trampling treatment conditions.There was a trade-off of resource allocation between K. humilis reproductive organs and storage organs. For the average of each indicator under different combination treatments, the vegetative reproductive effort was 11.1 times that of sexual reproduction effort. The comprehensive evaluation of K. humilis phenotypic traits showed that the trampling treatments could be divided into excellent (prophase period of thawing), good (middle period of thawing), general (initial period of thawing), and inferior (initial regreening to regreening period) grades of Tibetan sheep and yak trampling.We suggest that the actual grazing process in the cold-season pastures of this alpine meadow should be fully used at the prophase of soil thawing, implement rest-grazing for grassland and confinement from initial period of soil thawing to the forage regreening period, and appropriately increase the proportion of Tibetan sheep and reduce the number of yaks to avoid the high-intensity trampling of grassland. This will not only make optimum use of the limited grassland resources but also promote their recuperation.

Influence of snow cover on temperature field of frozen ground

Research on the effect of snow on the temperature field of frozen ground is of great significance to the laying of underground oil pipelines, design of roads, and control of frost damage in cold regions. The heat transport laws of frozen ground with phase changes under periodic temperature boundary conditions were analyzed based on data monitoring in this paper. Based on the boundary conditions determined by the monitoring data, the numerical calculations of frozen ground and subgrade with/without snow cover were carried out, and the effects of snow cover on the temperature fields of frozen ground and subgrade in cold regions were explored. Monitoring results demonstrate that the temperature at different sections of frozen ground with phase change presents a sine-like function under the periodic temperature boundary condition. According to monitoring data, when the thickness of the natural surface snow cover is about 25 cm, the daily average minimum temperature of soil at 0.1 m from the surface will rise by about 10 °C compared to that without snow cover during a year (in a cycle); nevertheless, when combined with numerical calculation, the permafrost table increases by about 2.87 m, and the permafrost base decreases by more than 5.59 m. Under the boundary conditions set in this paper, the permafrost under the subgrade disappears in a greater area due to the construction of the subgrade in the snow-covered area. In addition, the elliptical thawing soil area produced by the lower part of the slope of a snow-covered subgrade will adversely affect its stability.

Clinical Examples of Hypermirroring, Emotionally Gifted Heart Kids

Studying the effects of trampling at different stages on plant reproduction is necessary to provide the basis for grassland management. However, the changes in forage growth characteristics are still unclear under the action of livestock trampling from soil thawing to regreening stage of alpine meadows.We studied the changes of growth, reproduction, and storage characteristics of Kobresia humilis in the alpine meadow of Tianzhu, Gansu Province, after 2 yr of simulated Tibetan sheep and yak trampling at five periods (prophase, initial, and middle period of thawing, initial regreening, and regreening period).Trampling period had the highest influence on K. humilis phenotypic traits, followed by livestock species. Considering the same trampling period, the negative effects of Tibetan sheep trampling on the sexual reproduction, different modular biomass, and root growth of K. humilis were lower than those of yak trampling. Sexual reproduction effort and storage growth effort were higher in Tibetan sheep trampling conditions, and vegetative reproductive effort was lower in sheep compared with yak trampling treatment conditions.There was a trade-off of resource allocation between K. humilis reproductive organs and storage organs. For the average of each indicator under different combination treatments, the vegetative reproductive effort was 11.1 times that of sexual reproduction effort. The comprehensive evaluation of K. humilis phenotypic traits showed that the trampling treatments could be divided into excellent (prophase period of thawing), good (middle period of thawing), general (initial period of thawing), and inferior (initial regreening to regreening period) grades of Tibetan sheep and yak trampling.We suggest that the actual grazing process in the cold-season pastures of this alpine meadow should be fully used at the prophase of soil thawing, implement rest-grazing for grassland and confinement from initial period of soil thawing to the forage regreening period, and appropriately increase the proportion of Tibetan sheep and reduce the number of yaks to avoid the high-intensity trampling of grassland. This will not only make optimum use of the limited grassland resources but also promote their recuperation.

Cooling of near-pile permafrost soils in the Arctic region

This work is performed to improve or strengthen the soil in the permafrost region under building foundations or engineering structures in the conditions of the Far North. Freezing in winter and partial thawing in summer of the surface layer of permafrost are analyzed. According to the surveys on soil temperature, thawing of permafrost soils is predicted. Promising solutions are considered for the permafrost soil stabilization. The latest design solutions and developments are presented for the creation of many systems and devices for thermal stabilization of permafrost soils. A schematic diagram is suggested for the experimental installation for recording changes in ambient air temperatures and permafrost. The equipment is selected for studying the automated control system for the cooling process of casing pipe of the foundation pile and near-pile permafrost soil. An experimental installation is proposed to study the effectiveness of the automated control system. The model and simulation of this system is imple- mented in the SimInTech program. The automatic control system provides control for thermoelectric modules in automatic mode in order provide their best orientation in the ambient air temperature, depending on the soil temperature in the near-pile space of the foundation. A device is patented for stabilizing the frozen ground of a pile foundation with casing pipes containing a system for automated control for cooling process of the near-pile foundation.

Storm‐Scale and Seasonal Dynamics of Carbon Export From a Nested Subarctic Watershed Underlain by Permafrost

AbstractSubarctic catchments underlain by permafrost sequester a major stock of frozen organic carbon (C), which may be mobilized as the Arctic warms. Warming can impact C export from thawing soils by altering the depth and timing of runoff related to changing storm and fire regimes and altered soil thaw depths. We investigated C export in a first order headwater stream (West Twin Creek) and its receiving third order river (Beaver Creek) in interior Alaska using discrete sampling of dissolved organic and inorganic C (DOC and DIC) and 15‐min collection of specific conductance (SC), fluorescent dissolved organic matter (fDOM) and water discharge (Q). Storm SC‐Q relationships displayed negative slopes, indicating solute limitation and limited influence of seasonal soil thaw on storm runoff chemistry. Concurrently, fDOM‐Q displayed positive slopes that decreased over the summer, indicating flushing of a limited fDOM pool. Baseflow DIC increased over the season concurrent with soil thaw, with higher DIC at the larger scale indicating greater influence of deeper, mineral‐rich flow paths. Storm and seasonal trends were generally similar at both scales. The biggest difference was in fDOM, which displayed higher concentrations and slower depletion in the first order stream. Improved process understanding from this study can be used to better predict carbon export and cycling by stream networks as northern forests and arctic regions continue to warm.

The impacts of vegetation on the soil surface freezing-thawing processes at permafrost southern edge simulated by an improved process-based ecosystem model

Permafrost degradation due to climate warming would potentially increase the release of previously frozen soil carbon and change the carbon budget of the cold region ecosystem. The underlying permafrost degradation would be effectively mediated by soil surface freezing-thawing (FT) processes. Aboveground vegetation can regulate soil FT processes, however its effects on ground thermal transfer have not been well represented by ecosystem models. In this study, we improved the hydrothermal module of the Boreal Ecosystem Productivity Simulator (BEPS) through more careful parameterization of snowpack density, puddled water, soil organic matter and super-cooled soil water. The impacts of vegetation on the soil surface FT processes have also been investigated using the improved BEPS model and the measured soil temperature data at forest and grassland sites on the southern edge of permafrost region in Mongolia and northeastern China. The improved BEPS model performs better than the original model in simulations of soil temperature and soil FT processes. Smaller amplitudes of soil diurnal FT cycles were found in forest sites compared to grassland sites. Forest sites have delayed soil thaw timing and similar soil freezing time compared to grassland sites. Differences in snow depths and soil organic matter content due to distinct vegetation community structures have considerable influences on the disparity in soil FT processes. Thus, it is important to improve the simulation of the impacts of vegetation on soil surface FT processes for better forecasting the permafrost degradation.

Implications of measurement metrics on soil freezing curves: A simulation of freeze–thaw hysteresis

AbstractSoil freeze–thaw events have important implications for water resources, flood risk, land productivity, and climate change. A property of these phenomena is the relationship between unfrozen water content and sub‐freezing temperature, known as the soil freezing characteristic curve (SFC). It is documented that this relationship exhibits hysteretic behaviour when frozen soil thaws, leading to the definition of the soil thawing characteristic curve (STC). Although explanations have been given for SFC/STC hysteresis, the effect that ‘scale’ – particularly ‘measurement scale’ – may have on these curves has received little attention. The most commonly used measurement scale metric is the ‘support’, which is the spatial (or temporal) unit within which the measured variable is integrated or soil volume sampled. We show (a) measurement support can influence the range and shape of the SFC and (b) hysteresis can be attributed, in part, to the support and location of the measurements comprising the SFC/STC. We simulated lab measured temperature, volumetric water content (VWC), and permittivity from soil samples undergoing freeze–thaw transitions using Hydrus‐1D and a modified Dobson permittivity model. To assess the effect of measurement support and location on SFC/STC, we masked the simulated temperature and VWC/permittivity extent to match the instrument's support and location. By creating a detailed simulation of the intra‐ and inter‐support variability associated with the penetration of a freezing front, we demonstrate how measurement support and location can influence the temperature range over which water freezing events are captured. We show it is possible to simulate hysteresis in homogenous media with purely geometric considerations, suggesting that SFC/STC hysteresis may be more of an apparent phenomenon than mechanistically real. Lastly, we develop an understanding of how the location and support of soil temperature and VWC/permittivity measurements influence the temperature range over which water freezing events are captured.

Characterization of spring thaw and its relationship with carbon uptake for different types of southern boreal forest

The timing of spring thaw is of great biological and hydrological significance in seasonally frozen boreal forests, and may significantly vary for different forest types because of variability in canopy architecture, forest floor characteristics, and soil types. This study explores inter-site variability of spring thaw and its controlling factors between two boreal coniferous (jack pine and black spruce) and one deciduous (aspen) forest sites located in Western Canada. The linkages between spring thaw and carbon uptake were also investigated. Long-term (1998 to 2015) observations of snowfall, snow water equivalent (SWE), snow temperature, soil temperature, soil water content, and CO2 fluxes were analyzed. Average annual peak SWE was 112±27, 98±22, and 93±23 mm for aspen, jack pine and black spruce sites, respectively. Snow accumulation was 15% to 20% higher for the deciduous forest site than for the coniferous forest sites despite similar seasonal snowfall of 117–122 mm. The onset of snowmelt, soil thaw start date and the time to complete snow ablation were quite similar across sites but the differences in soil thaw end date were large. Completion of soil thaw at the aspen site was about 18 and 30 days earlier than the jack pine and black spruce sites, respectively. An earlier soil thaw completion at the aspen site was likely driven by the higher sub-canopy net radiation because of the leafless canopy in spring. Between the two coniferous forest sites, soil thaw completion was delayed by about 2 weeks at the black spruce site where the thicker forest floor (ground cover i.e. moss/lichen and organic soil layer) caused higher ice content and also provided better insulation to the underlying soils. Onset and net annual carbon uptake were strongly correlated with snowmelt start and end dates as well as with soil thaw start and end dates for the coniferous forest sites but the correlations were not statistically significant for the aspen site. This study advances our understanding about the variability of spring thaw, its dynamics and controls, and its relationship to carbon uptake for different forest types in the southern boreal forest.

A finite volume-based model for the hydrothermal behavior of soil under freeze-thaw cycles.

Freeze–thaw cycles in soil are driven by water migration, phase transitions, and heat transfer, which themselves are closely coupled variables in the natural environment. To simulate this complex periglacial process at different time and length scales, a multi-physics model was established by solving sets of equations describing fluid flow and heat transfer, and a dynamic equilibrium equation for phase changes in moisture. This model considers the effects of water–ice phase changes on the hydraulic and thermal properties of soil and the effect of latent heat during phase transition. These equations were then discretized by using the finite volume method and solved using iteration. The open-source software OpenFOAM was used to generate computational code for simulation of coupled heat and fluid transport during freezing and thawing of soil. A set of laboratory freezing tests considering two thermal boundary conditions were carried out, of which the results were obtained to verify the proposed model. In general, the numerical solutions agree well with the measured data. A railway embankment problem, incorporating soil hydrothermal behavior in response to seasonal variations in surface temperature, was finally solved with the finite volume-based approach, indicating the algorithm’s robustness and flexibility.