Seasonal Freeze Thaw Research Articles

Effects of seasonal freeze–thaw and wind erosion on runoff and sediment yields of three loamy slopes of Loess Plateau, China

Soil erosion is very pronounced during late winter and early spring when frozen soil thaws on the Loess Plateau of China. The alternating action of seasonal freeze–thaw and wind erosion provides sufficient material sources for water erosion in the rainy season, greatly increasing the risk and intensity of soil erosion. To quantify the effect of seasonal freeze–thaw, wind erosion and their alternating action on runoff and sediment of different slopes, rainfall tests of different slopes (control, seasonal freeze–thaw, wind erosion and seasonal freeze–thaw + wind erosion of sandy loam, silty loam and clay loam) were carried out indoors. The results showed that the mean runoff and sediment yield start times of sandy loam (9.84 and 12.75 min) were significantly greater than those of silty loam (8.92 and 9.98 min) and clay loam (4.92 and 5.98 min, P < 0.05). The start time of runoff yield after wind erosion, freeze–thaw and alternating action slopes increased by 1.14, 1.35 and 1.62 times, respectively, and the time of runoff and sediment yield on the control slope were all the lowest. The runoff rates under different slopes all substantially increased first and then gradually stabilized. On different slopes, the mean runoff rates of the three soils decreased in the order of wind erosion > alternating action > freeze–thaw > control slopes. The minimum value occurred on the alternating action slope with silty loam (161.56 ± 24.78 g/(m2 min)), and the maximum occurred on the wind erosion slope with clay loam (360.77 ± 35.98 g/(m2 min)). The process of sedimentation was similar to that of runoff. The mean sediment yield values of sandy loam (4.82 ± 0.83 kg) and silty loam (4.66 ± 0.58 kg) were much greater than those of clay loam (0.65 ± 0.17 kg). In addition, the sediment yield increase magnitudes of silty loam under freeze–thaw, wind erosion and their alternating action slopes (58.86 %, 17.47 % and 58.18 %, respectively) were higher than those of sandy loam (29.96 %, 3.23 % and 44.28 %, respectively) and clay loam (20.50 %, 13.16 % and 46.19 %, respectively). The contribution rate to sediment yield of soil types was greatest (84.01 %), followed by freeze–thaw (9.56 %) and wind erosion (0.79 %). This study can provide a reference for the study of compound erosional mechanisms and soil and water conservation in seasonal freezing-thaw zones.

Model experiments to study the hydrothermal variation and resilient modulus of soil subgrade subjected to freeze-thaw conditions

Freeze-thaw (FT) cycles are highly destructive actions on roads in seasonal frozen regions. To examine the mechanical behavior of the subgrade subjected to seasonal FT conditions in close to the actual hydrothermal environment. A hydro-thermal-mechanical (HTM) coupling model test apparatus was developed, FT tests under closed and open boundary conditions were conducted on it. In the tests, hydrothermal variations were investigated and variation behaviors of resilient modulus (MR) were analyzed and compared from the perspective of HTM coupling. The results showed that (i) the models of closed system test (CST) and open system test (OST) experienced similar freezing processes, but the difference in boundary conditions caused a significant freezing rate gap between them; (ii) hydrothermal variations in the two tests were greatly different during the freezing, moisture field variation in CST was relatively typical, while it was more complicated in OST, especially in the unfrozen zone of OST model. In addition, continuous replenishment caused the water content in OST model to be much higher than that in CST model after thawing; (iii) MR was principally related to the state of upper soil layers in both FT tests due to the distribution characteristic of additional stress, and was also affected by the water content of other frozen and unfrozen soil layers. The influence mechanism of water content on OST MR was sophisticated because of the complicated moisture field variation process; (iv) the CST MR tended towards stability after 3 FT cycles. The open system was more adverse to the bearing capacity of the subgrade, with the OST MR after 1 FT cycle even lower than that in CST after 6 cycles.

Effect of varying pore water salinity on frost susceptibility behaviour of soils

The susceptibility of soil to frost action is a major distress for engineering infrastructure constructed over it in regions that experience seasonal freezing and thawing. The soil deposits which are not otherwise problematic for use as a subgrade/foundation material can become very problematic under seasonal freeze-thaw. Since presence of dissolved salts in pore water depresses the freezing-point and increases the unfrozen water content, it can be ascertained that pore water salinity can affect soil frost susceptibility due to seasonal temperature variations by reducing the total ice content during freezing. An experimental investigation was carried out to assess the effect of pore water solute content on the behaviour of a frost susceptible soil subjected to freeze-thaw cycles in a laboratory test setup as per ASTM D5918-13. The presence of solute primarily depressed the freezing point of the soil. The heave rate, maximum heave and the frost penetration depth was found to decrease with increasing solute concentration in pore water. The effect on the thaw-CBR value, variation in water migration pattern and micro-structural changes along the depth of the sample was also examined. It was found that the presence of solutes negates the undesirable effects during freezing by controlling ice segregation, frost penetration and heaving of the soil which in turn limit the adverse weakening during thawing. The destruction to soil at micro-structural level was also restricted in the samples containing solute in their pore water.

Contrasting soil dynamics in a formerly glaciated and non-glaciated Mediterranean mountain plateau (Serra da Estrela, Portugal)

Few data are available on how soil erosion rates compare between surfaces of different ages because short-term processes often overprint the longer-term erosion signal. This study investigated the soil dynamics among two end-member sites, a formerly glaciated ('young', maximum glacial extent at 22–30 ka BP) and a non-glaciated ('old') area at the Serra da Estrela (Portugal). To disentangle soil distribution rates over different timeframes, isotopes for long-term (10Be), mid-term (δ13C) and short-term (239+240Pu) periods were applied together with principles of the percolation theory.The formerly glaciated area has soils with a lower degree of weathering and lower carbon content compared to soils of the ‘old‘, non-glaciated area. The selected isotopes and their distribution along the soil profiles revealed temporal differences in soil mixing process. It is hypothesised that the slightly higher elevation and formerly glaciated sites experienced cryoturbation effects over a longer period, while being less active or absent for the last few decades at the older, non-glaciated soils.The average long-term (millennia) soil erosion rates correspond to the expected higher rates at the younger surface and lower rates at the older surface. Once the formerly glaciated area became ice-free, soil erosion rates were high and decreased giving rise to average long-term rates of 101–140 [t km−2 yr−1] for the older surfaces and 176–248 [t km−2 yr−1] for the younger surfaces. In addition, seasonal freeze–thaw of the soils has persisted over a long period and affected the younger soils more intensively than the older soils. The current (last decades) soil redistribution rates, however, are up to one order of magnitude higher than the millennia rates and are controlled by surface angle and vegetation cover and less by soil texture. The more undulated, non-glaciated older surface had the highest short-term (decades) soil erosion rates in the range of 900–1700 [t km−2 yr−1], exhibits degrading conditions and relatively shallow soils. The younger soils, however, showed short-term (last few decades) average soil deposition rates of ∼ 230 [t km−2 yr−1]. Human impact (bush fires, grazing) is the cause for the currently strong soil degradation at the non-glaciated area.

Mechanism of snowmelt infiltration coupled with salt transport in soil amended with carbon-based materials in seasonally frozen areas

In midlatitude seasonally frozen areas, the freeze–thaw cycle affects the movement of soil water, which increases the uncertainty in salt transport and aggravates the risk of soil salinization. Based on this, a two-year field study was established on the Songnen Plain, a seasonally frozen area in northern China. Four treatments were set up: (i) control, (ii) corn stover, (iii) biochar, and (iv) combined (joint application of biochar and corn stover). The modified soil underwent seasonal freeze–thaw cycling, accompanied by the evaporation and infiltration of snowmelt water, and the soil salt migration and diffusion characteristics were determined. Both biochar and corn stover regulated the pore structure of the soil and enhanced the infiltration capacity of snowmelt water; notably, the maximum soil moisture contents in the corn stover, biochar and combined treatments increased by 9.33%, 22.12% and 16.37%, respectively, compared with that in the control group. However, biochar with abundant functional groups increased the cation exchange capacity and promoted the migration of salt ions (i.e., Na+, K+ and Cl−), and the surface soil salt content in the biochar treatment was 0.12–0.53 g/kg lower than that for the other three modes during the infiltration period. Additionally, soil water evaporation carried salts upwards, which greatly increased the salt content of the surface soil. Conversely, biochar presented a strong water-holding capacity, which reduced the ineffective evaporation of soil water, while stover acted as a barrier to hinder the return of salt. Among the treatments, the synergistic transport ability of soil salt and water was the lowest in the combined treatment. Overall, the combination of biochar and corn stover had advantages in terms of soil salt leaching and offered a healthy, effective strategy for soil salinization control in cold areas.

Interactive Effects of Rainfall Intensity and Initial Thaw Depth on Slope Erosion

Seasonal freeze–thaw processes have led to severe soil erosion in the middle and high latitudes of the world, so understanding the freeze–thaw erosion process is of great significance for soil and water conservation as well as for ecological engineering. The area affected by freeze–thaw erosion in China exceeds 13% of the national territory. However, there is little data regarding the impact of rainfall intensity and initial thaw depth on soil erosion. Here, the effects that different rainfall intensities (0.6 mm/min, 0.9 mm/min and 1.2 mm/min) and different initial thaw depths (0 cm, 2 cm, 4 cm and 6 cm) had on the soil erosion process on the loess slope were studied under simulated rainfall conditions. The results showed that the infiltration rate decrease with prolonged runoff time, and then stabilized. Runoff occurred more quickly during increasingly intense rainfall, especially when little soil had thawed. The variation in runoff and sediment yield occurred in two stages: slow growth and rapid growth. As soil thawed to greater depths, rainfall intensity had less influence on the sediment. A linear relationship existed between the cumulative runoff and the sediment yield of all treatments. (R2 &gt; 0.92, p &lt; 0.01). Rainfall intensity and thaw depth had interacting effects on erosion. At low rainfall intensities, the initial thaw depth played a leading role in the erosion process, but at higher rainfall intensities, rainfall intensity played a larger role. Stage II erosion amount accounted for more than 90% of the total erosion across all treatments. The results of this research provide a guide for furthering the understanding of the soil water erosion mechanism of thawing slopes.

Effect of Thaw Depth on Nitrogen and Phosphorus Loss in Runoff of Loess Slope

Seasonal freeze-thaw erosion is a form of soil erosion caused by the topographical characteristics and climatic factors of the hilly and gully loess regions. Seasonal freeze-thaw can damage the soil pores and cause its bulk density to change. The effects of thawing depth on runoff and Nitrogen and Phosphorus loss on the rainfall erosion of an artificial slope filled with loess soil were analyzed after a rainfall test that simulated the spring thaw period in China. The results showed that: (1) The maximum runoff yield was 33.35 mm at 4 cm thawing depth, and the minimum was 12.95 mm at 6 cm thawing depth. With the increase in runoff time, the slope infiltration rate had a decreasing trend. The loss rate of available and total Phosphorus increased with the increase in runoff rate. The rate of increase was fastest when the thawing depth was 4 cm. (2) The relationships between runoff rate and Nitrogen loss and Phosphorus loss rate can be explained by linear regression equations, and the loss rate increased as the runoff rate rose for all thawing depths. Within the 0–6 cm thawing depths, the loss of total phosphorus was the largest when the thawing depth was 4 cm, and the loss of available phosphorus was the smallest when the thawing depth was 6 cm. At the shallower thawing depths, the available Nitrogen loss represented a smaller proportion of the total Nitrogen loss compared to nitrate Nitrogen loss. However, there was a gradual rise in the available Nitrogen proportion in the total amount of inorganic Nitrogen as the thawing depth increased. (3) Total Phosphorus was the available Phosphorus with a quadratic function relationship with runoff energy and runoff power. Runoff energy mainly affected the total Nitrogen and available Nitrogen loss in runoff, whereas runoff power mainly affected total Nitrogen loss in runoff. The results of this paper can improve the understanding of runoff and Nitrogen and Phosphorus loss caused by runoff during freeze-thaw conditions.

Effects of Seasonal Freeze-Thaw and Wind Erosion on Runoff and Sediment Yields of Three Loamy Slopes of Loess Plateau, China

Effects of Seasonal Freeze-Thaw and Wind Erosion on Runoff and Sediment Yields of Three Loamy Slopes of Loess Plateau, China

Kuwait: Az Zour delayed again

The litterbags with different mesh sizes (0.125, 1.000 and 3.000 mm) were placed on the forest floor in October 2010, and collected after each of the three stages in the freeze-thaw season (OF: the onset of freezing stage; DF: the deeply frozen stage; and TS: the thawing stage). Over the whole freeze-thaw period, 14.01% ± 1.26, 20.64% ± 1.61 and 30.89% ± 0.70 of N released from fir litter in the litterbags with 0.125, 1.000 and 3.000 mm, respectively. The contributions of meso- and macro-fauna to N releases were 21.45% ± 3.80 and 33.18% ± 5.39, respectively. Macro-fauna contributed more to N releases than meso-fauna regardless of decomposition stages in the freeze-thaw period. Compared with other stages in the freeze-thaw period, higher contributions of both macro- and meso-fauna were observed at DF stage, and the lower contributions at TS stage. The results suggested that soil fauna have a great contribution to N releases during litter decomposition in the freeze-thaw period, but the contribution was significantly affected by temperature dynamics and the body size of soil fauna.

Freeze/thaw onset detection combining SMAP and ASCAT data over Alaska: A machine learning approach

In the context of global warming, permafrost degrades gradually. To cope with the instability of the cryosphere, it is very important to strengthen the monitoring of the seasonal freeze–thaw cycle. At present, active and passive microwave remote sensing data are widely used in freeze/thaw (F/T) onset detection. There is some potential to improve accuracy through the combination of active and passive microwave data. Compared with the traditional method for combination, the machine learning algorithm has a stronger nonlinear expression ability. Therefore, it is advisable to use machine learning to combine multi-source data for freeze/thaw onset detection. In this study, the temporal change detection method is applied to SMAP data and ASCAT data respectively for preliminary detection. Then the Random Forest algorithm (RF) is used to combine the preliminary results of active and passive microwave data with site observation to estimate the freeze/thaw onsets more accurately. The method is validated with data obtained in Alaska from 2015 to 2019. The accuracy evaluation shows that the proposed method can effectively improve the accuracy of freeze/thaw onset detection. The predicted distribution of the freeze/thaw cycle indicates that the variation of the freeze–thaw cycle is closely related to latitude. In general, the proposed method based on machine learning is promising in the research of freeze–thaw state monitoring.

Do freeze-thaw cycles affect the cadmium accumulation, subcellular distribution, and chemical forms in spinach (Spinacia oleracea L.)?

To date, although there are many studies investigating the toxicity of heavy metal to plant, little research exists in the seasonal freeze-thaw (FT) regions where FT cycles often happen during the plant growing process. To reveal the adaptive mechanisms of plants to the combination stresses of cadmium (Cd) and FT, the Cd accumulation, subcellular distribution, chemical forms, and antioxidant enzyme activity (peroxidase (POD)) were investigated in spinach (Spinacia oleracea L.) growing under different soil Cd levels (i.e., 0.10 mg Cd kg−1 soil (low), 1.21 mg Cd kg−1 soil (medium), and 2.57 mg Cd kg−1 soil (high)). Compared to the non-freeze-thaw (NFT) treatments, higher Cd concentrations in the root and lower translocation factors from root to leaf were found for the plants experiencing FT cycles. FT significantly decreased the Cd concentrations in the leaves under the low- and medium-Cd treatments, while similar values were found for the high-Cd treatments. Generally, FT could decrease the concentrations and proportions of Cd stored in the cell wall and soluble fractions and increase them in the organelle fractions for the medium- and high-Cd treatments, while opposite tendency was found for the low-Cd treatments. Moreover, larger Cd amounts in the inorganic and water-soluble forms were found for the low- and medium-Cd treated plants under FT, while lower values were found for the high-Cd treatments. Additionally, POD, which presented higher activities at the low- and medium-Cd treatments and lower activities at the high-Cd treatments under FT, were also significantly influenced by the Cd × FT interaction. This study indicated that FT could significantly change the accumulations of Cd in plant, and it provided a new insight into the Cd accumulation by plants in the seasonal FT region.

Freeze-thaw cycles change the physiological sensitivity of Syntrichia caninervis to snow cover

Spring, especially the freeze–thaw season, is considered the key period for the growth and carbon sequestration of desert mosses. It is not clear how the change in environment water and temperature affects the physiological characteristics of desert mosses in freeze–thaw season. In this study, the effects of water and freeze–thaw cycles on the physiological characteristics of Syntrichia caninervis were assessed by manipulating the increase or removal of 65% snow and changes in the freeze–thaw cycles. The results showed that the changes in snow depth, freeze–thaw cycles, and their interaction significantly affected the plant water content, osmoregulatory substances content, antioxidant substance, and antioxidant enzyme activities. The contents of free proline, soluble sugar, ascorbic acid (AsA), reduced glutathione (GSH), and malondialdehyde (MDA), and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities increased significantly with the decrease in snow depth and freeze–thaw cycles. POD and free proline were the most sensitive to the snow depth and freeze–thaw cycles, while SOD and CAT were the least sensitive. Therefore, compared with the increase in freeze–thaw cycles, the reduction in freeze–thaw cycles weakened the physiological sensitivity of S. caninervis to snow depth changes.

Response of soil bacterial communities to organic carbon input under soil freeze-thaw in forest ecosystems

The soil microbial community controls the biogeochemical cycle of elements critical to plant growth. Different carbon input modes have different effects on soil carbon storage and the microbial community, but the effects of carbon input control on soil microbial diversity and community structure in temperate forests remain unclear. We used high-throughput 16SrRNA gene sequencing and ecological network analysis methods to analyze the soil bacterial community, symbiotic network, and key species of three different carbon input treatments (litter removal, root removal, litter and root removal) in temperate natural secondary forests during the freeze-thaw season and growing season. The results showed that the change in the carbon source input led to a change in the way in which soil bacteria used carbon, which was mainly manifested as follows: (1) The relative abundance of Acidobacteria, which was oligotrophic bacteria, significantly decreased in the sample plots where the root system was removed. (2) In the litter removal treatment, the abundance of bacteria with functions related to the absorption of CH4 decreased. (3) The correlation between the module characteristic genes in the bacterial network analysis and the physical and chemical properties of soil, CK modules were grouped separately, and the change in the correlation may also indicate the change in the way soil bacteria use carbon. Second, the influence of belowground roots on the soil bacterial community structure was more significant than that of aboveground litter. The root system had a greater influence on the soil bacterial community. Third, the decrease of organic carbon input reduced the stability of the soil bacterial network, and the proportion of positive connections in the bacterial network for litter removal and root treatment increased significantly, indicating that these bacterial communities had the same change trend as the fluctuation of the environment. Finally, the freeze-thaw season had a greater impact than the growing season on bacterial diversity, community structure, and function. The freeze-thaw process allowed the bacterial community to respond to root removal more significantly, and the structural changes were mainly due to changes in temperature, water content, dissolved organic carbon, and nitrate nitrogen.

Effects of Biochar on Sediment Transport and Rill Erosion after Two Consecutive Years of Seasonal Freezing and Thawing

This research explored the effects of biochar on slope runoff and sediment transport processes and the hydrodynamic mechanism of rill erosion under the seasonal freeze–thaw climate in the black soil area of Northeast China. The four slopes of 1.8, 3.6, 5.4 and 7.2° were set, corn straw biochar was used, and three biochar contents of 0 kg m−2 (B0 treatment), 6 kg m−2 (B6 treatment) and 12 kg m−2 (B12 treatment) were applied. The experimental plot was placed outdoors to simulate the freeze–thaw cycle of sloping farmland under natural conditions. Three artificial simulated rainfall tests were carried out before the end of seasonal freeze–thaw cycles and spring sowing date (May) in 2018 and 2019. The sediment transport process of runoff and the variation of hydrodynamic parameters in rills were analyzed under one and two seasons of freezing and thawing in natural outdoor conditions. The results show that biochar has a positive effect on reducing rainfall runoff and soil loss after one year and two years of seasonal freezing and thawing. The effect of biochar on the sediment concentration of slope runoff increased with increasing application time; in the second year, the B6 and B12 treatments reduced the sediment concentration by 5.5–14.8% and 3.3–13.6%, respectively, compared with the values of the first year. The Reynolds number (Re) in the rill flow after the B6 and B12 treatments decreased with increasing duration, which effectively reduced the turbulence degree of the flow on the rill of the slope. With the increase in duration, the rill critical erosion power increased; in 2018 and 2019, the critical shear force, critical runoff power and critical unit runoff power were 0.403 Pa, 0.098 m s−1, and 0.002 N m−1 and 0.497 Pa, 0.124 m s−1, and 0.003 N m−1, respectively. This result indicates that increasing the duration and number of seasonal freeze–thaws can promote the development of biochar control of the runoff and sediment processes on slope and rill development.

Analysis of Groundwater Depletion/Inflation and Freeze–Thaw Cycles in the Northern Urumqi Region with the SBAS Technique and an Adjusted Network of Interferograms

This work investigated the large-scale ground deformations threatening the Northern Urumqi district, China, which are connected to groundwater exploitation and the seasonal freeze–thaw cycles that characterize this frozen region. Ground deformations can be well captured by satellite data using a multi-temporal interferometric synthetic aperture radar (Mt-InSAR) approach. The accuracy of the achievable ground deformation products (e.g., mean displacement time series and related ground displacement time series) critically depends on the number and quality of the selected interferograms. This paper presents a straightforward interferogram selection algorithm that can be applied to identify an optimal network of small baseline (SB) interferograms. The selected SB interferograms are then used to produce ground deformation products using the well-known small baseline subset (SBAS) Mt-InSAR algorithm. The developed interferogram selection algorithm (ISA) permits the selection of the group of SB data pairs that minimize the relative error of the mean ground deformation velocity. Experiments were carried out using a group of 102 Sentinel-1B SAR data collected from 12 April 2017 to 29 October 2020. This research study shows that the investigated farmland region is characterized by a maximum ground deformation rate of about 120 mm/year. Periodic groundwater overexploitation, coupled with irrigation and freeze–thaw phases, is also responsible for seasonal (one-year) ground displacement signals, with oscillation amplitudes up to 120 mm in the zones of maximum displacement.

Metaplasmidome-encoded functions of Siberian low-centered polygonal tundra soils

Plasmids have the potential to transfer genetic traits within bacterial communities and thereby serve as a crucial tool for the rapid adaptation of bacteria in response to changing environmental conditions. Our knowledge of the environmental pool of plasmids (the metaplasmidome) and encoded functions is still limited due to a lack of sufficient extraction methods and tools for identifying and assembling plasmids from metagenomic datasets. Here, we present the first insights into the functional potential of the metaplasmidome of permafrost-affected active-layer soil—an environment with a relatively low biomass and seasonal freeze–thaw cycles that is strongly affected by global warming. The obtained results were compared with plasmid-derived sequences extracted from polar metagenomes. Metaplasmidomes from the Siberian active layer were enriched via cultivation, which resulted in a longer contig length as compared with plasmids that had been directly retrieved from the metagenomes of polar environments. The predicted hosts of plasmids belonged to Moraxellaceae, Pseudomonadaceae, Enterobacteriaceae, Pectobacteriaceae, Burkholderiaceae, and Firmicutes. Analysis of their genetic content revealed the presence of stress-response genes, including antibiotic and metal resistance determinants, as well as genes encoding protectants against the cold.

Responses of aggregates and associated soil available phosphorus, and soil organic matter in different slope aspects, to seasonal freeze–thaw cycles in Northeast China

Freeze-thaw is an important factor that affects soil aggregate size and integrity in mid-high latitudes or mountainous regions, which in turn impacts soil erosion. However, there are limited studies on the responses of aggregates and associated soil available phosphorus (AP), as well as soil organic matter (SOM) in different slope aspects to seasonal freeze–thaw cycles (FTCs). In this regard, soil samples at different depths (0–5 [D5], 5–10 [D10], 10–15 [D15], and 15–20 cm [D20]) were collected from sunny (SW) and shady (NE) slopes in Meihekou, Northeastern China. Temporal changes in aggregate size distribution, AP (extracted with 0.5 mol L−1 NaHCO3), and SOM of SW and NE were analyzed during one FTCs season (from October 2017 to March 2018). Seasonal FTCs significantly (p < 0.05) influenced aggregate size distribution and associated AP content. The results indicated that although there were similar patterns of change in soil aggregate size distribution over time between SW and NE, NE was more sensitive to seasonal FTCs than SW. The greatest reduction and increment rates were observed in aggregates sized > 5 mm and < 0.25 mm, respectively, at D5 in both SW (reduction rate = 44.9%, increment rate = 63.1%) and NE (reduction rate = 73.3%, increment rate = 76.3%). The mean weight diameters were significantly (p < 0.05) decreased by 0–22.6% in SW and 13.4–43.7% in NE at different soil depths after the seasonal FTCs. Good linear function relationships were observed between the proportion of aggregate fractions and associated AP content for aggregate sizes < 0.25 mm (r2 = 0.38**), 1–2 mm (r2 = 0.32**), and 2–5 mm (r2 = 0.42**) in SW and for > 0.25 mm (r2 = 0.68**), 0.25–1 mm (r2 = 0.38**), 1–2 mm (r2 = 0.52**), and 2–5 mm (r2 = 0.64**) in NE during the seasonal FTCs. The associated AP content showed positive correlations with the proportion of aggregates sized <0.25 mm and 0.25–1 mm and negative correlations with the proportion of aggregates sized 1–2 mm, 2–5 mm, and >5 mm in both SW and NE. The SOM was less sensitive to seasonal FTCs. After the seasonal freeze–thaw period, only the SOM content of partial aggregate sizes decreased significantly (p < 0.05) in NE, whereas there were no such significant changes in SW. Our results demonstrated that slope aspect is a key driver of the different responses of aggregates and associated AP and SOM content during the seasonal FTCs and that slope information could be useful for exploring soil erosion and nutrient loss in freeze–thaw agricultural ecosystems.

Numerical Study on Thermal Insulation of a Roadway Tunnel at Southeast Edge of the Qinghai-Tibet Plateau

Tunnels in seasonal frost regions are heavily affected by damage related to icing problem and cyclic freeze-thaw of surrounding rock. To mitigate frost related damage, thermal insulation is widely used at entrance and exit section of tunnels. In thermal insulation design, length of the insulated section and thickness of the thermal insulation layer (TIL) are two important parameters. In this study, a coupled mathematical model of heat and moisture transfer was built for tunnels in cold regions. Then, field observed air temperatures at entrance section of a roadway tunnel at Altun Mountain, southeast edge of the Qinghai-Tibet Plateau, were collected and analysed. Based on the mathematical model and field observed inside air temperatures, seasonal freeze-thaw of surrounding rocks of the tunnel entrance was numerically investigated with consideration of the thicknesses and thermal conductivities of insulation layer. The results showed that, within the tunnel, the air has its mean annual temperature increase and the its amplitude decrease with increase in the distance from the entrance. The significant variations mainly occurred within the section 375 m from the entrance. Without the TIL, the maximum seasonal freeze depth of surrounding rocks at the entrance can reach to 1.5 m. To ensure that the surrounding rocks do not experience freezing, the minimum thickness of the TIL with a thermal conductivity of 0.037 W/(m·°C) should be 7 cm. While when the thickness of the TIL is 5 cm, its thermal conductivity should be not greater than 0.014 W/(m·°C).

Ground‐penetrating radar, electromagnetic induction, terrain, and vegetation observations coupled with machine learning to map permafrost distribution at Twelvemile Lake, Alaska

AbstractWe collected ground‐penetrating radar (GPR) and frequency‐domain electromagnetic induction (FDEM) profiles in 2011 and 2012 to identify the extent of permafrost relative to surface biomass and solar insolation around Twelvemile Lake near Fort Yukon, Alaska. We compared a Landsat‐derived biomass estimate and modeled solar insolation from a digital elevation model to the geophysical measurements. We show correspondence between vegetation type and biomass relative to permafrost extent and seasonal freeze–thaw. Thicker permafrost (≥25 m) was covered by greater biomass, and seasonal thaw depths in these regions were minimal (1 m). Shallow (1–3 m depth) and thin (20–50 cm) newly forming permafrost or frozen layers from the previous winter occurred below northward oriented slopes with thin biomass cover. South‐facing slopes exhibited permafrost when there was enough biomass to shield incoming solar energy. We developed an artificial neural network to predict permafrost extent across the broader region by mapping GPR‐observed instances of permafrost to FDEM, biomass, and terrain observations with 90.2% accuracy. We identified a strong linear correlation (r = −0.77) between permafrost probability and seasonal thaw depth, indicating that our models may also be used to explore thaw patterns and variability in active layer thickness. This study highlights the combined influence of biomass and terrain on the presence of permafrost and the value of evaluating such parameters via remote sensing to predict permafrost spatial or temporal variability. Incorporating diverse geophysical datasets with in‐situ validation into machine learning models demonstrates a useful approach to upscale estimated permafrost extent across large Arctic expanses.

Mechanistic Investigation of Typical Loess Landslide Disasters in Ili Basin, Xinjiang, China

In the period from 2010 to 2018, a total of 302 geological disasters occurred in the Xinjiang Autonomous Region, China, of which 136 occurred in the Ili Basin. Compared with those in other regions, the loess landslides in the Ili Basin are strongly influenced by the seasonal freeze–thaw effect. Taking the No. 2 Piliqinghe landslide as an example and based on the field geological investigation, it was found in the present study that the main triggering factors of this landslide were the snowmelt erosion of the slope toe and meltwater infiltration into the trailing edge of the slope. The mechanism of loess landslide instability was studied using numerical simulation. The results showed that (1) the Piliqinghe landslide disaster was formed through a process composed of the local sliding of the leading edge → the creep sliding and tension cracking of the slope surface → the overall sliding stage; (2) the infiltration of snowmelt was the direct cause of the landslide formation; (3) the fluvial erosion and softening caused the soil of the slope toe to slide. The results can be used as a reference for the analysis of the disaster mechanism and movement characteristics of similar loess landslides.