Soil Freezing Research Articles

Freezing and Thawing of Enclosing Structures and Foundation Soils Taking into Account the Effects of Solar Energy: Part 2. Problem Statement

Part 1 provides general information about some of the physical properties of water, ice, and snow necessary to understand the non-stationary processes of freezing and thawing of enclosing structures of wet foundation soils. Part 2 presents the physical and mathematical formulation of the problem of freezing of wet soil, the solution of Lyame and Clapeyron, the solution of Stefan, the physical and mathematical formulation of the problem of freezing of the ribbon foundation. The following are considered: description of the process of freezing of a single-layer enclosing structure considering the phase transformations of moisture in the material of the structure according to V.N. Bogoslovsky and the process of freezing of an unlimited plate considering the phase transformations of moisture in the material of the structure according to A.V. Lykov. Mathematical model of non-stationary heat transfer process in wet layered media. Based on the method of small-time intervals, solutions of boundary value problems for frozen and thawed zones in the region of large and small Fourier numbers are given. Prospects for the application of the proposed mathematical models to describe the processes of freezing and enclosing structures and foundation soils are outlined.

Analysis and partitioning of terrestrial water storage in the Yellow River source region

AbstractIn order to increase the capability to understand and quantify the spatial differences in terrestrial water storage (TWS), and to reflect the unique energy balance processes and soil freeze–thaw mechanisms in the Qinghai‐Tibet Plateau (QTP), this study improved the energy balance processes of the water and energy transfer processes model, including its surface radiation calculations and snowmelt module. By integrating these improvements, a water and energy transfer processes model in Qinghai‐Tibet Plateau (WEP‐QTP) for the Yellow River source region (YRSR) is developed. Using the improved WEP‐QTP model to perform simulations, we assessed the daily changes in snow cover, soil moisture (SM), permafrost (PM), and groundwater storage (GWS) in the YRSR. Our analysis revealed an increase in TWS of 0.24 mm/yr from 1961 to 2020. Snow water equivalent (SWE), SM, PM, and GWS have proportional contributions of 8.33%, 216.67%, −154.17%, and 29.17% to the increased TWS, respectively. SM is the primary component of TWS. Temperature (T), precipitation (P), evapotranspiration (E), and solar radiation (Rs) influence the spatiotemporal variations in TWS, as well as those of its components. The increase in P is the primary cause for the rise in TWS, SWE, and SM, while the increase in T predominantly contributes to the decrease in PM. Furthermore, permafrost degradation and climate‐induced warming and humidification lead to increased infiltration, resulting in elevated GWS.

Pore‐scale freezing of a sandy saline soil visualized with micro‐computed tomography

AbstractSandy saline soils are widely distributed and commonly experience seasonal or long‐term freezing, yet the freezing process in these soils is rarely studied. This research utilized in situ X‐ray computed tomography (CT) to visualize pore‐scale freezing processes in sandy saline soils under various initial water and salt contents. Micron‐resolution observations of pore ice and unfrozen water produced new insights into the preferential orientation and grouping of pore ice crystals, intersections between different pore ice crystal groups causing anisotropic behavior, decreasing pore ice crystal size under faster freezing rates, and the formation of interconnected networks of both pore ice and unfrozen water upon freezing. From a thermodynamic perspective, the salt content in the unfrozen liquid is dependent on the local temperature as described by water–salt phase diagram. Furthermore, the local volume ratio between unfrozen water and pore ice reflects the initial salt content and salt mass transfer occurring due to both diffusion and fluid flow processes. This work improves the understanding of complex freezing phenomena in sandy saline soils through high‐resolution evidence of crystallization patterns, transformation mechanisms, and coupled heat‐mass transfer.

Influence paradigms of soil moisture on land surface energy partitioning under different climatic conditions

Soil moisture (SM) directly controls the land surface energy partition which plays an important role in the formation of extreme weather events. However, its dependence on specific climatic conditions is not thoroughly understood due to the complexity of soil moisture effects. Here, we examine the relationship between SM and surface energy partitioning under different climate conditions, and identify the influence paradigms of soil moisture on surface energy partition. We find that temperature changes can explicitly determine the impact paradigm of different physical processes, i.e. evapotranspiration, soil freezing and thawing, and such influence paradigms are also affected by atmospheric aridity (VPD). Globally, there are five paradigms that effects on surface energy partitioning, including the warm-wet paradigm (WW), transitional paradigm (TP), warm-dry paradigm (WD), cool-wet paradigm (CW) and cold paradigm (CP). Since 1981, the global area proportion for TP is observed to increase pronouncedly. We also find that the critical SM threshold exhibits regional variations and the global average is 0.45 m3/m3. The identified paradigms and their long-term change trends provide new insights into the global intensification of land-atmosphere interaction, which has important implications for global warming and the formation of heatwaves.

Soil freeze–thaw cycles affect spring phenology by changing phenological sensitivity in the Northern Hemisphere

The use of frozen soil-vegetation feedback for predictive models is undergoing enormous changes under rapid climate warming. However, the influence of soil freeze–thaw (SFT) cycles on vegetation phenology and the underlying mechanisms remain poorly understood. By synthesizing a variety of satellite-derived data from 2002 to 2021 in the Northern Hemisphere (NH), we demonstrated a widespread positive correlation between soil thawing and the start of the growing season (SOS). Our results also showed that the SFT cycles had a significant impact on vegetation phenology mainly by altering the phenological sensitivities to daytime and nighttime temperatures, solar radiation and precipitation. Moreover, the effects of SFT cycles on the sensitivity of the SOS were more pronounced than those on the sensitivity of the end of the growing season (EOS) and the length of growing season (LOS). Furthermore, due to the degradation of frozen soil, the changes in phenological sensitivity in the grassland and tundra biomes were significantly larger than those in the forest. These findings highlighted the importance of incorporating the SFT as an intermediate process into process-based phenological models.

Combined Effect of Freeze–Thaw Cycles and Biochar Addition on Soil Nitrogen Leaching Characteristics in Seasonally Frozen Farmland in Northeast China

Global climate warming and increased climate variability may increase the number of annual freeze–thaw cycles (FTCs) in temperate zones. The occurrence of more frequent FTCs is predicted to influence soil carbon and nitrogen cycles and increase nitrogen leaching. Biochar has the potential to increase soil organic carbon storage and decrease nitrogen leaching. This study aims to investigate the impact of freeze–thaw cycles (FTCs) on soil nitrogen leaching in temperate zones, considering the potential exacerbation of FTCs due to global climate warming and increased climate variability. This study focuses on how biochar, a carbon-rich material produced from biomass, might mitigate nitrogen leaching by influencing soil characteristics. This study explores the interactions between different laboratory-simulated FTC frequencies (ranging from 0 to 12 cycles) and various biochar addition ratios (0%, 2%, 4%, and 6% w/w) on soil nitrogen leaching based on a total of 60 soil columns. Pearson correlations between the soil quality indicators and nitrogen leaching characteristics were detected, and partial least squares path modeling (PLS-PM) was used to assess the effects of the FTCs, biochar addition ratios, and soil quality indicators on the nitrogen leaching content. The results showed that the amount of leached soil NH4+-N and NO3−-N reached 0.129–1.726 mg and 2.90–7.90 mg, respectively. NH4+-N and NO3−-N first increased and then decreased under the FTCs, with the highest values being observed after the 6th FTC. As the biochar addition ratio increased, the NH4+-N and NO3−-N contents decreased. Correlation analysis showed that the nitrogen leaching content was significantly related to the soil pH, soil organic matter (SOM), NH4+-N content, and microbial biomass carbon content (MBC) (p < 0.01). The results of the conceptual path model revealed that nitrogen leaching characteristics were significantly affected by the pH, SOM, soil nitrogen content, and biochar addition ratio. Our results suggest that biochar addition can help reduce nitrogen leaching in farmland soil in areas with black soil and seasonal freeze–thaw cycles.

Non-local modelling of freezing and thawing of unsaturated soils

A large part of the earth’s surface is covered by seasonally or permanently frozen soils. Considering the negative impact of climate change, future development of such regions can be underpinned by mathematical methods for accurate analysis of heat and moisture transport in freezing and thawing soils. Reported in this paper is a novel non-local formulation of water and heat transport in unsaturated soils. The formulation uses bond-based peridynamics (PD) and consists of a set of integral–difference formulations of energy and mass conservation. Specific features of freezing/thawing soils are incorporated by a combination of van Genuthcen and Clausius–Clapeyron relations. Computational results are compared with four sets of laboratory experiments to demonstrate the efficiency of the developed approach. The model can be used to analyse the effect of water flow on heat transfer in soils during thawing of permafrost soils. Further, it can be applied in modelling climate change effects, and can be used for construction of coupled physically justified models of frost heave.

Effect of Freeze-Thaw Cycles on the Shear Strength of Root-Soil Composite.

A large alpine meadow in a seasonal permafrost zone exists in the west of Sichuan, which belongs to a part of the Qinghai-Tibet Plateau, China. Due to the extreme climates and repeated freeze-thaw cycling, resulting in a diminishment in soil shear strength, disasters occur frequently. Plant roots increase the complexity of the soil freeze-thaw strength problem. This study applied the freeze-thaw cycle and direct shear tests to investigate the change in the shear strength of root-soil composite under freeze-thaw cycles. This study examined how freeze-thaw cycles and initial moisture content affect the shear strength of two sorts of soil: uncovered soil and root-soil composite. By analyzing the test information, the analysts created numerical conditions to foresee the shear quality of both sorts of soil under shifting freeze-thaw times and starting moisture levels. The results showed that: (1) Compared to the bare soil, the root-soil composite was less affected by freeze-thaw cycles in the early stage, and the shear strength of both sorts of soil was stabilized after 3-5 freeze-thaw cycles. (2) The cohesion of bare soil decreased more than that of root-soil composite with increasing moisture content. However, freeze-thaw cycles primarily influence soil cohesion more than the internal friction angle. The cohesion modification leads to changes in shear quality for both uncovered soil and root-soil composite. (3) The fitting equations obtained via experiments were used to simulate direct shear tests. The numerical results are compared with the experimental data. The difference in the soil cohesion and root-soil composite cohesion between the experiment data and the simulated result is 8.2% and 17.2%, respectively, which indicates the feasibility of the fitting equations applied to the numerical simulation of the soil and root-soil composite under the freeze-thaw process. The findings give potential applications on engineering and disaster prevention in alpine regions.

Psychrophiles to control ice-water phase changes in frost-susceptible soils

The phase changes of soil water or porous media have a crucial influence on the performance of natural and man-made infrastructures in cold regions. While various methods have been explored to address the impacts of frost-action arising from these phase changes, conventional approaches often rely on chemicals, mechanical techniques, and the reuse of waste materials, which often exhibit certain limitations and environmental concerns. In contrast, certain organisms produce ice-binding proteins (IBPs) or antifreeze proteins (AFPs) to adapt to low temperatures, which can inhibit ice crystal growth by lowering the freezing point and preventing ice crystallization without the need for external intervention. This study explores the potential of three psychrophilic microbes: Sporosarcina psychrophile, Sporosarcina globispora, and Polaromonas hydrogenivorans, to induce non-equilibrium freezing point depression and thermal hysteresis in order to control ice lens growth in frost-susceptible soils. We hypothesize that the AFPs produced by psychrophiles will alter the phase changes of porous media in frost-susceptible soils. The growth profiles of the microbes, the concentration of released proteins in the extracellular solution, and the thermal properties of the protein-mixed soils are monitored at an interval of three days. The controlled soil showed a freezing point of − 4.59 °C and thermal hysteresis of 4.62 °C, whereas protein-treated soil showed a maximum freezing point depression of − 8.54 °C and thermal hysteresis of 7.71 °C. Interestingly, except for the controlled sample, all the protein-treated soil samples were thawed at a negative temperature (minimum recorded at − 0.85 °C). Further analysis showed that the treated soils compared to porous media mixed soil freeze (1.25 °C vs. 0.51 °C) and thaw (2.75 °C vs. 1.72 °C) at extensive temperature gap. This freezing and thawing temperature gap is the temperature difference between the beginning of ice core formation and completed frozen, and the beginning of ice core thawing and completed thawed for the treated soil samples selected from different incubation days. Overall, this study presents a novel bio-mediated approach using psychrophilic microbes to control ice formation in frost-susceptible soils.

Predicted Contribution of Snowmelt to Subsurface Drainage Discharge in Two Subsurface-Drained Fields in Southern Quebec and Ontario

Highlights RZ-SHAW model delivered a satisfactory simulation for winter subsurface drainage discharge. Snowmelt dominated the drainage discharge during the winter and spring snowmelt seasons in southern Quebec. Snowmelt contributed to 29% and 18% of winter and annual drainage discharge, respectively, in southern Ontario. Abstract. Late winter/early spring has been recognized as a critical period for subsurface drainage discharge and associated nutrient losses due to snowmelt and rainfall in croplands under cold, humid climates in North America and Europe. Although the detachment and transport processes of soil particles under snowmelt and rainfall are known to be different, studies quantifying the contribution of snowmelt to winter drainage discharge are limited. This study aims to investigate the contribution of snowmelt to subsurface drainage discharge at two winterized experimental sites in southern Quebec and Ontario, Canada, using observed data and the Root Zone Water Quality Model-Simultaneous Heat and Water model (RZ-SHAW model). The RZ-SHAW model was calibrated and validated against the measured snow depth and year-round subsurface drainage discharge data from 2021 to 2023 at St. Emmanuel, Quebec, and from 2000 to 2003 at Harrow, Ontario. RZ-SHAW demonstrated satisfactory Nash-Sutcliffe model efficiency values (NSE = 0.50) for simulating snow depth, soil temperature, and winter subsurface drainage discharge. The calibrated RZ-SHAW model was used to simulate the contribution of snowmelt to subsurface drainage for the two sites from 1990 to 2022. The snowmelt was predicted to contribute 55% and 44% of the winter and annual subsurface drainage discharge for the cropland in Southern Quebec. In contrast, for the southern Ontario site, the contribution of snowmelt to winter and annual subsurface drainage discharge was 29% and 18%, respectively. Considering that snowmelt in Southern Quebec contributed a significant fraction of winter and annual subsurface drainage discharge, more attention should be devoted to adapting and developing new winter management for nutrient loss in future research in the region. Keywords: Cold region, Cropland drainage, Drainage partition, RZ-SHAW, RZWQM2, Snowmelt, Soil freeze and thaw, Winter subsurface drainage.

Ограничения применения колесных тракторов в технологиях растениеводства по уплотняющему воздействию (в условиях Приамурья)

The natural conditions of the Amur region are characterized by seasonal soil freezing and thawing. In winter, it freezes to a depth of 2.5 m. In July, it completely thaws. Field work on soil preparation and sowing of early grain crops begins at a time when the soil thaws by only 0.08–0.10 m. In early spring field work, a tractor with high values of normal soil pressures can be used (without limiting the operating weight). The frozen under layer saves the soil from degradation. As the soil thaws, it is necessary to adhere to the established norms of mechanical action on soil, taking into account its physical and mechanical characteristics. The purpose of research is to reduce soil compaction from mechanical effects of tractor wheel thrusters. The objective of research is to substantiate the limits of wheeled tractor use in field work according to the permissible level of sealing effect. Theoretical and empirical methods are applied using statistical processing of experimental data. The change in soil density and compaction effect index are studied depending on the normal load transmitted by wheeled tractor movers. The values of distribution of operating weight along axes, maximum loads and value of compaction effect index of running systems of domestic and imported wheeled tractors used in crop production technologies of the Amur region are given. The limits of change in soil density depending on normal load under the wheel drive are given. The dependence of compaction effect index on the operating weight of tractor, axle load, wheel formula and number of unit passes along the track is established. Recommendations on the use of wheeled tractors in field work, depending on the time of their execution are given.

Analysis on the synergistic variation of soil freezing and pile foundation bearing capacity in permafrost regions

The construction of bored piles in permafrost regions disturbs the thermal stability of frozen soil, leading to decreased early bearing capacity of the pile foundation. As the permafrost ground temperature influences the area, the pile-soil gradually undergoes refreezing, resulting in a continuous enhancement of the pile foundation's bearing capacity. To study the synergistic variation law of soil refreezing and bearing capacity of bridge pile foundation in permafrost regions, two test piles with a length of 15 m and a diameter of 1.2 m were poured based on the actual bridge engineering construction project in the permafrost region of Daxing’an mountains, China. The intelligent temperature monitoring system was set up inside and in the area where the test pile was located. Combined with the collected temperature data, the refreezing state of pile-soil was comprehensively judged. The self-balancing method was employed to assess the bearing capacity of pile foundation before and after refreezing, unveiling the variation patterns in friction resistance at different soil layers and pile-end resistance. On this basis, a finite element model was established to analyze the interaction between pile side friction and pile tip resistance at varying depths of frozen soil. The test and analysis results revealed that the permafrost temperature in the pile foundation area was −1.9℃.Following pile-soil refreezing, the ultimate bearing capacity of the pile foundation increased by 2232 kN, and the growth rate was 42.9%. The friction resistance of each soil (rock) layer on the pile side increased, with the growth rate ranging from 15% −75%.

Experimental Investigation on the Effect of Salt Solution on the Soil Freezing Characteristic Curve for Expansive Soils

With the development of the Belt and Road Initiative in China, high-speed railways are booming and inevitably pass through seasonal frost regions. In Nanyang basin, due to seasonal changes, railway subgrades will undergo frost heaving and thawing subsidence. The freezing characteristics of the soil are characterized by the freezing characteristic curve, and the important factors affecting the freezing characteristic curve are the content of expansive clay minerals in the soil and the salt solution. Therefore, three soil samples with different montmorillonite contents were saturated with salt solutions of different concentrations, and the freezing temperature of the soil samples was controlled by a cold bath. After the temperature equilibrium, the frozen stable soil samples were put into a nuclear magnetic resonance instrument to test the unfrozen water content, and the relationship between the freezing temperature and the unfrozen water content of expansive soil under different salt solution concentrations was obtained. Additionally, a unified model was used to simulate the test results. The results show that SFCC shifts to the left, that is, the sodium chloride salt solution reduces the freezing point of the soil sample so that it has more unfrozen water at the same temperature. At the same time, the soil’s freezing characteristic curves are closely related to content of expansive clay minerals in the soil. The more expansive clay mineral content, the greater the corresponding unfrozen water content. These results provide some basic insights for improving the frost heave and thaw subsidence problems of railway subgrades in seasonal permafrost regions, which will have a positive impact on promoting the management and rational application of land resources and the promotion of sustainable development.

Retrieving freeze-thaw states using deep learning with remote sensing data in permafrost landscapes

The soil freeze–thaw (FT) cycle is a critical component of the terrestrial cryosphere and plays a significant role in hydrological, ecological, climatic, and biogeochemical processes within permafrost landscapes. The FT states can be monitored with in-situ field measurements, but these procedures are costly and limited to single chosen sites. Remote sensing data provides the opportunity to collect information repeatedly across extensive geographical areas. To explore a more effective way to monitor the FT states in the terrestrial cryosphere, in this study, we used microwave and optical remote sensing data and introduced the Deep Learning approach to simulate the soil FT states in the western part of Nunavik, Canada.Two networks, Multilayer Perceptron (MLP) and Convolutional Neural Network (CNN), were trained and tested with over 35,000 and approximately 54,000 randomly selected data samples, respectively. The trained CNN networks outperformed the MLP networks, achieving the highest testing accuracy of 95.67% and the highest validation accuracy of 87.28% based on ground truth data from 32 measurement stations from all seasons across the year. This study proposed the reference periods concept for convenient labeling in data preparation and tested different combinations of influence variables to achieve better transferability of the method for future studies. Our findings offer a more effective way to monitor FT states in the terrestrial cryosphere, offering valuable insights into the consequences of climate change on permafrost landscapes. Moreover, the suggested deep learning approach can be easily expanded when additional input sources are accessible. This expansion has the potential to further improve the model's performance for the FT retrieval.

Determination of parameters of anti-heave structures of the subgrade taking into account the freezing system

Background: in the Northern Hemisphere, during the construction and operation of railways, one of the pressing problems is frost heaving. One of the key factors influencing the amount of frost heaving is the occurrence of groundwater relative to the freezing front of the subgrade soils, which is not fully taken into account by existing approaches to determining the parameters of anti-heaving structures. This factor is usually characterized by freezing regimes, there are two of them - open and closed freezing systems. An open system is characterized by the proximity of groundwater to the freezing front, at which there is a constant influx of water (migration) to the zone of phase transitions, which makes the process of frost heaving unpredictable, and the determination of the frost heave ratio incorrect. A closed freezing system assumes the absence or deep location of groundwater (the difference in the level of the freezing front and groundwater exceeds the height of the capillary rise of water).
 Aim: development of a method for calculating the parameters of anti-heaving. structures depending on the freezing regime of railway subgrades.
 Materials and Methods: comparative analysis of methods for calculating the parameters of anti-heaving structures, experimental studies of the process of frost heaving in an open system of freezing of clay soils.
 Results: based on experimental studies of freezing regimes, a differentiated approach to assessing the characteristics of frost heaving is proposed, taking into account the peculiarities of the frost heaving process.
 Conclusion: the proposed method with a differentiated approach compares favorably with existing ones, allowing to reduce the consumption of building materials when designing anti-heaving measures.

Large-Scale Freezing and Thawing Model Experiment and Analysis of Water–Heat Coupling Processes in Agricultural Soils in Cold Regions

Heilongjiang Province, the largest commercial grain base in China, experiences significant challenges due to the environmental effects on its soil. The freezing and thawing cycle in this region leads to the transport of water and heat, as well as the exchange and transfer of energy. Consequently, this exacerbates the flooding disaster in spring and severely hampers farming activities such as plowing and sowing. To gain a better understanding of the freezing and thawing mechanisms of farmland soil in cold regions and prevent spring flooding disasters, this study focuses on Heilongjiang Province as a representative area in northeast China. The research specifically investigates the frozen and thawed soil of farmland, using a large-scale low-temperature laboratory to simulate both artificial and natural climate conditions in the cold zone. By employing the similarity principle of geotechnical model testing, the study aims to efficiently simulate the engineering prototypes and replicate the process of large-span and long-time low temperatures. The investigation primarily focuses on the evolution laws of key parameters, such as the temperature field and moisture field of farmland soil during the freeze–thaw cycle. The findings demonstrate that the cooling process of soil can be categorized into three stages: rapid cooling, slow cooling, and freezing stabilization. As the soil depth increases, the variability of the soil temperature gradually diminishes. During the melting stage, the soil’s water content exhibits a gradual increase as the temperature rises. The range of water content variation during thawing at depths of 30 cm, 40 cm, 50 cm, and 80 cm is 0.12% to 0.52%, 0.47% to 1.08%, 0.46% to 1.96%, and 0.8% to 3.23%, respectively. To analyze the hydrothermal coupling process of farmland soil during the freeze–thaw cycle, a theoretical model of hydrothermal coupling was developed based on principles of mass conservation, energy conservation, Darcy’s law of unsaturated soil water flow, and heat conduction theory. Mathematical transformations were applied after defining the relative degree of saturation and solid–liquid ratio as field functions with respect to the relative degree of saturation and temperature. The simulated temperature and moisture fields align well with the measured data, indicating that the water–heat coupling model established in this study holds significant theoretical and practical value for accurately predicting soil temperature and moisture content during the spring sowing period, as well as for efficiently and effectively utilizing frozen soil resources in cold regions.

Frost soil interaction with the cement-sand mortar of a driven precast pile

Introduction. The drilling method of pile driving represents the most common method of constructing foundations on permafrost soils. In order to reduce the tangential forces of frost heaving, the space between the pile surface and a leader well wall within the layer of seasonal freezing-thawing is filled with non-heaving sandy soil. This technology complicates the process of installing driven precast piles. In this case, a significant simplification involves filling the space between the pile and the soil with a cement-sand mortar (CSM) along the entire height of the pile. However, at present, no method is valid for calculating driven precast piles for the action of frost heaving tangential forces during CSM freezing.Aim. To develop a methodology for calculating driven precast piles for the action of frost heaving tangential forces during CSM freezing.Materials and methods. A set of laboratory tests, modeling the processes in soils during cold and warm pile installation periods, was carried out. Laboratory tests were performed using a method of a single-plane cut along the surface of a CSM freezing with clay soils, as well as with the foundation material at a constant rate in accordance with State Standard R 56726-2015 and statistical data processing according to State Standard 20522-2012.Results. The article presents the results of laboratory studies on effects, caused by frost heaving tangential forces on piles during soil and CSM freezing, taking into account various factors (clay soil liquidity index, test temperature). Based on the obtained data, the authors propose a methodology for calculating the stability of driven precast piles. The method consists in determining the heaving force per unit area by adding the products of the seasonal freezing-thawing fractional depth, obtained by thermal engineering calculations or according to the plots, given in the article, by the tangential forces of frost heaving, obtained in laboratory studies.Conclusions. The developed methodology improves the reliability and accuracy of foundation calculations, enhances the efficiency of base and foundation design solutions, and reduces the labor capacity of driven precast pile installation.

Response of spring vegetation phenology to soil freeze–thaw state in the Northern Hemisphere from 2016 to 2022

IntroductionThe research on spring vegetation phenology is crucial to the investigation of terrestrial ecosystems and climate change. Changes in the soil freeze–thaw (F/T) lead to variations in soil moisture, directly impacting vegetation activity. The start of the season (SOS) is the initial and important phenophase for vegetation activity, and thus, this highlights the need to understand the response of spring vegetation phenology to soil F/T state.MethodsThis study first comprehensively investigates the consistency of the SOS and three soil F/T state indexes, i.e., the start day of the F/T state (SFT), the end day of the F/T state (EFT), and the length of days of the F/T state (LFT) via satellite data source.ResultsResults reveal that: (1) All 3 F/T state indexes impact SOS values, and the EFT outperforms others. The correlation coefficients between EFT and SOS gain around 3.07%. (2) A temporal overlap between SOS and EFT occurs in May, suggesting that parts of the plants begin active growth before average temperatures reach above 0°. (3) Small differences of SOS and EFT exist between savannas, and croplands, with an average difference of less than 10 days; in contrast, the largest differences occur in broadleaf evergreen forests. The results can fill the knowledge gap on the response of spring vegetation phenology to soil F/T state, and help to investigate the reasons for the nonlinear dynamics of SOS under global warming.

Environmental and Seasonal Variability of High Latitude Methane Emissions Based on Earth Observation Data and Atmospheric Inverse Modelling

Drivers of natural high-latitude biogenic methane fluxes were studied by combining atmospheric inversion modelling results of methane fluxes (CTE-CH4 model) with datasets on permafrost (ESA Permafrost CCI), climate (Köppen–Geiger classes) and wetland classes (BAWLD) and seasonality of soil freezing (ESA SMOS F/T) for the years 2011–2019. The highest emissions were found in the southern parts of the study region, while areas with continuous permafrost, tundra climate, and tundra wetlands had the lowest emissions. The magnitude of the methane flux per wetland area followed the order of permafrost zones excluding non-permafrost, continuous permafrost having the smallest flux and sporadic the largest. Fens had higher fluxes than bogs in the thaw period, but bogs had higher fluxes in the colder seasons. The freezing period when the soil status is between complete thaw and frozen contributed to annual emissions more in the warmest regions studied than in other regions. In the coldest areas, freezing period fluxes were lower and closer to wintertime values than elsewhere. Emissions during freezing periods were smaller than those during winter periods, but were of comparable magnitude in warm regions. The contribution of the thaw period to the total annual emission varied from 86% in warmest areas to 97% in the coldest areas, suggesting that the longest winter periods did not contribute significantly to the annual budget.

Nitrate losses from forest during snowmelt: An underestimated source in mid-high latitude watershed

The forest nitrate cycle is a crucial part of the watershed nitrate load but has received limited attention compared to that of agricultural and residential land. Here, we analyzed the status and sources of riverine nitrate fluxes and identified the characteristics and contribution of forest nitrate loss to the riverine system in a mid-high latitude forested watershed using monthly field sampling and a modified Soil and Water Assessment Tool (SWAT) with enhanced forest nutrient cycle representation. The results indicate that nitrate losses in the headwater stream and downstream exhibit different seasonal characteristics. The nitrate losses in the headwater stream show a bimodal pattern due to lower temperatures and snowmelt runoff. Redundancy analysis (RDA) revealed that, unlike nitrogen (N) fertilizer-induced nitrate loss in the rainy season, forest loss has a positive effect on headwater stream nitrate concentration during the snowmelt season. The modified SWAT was then utilized to simulate nitrate losses in forest lands. The forest nitrate export per unit area of the headwater stream (1.58 ± 1.78 kg/ha/yr) was observed to be higher than that of the downstream (0.67 ± 0.74 kg/ha/yr) due to high snowmelt and mineralization of active organic N. At watershed scale, forest lands contributed 8.18 ± 3.94 % of the total nitrate losses to the water system in the headwater watersheds during the snowmelt season, representing the highest level within the entire basin. A comparison with forest streams in similar low-temperature conditions worldwide revealed that increasing nitrate loss occurred after extreme cold weather or soil freezing events, with an average increment of 6.32 kg/ha/yr. Therefore, forest nitrate losses should be better characterized and included in future watershed N budgets in low-temperature regions, which might help to reduce the N budget uncertainty and improve watershed management.