Seasonal Freeze-thaw Cycles Research Articles

Correction: Metal(loid)s Removal Response to the Seasonal Freeze–Thaw Cycle in Semi-passive Pilot Scale Bioreactors

Correction: Metal(loid)s Removal Response to the Seasonal Freeze–Thaw Cycle in Semi-passive Pilot Scale Bioreactors

Chestnut soil organic carbon is regulated through pore morphology and micropores during the seasonal freeze–thaw process

Soil aggregates are basic structural units in soil organic carbon (SOC) protection. In alpine ecosystems, the seasonal freeze–thaw (FT) process characterizes soil formation and nutrient cycling. However, previous studies were mostly based on simulated FT experiments, which amplified the effects of natural FT processes. And, the regulations of pore structure on SOC protection/loss of aggregates during the FT processes were still not well understood. To investigate the effect of the seasonal FT process on SOC and pore structure of aggregates, as well as the interactions among them, soil samples were selected during a whole seasonal FT cycle, which can be divided into four periods: unstable freezing (UFP), stable frozen (SFP), unstable thawing (UTP), and stable thawed periods (STP). The results demonstrated that freezing increased SOC concentration as the total organic carbon (TOC) content of all aggregate fractions peaked in the SFP (17.46 g/kg on average). The TOC content of aggregates in the UFP dropped to 7.91 g/kg on average, which revealed a dramatic SOC loss after thawing began. Thawing also decreased the proportions of particulate organic carbon (POC) compared with mineral-associated organic carbon (MAOC). The highest microbial abundance was also found in the SFP. Freezing promoted the formation of pores > 80 μm while thawing increased the regularity of pore morphology. Pore structure explained 48.77 % of the SOC variance in the thawing period, but only 19.29 % of that in the freezing period. Overall, in the freezing process, soil pore structure impacted the SOC input by mediating pore morphology. In the thawing process, soil pore structure inhibited SOC loss by enhancing the formation of pores < 15 μm. These results demonstrate new perspectives on the soil aggregate microstructure–microbe–SOC interactions.

Case study on the relationship between transmission of antibiotic resistance genes and microbial community under freeze-thaw cycle on cold-region dairy farm

Freeze-thaw cycle (FTC) is a naturally occurring phenomenon in high-latitude terrestrial ecosystems, which may exert influence on distribution and evolution of microbial community in the soil. The relationship between transmission of antibiotic resistance genes (ARGs) and microbial community was investigated upon the case study on the soil of cold-region dairy farm under seasonal FTC. The results demonstrated that 37 ARGs underwent decrease in the abundance of blaTEM from 80.4 % for frozen soil to 71.7 % for thawed soil, and that sul2 from 8.8 % for frozen soil to 6.5 % for thawed soil, respectively. Antibiotic deactivation was identified to be closely related to the highest relative abundance of blaTEM, and the spread of sulfonamide resistance genes (SRGs) occurred mainly via target modification. Firmicutes in frozen soil were responsible for dominating the abundance of ARGs by suppressing the native bacteria under starvation effect in cold regions, and then underwent horizontal gene transfer (HGT) among native bacteria through mobile genetic elements (MGEs). The TRB-C (32.6–49.1 %) and tnpA-06 (0.27–7.5 %) were significantly increased in frozen soil, while Int3 (0.67–10.6 %) and tnpA-04 (11.1–19.4 %) were up-regulated in thawed soil. Moreover, the ARGs in frozen soil primarily underwent HGT through MGEs, i.e. TRB-C and tnpA-06, with increased number of Firmicutes serving as carrier. The case study not only demonstrated relationship between transmission of ARGs and microbial community in the soil under practically relevant FTC condition, but also emphasized the importance for formulating better strategies for preventing FTC-induced ARGs in dairy farm in cold regions.

Metal(loid)s Removal Response to the Seasonal Freeze–Thaw Cycle in Semi-passive Pilot Scale Bioreactors

There is an increasing demand for cost-effective semi-passive water treatment that can withstand challenging climatic conditions and effectively and sustainably manage mine-impacted water in (sub)arctic regions. This study investigated the ability of four pilot-scale bioreactors inoculated with locally sourced bacteria and affected by a freeze–thaw cycle to remove selenium and antimony. The bioreactors were operated at a Canadian (sub)arctic mine for a year. Two duplicate bioreactors were installed in a heated shed that was maintained at 5 °C over the winter, while two other duplicates were installed outdoors and left to freeze. The removal rate of selenium and antimony was monitored weekly, while a genomic characterization of the microbial populations in the bioreactors was performed monthly. The overall percentage of selenium and antimony removal was similar in the outside (10–93% Se, 20–96% Sb) and inside (35–94% Se, 10–95% Sb) bioreactors, apart from the spring thawing period when removal in the outdoor bioreactors was slightly lower for Se. The dominant taxonomic groups of microbial populations in all bioreactors were Bacteroidota, Firmicutes, Desulfobacterota and Proteobacteria. The microbial population composition was consistent and re-established quickly after spring thaw in the outside bioreactors. This demonstrated that the removal capacity of bioreactors inoculated with locally sourced bacteria was mostly unaffected by a freeze–thaw cycle, highlighting the strength of using local resources to design bioreactors in extreme climatic conditions.

Physical property responses of soils subjected to different degrees of erosion and seasonal freeze-thaw cycles in Northeast China

Changes in soil pores and aggregate stability due to freeze-thaw cycles (FTCs) are important causes of increased soil erosion during snowmelt. Soil erosion causes spatial redistribution of soils, enhancing soil heterogeneity and potentially impacting soil responses to FTCs. Nonetheless, there is minimal knowledge of the responses of soils subjected to different degrees of erosion to seasonal FTCs. To reveal the impact of seasonal FTCs, the dynamic variations of pore characteristics and aggregates of soils with four different degrees of erosion (original, degraded, deposited and parent soil) were measured, and the connections between influencing factors and soil properties were analyzed. The results showed that FTCs altered the structure of the soils and weakened their resistance to erosion and that soils with different degrees of erosion responded differently to FTCs. After seasonal FTCs, soil porosity increased (0.4 %-11.9 %) to some extent in all soils, with greater changes observed in the more eroded soils. Notably, capillary porosity exhibited a complex changing trend compared to total porosity. Degraded and parent soils showed a stable bulk density, while the original soil showed a decrease (2.1 %) in bulk density and the deposited soil showed an increase (18.4 %) in bulk density. With the increase of FTCs, the field capacity of original, degraded, and deposited soils exhibited a gradual decrease (15.1 %-18.5 %), while that of the parent soil slightly increased (0.9 %). After seasonal FTCs, the saturated hydraulic conductivity decreased for original and deposited soils (19.5 %-41.5 %), while it increased for degraded and parent soils (29.2 %-41.6 %). Throughout the FTCs, the proportion of the large aggregates decreased and the small aggregates increased, and the transformation was greater on the less eroded soils. The mean weight diameter and geometric mean diameter of the soils gradually decreased with increasing FTCs, while the change was smaller for the more eroded soils. After seasonal FTCs, the less eroded soils were at greater risk of erosion. Our results demonstrated that the number of FTCs had a more significant impact on soil physical properties compared to the temperature difference and soil water content. Overall, freeze-thaw action reinforced the spatial heterogeneity of soil properties, potentially intensifying soil erosion. These findings help reveal the effects of FTCs on the physical properties of soils with different degrees of erosion and deepen the understanding of the mechanism of FTCs on soil erosion processes.

Dynamic responses of soil microbial communities to seasonal freeze-thaw cycles in a temperate agroecosystem

Soil freeze-thaw cycles (FTCs) are common in temperate agricultural ecosystems during the non-growing season and are progressively influenced by climate change. The impact of these cycles on soil microbial communities, crucial for ecosystem functioning, varies under different agricultural management practices. Here, we investigated the dynamic changes in soil microbial communities in a Mollisol during seasonal FTCs and examined the effects of stover mulching and nitrogen fertilization. We revealed distinct responses between bacterial and fungal communities. The dominant bacterial phyla reacted differently to FTCs: for example, Proteobacteria responded opportunistically, Actinobacteria, Acidobacteria, Choroflexi and Gemmatimonadetes responded sensitively, and Saccharibacteria exhibited a tolerance response. In contrast, the fungal community composition remained relatively stable during FTCs, except for a decline in Glomeromycota. Certain bacterial OTUs acted as sensitive indicators of FTCs, forming keystone modules in the network that are closely linked to soil carbon, nitrogen content and potential functions. Additionally, neither stover mulching nor nitrogen fertilization significantly influenced microbial richness, diversity and potential functions. However, over time, more indicator species specific to these agricultural practices began to emerge within the networks and gradually occupied the central positions. Furthermore, our findings suggest that farming practices, by introducing keystone microbes and changing interspecies interactions (even without changing microbial richness and diversity), can enhance microbial community stability against FTC disturbances. Specifically, higher nitrogen input with stover removal promotes fungal stability during soil freezing, while lower nitrogen levels increase bacterial stability during soil thawing. Considering the fungal tolerance to FTCs, we recommend reducing nitrogen input for manipulating bacterial interactions, thereby enhancing overall microbial resilience to seasonal FTCs. In summary, our research reveals that microbial responses to seasonal FTCs are reshaped through land management to support ecosystem functions under environmental stress amid climate change.

Microbially-mediated reductive dissolution of Fe-bearing minerals during freeze-thaw cycles

Constraining the role of microbes in the structural iron (Fe) reduction of iron-bearing minerals improves our understanding of sediments and ice sheets as a source of dissolved Fe (dFe) to the oceans. However, bio-mediated structural Fe-reduction has yet to be studied in cryospheric environments. Here, we show that the Fe reducing psychrophile bacterium Shewanella vesiculosa, isolated from sea ice in Antarctica, reduced structural Fe in nontronite (NAu-2) and maghemite (γ-Fe2O3), common mineral phases in glacial ice, and marine sediments in Antarctica, during two freeze–thaw cycles (−10 °C to +15 °C), resulting in the release of dFe. The modification of turbostratically disordered nontronite (ferric iron dominant phase) to discrete ordered illite-like structure (ferrous iron dominant phase), and the aggregation of altered small maghemite particles with neoformation of vivianite (Fe3(PO4)2·nH2O) indicated the microbially induced reductive dissolution of nontronite and maghemite, respectively. The biotic Fe-reduction gradually decreased and ceased as the temperature approached freezing (−8 °C), however the rection reactivated in the thawing cycle (−7 to +15 °C). No discernable biotic Fe-reduction was measured for either mineral under freezing conditions, suggesting that temperature limits the activity of the microbes. Further, and regardless of temperatures during two freeze–thaw cycles, Fe-reduction was not observed in abiotic control. Overall, these results highlight the importance of microbially induced Fe reduction during seasonal freeze–thaw cycles of ice and sediments in continuous supplying bioavailable dFe to cryospheric environments and the often Fe-limited polar oceans.

Study on the formation mechanism and preventive measure of pot cover effect for subgrade in seasonal frozen soil area under freeze–thaw cycles

AbstractThe presence of an impervious cover layer inhibits the free evaporation of moisture in the soil during seasonal freeze–thaw cycles, leading to a phenomenon known as the pot cover effect. This can result in severe frost heave issues in airport runways, highway subgrades, railway subgrades, and other similar infrastructure. In this study, a disease investigation was conducted at a gas transmission station situated in an area with seasonally frozen soil. Meanwhile, the causes of moisture accumulation and frost heave in the lower part of concrete pavement slabs were analyzed. A coupled water–vapor–heat model for unsaturated frozen soil is then established to analyze the formation mechanism of the pot cover effect in the subgrade. Finally, the preventive effect of the impervious layer on moisture migration in the pot cover effect was analyzed. The results indicate that the pot cover effect causes a significant accumulation of moisture beneath the concrete pavement at the gas transmission station, resulting in a moisture content increase of 5%–35%. During the freezing period, the vapor of shallow soil migrates upward, while the liquid water remains unchanged. During the melting period, both vapor and liquid water migrate downward. The laying of the impervious layer can prevent moisture migration of the pot cover effect. When the impervious layer is placed on the freezing front (0°C), the prevention effect of the pot cover effect is the best.

Underlying mechanisms governing on distribution and stratification of DOM during seasonal freeze-thaw cycles

During the freeze-thaw cycles of ice-covered lakes, DOM undergoes a series of transformations including enrichment, dispersion, and filtration. However, the mechanisms and influence factors on lake pollution processes remain unclear. Therefore, this study investigates the distribution of DOM components and elucidate the role of ice-layer sieving its mechanisms within ice-water-sediments. Study identifies significant variations in the characteristics of DOM, protein-like substances tend to migrate towards the ice layer, while humic-like substances predominantly remain in water. This selective distribution is primarily influenced by the physical and chemical properties of DOM during the freezing process. The ice layer acts as a sieve, allowing smaller molecules such as protein-like substances to pass through more easily, while larger molecules like humic-like substances are retained in the water. Additionally, Temperature plays a pivotal role in affecting the contents of DOM. As the temperature decreases, the solubility of DOM decreases, leading to its precipitation and enrichment in sediments. Conversely, an increase in temperature can facilitate the release of DOM from sediments into the water. Furthermore, high content of total dissolved solids can affect the solubility and stability of DOM, potentially leading to changes in its composition and distribution. These insights provide a deeper understanding of the complex interplay between thermal processes and chemical dynamics within ice-covered aquatic environments. They offered valuable insights into the behavior of organic pollutants in frozen lake systems. The findings have potential implications for environmental management strategies aimed at mitigating the effects of climate.

Experimental and Numerical Modeling of the Freeze–thaw Response of U-Shaped Channel Lining on Sulfate Saline Soil Foundation

Under the influence of seasonal freeze-thaw cycles, the concrete lining of channels situated on saline soil foundations is highly vulnerable to an array of deleterious phenomena, such as frost heave, salt expansion, and corrosion. To investigate the synergistic interplay among saline soil substrates, U-shaped channel lining structures, and ambient temperatures during freeze-thaw cycles, a novel Hydraulic-Thermal-Salt-Mechanical (HTSM) model is established in this study. The HTSM model elucidates the migration of moisture and salt solute, ice-water phase transitions, and sodium sulfate crystallization within unsaturated saline soils throughout the freeze-thaw cycles. It considers the variations in volume and pore solution volume before and after the phase transition of sodium sulfate. Temperature and salt frost heaving force measurements obtained from outdoor freeze-thaw cycles are compared with numerical simulation results to validate the efficacy of the HTSM model and investigate the distribution patterns of salt frost heaving force (frost swelling force) along the channel. The results showed that the frost swelling force and depth exhibit a great linear relationship and the maximum stress of the U-shaped channel appears at the bottom of the channel, highlighting the good arching force characteristics of the U-shaped structure which prove that bottom of the channel is also the most prone to fracture. Significantly, the initial water content significantly impacts the frost swelling force—it increases by 4% while the frost swelling force increases by 76%. Comparing the numerical simulation results of temperature variations, moisture changes, and salt-frost heaving forces with the outdoor experimental data, it is evident that the proposed HTSM model effectively simulates the salt-frost heaving patterns observed in U-shaped channel linings.

Compression behavior of CFST columns under combined influence of gap and freeze-thaw

Owing to factors related to construction quality and environment, concrete-filled steel tube (CFST) structures that have been in use for many years in regions experiencing seasonal freeze–thaw cycles are susceptible to the combined effects of a spherical-cap gap and freeze–thaw cycling. Therefore, in this study, a combination of experiments and the finite element method is used to investigate the effects of these two factors on the axial compression behavior of CFST stub columns. The experimental results show that the main failure mode of the specimen is local buckling at the end or the middle and inward depression of the steel tube on the existing gap side. The degradation of mechanical parameters, such as the ultimate bearing capacity and ductility of the specimens, gradually increased with increasing gap ratio and number of freeze–thaw cycles. In the numerical simulation section, the change in the stress response to freeze–thaw cycling on the gap side is analysed. The impact of the constraint effect coefficient on the ultimate bearing capacity degradation of the specimens is also investigated. Finally, a formula for calculating the ultimate capacity of CFST stub columns affected by the two factors is proposed, and the formula for calculating the ultimate bearing capacity in the code is improved. The results of this study can provide a reference for durability prediction and structural safety evaluation of CFST structures with a spherical-cap gap in cold regions.

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 &lt; 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.

Field observations on hydro-thermal regimes of loess cut slopes in cold and arid regions: A comparative study of sunny and shady slopes

In cold and arid regions, the maintenance of roadways and railways faces significant challenges due to serious spalling and sheet erosion, rill erosion, and shallow sliding of loess slopes. Moreover, the frequency and severity of these shallow failures, as well as the vegetation cover, differ greatly between sunny and shady slopes, further complicating slope maintenance. This study focuses on field observations conducted over two consecutive years along a highway at the western end of Chinese Loess Plateau, specifically examining soil temperatures and moisture content within two cut slopes. By analyzing the differences in hydro-thermal regimes within a depth of 100 cm between the sunny and shady slopes, and considering the meteorological data collected at the study site, the research aims to provide insights into these failures of loess slopes. The results indicate that the shady slope undergoes significant seasonal freeze-thaw cycles from the surface down to a depth of 100 cm. The freezing duration ranges from 96 to 120 days, with a freezing index ranging from −250 °C·d to −850 °C·d. Additionally, the shallow layer on the shady slope experiences significant daily freeze-thaw cycles in late autumn and early winter. In contrast, the sunny slope experiences minimal seasonal freeze-thaw processes. Although the shallow surface layer of the sunny slope undergoes some daily freeze-thaw cycles in late winter and early spring, the amplitudes of soil temperature fluctuations are significantly smaller compared to those on the shady slope. Given that the precipitation is concentrated in summer and autumn, the moisture content of the soil on the shady and sunny slopes exhibits noticeable seasonal changes. The soil layers on the shady slope tend to be relatively dry, while those on the sunny slope remain relatively moist. The moisture content within the observed depth on the sunny slope remains relatively consistent, while on the shady slope, a clear gradient is evident. The moisture content of the shallow slope layers within a depth25 cm primarily responses to heavy rainfall events, with a greater response observed on the shady slope compared to the sunny slope. The field-observed hydro-thermal data collected in this study serve a valuable basis for implementing revegetation strategies and enhancing the stability of loess slopes in cold and arid regions.

Mechanical properties and microscopic mechanism of active MgO-fly ash solidified saline soil in seasonal freezing areas

This paper presents an innovative method for improving the strength of salt-bearing clay under freeze–thaw cycles. The active magnesium oxide (MgO) and industrial waste fly ash were employed as primary solidifying materials in the seasonal freezing soil reinforcement process, and the reinforcement effect is achieved through carbonate crystals generated through carbonization tests. The solidification effect was investigated with varying ratios of solidifying materials, salt content, and freeze–thaw cycles. The experiment results revealed that the combination of active MgO and fly ash effectively enhances the strength of salt-bearing clay. Specifically, compared to unsolidified soil, the soil solidified with 8 % active MgO (8M0F) and a combination of 4 % active MgO and 4 % fly ash (4M4F) demonstrated a significant increase in ultimate strength by 14 and 12 times, respectively. Moreover, the number of freeze–thaw cycles exhibited a negative correlation with ultimate strength, whereas the salt content demonstrated a similar negative correlation. Microscopic analysis revealed that the 8M0F sample produced mainly magnesium carbonates and hydrogen and oxygen compounds, whereas the 4M4F sample generated primarily magnesium and calcium carbonates. The resulting compound crystals efficiently filled the internal pores and cemented the soil particles, leading to a substantial increase in strength. Overall, these results indicate that the active MgO combined with fly ash solidifying method can offer a viable and sustainable solution for improving the strength of salt-bearing clay in areas with seasonal freeze–thaw cycles.

CO2 and CH4 fluxes from forest soil in the northern Da Xing’anling Mountains in Northeast China during the freezing and thawing periods of near-surface soil in 2018–2019

ABSTRACT Under a warming climate, the studies on effects of seasonal freeze–thaw cycles on soil respiration are key to understanding the soil carbon cycles and ecosystem responses and resilience at mid- and high latitudes. In this study, the effluxes of soil surface CO2 and absorption rates of CH4 were measured in the Xing'an larch (Larix gmelinii) forest in the northern Da Xing’anling Mountains, Northeast China using an automatic multichannel soil greenhouse gas measurement system (dynamic gas chamber method) during the periods of October–November 2018 and April–May 2019. The results showed that during the freezing period of near-surface soil, CO2 and CH4 fluxes significantly declined, approaching zero, at the end of November. During the thawing period of near-surface soil, CO2 and CH4 fluxes from surface soil fluctuated markedly at first and then rose rapidly. The respective Q10 values of 3.86 and 4.89 during the freezing and thawing periods of near-surface soil, respectively, indicate the important role of ground freeze–thaw cycles in the modifications of CO2 and CH4 fluxes. The results of this study could help assess the stability of the soil carbon pool and carbon flux strength in taiga-forested permafrost regions in the northern Da Xing’anling Mountains, Northeast China.

Effect of the seasonal freeze–thaw cycle of the active layer on the seismic response of the free field in the permafrost region

Seasonal freezing and thawing of the active layer in permafrost can significantly alter the seismic response of the free field. In this study, a specific laminar shear model box with a soil-freezing system was designed, and shaking table tests of free fields under different soil-freezing conditions were conducted for ground motions with different intensities. The lateral displacement and acceleration responses of the free field were collected. Based on these results, the acceleration spectrum, shear stress–strain relationship, and frequency component of the ground motions of the free field were analysed. During the tests, the lateral displacement of the free field during both warm (thawed active layer) and cold (frozen active layer) seasons transitioned from linear to nonlinear relationships. The permafrost layer suppressed the amplification effect under ground motion with low intensity, and the frozen active layer enhanced the global stiffness of the free field during the cold season. As the seismic intensity increased, the restraining effect of the permafrost layer on ground motion decreased to a certain extent, and the frozen active layer had a restraining effect on the propagation of seismic waves. In addition, the transition layer (the unfrozen interlayer between the frozen active layer and the permafrost layer) during the cold season undergoes compaction during the nonlinear deformation stage. In the event of strong earthquakes, different soil layers exhibited selective amplification effects, and the frozen active layer exhibited an obvious influence on the filtering effect of the lower soil layers. These results can provide a reference basis for the seismic risk analysis of free field in permafrost regions.

Linking pore structure characteristics to soil strength and their relationships with detachment rate of disturbed Mollisol by concentrated flow under freeze–thaw effects

In mid-high latitude areas, seasonal freeze–thaw cycles generate significant effects on pore structure of soils, and in turn, affect soil mechanical properties and soil erosion processes. Furthermore, soil particles can be detached on ridged farmland by snowmelt or rainfall concentrated flow due to topographic relief during the spring snowmelt period. To explore the changes in pore structure characteristics under freeze–thaw effects on soil detachment rates under simulating concentrated flow, fifteen soil columns and twenty soil tanks underwent a freeze–thaw pre-treatment of zero, one, five, ten, and fifteen cycles. Soil structure characteristics were quantitatively obtained by scanning soil columns with industrial computer tomography at a 25-μm resolution. Soil strength was measured by a portable vane shear instrument on the surface of soil tanks. Detachment rates of soil tanks were measured in a flume under changeless flow shear stress (τ = 2.32 Pa). Results indicated that freeze–thaw effects significantly decreased soil strength by changing pore network structure, including increasing total imaged porosity and elongated-pore porosity. The detachment rate significantly rose with the rising freeze–thaw cycles (p < 0.05) and had a power relationship with the soil strength (R2 = 0.503, p < 0.05). Thus, the increase in detachment rate was mainly caused by the decrease in soil strength, which is dependent on large and elongated pores that formed during freeze–thaw cycles and on the geometrical characteristics of the pore network. The findings improve the understanding of the generation mechanism of soil erosion as a result of changes in pore structure characteristics during the spring snowmelt period.

Temperature Distributions in Geogrid-Reinforced Soil Retaining Walls Subjected to Seasonal Freeze–Thaw Cycles

Temperature Distributions in Geogrid-Reinforced Soil Retaining Walls Subjected to Seasonal Freeze–Thaw Cycles

Thinning intensity affects carbon sequestration and release in seasonal freeze–thaw areas

To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning, we assessed the potential impact of thinning intensity on carbon cycle dynamics. By varying the number of temperature cycles, the effects of various thinning intensities in four seasons. The rate of mass, litter organic carbon, and soil organic carbon (SOC) loss in response to temperature variations was examined in two degrees of decomposition. The unfrozen season had the highest decomposition rate of litter, followed by the frozen season. Semi-decomposed litter had a higher decomposition rate than undecomposed litter. The decomposition rate of litter was the highest when the thinning intensity was 10%, while the litter and SOC were low. Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons, while the converse was confirmed in the frozen and thaw seasons. The best carbon sequestration impact was identified in litter, and soil layers under a 20–25% thinning intensity, and the influence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter. Both litter and soil can store carbon: however, carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time. In summary, the best thinning intensity being 20–25%.

Spatiotemporal characteristics of arsenic and lead with seasonal freeze-thaw cycles in the source area of the Yellow River Tibet Plateau, China

Study regionThe source region of the Yellow River, China (SAYR) Study focusThis study focuses on demonstrating the impact of seasonal freeze-thaw process on the seasonally arsenic (As) and lead (Pb) concentration in the water bodies, such as river, lake, and spring. 113 surface water samples in April (freeze permafrost), 164 in July (active layer in permafrost thawed), and 86 soil samples at various depths in July were collected. Statistical correlation and principle analysis were applied to find the connection between tracer metals in water bodies and the various environmental factors. The percentage of soil particle size (5–50 µm), which can reflect the intensity of the freeze-thaw process in the permafrost soil, influenced the soil and water As and Pb trace metal concentrations differently in the permafrost area. New hydrological insights for the regionIn April, the average As concentrations were 23.4 ± 16.7, 39.4 ± 32.6, 26.5 ± 24.4 μg/L, respectively in river, lake and spring water samples, and Pb concentrations were 34.9 ± 27.1, 47.4 ± 38 and 48.9 ± 33.4 μg/L. While the As concentrations in waters in July all decreased by 2 or 3 times compared with those in April, Pb concentrations slightly increased. Permafrost thawing enhanced the weathering of As and Pb, but the high As adsorption on fine soil particles, resulting from the seasonal freeze-thaw cycles, leaded to the significant decrease in the water As concentration in July, in addition to the rainfall dilution. The slight increase in Pb water concentration in July suggesting the effects of enhanced weathering and dilution were equally important. The higher As and Pb concentrations around the large Gyaring and Ngoring lakes than other SAYR area, shaping the spatial distribution of As and Pb, might be due to evaporative enrichment and the high phosphate content in the lakes. Results are helpful in assessing the ecological impact of trace metals in the permafrost area with climate change.