Soil Thawing Research Articles

Multi-objective optimization of winter irrigation for cotton fields in salinized freeze-thaw areas

The adaptive management of saline-alkali land and water resources can effectively alleviate land degradation and water depletion, and appropriate irrigation can improve crop yield and production efficiency. Based on the soil changes and comprehensive crop benefits under different initial soil environments, the optimization of the irrigation amount of cotton in saline-alkali areas is of great significance for the improvement of agricultural production of these areas in developing countries and even worldwide. The responses of farmland with various degree of salinization to different winter irrigation amounts in seasonal freeze-thaw arid areas should therefore be further explored. In this study, the soil moisture-temperature-salinity changes and the crop growth responses of three cotton fields with different salinization levels (5.15, 8.17, and 11.15 g·kg-1) under four winter irrigation amounts (0, 3000, 3600, and 4200 m3·ha-1) were intensively investigated via a two-year field experiment in Xinjiang Province, China. The results demonstrate that winter irrigation significantly improved the soil moisture-temperature-salinity environment during the freeze-thaw period, and the influence was affected by the field salinization level. The initial salinity of salinized field promoted soil thawing and water storage, and inhibited soil freezing and salt leaching. The intraspecific relationship of salinized cotton fields changed from competition to promotion under winter irrigation, and soil salinity weakened the optimization of the intraspecific relationship. The multiple correlations between the benefit indexes of cotton were significantly strengthened under winter irrigation, and the negative effect of the soil salinization level on the cotton benefit indexes was stronger than that of the winter irrigation amount. Based on a multiple regression analysis, the optimal winter irrigation amounts for cotton fields with mild, moderate, and severe salinization were found to be 3416.83–4256.14, 4256.14–6502.96, and 6502.96–9614.24 m3·ha-1, respectively. This research provides a theoretical basis for determining the appropriate winter irrigation amount for cotton fields with various degrees of salinization in seasonal freeze-thaw arid regions.

Dynamics of soil freezing and thawing in the agroforestry landscape

The article presents the dynamics of soil freezing and thawing in the agroforestry landscape of the dry-steppe zone. These processes in winters with unstable snow cover have their own characteristics. The purpose of this study was to investigate the character of soil freezing and thawing in the agroforestry landscape under conditions of low snowfall winters. Observations were carried out in the winter period of 2020–2021 at the existing runoff-erosion research station in Volgograd. The dynamics of soil freezing and thawing was studied using Danilin freeze-thaw meters installed in the field and in the center of a four-row forest belt. Simultaneously, snow cover height was measured in triplicate with a snow measuring rod. The weather conditions were characterized by alternating thaws, which promoted snow cover melt, and frosts, which increased the depth of soil freezing. The formation of a 10-15 cm snow cover did not affect soil freezing. In the absence of snow on the background of a brief thaw, the lower boundary of the frozen layer in the field decreased by 11 cm compared to the forest belt, which even in the leafless state affected the inflow of solar thermal energy. Average freezing at the end of winter was 85 cm in the field and 67 cm in the forest belt. Thawing in the field was faster. During the first two weeks, the rate of soil thawing averaged 2.3 cm/day in the field and 1.3 cm/day in the forest belt. After that, the depth of freezing in the whole agroforestry landscape became equal. During the next two weeks, the thawing rate doubled. After complete soil thawing in the field in the forest belt, the thickness of the frozen layer averaged 32 cm.

Quantification and machine learning based N2O–N and CO2–C emissions predictions from a decomposing rye cover crop

AbstractCover crops improve soil health and reduce the risk of soil erosion. However, their impact on the carbon dioxide equivalence (CO2e) is unknown. Therefore, the objective of this 2‐yr study was to quantify the effect of cover crop‐induced differences in soil moisture, temperature, organic C, and microorganisms on CO2e, and to develop machine learning algorithms that predict daily N2O–N and CO2–C emissions. The prediction models tested were multiple linear regression, partial least square regression, support vector machine, random forest (RF), and artificial neural network. Models’ performance was accessed using R2, RMSE and mean of absolute value of error. Rye (Secale cereale L.) was dormant seeded in mid‐October, and in the following spring it was terminated at corn's (Zea mays L.) V4 growth stage. Soil temperature, moisture, and N2O–N and CO2–C emissions were measured near continuously from soil thaw to harvest in 2019 and 2020. Prior to termination, the cover crop decreased N2O–N emissions by 34% (p = .05), and over the entire season, N2O–N emissions from cover crop and no cover crop treatments were similar (p = .71). Based on N2O–N and CO2–C emissions over the entire season and the estimated fixed cover crop‐C remaining in the soil, the partial CO2e were −1,061 and 496 kg CO2e ha–1 in the cover crop and no cover crop treatments, respectively. The RF algorithm explained more of the daily N2O–N (73%) and CO2–C (85%) emissions variability during validation than the other models. Across models, the most important variables were temperature and the amount of cover crop‐C added to the soil.

Characterization of unfrozen water in highly organic turfy soil during freeze–thaw by nuclear magnetic resonance

The unfrozen water content (ωu) is an important parameter affecting the hydrothermal-mechanical characteristics of soil and is of important significance with regard to engineering construction and environmental effects in cold regions. In this study, a widely-distributed special humus soil called turfy soil, with poor engineering geological properties, from seasonally frozen regions of northeastern China was investigated. Soil fundamental properties were determined, and ωu under various temperatures during a freeze–thaw process was measured by the nuclear magnetic resonance (NMR) method. Based on NMR theory and transverse relaxation time (T2) distribution curves, two thresholds were determined to divide the types of pore water in soil. Soil freezing characteristic curves (SFCC) of the total and pore water were drawn, and changes in the internal microstructure and pore characteristics of the soil during the freeze–thaw process were analyzed. The results showed that a drastic phase change within the soil occurs during −2 °C to −4 °C, and the freezing process can be divided into three stages. The formation of small pores and the connection of large pores make the soil looser after freeze–thaw. The division of pore water and variation in ωu show that freezing starts from large pores, while thawing starts from small pores. The capillary water content significantly decreases after freeze–thaw, and the bulk water content tends to increase. At freezing Stage I, ωu is closely related to the initial properties of the soil, whereas ωu at −3 °C almost determines the value of ωu during subsequent freeze–thaw. Finally, a ωu-power function for turfy soil was proposed, and good fitting results were obtained for both freezing and thawing soil. This work can serve as the basis of studies on soil with high organic matter content as well as soil unfrozen water content during freeze–thaw cycles in cold regions.

Control of Mosses on Water Flux in an Alpine Shrub Site on the Qilian Mountains, Northwest China.

Mosses are an important component of the alpine shrub, but little is known about their contribution to ecosystem water and energy exchange, especially potential opportunities for alpine shrub expansion under a warming climate. We studied the role of mosses in alpine shrub evapotranspiration by conducting herb and moss removal experiments with different Potentilla fruticosa L. shrub coverage in the Qilian Mountains, Northwest China. The understory evapotranspiration was measured using lysimeters in different shrub coverage (dense shrub cover, medium shrub cover, and thin shrub cover) during the growing season of 2012. The understory evapotranspiration is about 1.61 mm per day in the control treatment (intact moss and herbs) during the growing season, and the evapotranspiration rates differed significantly between canopy covers. We found a 22% increase in evapotranspiration losses after removing the moss layer compared to the control treatment lysimeter with an intact moss layer in the shrub site. This suggests that most of the understory evaporation originated from the organic layer underlying the moss layer. Given this study's large moss evaporation rates, understory contributions cannot be ignored when interpreting eddy covariance data for the whole alpine ecosystem. Our results show that mosses may exert strong controls on understory water fluxes in alpine shrub meadow ecosystems and suggest that changes in moss cover may have significant consequences for season frozen soil thaw.

Methane and Nitrous Oxide Fluxes with Different Land Uses in the Temperate Meadow Steppe of Inner Mongolia, China

Background and aims: Grazing and mowing are widely adopted management practices for the semiarid steppe in China that profoundly affect the greenhouse gas (GHG) flux in grassland ecosystems. However, the general mechanisms for CH4 and N2O fluxes in response to grazing and mowing remain poorly understood. Thus, we conducted year-round flux measurements of CH4 and N2O fluxes to investigate the effect of grazing and mowing on CH4 and N2O fluxes. Methods: Using manual static chamber and gas chromatography, we measured the fluxes of CH4 and N2O from grazing-exclusion, grazing and mowing sites from June 2019 to June 2020 in the Hulunbuir Grassland, Inner Mongolia. Results: Grazing and mowing increased soil temperature and reduced soil water content and soil inorganic N content. Compared with grazing and mowing, lower mean CH4 uptake (−67.58 ± 8.9 μg m−2 h−1) and higher mean N2O emissions (29.17 ± 6.8 μg m−2 h−1) were found at the grazing-exclusion site. No pulse emissions of N2O were found for all sites during the spring thaw period (STP), and only two small N2O emission peaks due to soil thawing were captured on April 2nd and 5th. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 10%, 13% and 12% of the annual fluxes at the grazing-exclusion, grazing and mowing sites, respectively. Conclusion: Our results indicate that grazing and mowing enhance CH4 uptake and inhibit N2O emissions, primarily due to the increased soil temperature and reduced soil water content and soil inorganic N content. No apparent pulse N2O emissions were observed at any of the three sites during the STP in the Hulunbuir grassland.

Microbial Community in the Permafrost Thaw Gradient in the South of the Vitim Plateau (Buryatia, Russia).

Soil microbial communities play key roles in biogeochemical cycles and greenhouse gas formation during the decomposition of the released organic matter in the thawing permafrost. The aim of our research was to assess the taxonomic prokaryotic diversity in soil-ecological niches of the Darkhituy-Khaimisan transect during the initial period of soil thawing. We investigated changes in the microbial communities present in the active layer of four sites representing distinct habitats (larch forest, birch forest, meadow steppe and thermokarst lake). We explore the relationship between the biogeochemical differences among habitats and the active layer microbial community via a spatial (across habitats, and with depth through the active layer) community survey using high-throughput Illumina sequencing. Microbial communities showed significant differences between active and frozen layers and across ecosystem types, including a high relative abundance of Alphaproteobacteria, Firmicutes, Crenarchaeota, Bacteroidota and Gemmatimonadota in the active layer and a high relative abundance of Actinobacteriota and Desulfobacterota in the frozen layer. Soil pH, temperature and moisture were the most significant parameters underlying the variations in the microbial community composition. CCA suggested that the differing environmental conditions between the four soil habitats had strong influences on microbial distribution and diversity and further explained the variability of soil microbial community structures.

Warming soil temperature and increasing baseflow in response to recent and potential future climate change across northern Manitoba, Canada

AbstractThis study investigates the impacts of climate change on the hydrology and soil thermal regime of 10 sub‐arctic watersheds (northern Manitoba, Canada) using the Variable Infiltration Capacity (VIC) model. We utilize statistically downscaled and bias‐corrected forcing datasets based on 17 general circulation model (GCM) ‐ representative concentration pathways (RCPs) scenarios from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to run the VIC model for three 30‐year periods: a historical baseline (1981–2010: 1990s), and future projections (2021–2050: 2030s and 2041–2070: 2050s), under RCPs 4.5 and 8.5. Future warming increases the average soil column temperature by ~2.2°C in the 2050s and further analyses of soil temperature trends at three different depths show the most pronounced warming in the top soil layer (1.6°C 30‐year−1 in the 2050s). Trend estimates of mean annual frozen soil moisture fraction in the soil column show considerable changes from 0.02 30‐year−1 (1990s) to −0.11 30‐year−1 (2050s) across the study area. Soil column water residence time decreases significantly (by 5 years) during the 2050s when compared with the 1990s as soil thawing intensifies the infiltration process thereby contributing to faster conversion to baseflow. Future warming results in 40%–50% more baseflow by the 2050s, where it increases substantially by 19.7% and 46.3% during the 2030s and 2050s, respectively. These results provide crucial information on the potential future impacts of warming soil temperatures on the hydrology of sub‐arctic watersheds in north‐central Canada and similar hydro‐climatic regimes.

Contribution of water rejuvenation induced by climate warming to evapotranspiration in a Siberian boreal forest

Water age is a useful metric to evaluate the influence of anthropogenic and natural forcings on the terrestrial water cycle. Current climate warming is enhancing the warming of permafrost soil in the Arctic. Although permafrost is a crucial component of the Arctic terrestrial water cycle, its influence on processes regulating the fluxes and ages of Arctic terrestrial water, particularly soil storage and evapotranspiration, is not well understood. In this study, a water age calculation scheme was implemented into the coupled hydrological and biogeochemical model (CHANGE) to assess the mechanisms through which climate warming affects the soil water storage–evapotranspiration–water age feedback cycle in a boreal forest. Continuous air temperature increase from 1980 to 2016 caused earlier snowmelt and soil thawing, inducing decreasing age trends in snow- and rain-sourced water. The younger water contributed to higher spring evapotranspiration. In summer, the higher evapotranspiration dried the surface soil layer. In turn, the drier surface layer increased the loss of fresh rainwater. Autumn precipitation, preserved in the frozen winter soil until the following spring, became an additional source of water and enhanced plant transpiration in the following summer. This increase accounted for 4.2% of the annual total transpiration. These results suggest that permafrost warming, characterized by earlier soil thawing and later freezing, induced higher evapotranspiration, thereby shortening the residence time of precipitation-sourced water in the active layer and further rejuvenating water in soil layers and in evapotranspiration. Under future climate warming conditions, this effect is expected to intensify and the water cycle will accelerate.

Plant selection for roadside rain gardens in cold climates using real-scale studies of thirty-one herbaceous perennials

Plant selection for rain gardens along streets and roads in cold climates can be complicated, as the plants are subjected to combined stresses including periodic inundation, de-icing salts, road dust, splashes of water from the road, freezing and thawing of soil, and periods with ice cover during the winter. The purpose of this study was to identify species suited to grow in these conditions and determine their optimal placement within roadside rain gardens. Thirty-one herbaceous perennial species and cultivars were planted in real-scale rain gardens in a street in Drammen (Norway) with supplemental irrigation, and their progress was recorded during the following three growing seasons. The study highlights considerable differences between species’ adaptation to roadside rain gardens in cold climates, especially closest to the road. Some candidate species/cultivars had a high survival rate in all rain garden positions and were developed well. These were: Amsonia tabernaemontana, Baptisia australis, Calamagrostis × acutiflora ‘Overdam’, Hemerocallis ‘Camden Gold Dollar’, Hemerocallis ‘Sovereign’, Hemerocallis lilioasphodelus, Hosta ‘Sum & Substance’, Iris pseudacorus and Liatris spicata ‘Floristan Weiss’. Other species/cultivars appeared to adapt only to certain parts of the rain garden or had medium tolerance. These were: Calamagrostis brachytricha, Carex muskingumensis, Eurybia × herveyi ‘Twilight’, Hakonechloa macra, Hosta ‘Francee’, Hosta ‘Striptease’, Liatris spicata ‘Alba’, Lythrum salicaria ‘Ziegeunerblut’, Molinia caerulea ‘Moorhexe’, Molinia caerulea ‘Overdam’, and Sesleria autumnalis. Species/cultivars that showed high mortality and poor development at all rain garden positions should be avoided in roadside cold climate rain gardens. These include Amsonia orientalis, Aster incisus ‘Madiva’, Astilbe chinensis var. tacquettii ‘Purpurlanze’, Chelone obliqua, Dryopteris filix-mas, Eurybia divaricata, Geranium ‘Rozanne’, Helenium ‘Pumilum Magnificum’, Luzula sylvatica, Polygonatum multiflorum and Veronicastrum virginicum ‘Apollo’. The study also found considerable differences between cultivars within the same species, especially for Hosta cvv. and Liatris spicata. Further investigations are needed to identify the cultivars with the best adaption to roadside rain gardens in cold climates.

Effects of biochar addition on nitrous oxide emission during soil freeze-thaw cycles.

Biochar applied to soil can reduce nitrous oxide (N2O) emissions produced by freeze-thaw processes. Nonetheless, how biochar modification affects N2O emissions during freeze-thaw cycles is not completely clear. In our research, during freeze-thaw cycles, microcosm experiments were conducted to investigate the effects of maize straw biochar (MB) or rice straw biochar (RB) addition on soil N2O emissions under different water conditions. The N2O emissions peaked at the initial stage of thawing in all the soils, and the total N2O emissions were considerably greater in the flooded soils than in the nonflooded soils. Compared with the soils without biochar addition, RB and MB amendments inhibited N2O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB amoA genes decreased by 9-13%. Biochar addition significantly decreased the content of microbial biomass nitrogen (MBN) in flooded soil during thawing, which was significantly correlated with N2O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N2O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N2O emissions and indirectly affects N2O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N2O in flooded soil during freeze-thaw cycles.

Comprehensive Assessment of Seasonally Frozen Ground Changes in the Northern Hemisphere Based on Observations

AbstractSeasonally frozen ground (SFG) in the Northern Hemisphere (NH) plays a significant role in the earth system via changes in the freeze‐thaw cycle. Previous studies primarily focus on permafrost; however, the SFG response to climate change on a hemispheric scale is uncertain due to a lack of observations. We rectify this with a newly assembled comprehensive database of 1,220 stations with daily observations. To quantify the spatiotemporal characteristics of SFG in response to climate change, we calculate eight variables with these observations: the first date of soil freeze (FFD), freezing duration (FDR), maximum freeze depth (MFD), the date of maximum freeze depth (MFDD), the last date of soil thaw (TLD), thawing duration (TDR), freeze‐thaw duration (FTDR), and actual number of freezing days (AD). During the variables' common 1986–2005 period, MFD decreased 8.9 cm (9% change). FFD was later by 5.3 days (2% change), MFDD and TLD were earlier by 14.5 days (27% change) and 24.7 days (22% change), respectively, and FDR and TDR decreased by 9 days (11% change) and 4.6 days (10% change). FTDR and AD decreased 18.1 days (14% change) and 12.1 days (10% change), respectively. The spatial pattern of freeze‐thaw variables depends on latitude and elevation, and varies by climatic zone: FTDR increases, going from the warm temperate climate, to the arid climate, and the snow and polar climates. The variability in freeze‐thaw changes is mainly driven by air temperature and latitude, while precipitation, soil moisture, snow depth, and elevation are relatively insignificant at the hemispheric scale.

Effects of winter pulsed warming and snowmelt on soil nitrogen cycling in agricultural soils: A lysimeter study

In cold regions, climate change is expected to result in warmer winter temperatures and increased temperature variability. Coupled with changing precipitation regimes, these changes can decrease soil insulation by reducing snow cover, exposing soils to colder temperatures and more frequent and extensive soil freezing and thawing. Freeze-thaw events can exert an important control over winter soil processes and the cycling of nitrogen (N), with consequences for soil health, nitrous oxide (N2O) emissions, and nearby water quality. These impacts are especially important for agricultural soils and practices in cold regions. We conducted a lysimeter experiment to assess the effects of winter pulsed warming, soil texture, and snow cover on N cycling in agricultural soils. We monitored the subsurface soil temperature, moisture, and porewater geochemistry together with air temperature, precipitation, and N2O fluxes in four agricultural field-controlled lysimeter systems (surface area of 1 m2 and depth of 1.5 m) at the University of Guelph’s Elora Research Station over one winter (December 2020 to April 2021). The lysimeters featured two soil types (loamy sand and silt loam) which were managed under a corn-soybean-wheat rotation with cover crops. Additionally, ceramic infrared heaters located above two of the lysimeters were turned on after each snowfall event to melt the snow and then turned off to mimic snow-free winter conditions with increased soil freezing. Porewater samples collected from five depths in the lysimeters were analyzed for total dissolved nitrogen (TDN), nitrate (NO3−), nitrite (NO2−), and ammonium (NH4+). N2O fluxes were measured using automated soil gas chambers installed on each lysimeter. The results from the snow removed lysimeters were compared to those of lysimeters without heaters (with snow). As expected, the removal of the insulating snow cover resulted in more intense soil freeze-thaw events, causing increased dissolved N loss from the lysimeter systems as N2O (from the silt loam system) and via NO3− leaching (from the loamy sand system). In the silt loam lysimeter, we attribute the freeze thaw-enhanced N2O fluxes to de novo processes rather than gas build up and release. In the loamy sand lysimeter, we attribute the increased NO3− leaching to the larger pore size and therefore lower water retention capacity of this soil type. Overall, our study illustrates the important role of winter snow cover dynamics and soil freezing in modulating the coupled responses of soil moisture, temperature, and N cycling.

APPLICATION OF THE HYDRATION HEAT OF CONCRETE BORED PILES WHEN USING FOUNDATION SOILS ACCORDING TO PRINCIPLE II (ACTIVE METHOD)

Introduction . The use of bored piles in foundation works is a common construction technology, which has been successfully employed for construction in permafrost zones. However, up to the present time, the heat of hydration released during the hardening of cement mixes has been considered as an adverse event thus not being practically applied, particularly when preparing foundation soils according to Principle II, or the Active method. Aim : to study the process of cement hydration when hardening and to assess variations in its temperature in order to use the data obtained for thermal and deformation calculations in construction design. Materials and methods . An analysis of regulatory framework, as well as scientific and technical literature, was carried out. Experimental laboratory studies of different cement mixes were performed. The obtained results were analyzed, the directions for further studies were outlined along with design recommendations. Results . The experimental study showed the maximum increase in the temperature of cement mixes one day after laying to range between 8.2 and 29.9 °С depending on the composition and initial temperatures of the mixes. Thermal and geotechnical calculations for a particular designed project based on the obtained data proved the efficiency of the considered approach for foundation works. Hence, this allowed the requirements for a minimum temperature of a cement mix and an estimated period of soil thawing under the building foundation to be included in the design documentation. Conclusions . The conducted experiments and numerical calculations showed that, under a certain set of characteristics of cement mixes for bored pile foundations, the released heat of hydration can be sufficient for thawing permafrost soils and preparing the foundation soils for use in terms of Principle II. This approach ensures time and cost optimization during the construction period.

The Seasonal and Diurnal Variation Characteristics of Soil Moisture at Different Depths from Observational Sites over the Tibetan Plateau

Using observational data of soil moisture from the third Tibetan Plateau Experiment for atmospheric science (TIPEX III), the seasonal and diurnal variations characteristics of soil moisture at different depths of 5–160 cm from seven stations were analyzed, with emphasis on the comparative analysis of the differences of soil moisture between different sites and the differences of the synergistic relationship between soil moisture and temperature. The soil moisture was wet in the southeast and dry in the northwest. The studied sites were Lhari, Biru, Nyainrong, Amdo, Nagqu, Baingoin and Seng-ge Kambab in descending order, according to the soil moisture. The seasonal variation of soil moisture at the different sites showed a significant three-peak structure, which was more obvious in the shallow layer than in the deep layer. The first peak occurred from March to May, which was mainly due to the soil thawing in spring. The other two peaks corresponded to the two rainy seasons in the plateau. Soil moisture was the greatest during this rainy period. The diurnal variations of soil moisture and temperature in Amdo, Nagqu, Nyainrong and Baingoin showed a significant positive correlation in the four seasons. The soil moisture and temperature in Lhari and Biru were significantly positively correlated in winter and spring but negatively correlated in summer and autumn. The profiles of the soil moisture with depth varied greatly at different stations in different seasons. The distribution of soil water content at each observational site did not increase or decrease with depth but showed a certain high aquifer, which might be related to the types of the underlying surface and physical properties of soil. During the summer monsoon period, soil moisture in the shallow layer of 5–10 cm was higher at all observational sites. The spatial distribution of soil moisture in the plateau was more heterogeneous than that in the plain area, and only in the central part of the Tibetan Plateau, the soil moisture varied greatly from site to site. This also indicated that it was unreasonable to only use the soil moisture of several stations to represent the overall soil moisture of the region. The results provided a multi-angle observational basis for the validation of satellite data and parameterization of the numerical model of soil moisture over the Tibetan Plateau.

Normalizing time in terms of space: What drives the fate of spring thaw-released nitrogen in a sloping Arctic landscape?

In the Arctic tundra, snowmelt is followed by soil thaw allowing water and dissolved nutrients to move downslope. However, the fate of the released nitrogen (N) remains unclear, which includes the fraction of N that is lost to downslope transport or converted to N gasses.We have quantified the release of NO3− into the soil solution and the loss of gaseous N upon thaw and up to a month after first thaw in an Arctic hillslope in W Greenland. We further investigated which factors of the slope ecosystem that influence the NO3− concentrations and N2O fluxes throughout two snowmelt and growing seasons using a Structural Equation Model (SEM) linking physical, biological and biogeochemical characteristics across the slope.Snowmelt controls growing season onset, but varies in the landscape. To account for this, we normalized the spatiotemporal variation in snowmelt and soil thaw by measuring NO3− release and N2O loss in a controlled laboratory thaw experiment with topsoil cores from along the slope. We furthermore normalized seasonal progression of ecosystem variables in space based on the first day of soil thaw in the field. We tested the variable Day After Soil Thaw (DAST) as the temporal driver in our SEM, and found that season progression is the most important factor to describe patterns in NO3− concentrations and N2O fluxes. We conclude that DAST is a useful tool for analysing seasonal patterns in a spatially heterogeneous snowmelt landscape and between different snowmelt years.When normalizing based on first day of soil thaw, we saw that the decreasing NO3− content over the season did not control the increasing N2O emissions. Rather, nitrification replaced denitrification as the main N2O -source during the growing season, where soil temperatures increased and soil moisture decreased. The gaseous N loss from the slope during the first month of thaw was minor and amounted to 1% of the annual N deposition. A NO3− pulse released into solution after 24 h of thaw, when meltwater moves along the slope and connects upslope with downslope ecosystems, thus constituted a “hot moment” for interaction between landscape N pools, but the NO3− was immobilized by microorganisms or taken up by plants rather than denitrified and did thus not constitute a hot moment for N2O emissions. Thus, our results regarding what drives the fate of spring-thaw released N in the sloping Arctic landscape highlight the importance of snowmelt timing and the following number of Day After Soil Thaw as a normalizing factor for biogeochemical processes. This provides an analytical concept for reducing spatial and inter-annual variability to understand general seasonal patterns otherwise hidden.

Effects of different rest grazing periods on the reproduction and root characteristics of Carex capillifolia in subalpine meadow

Carex capillifolia is a dominant subalpine meadow plant species with considerable ecological and economic value. We studied the effects of different springtime rest grazing periods on C. capillifolia reproduction and the root characteristics. The rest grazing periods were established according to the soil thawing depth, plant regreening, and the local traditional rest grazing period. We set up five plots from the critical period of soil thawing (T1), the late period of soil thawing (T2), the early period of grass reviving (T3), the late period of grass growing (T4), and the local traditional rest grazing period (T5) to the start of the rest grazing. The end of the rest grazing in each plot was the plant withering period. Results showed that the sexual reproduction effort of T1 was 64.3% higher than that of T5. The root biomass of T5 was significantly lower than that of all the other treatments. The plant height, ear length, number of seeds per ear, reproductive branch density, and the seed yield of T1 were significantly higher than those of all the other plots. The reproductive branch density was significantly positively correlated with the seed yield. The seed yield of T1 was 200.0%, 349.1%, and 340.4% higher than those of T3, T4, and T5, respectively. The root length, surface area, and volume were the highest for T3. The root phenotypic traits and the nutrient storage content indirectly affected each other and jointly formed part of risk diversification strategies. A grey correlation analysis demonstrated that rest grazing during the critical soil thawing period (T1) was conducive to the growth of C. capillifolia. Therefore, springtime rest grazing should start from the critical soil thawing period in subalpine meadows.

Understanding the hydrological regime based on the runoff events in a mountainous catchment with seasonally frozen soil in the Qinghai‐Tibet plateau

AbstractSeasonal thawing of frozen soil will significantly affect the hydrological regime, water storage capacity and ecosystem services in the future, which contributes to the uncertainty of regional water resources. However, based on the scale of runoff events, the mechanism of seasonal frozen soil thawing on the hydrological regime are still unclear. In this study, we systematically analysed the runoff characteristics and interactive effects of environmental factors and pre‐event catchment state on runoff processes based on the runoff event scale, using data sets of air temperature, precipitation, runoff, soil moisture, and soil temperature observed in a mountainous catchment with seasonally frozen soil distribution on the Qinghai‐Tibet Plateau from 2010 to 2019. It was found that the event runoff coefficient did not increase significantly with the increase of precipitation. Event runoff coefficients exhibited strong seasonality. The catchment exhibited a gradual increase in the event runoff coefficient with increasing pre‐event baseflow and antecedent soil moisture, especially during stable period (August to November). Event runoff generation through infiltration excess as the result of intensive rainfall seemed to be only possible in the stable period, while heavy precipitation events were common during this period. Normalized event peak discharge and event runoff coefficient showed positive trends with changes in pre‐event catchment state indicators, which were commonly observed phenomena in runoff events. For this catchment, the increased storage capacity pre‐event saturation may be the main mechanism of event runoff generation, as it was unlikely that a single precipitation event would lead to catchment saturation. Soil temperature affects runoff processes through both direct effects on runoff processes and indirect effects on pre‐event catchment state. Temperature indicators were the most important predictors of runoff changes in the Qinghai‐Tibet Plateau.

Possible negative effects of earlier thaw onset and longer thaw duration on vegetation greenness over the Tibetan Plateau

The Tibetan Plateau (TP), also known as the world's Third Pole, is underlain by frozen ground and is highly sensitive to climate change. However, it remains unclear how the variations in soil freeze-thaw could affect vegetation dynamics across the TP. In this study, we adopted the latest datasets for vegetation, climate and soil freeze-thaw in the past two decades to explore the possible impacts of changes in soil freeze-thaw on vegetation greenness and phenology on the TP. According to the satellite-based observations, the TP showed an overall greening trend during 2001-2020, and the growing season length increased significantly at a rate of 3.6 days/10a, mainly contributed by the advances of the start of the growing season (2.7 days/10a). Based on ridge regression and partial correlation analysis, air temperature and precipitation were found to be the major dominant factors of vegetation dynamics on the TP, and precipitation played a dominant role in the relatively warm-dry southwestern TP where vegetation browning and spring phenology delays were observed. In the relatively cold regions, earlier soil thaw onset generally facilitated spring phenology, and longer soil thaw duration tended to increase the growing season soil moisture content, which could in turn enhance vegetation greenness. In the relatively warm regions, however, earlier thaw onset and longer thaw duration could possibly exacerbate the growing season water stress and limit vegetation growth. The negative impacts were more evident in the regions with unstable and completely degraded permafrost according to the results in the source region of Yellow and Yangtze rivers. Our findings highlight the spatially varying role of soil freeze-thaw changes in vegetation dynamics, which have important implications for the carbon budget of the TP in a warming future climate as frozen ground continues to degrade.

Совершенствование конструктивных решений низконапорных гидромелиоративных объектов в условиях меняющегося климата в Заречной группе Якутии

The regional temperature increase observed in recent decades has led to a noticeable increase in the amount of atmospheric precipitation, as well as to an increase in the water content of small rivers. As a result of these phenomena, changes in the engineering and geocryological conditions of the foundations of hydraulic structures occurred, cryogenic processes in the water areas of reservoirs became more active, which significantly reduced the stability of irrigation and drainage facilities. On the example of a typical low-pressure hydroelectric complex of the Zarechnaya group of Yakutia, the possibility of improving the design solutions of existing irrigation and drainage facilities based on the substantiation and development of measures to increase water availability in a changing climate is considered. The analysis of the data obtained in the course of the study confirms that due to the warming of the climate observed in recent years, there have been changes that negatively affect the stability of the frozen foundations of irrigation and drainage facilities, in particular, an increase in the layer of seasonal thawing of permafrost soils and an increase in the water content of small rivers exceeding the established initial carrying capacity. structures. In order to increase water availability in a changing climate, additional measures have been justified and introduced to improve the design solutions of the existing hydraulic structure, which consist in increasing the throughput of the structure and improving anti-seepage, heat-insulating and anti-heaving measures.