Soil Thawing Research Articles

The Effect of Post-Fire Temperature Anomalies on Seasonal Thawing of Soils in the Permafrost Zone f Central Siberia Evaluated Using Remote Data

The Effect of Post-Fire Temperature Anomalies on Seasonal Thawing of Soils in the Permafrost Zone f Central Siberia Evaluated Using Remote Data

Nitrous oxide emissions following seasonal freeze-thaw events from arable soils in Northeast China

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide (N2O) emissions in cold regions. However, the mechanisms of soil N2O emission during the freeze-thaw cycling in the field remain unclear. We evaluated N2O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China, and the structural equation model (SEM) was used to determine which factors affected N2O production during non-growing season. Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period, but simultaneously increased the gaseous N2O-N losses at the annual time scale under field condition. The N2O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha−1 for the paddy and maize fields, respectively, and contributed to 66 and 18% of the annual total. The highest emission rates (199.2–257.4 µg m−2 h−1) were observed during soil thawing for both fields, but we did not observe an emission peak during soil freezing in early winter. Although the pulses of N2O emission in spring were short-lived (18 d), it resulted in approximately 80% of the non-growing season N2O-N loss. The N2O burst during the spring thawing was triggered by the combined impact of high soil moisture, flush available nitrogen and carbon, and rapid recovery of microbial biomass. SEM analysis indicated that the soil moisture, available substrates including NH4+ and dissolved organic carbon (DOC), and microbial biomass nitrogen (MBN) explained 32, 36, 16 and 51% of the N2O flux variation, respectively, during the non-growing season. Our results suggested that N2O emission during the spring thawing make a vital contribution of the annual nitrogen budget, and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.

Сезонное протаивание пород в Берингии на фоне современных климатических изменений

Сезонное протаивание пород в Берингии на фоне современных климатических изменений

Complex effects of mammalian grazing on extramatrical mycelial biomass in the Scandes forest-tundra ecotone.

Mycorrhizal associations are widespread in high‐latitude ecosystems and are potentially of great importance for global carbon dynamics. Although large herbivores play a key part in shaping subarctic plant communities, their impact on mycorrhizal dynamics is largely unknown. We measured extramatrical mycelial (EMM) biomass during one growing season in 16‐year‐old herbivore exclosures and unenclosed control plots (ambient), at three mountain birch forests and two shrub heath sites, in the Scandes forest‐tundra ecotone. We also used high‐throughput amplicon sequencing for taxonomic identification to investigate differences in fungal species composition. At the birch forest sites, EMM biomass was significantly higher in exclosures (1.36 ± 0.43 g C/m2) than in ambient conditions (0.66 ± 0.17 g C/m2) and was positively influenced by soil thawing degree‐days. At the shrub heath sites, there was no significant effect on EMM biomass (exclosures: 0.72 ± 0.09 g C/m2; ambient plots: 1.43 ± 0.94). However, EMM biomass was negatively related to Betula nana abundance, which was greater in exclosures, suggesting that grazing affected EMM biomass positively. We found no significant treatment effects on fungal diversity but the most abundant ectomycorrhizal lineage/cortinarius, showed a near‐significant positive effect of herbivore exclusion (p = .08), indicating that herbivory also affects fungal community composition. These results suggest that herbivory can influence fungal biomass in highly context‐dependent ways in subarctic ecosystems. Considering the importance of root‐associated fungi for ecosystem carbon balance, these findings could have far‐reaching implications.

Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest.

Increasing wildfire activity in Alaska's boreal forests has led to greater fuel-reduction management. Management has been implemented to reduce wildfire spread, but theecological impacts of these practices are poorly known. We quantified the effects of hand-thinning and shearblading on above- and belowground stand characteristics, plant species composition, carbon (C) and nitrogen (N) pools, and soil thaw across 19 sites dominated by black spruce (Picea mariana) in interior Alaska treated 2-12years prior to sampling. The density of deciduous tree seedlings was significantly higher in shearbladed areas compared to unmanaged forest (6.4 vs. 0.1 stems/m2 ), and unmanaged stands exhibited the highest mean density of conifer seedlings and layers (1.4 stems/m2 ). Understory plant community composition was most similar between unmanaged and thinned stands. Shearblading resulted in a near complete loss of aboveground tree biomass C pools while thinning approximately halved the C pool size (1.2kg C/m2 compared to 3.1kg C/m2 in unmanaged forest). Significantly smaller soil organiclayer (SOL) C and N pools were observed in shearbladed stands (3.2kg C/m2 and 116.8g N/m2 ) relative to thinned (6.0kg C/m2 and 192.2g N/m2 ) and unmanaged (5.9kg C/m2 and 178.7g N/m2 ) stands. No difference in C and N pool sizes in the uppermost 10cm of mineral soil was observed among stand types. Total C stocks for measured pools was 2.6kg C/m2 smaller in thinned stands and 5.8kg C/m2 smaller in shearbladed stands when compared to unmanaged forest. Soil thaw depth averaged 13cm deeper in thinned areas and 46cm deeper in shearbladed areas relative to adjacent unmanaged stands, although variability was high across sites. Deeper soil thaw was linked to shallower SOL depth for unmanaged stands and both management types, however for any given SOL depth, thaw tended to be deeper inshearbladed areas compared to unmanaged forest. These findings indicate that fuel-reduction management alters plant community composition, C and N pools, and soil thaw depth, with consequences for ecosystem structure and function beyond those intended for fire management.

Применение «условия Cтефана» для решения тепловых задач в объектах лесного комплекса

A two-phase formulation of the problems of "thermal shock" is considered when two homogeneous half-spaces come into contact at an initial instant of time with different phases and temperatures different from the phase transition temperature. In the absence of convection and thermal sources for constant thermophysical parameters, which can be formulated as the problem of conjugation of two temperature fields on the moving solidification front with additional boundary conditions (Stefan conditions). From a practical point of view, this kind of problem can be the arrival of processes occurring in the objects of the forest complex: in the production of particle board, the processing of ponds and reservoirs, the freezing (thawing) of soils, etc. The solution was carried out using the Laplace integral transformation. The exact analytical dependence obtained in this way explicitly determines the law of interference in each phase. These functions are used for integral transformations. The resulting temperature field corresponds to the known Gaussian distribution, and the velocity of the interphase boundary movement is inversely proportional to the square root of the crystallization time. The data of the approximate numerical calculation carried out for the water-ice system corresponds to a freezing (thawing) rate of approximately 10-3 mm / s. The obtained results can be used for research work in the field of construction thermal physics, geophysics and metallurgy.

Temperature regime of solonetzic meadow-chernozemic permafrost-affected soil in a long-term cycle

The characteristics of temperature dynamics in a solonetzic meadow-chernozemic soil of alas depression in Central Yakutia are described on the basis of long-term (2005–2014) stationary studies. Quick changes in weather conditions accompanied by changes in the soil temperature regime were observed during that period. Thus, the beginning of soil thawing in the spring shifted to earlier dates, and the beginning of soil freezing in the fall shifted to later dates. Temperature trends demonstrate an increase in the mean annual soil temperatures at all the depths. In total, the period of the frozen state of the soil became considerably shorter: in the middle-profile horizons, by 30–39 days. The obtained results attest to the high dynamism in temperature parameters of meadow soils in alas depressions of Central Yakutia under conditions of global climate changes.

A modelling framework to simulate field‐scale nitrate response and transport during snowmelt: The WINTRA model

AbstractModelling nutrient transport during snowmelt in cold regions remains a major scientific challenge. A key limitation of existing nutrient models for application in cold regions is the inadequate representation of snowmelt, including hydrological and biogeochemical processes. This brief period can account for more than 80% of the total annual surface runoff in the Canadian Prairies and Northern Canada and processes such as atmospheric deposition, overwinter redistribution of snow, ion exclusion from snow crystals, frozen soils, and snow‐covered area depletion during melt influence the distribution and release of snow and soil nutrients, thus affecting the timing and magnitude of snowmelt runoff nutrient concentrations.Research in cold regions suggests that nitrate (NO3) runoff at the field‐scale can be divided into 5 phases during snowmelt. In the first phase, water and ions originating from ion‐rich snow layers travel and diffuse through the snowpack. This process causes ion concentrations in runoff to gradually increase. The second phase occurs when this snow ion meltwater front has reached the bottom of the snowpack and forms runoff to the edge‐of‐the‐field. During the third and fourth phases, the main source of NO3 transitions from the snowpack to the soil. Finally, the fifth and last phase occurs when the snow has completely melted, and the thawing soil becomes the main source of NO3 to the stream.In this research, a process‐based model was developed to simulate hourly export based on this 5‐phase approach. Results from an application in the Red River Basin of southern Manitoba, Canada, shows that the model can adequately capture the dynamics and rapid changes of NO3 concentrations during this period at relevant temporal resolutions. This is a significant achievement to advance the current nutrient modelling paradigm in cold climates, which is generally limited to satisfactory results at monthly or annual resolutions. The approach can inform catchment‐scale nutrient models to improve simulation of this critical snowmelt period.

Seasonal patterns of soil nitrogen availability in moist acidic tundra

Our ability to predict effects of changing soil nitrogen (N) in Arctic tundra has been limited by our poor understanding of the intra-annual variability of soil N in this strongly seasonal ecosystem. Studies have shown that microbial biomass declines in spring accompanied by peaks in inorganic nutrients. However, subsequent to this early pulse, there are few high temporal resolution measurements during the growing season. We hypothesized that (1) low N would be maintained throughout the growing season, (2) peaks of total free primary amines (TFPA), ammonium (NH4+), and nitrate (NO3−) would follow a sequential pattern driven by mineralization and nitrification, and (3) a peak in soil N would occur as plants senesce. We conducted weekly measurements of TFPA, NH4+, and NO3− in two tundra sites, from soil thaw in spring to freeze in fall. At each site, NH4+ peaks were followed by smaller peaks in NO3−, supporting the hypothesis that excess NH4+ would be nitrified. Furthermore, peaks in NH4+ were observed both shortly after leaf expansion and at plant senescence. The variation in timing between sites and the peaks in NH4+ subsequent to thaw indicates that nutrient limitation in these ecosystems is more dynamic and spatially variable than previously thought.

Influence of snowmelt on soil moisture and on near surface air temperature during winter–spring transition season

This study examines relationships between snowmelt and soil moisture (SM), in particular, the influence of snowmelt on soil moisture memory (SMM) and on near surface air temperature (T2M) over the extra-tropical northern hemisphere (ENH) using four state-of-the-art reanalysis products: ERA-Interim, ERA-Interim Land, MERRA-Land, and GLDAS, as well as using Canadian Seasonal and Interannual Prediction System (CanSIPS) seasonal hindcast data, over a 20 year period (1986–2005). We use correlation-based metrics along with a simple classification-based on when the top layer soil temperature ( $$T_g$$ ) rises above freezing point during the annual freeze–thaw season, to evaluate the influence of snowmelt on SM. Our results show considerable differences across reanalyses as well as CanSIPS hindcasts regarding timing of maximum SWE ( $${\rm{SWE}}_{\rm{max}}$$ ) occurrences as well as the onset of thawing of the frozen soil. Correlation statistics indicate that $${\rm{SWE}}_{\rm{max}}$$ strongly influences SM. As a measure of the persistence of this relationship, a decay time is defined by lag in days over which the correlation of SM with lagged $${\rm{SWE}}_{\rm{max}}$$ decays to 1/e of its peak value. For a majority of grid cells over ENH this decay time is less than 45 days, which suggests $${\rm{SWE}}_{\rm{max}}$$ does not strongly influence the SM beyond subseasonal time scales. The interannual autocorrelation of SM indicates strong persistence over subseasonal time scales, consistently across reanalyses as well as CanSIPS hindcasts. However, intra-seasonal autocorrelations of ERA-Interim and MERRA-Land SM over North America show anomalous sudden decline of SMM compared to the other products, likely due to the offline forcing of atmospheric variables which blocks the atmosphere’s response to land feedbacks. One of the models used in CanSIPS, the Canadian Climate Model version 4 (CanCM4), also shows a sudden decline of intra-seasonal autocorrelation over Central Asia which is most likely due to weak land–atmosphere coupling over the region. Lag–lead correlation statistics between SM and T2M during the soil thaw period suggests that SM anomalies have measurable lagged influence on T2M with varying decay time over different regions and across different datasets.

Long-term grazing effects on soil-atmosphere exchanges of CO2, CH4 and N2O at different grasslands in Inner Mongolia: A soil core study

Regional greenhouse gas (GHG) budgets in vast grasslands may be changing due to overgrazing and grassland types. However, the comprehensive effects of grazing patterns, environmental factors and grassland types on soil carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) exchanges have been poorly studied. This study investigates the effects of long-term grazing on the soil-atmosphere exchanges of CO 2 , CH 4 and N 2 O in important processes within different grasslands in Inner Mongolia, China. Using manual static chamber and gas chromatography, we measured the fluxes of CO 2 , CH 4 and N 2 O from intact soil cores of paired grazed/ungrazed sites collected from two typical steppes (S tipa grandis and Leymus chinensis ): one wetland in a flood plain and one desert steppe in the region of the Xilin River catchment, Inner Mongolia. Soil gas flux and concentration measurements were conducted in four simulated conditions ( i.e. , drought, dry-wet, intense rainfall and freeze-thaw), which represent important processes in annual GHG exchanges. Extreme drought significantly inhibited CO 2 and N 2 O emissions in all plots but did not change the CH 4 uptake by typical steppes. Dry-wet transition and intense rainfall could remarkably promote soil CO 2 emission pulses at different types, significantly decrease CH 4 uptake by typical steppes, and arouse N 2 O emission pulses at all plots with different times of occurrence. During the freeze-thaw simulation, temperature-induced soil CO 2 emission and CH 4 uptake/emission presented a clear alternative variation, while soil thaw only slightly increased (<15 μg N m −2 h −1 ) in the steppes and sand dunes and was significantly higher in the wetland (11–96 μg N m −2 h −1 ). Long-term grazing significantly inhibited soil respiration rates at all grassland types, significantly decreased CH 4 uptake by the Leymus chinensis steppes, and did not show significant influence on N 2 O emission due to large spatial variations for all types. Compared to the ungrazed Leymus steppes, Stipa steppes, sand dune and wetland, continuously grazed sites were significantly reduced by 22%, 38%, 48% and 47% in total GHG emissions, respectively. Our results indicate that the potential of the steppe soil CH 4 sink function can be offset by N 2 O emission, especially in over-grazed plots. Furthermore, N 2 O emissions should be considered in wetland rangelands with significantly higher N 2 O emission potential (range: 0–343 μg N m −2 h −1 ) more than steppes (range: 0–132 μg N m −2 h −1 ) and sand dunes (range: 0–49 μg N m −2 h −1 ). Nevertheless, comprehensive evaluation of the grazing effect on ecosystem GHG emissions merits consider in both field observation and incubation experiments because soil properties and environmental factors could be changed by vegetation growth in different grazing practices.

Evaluating the performance of coupled snow–soil models in SURFEXv8 to simulate the permafrost thermal regime at a high Arctic site

Abstract. Climate change projections still suffer from a limited representation of the permafrost–carbon feedback. Predicting the response of permafrost temperature to climate change requires accurate simulations of Arctic snow and soil properties. This study assesses the capacity of the coupled land surface and snow models ISBA-Crocus and ISBA-ES to simulate snow and soil properties at Bylot Island, a high Arctic site. Field measurements complemented with ERA-Interim reanalyses were used to drive the models and to evaluate simulation outputs. Snow height, density, temperature, thermal conductivity and thermal insulance are examined to determine the critical variables involved in the soil and snow thermal regime. Simulated soil properties are compared to measurements of thermal conductivity, temperature and water content. The simulated snow density profiles are unrealistic, which is most likely caused by the lack of representation in snow models of the upward water vapor fluxes generated by the strong temperature gradients within the snowpack. The resulting vertical profiles of thermal conductivity are inverted compared to observations, with high simulated values at the bottom of the snowpack. Still, ISBA-Crocus manages to successfully simulate the soil temperature in winter. Results are satisfactory in summer, but the temperature of the top soil could be better reproduced by adequately representing surface organic layers, i.e., mosses and litter, and in particular their water retention capacity. Transition periods (soil freezing and thawing) are the least well reproduced because the high basal snow thermal conductivity induces an excessively rapid heat transfer between the soil and the snow in simulations. Hence, global climate models should carefully consider Arctic snow thermal properties, and especially the thermal conductivity of the basal snow layer, to perform accurate predictions of the permafrost evolution under climate change.

Rainfall–runoff responses on Arctic hillslopes underlain by continuous permafrost, North Slope, Alaska, USA

AbstractThe Arctic hydrologic cycle is intensifying, as evidenced by increased rates of precipitation, evapotranspiration, and riverine discharge. However, the controls on water fluxes from terrestrial to aquatic systems in upland Arctic landscapes are poorly understood. Upland landscapes account for one third of the Arctic land surface and are often drained by zero‐order geomorphic flowpath features called water tracks. Previous work in the region attributed rapid runoff response at larger stream orders to water tracks, but models suggest water tracks are hydrologically disconnected from the surrounding hillslope. To better understand the role of water tracks in upland landscapes, we investigated the surface and subsurface hydrologic responses of 6 water tracks and their hillslope watersheds to natural patterns of rainfall, soil thaw, and drainage. Between storms, both water track discharge and the water table in the hillslope watersheds exhibited diel fluctuations that, when lagged by 5 hr, were temporally correlated with peak evapotranspiration rate. Water track soils remained saturated for more of the summer season than soils in their surrounding hillslope watersheds. When rainfall occurred, the subsurface response was nearly instantaneous, but the water tracks took significantly longer than the hillslopes to respond to rainfall, and longer than the responses previously observed in nearby larger order Arctic streams. There was also evidence for antecedent soil water storage conditions controlling the magnitude of runoff response. Based on these observations, we used a broken stick model to test the hypothesis that runoff production in response to individual storms was primarily controlled by rainfall amount and antecedent water storage conditions near the water track outlet. We found that the relative importance of the two factors varied by site, and that water tracks with similar watershed geometries and at similar landscape positions had similar rainfall–runoff model relationships. Thus, the response of terrestrial water fluxes in the upland Arctic to climate change depends on the non‐linear interactions between rainfall patterns and subsurface water storage capacity on hillslopes. Predicting these interactions across the landscape remains an important challenge.

Spatial Variability of L-Band Brightness Temperature during Freeze/Thaw Events over a Prairie Environment

Passive microwave measurements from space are known to be sensitive to the freeze/thaw (F/T) state of the land surface. These measurements are at a coarse spatial resolution (~15–50 km) and the spatial variability of the microwave emissions within a pixel can have important effects on the interpretation of the signal. An L-band ground-based microwave radiometer campaign was conducted in the Canadian Prairies during winter 2014–2015 to examine the spatial variability of surface emissions during frozen and thawed periods. Seven different sites within the Kenaston soil monitoring network were sampled five times between October 2014 and April 2015 with a mobile ground-based L-band radiometer system at approximately monthly intervals. The radiometer measurements showed that in a seemingly homogenous prairie landscape, the spatial variability of brightness temperature (TB) is non-negligible during both frozen and unfrozen soil conditions. Under frozen soil conditions, TB was negatively correlated with soil permittivity (εG). This correlation was related to soil moisture conditions before the main freezing event, showing that the soil ice volumetric content at least partly affects TB. However, because of the effect of snow on L-Band emission, the correlation between TB and εG decreased with snow accumulation. When compared to satellite measurements, the average TB of the seven plots were well correlated with the Soil Moisture Ocean Salinity (SMOS) TB with a root mean square difference of 8.1 K and consistent representation of the strong F/T signal (i.e., TB increases and decreases when soil freezing and thawing, respectively). This study allows better quantitative understanding of the spatial variability in L-Band emissions related to landscape F/T, and will help the calibration and validation of satellite-based F/T retrieval algorithms.

Thaw pond development and initial vegetation succession in experimental plots at a Siberian lowland tundra site

Background and aimsPermafrost degradation has the potential to change the Arctic tundra landscape. We observed rapid local thawing of ice-rich permafrost resulting in thaw pond formation, which was triggered by removal of the shrub cover in a field experiment. This study aimed to examine the rate of permafrost thaw and the initial vegetation succession after the permafrost collapse.MethodsIn the experiment, we measured changes in soil thaw depth, plant species cover and soil subsidence over nine years (2007–2015).ResultsAfter abrupt initial thaw, soil subsidence in the removal plots continued indicating further thawing of permafrost albeit at a much slower pace: 1 cm y−1 over 2012–2015 vs. 5 cm y−1 over 2007–2012. Grass cover strongly increased after the initial shrub removal, but later declined with ponding of water in the subsiding removal plots. Sedges established and expanded in the wetter removal plots. Thereby, the removal plots have become increasingly similar to nearby ‘natural’ thaw ponds.ConclusionsThe nine years of field observations in a unique shrub removal experiment at a Siberian tundra site document possible trajectories of small-scale permafrost collapse and the initial stage of vegetation recovery, which is essential knowledge for assessing future tundra landscape changes.

Water, Salt and Heat Influences on Carbon and Nitrogen Dynamics in Seasonally Frozen Soils in Hetao Irrigation District, Inner Mongolia, China

To investigate carbon (C) and nitrogen (N) dynamics in seasonally frozen soils under saline and shallow groundwater supply conditions, in-situ lysimeter experiments with different groundwater table depths (WTD = 1.8 and 2.2 m) were conducted in Inner Mongolia, China during the wintertime of 2012–2013. Changes in soil organic C and total N in multiple layers during various periods, as well as their relationships with soil water, salt, and heat dynamics were analyzed. Accumulation of soil organic C and total N during freezing periods was strongly related to water and salt accumulation under temperature and water potential gradients. Water and salt showed direct influences on soil C and N dynamics by transporting them to upper layer and changing soil microbial activity. Salt accumulation in the upper layer during freezing and thawing of soil affected microbial activity by lowering osmotic potential, resulting in lower C/N ratio. Nitrogen in soil tended to be more mobile with water during freezing and thawing than organic C, and the groundwater table also served as a water source for consecutive upward transport of dissolved N and C. The changes in C and N in the upper 10 cm soil layer served as a good sign for identification of water and salt influences on soil microbial activity during freezing/thawing.

Simultaneous measurement of unfrozen water content and hydraulic conductivity of partially frozen soil near 0 °C

It is important to know the unfrozen water content and hydraulic conductivity of frozen soils when assessing water, heat, and solute transport in freezing and thawing soils for frozen soil engineering. To study these effects, an Andisol was packed into an acrylic column with an inner diameter of 70mm and a height of 30mm. First, the soil was frozen and thawed at different rates, and the soil freezing and thawing curves were measured. Second, water was added to flow through the thawing soil, and change in hydraulic conductivity with temperature was measured simultaneously with the thawing curve. The frozen soil contained more unfrozen water under a faster freezing rate and less unfrozen water under a faster thawing rate, resulting in a hysteresis-like behavior in the soil freezing and thawing curves. This is considered to be related to the pore ice growth lagging behind the change in the bulk soil temperature. Frozen soil below −0.5°C was practically impermeable. When water flows through a frozen soil, the soil has a higher unfrozen water content than without water flow. For a temperature increase from −0.5 to −0.2°C, the hydraulic conductivity increased by more than four orders of magnitude with increasing unfrozen water content. No significant difference was observed in the hydraulic conductivity of soils with different bulk densities or water flow rates. The hydraulic conductivity of the frozen soil was higher than that estimated from the unsaturated hydraulic conductivity of unfrozen soil through the Clausius–Clapeyron equation. This is likely related to the frozen soil having more unfrozen water than the amount estimated from the water retention curve of the unfrozen soil. At temperatures warmer than −0.2°C, the hydraulic conductivity approached a constant value, while the unfrozen water content continuously increased. Near 0°C, pore ice, which does not contribute to the water flow path, would remain frozen such as in inner-aggregate pores.

The fate of 13C15N labelled glycine in permafrost and surface soil at simulated thaw in mesocosms from high arctic and subarctic ecosystems

Nutrient distribution and carbon fluxes upon spring thaw are compared in mesocosms from high arctic and subarctic ecosystems dominated by Cassiope tetragona or Salix hastata/Salix arctica, in order to evaluate the possibility of plant and microbial utilization of an organic compound in thawing permafrost and surface soil. Double labeled glycine (13C15N) was added to soil columns with vegetation and to permafrost. During thaw conditions ecosystem respiration 13C was measured and 13C and 15N distribution in the ecosystem pools was quantified one day and one month after glycine addition. Near-surface soil microbes were more efficient in the uptake of intact glycine immediately upon thaw than plants. After one month plants had gained more 15N whereas microbes seemed to lose 15N originating from glycine. We observed a time lag in glycine degradation upon permafrost thaw, in contrast to surface soil thaw. Our results suggest that both arctic plants and microorganisms acquire amino acids released upon spring and permafrost thaw. Despite indications of more efficient utilization of added substrate in the High Arctic than the Subarctic, we conclude that patterns of nutrient distribution are similar and predictions based on subarctic data valid for high arctic settings.

Effects of soil temperature on bud break, shoot and needle growth, and frost hardiness in Pinus sylvestris var. mongolica saplings during dehardening

The present study evaluated the influence of delayed soil thawing on the growth and frost hardiness of Pinus sylvestris var. mongolica saplings between September 2011 and August 2012 in Northern China (41°35′N, 116°32′E). The saplings were randomly divided into three treatments: control, snow removal, and snow removal + insulation. The control saplings were grown under natural conditions. Snow cover was removed from the saplings in the snow removal treatment. For the snow removal + insulation treatment, snow cover was removed and soil surface was covered with a layer of hay (15 cm). The bud break, current-year shoot elongation and diameter as well as current-year needle elongation were measured and compared among the three treatments. The frost hardiness of previous-year stems and needles was assessed using the electrical impedance spectroscopy method. The saplings in the snow removal + insulation treatment exhibited delayed bud break, needle and shoot growth, as well as cessation of needle and shoot growth compared to the other treatments. In contrast, the growth of shoots and needles was generally higher in the snow removal treatment. A linear relationship was observed between plant growth, especially needle elongation, and temperature sum at soil depth of 20 cm. During dehardening, there were no differences in frost hardiness for both stems and needles among the treatments. In conclusion, snow removal + insulation delayed growth, whereas snow removal accelerated the growth. The frost hardiness of saplings during dehardening did not differ among treatments significantly. The possible reduction of snow cover and increase of soil freezing under warming climate would not have negative impacts on saplings in terms of frost hardiness during dehardening. Nevertheless, increased soil freezing would have unfavorable influences in terms of shoot and needle growth.

Simulating cold-region hydrology in an intensively drained agricultural watershed in Manitoba, Canada, using the Cold Regions Hydrological Model

Abstract. Etrophication and flooding are perennial problems in agricultural watersheds of the northern Great Plains. A high proportion of annual runoff and nutrient transport occurs with snowmelt in this region. Extensive surface drainage modification, frozen soils, and frequent backwater or ice-damming impacts on flow measurement represent unique challenges to accurately modelling watershed-scale hydrological processes. A physically based, non-calibrated model created using the Cold Regions Hydrological Modelling platform (CRHM) was parameterized to simulate hydrological processes within a low slope, clay soil, and intensively surface drained agricultural watershed. These characteristics are common to most tributaries of the Red River of the north. Analysis of the observed water level records for the study watershed (La Salle River) indicates that ice cover and backwater issues at time of peak flow may impact the accuracy of both modelled and measured streamflows, highlighting the value of evaluating a non-calibrated model in this environment. Simulations best matched the streamflow record in years when peak and annual discharges were equal to or above the medians of 6.7 m3 s−1 and 1.25 × 107 m3, respectively, with an average Nash–Sutcliffe efficiency (NSE) of 0.76. Simulation of low-flow years (below the medians) was more challenging (average NSE &lt; 0), with simulated discharge overestimated by 90 % on average. This result indicates the need for improved understanding of hydrological response in the watershed under drier conditions. Simulation during dry years was improved when infiltration was allowed prior to soil thaw, indicating the potential importance of preferential flow. Representation of in-channel dynamics and travel time under the flooded or ice-jam conditions should also receive attention in further model development efforts. Despite the complexities of the study watershed, simulations of flow for average to high-flow years and other components of the water balance were robust (snow water equivalency (SWE) and soil moisture). A sensitivity analysis of the flow routing model suggests a need for improved understanding of watershed functions under both dry and flooded conditions due to dynamic routing conditions, but overall CRHM is appropriate for simulation of hydrological processes in agricultural watersheds of the Red River. Falsifications of snow sublimation, snow transport, and infiltration to frozen soil processes in the validated base model indicate that these processes were very influential in stream discharge generation.