Soil Active Layer Research Articles

An experimental study of a forced ventilation pile

Introduction. Thermal stabilization of foundation soils is a most widely spread method of engineering protection of structures in the cryolithic zone. Presently, as a rule, any construction is feasible if the footing temperature remains negative in the regions that have permafrost soils. In the article, the co-authors have analyzed a conceptually new method of thermal stabilization of soil, that is, the application of forced ventilation piles. The goal of the laboratory experiments is to simulate the frozen soil behaviour in case of its exposure to a ventilated and cooled pile. The co-authors have solved the problem of soil temperature reduction to ensure the soil transition from the thawed state into the frozen or plastic frozen state. Besides, the co-authors have substantiated the efficiency of this thermal stabilization method. The subject of this research is a ventilated pile, driven into sandy soil and ventilated by the cool air generated by the refrigerating unit.
 Materials and methods. A laboratory study of a scaled model.
 Results. According to the data provided by the temperature sensors, a forced ventilation pile kept the soil frozen in the radius of 10 cm as of the end of the second winter, which means 2 meters, given the scale factor of the experiment. This methodology can also be applied as a method of thermal stabilization and refrigeration of soils. In the course of the experiment, thawed soil froze. In summer, the seasonal active soil layer thawed, and negative temperatures remained unchanged and generated a frost table registered by the temperature fields, used in the summer period.
 Conclusions. Soil remains frozen in summer; the bearing capacity of the pile remains unchanged.
 Acknowledgements: The co-authors would like to express thanks to the Central research and development laboratory of permafrost research of the Federal State Budgetary Educational Institution of Higher Education Tyumen Industrial University, and to anonymous reviewers.

Soil thermal regime alteration under experimental warming in permafrost regions of the central Tibetan Plateau

Soil thermal regime in permafrost regions is sensitive to climate change and may cause vast ecological consequences under future warming scenarios. However, there still lacks a systematic evaluation on the effect of warming on soil thermodynamics in the different ecosystems of permafrost regions. This study investigated the alterations of soil thermodynamics in alpine swamp meadow and alpine steppe under experimental warming by open-top chambers in permafrost regions of the central Tibetan Plateau. The results showed that air temperature increased significantly with an annual mean increase of 1.4 °C under warming. Compared to alpine swamp meadow, soil thermodynamics represented by soil temperature, soil thermal parameters, soil freeze-thaw process and active layer thickness in alpine steppe was more susceptible to warming. Specifically, soil temperature at 5–40 cm depths increased more in alpine steppe than alpine swamp meadow under warming, especially at topsoil (5–20 cm). Moreover, the increase in soil temperature at topsoil was greater during cold season than warm season. Greater alterations of soil thermal parameters were likely because soil moisture content reduced more in alpine steppe. Regarding soil freeze-thaw process, warming significantly postponed the onset of completely frozen stage and reduced the completely frozen days in alpine steppe. Active layer thickness in alpine steppe distinctly increased by 46 cm on average and showed an increasing trend under warming from 2009 to 2011. Overall, vegetation coverage and soil moisture content were responsible for the different responses of soil thermodynamics to experimental warming. The study has important implications for future scenarios as permafrost and grassland degradation may intensify under climate warming.

Chemical composition of soil organic matter and potential enzyme activity in the topsoil along a moisture gradient in the High Arctic (Svalbard)

The soil active layer in the High Arctic is a reservoir for nutrients and microbial communities, but their behavior and interactions remain unclear. Therefore, the objective of this study was to characterize soil organic matter (SOM) composition and potential enzyme activities in soil active layer of Svalbard. Samples from two different sites and two different soil layers (biocrust: 0–1 cm; mineral soil: 5–10 cm depth) were collected along a moisture gradient. The molecular SOM composition was assessed using pyrolysis-field ionization mass spectrometry (Py-FIMS), and the potential activities of seven extracellular enzymes characteristic for different soil microbial processes were measured. In general, SOM in both sites was dominated by lipids/sterols, alkylaromatics and phenols/lignin monomers. Dehydroergosterol prevailed in a majority of the samples. Biocrusts samples in both sites had higher total ion intensity and volatile matter, but lower lipid and alkylaromatics contents. The potential enzyme activities varied significantly across the sites, depths and moisture gradients and, in general, were higher in the biocrusts than in underlying soils. Besides, majority of measured enzyme activities were lower in the wetter plots. Taken together, our results expand the knowledge of SOM and enzyme activity in High Arctic topsoil, which is important for better understanding the dynamic of soil biotic and abiotic processes in polar environments, particularly in the context of climate change.

Long-term ecological consequences of forest fires in the continuous permafrost zone of Siberia

Wildfires are an important factor in controlling forest ecosystem dynamics across the circumpolar boreal zone. An improved understanding of their direct and indirect, short- to long-term impacts on vegetation cover and permafrost–vegetation coupling is particularly important to predict changes in carbon, nutrient and water cycles under projected climate warming. Here, we apply dendrochronological techniques on a multi-parameter dataset to reconstruct the effect of wildfires on tree growth and seasonal permafrost thaw depth in Central Siberia. Based on annually-resolved and absolutely dated information from 19 Gmelin larch (Larix gmelinii (Rupr.) Rupr.) trees and active soil layer thickness measurements, we find substantial stand-level die-off, as well as the removal of ground vegetation and the organic layer following a major wildfire in 1896. Reduced stem growth coincides with increased δ13C in the cellulose of the surviving trees during the first decade after the wildfire, when stomatal conductance was reduced. The next six to seven decades are characterized by increased permafrost active soil layer thickness. During this period of post-wildfire ecosystem recovery, enhanced tree growth together with positive δ13C and negative δ18O trends are indicative of higher rates of photosynthesis and improved water supply. Afterwards, a thinner active soil layer leads to reduced growth because tree physiological processes become limited by summer temperature and water availability. Revealing long-term effects of forest fires on active soil layer thickness, ground vegetation composition and tree growth, this study demonstrates the importance of complex vegetation–permafrost interactions that modify the trajectory of post-fire forest recovery across much of the circumpolar boreal zone. To further quantify the influence of boreal wildfires on large-scale carbon cycle dynamics, future work should consider a wide range of tree species from different habitats in the high-northern latitudes.

Soil Moisture Calibration Equations for Active Layer GPR Detection—a Case Study Specially for the Qinghai–Tibet Plateau Permafrost Regions

Ground-penetrating radar (GPR) is a convenient geophysical technique for active-layer soil moisture detection in permafrost regions, which is theoretically based on the petrophysical relationship between soil moisture (θ) and the soil dielectric constant (ε). The θ–ε relationship varies with soil type and thus must be calibrated for a specific region or soil type. At present, there is lack of such a relationship for active-layer soil moisture estimation for the Qinghai–Tibet plateau permafrost regions. In this paper, we utilize the Complex Refractive Index Model to establish such a calibration equation that is suitable for active-layer soil moisture estimation with GPR velocity. Based on the relationship between liquid water, temperature, and salinity, the soil water dielectric constant was determined, which varied from 84 to 88, with an average value of 86 within the active layer for our research regions. Based on the calculated soil-water dielectric constant variation range, and the exponent value range within the Complex Refractive Index Model, the exponent value was determined as 0.26 with our field-investigated active-layer soil moisture and dielectric data set. By neglecting the influence of the soil matrix dielectric constant and soil porosity variations on soil moisture estimation at the regional scale, a simple active-layer soil moisture calibration curve, named CRIM, which is suitable for the Qinghai–Tibet plateau permafrost regions, was established. The main shortage of the CRIM calibration equation is that its calculated soil-moisture error will gradually increase with a decreasing GPR velocity and an increasing GPR velocity interpretation error. To avoid this shortage, a direct linear fitting calibration equation, named as υ-fitting, was acquired based on the statistical relationship between the active-layer soil moisture and GPR velocity with our field-investigated data set. When the GPR velocity interpretation error is within ±0.004 m/ns, the maximum moisture error calculated by CRIM is within 0.08 m3/m3. While when the GPR velocity interpretation error is larger than ±0.004 m/ns, a piecewise formula calculation method, combined with the υ-fitting equation when the GPR velocity is lower than 0.07 m/ns and the CRIM equation when the GPR velocity is larger than 0.07 m/ns, was recommended for the active-layer moisture estimation with GPR detection in the Qinghai–Tibet plateau permafrost regions.

Development of a Shallow-Depth Soil Temperature Estimation Model Based on Air Temperatures and Soil Water Contents in a Permafrost Area

A model for predicting shallow depth soil temperatures is important and effective to assess the changes in soil conditions related to global climate change and local disturbances. Shallow-depth soil temperature estimation model in cold region in Alaska is developed based on thermal response using air temperature and shallow-depth soil water content during active layer development period of 160 days from May to October. Among the seven soil temperature measurement sites, data from four sites were used for model development, and the remaining three sites were used for model validation. Near the middle of the seven measurement sites, air temperature is monitored at one location. The proposed model implemented concepts of thermal response and cumulative temperature. Temperatures and soil water contents were measured using automated remote sensing technology. Consequently, it was confirmed that the developed model enables fast and accurate assessment of shallow-depth soil temperature during active soil layer development period.

Mycobiont contribution to tundra plant acquisition of permafrost-derived nitrogen.

As Arctic soils warm, thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon losses from tundra ecosystems. Although mycorrhizal fungi could facilitate plant access to permafrost-derived N, their exploration capacity beyond host plant root systems into deep, cold active layer soils adjacent to the permafrost table is unknown. We characterized root-associated fungi (RAF) that colonized ericoid (ERM) and ectomycorrhizal (ECM) shrub roots and occurred below the maximum rooting depth in permafrost thaw-front soil in tussock and shrub tundra communities. We explored the relationships between root and thaw front fungal composition and plant uptake of a 15 N tracer applied at the permafrost boundary. We show that ERM and ECM shrubs associate with RAF at the thaw front providing evidence for potential mycelial connectivity between roots and the permafrost boundary. Among shrubs and tundra communities, RAF connectivity to the thaw boundary was ubiquitous. The occurrence of particular RAF in both roots and thaw front soil was positively correlated with 15 N recovered in shrub biomass Taxon-specific RAF associations could be a mechanism for the vertical redistribution of deep, permafrost-derived nutrients, which may alleviate N limitation and stimulate productivity in warming tundra.

Использование методов релаксации в модели WRF для анализа метеорологических условий в Украине за длительный период

The possibility of using grid and spectral relaxation methods and other options in the WRF mesoscale model for long-term continuous calculations has been investigated. Results of comparison of selected me-teorological parameters with surface measurements are presented. The basic recommendations for select-ing the optimal combination of long-term calculation parameters are given. The use of the selected param-eters allowed to obtain continuous meteorological fields over a long period (several months), which are well consistent with surface measurements, retain large scale synoptic structures and have a deviation from measurements commensurate with the results of short-term simulations over corresponding time peri-od. The selected optimal combination of parameters allowed us to perform continuous calculation for the period from January 1, 2019 to November 6, 2019 without accumulating errors. In a long-run calculation of meteorological conditions in Ukraine with spatial resolution 0.15 deg. for a temperature at a height of 2 meters was obtained a mean absolute error of MAE=2,05 ºC, a correlation coefficient of Corr=0,97, for a wind speed at a height of 10 meters of MAE=1.4 m/s, of Corr=0,75, and for a wind direction at a height of 10 meters of MAE=24,6 degrees, Corr=0,66. The influence of the parametrizations of the underlying sur-face and the active soil layer on the quality of calculation of meteorological fields is studied. Using the option to update the water surface temperature allowed to reduce the MAE for the temperature from 2,17 ºС to 2,05 ºС. Each of the investigated surface models showed its advantages and disadvantages. The pa-rameterizations RUC and NOAH LSM showed good agreement with the measurements for all studied pa-rameters and can be recommended for use in long-term continuous calculations. A long calculation made it possible to describe the process of accumulation and melting of snow correctly, and made it possible to reproduce the temperature of the upper soil layer correctly as well. The paper shows that the disadvantage of long- term calculations is the inability to determine the temperature of the lower layers of the soil cor-rectly.

Innovative soil leaching technology: A case study from Bukhara region of Uzbekistan

The paper presents the results of field experiments on improving leaching technology in salty fields of Bukhara oasis through Biosolvent chemical compound (BChC). Scientific researches were carried in irrigated fields of scientific-research center of Tashkent Institute of Irrigation and Agricultural Mechanization Engineers Bukhara Branch which is located in Bukhara region, Kagan district, during 2017-2019 years. Leaching saline soils through Biosolvent reduces salt content in the active soil layer from 0.417 % to 0.204, while desalinization ratio will be 1.84. With this innovative technology leaching norm was 30% less compared to the control.

The impact of tillage row orientation on physical and chemical sediment enrichment

AbstractThis study aimed to better understand how tillage row orientation with respect to dominant flow‐pathway along hillslope impacts runoff and the transport of different sediment size fractions. Experimental plots were constructed in contour ridge till (CRT) and parallel ridge till (PRT) sites to monitor runoff and sediment fluxes. Particle size fractions of the sediment, along with organic C and N contents were measured to quantify physical and chemical enrichment ratios for the two tillage orientations. In the CRT plot, tillage produced large oriented roughness elements along the contours, which acted as little check dams, while in the PRT site, the roughness elements helped confine and concentrate the runoff. In the CRT, the “check dams” resulted in a runoff coefficient of .03, while in the PRT, the flow confinement between rows produced a runoff coefficient of .82. Moreover, the erosion rates at the CRT site were 97% less than those in the PRT plot. Large contours produced finer sediment fractions due to the selective sorting in ponded furrows. More aggregate sediment fractions were present in the PRT site, which was dominated by rill erosion. Physical enrichment revealed selective entrainment of finer sediment particles during erosion. Finer‐grain particles with higher specific surface areas, attached more organic C resulting in chemical enrichment. Physical and chemical enrichment methods were found to be in good agreement. These findings suggest transport models that can simulate size fraction updates to the soil active layer can be used to estimate SOC redistribution and hence more accurate C budgets.

ГІДРОГЕОЛОГІЧНА ДІЯ ДРЕНАЖУ ТА ДРЕНАЖНИХ СИСТЕМ ЗОНИ ПОЛІССЯ У ЗМІННИХ КЛІМАТИЧНИХ УМОВАХ

We have analyzed various methods and models for determining and calculating drainage module. The drainage module is an important indicator of the hydrogeological effect of drainage and soil drainage. For the calculation of the drainage calculation module, an empirical, analytical, water-balance method is used, or it is accepted on the recommendations without sufficient economic and environmental justification. This does not meet the modern requirements for the creation and operation of such objects. Traditionally, the designs and parameters of agricultural drainage are determined by the drainage module. It provides the necessary conditions for the removal of excess moisture of the active soil layer in the spring (as the main calculation) and corresponds to a certain level of the calculated security of the formation of the runoff hydrograph. According to the generalized results of the research, in the calculation of drainage parameters, the values of drainage modules were taken within: for mineral soils – 0.4… 0.6 l/sꞏha, for peat soils 0.2… 0.6 l/sꞏha. These recommended values are not correct because then the defined drainage parameters take into account only the technological conditions of its operation. But this does not take into account the conditions of formation of economic and environmental effect within the system, and they are not economically and environmentally optimal for the calculation of the drainage system and its elements. We have performed research and evaluation of the hydrogeological effect of the drainage and drainage systems. The results of these researches showed the variability of values of drainage modules in time and space. We have also identified many influencing factors and confirmed their difference with the calculated value. A new evaluation of the effectiveness of drainage systems and the calculation of drainage modules are proposed. This evaluation includes the yield criterion for variable natural (climatic) and agricultural conditions. New optimal values of drainage modules are proposed. These values are also presented for critical conditions (maximum daily rainfall of different levels of probability).

Permafrost degradation enhances the risk of mercury release on Qinghai-Tibetan Plateau

Permafrost on the Qinghai-Tibetan Plateau (QTP) has been degrading in the past decades. While the degradation may mobilize previously protected material from the permafrost profile, little is known about the stocks and stability of mercury (Hg) in the QTP permafrost. Here we measured total soil Hg in 265 samples from 15 permafrost cores ranging from 3 to 18 m depth, and 45 active layer (AL) soil samples from different land cover types on the QTP. Approximately 21.7 Gg of Hg was stored in surficial permafrost (0–3 m), with 16.58 Gg of Hg was stored in the active layer. Results from six permafrost collapse areas showed that much of the thawed Hg is mobile, with decreases in total Hg mass of 17.6–30.9% for the AL (top 30 cm) in comparison with non-thermokarst surfaces. We conclude that the QTP permafrost region has a large mercury pool, and the stored mercury is sensitive to permafrost degradation.

A carbon mass-balance budget for a periglacial catchment in West Greenland – Linking the terrestrial and aquatic systems

Climate change is predicted to have far reaching consequences for the mobility of carbon in arctic landscapes. On a regional scale, carbon cycling is highly dependent on interactions between terrestrial and aquatic parts of a catchment. Despite this, studies that integrate the terrestrial and aquatic systems and study entire catchments using site-specific data are rare. In this work, we use data partly published by Lindborg et al. (2016a) to calculate a whole-catchment carbon mass-balance budget for a periglacial catchment in West Greenland. Our budget shows that terrestrial net primary production is the main input of carbon (99% of input), and that most carbon leaves the system through soil respiration (90% of total export/storage). The largest carbon pools are active layer soils (53% of total carbon stock or 13 kg C m−2), permafrost soils (30% of total carbon stock or 7.6 kg C m−2) and lake sediments (13% of total carbon stock or 10 kg C m−2). Hydrological transport of carbon from the terrestrial to aquatic system is lower than in wetter climates, but the annual input of 4100 kg C yr−1 (or 3.5 g C m−2 yr−1) that enters the lake via runoff is still three times larger than the eolian input of terrestrial carbon. Due to the dry conditions, the hydrological export of carbon from the catchment is limited (5% of aquatic export/storage or 0.1% of total export/storage). Instead, CO2 evasion from the lake surface and sediment burial accounts for 57% and 38% of aquatic export/storage, respectively (or 0.8% and 0.5% of total export/storage), and Two-Boat Lake acts as a net source of carbon to the atmosphere. The limited export of carbon to downstream water bodies make our study system different from wetter arctic environments, where hydrological transport is an important export pathway for carbon.

Freshwater microbial community diversity in a rapidly changing High Arctic watershed.

Current models predict increases in High Arctic temperatures and precipitation that will have profound impacts on the Arctic hydrological cycle, including enhanced glacial melt and thawing of active layer soils. However, it remains uncertain how these changes will impact the structure of downstream resident freshwater microbial communities and ensuing microbially driven freshwater ecosystem services. Using the Lake Hazen watershed (Nunavut, Canada; 82°N, 71°W) as a sentinel system, we related microbial community composition (16S rRNA gene sequencing) to physicochemical parameters (e.g. dissolved oxygen and nutrients) over an annual hydrological cycle in three freshwater compartments within the watershed: (i) glacial rivers; (ii) active layer thaw-fed streams and waterbodies and (iii) Lake Hazen, into which (i) and (ii) drain. Microbial communities throughout these freshwater compartments were strongly interconnected, hydrologically, and often correlated with the presence of melt-sourced chemicals (e.g. dissolved inorganic carbon) as the melt season progressed. Within Lake Hazen itself, water column microbial communities were generally stable over spring and summer, despite fluctuating lake physicochemistry, indicating that these communities and the potential ecosystem services they provide therein may be resilient to environmental change. This work helps to establish a baseline understanding of how microbial communities and the ecosystem services they provide in Arctic watersheds might respond to future climate change.

ЭФФЕКТИВНАЯ ТЕХНОЛОГИЯ ПРОМЫВКИ ЗАСОЛЕННЫХ ПОЧВ

Relevance One of the main factors negatively affecting agriculture and the environment in Uzbekistan is soil salinization. Methods In this article given the results of field experiments on improving leaching technology in the salty fields of Bukhara oasis with using chemical component Biosolvent. Scientific researches were carried in irrigated fields of scientific-research center of Tashkent institute of irrigation and agricultural mechanization engineers Bukhara Branch (TIIAME BB) which is located in Bukhara region, Kagan district, during 2017-2019 years. Results Leaching saline soils with using Biosolvent reduces salt content in the active soil layer from 0.376% to 0.204, while desalinization ratio will be 1.84. With this technology leaching norm was 30% less compared to the control.

Soil moisture as a key factor in carbon release from thawing permafrost in a boreal forest

The feedback between the atmosphere and permafrost soils containing large carbon stocks is currently considered the most important carbon-cycle feedback, but it is missing from climate models due to many uncertainties. Knowledge of how differences in post-thaw hydrological conditions affect carbon (C) release is critical for predicting permafrost feedback, but this knowledge remains limited. In this study, permafrost and active layer soils from the southern margin of the Eurasian boreal permafrost region in Northeast China were collected and incubated under experimentally modified moisture to monitor their CO2 and CH4 productions under simulated natural, drier and flooded conditions. We also characterized soil properties related to soil organic carbon (SOC) quality and microbial activities to determine their relations with measured C productions. We found that permafrost had higher C release per gram of SOC basis (C vulnerability) than the active layer, which suggested that there would be a high risk for C emissions in the permafrost region when permafrost thaws in the warming future. However, hydrological conditions following the permafrost thaw control these emissions. Permafrost C decomposed in relatively aerobic upland systems had higher C emissions than that decomposed in anaerobic wetland environments. Our results suggest a greater climate forcing of C release in aerobic than anaerobic conditions, but there are some uncertainties resulting from the unknown long-term CH4 production rates. Moreover, we found that the aerobic C production in permafrost after thawing could be constrained by water stress, suggesting that previous predictions based on soil incubations at natural soil moisture might overestimate the aerobic permafrost C release.

Influence of snow cover on soil temperatures: Meso- and micro-scale topographic effects (a case study from the northern West Siberia discontinuous permafrost zone)

Snow cover distribution has a profound impact on ground temperature, on thickness of the active layer, and on permafrost. The purpose of this study was to evaluate the effects of snow cover on soil thermal regimes in West Siberia and to characterize the meso- and micro-scale spatial variation of winter ground surface temperature (GST). Maximum snow cover thickness (>80 cm) and duration (~8 months) were recorded for the lower elevation areas and in the forest site (using a vertical array of iButtons). Shallow snow cover and a late snow formation characterized open raised areas with shallow permafrost. Our results indicate that 20 cm snow cover thickness is the minimum for generating a significant insulating effect. Date of snow cover formation with thickness >20 cm had the strongest influence on soil temperature regimes. We found a significant negative correlation between winter GST and elevation. This relationship is indirectly controlled by snow cover redistribution. We additionally have shown that elevation, n-factor and winter GST are the variables most significantly affecting thaw depth in permafrost-affected soils. This research dictates the need for taking into account snowfall, and its redistribution due to the variability of local factors, in predicting the effects of climate change on soil temperatures and active layer depth. According to long-term meteorological data for West Siberia, a temporal trend in snowfall is not observed. Nevertheless, considerable interannual fluctuations in snow cover thickness can lead to interannual variations in the soil thermal regimes.

Retrieval of Permafrost Active Layer Properties Using Time-Series P-Band Radar Observations

We propose a method to estimate the active layer properties, including soil dielectric profiles and active layer thickness (ALT), in permafrost regions using time-series P-band polarimetric synthetic aperture radar (SAR) observations. The active layer and underlying permafrost are modeled as a three-layer dielectric structure with the layer dielectric constants representing the soil moisture and freeze-thaw state of the layer. To resolve the ambiguity of the retrieved layer thicknesses, an approach of finding the largest possible depths (LPDs) is combined with time-series observations, where the ALT is assumed time-invariant between the maximum thaw and before the upward freezing front rises significantly from the permafrost table. The LPD-assisted time-series retrieval algorithm is applied to the radar data acquired by the Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) P-band SAR in August and October 2014 and 2015 over the Alaska North Slope. The results show that the retrieved ALT values are generally underestimated for the sites where the in situ ALT is larger than the P-band sensing depth, with a retrieval bias ranging from −0.05 to −0.24 m as validated against the in situ ALT collected at Circumpolar Active Layer Monitoring (CALM) sites. For the sites where the in situ ALT is smaller than 0.55 m, the retrieval errors are generally less than 0.1 m. The retrieval results also show that the active layer properties are strongly influenced by the land cover types at the regional scale, and not as much by the North–South temperature gradient across a 180-km-long transect along the Deadhorse flight line.

Effects of the freeze-thaw cycle on potential evapotranspiration in the permafrost regions of the Qinghai-Tibet Plateau, China

Potential evapotranspiration (ET0) is one of the important indicators for characterizing atmospheric evapotranspiration, but arduous observation conditions lead to a relative lack in the understanding of the ET0 mechanism in cold, high-elevation regions. The study of the sensitivity coefficient and contribution rate of meteorological elements to ET0 under the effects of the freeze-thaw cycle in the permafrost regions of the Qinghai-Tibet Plateau (QTP) showed that air temperature (T) and ET0 had similar change trends, which reached a peak during the summer thawing period (ST). Furthermore, analysis of meteorological elements in different freeze-thaw stages of the active layer soil revealed that the contribution rate of each meteorological element to ET0 showed a seasonal distinction. The sensitivity coefficient and contribution rate of the net radiation (Rn) and vapor pressure deficit (VPD) to ET0 were high, and their mean values were 0.52 and 0.44, respectively. In contrast, the sensitivity coefficient and contribution rate of wind speed (u2) and T to ET0 were very small, and the mean values of the sensitivity coefficient were 0.08 and 0.01, respectively. Additionally, T had the lowest contribution rate to ET0. These results indicated that permafrost had a stable regulatory effect on T. The results are expected to be helpful in developing a process-based frozen soil hydrological model.

Hydro-meteorological influences on the growing season CO2 exchange of an alpine meadow in the northeastern Tibetan Plateau permafrost region: observations using eddy covariance method

Hydro-meteorological variations are fundamental environmental factors affecting site-level ecosystem carbon balance variations; however, how hydro-meteorological variations influence continuous CO2 exchange over alpine meadows during the growing season in permafrost regions on the Tibetan Plateau is poorly understood. Net ecosystem CO2 exchange (NEE) measured using the eddy covariance method was partitioned into its components of ecosystem respiration (ER) and gross ecosystem CO2 exchange (GPP). ER and GPP had a significant relationship with air temperature, vapor pressure deficit, and net radiation, during the growing season of an alpine meadow. There was a positive correlation between GPP and active layer soil temperatures at 5–40 cm except soil temperature at 80 cm, located in the vicinity of the bottom of the active layer. The microbial activity of underground rhizospheric microorganism, mainly distributed in in shallow soil layers at 0–20 cm in alpine permafrost regions on the Tibetan Plateau, can significantly promote plant photosynthesis. Thus, the correlation between GPP and soil temperatures at 5–20 cm was stronger than that between GPP and air temperature. The correlation between ER (GPP) and active layer soil moisture at 5–80 cm was complicated, especially for soils at 5–20 cm. With the increase of active layer soil moisture, ER (GPP) increased first and then decreased. This was related to the thawing process of the active layer, increase of rainfalls, the frozen layer acting as a weak permeable layer, and the replenishment of super-permafrost water. Our results suggested that long-term observations on how hydro-meteorological variations affect the continuous CO2 exchange of alpine meadows with different active layer thicknesses should be carried out in alpine permafrost regions.