Soil Temperature Gradient Research Articles

Study on temperature field distribution and leakage point localization of buried carbon dioxide pipeline leakage

Leakage from buried CO2 pipelines is a critical issue in the context of carbon capture and storage (CCS). Therefore, we developed a small-scale experimental system for buried CO2 pipeline leakage. to investigate the effects of leak pressure, leak aperture size, and soil type on the temperature distribution near the leak point. The results of the study showed that the lowest soil temperature appeared directly above the leak. The minimum temperature at the soil axial measurement point increased with increasing leak pressure, but the peak maximum temperature difference decreased. 3 mm and 5 mm leak pore sizes, the peak maximum temperature difference occurred at 10 cm and 20 cm, respectively. At all pressures, the maximum temperature difference peaked at 20 cm. Soil surface temperature variations were mainly influenced by leak pressure. The maximum peak temperature difference at the soil surface measurement points also increased with increasing leak pressure. Smaller leakage apertures slowed down the decrease of soil surface temperature. In addition, based on the experimental results, we propose a new method to locate leaks based on the soil temperature gradient.

Radon indoors source potential from soil gas in a temperate climate: impact of infiltration rate and seismicity

Indoor radon source potential from unground soil was monitored using prototype devices approaching a dwelling with a cellar basement at 1 depth from the soil-atmosphere interface. Therefore, the radon concentrations in soil gas were monitored at 1 m depth. Integrated radon measurements were performed, and the results correlated with meteorological parameters. The influence of the difference in outdoor and device-soil temperature was considered, and the infiltration rate was calculated. The effect of the soil temperature gradient on the soil radon entry rate was evaluated. The indoor radon entry rate due to the soil gas was 7.0 ± 2.7 Bq m−3 h−1. The radon entry rate was 5.0 ± 0.8 Bq m−3 h−1 due to diffusion. In contrast, the advection-drive flow of soil gas is ranged up to ± 4.0 Bq m−3 h−1. So, the infiltration rate of the model dwelling was 0.7 (± 0.5) × 10−1 h−1 if only the stack effect occurred. The radon levels in tap water were measured, and the radon entry rate was estimated at 1.3 ± 0.7 Bq m−3 h−1. If the ventilation rate is low or seismic faulting appears, the soil radon entry is increased by one order of magnitude. The soil radon appeared like the building materials, having 1/3 of the total indoor radon entry, while outdoor air was slightly lower (28%), with tap water at 5%. The resident’s mortality risk occurred at < 2.5% for typical dwellings in temperate climate areas founded on sand-gravel underground. The risk rises to 34% with an extremely low ventilation rate between indoors and outdoors or high radon entry from the soil due to seismic faulting.

Thermal conductivity in a vadose zone: A novel spectral solution and application by the implication of significant coherence of thermal condition in the shallow soil water layer

AbstractIn the context of the heterogeneity in the unsaturated or vadose zone, accurately representing the analytical mechanisms and in‐situ water content within the soil layer poses a significant challenge. Particularly in shallow layers, thermal conditions exhibit rapid changes in response to evolving surface temperatures. This study proposes a hypothesis suggesting that the in situ heat mechanism may notably impact the soil water layer. The research introduces an innovative approach to theoretically uncover thermal conditions, including soil temperature, soil temperature gradients, and heat flux, within the shallow Quaternary gravel layer at various depths through spectral analysis of temporal observations. The study presents a stochastic inverse solution to estimate thermal conductivity by leveraging spectral analysis of soil heat flux and temperature gradients. The findings reveal that thermal conditions exhibit the most prominent periodic fluctuations during the diurnal process over a 24‐hour cycle. The soil temperature gradients and heat flux measurements at depths of 0.1, 0.3, 0.6, and 1.2 m demonstrate their ability to capture changes in soil temperature and air temperature to a certain extent within the frequency domain. Furthermore, the analysis highlights the intrinsic uncertainty and sensitivity of estimating thermal conductivity in heterogeneous soil environments. The wide variability observed in thermal conductivity values, coupled with their dependence on soil type and environmental conditions, underscores the need for careful consideration of these factors in future studies and modeling efforts. Applying the derived inverse spectral solution allows for determining thermal conductivity throughout the soil‐water system across depths ranging from 0.1 to 1.2 m. As a result, this research demonstrates the feasibility and practicality of assessing the thermal conductivity of the soil layer in conjunction with heat flux and temperature gradients through spectral analysis.

Microorganisms in subarctic soils are depleted of ribosomes under short-, medium-, and long-term warming.

Physiological responses of soil microorganisms to global warming are important for soil ecosystem function and the terrestrial carbon cycle. Here, we investigate the effects of weeks, years, and decades of soil warming across seasons and time on the microbial protein biosynthesis machineries (i.e. ribosomes), the most abundant cellular macromolecular complexes, using RNA:DNA and RNA:MBC (microbial biomass carbon) ratios as proxies for cellular ribosome contents. We compared warmed soils and non-warmed controls of 15 replicated subarctic grassland and forest soil temperature gradients subject to natural geothermal warming. RNA:DNA ratios tended to be lower in the warmed soils during summer and autumn, independent of warming duration (6weeks, 8-14years, and > 50years), warming intensity (+3°C, +6°C, and +9°C), and ecosystem type. With increasing temperatures, RNA:MBC ratios were also decreasing. Additionally, seasonal RNA:DNA ratios of the consecutively sampled forest showed the same temperature-driven pattern. This suggests that subarctic soil microorganisms are depleted of ribosomes under warm conditions and the lack of consistent relationships with other physicochemical parameters besides temperature further suggests temperature as key driver. Furthermore, in incubation experiments, we measured significantly higher CO2 emission rates per unit of RNA from short- and long-term warmed soils compared to non-warmed controls. In conclusion, ribosome reduction may represent a widespread microbial physiological response to warming that offers a selective advantage at higher temperatures, as energy and matter can be reallocated from ribosome synthesis to other processes including substrate uptake and turnover. This way, ribosome reduction could have a substantial effect on soil carbon dynamics.

Biofuel, solar-biofuel or geothermal energy; which resource can better contribute to an integrated energy system for residential energy demands

In this study, an integrated energy system is deployed to generate electricity, heating, cooling, and domestic hot water for a community considering three fully renewable energy source scenarios: biofuel (Case I), solar-biofuel (Case II), and geothermal energy (Case III). The proposed systems are modeled, assessed, optimized, and compared thermodynamically, economically, and environmentally; in addition, a proton exchange membrane electrolyzer (PEME) is utilized to convert the surplus electricity to stored hydrogen to raise the exergy efficiency and package value-added. Mathematical models are fully developed from thermodynamic and economic perspectives, taking a cumulative inflation rate into account via the Consumer Price Index (CPI). The novelty of the study is to focus on the comparison of the proposed renewable resources as energy inputs for the same condition (community loads), as there is a gap in this regard in the literature. Presented systems are optimized using Non-dominated Sorting Genetic Algorithm-II (NSGA-II) for minimum net costs as well as maximum exergy efficiency to reach the optimum operating conditions for each case during the peak cooling and heating loads. Moreover, for a more precise comparison of the proposed cases from an exergetic, economic, and environmental point of view, dynamic (hourly) behaviors of systems are analyzed over a year. A comprehensive parametric study is carried out to reckon the influence of borehole drilling depth, geofluid mass flow rate, and soil temperature gradient on case III to appraise its competitiveness in different locations, as well as the effects of the number of collectors on total cost rate and exergy efficiency for case II. Results indicate the annual net costs of $107.1k, $99.5k, and -$505.1k (where the negative sign stands for "income" instead of "cost") and average exergy efficiencies of 19.1 %, 26.3 %, and 41.3 % for cases I, II and III respectively.

Spatiotemporally heterogeneous soil thermohydraulic processes in the frozen soil of the Tibetan Plateau

Frozen soil properties and thermohydraulic processes are still not fully understood due to lack of in-situ measurements, especially in the high altitudes and high latitudes (HAHL). Based on hourly measurements at 10, 40, 80 and 120 cm depths at 21 sites in the west, south and northeast regions of the Tibetan Plateau (TP) during July 2018 - July 2019, we examined soil particles, spatiotemporal variations of soil thermohydraulic processes and their connections with environmental factors to reveal the heterogenous frozen soil properties on the TP. Sand and silt are the dominant soil particles and clay is less than 10% at the sites. Existing and widely used soil products underestimates (significantly overestimates) sand (clay) content on the TP which raises the uncertainty in the thermohydraulic parameters derived from these products. Diurnal soil moisture and temperature variations are seen only above 40 cm, but seasonal variations occur down to 120 cm due to the soil memory effect. Seasonally frozen soil and permafrost soil show different freezing and melting processes. Dry soil features greater soil temperature temporal variability and deeper maximum frozen depth than wet soil. Zero curtain occurs in both dry and wet soil, and displays high (low) frequency but short (long) duration at 10 (80) cm that vary spatially. Moisture depression exists in seasonally frozen soil and is determined by the initial soil moisture and temperature gradient strength. The strong thermohydraulic coupling existed in cold season collapses in warm season. Soil moisture exhibits higher spatiotemporal variability than soil temperature. At daily time scale, the influences of precipitation, wind speed and relative humidity on soil moisture and temperature vary under different climate conditions. These findings fill the knowledge gaps in the soil thermohydraulic processes in the HAHL, and improve the understanding of frozen soil properties and heat-water coupling processes in soil in the HAHL. The study will benefit the Earth system model development and improve the quality of soil temperature and moisture assimilation and remote sensing products in the HAHL.

Effect of Soil Texture on Water and Salt Transport in Freeze—Thaw Soil in the Shallow Groundwater Area

Research on the variation in soil water, heat, and salt in unsaturated zones during the freeze–thaw process has great significance in efficiently utilizing water resources and preventing soil salinization. The freeze–thaw field experiment was carried out with the lysimeter as the test equipment to analyze characteristics of the soil freeze–thaw process, profile water content, main ion content, and salt content of three textured soils with the groundwater table depth of 0.5 m. The results showed that the soil temperature gradient and freezing depth were greater as the average soil particle size increased. The increment of water content at the depth of 0 to 30 cm in sandy loam and loamy sand decreased by 40.20~93.10% and 28.14~65.52% compared with that in sandy soil, and the average increment of salt content at the depth of 0 to 30 cm decreased as the average soil particle size increased during the freeze–thaw period. The average content of Ca2+, Na+, Cl−, and SO42− in loamy sand and sandy soil decreased by 4.37~45.50% and 22.60~70.42% compared with that in sandy loam at the end of the freeze–thaw period, and the correlation between soil salt content and water content decreased with the increase in the average soil particle size. The research results can provide a theoretical basis for soil salinization prevention and crop production in shallow groundwater areas.

Role of Temperature Gradient and Soil Thermal Properties on Frost Heave

In cold regions, the soil temperature gradient and depth of frost penetration can significantly affect roadway performance because of frost heave and thaw settlement of the subgrade soils. The severity of the damage depends on the soil index properties, temperature, and availability of water. While nominal expansion occurs with the phase change from pore water to ice, heaving is derived primarily from a continuous flow of water from the vadose zone to growing ice lenses. The temperature gradient within the soil influences water migration toward the freezing front, where ice nucleates, coalesces into lenses, and grows. This study evaluates the frost heave potential of frost-susceptible soils from Iowa (IA-PC) and North Carolina (NC-BO) under different temperature gradients. One-dimensional frost heave tests were conducted with a free water supply under three different temperature gradients of 0.26°C/cm, 0.52°C/cm, and 0.78°C/cm. Time-dependent measurements of frost penetration, water intake, and frost heave were carried out. Results of the study suggested that frost heave and water intake are functions of the temperature gradient within the soil. A lower temperature gradient of 0.26°C/cm leads to the maximum total heave of 18.28 mm (IA-PC) and 38.27 mm (NC-BO) for extended periods of freezing. The maximum frost penetration rate of 16.47 mm/hour was observed for a higher temperature gradient of 0.78°C/cm and soil with higher thermal diffusivity of 0.684 mm2/s. The results of this study can be used to validate numerical models and develop engineered solutions that prevent frost damage.

Effect of freeze–thaw process on heat transfer and water migration between soil water and groundwater

Understanding the mechanisms of water migration and heat transfer in frozen soil is essential for the selection of water resource management measures and determination of irrigation schemes for winters. However, the dynamics of the groundwater level and temperature caused by freezing and thawing and their impact on soil water redistribution remain unclear. In this field study, the mechanisms of water migration and heat transfer in the soil during the freeze–thaw period under the combined action of the surface temperature change (upper boundary) and groundwater level fluctuation (lower boundary) were comprehensively considered with the theory and method of heat transfer, freeze–thaw characteristic curves of soil, and water balance model. The results showed that: (1) The soil temperature distribution and groundwater temperature dynamics can be interpreted intuitively by the soil temperature gradient and accumulated heat storage. (2) The freeze–thaw characteristic curves of soil indicated that the soil temperature dynamics caused a phase transition of the soil water. This further changed the soil water potential and permeability by 1–2 magnitudes and 1–5 magnitudes, respectively, which affected the direction and quantity of water migration. (3) The water balance quantitatively revealed the controlling effect of groundwater level changes caused by freezing and thawing on soil moisture dynamics. About 20% of the ice in the frozen layer was formed by the upward recharge of the groundwater during the freezing period. In the thawing period, most of this water returned to the groundwater (84%), while the rest (16%) increased the soil water content. These results systematically explain the mechanisms of heat transfer and water migration between the soil water and the groundwater during the freeze–thaw period, providing a theoretical reference for agricultural water management in seasonally frozen regions.

Community adaptation to temperature explains abrupt soil bacterial community shift along a geothermal gradient on Iceland

Understanding how and why soil microbial communities respond to temperature changes is important for understanding the drivers of microbial distribution and abundance. Studying soil microbe responses to warming is often made difficult by concurrent warming effects on soil and vegetation and by a limited number of warming levels preventing the detection of non-linear effects. A unique area in Iceland, where soil temperatures have recently increased due to geothermic activity, created a stable warming gradient in both grassland (dominated by Agrostis capillaris) and forest (Picea sitchensis) vegetation. By sampling soils which had been subjected to four years of temperature elevation (ambient (MAT 5.2 °C) to +40 °C), we investigated the shape of the response of soil bacterial communities to warming, and their associated community temperature adaptation. We used 16S rRNA amplicon sequencing to profile bacterial communities, and bacterial growth-based assays (3H-Leu incorporation) to characterize community adaptation using a temperature sensitivity index (SI, log (growth at 40 °C/4 °C)). Despite highly dissimilar bacterial community composition between the grassland and forest, they adapted similarly to warming. SI was 0.6 (equivalent to a minimum temperature for growth of between −6 and −7 °C) in both control plots. Both diversity and community composition, as well as SI, showed similar threshold dynamics along the soil temperature gradient. There were no significant changes up to soil warming of 6–9 °C above ambient, beyond which all indices shifted in parallel, with SI increasing from 0.6 to 1.5. The consistency of these responses provide evidence for an important role for temperature as a direct driver of bacterial community shifts along soil temperature gradients.

Heat flux in volcanic and geothermal areas: Methods, principles, applications and future directions

The measurement and assessment of heat flux in volcanic and geothermal areas are crucial to studying the thermodynamic process, locating the activity of a geothermal field, evaluating geothermal resources, and assessing volcanic hazards. Several methods exist for conducting heat flux measurements, including assessing the soil temperature gradient, thermal infrared remote sensing, ground calorimeter, and other direct calorimetric methods; as well as assessing soil CO2 flux, chloride inventory balance, eddy covariance, and other indirect calorimetric methods; and integrated methods from those mentioned above. Here, we review the history, basic principles, field operation procedures, suitability, and application of these heat flux measurement methods. The relationship between these direct and indirect calorimetric methods and the conduction, convection, advection, and radiation heat transfer mechanisms near the surface are also discussed. Characterization of the intensity of heat accumulation in volcanic and geothermal areas and its potential value for heat and mass transfer near the surface are also recommended. We suggest that the soil temperature gradient and soil CO2 flux methods are promising and representative heat flux measurement methods after comparative analysis of their advantages and disadvantages, accuracy of results, relationship with the heat transfer mechanism, characterization of heat accumulation intensity, convenient operation, clear principle, wide range of characterization, and abundant application scenarios. With the increasing demand for these technologies, heat flux measurement methods can be applied in unconventional volcanic and geothermal areas, such as polar regions, the moon, and large lakes. The results are beneficial to the targeting of geothermal resources, as well as revealing the mechanism of heat and mass transfer in the upper crust.

Selection against early flowering in geothermally heated soils is associated with pollen but not prey availability in a carnivorous plant.

In high-latitude environments, plastic responses of phenology to increasing spring temperatures allow plants to extend growing seasons while avoiding late frosts. However, evolved plasticity might become maladaptive if climatic conditions change and spring temperatures no longer provide reliable cues for conditions important for fitness. Maladaptative phenological responses might be related to both abiotic factors and mismatches with interacting species. When mismatches arise, we expect selection to favor changes in phenology. We combined observations along a soil temperature gradient in a geothermally heated area with pollen and prey supplementation experiments and examined how phenotypic selection on flowering time in the carnivorous plant Pinguicula vulgaris depends on soil temperature, and pollen and prey availability. Flowering advanced and fitness decreased with increasing soil temperature. However, in pollen-supplemented plants, fitness instead increased with soil temperature. In heated soils, there was selection favoring later flowering, while earlier flowering was favored in unheated soils. This pattern remained also after artificially increasing pollen and prey availability. Plant-pollinator mismatches can be an important reason why evolved plastic responses of flowering time to increasing spring temperatures become maladaptive under novel environmental conditions, and why there is selection to delay flowering. In our study, selection for later flowering remained after artificially increasing pollen availability, suggesting that abiotic factors also contribute to the observed selection. Identifying the factors that make evolved phenological responses maladaptive under novel conditions is fundamental for understanding and predicting evolutionary responses to climate warming.

Data‐Guided Exploration of the Energy Partitioning at Land Surface in the Contiguous US

AbstractThis study explores the climatic controls of the long‐term energy partitioning of net radiation into sensible heat and latent heat at watershed scale, by following a data‐guided approach. Collected data shows that the relationship between the evaporative fraction (ratio of latent heat to net radiation) and the aridity index (ratio of energy supply to water supply), which represents the climatic conditions at watershed scale, follows a trend similar to the Budyko curve. To explore the physical basis of this relationship, we hypothesize that there are mediating factors connecting energy partitioning with climate. Two potential mediating factors are considered, namely the equilibrium root zone soil moisture and land‐air temperature difference. We extract empirical relationships between the mediating factors and the partitioning fractions of water and energy fluxes based on observational data in 219 study watersheds across the contiguous US. With the obtained empirical relationships, we analytically derive two alternate Budyko‐type equations for energy partitioning, for each of the two mediating factors separately. Both equations show similar trends as the Budyko curve. We also derive a function to relate energy partitioning to water partitioning Budyko‐type equations, suggesting a close connection between the two. The study brings out the mediating roles of soil moisture and temperature gradient that connect water/energy partitioning with climate over long timescales in watersheds. In the process, the analysis results also provide useful insights about complex watershed system behavior. The observed relationships can be used to constrain hydrological and Earth system models and thus improve modeling performance.

Probabilistic estimation of depth-resolved profiles of soil thermal diffusivity from temperature time series

Abstract. Improving the quantification of soil thermal and physical properties is key to achieving a better understanding and prediction of soil hydro-biogeochemical processes and their responses to changes in atmospheric forcing. Obtaining such information at numerous locations and/or over time with conventional soil sampling is challenging. The increasing availability of low-cost, vertically resolved temperature sensor arrays offers promise for improving the estimation of soil thermal properties from temperature time series, and the possible indirect estimation of physical properties. Still, the reliability and limitations of such an approach need to be assessed. In the present study, we develop a parameter estimation approach based on a combination of thermal modeling, sliding time windows, Bayesian inference, and Markov chain Monte Carlo simulation to estimate thermal diffusivity and its uncertainty over time, at numerous locations and at an unprecedented vertical spatial resolution (i.e., down to 5 to 10 cm vertical resolution) from soil temperature time series. We provide the necessary framework to assess under which environmental conditions (soil temperature gradient, fluctuations, and trend), temperature sensor characteristics (bias and level of noise), and deployment geometries (sensor number and position) soil thermal diffusivity can be reliably inferred. We validate the method with synthetic experiments and field studies. The synthetic experiments show that in the presence of median diurnal fluctuations ≥ 1.5 ∘C at 5 cm below the ground surface, temperature gradients &gt; 2 ∘C m−1, and a sliding time window of at least 4 d the proposed method provides reliable depth-resolved thermal diffusivity estimates with percentage errors ≤ 10 % and posterior relative standard deviations ≤ 5 % up to 1 m depth. Reliable thermal diffusivity under such environmental conditions also requires temperature sensors to be spaced precisely (with accuracy to a few millimeters), with a level of noise ≤ 0.02 ∘C, and with a bias defined by a standard deviation ≤ 0.01 ∘C. Finally, the application of the developed approach to field data indicates significant repeatability in results and similarity with independent measurements, as well as promise in using a sliding time window to estimate temporal changes in soil thermal diffusivity, as needed to potentially capture changes in bulk density or water content.

Soil organic matter, rather than temperature, determines the structure and functioning of subarctic decomposer communities.

The impacts of climate change on ecosystem structure and functioning are likely to be strongest at high latitudes due to the adaptation of biota to relatively low temperatures and nutrient levels. Soil warming is widely predicted to alter microbial, invertebrate, and plant communities, with cascading effects on ecosystem functioning, but this has largely been demonstrated over short‐term (<10 year) warming studies. Using a natural soil temperature gradient spanning 10–35°C, we examine responses of soil organisms, decomposition, nitrogen cycling, and plant biomass production to long‐term warming. We find that decomposer organisms are surprisingly resistant to chronic warming, with no responses of bacteria, fungi, or their grazers to temperature (fungivorous nematodes being an exception). Soil organic matter content instead drives spatial variation in microorganism abundances and mineral N availability. The few temperature effects that appear are more focused: root biomass and abundance of root‐feeding nematodes decrease, and nitrification increases with increasing soil temperature. Our results suggest that transient responses of decomposers and soil functioning to warming may stabilize over time following acclimation and/or adaptation, highlighting the need for long‐term, ecosystem‐scale studies that incorporate evolutionary responses to soil warming.

The Ability of a Soil Temperature Gradient-Based Methodology to Detect Leaks from Pipelines in Buried District Heating Channels

We carried out several numerical experiments to analyze how different boundary conditions affect the ability to detect small pipeline leaks. Our method is based on determining the soil temperature gradient above a buried district heating channel. The equivalent thermal conductivity of a wet insulation (λeq) value of 0.5 W/(m·K) was used to mimic a small water leakage. To evaluate the heat loss through the channel cross section, the heat conduction model was used for the pipe insulation, the concrete, and the soil, while the convection model was considered within the channel. The following effects were used to simulate different operating conditions: heat convection at the soil surface, leakage only from the supply or return pipe, soil height above the channel, soil thermal conductivity, and pipe diameter. With the exception of leakage only from the return pipe and low soil thermal conductivity 0.4 W/(m·K), the results showed a doubling of the soil temperature gradient when compared with the no-leakage case. This fact undoubtedly confirms the potential of the method, which is particularly suitable for leak detection in old pipelines that have priority for renovation. A key added value of this research is that the soil temperature gradient-based leak detection technique was found useful in most foreseeable DH operating situations.

Impacts of soil temperature, phenology and plant community composition on invertebrate herbivory in a natural warming experiment

Species and community‐level responses to warming are well documented, with plants and invertebrates known to alter their range, phenology or composition as temperature increases. The effects of warming on biotic interactions are less clearly understood, but can have consequences that cascade through ecological networks. Here, we used a natural soil temperature gradient of 5–35°C in the Hengill geothermal valley, Iceland, to investigate the effects of temperature on plant community composition and plant–invertebrate interactions. We quantified the level of invertebrate herbivory on the plant community across the temperature gradient and the interactive effects of temperature, plant phenology (i.e. development stage) and vegetation community composition on the probability of herbivory for three ubiquitous plant species, Cardamine pratensis, Cerastium fontanum and Viola palustris. We found that the percentage cover of graminoids and forbs increased, while the amount of litter decreased, with increasing soil temperature. Invertebrate herbivory also increased with soil temperature at the plant community level, but this was underpinned by different effects of temperature on herbivory for individual plant species, mediated by the seasonal development of plants and the composition of the surrounding vegetation. This illustrates the importance of considering the development stage of organisms in climate change research given the variable effects of temperature on susceptibility to herbivory at different ontogenetic stages.

Flower phenological events and duration pattern is influenced by temperature and elevation in Dhauladhar mountain range of Lesser Himalaya

Studying phenology is undeniably one of the most effective ways to monitor and perceive how a particular plant species interact and respond to varying environmental conditions. In this study, the shifts in flowering phenological events of 24 herbaceous species with the changing elevation and temperature were observed in Dhauladhar Mountain range of Lesser Himalaya. Five permanent plots (20 × 20 m2) were established from 2,000 m to 4,000 m elevation at each rising 500 m distance for the documentation of herbaceous flora. Abundance-based documentation of flowering phenological events (onset of flowering duration [OFD] ≥ 10% to 30%, the peak of flowering duration [PFD] > 30% to 80%, the end of flowering duration [EFD] > 80% and total flowering duration [FD] as the difference of end and onset of flowering DOY) was done in each plot. The onset, the peak, and the end of the flowering day of the year (DOY) were recorded at 20%, 55%, and 90% floral abundance, respectively, from 1st of January. Upon analyses, the Linear-mixed effects model depicted significant differences in the flowering phenological events with elevation and soil temperature. The onset of flowering DOY and peak of the flowering DOY varied significantly with soil temperature gradient, while the end of flowering DOY showed non-significant interaction. The linear model of ANOVA demonstrated that OFD, PFD, EFD and FD varied significantly with elevation at p < 0.001. FD increased with elevation for most of the species, whereas two species, Aquilegia pubiflora and Primula denticulata, showed early incidences of flowering compared to other species. Temperature played an imperative role in influencing the day of initiation and duration of these phenological events. High plasticity of flowering phenological events is advantageous in high elevation regions where pollinators are scarcely present. Therefore, documenting shifting incidences of flowering phenological events would help the researcher to effectively predict climate change effects on alpine communities in near future.

Development of the Hydrus-1D freezing module and its application in simulating the coupled movement of water, vapor, and heat

In cold regions, freeze-thaw cycles play a critical role in many engineering and agricultural applications and cause soil water flow and heat transport studies to be much more complicated due to phase changes involved. A fully coupled numerical module for simulating the simultaneous movement of water, vapor, and heat during freezing-thawing periods was developed and incorporated in the Hydrus-1D software in this study. To avoid numerical instabilities caused by a sudden increase in the apparent heat capacity during a phase change, a new approach based on the available energy concept was adopted to adjust soil temperature when the freezing temperature is reached. The proposed freezing module's performance was then validated using experimental data collected at three field sites with typical seasonal freezing/thawing processes. Results showed that the model could efficiently obtain a convergent solution and that simulated soil moisture and temperature variations captured the observed data well. Driven by soil matric potential and temperature gradients, both liquid water and water vapor flowed towards the freezing front. The isothermal liquid flux was the most significant component of overall flow in most soil depths except in the frozen layer, where it decreased by 1–5 orders of magnitude from values before freezing. Instead, the thermal vapor flux was the dominant moisture transfer mechanism in the frozen layer and contributed about 10% to the ice formation. These results indicate that the model, which considers the coupled movement of water, vapor, and heat, can better describe the physical mechanisms of the hydrological cycle in the vadose zone during the freezing-thawing periods.

Temperature effects on the temporal dynamics of a subarctic invertebrate community.

Climate warming is predicted to have major impacts on the structure of terrestrial communities, particularly in high latitude ecosystems where growing seasons are short. Higher temperatures may dampen seasonal dynamics in community composition as a consequence of earlier snowmelt, with potentially cascading effects across all levels of biological organisation. Here, we examined changes in community assembly and structure along a natural soil temperature gradient in the Hengill geothermal valley, Iceland, during the summer of 2015. Sample collection over several time points within a season allowed us to assess whether temperature alters temporal variance in terrestrial communities and compositional turnover. We found that seasonal fluctuations in species richness, diversity and evenness were dampened as soil temperature increased, whereas invertebrate biomass varied more. Body mass was found to be a good predictor of species occurrence, with smaller species found at higher soil temperatures and emerging earlier in the season. Our results provide more in-depth understanding of the temporal nature of community and population-level responses to temperature, and indicate that climate warming will likely dampen the seasonal turnover of community structure that is characteristic of high latitude invertebrate communities.