Variation In Soil Temperature Research Articles

Spatial variation in soil respiration is determined by forest canopy structure through soil water content in a mature beech forest

For accurate estimation of soil respiration (SR) in forest ecosystems, temporal and spatial variation in SR and the factors that control these variations must be considered. Although some of the factors underlying temporal variation in SR have been elucidated in recent decades, a large part of spatial variation in SR remains unexplained especially in forest ecosystems with complex structures. Our objectives were to demonstrate spatial variation in daily summed SR (SRdaily) and to examine if spatial variation in SRdaily can be explained by canopy openness which is one of the indexes of forest structure. We conducted simultaneous measurements of SRdaily, soil temperature (ST), and soil water content (SWC) at 121 points. We also measured canopy openness and some forest stand structure indexes in different seasons in 2012 and 2013. The coefficient of variation (CV) of SRdaily ranged from 25 % to 28 %, which was similar to that of SWC (21 % to 28 %). We also found that the spatial variation in SR in other forest ecosystems ranged widely (CV = 14 % to 62 %), and that in our site fell within the range. There was no significant relationship between ST and spatial variation in SRdaily; however, a significant relationship was observed between SWC and spatial variation in SRdaily (P < 0.01) excepted for the measurement conducted in June 2013. Multiple linear regression analysis indicated that canopy openness showed significant positive correlations with SWC during the growing season. And there was no significant relationships between SWC and forest stand structure indexes.In this study, we found that canopy structure influenced SWC, which in turn determined the spatial variation in SR in this mature beech forest. The possible connections could give us new insight for adequate forest carbon management.

Mercury distribution around the Siele Hg mine (Mt. Amiata district, Italy) twenty years after reclamation: Spatial and temporal variability in soil, stream sediments, and air

The Siele mine and its smelting plant are part of the world class Monte Amiata Hg district (southern Tuscany, Italy). After closure in 1981, the area was subjected to the first reclamation in the district, completed in 2001. However, stream sediments in the Siele creek downstream of the mine still present highly anomalous Hg values (up to 5400 mg/kg). Gaseous elemental mercury (GEM) concentrations in air near the former metallurgical buildings, and immediately downstream of the mining area, are also high (up to 16,233 ng/m3), although lower than before reclamation, when values up to 237,000 ng/m3 had been measured. On the other hand, Hg mobility, determined by leaching tests, is mostly below the limits defined by pending regulations (1 μg/L), and methyl-Hg concentrations are mostly below 1 ng/kg (with a single value of 6 ng/kg). Therefore, the actual risk to environment and health is deemed low. In summary, reclamation reduced, but did not stop, the release of Hg from the Siele mining area. Results show that the Siele system has a low resilience and natural recovery will take many years (probably decades), during which the area will remain an important source of Hg for the Paglia and Tiber River systems, and eventually for the Mediterranean Sea.

Synergetic variations of active layer soil water and salt in a permafrost-affected meadow in the headwater area of the Yellow River, northeastern Qinghai–Tibet plateau

The coupling effects and mechanisms of water, heat, and salt in frozen soils are considered to be one of the core scientific issues in frozen soil studies. This study was based on in situ observation data of active layer soil volumetric water content (VWC), temperature, and bulk electrical conductivity (EC) obtained at an alpine meadow site from October 2016 to November 2019. The site is located in the headwater area of the Yellow River (HAYR). We analyzed the synergetic variations of active layer soil VWC, temperature, and bulk EC during the freeze and thaw processes and discussed the underlying mechanisms. When the thaw process occurred from 10 to 80 cm depths, the VWC and bulk EC at a 10 cm depth showed synchronous high-frequency fluctuations and both increased linearly. The linear decreasing rate of the VWC (bulk EC) at an 80 cm depth in the freeze depths between 0 and 40 cm was 2 (1.6–2.3) times that of the VWC (bulk EC) at an 80 cm depth in the freeze depths occurring 0–10 cm. As soil temperature decreased in the frozen layer, unfrozen water content (bulk EC) decreased nonlinearly along with the absolute value of soil temperature (|T|), following a power (logarithmic) function. This study provided data that partly elucidate the interactions among permafrost, meadow, and ecohydrological processes in the HAYR. Also, our results can be used as a scientific basis for decision making on the protection and restoration of alpine grasslands, as well as for soil salinization studies.

Influence of seasonal soil temperature variation and global warming on the seismic response of frozen soils in permafrost regions

AbstractThere has been growing interest in seismic hazards in permafrost regions as development in those regions has increased. Because major infrastructure, such as natural gas pipelines, has been constructed in permafrost regions, it is necessary to evaluate the seismic safety of such a network system. As frozen soil's dynamic properties differ from those of its unfrozen state, the characteristics of seismic waves propagated through frozen soil layers in permafrost differ from those propagated through unfrozen soil. Thus, the dynamic properties and composition of frozen soil layers located between bedrock and the ground surface need to be realistically considered in evaluating the seismic hazards of permafrost regions. The frozen soil layer's composition greatly depends on soil temperatures which vary seasonally and are gradually increasing due to global warming, therefore it is necessary to consider soil temperature variation. In this study, comprehensive parametric site response analysis was carried out based on measured data regarding seasonal and annual temperature variation to investigate seismic hazards. The soil temperature variation between summer and winter and temperature increases due to global warming were the main considerations. The analysis results clearly show that the soil temperature variation significantly impacts seismic hazards in the permafrost region, leading to different site response characteristics than those in the non‐permafrost region.

Population Genomics Reveals Gene Flow and Adaptive Signature in Invasive Weed Mikania micrantha.

A long-standing and unresolved issue in invasion biology concerns the rapid adaptation of invaders to nonindigenous environments. Mikania micrantha is a notorious invasive weed that causes substantial economic losses and negative ecological consequences in southern China. However, the contributions of gene flow, environmental variables, and functional genes, all generally recognized as important factors driving invasive success, to its successful invasion of southern China are not fully understood. Here, we utilized a genotyping-by-sequencing approach to sequence 306 M. micrantha individuals from 21 invasive populations. Based on the obtained genome-wide single nucleotide polymorphism (SNP) data, we observed that all the populations possessed similar high levels of genetic diversity that were not constrained by longitude and latitude. Mikania micrantha was introduced multiple times and subsequently experienced rapid-range expansion with recurrent high gene flow. Using FST outliers, a latent factor mixed model, and the Bayesian method, we identified 38 outlier SNPs associated with environmental variables. The analysis of these outlier SNPs revealed that soil composition, temperature, precipitation, and ecological variables were important determinants affecting the invasive adaptation of M. micrantha. Candidate genes with outlier signatures were related to abiotic stress response. Gene family clustering analysis revealed 683 gene families unique to M. micrantha which may have significant implications for the growth, metabolism, and defense responses of M. micrantha. Forty-one genes showing significant positive selection signatures were identified. These genes mainly function in binding, DNA replication and repair, signature transduction, transcription, and cellular components. Collectively, these findings highlight the contribution of gene flow to the invasion and spread of M. micrantha and indicate the roles of adaptive loci and functional genes in invasive adaptation.

Modelling the seasonal variations of soil temperatures in the Arctic coasts

The soil temperature within the Arctic coasts within the continuous permafrost is not widely measured; the temporal and spatial resolutions of the measured temperature observations are relatively high. In this study, we examined the methods to interpolate, hindcast and forecast temperature measurements within the active layer and shallow permafrost when the temperature measurements at the surface or near the surface are available. The temperature variations along the year are periodic, and hence attempts are made to express the seasonal variations with a combination of periodic function (Fourier components); which are used as boundary conditions to reach the analytical solutions. The temperature measurements from surface to about 10 metre of depths at the Baydaratskaya Bay, Kara Sea are available. We adopted a data-driven model based on simplified analytical closed-form solution derived from the boundary conditions. The parameters of the solution are calibrated from the field measurements and validated with field observations. The model then can be used to hindcast and forecast temperature at any points within the soil.

Effect of elevation, season and accelerated snowmelt on biogeochemical processes during isolated conifer needle litter decomposition.

Increased drought and temperatures associated with climate change have implications for ecosystem stress with risk for enhanced carbon release in sensitive biomes. Litter decomposition is a key component of biogeochemical cycling in terrestrial ecosystems, but questions remain regarding the local response of decomposition processes to climate change. This is particularly complex in mountain ecosystems where the variable nature of the slope, aspect, soil type, and snowmelt dynamics play a role. Hence, the goal of this study was to determine the role of elevation, soil type, seasonal shifts in soil moisture, and snowmelt timing on litter decomposition processes. Experimental plots containing replicate deployments of harvested lodgepole and spruce needle litter alongside needle-free controls were established in open meadows at three elevations ranging from 2,800–3,500 m in Crested Butte, Colorado. Soil biogeochemistry variables including gas flux, porewater chemistry, and microbial ecology were monitored over three climatically variable years that shifted from high monsoon rains to drought. Results indicated that elevation and soil type influenced baseline soil biogeochemical indicators; however, needle mass loss and chemical composition were consistent across the 700 m elevation gradient. Rates of gas flux were analogously consistent across a 300 m elevation gradient. The additional variable of early snowmelt by 2–3 weeks had little impact on needle chemistry, microbial composition and gas flux; however, it did result in increased dissolved organic carbon in lodgepole porewater collections suggesting a potential for aqueous export. In contrast to elevation, needle presence and seasonal variability of soil moisture and temperature both played significant roles in soil carbon fluxes. During a pronounced period of lower moisture and higher temperatures, bacterial community diversity increased across elevation with new members supplanting more dominant taxa. Microbial ecological resilience was demonstrated with a return to pre-drought structure and abundance after snowmelt rewetting the following year. These results show similar decomposition processes across a 700 m elevation gradient and reveal the sensitivity but resilience of soil microbial ecology to low moisture conditions.

Assessing Daily Evapotranspiration Methodologies from One-Time-of-Day sUAS and EC Information in the GRAPEX Project.

Daily evapotranspiration (ETd) plays a key role in irrigation water management and is particularly important in drought-stricken areas, such as California and high-value crops. Remote sensing allows for the cost-effective estimation of spatial evapotranspiration (ET), and the advent of small unmanned aerial systems (sUAS) technology has made it possible to estimate instantaneous high-resolution ET at the plant, row, and subfield scales. sUAS estimates ET using “instantaneous” remote sensing measurements with half-hourly/hourly forcing micrometeorological data, yielding hourly fluxes in W/m2 that are then translated to a daily scale (mm/day) under two assumptions: (a) relative rates, such as the ratios of ET-to-net radiation (Rn) or ET-to-solar radiation (Rs), are assumed to be constant rather than absolute, and (b) nighttime evaporation (E) and transpiration (T) contributions are negligible. While assumption (a) may be reasonable for unstressed, full cover crops (no exposed soil), the E and T rates may significantly vary over the course of the day for partially vegetated cover conditions due to diurnal variations of soil and crop temperatures and interactions between soil and vegetation elements in agricultural environments, such as vineyards and orchards. In this study, five existing extrapolation approaches that compute the daily ET from the “instantaneous” remotely sensed sUAS ET estimates and the eddy covariance (EC) flux tower measurements were evaluated under different weather, grapevine variety, and trellis designs. Per assumption (b), the nighttime ET contribution was ignored. Each extrapolation technique (evaporative fraction (EF), solar radiation (Rs), net radiation-to-solar radiation (Rn/Rs) ratio, Gaussian (GA), and Sine) makes use of clear skies and quasi-sinusoidal diurnal variations of hourly ET and other meteorological parameters. The sUAS ET estimates and EC ET measurements were collected over multiple years and times from different vineyard sites in California as part of the USDA Agricultural Research Service Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX). Optical and thermal sUAS imagery data at 10 cm and 60 cm, respectively, were collected by the Utah State University AggieAir sUAS Program and used in the Two-Source Energy Balance (TSEB) model to estimate the instantaneous or hourly sUAS ET at overpass time. The hourly ET from the EC measurements was also used to validate the extrapolation techniques. Overall, the analysis using EC measurements indicates that the Rs, EF, and GA approaches presented the best goodness-of-fit statistics for a window of time between 1030 and 1330 PST (Pacific Standard Time), with the Rs approach yielding better agreement with the EC measurements. Similar results were found using TSEB and sUAS data. The 1030–1330 time window also provided the greatest agreement between the actual daily EC ET and the extrapolated TSEB daily ET, with the Rs approach again yielding better agreement with the ground measurements. The expected accuracy of the upscaled TSEB daily ET estimates across all vineyard sites in California is below 0.5 mm/day, (EC extrapolation accuracy was found to be 0.34 mm/day), making the daily scale results from TSEB reliable and suitable for day-to-day water management applications.

Tracking the Endogenous Dynamics of the Solfatara Volcano (Campi Flegrei, Italy) through the Analysis of Ground Thermal Image Temperatures

In the last decades, thermal infrared ground-based cameras have become effective tools to detect significant spatio-temporal anomalies in the hydrothermal/volcanic environment, possibly linked to impending eruptions. In this paper, we analyzed the temperature time-series recorded by the ground-based Thermal Infrared Radiometer permanent network of INGV-OV, installed inside the Solfatara-Pisciarelli area, the most active fluid emission zones of the Campi Flegrei caldera (Italy). We investigated the temperatures’ behavior in the interval 25 June 2016–29 May 2020, with the aim of tracking possible endogenous hydrothermal/volcanic sources. We performed the Independent Component Analysis, the time evolution estimation of the spectral power, the cross-correlation and the Changing Points’ detection. We compared the obtained patterns with the behavior of atmospheric temperature and pressure, of the time-series recorded by the thermal camera of Mt. Vesuvius, of the local seismicity moment rate and of the CO2 emission flux. We found an overall influence of exogenous, large scale atmospheric effect, which dominated in 2016–2017. Starting from 2018, a clear endogenous forcing overcame the atmospheric factor, and dominated strongly soil temperature variations until the end of the observations. This paper highlights the importance of monitoring and investigating the soil temperature in volcanic environments, as well as the atmospheric parameters.

Tsallis q-Stat and the Evidence of Long-Range Interactions in Soil Temperature Dynamics.

The complexities in the variations of soil temperature and thermal diffusion poses a physical problem that requires more understanding. The quest for a better understanding of the complexities of soil temperature variation has prompted the study of the q-statistics in the soil temperature variation with the view of understanding the underlying dynamics of the temperature variation and thermal diffusivity of the soil. In this work, the values of Tsallis stationary state q index known as q-stat were computed from soil temperature measured at different stations in Nigeria. The intrinsic variations of the soil temperature were derived from the soil temperature time series by detrending method to extract the influences of other types of variations from the atmosphere. The detrended soil temperature data sets were further analysed to fit the q-Gaussian model. Our results show that our datasets fit into the Tsallis Gaussian distributions with lower values of q-stat during rainy season and around the wet soil regions of Nigeria and the values of q-stat obtained for monthly data sets were mostly in the range for all stations, with very few values q closer to 1.2 for a few stations in the wet season. The distributions obtained from the detrended soil temperature data were mostly found to belong to the class of asymmetric q-Gaussians. The ability of the soil temperature data sets to fit into q-Gaussians might be due and the non-extensive statistical nature of the system and (or) consequently due to the presence of superstatistics. The possible mechanisms responsible this behaviour was further discussed.

Variation in Alpine Plant Diversity and Soil Temperatures in Two Mountain Landscapes of South Patagonia

Alpine environments and their temporal changes are rarely studied at high latitudes in the southern hemisphere. We analyzed alpine plants, soil temperatures, and growing-season length in mountains of two landscapes of South Patagonia (46° to 56° SL): three summits (814–1085 m a.s.l) surrounded by foothill grasslands in Santa Cruz province (SC), and four summits (634–864 m a.s.l.) in sub-Antarctic forests of Tierra del Fuego province (TF). Sampling followed the protocolized methodology of the Global Observational Research Initiative in Alpine Environments (GLORIA). Factors were topography (elevation and cardinal aspect) and time (baseline vs. re-sampling for plants, five annual periods for temperatures), assessed by univariate and multivariate tests. Plant composition reflected the lowland surrounding landscapes, with only 9 mountain species on 52 totals in SC and 3 on 30 in TF. Richness was higher in re-sampling than baseline, being assemblages more influenced by aspect than elevation. Mean annual soil temperature and growing-season length, which varied with topography, were related to the Multivariate El Niño Southern Oscillation Index (MEI) but did not show clear warming trends over time. We highlight the importance of long-term studies in mountainous regions of extreme southern latitudes, where factors other than warming (e.g., extreme climate events) explain variations.

Spring water table depth mediates within‐site variation of soil temperature in groundwater‐fed mires

AbstractGroundwater‐dependent ecosystems represent globally rare edaphic islands of scattered distribution, often forming areas of regionally unique environmental conditions. A stable groundwater supply is a key parameter defining their ecological specificity, promoting also soil thermal buffering. Still, a limited number of studies dealt with the importance of water temperature in mire ecosystems and virtually no data exist on within‐site variation in the temperature buffer effect. Three temperature dataloggers, placed in patches potentially differing in groundwater supply, were installed in each of 19 Western Carpathian spring mire sites from May 2019 to July 2020. Spring source plots statistically differed in water temperature parameters from the plots located towards the spring mire margin, which did not significantly differ from one another. At the majority of sites, the temperature values changed gradually from spring source to mire margins, fitting the pattern expected in the groundwater temperature buffering scenario. Dataloggers placed in the spring sources were the most distinctive from the others in thermal buffering parameters in conditional principal component analysis. The difference between the spring source and its margin was on average 3.25 °C for 95th percentile of the recorded water temperature data points (i.e. warm extremes) and 1.91 °C for 5th percentile (i.e. cold extremes). This suggests that if the temperature at spring source area is considered, thermal buffering within a site may mitigate mainly warm extremes. Thus, our data may provide an important baseline for predictions of possibly upcoming changes in spring mire hydrology caused by climate change. Both warming and precipitation decrease can give rise to the loss or substantial reduction of buffering effect if the contrasting parameters now recorded at the central part shift to those found towards the margins of groundwater‐fed areas.

Interannual Variability of Atmospheric CH4 and Its Driver Over South Korea Captured by Integrated Data in 2019

Understanding the temporal variability of atmospheric methane (CH4) and its potential drivers can advance the progress toward mitigating changes to the climate. To comprehend interannual variability and spatial characteristics of anomalous CH4 mole fractions and its drivers, we used integrated data from different platforms such as in situ measurements and satellites (TROPOspheric Monitoring Instrument (TROPOMI) and Greenhouse Gases Observing SATellite (GOSAT)) retrievals. A pronounced change of annual growth rate was detected at Anmyeondo (AMY), Republic of Korea, ranging from −16.8 to 31.3 ppb yr−1 as captured in situ through 2015–2020 and 3.9 to 16.4 ppb yr−1 detected by GOSAT through 2014–2019, respectively. High growth rates were discerned in 2016 (31.3 ppb yr−1 and 13.4 ppb yr−1 from in situ and GOSAT, respectively) and 2019 (27.4 ppb yr−1 and 16.4 ppb yr−1 from in situ and GOSAT, respectively). The high growth in 2016 was essentially explained by the strong El Niño event in 2015–2016, whereas the large growth rate in 2019 was not related to ENSO. We suggest that the growth rate that appeared in 2019 was related to soil temperature according to the Noah Land Surface Model. The stable isotopic composition of 13C/12C in CH4 (δ13-CH4) collected by flask-air sampling at AMY during 2014–2019 supported the soil methane hypothesis. The intercept of the Keeling plot for summer and autumn were found to be −53.3‰ and −52.9‰, respectively, which suggested isotopic signature of biogenic emissions. The isotopic values in 2019 exhibited the strongest depletion compared to other periods, which suggests even a stronger biogenic signal. Such changes in the biogenic signal were affected by the variations of soil temperature and soil moisture. We looked more closely at the variability of XCH4 and the relationship with soil properties. The result indicated a spatial distribution of interannual variability, as well as the captured elevated anomaly over the southwest of the domain in autumn 2019, up to 70 ppb, which was largely explained by the combined effect of soil temperature and soil moisture changes, indicating a pixel-wise correlation of XCH4 anomaly with those parameters in the range of 0.5–0.8 with a statistical significance (p &lt; 0.05). This implies that the soil-associated drivers are able to exert a large-scale influence on the regional distribution of CH4 in Korea.

Balsam Fir and American Beech Influence Soil Respiration Rates in Opposite Directions in a Sugar Maple Forest Near Its Northern Range Limit

Conifers and deciduous trees greatly differ in regard to their phylogenetics and physiology as well as their influence on soil microclimate and chemical properties. Soil respiration (Rs) in forests can therefore differ depending on tree species composition, and assessments of the variation in Rs in various forest types will lead to a more thorough understanding of the carbon cycle and more robust long-term simulations of soil carbon. We measured Rs in 2019 and 2020 in stands of various species composition in a sugar maple forest near the northern range limit of temperate deciduous forests in Quebec, Canada. Seasonal variations in soil temperature had the largest influence on Rs, but conditions created by the stands also exerted a significant effect. Relative to the typical sugar maple-yellow birch forest (hardwoods), Rs in stands with &amp;gt;20% of basal area from balsam fir (mixedwoods) was increased by 21%. Whilst, when American beech contributed &amp;gt;20% of litterfall mass (hardwood-beech stands), Rs was decreased by 11 and 36% relative to hardwoods and mixedwoods, respectively. As a whole, Rs was significantly higher in mixedwoods than in other forest types, and Rs was significantly higher in hardwoods than in hardwood-beech stands. Sugar maple and American beech at the study site are near their northern range limit, whereas balsam fir is near its southern limit. Rs in mixedwoods was therefore higher than in hardwoods and hardwood-beech stands due to high root activity in the presence of fir, despite colder and drier soils. We estimated that root respiration in mixedwoods was more than threefold that in hardwoods and hardwood-beech stands. The lower Rs in hardwood-beech stands compared to hardwoods points to the lower soil temperature as well as the poor quality of beech litter (low decomposability) as indicated by a generally lower heterotrophic respiration. Other than soil temperature, regression models identified mixedwoods, soil water potential and Mg2+ activity in the soil solution as important predictor variables of Rs with about 90% of its variation explained. Our study shows the benefits of combining forest-specific properties to climatic data for more robust predictions of Rs.

The Characteristics and Seasonal Variation of Methane Fluxes From an Alpine Wetland in the Qinghai Lake watershed, China

Alpine wetlands are an important natural source of methane (CH4) to the atmosphere. However, the temporal variations and main driving factors of CH4 fluxes in alpine wetlands are not yet well understood. In this study, CH4 fluxes were measured from an alpine wetland in the Qinghai Lake using eddy covariance (EC) technique. Strong seasonal variability in the daily CH4 fluxes was observed, ranging from − 18.24 mg CH4 m− 2 d− 1 during the non-growing season to 117.44 mg CH4 m− 2 d− 1 during the growing season in 2017. The annual CH4 budget was 9.41 g CH4 m− 2. The growing season CH4 flux accounted for 91.5 % of the annual budget. At the daily scale, the CH4 fluxes increased significantly as the net radiation, air temperature, vapor pressure deficit, soil temperature, and soil volumetric water content at 5 cm depth increased. Additionally, correlation analysis also revealed that daily CH4 flux was significantly related to CO2 flux when daily CO2 flux was negative, but there was no correlation when daily CO2 flux was positive. Path analysis showed that seasonal variations of soil temperature at 5 cm depth and CO2 flux had strong direct effects on daily CH4 fluxes.

Dynamics and characteristics of soil temperature and moisture of active layer in the central Tibetan Plateau

Hydro-thermal characteristics of the active layer are critical during freezing-thawing cycles, causing the moisture and heat exchanges between both permafrost and atmosphere in permafrost regions. There is better understanding of these characteristics in high-latitude permafrost areas, while comparatively little is known in the middle-low latitude areas. Here, we used field monitoring data along with statistical models to quantitatively analyze the hydro-thermal dynamics of the freezing-thawing processes at the Tanggula (TGL) site in permafrost regions of Qinghai-Tibetan Plateau (QTP). This combined approach was used to examine the hydro-thermal characteristics in high-altitude permafrost regions. Our results revealed that the duration of the freezing process was much shorter than that of the thawing process. During freezing-thawing processes, the amplitude variation in soil temperature had a significant logarithmic relationship with depth. There was a significant exponential relationship between soil water content at a depth of 5 cm and monthly precipitation. The averaged energy in the active layer consumed for phase change from water to ice was 145.53 MJ/m2. Finally, we analyzed the quantitative hydro-thermal characteristics and influential factors during the freezing and thawing processes; the different hydro-thermal processes occurring in high-altitude permafrost regions were compared with those in high latitude permafrost regions. Collectively, these results offer a perspective on the difference in permafrost across different region and also provide a reference for the parameterization of land surface models.

Links between the complexities in atmospheric-soil energy exchange and temperature dynamics in tropical regions

In this work, the variations in the dynamical complexities in soil temperature variations were compared with that of air temperature using measured temperature parameters from different stations located in Nigeria. These parameters were also compared to the monthly averages of rainfall. The data sets were analysed using nonlinear time series analytical techniques. The results reveal that the annual trend of dynamical complexity follows a reverse trend of the rainfall peak period and the Lyapunov exponent for the un-detrended air temperature time series does not follow the same annual trend as that of the soil temperature. Also, dynamical properties of the two parameters are highly associated with correlation coefficients that are in some cases as high as 0.85 especially for the entropy measure for both air and soil. It was observed, however, that the degree of correlations between these parameters varies with time and location. An observed graduated response of Tsallis entropy computed for detrended soil temperature revealed a steady increase of the values of Tsallis entropy from north to south of Nigeria across the geographical belts. The observed variations have been associated with varying atmospheric factors and the changes in the properties of the soil with location. These factors might be influential in conjunction with other factors in the air-soil interface.

Numerical analysis of ground temperature response characteristics of a space-heating ground source heat pump system by utilizing super-long flexible heat pipes for heat extraction

In this work, the ground temperature variation characteristics of a ground source heat pump system equipped with super-long flexible heat pipes for the extraction of shallow geothermal energy were investigated by computational fluid dynamics for the application of space heating. The study was based on the dynamic analysis results from the coupling of the thermal resistance model of super-long flexible heat pipes and the heat pump performance. The effects of groundwater advection, soil thermal properties, the layout of super-long flexible heat pipes, and the operational conditions were considered. Results show that groundwater advection plays the most important role in the variation of soil temperature. With no activity of groundwater advection, the ground temperature near boreholes continuously decreased throughout the heating season from approximately 290.6 K to 279.3 K, and it cannot recover to the initial temperature before the end of the transition season. The area of thermal plume of the upstream boreholes is much smaller than the downstream under the influence of groundwater advection. The thermal interaction of boreholes in the vertical direction of groundwater advection almost disappeared when the advection velocity exceeded 0.5 m/d. The cold accumulation near the boreholes can be alleviated under the intermittent operation by reducing the working time. The high soil thermal conductivity weakened the cold accumulation phenomenon. This work provides a theoretical basis for the optimization of the design and installation of ground source heat pump systems equipped with super-long flexible heat pipes.

Seasonal variation in soil temperature and moisture of a desert steppe environment: a case study from Xilamuren, Inner Mongolia

Soil temperature and moisture are important factors affecting vegetation growth and drought in desert steppe environments. These factors also strongly influence grassland ecosystems. This study interpreted long-term (2009–2019) ground observation data on soil temperature, soil moisture, and meteorological factors from a study area in Inner Mongolia. The monitoring station collected soil moisture, soil temperature, and precipitation data. Covarying relationships indicated how soil properties influence each other throughout the year. Soil temperature was clearly affected by atmospheric changes, solar radiation, and freeze/thaw processes. The surface soil layers showed the greatest degree of variation, while middle and lower layers showed less seasonal variation and smaller differences between daily highs and lows. Surface soil moisture correlates strongly with the vertical temperature decline in soil. Time series revealed major variation in soil moisture throughout the year with lower soil layers showing obvious hysteresis effects. Multi-year soil moisture data allowed for subdivision of the year into seven intervals based maximum and minimum values. Soil temperature showed unique patterns of covariation with soil moisture during different time periods. Differences in soil moisture cause more rapid changes in temperature during soil thawing relative the moisture-induced temperature changes observed 1 month after soil freezing. When soil temperature was greater than 0 °C (32 ℉), soil temperature and soil moisture showed inverse correlation. A dependency of evapotranspiration on soil temperature can explain its effect on soil moisture. When soil temperature fell below 0 °C(32 ℉), soil temperature and soil moisture showed a positive correlation. During an interval defined as the summer fluctuation (SF), precipitation and soil moisture showed a significant positive correlation. During other periods, soil moisture did not clearly covary with precipitation.

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.