Soil Temperature Distribution Research Articles

The Effect of Groundwater Flow on the Thermal Performance of a Novel Borehole Heat Exchanger for Ground Source Heat Pump Systems: Small Scale Experiments and Numerical Simulation

New small-scale experiments are carried out to study the effect of groundwater flow on the thermal performance of water ground heat exchangers for ground source heat pump systems. Four heat exchanger configurations are investigated; single U-tube with circular cross-section (SUC), single U-tube with an oval cross-section (SUO), single U-tube with circular cross-section and single spacer with circular cross-section (SUC + SSC) and single U-tube with an oval cross-section and single spacer with circular cross-section (SUO + SSC). The soil temperature distributions along the horizontal and vertical axis are measured and recorded simultaneously with measuring the electrical energy injected into the fluid, and the borehole wall temperature is measured as well; consequently, the borehole thermal resistance (Rb) is calculated. Moreover, two dimensional and steady-state CFD simulations are validated against the experimental measurements at the groundwater velocity of 1000 m/year with an average error of 3%. Under saturated conditions without groundwater flow effect; using a spacer with SUC decreases the Rb by 13% from 0.15 m·K/W to 0.13 m·K/W, also using a spacer with the SUO decreases the Rb by 9% from 0.11 m·K/W to 0.1 m·K/W. In addition, the oval cross-section with spacer SUO + SSC decreases the Rb by 33% compared with SUC. Under the effect of groundwater flow of 1000 m/year; Rb of the SUC, SUO, SUC + SSC and SUO + SSC cases decrease by 15.5%, 12.3%, 6.1% and 4%, respectively, compared with the saturated condition.

Effects of aquifers on soil temperature distribution around deep buried heat exchanger

Deep buried heat exchanger has been increasingly applied into the building heat source through the utilization of geothermal energy. During the geothermal system design process, the aquifer is an important factor that affects the overall performance prediction. The flow of underground water at different positions changes the temperature distribution of the soils around the buried pipe and then influences the heat exchange at different depths. Consequently, the variation of the temperature field causes the thermal radius of the heat exchanger no longer regularly distributed, which affects the determination of the well spacing. With the aims of improving the accuracy of performance estimation, the aquifer effect is carried out by this study. The solution to the moving line source theory is used to acquire the temperature response at different positions. The overall effect of the underground water with different velocities on the performance is evaluated. The soil temperature distribution in the heat exchange zone with aquifers at different depths is studied in detail. The predicted thermal influence radius at different depths with various groundwater velocities and soil thermal properties showed that the temperature distribution around the buried heat exchanger is largely influenced by the groundwater movement. Under the simulation condition, the thermal radius increases from less than 10 m for pure conduction condition to a maximum value of 25.3 m with groundwater flow. The aquifer enhances the heat absorption of the heat exchanger, but the high flow rate also leads to a large thermal radius. The obtained thermal influence radius under different conditions can provide guidance for the design of the geothermal system.

Influence of Soil Particle Size on the Temperature Field and Energy Consumption of Injected Steam Soil Disinfection

Soil steam disinfection (SSD) technology is an effective means of eliminating soil borne diseases. Among the soil cultivation conditions of facility agriculture in the Yangtze River Delta region of China, the clay soil particles (SPs) are fine, the soil pores are small, and the texture is relatively viscous. When injection disinfection technology is applied in the clay soil, the diffusion of steam is hindered and the heating efficiency is substantially affected. To increase the heating efficiency of SSD, we first discretized the continuum model of Philip and De Vries into circular particle porous media of different sizes and random distribution. Then with Computational Fluid Dynamics (CFD) numerical simulation technology, a single-injection steam disinfection model for different SP size conditions was constructed. Furthermore, the diffusion pattern of the macro-porous vapor flow and matrix flow and the corresponding temperature field were simulated and analyzed. Finally, a single-pipe injection steam disinfection verification test was performed for different SP sizes. The test results show that for the clay soil in the Yangtze River Delta region of China, the test temperature filed results are consistent with the simulation results when the heat flow reaches H = 20 cm in the vertical direction, the simulation and test result of the heat flow in the maximum horizontal diffusion distance are L = 13 cm and 12 cm, respectively. At the same disinfection time, the simulated soil temperature change trend is consistent with the test results, and the test temperature is lower than the simulated temperature. The difference between the theoretical temperature and the experimental temperature may be attributed to the heat loss in the experimental device. Further, it is necessary to optimize the CFD simulation process and add the disintegration and deformation processes of soil particle size with the change of water content. Furthermore, the soil pores increase as the SP size increases and that a large amount of steam vertically diffuses along the macropores and accumulates on the soil surface, causing ineffective heat loss. Moreover, soil temperature distribution changes from oval (horizontal short radius/vertical long radius = 0.65) to irregular shape. As the SP size decreases, the soil pore flow path becomes fine; the steam primarily diffuses uniformly around the soil in the form of a matrix flow; the diffusion distance in the horizontal direction gradually increases; and the temperature distribution gradually becomes even, which is consistent with the soil temperature field simulation results. Similar to the energy consumption analysis, the maximum energy consumption for SP sizes>27mm and <2mm was 486and 477kJ, respectively. Therefore, proper pore growth was conducive to the diffusion of steam, but excessive pores cause steam to overflow, which increased energy consumption of the system. Considering that the test was carried out in an ideal soil environment, the rotary tiller must be increased for fine rotary tillage in an actual disinfection operation. Although large particles may appear during the rotary tillage process, an appropriate number of large particles contributes to the formation of a large pore flow, under the common effect of matrix flow, it will simultaneously promote greater steam diffusion and heating efficiency. The above theoretical research has practical guiding significance for improving the design and disinfection effect of soil steam sterilizers in the future.

Improved analytical modeling and system performance evaluation of deep coaxial borehole heat exchanger with segmented finite cylinder-source method

The deep borehole heat exchanger is attracting more and more attention due to its higher performance. But there is no suitable analytical model for its fast simulation and system design. Classic analytical models of borehole heat exchangers (BHEs), assume that the initial soil temperature and heat flux of the borehole wall are uniform. Those makes them not applicable to deep borehole systems in which geothermal gradient is dominant. This study introduced and formulated a segmented finite cylinder-source model (SFCS), which can provide an accurate simulation tool. Data of distributed thermal response test and finite difference model are used for model comparison. A comprehensive comparative study is implemented to identify the performance differences between the classical and the new model. It is shown from simulation results that the newly proposed SFCS model can better describe the water as well as soil temperature field, especially for deeper borehole systems. In addition, three new influencing factors, namely pipe sizing ratio, inlet thermal flow rate and initial soil temperature distribution function, are introduced for system performance evaluation. Some valuable findings are identified, which can promote a better system design and achieve a higher system performance.

The Space–Time Distribution of Soil Water and Temperature of a Desert Ecosystem Using Spatio-Temporal Kriging and PCA Analysis

Straw checkerboard and vegetation restoration are used for soil and water conservation on this area. This study presents soil moisture and temperature spatial distribution in different seasons from the restoration sites using the geostatistical analysis expansion module of ArcGIS. The results suggested that the soil temperature shows an overall decreasing trend accompanied with the increasing of the depth in June and August; while, there was no obvious temperature differences among all the depths of September. In addition, the humidity in August and September increased with the increase of depth. However, the mean soil moisture of June did not follow any rules. The spatial distributions of soil temperature were high in the south of the survey area. Compared with the temperature, the spatial distribution of moisture shows a much larger variation. Principal component analysis was also used in this study. The results showed the high similarity of temperatures with different depths, while the soil moisture showed an obvious spatial differences between deep and top layers. Taking a shifting sand dune as the control area, we examined the effects of ecological restoration project on soil temperature and moisture of the study area. The data indicated a remarkable environmental improvement in the restoration area.

Effects of ant nesting on soil microbial biomass carbon and quotient in tropical forest of Xishuangbanna.

Ant nesting can modify soil physicochemical conditions in the tropical forest, exerting a crucial effect on spatiotemporal variation in soil microbial biomass carbon and quotient. In this study, the chloroform fumigation method was used to measure the spatiotemporal dynamics of microbial biomass carbon and quotient in ant nests and the reference soils in Syzygium oblatum community of tropical Xishuangbanna. The results were as following: 1) Microbial biomass carbon and quotient were significantly higher in ant nests (1.95 g·kg-1, 6.8%) than in the reference soils (1.76 g·kg-1, 5.1%). The microbial biomass carbon in ant nests and the reference soils showed a signifi-cantly unimodal temporal variation, whereas the temporal dynamics of microbial biomass quotient presented a distribution pattern of "V" type. 2) The microbial biomass carbon and quotient showed significant vertical changes in ant nests and the reference soils. The microbial biomass carbon decreased, and microbial biomass quotient increased significantly along the soil layers. The vertical variations in microbial biomass carbon and quotient were more significant in ant nests than in refe-rence soils. 3) Ant nesting significantly changed the spatiotemporal distributions of soil water and temperature in ant nests, which in turn affected spatiotemporal dynamics of soil microbial biomass carbon and quotient. Soil water content could explain 66%-83% and 54%-69% of the variation of soil microbial biomass carbon and quotient, respectively. Soil temperature could explain 71%-86% and 67%-76% of the variation of soil microbial biomass carbon and quotient in ant nests and the reference soils, respectively. 4) Changes in soil physicochemical properties induced by ant nesting had significant effect on the soil microbial biomass carbon and quotient. There were positive correlations of soil microbial biomass carbon to soil organic carbon, soil temperature, total nitrogen and soil water content, and to bulk density, nitrate nitrogen and hydrolyzed nitrogen; whereas a negative correlation of them was observed with soil pH. Soil pH was positively and other soil physicochemical properties were negatively correlated with microbial biomass quotient. Total organic carbon, total nitrogen and soil temperature had greater contribution to microbial biomass carbon, while total organic carbon and total nitrogen had the least negative effect on microbial biomass quotient. Therefore, ant nesting could modify microhabitats (e.g., soil water and soil temperature) and soil physicochemical properties (e.g., total organic carbon and total nitrogen), thereby regulating the spatiotemporal variation in soil microbial biomass carbon and quotient in tropical forests.

Controlling factors of plant community composition with respect to the slope aspect gradient in the Qilian Mountains

AbstractSlope aspect can affect soil temperature and soil type distribution, which, in turn, is likely to influence plant community composition. Three Qilian mountains, located in the northeastern part of the Qinghai–Tibetan Plateau, China, with four distinct slope aspects including south‐facing (SF), southwest‐facing (SW), northwest‐facing (NW), and north‐facing (NF) slope aspects, were studied to investigate the impact of slope aspect on plant assemblages. The results indicated that the environmental conditions were favorable under the NF and NW slope aspects as the soil water, soil organic carbon (SOC), and soil total nitrogen (STN) contents were significantly higher, and soil temperature (ST) and soil bulk density (SBD) were significantly lower than under the SF and SW aspects. Under all slope aspects, however, SOC, STN, and soil total phosphate in the top 0.2 m of topsoil accounted for about 60% of its total quantity, to a soil depth of 0.6 m. The plant communities on the SF and SW slopes were found to be primarily composed of Poa pratensis, Potentilla anrisena, and Carex aridula. In contrast, the plant community on the NW slope was mainly composed of Kobresia humilis, Carex crebra, and Potentilla bifurca, while on the NF slope it was mainly composed of Picea crassifolia, Carex scabrirostris, and Polygonum macrophyllum. The order of the influence of environmental factors on species distributions was ST > SBD > sand > STN. Results suggest that the slope aspect has an important role in the regulation of the soil environment and plant assemblages and that ST and SBD were the main factors influencing plant community composition. Furthermore, evidence from this study suggests that these mountains will become increasingly vulnerable to global warming. Thus, the plant community composition on these mountains must be monitored continuously in order to allow for strategic adaptive management.

Stream salamander persistence influenced by the interaction between exurban housing age and development

Exurban development is the fastest growing form of land use in the United States and already predominates southern New England. These housing developments alter stream ecosystems in a predictable manner described as urban stream syndrome. Yet, many stream salamanders are considered ubiquitous in the region. To determine what stream and watershed features enhance long-term population persistence in an exurban landscape, we compared the occupancy and abundance of two stream salamanders, Eurycea bislineata (northern two-lined salamander) and Desmognathus fuscus (northern dusky salamander), in watersheds that differed in housing density and time since construction. We estimated E. bislineata occupancy at 100% and found strong support for an interaction between the quadratic of average housing development age and housing density in watersheds influencing abundance. Abundance was sensitive to new and high-density housing developments and increased in watersheds that were more than 20 years post-construction when housing density was low. In comparison, D. fuscus occupancy was estimated at 18% and best explained by fine-scale stream features including soil temperature, water conductivity, dissolved oxygen, discharge, and sediment distribution. Notably, estimates of D. fuscus relative abundance within watersheds, including watersheds with low housing densities, were much lower than comparable estimates in the literature. We suggest an adaptive management approach to monitor and manage D. fuscus populations in the region. Future wildlife management decisions in exurban landscapes should consider interactions between housing age and density as well as development legacy effects.

The effect of exogenous organic matter on the thermal properties of tilled soils in Poland and the Czech Republic

PurposeOrganic matter improves soil fertility and water and thermal properties, but its content often decreases. This decrease may be mitigated by the addition of exogenous organic matter (EOM). The aim of this study was to assess the effect of EOMs, including compost from manure, slurry, and straw (Ag); industrial organic compost from sewage sludge (Ra); animal meal from animal by-products (Mb); and digestate from a biogas fry factory (Dg) on soil thermal conductivity, heat capacity, thermal diffusivity, water content, and bulk density in the top (0–15-cm) layer of two soils in Poland and the Czech Republic.Materials and methodsIrrespective of EOM type, the total yearly nitrogen application rate being 200 kg N ha−1 (100%) was from a given EOM at the rates 0, 50, 75, and 100% and the remaining parts from the mineral fertilizer. The study was conducted in 2013–2014 in Poland (Braszowice) and the Czech Republic (Pusté Jakartice) on loam silt and clay silt loam, respectively, as part of a cross-border cooperation project. The soil properties were examined using classical descriptive statistics, semivariograms, and kriging-interpolated maps.Results and discussionAnalysis of linear regressions (trends) showed that the EOM application rate influenced (positively or negatively) the soil properties in most measurement occasions. The variability of all soil properties was low and medium (coefficient of variation 7.3–34%). Geostatistical analysis indicated that the spatial dependence (C0/(C0 + Cs)) of the soil properties on the EOM-amended plots was very strong or moderate. The maps revealed that the heterogeneity and degree of patch fragmentation were greater for thermal conductivity and heat capacity than for thermal diffusivity, water content, and bulk density. In general, all the soil properties were spatially more variable in the Braszowice than Pusté Jakartice soil and in spring than autumn in both sites.ConclusionsThe spatial analysis and maps enhance the comprehensive understanding of changes in soil thermal properties in response to EOM application. Suitability of the results from the field experiments in models predicting some thermal properties based on soil bulk density and water content in relation to EOM addition was indicated. Expressing the amount of EOMs added using the organic carbon content basis (% kg OC/kg of soil) instead of the nitrogen content basis allowed identifying areas on the kriging-interpolated maps where the distribution of soil thermal properties resembled that of soil organic carbon content, water content, and bulk density. Thus, the effect of EOMs on soil thermal properties is considered along with changes in soil water content and bulk density.The results will be helpful in forecasting effects of exogenous organic matter on the soil thermal properties affecting surface-energy partitioning, temperature distribution in soil, and plant growth.

Numerical simulation model of artificial ground freezing for tunneling under seepage flow conditions

Artificial ground freezing (AGF) is a reliable technique for ground improvement to address adverse geotechnical engineering conditions. The formation of a freezing curtain during the AGF process is crucial as it serves to control groundwater flow and enhances the strength of the soil. However, groundwater flow has a considerable influence on the formation of the freezing curtain because it provides a continuous source of heat. Thus, to investigate the influence of water flow on the freezing process during AGF, a moisture–heat coupling model was proposed considering ice/water phase transition to quantify the temperature distribution in soil during the freezing process. The proposed numerical model was further validated using thorough laboratory tests under various seepage flow conditions. Finally, a numerical simulation of AGF was conducted for the end well of the Harbin metro station in China. Five representative monitoring points on the end well were selected and continuously monitored for 30 days to predict the formation of a freezing curtain. It was observed that the temperature results obtained using the proposed model are consistent with actual field monitoring data.

The effects of topographical factors on the distribution of plant communities in a mountain meadow on the Tibetan Plateau as a foundation for target-oriented management

Abstract Mountains are storehouses of biodiversity and natural resources. However, mountain rangeland is one of the most fragile ecosystems in the world due to the harsh natural conditions. The biodiversity and productivity in mountain regions are further under severe threat because of topography heterogeneity and poor management. To improve mountain rangeland management to sustain ecosystem services, we should better understand the relationships between topographical factors and plant distributions. The purpose was to elaborate on an alternative management strategy for mountain rangelands. In this study, we selected a hill covered by alpine meadow on the north-eastern Tibetan Plateau and quantified the effects of hill aspect and altitude on soil temperature, soil moisture, and plant and functional group distribution in terms of cover, height, frequency, richness, abundance and biomass in 189 quadrats on the hill. The results show that 1) with increasing altitude, the plant species cover, height, abundance, richness and biomass first increased and then decreased on the shadow aspect and on the ridge, whereas they increased linearly on the sunny aspect, 2) the altitude and aspect explained 58.6% of the total variance in the distribution of soil temperature and moisture, with aspect alone explaining 52.1% of the total variance and making the greatest contribution to the alpine meadow, and 3) the hill aspect had higher effects than the altitude on the distribution of species and functional groups in the community. The combined contributions of hill aspect and altitude and the individual effect of aspect alone were greater at the functional group level than at the species level. In conclusion, priority should be given to the differences in the soil and plant distribution caused by different aspects to provide a framework for designing tailored management plans for local farmers to preserve biodiversity on one hand whilst increasing productivity for economically viable farming and for preserving the provisioning of ecosystem services in mountain rangeland ecosystems on the other hand.

Plant diversity is closely related to the density of zokor mounds in three alpine rangelands on the Tibetan Plateau.

BackgroundPlateau zokor (Myospalax baileyi) is a subterranean rodent endemic to the Tibetan Plateau. This species has been generally viewed as a pest in China due to the competition for food with livestock and also causing soil erosion. As a result, plateau zokor has been the target of widespread poisoning or trapping campaigns designed to control or eliminate it since 1970s. But there is little research on the effect of plateau zokor on plant diversity in alpine rangelands. Therefore, objectively evaluating the positive effects of the plateau zokors disturbance on their living environment and plant communities is of great significance to understand the function of plateau zokor in alpine ecosystem.MethodsHere, we selected three rangelands (alpine meadow, alpine steppe and alpine shrub meadow) in which plateau zokors are typically distributed on the Tibetan Plateau, and five zokor mound density gradients were selected in each rangeland type to study the effects of the mounds on soil moisture and temperature related to plant species diversity.ResultsThe results showed that, with the mound density increasing, the soil temperature decreased significantly in all three rangeland types, and the soil moisture significantly increased in all three rangeland types. In the alpine meadow, both the plant diversity and cumulative species richness increased significantly with increasing mound density. The increase in broad-leaved forbs is the main reason for the increase of plant diversity in the alpine meadow disturbed by zokor mounds. In the alpine steppe, the plant diversity decreased significantly with increasing mound density, while the cumulative species richness initially decreased and then increased. In the alpine shrub meadow, the plant diversity first increased and then decreased with increasing mound density as did the cumulative species richness. In conclusion, plateau zokor mounds dominated the distribution of soil moisture and temperature and significantly affected plant diversity in these three rangelands on Tibetan Plateau; the results further deepen our understanding toward a co-evolved process.

Pore Network Simulation and Experimental Investigation on Water-Heat Transport Process of Soil Porous Media

The research on water-heat transport of soil porous media has important theoretical and practical significance for the problem of agricultural production and environmental governance. In this work, the water-heat transport characteristics of sandy soil porous media are analyzed. The two-dimensional continuum physical model is constructed by continuum method, and the two-dimensional pore network physical model is constructed directly at pore scale by taking into account the complicated pore and skeleton structures of soil. Mathematical models of water-heat transport process of sandy soil are constructed based on heat-mass transfer mechanism. Mathematical models of the continuum method and pore network method are solved by ANSYS and self-designed solving algorithm, respectively. The numerical simulation results of soil temperature distributions and moisture distributions are in good agreement with the experimental results. The pore network simulation results are in good agreement with the measured data and are superior to the existing continuous scale method. The pore network simulation results can directly present the characteristics of the preferential flow and wetting front during the water-heat transport process of soil.

Modelling soil hydrothermal regimes in pigeon pea under conservation agriculture using Hydrus-2D

Limited information is available about the effects of conservation agriculture (CA) practices on soil temperature moderation and distribution of water in the soil profile during crop growth, particularly on the changes in the components of water and energy balance. Hence, the objective of this study was to assess soil hydrothermal regimes and water and energy balance components in pigeon pea (Cajanas cajan) grown under CA in a pigeon pea-wheat (Triticum aestivum) cropping system using the Hydrus-2D model. There were seven treatments: permanent broad bed (PBB), PBB with crop residue (PBB + R), permanent narrow bed (PNB), PNB with crop residue (PNB + R), zero tillage (ZT), ZT with crop residue (ZT + R), and conventional tillage (CT). Results during the seventh year of the experiment showed that the PBB, PBB + R, PNB, PNB + R and ZT + R treatments significantly reduced surface soil bulk density (BD), increased field saturated hydraulic conductivity (Ksat) and improved soil water retention over the CT. The Ksat values obtained as the output of the Rosetta-Lite model which is implemented in Hydrus-2D) were very low. Hence, experimentally measured Ksat values were optimized along with parameters α and n that were obtained as output of the Rosetta Lite model, through inverse modelling (IM). The model predicted daily changes in profile soil water content (SWC) with reasonable accuracy (R2 = 0.77, RMSE = 0.012; n = 84). Soil water balance simulated from the model indicated higher cumulative transpiration (CTr), lower cumulative evaporation (CE) and higher soil water retention in the PNB + R and PBB + R plots than CT. Computed values of thermal conductivity (λ) obtained from the observed soil temperature (ST) data at different SWC values showed significant correlations with those optimized through IM. In general, Hydrus-2D model over-predicted the ST values during a simulation period of 10 days. However, reasonably accurate (R2 = 0.91, RMSE = 1.41 °C; n = 102) predictions were observed for the 0–20 cm soil layer using the optimized values. It was also observed that PBB + R and PNB + R treatments improved soil hydrothermal regimes, root growth, radiation interception, leaf area index and biomass production of the pigeon pea crop. Hydrus-2D used in this study could also satisfactorily simulate the temporal changes in energy balance components, such as soil heat flux (G) and evaporative heat flux (LE). Hence, this model may be adopted for evaluating arable management practices for characterizing different components of water and energy balance in pigeon pea.

Numerical modeling and parametric study of a vertical earth-to-air heat exchanger system

A numerical model of a vertical earth-to-air heat exchanger (VEAHE) system was developed for the first time. Compared to conventional EAHE system models, the developed model considered the vertical distribution of soil temperature and thermal conductivity. The model validation against experimental data showed a good agreement. A parametric study was then conducted to investigate the effects of tube parameters, insulation parameters, mass flow rates and soil types. Results indicate that a system with a smaller tube diameter provides more thermal capacity with a fixed air mass flow rate, while a larger tube diameter can enhance the system's COP. An increase in tube depths causes the outlet air temperatures to decrease/increase in summer/winter, with a smaller daily oscillation. Compared to PVC and PE, stainless steel can be recommended as the most appropriate tube material, taking into account both heat exchange and soil pressure. Polyurethane, rubber or rock wool as insulation materials can be used as thermal barriers to shield the undesirable heat gains from the shallow soil with the almost same insulation effects. A thickness of 30 mm and a length of from 4 to 5 m can be recommended as the most appropriate insulation parameters for this proposed system.

三江平原碟形洼地-岛状林土壤氮磷空间分布及生态化学计量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 三江平原碟形洼地-岛状林土壤氮磷空间分布及生态化学计量特征 DOI: 10.5846/stxb201808231793 作者: 作者单位: 吉林师范大学,唐山师范学院,吉林师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41271113）；吉林省科技厅项目（20180101085JC） Spatial distribution and ecological stoichiometric characteristics of nitrogen and phosphorus in soils from saucer-shaped depressions to island forests in the Sanjiang Plain Author: Affiliation: jilin normal university,tangshan normal university,jilin normal university Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为阐明由碟形洼地-岛状林方向土壤养分的空间分布特征，选取非生长季中国科学院三江平原沼泽湿地生态试验站内的碟形洼地为研究对象，探讨土壤全氮和全磷含量及其化学计量比的空间分布特征及其影响因素。结果表明：由碟形洼地-岛状林方向，全氮、全磷和氮磷比在各样点的平均值分别呈"V "字、倒" N"字和"V"字型分布，土壤全氮、全磷与氮磷比含量的平均值分别为2278.11 mg/kg、820.50 mg/kg与2.44，变异系数为全氮（51.77%） > 氮磷比（36.07%） > 全磷（13.65%）。在0-50 cm土层内，全氮、全磷和氮磷比总体呈随土壤深度增加而逐渐降低的趋势，其中全氮主要集中于不同样点土壤的中上层，各样点的最高值均分布在土壤表层区域；全磷的富集深度与全氮相同，但在土壤20 cm深度各样点含量相近，后在20-50 cm深度内呈逐渐下降趋势；氮磷比在各样点的最高值与全氮和全磷分布总体一致，富集深度与两元素呈基本一致趋势。相关性分析表明，碟形洼地-岛状林方向土壤全氮与全磷之间均呈现出良好的相关关系，其中土壤有机质的分布，植物与水文状况、季节变化和土壤温度也在养分分布中起重要作用。 Abstract:In order to illuminate the spatial distribution characteristics of soil nutrients from saucer-shaped depressions to island forests, this paper chose the saucer-shaped depression within the wetland ecological test station on the Sanjiang Plain, part of the Chinese academy of sciences, as a study site during the non-growing season, and discusses the spatial distribution characteristics of total nitrogen (TN) content, total phosphorus (TP) content, and their stoichiometric ratios and influential factors. The results showed that the average TN, TP and N/P, respectively, displayed a tendency towards "V", inverted "N", and "V" type distributions in soil from saucer-shaped depression to island forests, the average of each was 2278.11 mg/kg, 820.50 mg/kg and 2.44 respectively, and the Coefficient of Variation (CV) was TN (51.77%) > N/P (36.07%) > TP (13.65%). In soil layers from 0 to 50 cm, TN, TP, and N/P decreased gradually with increasing soil depth, but TN was mainly concentrated in the upper middle layer of soil at the different points, and the highest values at all points were found in the surface area of soil. The enrichment depth of total phosphorus was the same as that of TN, but the content was similar at various points at the depth of 20 cm in the soil, and gradually decreased within the depth of 20-50 cm. The maximum value of N/P at various points was consistent with the distribution of TN and TP, and the enrichment depth was consistent with the two elements. The correlation analysis showed that TN and TP in soils both had a good correlation from saucer-shaped depressions to island forests, and the distribution of soil organic matter (SOM), plants, hydrological conditions, seasonal variation, and soil temperature played an important role in nutrient distribution. 参考文献 相似文献 引证文献

A Coupled Model for Simulating Water and Heat Transfer in Soil-Plant-Atmosphere Continuum with Crop Growth

Crop growth is influenced by the energy partition and water–heat transfer in the soil and canopy, while crop growth affects the land surface energy distribution and soil water-heat dynamics. In order to simulate the above processes and their interactions, a new model, named CropSPAC, was developed considering both the growth of winter wheat and the water–heat transfer in Soil-Plant-Atmosphere Continuum (SPAC). In CropSPAC, the crop module depicts the dynamic changes of leaf area index (LAI), crop height, and the root distribution and outputs them to the SPAC module, while the latter outputs soil moisture conditions for the crop module. CropSPAC was calibrated and validated by field experiment of winter wheat in Yongledian, Beijing, with five levels of irrigation treatments, namely W0 (0 mm), W1 (60 mm), W2 (110 mm), W3 (170 mm), and W4 (230 mm). Results show that CropSPAC could predict the soil water and temperature distribution, and winter wheat growth with acceptable accuracy. For example, for the 0–1 m soil water storage, the R2 for W0, W1, W2, W3, and W4 is 0.90, 0.88, 0.90, 0.91, and 0.79, and the root mean square error (RMSE) is 17.24 mm, 27.65 mm, 20.47 mm, 22.35 mm, and 12.88 mm, respectively. For soil temperature along the soil profile, the R2 ranges between 0.96 and 0.98, and the RMSE between 1.22 °C and 1.94 °C. For LAI, the R2 varied from 0.76 to 0.96, and the RMSE from 0.52 to 0.67. We further compared the simulation results by CropSPAC and its two detached modules, i.e., crop and the SPAC modules. Results demonstrate that the coupled model could better reflect the interactions between crop growth and soil moisture condition, more suitable to be used under deficit irrigation conditions.

The use of biological waste as a source of low-temperature heat for hotbeds in spring in north-eastern Poland

This article proposes a method for using biological waste, including kitchen waste and garden waste, as a substrate for hotbeds. Hotbeds have been long used in home gardens, but most of them are supplied with animal manure, usually horse manure. In this study, the temperature of ambient air, soil temperature and temperature distribution in a hotbed and a cold frame were measured with a thermographic camera. The measurements were performed in three experimental treatments – one hotbed, one cold frame and in the garden. Each treatment was sown with radishes (Raphanus sativus). The experiment began on 7 April, and temperature was measured until the temperature of garden soil reached the temperature inside the hotbed and the cold frame. After the experiment, the hotbed was left in place until the end of August to complete the composting process and grow other plants. The amount of heat generated inside the hotbed during the experiment was calculated, and the thermal efficiency of the hotbed was compared with the maximum heat capacity of composting. During the experiment, the hotbed generated 98.7 MJ of heat, and its thermal efficiency reached 12% of maximum capacity. Radishes grown in the hotbed were harvested 5 days earlier than those grown in the cold frame and 12 days earlier than those grown in the garden treatment. The compost produced in the hotbed fully meets Polish Standards for organic fertilizers. The proposed solution minimizes the quantity of biological waste collected from households.

Transient heat transfer performance of a vertical double U-tube borehole heat exchanger under different operation conditions

Abstract The transient thermal performance of a vertical double U-tube borehole heat exchanger (BHE) was numerically studied by validated heat transfer model. Further, the influence of several operation parameters, including inlet velocity, temperature and operation interval, on radial/axial soil temperature distribution were investigated. The simulation result showed that the increased amplitude of the BHE’s heat transfer rate was similar when charging temperature was increased under the same velocity conditions. Meanwhile, the difference of the heat transfer rate between 0.1 and 0.3 m/s was greater than that of the 0.3 and 0.5 m/s when the inlet temperature kept constant. The charging temperature had a more vital influence than the flow velocity on soil temperature lifting, and the flow velocity around 0.3 m/s was recommended under the conditions in this work. Moreover, the heat charging time had a more obvious effect on the heat transfer sensitive zone in the radial direction than the other two parameters. Finally, the choice of charging temperature, appropriate interval, space and depth of borehole were discussed. This study could contribute to the comprehensive understanding of the dynamic thermal behaviour and operation parameter optimization of BHE and its further application in the field of borehole thermal energy storage.

A novel truncated cone helix energy pile: Numerical and laboratory investigations of thermal performance

As for the cylinder helix energy pile (CyHEP), in order to reduce thermal interference and improve heat transfer efficiency, a novel truncated cone helix energy pile (CoHEP) was proposed in this paper. A 3-D numerical model both considering the dynamic surface condition and the initial soil temperature distribution was developed to investigate its thermal performance, and three main influencing factors (inlet water temperature, water flow rate, cone angle) were studied by the established model. In addition, the laboratory investigation was carried out to verify the accuracy of the numerical model. The results indicate that the heat flux per unit pipe length of the 20° cone angle CoHEP is 6.16% larger than the traditional CyHEP. The whole pipe of CoHEP can be divided into four stages along the flow direction of the pipe length: the entrance stage → the thermal short circuit stage → the small temperature difference stage → the exit stage. During the design of CoHEP, the proportion of the thermal short circuit stage and the small temperature difference stage should be reduced to ensure the overall heat transfer capability. Heat flux per unit pipe length of the CoHEP increases linearly with the inlet water temperature. Increasing the water flow rate can increase the heat flux per unit pipe length of the CoHEP, but it can also reduce the flow time in the pipe, resulting in insufficient heat exchange. As for the cone angle, increasing the cone angle can effectively reduce the radial thermal interference at the upper part of CoHEP and the axial thermal interference. When the system running time is 12 h, as the cone angle increases from 0° to 10° to 20°, the growth rates of heat flux per unit pipe length are 2.54% and 3.53% respectively. Moreover, there must be an allowable maximum cone angle considering the minimum spiral radius of PE pipe, for example, the allowable optimal cone angle is 21° for the model built in the paper.