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1.
In 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.  相似文献   

2.
Effect of macropores on soil freezing and thawing with infiltration   总被引：3，自引：0，他引：3       下载免费PDF全文
An understanding of heat transport and water flow in unsaturated soils experiencing freezing and thawing is important when considering hydrological and thermal processes in cold regions. Macropores, such as cracks, roots, and animal holes, provide efficient conduits for enhanced infiltration, resulting in a unique distribution of water content. However, the effects of macropores on soil freezing and thawing with infiltration have not been well studied. A one‐directional soil‐column freezing and thawing experiment was conducted using unsaturated sandy and silt loams with different sizes and numbers of macropores. During freezing, macropores were found to retard the formation of the frozen layer, depending on their size and number. During thawing, water flowed through macropores in the frozen layer and reached the underlying unfrozen soil. However, infiltrated water sometimes refroze in a macropore. The ice started to form at near inner wall of the macropore, grew to the centre, and blocked flow through the macropore. The blockage ice in the macropore could not melt until the frozen layer disappeared. Improving a soil freezing model to consider these macropore effects is required. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Summary The study of heat exchanges or temperature changes in the surface layers of the soil are important in agricultural science at tropical latitudes. The quantity, thermal diffusivity largely determines the temperature change produced in any layer of the soil when heat is conducted there from an adjacent layer. Therefore, the authors have determined the thermal diffusivity of the soil from range and lag methods suggested byJohnson andDavies [15]2) andCoutis [7] respectively. The values of diffusivity cbtained from these methods agree well with each other. The effect of soil moisture on diffusivity has been studied. The diffusivity increases with the increase of moisture in the surface layers of the scil. The ratio of ranges of soil temperature at different depths is found to be approximately constant which is in agreement with the theory of heat flow into the soils. The results of diffusivity obtained from these methods agree well with those results of past workers. The mean value of the thermal diffusivity of red sandy soil at the experimental site of Waltair is found to be 6.336×10–3 cm2/sec.  相似文献   

4.
We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required.  相似文献   

5.
基于GRACE资料研究南极冰盖消减对海平面的影响   总被引：15，自引：10，他引：5       下载免费PDF全文
利用5年的GRACE重力数据,计算了南极1°×1°等效水量时间序列,得到每个格网的趋势项,结果表明在西南极Amundsen区域有明显的负增长,超过-80 mm/a,南极半岛存在着负增长,东南极Enderby Land地区质量增长;计算得到2002年7月到2007年9月南极、东南极和西南极冰盖的等效体积变化分别为-78±37 km3/a,-3±46 km3/a和-75±50 km3/a,对应海平面变化的贡献为0.21±0.1 mm/a,0.008±0.127 mm/a和0.2±0.14 mm/a.该结果与国际最新研究结果一致.同时发现冰后回弹是影响利用GRACE研究南极冰盖质量变化的关键因素.  相似文献   

6.
Pesticides used to maintain golf course turf can threaten ground water. This concern is particularly important in most of New York's Long Island, where generally sandy soils overlie a sole source aquifer. This study uses two methods to evaluate the potential for pesticides that are commonly used on Long Island's golf courses to leach to ground water.
Adapting the Pesticide Root Zone Model (PRZM). Release 1. for dense turf and applying site-specific soil data, certain pesticides, including metalaxyl and trichlorfon, are identified as potential problem leachers. PRZM simulations also identify the Long Island soils, including the sandy Plymouth and Carver soils, which arc most vulnerable to leaching.
When adequate input data for PRZM is unavailable, the ground water ubiquity score (GUS) method may be useful. GUS teachability classifications of pesticides commonly applied on Long Island golf courses, and of pesticides actually detected in ground water samples taken on Long Island, agree with PRZM predictions and the field data. The GUS method is applied to the evaluation of the leaching potential of pesticide degradation products (DCPA, maneb, and mancozeb metabolites), and the degradation products are shown to be a greater threat to ground water than their parent compounds.
These methods are potentially useful in designing ground water monitoring programs and for guiding the pesticide use and selection decisions of golf course managers.  相似文献   

7.
Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m2.  相似文献   

8.
Freeze-thaw processes in soils,including changes in frost and thaw fronts(FTFs),are important physical processes.The movement of FTFs affects soil hydrothermal characteristics,as well as energy and water exchanges between the land surface and the atmosphere and hydrothermal processes in the land surface.This paper reduces the issue of soil freezing and thawing to a multiple moving-boundary problem and develops a soil water and heat transfer model which considers the effects of FTF on soil hydrothermal processes.A local adaptive variable-grid method is used to discretize the model.Sensitivity tests based on the hierarchical structure of the Community Land Model(CLM)show that multiple FTFs can be continuously tracked,which overcomes the difficulties of isotherms that cannot simultaneously simulate multiple FTFs in the same soil layer.The local adaptive variable-grid method is stable and offers computational efficiency several times greater than the high-resolution case.The simulated FTF depths,soil temperatures,and soil moisture values fit well with the observed data,which further demonstrates the potential application of this simulation to the land-surface process model.  相似文献   

9.
The interaction effects of different applied ratios of a hydrophilic polymer (Superab A200) (0, 0.2, 0.6% w/w) under various soil salinity levels (initial salinity, 4 and 8 ms/cm) were evaluated on available water content (AWC), biomass, and water use efficiency for corn grown in loamy sand and sandy clay loam soils. The results showed that the highest AWC was measured at the lowest soil salinity. The application of 0.6% w/w of the polymer at the lowest salinity level increased the AWC by 2.2 and 1.2 times greater than those of control in the loamy sand and sandy clay loam soils, respectively. The analysis of variance of data showed that the effect of salinity was significant on biomass and water use efficiency of corn in the loamy sand and sandy clay loam soils. The highest amounts of these traits were measured in soils with the lowest salinity level. Application of polymer at the rate of 0.6% in the loamy sand soil and at the rate of 0.2% in the sandy clay loam soil resulted in the highest aerial and root biomass and water use efficiency for corn. At these polymer rates the amounts of water use efficiency for corn were 2.6 and 1.7 times greater than those of control in the loamy sand and sandy clay loam soils, respectively. Thus, the use of hydrophilic polymer in soils especially in the sandy soils increases soil water holding capacity, yield, and water use efficiency of plant. On the other hand, decreases the negative effect of soil salinity on plant and helps for irrigation projects to succeed in arid and semi‐arid areas.  相似文献   

10.
Isolated, Late Miocene volcanogenic sequences in northern Alexander Island, Antarctic Peninsula, form an unusual, cogenetic association of volcaniclastic, sandy-gravelly lithofacies (including tillites) and volcanic (lava/hyalocalstite) lithofacies. Using simple lithofacies analysis and theoretical considerations of hydrodynamic effects of subglacial eruptions, valley-confined volcanic activity beneth thin, wet-based ice is suggested. The Alexander Island successions are complete enough to be regarded as model sequences for this uncommonly recorded type of eruptive/depositional activity. The sedimentary lithofacies represent resedimented tuffs and meltout or flow tills, which were probably deposited in subglacial ice tunnels eroded or enlarged by volcanically heated meltwater. The volcanic lithofacies formed by the interaction of hot magma with the ice tunnel walls (generating abundant meltwater) and water-saturatedsediments, resulting in the formation of heterogeneous masses of lava and hyaloclastite. There is no obvious sequence organisation in the sedimentary sections. This is probably due to a complex interplay of eruption-related and environmental hydrodynamic factors affecting the relative proportions of water and entrained sediment.  相似文献   

11.
This study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long-Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time-lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process-based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.  相似文献   

12.
Several studies illustrate the wind and water erosion‐reducing potential of semi‐permanent microbiotic soil crusts in arid and semi‐arid desert environments. In contrast, little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter. This study attempts to fill the research gap through (a) a field survey assessing the occurrence of biological soil crusts on loess‐derived soils in central Belgium in space and time and (b) laboratory flume (2 m long) experiments simulating concentrated runoff on undisturbed topsoil samples (0.4 × 0.1 m2) quantifying the microbiotic crust effect on soil erosion rates. Three stages of microbiotic crust development on cropland soils are distinguished: (1) development of a non‐biological surface seal by raindrop impact, (2) colonization of the soil by algae and gradual development of a continuous algal mat and (3) establishment of a well‐developed microbiotic crust with moss plants as the dominant life‐form. As the silt loam soils in the study area seal quickly after tillage, microbiotic soil crusts are more or less present during a large part of the year under maize, sugar beet and wheat, representing the main cropland area. On average, the early‐successional algae‐dominated crusts of stage 2 reduce soil detachment rates by 37%, whereas the well‐developed moss mat of stage 3 causes an average reduction of 79%. Relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover (b = 0·024 for moss‐dominated and b = 0·006 for algae‐dominated crusts). In addition to ground surface cover by vegetation and crop residues, microbiotic crust occurrence can therefore not be neglected when modelling small‐scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

13.
Irregular wetting, water repellency, and preferential flow are well‐documented properties of coastal sandy podzols, though little is known about the effect of fire on unsaturated zone processes in this environment. This study investigates water repellency at and below the soil surface in two coastal sandy podzols following bushfire. Water drop penetration time tests were applied to burned and unburned soils at a high dune field site in South East Queensland, Australia. It was found that the mean water drop penetration time of the burned soil was four times that of the unburned soil, but both soils were largely non‐repellent. Post‐fire repellency peaked below the surface in a patchy layer, in contrast to the laterally extensive layer reported in other studies, and high organic matter content in the soil did not appear to significantly influence repellency post‐burn. Non‐parametric statistics were used to quantify the high spatial variability in water repellency, which was ultimately insufficiently captured by atypically large (n = 1000 drop) datasets. This study confirms the presence of naturally occurring repellency and patchy infiltration in sandy soils while demonstrating that conclusively describing the influence of fire is challenging in a soil with heterogeneous infiltration characteristics. With respect to this uncertainty, it appears that fire does not increase soil water repellency such that infiltration and runoff processes due to fire‐induced water repellency would differ post‐burn.  相似文献   

14.
In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.  相似文献   

15.
Northern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long‐term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using HYDRUS‐1D were run for different soil profile depths, compositions, and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations, either primarily conserving water by limiting evapotranspiration or maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America, the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.  相似文献   

16.
Antarctic tabular icebergs are important active components in the ice sheet-ice shelf-ocean system. Seafloor topography is the key factor that affects the drifting and grounding of icebergs, but it has not been fully investigated. This study analyzes the impact of seafloor topography on the drifting and grounding of Antarctic tabular icebergs using Bedmap-2 datasets and iceberg route tracking data from Brigham Young University. The results highlight the following points. (1) The quantitative distributions of iceberg grounding events and the tracking points of grounded icebergs are mainly affected by iceberg draft and reach their peak values in sea water with depths between 200 m and 300 m. The peak tracking point number and linear velocity of free-drifting icebergs are found in the Antarctic Slope Front (water depth of approximately 500 m). (2) The area of possible grounding regions of small-scale icebergs calved from ice shelf fronts accounts for 28% of the sea area at water depths less than 2000 m outside the Antarctic coastline periphery (3.62 million km2). Their spatial distribution is mainly around East Antarctica and the Antarctic Peninsula. The area of possible grounding regions of large tabular icebergs with long axes larger than 18.5 km (in water depths of less than 800 m) accounts for 74% of the sea area. (3) The iceberg drifting velocity is positively correlated with ocean depth in areas where the depth is less than 2000 m (R=0.85, P<0.01). This result confirms the effect of water depth variations induced by seafloor topography fluctuations on iceberg drifting velocity.  相似文献   

17.
有色噪声广泛存在于各种连续GPS站坐标时间序列,对GPS时间序列分析有重要影响.利用GAMIT/GLOBK软件解算了南极半岛地区8个GPS测站2010—2014年的实测数据,对坐标时间序列使用主分量分析法(PCA)进行了空间滤波,利用CATS软件估计了不同噪声模型下和空间滤波前后的噪声量级、站坐标时间序列参数及其不确定度,最后对南极半岛地区水平和垂向的形变模式进行了分析和讨论.结果表明,南极半岛地区GPS时间序列不仅存在白噪声,还存在较大量级的闪烁噪声,部分测站E方向在滤波前可能存在随机游走噪声;空间滤波能够有效降低这三种噪声的量级,从而有效减小线性项和周期项估计的不确定度;南极半岛地区在水平方向主要表现为板块运动,还可能存在局部性构造运动;在垂直方向上由冰川均衡调整(Glacial Isostatic Adjustment,GIA)因素引起的抬升较小,主要表现为现今冰雪质量损失引起的弹性抬升运动.  相似文献   

18.
A new analysis of palaeomagnetic data for igneous rocks from Deception Island, 25 de Mayo Island (King George Island) and Cape Spring, are given.K-Ar age determinations indicate that most of the igneous samples from 25 de Mayo Island included in the palaeomagnetic study are of Late Mesozoic/Early Tertiary age. The significance of these palaeomagnetic-radiometric data on the hypothesis of oroclinal bending of the Antarctic Peninsula and on the apparent polar movement of Antarctica is discussed.The positions of palaeomagnetic poles for the Andean igneous complex indicate that there has not been any apparent post-Late Cretaceous/Early Tertiary oroclinal bending in the Antarctic Peninsula from 74°S to 62°S.A comparison of the positions of palaeomagnetic poles for Antarctica and Australia suggests that the direction of apparent polar movement relative to Antarctica reversed after the Miocene.  相似文献   

19.
Seismic refraction measurements were made in two areas of the Baltic Sea in June 1967. The refraction data were obtained in the course of the transmission measurements program of Operation MILOC BALTIC 67. Three profile pairs were obtained, two in the area south of Öland Island, Sweden, the third to the east, north of the peninsula of Hel, Poland. The water depths vary from 60 to 90 meters between the areas. The receiving positions for the two profiles south of Oland Island are only 46 km apart but the structures differ markedly. The northern section, only 500 m thick, shows a rather thin sedimentary cover above 350 m of 3.7 km/sec material that in turn overlies 5.6 - 5.9 km/sec velocity material. The southern section, almost 2 km thick, has an equivalent amount of low velocity material, and a layer about 1 km thick having velocity 4.8 km/sec that overlies 6.0 km/sec velocity material. The eastern profile shows high velocity material, 5.6 km/sec, at 2.5 km depth. Correlation of the layers determined by seismic refraction with nearby geology suggests that the structural change south of Öland Island may represent the boundary of the Sarmatian Shield in this region.  相似文献   

20.
Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem‐van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17 < n < 2.35 and 0.08 < α < 0.13 cm?1) ranged between values that are typical for sandy loam and loamy sand. The shapes of the hydraulic conductivity functions of moss and lichen species diverged from those of mineral soils, because of strong negative pore‐connectivity parameters (?2.840 < l < ?2.175) and low hydraulic conductivities at slightly negative pressure heads (0.016 < K0 < 0.280 cm/d). These K0 values are surprisingly low, considering that mosses are very porous. However, during evaporation, large pores and voids were air filled and did not participate in capillary water flow. Small K0 values cause mosses and lichens to be conservative with water during wet conditions, thus tempering evaporation compared to mineral soils. On the other hand, under dry conditions, mosses and lichens are able to maintain a moisture supply from the soil, leading to a higher evaporation rate than mineral soils. Hence, the modulating effect of mosses on evaporation possibly differs between wet and dry climates. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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