Thermodynamic transport mechanism of water freezing-thawing in the vadose zone in the alpine meadow of the Tibet Plateau

High altitude,cold and dry climate,strong solar radiation,and high evapotranspiration intensity have created an extremely fragile ecological and geological environment on the Tibet Plateau.Since the heat in the vadose zone is primarily generated by the external solar radiation energy,and evapotranspiration is contingent on the consumption of vadose heat,the intensity of evapotranspiration is associated with the intensity of solar radiation and the heat budget in the vadose zone.However,the spatial and temporal variation of heat budget and thermodynamic transfer process of the vadose zone in the frigid region are not clear,which hinders the revelation of the dynamic mechanism of evapotranspiration in the vadose zone in the frigid region.With the moisture content of the vadose zone in the alpine regions being the research object,the paper conducts in-situ geothermal observation tests,takes meteorological characteristics into consideration,and adopts the method of geothermal gradient and numerical computation to analyse the temporal and spatial variation rule of heat budget and thermodynamic transmission process of the vadose zone in the high and cold regions.The results show there is a positive correlation between air temperature,ground temperature,and water content of the vadose zone in both thawing and freezing periods.According to the change law of geothermal gradient,the thermodynamic transfer process of the vadose zone has four stages:slow exothermic heating,fast endothermic melting,slow endothermic cooling,and fast exothermic freezing.From the surface down,the moisture freezing rate of the vadose zone is slightly higher than the melting rate.This is of great significance for understanding the evapotranspiration dynamic process of the vadose zone and protecting and rebuilding the ecological and geological environment in the high and cold regions.

Development of a new method for efficiently calculating of evaporation from the phreatic aquifer in variably saturated flow modeling

In this paper, we proposed a new method that has been developed based on the surface soil moisture content(SSMC) to more efficiently calculate the groundwater evaporation in variably saturated flow modeling. In this method, the empirical formula to calculate evaporation was modified and the value of the formula varies from zero to one as a closed interval. In addition, the simulation code for calculating the groundwater evaporation based on the SSMC method was incorporated into the EOS9 module of Tough2, a variably saturated flow modeling code. Finally, two numerical tests and a case simulation were conducted to verify the feasibility and accuracy of the SSMC method. Simulation results indicate that the SSMC method is capable of appropriately simulating the characteristics of water flow in vadose zone and the amount of evaporation with the variable water table. And such results are in coincidence with the value calculated by the logistic function method, and fit well with the measured data globally rather than locally.

Modeling regional landslide susceptibility using dynamic soil moisture profiles

A landslide susceptibility mapping study was performed using dynamic hillslope hydrology. The modified infinite slope stability model that directly includes vadose zone soil moisture(SM) was applied at Cleveland Corral, California, US and Krishnabhir, Dhading, Nepal. The variable infiltration capacity(VIC-3L) model simulated vadose zone soil moisture and the wetness index hydrologic model simulated groundwater(GW). The GW model predictions had a 75% NASH-Sutcliffe efficiency when compared to California's in-situ GW measurements. The model performed best during the wet season. Using predicted GW and VIC-3L vadose zone SM, the developed landslide susceptibility maps showed very good agreement with mapped landslides at each study region. Previous quasi-dynamic model predictions of Nepal's hazardous areas during extreme rainfall events were enhanced to improve the spatial characterization and provide the timing of hazardous conditions.

Root zone soil moisture redistribution in maize (<i>Zea mays</i>L.) under different water application regimes

Soil moisture availability to plant roots is very important for crop growth. When soil moisture is not available in the root zone, plants wilt and yield is reduced. Adequate knowledge of the distribution of soil moisture within crop’s root zone and its linkage to the amount of water applied is very important as it assists in optimising the efficient use of water and reducing yield losses. The study aimed at evaluating the spatial redistribution of soil moisture within maize roots zone under different irrigation water application regimes. The study was conducted during two irrigatation seasons of 2012 at Nkango Irrigation Scheme, Malawi. The trials consisted of factorial arrangement in a Randomised Complete Block Design (RCBD). The factors were water and nitrogen and both were at four levels. The Triscan Sensor was used to measure volumetric soil moisture contents at different vertical and lateral points. The study inferred that the degree of soil moisture loss depends on the amount of water present in the soil. The rate of soil moisture loss in 100% of full water requirement regime (100% FWRR) treatment was higher than that in 40% FWRR treatment. This was particularly noticed when maize leaves were dry. In 100% FWRR treatment, the attraction between water and the surfaces of soil particles was not tight and as such “free” water was lost through evaporation and deep percolation, while in 40% FWRR, water was strongly attracted to and held on the soil particles surfaces and as such its potential of losing water was reduced.

融合Transformer和LSTM的蓝莓根区土壤含水量预测模型

针对土壤含水量预测模型存在难以解决非线性复杂特征、易陷入局部极小值等问题,构建融合Transformer和LSTM的土壤含水量深度学习预测模型(Transformer-LSTM)。采集山东省青岛市黄岛区丁家寨村蓝莓(Vaccinium spp.)生产区冷棚与露天2个站点的蓝莓根区土壤和气象数据作为建模数据,根据皮尔逊相关性和偏自相关性分析选择模型的数据输入特征与输入长度,与单一的Transformer模型和LSTM模型进行对比分析,评估模型对土壤含水量的预测性能。结果表明,Transformer-LSTM模型在预测精度上均优于单一的Transformer模型和LSTM模型,Transformer-LSTM模型的平均绝对误差(MAE)、均方根误差(RMSE)、平均绝对百分比误差(MAPE)、决定系数(R^(2))分别为0.245 9、0.572 0、0.012 1、0.960 6。Transformer-LSTM模型可以更全面地提取蓝莓种植环境因子输入序列中的特征信息,有效提升土壤含水量因子预测精度和水平。

黄河孟津段河岸带土壤有机碳分布特征及影响因素分析

【目的】探究黄河孟津段河岸带土壤有机碳空间分布差异及规律,为黄河河岸带土壤固碳和生态修复提供理论依据。【方法】以河岸带表层土壤为研究对象,采用克里金插值法和冗余分析对土壤有机碳空间分布及影响因素进行分析,探讨土壤有机碳含量与微地形、土壤物理性质及植被组合的相关关系。【结果】研究区土壤有机碳含量和土壤有机碳密度的平均值分别为1.94 g·kg^(-1)和0.11 kg·m^(-2),空间变异系数分别为69.9%和83.6%,均属于中等程度变异。研究区土壤有机碳含量在随垂直河流方向距离V1—V5样带的增加而增加,V5样带土壤有机碳含量显著高于V1—V3这3个样带。相关性分析和冗余分析中,研究区土壤有机碳含量与垂直河流距离、土壤含水率、土壤黏粒呈极显著正相关,与土壤砂粒呈极显著负相关,与植物群落、海拔无显著相关。【结论】河岸带土壤有机碳含量随垂直河流方向距离的增加而增加,空间自相关性强,河岸带微地形、土壤黏粒和土壤含水率显著影响土壤有机碳的空间分布。

基于共振柱试验的堆积层滑坡滑带土动力特性研究

动剪切模量和阻尼比是描述土体动力特性的两个关键参数。为研究堆积层滑坡滑带土的动力特性,开展不同剪应变、含水率及围压下滑带土的共振柱试验,来研究动剪切模量与阻尼比随动剪应变的变化规律,并利用Hardin-Drnevich模型对滑带土的动力特性参数进行拟合,得到了最大动剪切模量、动剪切模量比、阻尼比试验曲线以及动力本构模型拟合参数。研究结果表明:含水率和围压是影响滑带土最大动剪切模量的两大关键因素,相同含水率条件下,最大动剪切模量随围压的增大而增大。低围压条件下,最大动剪切模量随含水率的增大而降低,且各级含水率下动剪切模量与动剪应变近似呈现线性关系,围压较高时,随着动剪应变的增加,动剪切模量的减小速度明显加快,且线性关系有所减弱。通过试验获取了不同含水率及围压条件下滑带土的动模量和阻尼比衰减曲线。基于实验数据进行回归拟合,得出了Hardin-Drnevich模型参数。为了评估滑带土的力学特性,将这些参数与袁晓铭所建议的一般黏土曲线进行了对比分析。结果显示滑带土的动剪切模量比要低于一般黏土的平均值,阻尼比大部分数据处于一般黏土的平均值。试验成果可为该类滑坡的动力稳定性分析及滑坡防治提供参考。

甘肃省张掖市荒漠—绿洲过渡带植被群落物种多样性及土壤水分变化特征

[目的]探究甘肃省张掖市荒漠—绿洲过渡带不同类型植被群落物种组成、多样性特征,以及植物群落特征和土壤水分含量的关系,为该区水土保持效益评估提供科学依据。[方法]选择不同类型荒漠植被,调查和测定了不同类型植被群落植物多样性和0—120 cm土壤水分含量。[结果](1)该区域共有6种植被类型,植被结构非常简单,物种组成以适生于干旱荒漠生境的红砂、合头藜、珍珠猪毛菜、三芒草、雾冰藜等耐旱、超耐旱的小灌木、半灌木、草本植物为主,植物群落为灌草群落类型,物种多样性指数较小。(2)土壤水分在垂直方向上的变化呈现“双峰形”,土壤湿度由表层向深层逐步升高,到20—40 cm处升到“第一个峰值”,40—60 cm处又降到了较低水平,到60—120 cm土壤湿度又逐步上升,直至120 cm处升高到“第2个峰值”。(3)各植物群落的植被高度、植被密度、植被盖度随土壤水分含量的升高而增高、增大,植被高度与40—120 cm土层土壤水分呈显著正相关,草本植物、灌木植物密度、植被盖度与其根系主要分布层的土壤水分含量呈显著正相关。[结论]在0—20 cm表层土壤、40—80 cm深层土壤水分含量均不足2%的荒漠绿洲过渡带,适宜种植红砂、合头藜、白刺等旱生灌木和三芒草、刺沙蓬、雾冰藜、画眉草、猪毛蒿等草本植物;表层土壤、深层土壤水分含量均超过2%的荒漠地带,适宜种植红砂、珍珠猪毛菜等旱生灌木和冷蒿、内蒙古旱蒿、寸草等草本植物,能够有效促进生态恢复和重建。

基于不同含水率滑带土水致破坏研究及防治方案建议

随着工程活动的愈发频繁,人为因素诱发滑坡地质灾害越来越多,其中由于加载作用诱发滑坡最为常见。本文依托“贵州省1:1万地质灾害+风险斜坡精细化调查示范项目”,采用野外调查、室内岩土试验及稳定性分析相结合的方法,对某矿区10号挡墙滑坡的形成机理进行了研究,通过对比研究不同含水率下粉质黏土和含碎石粉质黏土的物理力学参数变化,总结了不同滑带土剪切强度与含水率之间的关系,并提出了计算公式,为后期防治工程决策提供了依据。

Sorption and phase distribution of ethanol and butanol blended gasoline vapours in the vadose zone after release

The sorption and phase distribution of 20% ethanol and butanol blended gasoline （E20 and B20） vapours have been examined in soils with varying soil organic matter （SOM） and water contents via laboratory microcosm experiments. The presence of 20% alcohol reduced the sorption of gasoline compounds by soil as well as the mass distribution of the compounds to soil solids. This effect was greater for ethanol than butanol. Compared with the sorption coefficient （Kd） of unblended gasoline compounds, the Kd of E20 gasoline compounds decreased by 54% for pentane, 54% for methylcyclopentane （MCP） and 63% for benzene, while the Kd of B20 gasoline compounds decreased by 39% for pentane, 38% for MCP and 49% for benzene, The retardation factor （R） of E20 gasoline compounds decreased by 53% for pentane, 53% for MCP and 48% for benzene, while the R of B20 gasoline compounds decreased by 39% for pentane, 37% for MCP and 38% for benzene. For all SOM and water contents tested, the Kd and R of all gasoline compounds were in the order of unblended gasoline 〉 B20 〉 E20, indicating that the use of high ethanol volume in gasoline to combat climate change could put the groundwater at greater risk of contamination,

六盘山半干旱区华北落叶松林坡面土壤含水量的降雨响应

在宁夏六盘山外围半干旱区,土壤含水量是影响林木成活与生长的关键因子,需深入理解森林坡面不同坡位的土壤含水量对降雨量的响应差异。本文在宁夏六盘山叠叠沟小流域,选择一个华北落叶松人工林典型坡面,于2021年5—10月利用自动气象站和土壤水分仪连续监测降雨等气象条件和坡面土壤含水量变化,分析土壤含水量的坡位差异及对降雨量级的响应。观测期间总降水量为443.7 mm,虽然接近多年平均值,但夏季干旱严重。结果表明:(1)土壤含水量存在明显的生长季内变化,整体表现为先降低后升高的趋势,8月最低(0.112 m^(3)·m^(-3))。(2)土壤含水量存在明显的坡位差异,整体表现为:上坡[(0.191±0.044)m^(3)·m^(-3)]>中坡[(0.158±0.045)m^(3)·m^(-3)]>下坡[(0.146±0.034)m^(3)·m^(-3)],表明土壤含水量的坡位变化因处于干旱年,主要受植被蒸散耗水量大小的影响,而受坡面汇流影响不大。(3)在同一降雨量级时,因受土壤孔隙度和持水能力、林下草本截持、优先流等的影响差异,中坡的土壤含水量对降雨量增加的响应最敏感,其次是上坡,下坡最不敏感。(4)在本研究区,降雨以<10 mm的小降雨事件为主,7 mm是形成有效降雨的阈值,超过此阈值的降雨才有可能缓解0~20 cm土层土壤干旱和补给该层土壤水分。本研究有助于理解半干旱山区森林坡面的土壤含水量大小变化与分布特征,指导确定基于坡面土壤水分的植被承载力和进行林水综合管理。

干旱半干旱煤矿区土壤水分研究进展

本文重点评述了干旱半干旱煤矿区土壤水分与生态环境效应研究进展,系统总结了土壤水分运移机理与动态模拟方法。采煤塌陷会破坏土壤含水层构造并导致地下水位下降,间接改变土壤含水率空间分布特征;露天采矿与复垦过程中机械压实导致土壤孔隙数量减少,连通性减弱,土壤水分入渗受阻;土壤重构与植被重建技术能够有效改善土壤结构,缓解土壤水分流失。在未来研究中,首先应进一步丰富势能理论体系,完善数值模拟技术并引入动态指标;其次应结合干旱半干旱煤矿区环境的特殊性,加强土壤水分运移规律及其机理研究;最后应基于土壤–植被–水分间耦合关系优化调控措施,促进干旱半干旱煤矿区复垦与生态修复。

黄河河岸带不同人为干扰的土壤物理性质比较

【目的】研究人为干扰强度对黄河河岸带土壤物理性质的影响,为黄河河岸带生态系统生态恢复与调控提供科学依据。【方法】2021年10月,在黄河洛阳—郑州段选择地形地貌和地表植被覆盖相对一致的河岸带区域,依据人为踩踏程度的不同,选择3种不同干扰强度的样地类型。按照5×3网格化划分近河岸带200 m×200 m样地,共设置15个样点,系统比较分析不同人为干扰强度(轻度、中度和重度)黄河河岸带土壤容重、土壤含水率、土壤毛管持水量、土壤最大持水量、土壤最小持水量、土壤总孔隙度、土壤毛管孔隙度和土壤非毛管孔隙度等土壤物理性质的差异。【结果】①随人为干扰强度的增加,土壤容重、土壤非毛管孔隙度逐渐增加;土壤含水率先增加后减小;土壤毛管持水量、土壤最大持水量、土壤最小持水量、土壤总孔隙度与土壤毛管孔隙度逐渐减小。②土壤容重与土壤含水率、土壤毛管孔隙度呈负相关,但未达到显著水平;土壤容重与土壤毛管持水量、土壤最大持水量、土壤最小持水量、土壤总孔隙度呈极显著负相关(P<0.01),与土壤非毛管孔隙度呈极显著正相关(P<0.01)。【结论】过度的人为踩踏等干扰增加了河岸带土壤紧实度,导致土壤物理性质退化以及土壤保水和持水能力降低。

荒漠—绿洲过渡带典型混交灌木根区土壤含水率变化特征

土壤水分是干旱区植被生长的限制因子,研究荒漠—绿洲过渡带植被根区土壤水分时空变化对抵御沙漠化进程具有重要意义。以荒漠-绿洲过渡带3种典型混交灌木梭梭×泡泡刺(SS×PP)、泡泡刺×沙拐枣(PP×SG)、沙拐枣×梭梭(SG×SS)为研究对象,对3种典型混交灌木根区0~100 cm土层土壤进行连续采样并测定土壤含水率。结果表明:1)7-9月,3种混交灌木根区0~100 cm土层土壤含水率的变化范围依次为:梭梭×泡泡刺0.54%~2.75%、1.06%~2.41%、0.73%~4.72%;沙拐枣×梭梭0.42%~2.59%、0.96%~2.35%、0.57%~3.58%;泡泡刺×沙拐枣0.31%~2.38%、0.56%~2.33%、0.79%~3.71%。3种混交灌木在0~60 cm土层土壤含水率随深度增加而增大,60~100 cm土层各类型混交灌木土壤含水率变化逐渐趋于稳定。2)7月,0~100 cm土层混交灌木梭梭×泡泡刺的土壤含水率显著高于沙拐枣×泡泡刺,9月,20~40、60~100 cm土层混交灌木沙拐枣×梭梭的土壤含水率显著低于其他2种混交灌木类型。3)3种混交灌木土壤持水能力大小为梭梭×泡泡刺>泡泡刺×沙拐枣>沙拐枣×梭梭。研究结果为荒漠—绿洲过渡带防风固沙植被建设中植物种类的选择提供科学依据。

次降雨入渗补给系数评估雨水花园补给地下水可行性及计算方法研究

【目的】近年来雨水花园在海绵城市建设过程中得到了广泛应用,但其对浅层地下水的补给能力尚缺乏系统研究。【方法】通过柱状模拟试验,研究了不同降雨条件下,次降雨入渗补给系数(α)用于评估雨水花园补给地下水潜力的可行性。【结果】结果表明,α可用于评估雨水花园补给地下水潜力,数值变化范围为0.110~0.212,平均值为0.175;降雨重现期、降雨历时、雨型均对α具有重要影响,且随着重现期和降雨历时增加,α逐渐降低,不同雨型条件下,α大小顺序为均匀雨型>双峰雨型>单峰雨型。【结论】HYDRUS-1D模型模拟法和包气带含水率法计算α均具有较好的精度,不同降雨条件下,模型模拟法计算得出的次降雨入渗补给系数(α_(m))的相对偏差(RE)为-1.280%~7.801%,包气带含水率法计算得出的次降雨入渗补给系数(α_(b))的RE为-14.789%~6.660%。由于包气带含水率法容易实施、便于监测,工程实践中可优先考虑采用该方法。上述结果可为定量评估海绵城市建设过程中雨水花园补给浅层地下水潜力提供参考。

采煤塌陷裂缝对包气带水分运移规律影响数值模拟研究

采煤塌陷裂缝,影响包气带水分运移规律,诱发矿区生态地质环境问题。当前研究集中于塌陷裂缝对包气带含水率影响,往往忽略塌陷裂缝对包气带水分运移方向及其速度的影响。为此,综合考虑裂缝宽度、裂缝密度和土壤质地类型,基于HYDRUS 2D建立采煤塌陷区包气带水分运移数值模型,研究采煤塌陷裂缝对包气带水分运移规律。结果表明:单一裂缝时,含水率差距与裂缝宽度呈正相关关系;土壤水分运移方向向裂缝处偏转,同一土壤深度越靠近裂缝的区域偏转角度越大,最大偏转角度和发生运移方向变化的区域大小随裂缝宽度变大而变大;裂缝边缘与远离裂缝区域的平均水分运移速度差值随裂缝宽度变大而变大;裂缝密度增高时,同一土壤深度含水率会随之降低,裂缝之间区域的最大偏转角度与发生偏转的区域变小;采煤塌陷裂缝影响下壤土的含水率高于风沙土、水分运移速度低于风沙土,但土壤质地类型不影响水分运移方向。

贵州公路旁边坡滑带土抗剪强度特性研究

为了探究公路旁边坡滑带土的强度性质和法向变形性质的变化规律,以贵州山区公路为例,利用环剪仪研究了滑带土在不同含水率和不同法向应力下的抗剪强度特性.结果表明:不同含水率滑带土的峰值强度和残余强度与法向应力间具有良好的线性关系;法向应力越大,试样达到峰值强度所需要的剪切位移也会越大;含水率较高的条件下,滑带土从峰值强度下降到达残余强度期间内,剪应力有增加的趋势;随着含水率的增加,黏聚力呈现增大的趋势,内摩擦角在塑限附近达到峰值,之后逐渐减小.滑带土性质的研究可为公路旁滑坡识别与预防提供科学依据.

Vadose-zone moisture dynamics under radiation boundary conditions during a drying process

In order to better understand the soil moisture dynamics during a drying process, a soil column experiment is conducted in the laboratory, followed by the numerical modeling with consideration of the coupled liquid water, water vapor and heat transport in the vadose zone. Results show that there are three distinct subzones above the water table according to the temporally dynamic variation of the water content profiles. Zone 1 sees a decrease in the water contents in the upper profiles （0 m-0.05 m） due to a negative net water flux in this zone where the upward isothermal water vapor flux becomes the main flow mechanism in the soils. Irl contrast, the water content within Zone 2 in the depth ranging from 0.05 m to 0.37 m sees an apparent increase over the, resulting from the positive net thermal water-vapor and isothermal liquid-water fluxes into this layer. Zone 3 （0.37 m-0.65 m） also sees an apparent decrease in the water content since the isothermal liquid water flux carries the liquid water either upward out of this region for vaporization or downward to the water table as a recharge to the groundwater.

非灌期层状结构包气带含水率特征

包气带岩性、厚度和结构具有很强的时空变异性,包气带水分运移规律受其特征影响十分复杂。以野外钻孔和剖面调查为依据,总结了宁北灌区包气带岩性、厚度和结构特征;以3种典型层状结构包气带试验土柱为代表,探讨了非灌期层状结构包气带含水率特征。结果表明:①宁北灌区包气带岩性主要有粉砂、细砂、粉土、粉质黏土、黏土和砂卵砾石等;岩性结构既有单一岩性,又有上细下粗或者上粗下细的层状结构;②包气带厚度变化和结构特征受灌溉活动控制,包气带厚度整体上具有灌期小于非灌期的特点;③层状结构包气带土壤含水率在岩性界面处产生突变,当水分从细颗粒层进入粗颗粒层时,岩性界面处土壤含水率急剧减小,而由粗颗粒层进入细颗粒层时,岩性界面处土壤含水率急剧增大。

毛乌素沙地植被与地下水关系

以植被的种群和盖度、地下水埋深、包气带含水率、地下水矿化度和包气带含盐量等指标,研究毛乌素沙漠腹地地区植被与地下水的关系,确立了研究区优势植被沙蒿(Artemisia)、沙柳(Salix psammophila)和苔草(Carex)的适生地下水埋深、包气带含水率、地下水矿化度和包气带含盐量。研究表明:地下水埋深、包气带含水量对植被种群影响非常敏感,而地下水矿化度和包气带含盐量则为不敏感指标。另外,地下水埋深对以地下水为水分来源的植被盖度较为敏感,而总盖度为不敏感指标。