Impact of Initial Soil Conditions on Soil Hydrothermal and Surface Energy Fluxes in the Permafrost Region of the Tibetan Plateau

Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.

Characteristics of In-Situ Soil Water Hysteresis Observed through Multiple-Years Monitoring

A soil water retention curve (SWRC) is an essential soil physical property for analyzing transport and retention of water in a soil layer. A SWRC is often described as a single-valued function that relates the soil water potential ψ to volumetric water content θ of the soil. However, an in-situ ψ − θ relation should show soil water hysteresis, though this fact is often neglected in analyses of field soil water regimes while long-term in-situ soil water hysteresis is not well characterized. This study aimed at probing and characterizing in-situ ψ − θ relations. The developments of large hysteresis in the in-situ ψ − θ relations were observed only a few times during the study period of 82 months. Any of the large hysteretic behaviors in the ψ − θ relations began with an unusually strong continual reduction in ψ. The completion of a hysteresis loop required a recorded maximum rainfall. Because the study field had very small chances to meet such strong rainfall events, it took multiple years to restore the fraction of soil water depleted by the unusually strong continual reduction in ψ. While wetting-drying cycles had occurred within a certain domain of ψ, hysteretic behaviors tended to be so small that the in-situ ψ − θ relation can be approximated as a single-valued function of θ(ψ). These observed patterns of the in-situ ψ − θ relations were characterized by kinds of difference in dθ/dψ between a drying process and a wetting process at a given ψ. Thus, more amounts of experimental facts about wetting SWRCs in parallel with drying SWRCs should be needed for correct modelling, analyzing, and predicting soil water regimes in fields. It is also necessary to increase our understandings about the long-term trends of occurrences of extreme weather conditions associated with possible change in climate.

Spatial variability of leaf wetness under different soil water conditions in rainfed jujube (Ziziphus jujuba Mill.) in the loess hilly region, China

Leaf wetness provides a wide range of benefits not only to leaves,but also to ecosystems and communities.It regulates canopy eco-hydrological processes and drives spatial differences in hydrological flux.In spite of these functions,little remains known about the spatial distribution of leaf wetness under different soil water conditions.Leaf wetness measurements at the top(180 cm),middle(135 cm),and bottom(85 cm)of the canopy positions of rainfed jujube(Ziziphus jujuba Mill.)in the Chinese loess hilly region were obtained along with meteorological and soil water conditions during the growing seasons in 2019 and 2020.Under soil water non-deficit condition,the frequency of occurrence of leaf wetness was 5.45%higher at the top than at the middle and bottom of the canopy positions.The frequency of occurrence of leaf wetness at the top,middle and bottom of the canopy positions was over 80%at 17:00‒18:00(LST).However,the occurrence of leaf wetness at the top was earlier than those at the middle and bottom of the canopy positions.Correspondingly,leaf drying at the top was also latter than those at the middle and bottom of the canopy positions.Leaf wetness duration at the middle was similar to that at the bottom of the canopy position,but about 1.46-3.01 h less than that at the top.Under soil water deficit condition,the frequency of occurrence of leaf wetness(4.92%-45.45%)followed the order of top>middle>bottom of the canopy position.As the onset of leaf wetness was delayed,the onset of wet leaf drying was advanced and the leaf wetness duration was shortened.Leaf wetness duration at the top was linearly related(R^(2)>0.70)to those at the middle and bottom of the canopy positions under different soil water conditions.In conclusion,the hydrological processes at canopy surfaces of rainfed jujube depended on the position of leaves,thus adjusting canopy structure to redistribute hydrological process is a way to meet the water need of jujube.

Study on the mechanism of isotope fractionation in soil water during the evaporation process under equilibrium condition

In this study, with the method of vacuum extraction, two evaporative processes of soil water and free water under equilibrium condition were simulated. For each sample,water vapor was condensed by liquid nitrogen and was collected in four time intervals. From the analysis of hydrogen and oxygen isotopic compositions of the water collected at different times, it was discovered that the isotope fractionation of soil water also follows the mode, which is just the same as the evaporative process of free water. The relationship between the stable hydrogen and oxygen isotopes in residual water showed that the simulative evaporation line was close to the global meteoric water line (GMWL) under the equilibrium condition at about 20℃. Comparison of the two types of evaporative processes indicated that the isotope fractionation and evaporation velocity of soil water were only slightly modified by the Van der Waals force.

Study on potential evapotranspiration and wet-dry condition in the seasonal frozen soil region of northern Tibetan Plateau

This study was based on the CEOP/CAMP-Tibet observed data at AWS （Automatic Weather Station） of MS3478 in the seasonal frozen soil region of northern Tibetan Plateau from March 2007 to February 2008. The variation characteristics of PE （potential evapotransph＇ation） were analyzed based on the Penman-Monteith method recommended by FAO （the Food and Agriculture Organization of the United Na- lions）. The contributions of dynamic, thermal and water factors to PE were discussed, and the wet-dry condition of the plateau region was further studied. The results indicated that daily PE was between 0.52 mm and 6.46 mm for the whole year. Monthly PE was over 107 mm from May to September, but decreased to less than 41 mm from November to February. Annual PE was 1,037.8mm. In the summer, thermal PE was significantly more than dynamic PE, but conversely in the winter. Annual variation of thermal PE was of sine wave pattern. In addition, drought and semi-drought climate lasted for a long time while semi-humid climate was short. The effect of water and dynamic factors on PE varied considerably with the seasons. Annual variation of thermal PE was of sine wave pattern.

An Experimental Analysis of Water and Soil Conservation Effected by Micro-landscape Structure

[Objective] This comparative experiment was to explore the soil loss con- trol effects under cultivation combination of different soil and vegetation types, and to provide scientific basis for the upcoming pilot project of ecological recovery. [Method] Both the rudiment of water locomotion functioned by micro-landscape structures and different spatial combinations of various landscape constituents are considered, thus, the combination of multi-soil type, crop species and site conditions is designed in three different experimental sites. [Result] Soil loss estimates in experiments in South Wello significantly depended on various soil type, slope, vegetation and type of con- servation structure; grass cover tremendously reduces soil loss; legume cultivation performed better than cereal cultivation in soil loss control. [Conclusion] By conduct- ing the data analysis of the experiment, a scientific reference is proposed to the agri- culture planting and protective mode for the alleviation of water and soil loss in Amhara Region, Ethiopia.

黄河下游典型河段滩岸崩退特性研究

黄河下游局部河段滩岸崩退频繁,严重危害堤防及滩区安全。通过对黄河下游开展现场观测,结合已有断面地形实测数据,描绘滩岸崩退全过程及特点,评估土体特性及近岸水沙条件对崩岸的影响。研究表明:滩岸崩退引起黄河下游河道展宽,且崩岸规模具有时空差异性,2006年和2018年汛期重点河段平滩河宽分别增加了57.03 m和7.83 m,代表性横断面单侧滩岸最大崩退宽度高达207.20 m。黄河下游土体压实程度低,抗冲能力差,加之土体抗剪强度随含水量增大呈反向变化,致使在汛期崩岸频发。“大流量-小含沙量”的水沙组合易于造成崩岸,而在大含沙量下因泥沙在近岸河床淤积而降低了崩岸发生规模。建议对重点区域滩岸进行长期监测,并加强生态友好型护岸系统建设。

论煤-水-土多资源协调开发

煤炭及其伴生资源是地质体的重要组成部分,大规模和高强度开采会引起近地表岩石圈、土壤圈、水圈的联动响应,进而反向制约煤炭及其伴生资源的安全开采与开发。围绕煤矿区的煤-水-土多资源协调开发,基于多学科知识交叉的地球关键带理念,阐述煤-水-土协调开发的必要性以及多圈层、多过程、多尺度、多目标的耦合关系,为煤炭安全绿色开发和生态环境可持续发展提供战略思考。(1)立足煤炭安全高效开采、土壤-水资源安全和生态环境保护多目标多维度角度,剖析大规模、高强度开发背景下采前、采中、采后地质条件动态演化、多资源时空关系、生态环境响应特征,提出煤炭资源开发生命周期条件下的煤炭资源区的地质调查战略和开发策略。(2)开展煤-水-土多资源量的系统调查和地质结构精细表征,全面理解和综合评价煤-水-土赋存特征和相互依存关系,形成集资源禀赋、生态环境、人口经济等于一体的地质调查评价体系和方法,提出基于煤炭开发、多资源利用、水土保护、生态屏障、土地安全等一体化的全链条调控措施和开发策略与开发政策。(3)监控开发过程中地层地质功能结构变化,理解煤-水-土空间组合结构及分层界面效应和煤(岩)-水-土相互作用的动态演化规律,构建复杂地层结构煤炭安全开采和水-土资源协调开发覆岩变形的演化模型,厘清煤-水-土空间结构及其对开采活动的约束效应,发展地球科学、采矿学、生态学、水文学等多学科交叉的煤炭绿色开发地质保障理论与技术。煤-水-土协调开发研究服务于煤炭安全开采与地质环境保护协调发展,破解多资源开发瓶颈及其地质环境制约之间矛盾,通过对煤炭开采全生命周期内的地质条件和环境效应的关键影响因素、状态参数阈值、演化驱动机制的理解,构建地质环境约束、开采模式调控、系统规划利用的煤-水-土多资源协调开发时空格局。

富水砂层土压平衡盾构渣土改良技术研究

富水砂层土体具有流塑性差、渗透性强的特点,土压平衡盾构施工时易造成排土困难和喷涌事故。针对西安地铁10号线穿越富水砂层的土压平衡盾构工程,采用膨润土泥浆和泡沫剂改良盾构渣土,提出了改良渣土流塑性的评价方法,基于其流塑性和渗透性确定最佳改良方案,为工程提供借鉴和参考。结果表明:(1)当改良渣土塌落后无开裂或坍塌、塌落形状为梨形、塌落度为180~210 mm、塌落渣土与地面接触角θ为0°~90°时,流塑性合适,此时改良渣土的渗透系数于90 min内稳定在10-5cm/s,满足工程要求;(2)最佳改良方案为:渣土、膨润土、水三者质量比保持在200∶1∶40~200∶1.5∶44之间,泡沫剂溶液体积比浓度为2%,泡沫注入比为6%。

Shear strength degradation of gas hydrate-bearing sediment due to partial hydrate dissociation

Extraction of methane hydrate from subseafloor reservoir may potentially trigger seabed slides and induce subsidence.To address the problems,it is crucial to properly characterize the phase equilibrium condition of pore hydrate and the shear strength of the soil.As one of the key constitutive components,the phase equilibrium condition enforces a constraint over pore gas pressure,temperature and unhydrated water content.Such a constraint,however,has been traditionally ignored in analyzing the mechanical behavior of hydrate-bearing soil.In this paper,a series of stepwise hydrate dissociation tests was performed,and the phase equilibrium condition of pore hydrate was determined,providing an effective way to evaluate the unhydrated water content during hydrate dissociation.Meanwhile,a series of direct shear tests was also conducted to explore the shear strength characteristics of the soil.It is shown that the shear strength of the hydrate-bearing soil can be significantly influenced by pore gas pressure,unhydrated water content,hydrate saturation and several other factors.In particular,the measured shear strength depends upon the initial water content of the sample,pointing to a potential problem that the shear strength could be wrongly determined if not properly interpreted.A shear strength criterion,which enforces the equilibrium condition of pore hydrate,is developed for hydrate-bearing soil,establishing a link between the equilibrium condition and the shear strength.The proposed equation describes well the shear strength characteristics of hydrate-bearing soils,remarkably unifying the effects of pore pressure,temperature,water content and hydrate saturation.

灌草覆盖——干热河谷区植被修复新路径探析

干热河谷集中分布于中国西南横断山脉地区,受地形和局部小气候的影响,形成特殊的水热状况组合,是中国分布最北的一块“热区”。在长期剧烈的人为干扰和严酷的自然环境双重压力下,干热河谷的生态系统极度退化,结构与功能濒临崩溃,严重制约了当地经济社会发展,是中国典型的生态脆弱带、极度退化区和植被修复极端困难地区之一。本文先简要回顾了干热河谷区植被修复的历史,接着系统分析河谷区生态修复工作存在的机遇和挑战,明确提出灌草覆盖技术可能是该区域最为适合的一种生态修复方式。该技术可以克服干旱和高温两大河谷区植被修复的关键限制性因子,并实现保水、固土和增肥的植被修复技术目标。本研究首次提出干热河谷区植被修复3条原则:宜乔则乔、宜灌则灌、宜草则草、宜荒则荒原则;结合生态保护和产业发展实行分区修复原则;优选乡土物种进行植被修复原则。同时,建议从水土保持能力、土壤生态系统健康、植物群落健康和综合效益评价等4个方面来评估河谷区植被修复效果。最后,研究展望了干热河谷区植被修复研究的未来方向,包括加强群落演化规律及其适应性机制的研究,建立和完善动态监测机制,选育和培育乡土物种,以及开发和推广植被修复新技术。

复合微生物肥料对红壤退化区土壤的改良作用

针对红壤退化区肥力低下,保肥保水能力弱的现状,本研究利用项目组研制的复合微生物肥料,探讨其在改善红壤裸土区土壤物理化和生物学特征的调理作用。试验表明,施用复合微生物肥料有效改善土壤物理特性,减轻土壤酸化问题,显著提高有机质、有效磷、有效钾和有效硼的含量,促进植物促生菌Haliangium、纤维素降解菌的繁殖,抑制引起氮素散失的菌群的生长,从而提高肥料利用率。因此,该复合微生物肥料可作为一种提高红壤退化区土壤肥力,减少水土流失的新产品进行推广。

金沙江上游干热河谷表土保护设计

金沙江上游干热河谷地区存在较严重的生态障碍,主要是:土壤贫瘠、表土生产力不足、表土立地条件恶劣且土壤保水抗旱能力差,开展生态恢复工作十分困难。以恢复当地的旭龙水电站工程之生态环境为目的,以项目区的生态障碍为突破点,采用资料分析、现场调查及遥感法等,分析项目区的生态障碍,划定不同生态障碍的影响范围;采用类比法及演绎法,逐级推导表土保护和生态恢复问题的解决方法,包括:调查项目内表土资源的分布情况;详细分析项目区内的表土平衡,设计表土回覆、剥离及堆存方案,估算表土缺口;初步设计表土立地条件改良及其生产力恢复的作业方案,对剥离的表土进行表土培肥,对过筛的生土进行土壤熟化,并配套表土堆存临时防护及临时绿化。结果表明:上述表土保护设计可使表土达到绿化覆土要求,形成了“先分析生态障碍,然后开展表土保护设计,改良表土的立地条件改良、恢复其生产力,最后修复生态环境”的工作思路。研究成果可为生态脆弱地区的生态恢复工程提供借鉴。

Growth, Yield and Fruit Quality of Tahiti Lime on Eight Standard Rootstocks Affected by Soil Depth

Two Tahiti lime （Citrus latifolia Tan.） experiments were carried out to evaluate the performance of eight standard rootstocks on two different soil locations at Tecoman Colima, Mexico. Rootstocks were selected by their tolerance to Citrus tristeza virus （CTV） and acceptable adaptation to semi-add hot tropics environment. The first trial was planted in ＂Cerrito de Aguilar＂ （CA） location which had sandy-loam soil with a fluctuant water table at 100 cm depth. The second experiment was planted in ＂Crucero Tecoman＂ （CT） on a sandy deep soil with no water table restriction. At CT location the best Tahiti lime growth, yield and fruit quality were observed on Alemow rootstock. The same combination at CA showed a poor performance and was affected by diseases due to high moisture conditions by the superficial water table. Taiwanica, Swingle citrumelo and Rangpur lime rootstocks were less productive than Alemow, but showed a good adaptation and acceptable yield on both soil conditions. Among them, Swingle citrumelo was a promising rootstock because it showed standard tree growth, good yield and excellent fruit quality. Swingle citrumelo also showed an acceptable performance on soil with high presence ofPhytophthora sp. and moderate levels of calcium carbonate （near to 3,500 ppm）. Taiwanica and Rangpur lime performed well during the six years of the experiment, but trees began to be affected by root diseases. Better performance of most Tahiti lime/rootstocks were found on sandy depth soil than on superficial wet soils.

渣土改良下盾构掘进富水砾砂地层响应研究

为解决土压平衡盾构在富水砾砂地层中掘进土舱保压难度较大的问题,需对盾构渣土进行改良,减小其渗透性,提升土舱保压效果。依托昆明地铁4号线小—火区间盾构隧道工程,采用数值模拟手段,结合现场监测数据,对渣土改良下盾构掘进富水砾砂地层响应特征进行研究。研究结果表明:1)随着改良渣土渗透性的降低,开挖面孔压逐渐增大,当土舱渣土渗透系数降至5×10^(-5)cm/s后,开挖面孔压接近原始孔压,表明改良渣土具有良好的止水性能;随着地下水位的升高,开挖面孔压逐渐增大,表明高水位对渣土止水效果的要求更高。2)小—火区间渣土渗透性较低,开挖面近似止水条件,盾构掘进过程中,开挖面附近会产生一定的超孔压,超孔压影响范围主要位于盾构前方1.5倍洞径,开挖面中心位移远小于失稳时的开挖面中心位移,开挖面稳定性较高。3)由于盾构渣土渗透性较低,盾构掘进会在周围形成较大的超孔压,同时渗透系数较小的渣土可以有效阻止开挖面前方地下水的自由渗流,提高开挖面的稳定性,减小地表沉降。4)随着地下水位的升高,地表沉降和地层超孔压有增大的趋势,维持开挖面所需支护应力迅速增加,水位高度对开挖面支护应力的影响十分明显。

A Study on Measurement of Forest Soil Redox Potential

Redox potential has principal influences on formation and attribute of soils and it is necessary to research the measurement of soil redox potential. The self-made potentiometer and two indigenous FJA-5 potentiometers were employed to measure the Eh values of fir forest soils in situ, which lied in Savage Sea Beauty Spot in Sichuan Province. Simultaneously fresh soils in situ were collected and made into suspensions with various soil-water ratios and standing time to measure Eh values. The results demonstrated that the total tendency of Eh values measured by the self-made potentiometer was gradually falling with soil-water ratios increasing and standing time prolonging. There is a great difference between Eh values measured in laboratory and in situ. Only in situ may the measured Eh values show realistic oxidation-reduction conditions and formation characteristics of forest soil. The self-made potentiometer has a preferable performance than indigenous FJA-5 potentiometers and it can be applied to measuring forest soil Eh in situ.

关于构建“四预”措施和“四个链条”相结合的干旱灾害防御矩阵的思考

在充分借鉴洪水灾害防御“四个链条”基础上,考虑干旱及其灾害孕育、发生及发展规律和特点等,明晰干旱灾害“四个链条”,构建“四预”措施和“四个链条”相结合的干旱灾害防御矩阵迫在眉睫。提出要遵循“气象干旱—水文干旱—社会经济干旱”链式传导规律,加强雨情、水情、墒情、旱情的“四情”监测,精准“范围—对象—调度”,贯通“技术—料物—队伍—组织”的旱灾防御“四个链条”,实现滚动更新旱情预报、及时发布旱情预警信息、动态预演干旱灾害影响以及迭代更新抗旱预案。

基于GA-BP神经网络的富水砂层渣土改良效果预测

为了解决通过室内试验评价渣土改良效果存在耗时长、成本高,无法满足目前隧道掘进中的预测需求等问题,基于深度学习,引入遗传算法GA(genetic algorithm)对传统BP(back propagation)神经网络重新设计和优化,创建GA-BP模型;选择均方根误差GMSE、平均绝对误差MAE和决定系数R2作为评价模型预测效果的研究指标;利用机器学习中支持向量机算法与随机森林算法的预测结果与GA-BP模型的预测结果进行对比。试验结果表明:1)基于深度学习的传统BP模型和本文创建的GA-BP模型的各项评价指标皆高于机器学习算法;2)相较于传统BP网络的预测结果,GA-BP模型对内摩擦角、渗透系数和坍落度预测的最高相对误差分别降低了7.18%、5.02%、1.17%,且GA-BP模型的RMSE、MAE和R2值都优于传统BP模型和机器学习算法的预测结果。由此可得,基于深度学习的神经网络比机器学习算法更能提取到数据之间的关联性,且经过遗传算法优化后得到的GA-BP模型提高了传统BP模型的预测准确度。

半干旱雨养农业区春小麦水分利用效率变化及其年型划分

如何利用有限的水分获得更多的作物产量是干旱半干旱农业发展的目标和挑战。以半干旱雨养农业区春小麦为突破口,研究了其在不同气候年型下对不同来源的水分利用效率,以选择适宜种植春小麦的气候年型,旨在为半干旱雨养农业区农民种植决策提供依据。以半干旱雨养农业区的典型代表区域定西市安定区为例,采用定西地面气象观测站与定西农业气象试验站1987—2011年的观测资料,分析了当地春小麦对不同来源水分的利用效率及其影响因素。结果表明,定西市安定区1987—2011年25 a间春小麦主要生育期气候存在暖干化趋势,但春小麦降水利用效率和播前土壤水分利用效率均未出现明显的变化。播前土壤水分是影响生育期降水利用效率的主要因素,但生育期大气干湿状况对降水利用效率也有影响。同时,大气干湿状况影响播前土壤水分利用效率,而播前土壤水分的高低对大气干湿状况与播前土壤水分利用效率的关系亦有影响。根据播前土壤水分、主要生育期大气干湿状况、春小麦历年产量,可将半干旱雨养农业区(定西市安定区)春小麦生长的气候年型划分为5个,分别为高产年份、中高产年份、中产年份、中等偏低产量年份、低产水平年份。不同气候年型下,降水利用效率和播前土壤水分利用效率不相同。水分限制情形下,在春小麦达到最大水分利用效率之前,越是适宜的环境,越有利于提高春小麦水分利用效率。在相对适宜的气候条件下,春小麦对播前50 cm土壤水分的利用效率要高于对主要生育期降水的利用效率。因此,选择播前土壤水分高、大气湿润的气候年型种植春小麦能够保证获得较高产量。

谈咸阳市因地制宜精准施策的水土保持工作

当下,水资源保护、水土保持和水资源综合开发利用是一项造福子孙万代的重大工程。作为水资源短缺的咸阳市,在这方面下足了功夫,取得了一定的成效,为同类城市建设提供了一些经验。本文以咸阳市为例,在水土保持规划、区域重点工作划分、采取的措施、取得的经验、今后努力的方向等方面进行了详细阐述,以期可以提供一些借鉴,助力水资源综合开发和利用工作。