黄土丘陵沟壑区不同土地利用模式对土壤酶活性和土壤微生物影响研究

对黄土丘陵沟壑地区不同土地利用模式土壤酶活性和土壤微生物进行了测定,研究了土壤酶活性、微生物与土壤主要肥力指标对黄土丘陵沟壑地区不同土地利用模式下土壤肥力质量的关系。结果表明,不同土地利用模式0~20 cm土壤酶活性之间差异明显,而20~40 cm不同土地利用模式之间土壤酶活性差异较小,研究区域不同土地利用模式土壤微生物数量差距较大。本研究利用因子分析法来分析不同土地利用方式土壤酶活性、土壤微生物数量和土壤主要肥力指标,并根据各因子之间综合得分得出:日光温室的土壤肥力效益最好,然后依次为农田、拱棚、经济作物、果园。

氮肥缺失对旱地土壤细菌群落多样性的影响

本文旨在研究氮肥缺失对旱地土壤细菌群落多样性的影响。采用直接提取土壤微生物总DNA的方法,对不施肥(CK)、适量施肥(F1)、和缺氮施肥(F2)3种不同施肥水平土样DNA进行提取,扩增细菌16S rDNA基因片段,建立克隆文库。用限制性内切酶HhaI和RsaI进行PCR-RFLP分析,分别得到146、187、11个酶切类型。采用α多样性的测度对试验结果进行分析统计结果表明,不同处理间土壤细菌的多样性(H′、Ds和Dg)和物种丰富度(dMa、R2和E)均为F1>CK>F2;λ、dMa、E和H′指数在不同施肥处理间的变异系数达到56.96%~163.1%,尤其Simpson指数λ是非常敏感的指标,处理间的差异最大,表明氮肥缺失严重影响土壤细菌群落多样性,合理施肥有利于土壤细菌的多样性。

稠油污染土壤生物修复的微生物筛选及工艺调控

稠油组分非常复杂，胶质沥青质含量较高，使稠油污染土壤的生物修复难度很大。对稠油中胶质沥青质分的降解是彻底修复稠油污染土壤的关键。试验中利用辽河油田污染土壤中筛选并纯化出来的几株细菌、真菌和放线菌，以胶质沥青质作为碳源，考察不同菌株处理的去除率变化。发现0d-14d期间是微生物去除胶质沥青质的活跃期，42d之后土壤中胶质沥青质的减少趋缓，是生物修复的转折点。筛选出优势降解菌株：细菌22B；真菌中F2006、F2008、F9902，放线菌A2013、A2016混合菌F2006+22B、F6＋22B。同时考查了表面活性剂吐温-80对菌株去除胶质沥青质能力的影响，发现吐温-80对不同菌株有促进或抑制作用。利用上述优势菌株处理5ryn稠油污染土壤，并在42d时，通过采取补加菌液、添加N、P营养物质和添加碳源处理来提高微生物对土壤中稠油的去除能力。经过56天的处理，细菌22B对稠油的去除率最高，达27．420＆；混合菌的去除率在23.64％-26.24％。比较三种处理措施对微生物降解稠油能力的影响时，发现不同菌株对这三种措施的反应并不相同。同时土壤中残留石油烃的族分析证实了土壤中的重质成分是可以被微生物降解的；而稠油污染土壤中的烷烃和芳香烃的含量则呈现动态变化。稠油污染土壤的生物修复后的毒性检验表明，不同菌株处理土壤的毒性因选择的菌株及采取的措施不同而异，其中土壤毒性最小的是22B添加碳源处理；毒性最强的是F2008加菌处理。补加菌液、添加营养和碳源措施会使微生物对稠油降解能力有所加强，但是也加速了某些微生物产生毒性较稠油更大的中间产物的生成，使土壤更加不适合植物的生长。本研究从辽河油田污染土壤中筛选出石油烃降解菌株，对稠油中最难降解的胶质沥青质进行处理，从中选择优势的降解菌株对稠油污染土壤进行生物修复，为稠油污染土壤的生物修复打下理论基础。

水分梯度上不同灌木生长对干旱河谷土壤理化和生物学性质的影响

岷江上游干旱河谷区水土流失强烈，地质灾害频繁，生态环境十分脆弱，而土壤条件恶劣（水分不足和养分缺乏）是阻碍该区植被恢复的关键因子，因此研究水分和乡土灌木生长对土壤的影响对该区的生态恢复具有指导意义。本文通过定点模拟实验，选取三种优势豆科灌木为研究对象，分别是白刺花（Sophora davidii）、小马鞍羊蹄甲（Bauhinia faberi var. microphylla）和小雀花（Campylotropics polyantha），设置5 个水分梯度，分别为100%、80%、60%、40%和20%田间持水量（FC），对栽种植物与不种植物下土壤理化性质和酶活性进行测定分析，系统比较和研究了不同水分条件和不同乡土灌木生长对干旱河谷区土壤结构、养分循环、酶活性以及微生物量的影响。主要结果如下：1. 无论生长植物与否，土壤的毛管持水量和毛管孔隙度都随着水分含量的减少而降低，最大持水量、总孔隙度和容重变化不大，相应地，土壤中的非毛管孔隙随含水量的减少而升高。各水分条件下，种植植物的毛管持水量和毛管孔隙度低于无植物生长的土壤，非毛管孔隙度相应地高于无植物土壤。土壤含水量在100%－40% FC 时，三种豆科灌木的毛管持水量和毛管孔隙度存在差异，而20% FC 条件下，三种豆科灌木土壤的物理性质基本相同。2. 水分胁迫影响土壤中养分的矿化和积累，主要表现在降低了水溶性碳和铵态氮的含量，中等程度胁迫时（60% FC）促进了有机碳和硝态氮的富集，对速效钾和有效磷没有明显作用。种植豆科灌木后各水分梯度上都增加了有机碳、铵态氮、速效钾和有效磷的积累。增加程度上三种豆科灌木间有一定差异，对于土壤有机碳总量，种植白刺花和小马鞍羊蹄甲明显高于小雀花，同样的情况还出现在铵态氮和速效钾上，但是对于有效磷，种植小雀花后的增加程度则明显高于白刺花和小马鞍羊蹄甲。种植豆科灌木不仅增加了土壤养分的相对含量，也改变了其在水分梯度上的变化趋势及其变化幅度，这种作用主要体现在碳元素和氮元素上。3. 无植物生长时脲酶活性随水分含量的减少而升高，水分胁迫对磷酸酶和过氧化氢酶的作用不显著，蔗糖酶也保持在相对较高的水平。种植植物后，蔗糖酶、磷酸酶活性与无植物时相比有较大幅度的提高，种植白刺花的脲酶活性也升高，其升高的程度在不同水分含量时不同。种植植物还降低了酶活性在水分梯度上的变幅，使之在水分梯度间的差异显著性降低。脲酶活性在指示土壤性质改变方面是较敏感的指标，其它三种酶在不同植物间的差异不明显。4. 在无植物生长时，中等程度的水分胁迫（60% FC）提高了土壤微生物量碳含量，过高或过低的土壤水分均不利于微生物碳的积累。种植小马鞍羊蹄甲后微生物量碳在水分梯度上的变化趋势与无植物生长时一致，而种植白刺花和小雀花后微生物量碳随着水分含量的减少而降低。不同种类植物的微生物量碳在水分梯度上的变化特征也不同，100% FC 条件下三种植物间没有差异，80%和60% FC 条件下小马鞍羊蹄甲显著高于白刺花和小雀花，40%和20% FC 条件下白刺花和小马鞍羊蹄甲也显著高于小雀花，说明不同种类植物随着干旱胁迫程度的加深微生物量碳的降低幅度不同，在极度干旱时，白刺花和小马鞍羊蹄甲土壤依然保持了较高的微生物活性，而小雀花土壤微生物量则明显下降。The dry valley of the upper reaches of the Minjiang River is seriously degradedmountain ecosystem. It was endangered by extremely soil lost and frequentlygeological disaster. Previous studies showed that short of water and nutrients in soilwas the principal limiting factors of vegetation restoration in this area. The typical soiland three dominant leguminous shrubs Sophora davidii, Bauhinia faberi var.microphylla and Campylotropics polyantha in upper reaches of arid Minjiang Rivervalley were considered as experimental material. Two-month old seedlings of eachspecies were exposed to five water supplies (100%, 80%, 60%, 40% and 20% waterfield capacity (FC)) in a temperature and light-controlled greenhouse. Afterthree-month water treatment, soil physiochemical variables and soil microbialactivities were determined by conventional methods. The main results showed that:1. Soil capillary capacity and capillary porosity decreased along water supplyregimes in all treatments, while saturated water capacity, total porosity and bulkdensity kept in a relatively stable level, as a result, the non-capillary porosity andcapacity increased with decrease of water supply. Compared to non-planted soil, theplant-soil systems had a higher non-capillary porosity and capacity, suggestingappropriate oxygen was present in soil to maintain the living of microorganism. Soilof three type shrub species shared the same capillary capacity and capillary porosityunder 20% FC.2. Water soluble carbon and NH4+-N decreased in response to water stress, whiletotal organic carbon and NO3--N promoted by moderate water stress and inhibited by 100% and 20% FC. Total organic carbon, NH4+-N, rapidly available K and availableP increased after the planting of leguminous shrubs in five water supply regimescompared to non-planted soil. For TOC, NH4+-N and rapidly available K, thepromotion effect was higher in S. davidii and B. faberi var. microphylla than C.polyantha planted soil, while available P displayed the opposite side. The planting ofshrubs also reduced the variance of observed traits along water supply gradients.3. Drought stress increased urease activity in non-planted soil, while insignificantdifferences were observed in phosphatase and catalase activity among five watersupply regimes. The planting of leguminous shrubs facilitated the β-glucosidase andphosphatase activity compared to the non-planted soil. It also reduced the variance ofenzyme activity along water supply gradients. Urease was more sensitive to waterstress than other three enzymes.4. Soil water content significantly affected microbial biomass carbon andCmic:Corg. S. davidii and B. faberi var. microphylla showed more drought toleranceability than C. polyantha, attributing not only to their relatively smaller variance ofmicrobial biomass carbon along soil water supply gradients, but also to the highlevel of microbial activity under severe water stress. S. davidii and B. faberi var.microphylla benefited reproduction of soil microorganism at 60%-80% FC, whilesevere drought limited it due to the competition of water and nutrients between plantand soil microorganism.

The thermo-visco-plastic instability analysis of saturated soil

A theoretical analysis of instability of saturated soil is presented considering the simple shearing of a heat conducting thermo-visco-plastic material. It is shown that the instability is mainly the consequence of thermal softening which overcomes the strain hardening and the other type of instability is controlled by strain softening. The effects of other factors such as permeability to the instability are discussed in this paper.

On the shear instability of saturated soil

In this paper. the dynamic instability of simple shear of saturated soil is discussed. The governing equations are obtained based on mixture theory in which the inertia effect and the compressibility of grains are considered. Perturbation method is used to analyze and it is shown that two types of instability may exist. One of them is dominated by pore-pressure-softening, while the other by strain-softening.

An Analytical Solution for Three-Dimensional Diffraction of Plane P-Waves by a Hemispherical Alluvial Valley with Saturated Soil Deposits

An analytical solution for the three-dimensional scattering and diffraction of plane P-waves by a hemispherical alluvial valley with saturated soil deposits is developed by employing Fourier-Bessel series expansion technique. Unlike previous studies, in which the saturated soil deposits were simulated with the single-phase elastic theory, in this paper, they are simulated with Biot's dynamic theory for saturated porous media, and the half space is assumed as a single-phase elastic medium. The effects of the dimensionless frequency, the incidence angle of P-wave and the porosity of soil deposits on the surface displacement magnifications of the hemispherical alluvial valley are investigated. Numerical results show that the existence of a saturated hemispherical alluvial valley has much influence on the surface displacement magnifications. It is more reasonable to simulate soil deposits with Biot's dynamic theory when evaluating the displacement responses of a hemispherical alluvial valley with an incidence of P-waves.

Comparison of the Dynamic Response of a Saturated Soil Between Two Models

By comparing the dynamic responses of saturated soil to Biot's and Yamamoto's models, the properties of the two models have be pointed out. First of all, an analysis has been made for energy loss of each model from the basic equations. Then the damping of elastic waves in coarse sand and fine sand with loading frequency and soil's parameters have been calculated and the representation of viscous friction and Coulomb friction in the two models has been concluded. Finally, the variations of loading wave damping and stress phase angles with water depth and soil's parameters have been obtained as loading waves range in ocean waves.

Numerical Study on Rainfall Infiltration in Rock-Soil Blocks

A mathematical model for the rain infiltration in the rock-soil slop has been established and solved by using the finite element method. The unsteady water infiltrating process has been simulated to get water content both in the homogeneous and heterogeneous media. The simulated results show that the rock blocks in the rock-soil slop can cause the wetting front moving fast. If the rain intensity is increased, the saturated region will be formed quickly while other conditions are the same. If the rain intensity keeps a constant, it is possible to accelerate the generation of the saturated region by properly increasing the vertical filtration rate of the rock-soil slop. However, if the vertical filtration rate is so far greater than the rain intensity, it will be difficult to form the saturated region in the rock-soil slop. The numerical method was verified by comparing the calculation results with the field test data.

土壤传热特性的实验研究(Experimental Study of Soil Heat Diffusivity)

发展了测定实验室土样热扩散率的方法,介绍了研制的实验装置和建议的操作程序。给出的实验结果表明土壤热扩散率随土壤空隙率、含水量和温度等许多参数而变化。

The evolution of shear bands of saturated soil

The development of the shear bands of saturated soil in coupling-rate- and pore-pressure-dependent simple shear has been discussed, using a simple model and a matching technique at the moving boundary of a shear band. Tt is shown that the development of shear bands are dominated by the coupling-rate and pore-pressure effect of the material. The strength of the soil acts as a destabilizer, whilst pore pressure diffusion makes the band expand. The theory is discussed and some computational solutions have been presented.

Wave-soil-pipe coupling effect on submarine pipeline on-bottom stability

Wave-soil-pipe coupling effect on the untrenched pipeline stability on sands is for the first time investigated experimentally. Tests are conducted in the U-shaped water tunnel, which generates an oscillatory how, simulating the water particle movements with periodically changing direction under the wave action. Characteristic times and phases during the instability process are revealed. Linear relationship between Froude number and non-dimensional pipe weight is obtained. Effects of initial embedment and loading history are observed. Test results between the wavesoil-pipe interaction and pipe-soil interaction under cyclic mechanical loading are compared. The mechanism is briefly discussed. For applying in the practical design, more extensive and systematic investigations are needed.

Experimental study on pore pressure in rock-soil slope during reservoir water level fluctuation

A test system was developed for measuring the pore pressure in porous media, and a new model was devised for the pore pressure testing in both saturated and unsaturated rock-soil. Laboratory experiments were carried out to determine the pore pressure during water level fluctuation. The variations of transient pore pressure vs. time at different locations of the simulated rock-soil system were acquired and processed, and meanwhile the deformation and failure of the model are observed. The experiment results show that whether the porous media are saturated or not, the transient pore pressure is mainly dependent on the water level fluctuation, and coupled with the variation of the stress field.

Non-Linear Wave-Induced Transient Response of Soil Around a Trenched Pipeline

Submarine pipelines are always trenched within a seabed for reducing wave loads and thereby enhancing their stability. Based on Biot’s poroelastic theory, a two-dimensional finite element model is developed to investigate non-linear wave-induced responses of soil around a trenched pipeline, which is verified with the flume test results by Sudhan et al. [Sudhan, C.M., Sundar, V., Rao, S.N., 2002. Wave induced forces around buried pipeline. Ocean Engineering, 29, 533–544] and Turcotte et al. [Turcotte, B.R., Liu, P.L.F., Kulhawy, F.H., 1984. Laboratory evaluation of wave tank parameters for wave-sediment interaction. Joseph H. Defree Hydraulic Laboratory Report 84-1, School of Civil and Environmental Engineering, Cornell University]. Non-linear wave-induced transient pore pressure around pipeline at various phases of wave loading is examined firstly. Unlike most previous investigations, in which only a single sediment layer and linear wave loading were concerned, in this study, the influences of the non-linearity of wave loading, the physical properties of backfill materials and the geometry profile of trenches on the excess pore pressures within the soil around pipeline, respectively, were explored, taking into account the in situ conditions of buried pipeline in the shallow ocean zones. Based on the parametric study, it is concluded that the shear modulus and permeability of backfill soils significantly affect the wave-induced excess pore pressures around trenched pipeline, and that the effect of wave non-linearity becomes more pronounced and comparable with that of trench depth, especially at high wave steepness in shallow water.

The instability analysis of saturated soil under shear load

A theoretical description of shear instability is presented in a system of equations. It is shown that two types of instability may exist. One of them is dominated by pore pressure softening while the other by strain softening. A criterion combining pore pressure softening, strain hardening, and volume strain coefficient is obtained and practical implications are discussed.