Prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum

This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.

Liquefaction susceptibility and deformation characteristics of saturated coral sandy soils subjected to cyclic loadings-a critical review

Coral sandy soils widely exist in coral island reefs and seashores in tropical and subtropical regions.Due to the unique marine depositional environment of coral sandy soils,the engineering characteristics and responses of these soils subjected to monotonic and cyclic loadings have been a subject of intense interest among the geotechnical and earthquake engineering communities.This paper critically reviews the progress of experimental investigations on the undrained behavior of coral sandy soils under monotonic and cyclic loadings over the last three decades.The focus of coverage includes the contractive-dilative behavior,the pattern of excess pore-water pressure(EPWP)generation and the liquefaction mechanism and liquefaction resistance,the small-strain shear modulus and strain-dependent shear modulus and damping,the cyclic softening feature,and the anisotropic characteristics of undrained responses of saturated coral sandy soils.In particular,the advances made in the past decades are reviewed from the following aspects:(1)the characterization of factors that impact the mechanism and patterns of EPWP build-up;(2)the identification of liquefaction triggering in terms of the apparent viscosity and the average flow coefficient;(3)the establishment of the invariable form of strain-based,stress-based,or energy-based EPWP ratio formulas and the unique relationship between the new proxy of liquefaction resistance and the number of cycles required to reach liquefaction;(4)the establishment of the invariable form of the predictive formulas of small strain modulus and strain-dependent shear modulus;and(5)the investigation on the effects of stress-induced anisotropy on liquefaction susceptibility and dynamic deformation characteristics.Insights gained through the critical review of these advances in the past decades offer a perspective for future research to further resolve the fundamental issues concerning the liquefaction mechanism and responses of coral sandy sites subjected to cyclic loadings associated with seismic events in marine environments.

Experimental and numerical investigation on alternatives to sandy gravel

The NATO agreement STANAG 4569 defines the protection levels for the occupants of logistic and light armored vehicle.The Allied Engineering Publication,AEP-55,Volume 2 document outlines the test conditions for underbelly improvised explosive device(IEDs),which must be buried in water-saturated sandy gravel.The use of sandy gravel has some drawbacks,for instance reproducibility,time consumption,and cost.This paper focuses on the investigation of four alternatives to sandy gravel,which could produce similar specific and cumulative impulses:a concrete pot filled with water,a concrete pot filled with quartz sand,a steel pot without filling and a concrete pot filled with glass spheres(diameter 200μm—300μm)and different water contents.The impulses are measured with a ring technology developed at the Fraunhofer EMI.A numerical soil model based on the work of Marrs,2014 and Fi serov a,2006 and considering the soil moisture was used to simulate the experiments with glass spheres at different water contents,showing much better agreement with the experiments than the classical Laine&Sandvik model,even for high saturation levels.These results can be used to create new test conditions at original scale that are more cost-effective,more reproducible and simpler to manage in comparison to the current tests carried out with STANAG sandy gravel.

Vertical distribution characteristics of soil saturated hydraulic conductivity under different land use patterns in the Mu Us sandy land

Background,aim,and scope Soil saturated hydraulic conductivity(K_(s))is a key parameter in the hydrological cycle of soil;however,we have very limited understanding of K_(s) characteristics and the factors that inf luence this key parameter in the Mu Us sandy land(MUSL).Quantifying the impact of changes in land use in the Mu Us sandy land on K_(s) will provide a key foundation for understanding the regional water cycle,but will also provide a scientific basis for the governance of the MUSL.Materials and methods In this study,we determined K_(s) and the basic physical and chemical properties of soil(i.e.,organic matter,bulk density,and soil particle composition)within the first 100 cm layer of four different land use patterns(farmland,tree,shrub,and grassland)in the MUSL.The vertical variation of K_(s) and the factors that influence this key parameter were analyzed and a transfer function for estimating K_(s) was established based on a multiple stepwise regression model.Results The K_(s) of farmland,tree,and shrub increased gradually with soil depth while that of grassland remained unchanged.The K_(s) of the four patterns of land use were moderately variable;mean K_(s)values were ranked as follows:grassland(1.38 mm·min^(-1))<tree(1.76 mm·min^(-1))<farmland(1.82 mm·min^(-1))<shrub(3.30 mm·min^(-1)).The correlation between K_(s) and organic matter,bulk density,and soil particle composition,varied across different land use patterns.A multiple stepwise regression model showed that silt,coarse sand,bulk density,and organic matter,were key predictive factors for the K_(s) of farmland,tree,shrub,and grassland,in the MUSL.Discussion The vertical distribution trend for K_(s) in farmland is known to be predominantly influenced by cultivation,fertilization,and other factors.The general aim is to improve the water-holding capacity of shallow soil on farmland(0-30 cm in depth)to conserve water and nutrients;research has shown that the K_(s) of farmland increases with soil depth.The root growth of tree and shrub in sandy land exerts mechanical force on the soil due to biophysical processes involving rhizospheres,thus leading to a significant change in K_(s).We found that shallow high-density fine roots increased the volume of soil pores and eliminated large pores,thus resulting in a reduction in shallow K_(s).Therefore,the K_(s) of tree and shrub increased with soil depth.Analysis also showed that the K_(s) of grassland did not change significantly and exhibited the lowest mean value when compared to other land use patterns.This finding was predominantly due to the shallow root system of grasslands and because this land use pattern is not subject to human activities such as cultivation and fertilization;consequently,there was no significant change in K_(s) with depth;grassland also had the lowest mean K_(s).We also established a transfer function for K_(s) for different land use patterns in the MUSL.However,the predictive factors for K_(s) in different land use patterns are known to be affected by soil cultivation methods,vegetation restoration modes,the distribution of soil moisture,and other factors,thus resulting in key differences.Therefore,when using the transfer function to predict K_(s) in other areas,it will be necessary to perform parameter calibration and further verification.Conclusions In the MUSL,the K_(s) of farmland,tree,and shrub gradually increased with soil depth;however,the K_(s) of grassland showed no significant variation in terms of vertical distribution.The mean K_(s) values of different land use patterns were ranked as follows:shrub>farmland>tree>grassland;all land use patterns showed moderate levels of variability.The K_(s) for different land use patterns exhibited differing degrees of correlation with soil physical and chemical properties;of these,clay,silt,sand,bulk density,and organic matter,were identified as important variables for predicting K_(s) in farmland,tree,shrub,and grassland,respectively.Recommendations and perspectives In this study,we used a stepwise multiple regression model to establish a transfer function prediction model for K_(s) for different land use patterns;this model possessed high estimation accuracy.The ability to predict K_(s) in the MUSL is very important in terms of the conservation of water and nutrients.

Ecological effect of the plantation of Sabina vulgaris in the Mu Us Sandy Land,China

Vegetation restoration through artificial plantation is an effective method to combat desertification,especially in arid and semi-arid areas.This study aimed to explore the ecological effect of the plantation of Sabina vulgaris on soil physical and chemical properties on the southeastern fringe of the Mu Us Sandy Land,China.We collected soil samples from five depth layers(0-20,20-40,40-60,60-80,and 80-100 cm)in the S.vulgaris plantation plots across four plantation ages(4,7,10,and 16 years)in November 2019,and assessed soil physical(soil bulk density,soil porosity,and soil particle size)and chemical(soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),available potassium(AK),cation-exchange capacity(CEC),salinity,p H,and C/N ratio)properties.The results indicated that the soil predominantly consisted of sand particles(94.27%-99.67%),with the remainder being silt and clay.As plantation age increased,silt and very fine sand contents progressively rose.After 16 years of planting,there was a marked reduction in the mean soil particle size.The initial soil fertility was low and declined from 4 to 10 years of planting before witnessing an improvement.Significant positive correlations were observed for the clay,silt,and very fine sand(mean diameter of 0.000-0.100 mm)with SOC,AK,and p H.In contrast,fine sand and medium sand(mean diameter of 0.100-0.500 mm)showed significant negative correlations with these indicators.Our findings ascertain that the plantation of S.vulgaris requires 10 years to effectively act as a windbreak and contribute to sand fixation,and needs 16 years to improve soil physical and chemical properties.Importantly,these improvements were found to be highly beneficial for vegetation restoration in arid and semi-arid areas.This research can offer valuable insights for the protection and restoration of the vegetation ecosystem in the sandy lands in China.

Influence of wind-blown sand content on the mechanical quality state of ballast bed in sandy railways

During the operation of sandy railways, the challenge posed by wind-blown sand is a persistent issue. An in-depth study on the influence of wind-blown sand content on the macroscopic and microscopic mechanical properties of the ballast bed is of great significance for understanding the potential problems of sandy railways and proposing reasonable and adequate maintenance and repair strategies. Building upon existing research, this study proposes a new assessment indicator for sand content. Utilizing the discrete element method(DEM) and fully considering the complex interactions between ballast and sand particles, three-dimensional(3D) multi-scale analysis models of sandy ballast beds with different wind-blown sand contents are established and validated through field experiments. The effects of varying wind-blown sand content on the microscopic contact distribution and macroscopic mechanical behavior(such as resistance and support stiffness) of ballast beds are carefully analyzed. The results show that with the increase in sand content, the average contact force and coordination number between ballast particles gradually decrease, and the disparity in contact forces between different layers of the ballast bed diminishes. The longitudinal and lateral resistance of the ballast bed initially decreases and then increases, with a critical point at 10% sand content. At 15% sand content, the lateral resistance is mainly shared by the ballast shoulder. The longitudinal resistance sharing ratio is always the largest on the sleeper side, followed by that at the sleeper bottom, and the smallest on the ballast shoulder. When the sand content exceeds 10%, the contribution of sand particles to stiffness significantly increases, leading to an accelerated growth rate of the overall support stiffness of the ballast bed, which is highly detrimental to the long-term service performance of the ballast bed. In conclusion, it is recommended that maintenance and repair operations should be promptly conducted when the sand content of the ballast bed reaches or exceeds 10%.

Did Species and Functional Diversities of Sandy Intertidal Marine Nematodes Reveal Similar Response to Environmental Changes?

Free living marine nematodes were sampled from two sandy beaches in Dalian City,in December of 2015,and April,July,and October of 2016.The spatial and seasonal variations of marine nematode species diversity(based on species abundance dataset)and functional diversity(based on functional traits dataset:feeding types and life history strategies)were investigated to understand the environmental drivers and how they respond to specific environmental variations.Sediment granularity was revealed to be the main environmental factor causing spatial differences in nematode diversity indices between the two beaches.Species diversity indices,namely species number,Margalef index,Shannon-Wiener diversity index(H’),were higher in fine-grained sediments,while the functional diversity indices,including functional evenness,functional dispersion,and Rao’s quadratic entropy index(RaoQ),were higher in coarse-grained sediments.Nematode species diversity indices also fluctuated with seasonal variations of temperature,dissolved oxygen,pH,salinity,and sediment chlorophyll-a within the study beaches.However,functional diversity indices did not show significant seasonal variations and exhibited weak correlation with the studied environmental variables.Overall,the functional diversity indices were negatively correlated with the species diversity indices,suggesting an inconsistent response to environmental changes.A decrease in nematode species diversity in coarse sands,accompanied by an increase in functional diversity,can be regarded as an early warning signal of environment disturbance.If more biological traits are involved in calculating functional diversity indices,it will be helpful for the future study of the internal connections of species diversity and functional diversity.

Spatiotemporal variations in ecological quality of Otindag Sandy Land based on a new modified remote sensing ecological index

Otindag Sandy Land in China is an important ecological barrier to Beijing;the changes in its ecological quality are major concerns for sustainable development and planning of this area.Based on principal component analysis and path analysis,we first generated a modified remote sensing ecological index(MRSEI)coupled with satellite and ground observational data during 2001–2020 that integrated four local indicators(greenness,wetness,and heatness that reflect vegetation status,water,and heat conditions,respectively,as well as soil erosion).Then,we assessed the ecological quality in Otindag Sandy Land during 2001–2020 based on the MRSEI at different time scales(i.e.,the whole year,growing season,and non-growing season).MRSEI generally increased with an upward rate of 0.006/a during 2001–2020,with clear seasonal and spatial variations.Ecological quality was significantly improved in most regions of Otindag Sandy Land but degraded in the southern part.Regions with ecological degradation expanded to 18.64%of the total area in the non-growing season.The area with the worst grade of MRSEI shrunk by 15.83%of the total area from 2001 to 2020,while the area with the best grade of MRSEI increased by 9.77%of the total area.The temporal heterogeneity of ecological conditions indicated that the improvement process of ecological quality in the growing season may be interrupted or deteriorated in the following non-growing season.The implementation of ecological restoration measures in Otindag Sandy Land should not ignore the seasonal characteristics and spatial heterogeneity of local ecological quality.The results can explore the effectiveness of ecological restoration and provide scientific guides on sustainable development measures for drylands.

基于储层甜点特征的致密砂砾岩油气藏压裂增产技术研究

中拐凸起南斜坡二叠系佳木河组二段储层为一套含浊沸石的致密砂砾岩。早期,在有利构造上钻探的直井产量均较低,2014年钻探该区第一口水平井用于提产,但因未能有效控制缝高,致深部水体锥进过快,长期试采效果差。近年来,地震地质综合研究发现,储层存在局部甜点。因下部并无隔层,压裂时需严格控制裂缝下延。通过对储层甜点特征进行梳理,综合评价了各断块甜点的优质程度,为试油段优选和新井的部署提供依据。为了实现控缝高压裂,提高单井产量和试采效果,开展人工隔层导流能力室内实验、完成人工隔层支撑剂粒径的优选,进行压裂数值模拟研究、确定了研究区形成有效厚度人工隔板的临界施工参数。研究认为,前置液阶段,改变液体黏度和排量、铺置有效人工隔层能够抑制水力裂缝向下扩展;携砂液阶段,加入一定浓度纤维,可进一步提升支撑剂对上部优质储层的支撑。这种组合控缝高工艺技术投入该区压裂实施后,有效控制了裂缝下延高度,甜点层段得到充分改造,试油及后续试采期间维持了较高油气产能,压裂提产效果明显。

基于连续观测数据的毛乌素沙地生长季土壤水分动态及其对降雨的响应

水分是制约半干旱区沙地植物生长发育和生态建设的关键非生物因子。于2008—2010年和2018—2021年生长季(4—10月)对毛乌素沙地流动、半固定和固定沙地0~100cm深土壤水分进行了连续观测,系统分析了不同固定程度沙地土壤水分动态变化规律及其对降雨的响应。结果表明:(1)受降雨季节变化的影响,流动、半固定和固定沙地不同深度土壤水分季节变化一般呈∽型或双峰型,10 cm和30 cm深土壤水分含量波动较大,60 cm和100 cm深土壤水分含量波动较小。(2)3种固定程度沙地生长季土壤水分动态差异明显,总体来看,流动沙地土壤水分状况最好,且土壤水分含量变化相对平缓,固定沙地土壤水分状况最差,且土壤水分含量变化最为剧烈,半固定沙地居于二者之间;固定沙地10~30cm深土壤水分状况好于半固定沙地和流动沙地,30~100cm深土壤水分状况则相反。(3)降雨格局是形成土壤水分时空格局的主要原因,随降雨事件降雨量增加,降雨的入渗深度逐渐增加;但是固定沙地土壤水分的深层补充需较强的降雨和较长的时间。生长季降雨事件以小降雨事件为主,表层土壤水分波动更剧烈。生长季初期降雨较少且以小降雨事件为主,10cm以下土壤水分补充困难,土壤水分状况较差。流动沙地和半固定沙地10~30cm深土壤水分状况好于30~100cm深土壤,而固定沙地土壤水分状况则相反。研究结果可为半干旱区沙化土地近自然植被恢复与固沙植被稳定性维持提供科学依据。

断缝体识别及储层发育模式——以准噶尔盆地玛湖凹陷玛东地区百口泉组为例

断缝体是一种新的储集体类型。它是由断层、褶皱所伴生的裂缝与基质孔共同构成,具有立体不规则孔缝特征的构造地质体。断缝体包括断层滑动面、破碎带及诱导缝,既是致密砂砾岩油气藏富集的主要因素,又是钻井风险防控及储层精准改造的关键因素。准噶尔盆地玛湖凹陷玛东地区百口泉组致密砂砾岩储层具有埋深较大、岩性致密、非均质性强、异常压力高、压裂改造难度大等特征,其断缝体刻画成为制约油气效益开发的技术难点。文中以准噶尔盆地玛湖凹陷玛东地区三叠系百口泉组致密砂砾岩储层裂缝为研究对象,在地震、岩心、成像测井等资料分析的基础上,从不同尺度精细描述了裂缝响应特征及断缝体储层发育模式。通过钻井资料及压裂资料分析,断缝体识别方法得到了验证,同时也为油田地质工程一体化效益开发提供了重要的技术支撑。

渤海海域辽中凹陷南部古近系东营组三段重力流砂岩优质储层特征及成因

为解决渤海海域中-深层重力流砂岩储层物性差异大、优质储层预测较难的勘探难题,基于常规物性、铸体薄片、黏土矿物和地球化学等分析测试手段,结合测井、录井、岩心和地震等资料,研究了渤海海域辽中凹陷古近系东营组三段(东三段)深水重力流砂岩储层的沉积特征及优质储层主控因素。结果表明:渤海海域辽中凹陷东三段重力流的沉积类型为砂质碎屑流,储层以中-低孔、中-低渗为主。储集空间中的粒间溶蚀孔最发育,原生孔次之。中砂岩和粗砂岩储层物性最好,细砂岩次之,粉砂岩较差。控制优质储层发育的关键因素是:(1)物质基础好,表现为分选好、泥质含量低、富含长石。(2)东营组早成岩期的快速沉降形成欠压实超压条件,使原生孔隙得以大量保存;超压延长了有机酸的生成时间,为砂岩中的钾长石和方解石等矿物溶解提供了充足的酸性流体。(3)断层沟通了储层和烃源岩,进一步促进了中-深层储层的溶解作用,有利于大量溶蚀孔的形成。(4)构造抬升和侧向挤压造成的储层破裂作用又形成了大量裂缝和溶缝带,改善了储层物性。

富钼专用保水剂对东北典型土壤保墒性能及大豆幼苗生长的影响

在东北集约化种植体系中,苗期水肥供应强度直接影响作物生长状况,并最终导致产量变异。富钼大豆专用保水剂是基于高分子材料合成与钼肥技术的耦合。针对东北2种典型土壤类型开展温室盆栽试验,通过二因子五水平的试验设计,研究土壤类型、保水剂类型及施用量对大豆苗期土壤水分利用效率及幼苗生长的影响。结果表明:1)施用不同剂量普通保水剂(H 2020)和富钼专用保水剂(GH 2021)均可在不同程度上提高土壤保水性能,并促进苗期大豆生长及地上部植株干质量;2)土壤含水率和大豆幼苗株高均随用量的增大而增加,且用量为0.5%的GH 2021显著促进大豆幼苗的生长,在黑土和风沙土条件下增幅分别可达68.0%和44.9%;3)0.5%剂量的GH 2021使风沙土土壤含水率提高343.1%,相较于施用H 2020保水性能提升33.6%;4)与H 2020相比,施用量为0.5%的GH 2021使风沙土条件下苗期大豆株高和地上部干质量分别提高16.3%和34.0%。综上,富钼专用保水剂在东北大豆种植区最佳应用范围为:2种土壤条件下,保水剂理论田间推荐用量为0.5%,其对风沙土的保墒性能优于黑土。该保水剂可用于提升干旱区土壤保水性能,改善苗期大豆生长环境和营养状况,最大限度激发东北大豆的增产潜力。

基于离散元方法的混合砂土剪切特性细观分析

目的为研究不同成分的砂土剪切破坏时的抗剪强度和体积变形差异。方法采用室内试验与离散元模拟结合的方法,通过建立剪切带PFC2D模型,对剪切过程中单一质砂土和混合砂土细观参数的变化规律进行了研究。结果发现粗砂、细砂、标准砂与混合砂土的剪切带形态、体积应变率等细观参数存在明显差异。结论研究表明:砂土剪切应力大小受颗粒组成影响,表现为砂土剪切应力随粗颗粒含量的增加而增大,混合砂土剪切应力高于与其成分相同的单一质砂土;砂土中颗粒运动以上跨和下跨式为主,颗粒粒径越大运动位移越大,表现为体积应变率越大。砂土剪切时体积应变率受颗粒组成影响,表现为粗砂体积应变率高于标准砂和细砂;混合砂土体积应变率高于与其成分相同的单一质砂土。研究结果可为此类砂土地质结构破坏问题提供理论借鉴。

基于Biot理论的饱和砂质沉积物声传播模型及耗散机制分析

为研究海底浅表砂质沉积物的频散特性,利用由多孔介质理论发展而来的Biot模型、Biot-Stoll模型和附加接触喷流与剪切拖曳的Biot-Stoll模型(BICSQS模型),对比三种声传播模型描述下的典型砂质沉积物中纵波和横波频散特性,分析了模型中不同耗散机制对其声频散关系的影响;结合实测数据探讨了各模型对砂质沉积物的适用性。结果表明,沉积物的声频散特性是不同耗散机制共同作用的结果,不同频段内的主要耗散机制不同,相同频段内耗散机制对纵波和横波的传播影响亦不同;随着频率的增加,相比Biot和Biot-Stoll模型的预测结果,砂质沉积物的实测声速和衰减系数表现出更高的频散趋势,而BICSQS模型可更合理地预测和解释试验现象,适用性更好。

干旱地区砂质土壤棉花苗床土层构建装置的研制

针对新疆南部砂质土壤“干播湿出”棉花种植模式下,春季耕整地连续作业存在作业阻力大、苗床整不平、压不实,严重影响棉花出苗率的问题,该研究设计了一种适合砂质土壤的苗床整备装置,可一次完成碎土、平土、灭茬、镇压、耱地等作业。采用分段平土装置代替耙组进行联合整备作业,分段平土装置为两段式,首段刮土板呈“W”型对称分布,通过刮土板角度对土壤流动性、平整度和作业阻力的运动分析,确定当刮土板倾斜角为45°时碎土和平土效果最好;台架试验结果表明,镇压辊直径400 mm、碎土辊直径400 mm时综合评分最高。样机性能对比试验结果表明:较耙片式联合整地机综合工作阻力降低8.67%,作业效率提升6.6%;地表平整度标准差为11 mm;耕深稳定性变异系数为9.2%,碎土率为92.3%,表面未见秸秆残膜,分段平土装置能有效碎土、平土、灭茬;二次整备后浮动式土层构建装置能有效压实土壤构建出“上虚下实”土层结构,0~5cm播种土层平均土壤紧实度为169 kPa,适合砂质土壤精量铺膜播种作业和棉花生长,较对比机型种膜错位率下降62.5%,出苗率高于对比机型4.8%。研究结果可为砂质土壤苗床整地机研发与改进提供参考。

代钦塔拉自然保护区元宝枫不同年龄古树种子含油特征的研究

元宝枫为我国特有木本油料树种,选育高含油优质种源是其产业发展急需解决问题。采用野外单株采样和室内分析相结合的方法,测定了科尔沁沙地代钦塔拉自然保护区元宝枫不同年龄古树种仁脂肪酸及其组成的含量。结果表明,元宝枫古树种仁具有高含油特点,且不同树龄古树种仁脂肪酸及其组成含量差异不显著。元宝枫古树种仁油脂质量分数为46.76%~49.97%,平均质量分数48.19%;元宝枫古树种仁脂肪酸组成以油酸、亚油酸为主,平均质量分数分别为26.23%、34.91%;棕榈酸、顺-11-二十碳烯酸、13-二十二碳酸和二十四碳烯酸平均质量分数分别为4.44%、8.18%、14.54%和4.60%。脂肪酸随着古树年龄增加,脂肪酸含量总体呈现出增加趋势,神经酸含量总体呈现出降低的趋势。代钦塔拉自然保护区百年以上元宝枫古树具有相对稳定的高含油特征,树龄差异不是影响元宝枫种仁脂肪酸及其各组成含量的主要因素。

海南岛文昌现代红色沙质土壤的主量元素分析结果与意义

对海南岛东北部文昌坑尾园风成砂物质基础上发育的现代“红色沙壤”中SiO_(2)、Al_(2)O_(3)、TOFE、CaO、Na_(2)O、K_(2)O、MgO这7种主量元素的研究发现:现代红色沙壤土中SiO_(2)含量最高,MgO含量最低;CIA分别与Saf和ba存在负相关关系且剖面上下部数据变化符合土壤自剖面底到顶风化程度变弱的规律;坑尾园剖面高CIA值,与该地所处的热湿环境相关。在此环境下,水土流失带来元素迁移,使得除SiO_(2)外的6种元素值均因减少而处于低值状态。

毛乌素沙地包气带气态水同位素特征及其运移规律

为揭示包气带气态水在大气、土壤和地下水之间交换对内部水与能量传递的响应,该研究应用原位监测、同位素示踪与数值分析相结合的方法,对毛乌素沙地包气带气态水时空变化特征与运移规律进行分析。结果表明,受大气水汽来源和局地循环影响,降水δD_(L)和δ^(18)OL值均表现出春夏富集、秋冬贫化。各深度土壤气态水δ^(18)O_(a)与液态水δ^(18)OL值呈显著正相关(P<0.01),但在季节上,春夏季为极显著线性正相关(P<0.01),而秋冬季则无显著相关性(P=0.12)。表层水汽通量的增大伴随δ^(18)O_(a)富集,而水汽密度夏季的增大和冬季的减小均表现出表层δ^(18)O_(a)富集,夏季蒸发比冬季冻结更能引起表层土壤δ^(18)O_(a)富集。受包气带温度梯度驱动影响,夏季土壤深部气态水接受浅层水汽补给,冬季浅层接受中深层水汽的补给,而春、秋季剖面分别存在温度聚合和发散零通量面,使得补给关系复杂。该研究明确了土壤δ^(18)O_(a)的变化受水汽迁移模式、大气蒸发能力和土壤冻融的共同控制,表层δ^(18)O_(a)的富集在冬季受蒸发与向上的水汽传输共同影响,而夏季主要受土壤水的昼夜蒸发与凝结循环作用所致,该结果为厘清土壤水汽迁移机制以及进一步阐明包气带水循环过程提供科学依据。

毛乌素沙地不同人工林林下植物多样性及其与土壤理化性质的关系

[目的]研究不同人工林林下植物多样性特征及与土壤理化性质的关系,为探寻科学合理的沙地生态修复模式及近自然植被重建提供理论依据。[方法]以毛乌素沙地4种典型人工林(Ⅰ:樟子松人工林;Ⅱ:杨树人工林;Ⅲ:沙柳人工林;Ⅳ:小叶锦鸡儿人工林)为研究对象,分析不同人工林林下草本群落物种多样性及表层土壤理化性质,并进一步探讨二者间的关系。[结果]4种人工林林下草本植物种类由多到少依次为小叶锦鸡儿人工林>樟子松人工林>杨树人工林>沙柳人工林,其中,菊科、禾本科、豆科植物种类较多,占总植物种类的65.39%。4种人工林林下草本层Margalef丰富度指数(D)、Shannon-Wiener多样性指数(H)、Simpson优势度指数(H′)、Pielou均匀度指数(J)之间均无显著差异。不同人工林表层土壤pH值、有机质、有效磷、水解性氮和颗粒组成存在显著差异,樟子松人工林土壤pH值显著低于其他3种人工林,乔木林土壤有机质、水解性氮含量高于灌木林,灌木林土壤有效磷含量比乔木林高,4种人工林土壤速效钾含量无显著差异。影响林下草本植物多样性的土壤因子为有机质、有效磷、pH、水解性氮以及粒度成分。[结论]毛乌素沙地不同人工林林下植物组成和土壤理化性质具有差异,不同人工林对林下植物多样性无显著影响,有机质、有效磷、pH、水解性氮为影响人工林林下植物多样性的主要土壤因子。