不同砾石覆盖保持土壤水分有效性研究

土壤水分状况是制约金沙江干热河谷地区植被恢复和造林的主要因素,改善土壤水分状况是实现该地区生态恢复重建和农业持续发展的必然途径。为给干热河谷的造林以及作物种植提供切实可行的方法,进行了不同砾石覆盖保持土壤水分有效性的试验研究,结果表明:在起始条件相同的情况下,同一小区不同深度的土壤含水量是不同的,含水量随着土层深度的增加而增大;不同砾石覆盖厚度条件下,土壤含水量与砾石覆盖厚度成正相关关系;在相同覆盖厚度情况下,砾石粒径越小,覆盖抑制土壤蒸发效果越好,土层含水量也就越高。     

砂田砾石覆盖对土壤大孔隙特征及其土壤水文过程的影响研究进展

砂田是利用砾石覆盖地表的典型节水范例,砾石覆盖对土壤大孔隙的半径、数量、连通性和密度都有重要影响。大孔隙的研究方法可分为直接观测法和间接描述法,并讨论其适用性和局限性。因为大孔隙及优先流的成因复杂,应将大量的野外实验和室内实验相结合,同时改进观测方法。土壤大孔隙研究的最终目的是调控它,为减少地下水污染、控制养分和水分的流失提供一条新途径。砾石覆盖土壤能增加大孔隙并促进降水入渗,加快壤中流的发生,减少径流和抑制蒸发,改变了土壤水文循环过程,土壤水文生态功能也随之改变。并指出了砾石覆盖下土壤优先流研究中存在的问题和今后应该加强的研究领域。     

碎石含量对三峡库区坡耕地土壤氮磷流失特征的影响

坡耕地是三峡库区水土流失的主要来源,导致土壤养分的损失,严重影响库区生态环境建设与社会经济可持续发展。库区坡耕地土壤浅薄化和砾质化特征明显,但目前对含碎石坡耕地土壤侵蚀和养分流失特征的研究尚不多见。该研究通过设置3个降雨梯度（60、90、120 mm/h）和4种碎石含量（0、10%、20%、30%）,开展人工模拟降雨试验,分析各试验条件下含碎石土壤产流产沙和氮磷流失特征。结果表明：1）碎石主要通过改变土壤结构以增大产流产沙量来促进氮磷流失,而对相应流失速率与流失浓度的变化规律影响较小,不同碎石含量下泥沙产量的变异系数更高,且泥沙中不同碎石含量下的氮磷流失量显著性差异更强（P<0.05）;2）泥沙中累计磷流失量略微大于氮流失量,有效磷几乎不随泥沙流失,有效氮约占全氮流失量的15%;径流中氮素流失量几乎为磷素的10倍且以有效氮为主,占总氮流失量的75%,有效磷占总磷流失量的25%;3）不同碎石含量下有效氮流失规律大致相同,径流中硝态氮约占有效氮流失量的70%,而泥沙中则以铵态氮为主,约占65%;4）不同碎石含量下土壤中氮磷元素均以随侵蚀产沙流失为主,累计产沙量与氮磷元素随侵蚀产沙流失...     

季节冻土区路基冻胀翻浆防治措施试验研究

根据位于青海省109国道橡皮山试验段所观测的温度及水分数据,系统分析了传统砂砾垫层路基与隔水土工膜加碎石垫层路基在外界气候环境作用下,路基内各个观测位置温度与水分的变化以及造成这些变化的原因.比较了两个断面下路基各个观测位置的水分变化率的差异以及造成这些差异的原因,分析了这些差异对路基冻胀翻浆的影响.研究结果表明,在橡...     

基于Jensen模型的压砂地西瓜灌溉制度优化研究

针对压砂地西瓜水资源高效利用和合理灌溉制度问题,于2008年和2009年采用试坑对比试验方法进行了研究,利用水分生产函数Jensen模型分析了压砂地西瓜耗水规律及需水关键期,并用Jensen模型对压砂地西瓜灌溉制度进行了优化,结果表明:(1)压砂地西瓜全生育期耗水量为79.6~409.9 mm;(2)西瓜需水关键生育阶段顺序为"苗期开花坐果期膨大初期膨大中期伸蔓期膨大后期";(3)压砂地西瓜各生育阶段的水分敏感系数λ_1=0.6171,λ_2=0.2707,λ_3=0.0355,λ_4=0.1097,λ_5=0.1390,λ_6=0.1106;(4)通过灌溉制度优化发现:供水量范围为80~240 mm时增产效果最明显,供水量达到320 mm时,压砂地西瓜可获得高产。最优灌溉制度为:苗期灌水20~30 mm,伸蔓期灌水50~55 mm,开花坐果期灌水40~45 mm,膨大初期灌水70 mm,膨大中期灌水60~70mm,膨大末期灌水60~65 mm。     

Microbial diversity in the saline-alkali soil of a coastal Tamarix chinensis woodland at Bohai Bay,China

Soil salinization or alkalization is a form of soil desertification. Coastal saline-alkali soil represents a type of desert and a key system in the network of ecosystems at the continent-ocean interface. Tamarix chinensis is a drought-tolerant plant that is widely distributed in the coastal saline-alkali soil of Bohai Bay, China. In this study, we used 454 pyrosequencing techniques to investigate the characteristics and distribution of the microbial diversity in coastal saline-alkali soil of the T. chinensis woodland at Bohai Bay. A total of 20,315 sequences were obtained, representing 19 known bacterial phyla and a large proportion of unclassified bacteria at the phylum level. Proteobacteria, Acidobacteria and Actinobacteria were the predominant phyla. The coverage of T. chinensis affected the microbial composition. At the phylum level, the relative abundance of γ-Proteobacteria and Bacteroidetes decreased whereas Actinobacteria increased with the increasing coverage of T. chinensis. At the genus level, the proportions of Steroidobacter, Lechevalieria, Gp3 and Gp4 decreased with the increase of the vegetation coverage whereas the proportion of Nocardioides increased. A cluster analysis showed that the existing T. chinensis changed the niches for the microorganisms in the coastal saline-alkali soil, which caused changes in the microbial community. The analysis also distinguished the microbial community structure of the marginal area from those of the dense area and sparse area. Furthermore, the results also indicated that the distance to the seashore line could also affect certain groups of soil bacteria in this coastal saline-alkali soil, such as the family Cryomorphaceae and class Flavobacteria, whose population decreased as the distance increased. In addition, the seawater and temperature could be the driving factors that affected the changes.     

Optically stimulated luminescence dating of sandy deposits from Gulang county at the southern margin of the Tengger Desert,China

Aeolian deposits from the deserts in northern China have been used for palaeoenvironmental research to understand aeolian sedimentology and its dynamic connection to past climate conditions. The Tengger Desert in China is sensitive to the waxing and waning of the monsoonal system. In response to past climate change, the southern margin of the Tengger Desert has evolved significantly since the last glacial period. However, previous attempts to date aeolian deposits in this region were mainly based on radiocarbon dating, which has problems when applied to aeolian deposits. Moreover, sedimentary records are limited. Accordingly, past aeolian activity in this desert remains poorly understood. In the present study, we dated sand samples from Gulang county at the southern margin of the Tengger Desert using optically stimulated luminescence(OSL) to understand the history of aeolian activity in this region. Our samples represented well-sorted aeolian sands and sandy loess. Aeolian sands are evidence of dune field buildup and sparse vegetation cover whereas sandy loess is evidence of improved stabilization of sand dunes resulting from ameliorated vegetation cover. Certain samples showed a decline in the equivalent dose(De) values when successive integration intervals were applied, which resulted from unstable OSL signals from non-fast components in the initial part of the decay curve. In order to obtain reliable De estimates, we investigated component-resolved and different background subtraction approaches, and compared the resultant De estimates. We adopted the early background subtraction method to derive De values. Luminescence chronologies and sedimentary records indicated that sand dunes accumulation occurred before 10 ka, and sandy loess developed between 9.5 and 7.6 ka when sand dunes were stabilized as a result of increased effective moisture levels. The transition between sand dune mobilization and stabilization emphasizes the significance of an effective moisture threshold in controlling aeolian activity. Mobilization of sand dunes at ~2.3 ka might be related to an increased aridity during the Late Holocene.     

植被对含碎石土壤坡面降雨入渗和径流侵蚀的影响

[目的]研究植被对含碎石土壤坡面入渗和径流侵蚀的影响,为合理配置三峡地区含碎石土壤坡面植被提供科学依据。[方法]在建立的径流小区内铺设含碎石土壤,并配置不同种类、不同覆盖度的植被,进行人工降雨试验。[结果]各类小区径流量排序为:裸坡灌木坡面草本坡面草灌混合坡面,入渗量与径流量排序相反,有植被覆盖坡面的壤中流大于裸坡;入渗率服从对数函数规律,产流强度呈幂函数变化;草地对水沙的调控机制更多的是直接拦沙;累计径流量和累计侵蚀量的关系均满足幂函数形式。[结论]植被措施可有效地减少含碎石土壤坡面的水土流失,不同的植被措施减少的效益不同。     

北方风沙区砾石对堆积体坡面径流及侵蚀特征的影响

为了研究砾石对工程堆积体降雨侵蚀规律的影响,采用室内人工模拟试验,以土质堆积体(砾石质量分数为0)为对照,研究了10%、20%和30%砾石质量分数堆积体边坡在模拟降雨条件下的径流水力特征、产沙过程及侵蚀动力机制。结果表明:1)产流0~6 min,砾石促进堆积体坡面细沟间径流流动;产流12~30 min后,砾石阻碍堆积体坡面细沟径流流动;2)含砾石堆积体坡面粗糙度增大,水流流态变缓,水流速度降低,且均以层流为主。较土质堆积体而言,30%砾石质量分数堆积体坡面阻力系数增大88.8%~288.4%,弗汝德数降低28.9%~41.8%,水流速度降低0~45.8%;3)径流含沙量随产流历时经历快速降低-平稳过渡-波动上升3个阶段,土质及10%砾石质量分数堆积体高含沙水流现象频发,且随雨强增大,重力坍塌次数增加,重力侵蚀程度增强。20%、30%砾石质量分数堆积体发生高含沙水流的几率约为0。相对土壤流失比与砾石质量分数呈极显著负指数函数关系;4)土壤剥蚀率与各侵蚀动力参数均可用简单线性函数关系描述,单位径流功率是描述风沙区土质和10%砾石质量分数工程堆积体侵蚀产沙的最优因子,径流功率是刻画20%、30%砾石质量分数工程堆积体土壤侵蚀参数更为合理的因子。结果可为全国范围工程堆积体土壤侵蚀模型的建立提供科学依据。     

面向刚度曲线的汽车前保险杠缓冲块优化设计

以掺天然砂砾改良的红粘土为研究对象,采用室内承载板法测定回弹模量,通过不同初始干密度下的回弹模量试验,深入研究了天然砂砾改良红粘土的回弹模量随初始干密度的变化规律,建立了不同初始干密度下回弹模量的预估模型。试验结果表明:在同一天然砂砾掺量下,随着初始干密度的提高,红粘土的回弹模量逐渐增大。当初始干密度由低向最大干密度增大时,回弹模量增长速度较快,当初始干密度超过最大干密度继续增大时,回弹模量增长速度变缓;在同一初始干密度下,当天然砂砾掺量从0增至30%时,回弹模量的增长幅度较小,当天然砂砾掺量超过30%而继续增长时,回弹模量增长幅度较大;初始干密度由1.6 g·cm^-3增长至2.0 g·cm^-3时,回弹模量增长值随天然砂砾掺量的增加而逐渐增大。分别建立了回弹模量随初始干密度及天然砂砾掺量变化的预估模型,通过补充试验,验证了预估模型的准确性。