Dissolved organic matter in surface runoff in the Loess Plateau of China: The role of rainfall events and land-use     

Zhongwu Li  Hao Peng  Binggeng Xie  Chun Liu  Xiaodong Nie  Danyang Wang  Mei Huang  Haibing Xiao  Lin Shi  Xuqin Zhang  Jieyu Jiang 《水文研究》2020,34(6):1446-1459

Exploring the chemical characterization of dissolved organic matter (DOM) is important for understanding the fate of laterally transported organic matter in watersheds. We hypothesized that differences in water-extractable organic matter (WEOM) in soils of varying land uses and rainfall events may significantly affect the quality and the quantity of stream DOM. To test our hypotheses, characteristics of rainfall-runoff DOM and WEOM of source materials (topsoil from different land uses and gullies, as well as typical vegetation) were investigated at two adjacent catchments in the Loess Plateau of China, using ultraviolet–visible absorbance and excitation emission matrix fluorescence with parallel factor analysis (PARAFAC). Results indicated that land-use types may significantly affect the chemical composition of soil WEOM, including its aromaticity, molecular weight, and degree of humification. The PARAFAC analysis demonstrated that the soils and stream water were dominated by terrestrial/allochthonous humic-like substances and microbial transformable humic-like fluorophores. Shifts in the fluorescence properties of stream DOM suggested a pronounced change in the relative proportion of allochthonous versus autochthonous material under different rainfall patterns and land uses. For example, high proportions of forestland could provide more allochthonous DOM input. This study highlights the relevance of soils and hydrological dynamics on the composition and fluxes of DOM issuing from watersheds. The composition of DOM in soils was influenced by land-use type. Precipitation patterns influenced the proportion of terrestrial versus microbial origins of DOM in surface runoff. Contributions of allochthonous, terrestrially derived DOM inputs were highest from forested landscapes.  相似文献   

机载光学全谱段遥感林火监测   总被引：1，自引：1，他引：0  

庞勇  荚文  覃先林  斯林  梁晓军  林鑫  李增元 《遥感学报》2020,24(10):1280-1292

森林火灾是一种危害极大的自然灾害，是森林扰动的主要类型之一，直接影响森林生态系统结构、碳循环甚至全球气候的变化。近年来，航空平台和传感器的技术进步有效地提升了机载遥感系统探测和监测森林火灾的能力，推动了机载遥感在森林可燃物调查及载量评估、火险测报预测、火场态势及火情监测、灾害损失评估以及火烧迹地生态修复治理等方面的应用。本文首先介绍了中国林业科学研究院机载光学全谱段遥感系统CAF-LiTCHy（Chinese Academy of Forestry’s LiDAR，Thermal，CCD and Hyperspectral airborne observation system），描述了激光雷达扫描仪、热红外相机、CCD相机和高光谱传感器等传感器的参数；然后，阐明了集成方案和观测数据的处理方法；最后，以四川省西昌市“3.30森林火灾”作为该系统火后灾情遥感调查和灾情评估应用示例，综合多传感器数据特征，进行森林火烧程度评价，分析该系统采集的正射影像、冠层高度模型、高光谱影像、热红外影像在森林火灾监测评价中的潜力。研究结果表明CAF-LiTCHy机载遥感观测系统能有效获取森林火灾的灾情信息、火场及火环境参数，可为预防、预报预警、扑救指挥、灾害评估和生态修复提供支持。  相似文献   

碰撞非相干散射理论谱宏观法和微观法的比较研究          下载免费PDF全文

梁宇  赵必强  乐新安  丁锋  曾令旗  郝红连  宁百齐  万卫星 《地球物理学报》2020,63(2):387-393

非相干散射理论谱是理解非相干散射雷达探测的理论基础,其求解过程分为微观法和宏观法.在考虑碰撞不考虑磁场的条件下,本文使用这两种方法对理论谱分别进行求解,给出了关键求解过程,并对等离子体的归一化导纳和极化率以及非相干散射的微分散射截面和谱密度函数进行分析,得到了它们各自之间的数学关系,概括性分析了两种方法在理论选择、最终结论及多种因素下求解的异同点.  相似文献   

横观各向同性场地中埋置衬砌隧道对qP波的散射          下载免费PDF全文

巴振宁  安东辉  梁建文  高旭 《地震工程学报》2020,42(4):948-954

采用间接边界元法(IBEM)结合"分区契合"技术,研究qP波入射下横观各向同性(TI)场地中衬砌隧道的动力响应问题。方法充分利用半空间和全空间动力格林函数在分别构造含孔半无限空间域和闭合域内散射波场方面的优势,将含有衬砌隧道的层状弹性半空间分解为含孔半无限空间域和一个环形衬砌闭合域来分别进行波场构造,有效地降低了求解时间和存储量。文中验证方法的正确性,并以均匀TI半空间和基岩上单一TI土层为例,计算分析弹性半空间场地中隧道衬砌内表面动应力放大问题。结果表明qP波入射下,TI介质与各向同性介质场地中埋置衬砌隧道的动力响应差异显著,TI介质参数的变化导致场地动力特性的改变,进而改变场地与衬砌隧道的动力相互作用机制,显著影响着衬砌内表面动应力的大小及其空间分布。  相似文献   

基于反应位移法的复杂软土盾构隧道横断面抗震分析          下载免费PDF全文

刘前  刘瑜  梁建文  巴振宁  吴泽群  王智恺 《地震工程学报》2020,42(5):1217-1224

采用反应位移法，利用ABAQUS软件建立梁-弹簧有限元模型，进行复杂软土场地中盾构隧道横断面抗震分析，并结合天津滨海Z2线软土盾构隧道进行计算。研究表明，在地震作用下，最大弯矩值和剪力值一般出现在拱肩位置，最大轴力值一般出现在拱腰附近；处于复杂地层附近的隧道结构内力值较大，应加强该位置处的抗震构造措施或在选线时尽量避免复杂场地。本文对复杂软土场地中盾构隧道横断面抗震设计具有一定参考价值。  相似文献   

基于PS-InSAR技术的黄土大厚度挖方区回弹变形规律分析     

梁小龙  王建业  白泽朝  齐二恒  李攀 《测绘通报》2020,(3):163-166

以陕北某湿陷性黄土大厚度挖方地基工程为研究对象，采用PS-InSAR技术对2018-10—2019-11间获取的16景TerraSAR-X卫星影像进行处理，获取了湿陷性黄土挖方区回弹变形信息，总结了大厚度挖方区时序回弹变形特征。结果表明，由于上部土体应力卸载，在开挖区域存在地基土回弹变形现象，选取的高密度PS点变形信息较好地反映了研究区的真实变形情况，回弹变形范围与开挖边界吻合，另外挖方厚度越大，土体开挖引起的回弹变形越大；在开挖完成后的1年监测时间内，回弹区变形量随时间呈线性变化，在最大开挖厚度处，产生最大回弹量为29.3 mm；此外，PS-InSAR技术监测到的变形量与实地水准结果吻合性较好，表明该技术在黄土大厚度挖方区回弹变形监测中具有较好的应用效果。  相似文献   

Ediacaran integrative stratigraphy and timescale of China     

Zhou  Chuanming  Yuan  Xunlai  Xiao  Shuhai  Chen  Zhe  Hua  Hong 《中国科学:地球科学(英文版)》2019,62(1):7-24

Ediacaran successions occur widely in various depositional facies in South China and yield a series of fossil Lagerst?tten, providing a complete fossil record for the evolution of marine ecosystems after the terminal Cryogenian global glaciation. Carbonate-dominated Ediacaran successions in shallow water facies in South China record a nearly complete δ~(13)C profile that may reflect variations of marine carbon isotopic composition during the Ediacaran Period. The Ediacaran fossils andδ~(13)C profiles from South China permit stratigraphic correlation and subdivision of the Ediacaran strata. Based on biostratigraphic, chemostratigraphic, and geochronometric data from the Ediacaran successions in South China, we propose that the Ediacaran System in China can be subdivided into two series, with three stages in each series. The lower series is characterized by acanthomorphic acritarchs and the upper series by Ediacara-type macrofossils, and the two series are separated by the declining limb of a pronounced δ~(13)C negative excursion(EN3) in the upper Doushantuo Formation. The basal boundary of Stage1 is the same as the basal boundary of Ediacaran System, which has been defined at the base of the cap carbonate unit. Stage 2 represents the first radiation of Ediacaran microscopic organisms, with δ~(13)C feature representing by positive values(EP1). The base of the Stage 2 is placed at the first appearance level of a spiny acritarch species. Stage 3 is characterized by the occurrence of more diverse acritarchs and δ~(13)C feature EP2, with its basal boundary defined by a δ~(13)C negative excursion(EN2) occurring in the middle Doushantuo Formation. The basal boundary of Stage 4 is the same as the upper series. Stage 5 is marked by the occurrence of macrfossils of Miaohe biota, and its lower boundary can be placed at the level where δ~(13)C values transition from positive to negative in MNE, or the first appearance level of macrofossils of the Miaohe biota. Stage 6 is characterized by the occurrences of Ediacara-type Shibantan biota and Gaojiashan biota, with its lower boundary defined by the first appearance level of Conotubus hemiannulatus. The formal establishment of the aforementioned series and stages requires further and more detailed integrative stratigraphic study on the Ediacaran successions in China. Some of the Ediacaran successions in South China have great potential to become global standards in Ediacaran subdivision.  相似文献   

国内外割心钻具研发概况与分析          下载免费PDF全文

李鑫淼  梁健  尹浩  王志刚  梁楠 《探矿工程》2020,47(7):47-55

在松散、松软、破碎等复杂地层钻进时，与常规取心技术相比，割心技术能够获得更高的岩心采取率。国内外研发的割心钻具主要包括双动双管、单动双管和绳索取心割心钻具3种，钻具研发的关键点主要包括岩心爪结构设计和加压方式选择。从钻具研发情况看，三角形岩心爪具有良好的闭合性能，液力加压能够实现对割心压力的准确控制，绳索取心割心钻具钻进效率较高，但研发难度相对较大。本文详述了国内外割心钻具的结构设计特点及取心操作流程，分析了钻具设计原理的优缺点，提出了割心钻具发展趋势，为割心钻具的优化设计奠定了基础。  相似文献   

钻探参数实时采集系统研制与应用          下载免费PDF全文

汤小仁  孟义泉  訾兵  梁日旺 《探矿工程》2020,47(6):46-53

钻探参数实时采集系统研制的目的是向钻探技术及管理人员提供直观的钻探实时参数，通过该系统可全天候的掌握钻探工况。钻探参数采集的方法是通过传感器采集压力、转速、位移、流量、液位等物理参数，使用配套的软硬件设备进行数据转换和处理，在人机交互界面显示直观的工程参数。该系统根据野外现场不同工作环境可以使用互联网、GPRS终端或者北斗卫星终端把现场实时工程数据无线传输至远程服务器上，用户通过手机或电脑即可查看到现场的实时或历史工程数据。采用本系统可以预防和减少钻探事故，为事故处理提供数据支撑，为实现钻探自动化、智能化提供基础数据。  相似文献   

自由段先注浆对预应力锚索抗拔试验结果影响研究     

杨庆光  柳雄  刘杰  何杰  梁凌川  陈斌 《岩土力学》2020,41(10):3317-3325

为了解决无法采用已注浆锚索进行抗拔试验问题，基于界面脱黏剪切模型，利用荷载传递和弹性变形理论，考虑锚索锚固段与自由段长度比Lb /La的影响，建立了采用自由段已注浆锚索抗拔试验结果评价锚索抗拔性能的方法。结果表明：自由段注浆对锚索抗拔力有较大幅度的提高，尤其是当界面剪切阶段由弹性向脱黏过渡时，提高比例快速增加，并在脱黏后逐渐趋于稳定。其次，锚索自由段与锚固段交界面处剪切位移和轴力最大，并向两端逐渐降低。随着拉拔力的提高，界面剪切位移和轴力都不断增大，同时向锚索两端的衰减速度也加快。此外，弹性阶段时剪应力曲线为山峰型，而脱黏阶段为马鞍型，并随抗拔力的提高，马鞍开口逐渐扩大。最后，锚固段与自由段长度比Lb /La对锚索极限抗拔力的影响较小，其极限抗拔力折减系数?Q取值介于0.81～0.83之间，且Lb /La =2.5时，?Q计算值仅比实测结果小6.02%，验证了本文方法的可行性。  相似文献