Vegetation and climate history of Anggertu Lake in the Tengger Desert over the last millennium     

Duan  Futao  An  Chengbang  Zhao  Yongtao  Wang  Wei  Cao  Zhihong  Zhou  Aifeng 《中国海洋湖沼学报》2018,36(6):2166-2180

Reconstructing climate change of the last millennium is important to understand the current relationship between human-social activities and natural environmental changes. Pollen assemblages, losson-ignition(LOIo rg at 550°C), and grain size data collected from sediment core AGE15 A from the center of Anggertu lake(eastern Tengger Desert, Inner Mongolia) were used to reconstruct the regional vegetation and climate history of the last millennium. Desert or steppe desert, dominated by A rtemisia and Amaranthaceae, expanded around this region during the period of 988–1437 AD indicating a generally dry climate condition with two short humid periods(1003–1082 AD and 1388–1437 AD). These two wet periods were characterized by relatively high vegetation cover and bioproductivity, as reflected by high pollen concentrations and LOIo rg values. Increases in steppe and meadow vegetation communities(Poaceae, Cyperaceae) and vegetation cover during 1437–2015 AD suggest a wetting trend, which was also deduced from a gradual trend towards fine grains and higher lake biological productivity as reflected by LOIo rg values. An unstable lacustrine environment was identified via frequent fluctuations in pollen concentration and grain size after 1842 AD. This study also recorded a relatively dry Medieval Warm Period(MWP, 1082–1388 AD) and a wet Little Ice Age(LIA, 1437–1842 AD). Increased Amaranthaceae and high abundance of Poaceae may be related to overgrazing and agricultural activities that took place during those time periods. The evolution of vegetation in the lake region was influenced by climate change and human activities. These results could provide more fundamental support for studies of the environmental evolution of the Tengger Desert.  相似文献   

Effect of Wetland Reclamation on Soil Organic Carbon Stability in Peat Mire Soil Around Xingkai Lake in Northeast China     

Lili Huo  Yuanchun Zou  Xianguo Lyu  Zhongsheng Zhang  Xuehong Wang  Yi An 《中国地理科学(英文版)》2018,28(2):325-336

Content and density of soil organic carbon(SOC) and labile and stable SOC fractions in peat mire soil in wetland, soybean field and rice paddy field reclaimed from the wetland around Xingkai Lake in Northeast China were studied. Studies were designed to investigate the impact of reclamation of wetland for soybean and rice farming on stability of SOC. After reclamation, SOC content and density in the top 0–30 cm soil layer decreased, and SOC content and density in soybean field were higher than that in paddy field. Content and density of labile SOC fractions also decreased, and density of labile SOC fractions and their ratios with SOC in soybean field were lower than that observed in paddy field. In the 0–30 cm soil layer, densities of labile SOC fractions, namely, dissolved organic carbon(DOC), microbial biomass carbon(MBC), readily oxidized carbon(ROC) and readily mineralized carbon(RMC), in both soybean field and paddy field were all found to be lower than those in wetland by 34.00% and 13.83%, 51.74% and 35.13%, 62.24% and 59.00%, and 64.24% and 17.86%, respectively. After reclamation, SOC density of micro-aggregates( 0.25 mm) as a stable SOC fraction and its ratio with SOC in 0–5, 5–10, 10–20 and 20–30 cm soil layers increased. SOC density of micro-aggregates in the 0–30 cm soil layer in soybean field was 50.83% higher than that in paddy field. Due to reclamation, SOC density and labile SOC fraction density decreased, but after reclamation, most SOC was stored in a more complex and stable form. Soybean farming is more friendly for sustainable SOC residence in the soils than rice farming.  相似文献   

移动目标空间拓扑关系的度量描述     

李朋朋  刘纪平  罗安  张玉婷 《测绘通报》2019,(4):65-70

针对传统9交模型对移动目标空间拓扑关系表达及量化描述的不足,基于格网化思想,提出了度量参数量化描述的方法。首先对移动目标和参考目标进行格网化,划分为固定大小的格网阵列;然后利用9交模型确定空间目标间拓扑关系的形式化描述;最后引入内部分量、边界分量、外部分量3种度量参数对移动目标空间拓扑关系进行度量化描述。试验证明,该方法计算简单、直观,能更加有效地度量移动目标间的拓扑关系。  相似文献   

国外海底犁式开沟机技术进展     

张园  张树森  张葆华  顾安  王旭阳  赵敏  葛彤 《海洋科学》2019,43(9):114-121

总结了国外海底犁式开沟机技术进展,海底犁式开沟机可分为"V"型开沟犁和矩形开沟犁两种,"V"型开沟犁开沟截面面积较大,沟槽截面形状为V型,适合与海底管道埋设,其回填方式有专门回填犁回填和回填模块回填两种。矩形开沟犁开沟面积较小,截面狭长且为矩形,多适用于海底电缆埋设。其土壤排出方式有垂向排土和侧向挤压排土两种,沟槽靠重力自动回填。犁式开沟机开沟速度快,造价相对较低,目前正在朝大型化、模块化发展。开沟犁的关键技术包括犁式开沟机的开沟阻力减小方法以及在崎岖海底地形上开沟时的开沟深度稳定性等,这也是目前研究的重点。对国外犁式开沟机技术的总结,对开沟犁设计和海上施工作业有一定指导意义。  相似文献   

多源数据中尺度涡三维结构分析方法研究          下载免费PDF全文

张春华  安文韬  邵连军  赵钊  方乐 《海洋技术学报》2019,38(2)

作为重要的海洋中尺度现象之一,中尺度涡的研究受到人们的关注和重视。随着数值模式的进一步发展、卫星资料的累积、时间更长以及更多更有效的海上实测数据的取得,使得综合利用实测资料、卫星遥感资料、再分析/数值预报产品等数据源,对中尺度涡进行自动识别与三维结构分析成为中尺度涡研究的主要方向之一。在前期对卫星遥感资料中尺度涡自动检测算法进行研究的基础上,开展多源资料中尺度涡三维结构分析方法研究,以表面漂流浮标运动轨迹为中尺度涡的判定依据,综合利用高度计观测、红外遥感观测、以及再分析/数值预报产品分析中尺度涡三维结构信息,在此基础上,提出中尺度涡研究的发展方向,为全面分析中尺度涡的时空特性提供技术途径,为中尺度涡的动力机制研究奠定基础。  相似文献   

东昆仑山昆仑河纵剖面形貌分析及构造涵义     

曹凯  王国灿  王岸 《地球科学》2007,32(5):713-721

青藏高原东昆仑北部地区新构造活动强烈, 存在一系列活动断层, 控制了该地区的地貌格局和水系的发育.其中大部分活动断层是已经确定下来的, 还有一些活动断层还处在定性推测阶段.引进河流长度-坡度参数(以下简称“SL参数”) 和Hack剖面2个能够有效反映区域新构造活动的地质参数, 对昆仑河纵剖面坡度变化进行详细刻画和研究, 并对昆仑河河流阶地进行空间对比分析.研究结果表明, 昆仑河河流的Hack剖面与SL参数存在形貌上的对应关系, SL参数的突变主要是受断裂构造活动控制; 证实了昆仑河-野牛沟断裂和东昆中断裂第四纪以来存在构造活动性; 第四纪以来强烈的构造差异隆升作用控制了东昆仑地区的地貌水系发育格局, 并将产生更深远的影响.   相似文献   

甘肃北山拾金坡花岗岩特征及其与金成矿的关系   总被引：2，自引：0，他引：2       下载免费PDF全文

安国堡 《甘肃地质》2007,16(3):19-25

通过对拾金坡岩体宏观地质特征、岩石矿物学、岩石化学以及地球化学成果的全面分析,通过对区域成矿地质背景的研究,总结了该区金矿的控制因素。区内金成矿主要受岩体和构造控制。岩体是成矿的最主要因素,矿化与岩体有密切的时空关系,区内大多数金矿床产在拾金坡岩体的边缘。拾金坡复式花岗岩由早期到晚期可分出闪长岩、似斑状二长花岗岩和黑云母二长花岗岩共3期岩浆活动。岩石学和地球化学研究表明该岩体为下地壳或上地幔源,属Ⅰ型或同熔型;岩体相对富集轻稀土,δEu值为0.45～0.99。加里东晚期似斑状二长花岗岩提供了成矿物质,海西早期钾长花岗岩对含矿热液的运移起到了积极作用。处于深处的钾长花岗岩在上升过程中产生了含矿热液,并且在似斑状花岗岩中形成了一系列断层,这些断层为成矿流体的运移和富集提供了空间。海西期的构造岩浆活动不但为含金热液在二长花岗岩中的上升运移开辟了通道,而且为金矿化提供了热源,在似斑状二长花岗岩中形成石英脉型金矿床。  相似文献   

生态环境类电子地图集的研究与开发     

齐清文  姜莉莉  梁雅娟  李晋  徐莉  张岸 《地理信息世界》2007,5(3):26-36

针对生态环境类电子地图集这种新型的专题性电子地图集在信息构成和功能上的特殊性,首先,研究和确定了它的主题定位和功能定位,提出集信息可视化和空间分析、虚拟仿真等功能于一体的理念。其次,提出并构建了生态环境类电子地图集的新颖的数据模型,第三,研究并阐述了该类电子地图集的专题图型和表达方法,第四,设计并实现了这种电子地图集的体系结构和技术系统,通过丰富的电子地图实例阐述本文的技术和方法创新点。  相似文献   

Modification of the Sm–Nd isotopic system in garnet induced by retrogressive fluids          下载免费PDF全文

Shi‐Chao An  Shu‐Guang Li  Zhen Liu 《Journal of Metamorphic Geology》2018,36(8):1039-1048

Garnet, as a major constitutive mineral of eclogite, is important for Sm–Nd dating of eclogite due to its high Sm/Nd ratio and its stability during retrogression. However, a comprehensive study of the petrography, mineral chemistry, garnet water content, and Sm–Nd isotopic composition of eclogites from the Bixiling massif, Central Dabie Zone (CDZ), reveals significant modification of the Sm–Nd isotopic system in garnet as a result of retrogression. This problem constitutes a challenge for Sm–Nd dating of the Bixiling eclogites, with the Sm–Nd isochron ages of 218 ± 4 to 210 ± 9 Ma reported in the literature being younger than 226 ± 3 Ma, which is the generally accepted peak metamorphic age of the CDZ. Petrographic analysis reveals heterogeneity in colour within single fractured garnet grains. There are light‐pink garnet (Grt‐P) and red garnet (Grt‐R) types that possess distinct chemical compositions. Compared to Grt‐P, Grt‐R has higher Fe and andradrite contents but lower Al and grossular contents. Grt‐P also has lower water contents (15–35 ppm) than Grt‐R (34–65 ppm), which, together with the spatial association between Grt‐R and fractures, suggests that the colour change is related to fluid alteration. Grt‐P is an ultra‐high‐pressure (UHP) mineral, and Grt‐R is the product of the interaction between Grt‐P and a fluid during retrogression. Moreover, Grt‐R features lower Sm and Nd contents but higher Sm/Nd ratios than Grt‐P. The Sm–Nd isochrons defined by UHP minerals (Grt‐P+Omp+Rt or Grt‐P+Cpx+WR) from three eclogite samples yield consistent ages of 226.0 ± 3.8 Ma, 225.0 ± 3.9 Ma and 226.2 ± 6.9 Ma, which are identical to the peak metamorphic age of 226 ± 3 Ma for the CDZ. The retrogressed garnet (i.e., Grt‐R), omphacite and rutile, together define a pseudoisochron with younger ages of 218.9 ± 5.9 to 202.8 ± 4.8 Ma, which are geologically meaningless. The increase in the Sm/Nd ratio with constant or lower ¹⁴³Nd/¹⁴⁴Nd ratios during the transformation of Grt‐P to Grt‐R was probably the cause of these younger ages.  相似文献   

Spatial and temporal variability of 0‐ to 5‐m soil–water storage at the watershed scale          下载免费PDF全文

Zihuan Fu  Yunqiang Wang  Zhisheng An  Wei Hu  Khan M.G. Mostofa  Xuezhang Li  Bingxia Liu 《水文研究》2018,32(16):2557-2569

Dynamic relationships among rainfall patterns, soil water distribution, and plant growth are crucial for sustainable conservation of soil and water resources in water‐limited ecosystems. Spatial and temporal variation in deep soil water content at a watershed scale have not yet been characterized adequately due to the lack of deep soil water data. Deep soil–water storage (SWS) up to a depth of 5 m (n = 73) was measured at 19 sampling occasions at the LaoYeManQu watershed on the Chinese Loess Plateau (CLP). At a depth of 0–1.5 m, the annual mean SWS was highly correlated with rain intensity, and the correlation decreased with depth, but within the layers at 1.5–5.0 m, the changes in SWS indicated a lag between precipitation and the replenishment of soil water. Geostatistical parameters of SWS were also highly dependent on depth, and the mean SWS presented similar spatial structures in two adjacent layers. Temporal stability of SWS as indicated by mean relative difference, standard deviation of the relative difference (SDRD), and mean absolute bias error (MABE) was significantly weaker at the shallow than at deeper layers. Soil separates and organic carbon content controlled the spatial pattern of SWS at the watershed scale. One representative location (Site 57) was identified to estimate the mean SWS in the 1‐ to 5‐m layer of the watershed. Semivariograms of the SDRD and MABE were best fitted by an isotropic spherical model, and their spatial distributions were depth‐dependent. Both temporal stability and spatial variability of SWS increased over depth. This study is helpful for deep SWS estimation and sustainable management of soil and water on the CLP, and for other similar regions around the world.  相似文献