Soil erosion of unpaved loess roads subjected to an extreme rainstorm event: a case study of the Jiuyuangou watershed on the Loess Plateau,China

Rainfall can cause serious soil loss in the Loess Plateau hilly and gully region, but little focus has been placed on the extreme rainstorm effects on unpaved loess road soil erosion. A field survey method was used to investigate the erosional effects of the "7·26" heavy rainfall event on unpaved loess roads in the Jiuyuangou watershed of the Loess Plateau, China. The results showed that the average and maximum widths of the eroded gullies that formed on the unpaved roads were 0.65-1.48 m and 1.00-3.60 m, respectively. The average and maximum depths of theeroded gullies were 0.42-1.13 m and 0.75-4.30 m, respectively. The average width-to-depth ratio was 1.31, indicating that the widening effect was greater than the downcutting effect in the eroded gullies. In addition, the gully density ranged from 0.07 to 0.29 m m~(-2), and the road surface dissection degree ranged from 0.03 to 0.41 km~2 km~(-2). Eroded gullies generally developed at the slope toe of the cut bank side. The average eroded gully width and depth at turns in the road were 1.47-2.64 times and 1.30-3.47 times greater, respectively, than those in other road sections. The road erosion modulus increased from the upper section to the lower section of the roads. The average road erosion modulus of the study catchment was 235,000 t km~(-2). Turns in the road were associated with collapses, sinkholes and other gravitational erosion phenomena. The amount of road erosion under extreme rainfall conditions is mainly related to the interactions among road length, width, slope and soil bulk density. Our results provide a useful reference for developing further measures for preventing road erosion on the Loess Plateau.     

Local dynamical equivalence of certain food webs

An important challenge in theoretical ecology is to find good coarse-grained representations of complex food webs. Here, we use the approach of generalized modeling to show that it may be possible to formulate a coarse-graining algorithm that conserves the local dynamics of the model exactly. We show examples of food webs with a different number of species that have exactly identical local bifurcation diagrams. Based on these observations, we formulate a conjecture governing which populations of complex food webs can be grouped together into a single variable without changing the local dynamics. As an illustration, we use this conjecture to show that chaotic regions generically exist in the parameter space of a class of food webs with more than three trophic levels. While our conjecture is at present only applicable to relatively special cases, we believe that its applicability could be greatly extended if a more sophisticated mapping of parameters were used in the model reduction.     

新疆孔雀河北岸72~51 ka BP湖相沉积物的孢粉植物群初步研究

对新疆孔雀河北缘的LX02剖面湖相沉积物开展了OSL测年和孢粉记录研究。结果显示：该剖面湖相沉积自72.4 ka BP延续到51.0 ka BP。这一期间,研究区为针叶、阔叶混交林植被,林下生长灌木和草本,低洼潮湿的地方生长蕨类孢子和藻类。植被的主要类型有松（Pinus）、栎（Quercus）、栗（Castanea）、榛（Corylus）、莎草（Cyperaceae）、蒿（Artemisia）、藜（Chenopodiaceae）、水龙骨科（Polypodiaceae）等,同时还含有少量的山核桃（Carya）和枫杨（Pterocarya）等亚热带的孑遗植物花粉。具体来说,组合带Ⅰ（72.4~66.8 ka BP）、Ⅲ（56.1~51.0 ka BP）对应的沉积期间,研究区阔叶树花粉含量低而灌木和草本花粉含量高;组合带Ⅱ（66.8~56.1 ka BP）对应的沉积期阔叶树花粉含量都较高,而灌木和草本花粉相对较低,揭示72.4~51.0 ka BP研究区气候总体上呈现冷干-暖湿的气候波动特征。这与粘土矿物和地球化学特征所反映的古气候特征及其变化一致,亦与柴达木盆地东部介形类丰度特征研究、柴达木盆地东部古湖泊高湖面光释光年代学研究、北京平原区有机碳同位素研究等结果吻合较好,然而,这一气候变化规律的内部驱动机制还有待进一步的深入研究。     

Vertical atmospheric structure of the late summer clear days over the east Gansu loess plateau in China

In this paper, by using the sounding data collected in LOPEX05, we have analyzed the vertical atmospheric structure and boundary layer characteristics of temperature and humidity in the late summer over the east Gansu loess plateau. The results show that the bottom of the stratosphere is at about 16 500 m and varies between 14 000 m and 18 000 m above the ground. The center of the westerly jet is located between 8300 m and 14 300 m above the ground and its direction moves between 260° and 305°. There is an ...     

新疆和田河流域柽柳沙堆的生物地貌发育过程

Tamarix nabkha is one of the most widespread nabkhas,distributing in the arid region of China.Based on the observations outdoors and the simulation experiments in laboratories,analysis in this paper refers to the biological geomorphologic features and growth process of Tamarix nabkhas in the middle and lower reaches of the Hotan River,Xin- jiang.And the results indicate that the ecological type of Tamarix in the study area is a kind of Tugaic soil habitat based on the deep soil of the Populus Diversifolia f...     

金塔南山河流砾石特征指示的青藏高原东北缘地貌演化

青藏高原的隆升扩展不但塑造了高原及其周边的地貌,影响了气候的变化,而且极大地改造了其周缘的水系格局。其中,河流沉积物最直接地记录了河流演化与水系演变的过程。本研究主要利用河流砾石层的沉积特征分析金塔南山地区水系演化对高原东北缘扩展过程的响应。金塔南山顶面普遍沉积一套磨圆度较好、分选较好的河流砾石层,其砾石岩性主要组分为岩屑砂岩、石英砂岩和硅质岩,在局部地区也存在较多的砾岩和灰岩。祁连山北部主要的7条河流出山口主河道的砾石组分统计结果显示砾石岩性主要组分存在较大差异;河流之间的砾石岩性差异很好的解释了金塔南山顶面砾石岩性组分自东向西的变化。根据对比金塔南山顶面砾石组分和祁连山北部主要的7条河流主河道砾石组分中不同抗风化能力岩性的含量与分布,我们认为金塔南山顶面砾石主要来源于祁连山。对金塔南山顶面砾石ab面的测量发现：东段砾石倾向单一,指示古流向为北;而中西段倾向复杂。总体来说,砾石倾向指示的古水流方向是北向。结合砾石岩性组分与分布以及古流向,认为在金塔南山顶面沉积砾石层时,此处的河流处于摆荡状态且河流之间可能有汇合现象,造成局地砾石ab面指示的古流向与整体流向不一致;而后随着中更新世以来金塔南山的抬升,黑河和北大河下切分别形成正义峡和鸳鸯峡,形成两个相对独立和稳定的水系。     

Development of extended WRF variational data assimilation system (WRFDA) for WRF non-hydrostatic mesoscale model

The paper intends to present the development of the extended weather research forecasting data assimilation (WRFDA) system in the framework of the non-hydrostatic mesoscale model core of weather research forecasting system (WRF-NMM), as an imperative aspect of numerical modeling studies. Though originally the WRFDA provides improved initial conditions for advanced research WRF, we have successfully developed a unified WRFDA utility that can be used by the WRF-NMM core, as well. After critical evaluation, it has been strategized to develop a code to merge WRFDA framework and WRF-NMM output. In this paper, we have provided a few selected implementations and initial results through single observation test, and background error statistics like eigenvalues, eigenvector and length scale among others, which showcase the successful development of extended WRFDA code for WRF-NMM model. Furthermore, the extended WRFDA system is applied for the forecast of three severe cyclonic storms: Nargis (27 April–3 May 2008), Aila (23–26 May 2009) and Jal (4–8 November 2010) formed over the Bay of Bengal. Model results are compared and contrasted within the analysis fields and later on with high-resolution model forecasts. The mean initial position error is reduced by 33% with WRFDA as compared to GFS analysis. The vector displacement errors in track forecast are reduced by 33, 31, 30 and 20% to 24, 48, 72 and 96 hr forecasts respectively, in data assimilation experiments as compared to control run. The model diagnostics indicates successful implementation of WRFDA within the WRF-NMM system.     

苏北盆地高邮凹陷古近系戴南组沉积相及其与隐蔽油气藏的关系

苏北盆地高邮凹陷是江苏油田的主要油气勘探开发区，是一个南断北超的典型箕状断陷湖盆，其中的古近系戴南组为一套厚度近2 000 m的河湖相砂泥岩地层，从下到上分为一段和二段。通过沉积充填分析和沉积相编图，戴南组一段沉积时，苏北盆地断陷构造活动相对强烈，地形高差大，水体相对较深，水体范围相对较小，从南向北分别发育近岸水下扇、湖底扇、三角洲等沉积相类型。戴南组二段沉积时，构造活动有所减弱，地形高差变小，水体相对较浅，水体范围扩大至整个凹陷，从南向北分别发育扇三角洲、湖底扇、三角洲等沉积相类型。利用砂岩等厚图等资料，确定了戴南组的沉积相图。沉积相在平面上分布范围明确，纵向上既有差异性又有继承性。高邮凹陷边缘和内部的同沉积断层对沉积相和砂体的发育分布起着重要的控制作用，沉积相控制了油气分布，特别是对隐蔽油气藏形成起重要作用。高邮凹陷戴南组的隐蔽圈闭类型主要有地层超覆、断层-岩性、砂岩上倾尖灭及透镜体圈闭等。湖底扇、三角洲前缘、扇三角洲前缘、近岸水下扇中扇等为有利的储集岩相带。结合石油地质条件的分析，确定了联18-马18井区等几个有利的隐蔽油藏勘探区。     

伊犁蒙其古尔铀矿床含矿层砂岩中黄铁矿形成机制及对铀成矿的指示意义

蒙其古尔铀矿床为伊犁盆地南缘大型层间氧化带砂岩型铀矿床,为查明该矿床含矿层中黄铁矿成因及其形成机制,探讨微生物参与铀成矿过程。文章对含矿层砂岩中黄铁矿与铀矿物矿物学特征、黄铁矿S同位素与碳酸盐胶结物的C-O同位素开展细致研究。研究表明:①蒙其古尔铀矿床中铀主要以铀矿物与吸附铀形式存在,吸附铀主要为有机质吸附铀,铀矿物以沥青铀矿为主,多与黄铁矿、炭屑共生;②蒙其古尔铀矿床含矿层砂岩中黄铁矿主要以自形晶、草莓状和不规则状集合体产出,多与沥青铀矿、碳酸盐胶结物共生,其中黄铁矿S同位素(δ~(34)S_(V-CDT)=-68.4‰～22.1‰)与碳酸盐胶结物的C-O同位素(δ~(13)C_(V-PDB)=-10.2‰～-7.4‰,δ~(18)O_(V-PDB)=-9.6‰～-5.8‰)分析表明黄铁矿具有细菌硫酸盐还原(BSR)与有机物热解2种成因,并探讨了这2种不同成因黄铁矿的形成机制。③结合前人研究成果,认为硫酸盐还原菌(SRB)参与蒙其古尔铀矿床铀成矿过程,以间接还原方式为主,在有机质、黏土矿物与颗粒表面吸附U(Ⅵ)的基础上,通过硫酸盐还原菌(SRB)还原SO_4~(2-)产生的H_2S将U(Ⅵ)被还原成U(Ⅳ),形成铀矿物。