Ecological status of seagrass ecosystems: An uncertainty analysis of the meadow classification based on the Posidonia oceanica multivariate index (POMI)     

Bennett S  Roca G  Romero J  Alcoverro T 《Marine pollution bulletin》2011,62(8):1616-1621

Quantifying the uncertainty associated with monitoring protocols is essential to prevent the misclassification of ecological status and to improve sampling design. We assessed the Posidonia oceanica multivariate index (POMI) bio-monitoring program for its robustness in classifying the ecological status of coastal waters within the Water Framework Directive. We used a 7-year data set covering 30 sites along 500 km of the Catalonian coastline to examine which version of POMI (14 or 9 metrics) maximises precision in classifying the ecological status of meadows. Five factors (zones within a site, sites within a water body, depth, years and surveyors) that potentially generate classification uncertainty were examined in detail. Of these, depth was a major source of uncertainty, while all the remaining spatial and temporal factors displayed low variability. POMI 9 matched POMI 14 in all factors, and could effectively replace it in future monitoring programs.  相似文献   

Models of bed formation     

Michael F. Dacey 《Mathematical Geology》1979,11(6):655-668

The model for bed formation by Kolmogorov consists of an unending sequence of alternating periods of deposition and erosion of sediments, with the amounts of deposition and erosion being independent random variables. This paper examines this model in relation to recent mathematical studies that are relevant to, and simplify, the analysis of the thickness of the bed that remains after the sequence is operated for a long time. This thickness obeys the exponential probability law when the amounts of deposition and erosion also obey the exponential law distributed. For the discrete version formulated by Schwarzacher, the thickness obeys the geometric probability law when the amounts of deposition and erosion obey the geometric law.  相似文献   

毕节煤矿区晚二叠世煤层稀土元素的物质来源     

王强  杨瑞东  鲍淼  魏怀瑞  王伟 《贵州地质》2006,23(4):292-295

对取自毕节地区晚二叠世11个可采煤层的13个样品的稀土元素(REE)的物质来源进行分析。发现:海洋来源对稀土元素的富集作用极其微弱;来自植物成因的物质来源小于1%;煤样中δEu负异常,而陆源岩具有Eu负异常的特点。结合晚二叠世多期喷发的峨眉山玄武岩,因此认为稀土元素的物质来源主要受陆源影响和控制。  相似文献   

Modeling of Beams on Reinforced Granular Beds     

Priti Maheshwari  P. K. Basudhar  S. Chandra 《Geotechnical and Geological Engineering》2006,24(2):313-324

The paper describes a mechanical model for estimating the flexural response of a strip footing, supporting a column (imposing a concentrated load), resting on a compacted granular bed overlying a reinforcement layer for example, geogrids, geomats etc. below which lies a loose soil deposit. The footing is idealized as a beam and the reinforcing element is assumed to have finite bending stiffness and negligible frictional resistance. The upper and lower soil layers are idealized by a series of linear and discrete springs (Winkler springs) of different stiffness values. To find the response of such a model the governing differential equations have been derived and expressed in a nondimensional form. A closed form analytical solution of the same has been obtained subjected to appropriate boundary conditions. Using the present approach the resulting solution for a degenerated case of a long beam is found to be identical to the same of Hetenyi (1946, Beams on elastic foundations, University of Michigan press, Ann Arbor, MI). Parametric studies reveal that the ratio of flexural rigidity of upper and lower beam and the ratio of stiffness of the upper and lower soil layers affect significantly the response of the foundation.  相似文献   

Fe and Mn in calcites cementing red beds: A record of oxidation–reduction conditions: Examples from the Catalan Coastal Ranges (NE Spain)     

D. Parcerisa  D. Gmez-Gras  A. Trav  J.D. Martín-Martín  E. Maestro 《Journal of Geochemical Exploration》2006,89(1-3):318

Fe and Mn occur in calcite cements depending on the oxidizing–reducing conditions of cementing waters, which may change according to depositional and diagenetic environments. In red beds, Mn and Fe are available from the ferruginous matrix. Thus, it is possible to know the oxidizing–reducing conditions of fluids that precipitated calcite as a function of Mn and Fe content in calcite cement. A detailed petrological (with special attention to cathodoluminescence) and geochemical analysis of these cements is a useful tool to constrain the diagenetic evolution of red beds and the history of the basin where they deposited.  相似文献   

国道219线新-藏公路改建工程地质灾害评价   总被引：1，自引：0，他引：1  

李铁锋  刘长兵  李欣 《中国地质灾害与防治学报》2003,14(4):26-29

国道219线新-藏区界至红土达坂路段全长109．55km。大部分路段穿越湖盆槽谷中央部位，部分线路沿湖盆边缘台地布设，海拔高度介于5000-5400m之间，地势平坦开阔，多年冻土发育，工程地质条件较差；现有公路路基高度低，几乎没有排水设施。冬季易产生路基冻胀和涎流冰危害，春、夏季因冻土融化，常引起路基沉陷和翻浆，严重危害公路运输安全甚至阻断交通。公路工程修建活动将极大地改变冻土环境，使天然状态下的水分循环发生改变，导致多年冻土退化，上限加深，进一步诱发冻胀、融沉、热融滑塌等冻土灾害，加剧风沙灾害、诱发公路边坡失稳破坏。在即将进行的公路改、扩建工程中，应采取保护冻土的设计原则，优选线路，加强侧向排水，合理设置取弃土场。  相似文献   

Caractéristiques et signification d'un niveau coquillier majeur à brachiopodes,marqueur événementiel dans l'évolution dévonienne de la Saoura (Sahara du Nord-Ouest,Algérie)     

Abdelkader Ouali Mehadji  Serge Elmi  Patrick Rachebœuf  Larbi Mekahli 《Comptes Rendus Geoscience》2004,336(14):1283-1292

In the Saoura, the brachiopod shell beds, so-called niveau coralligène, correspond to a major shell deposit dated to the Late Emsian. Brachiopods and crinoids dominate the benthic assemblage that contains also corals, bryozoans, trilobites, goniatites, and orthocones. This major level has a large geographic distribution and it is characterized by a wide brachiopod diversity due to time-averaging, taphonomic feedback and alternate bottom conditions changing from soft to shelly and firm. This kind of brachiopod association is linked to a transgressive onlap system. At regional extent, we can correlate this major shell bed to similar shell deposits from the Ahnet-Mouydir, Tindouf, and Zemmour areas. It indicates an important transgressive event underlined by change in the sedimentation from detritic deposits to carbonate sediments. To cite this article: A. Ouali Mehadji et al., C. R. Geoscience 336 (2004).  相似文献   

疏降地下水引起地面塌陷浅析--以淮南煤矿区为例   总被引：4，自引：0，他引：4  

许光泉  沈慧珍 《中国地质灾害与防治学报》2004,15(4):64-68

以淮南西部矿区为例，介绍了该地区自20世纪60年代开采煤矿以来，由于疏降地下水，引起的地面塌陷。为了研究灰岩水动力场规律，先后在该区进行多时段、多水平放水试验。研究表明，覆盖粘土层、岩溶及人工疏降地下水，是该地区岩溶塌陷形成的基本条件。通过对粘土盖层性质、疏降地下水岩溶塌陷演化过程及塌陷机理与对应阶段过程综合分析，结合区域地质条件，掌握了塌陷点的分布规律。对目前西部地区塌陷“复活”、整治及未来城市规划，提出了建设性建议。  相似文献   

丹霞地貌概念讨论   总被引：8，自引：0，他引：8  

刘尚仁  刘瑞华 《山地学报》2003,21(6):669-674

关于丹霞地貌概念上的不同意见,主要是：①岩性岩相上是较单一的“陆相碎屑岩”还是涵盖多种岩性岩相的“沉积岩”;②地貌上是“丹崖”,还是“赤壁丹崖”,或是“赤壁丹崖群”。根据目前已知的中外丹霞地貌的基本特征,初步认为,丹霞地貌是由砂岩砾岩为主的沉积岩经侵蚀作用所形成的赤壁丹崖群地貌。近10a来,一些丹霞地貌概念,基本上属于“中国丹霞地貌”的概念,不完全符合世界丹霞地貌的实际情况。  相似文献   

Soluble salt deposit in the Nihewan beds and its environmental significance   总被引：2，自引：0，他引：2  

LI Rongquan  QIAO Jianguo  QIU Weili  ZHAI Qiumin  LI Yongliang 《中国科学D辑(英文版)》2000,43(5):464-479

Observation and experimental analysis of soluble salt deposit along four profiles across the strata deposited in Nihewan paleolake basin enabled us to recognize the nature and evolution stages of the Nihewan paleolake and its significance in stratigraphical division and pa-leo-environmental reconstruction. The Nihewan paleolake was at least a weak-saline to semi-saline lake and represents an intracontinental lake in the semi-arid region. The lower member of sedimentary strata in the paleolake contains gypsum layer and gypsum lamellae. Soluble salt is mainly composed of SO ₄ ^2- and Ca²⁺ ions, representing a trend of the paleolake evolving into a stage of sulfate lake. The upper member of the strata has predominantly Cl^-, K⁺, and Na⁺ ions in soluble salt, indicating a starting development of the paleolake to chlorite lake, but no salt rock was deposited, indicating a drying trend of the area.  相似文献