Erratum: Carling,P.A., et al., Formation of mud ridge and runnels in the intertidal zone of the Severn Estuary,UK. Continental Shelf Research (2009), doi:10.1016/j.csr.2008.12.009     

Paul Carling  Jon WilliamsIan Croudace  Carl Amos 《Continental Shelf Research》2009

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Field investigation of ridge–runnel dynamics on an intertidal mudflat     

Jon J. Williams  Paul A. Carling  Carl L. Amos  Charlie Thompson 《Estuarine, Coastal and Shelf Science》2008

Flow-parallel linear ridge–runnel (R–R) bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at Hills Flats in the Severn Estuary, UK. It is argued that the sequences of sand–mud laminae in the ridge sediments indicate strongly that R–R are depositional bedforms. Faint R–R topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth. Bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion [mechanical erosion by turbulent flows that may also carry sand and/or gravel] during Spring tidal flow ca. 60 cm/s. Differences in flow characteristics between ridges and runnel are minor. Corrasion [to erode or be eroded by abrasion] by sparse coarse sediment largely prevents net deposition in the runnels. Over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and/or sediment supply.  相似文献   

Tentative nitrogen budget for pit latrines – eastern Botswana     

G. Jacks  F. Sefe  M. Carling  M. Hammar  P. Letsamao 《Environmental Geology》1999,38(3):199-203

 A major problem with on-site sanitation is nitrate pollution of the groundwater. A tentative nitrogen budget is established for pit latrines in eastern Botswana. The ammonia volatilisation was found to be negligible while leaching varied largely from about 1 to 50%. Leaching of nitrate was assessed by using chloride as tracer, assuming two sources of chloride, atmospheric deposition and the use of common salt in food. The initial content of nitrogen in excreta was assessed from nutritional data. The residual nitrogen in abandoned latrines as found by analysis, was 15–20%. The remainder should be denitrification which would then be in the order of 30–70%. That denitrification is important is supported by an elevated N-isotope ratio in groundwater and in deep-rooted non-N-fixing trees. The varying leaching rate provides a possibility of checking it by sealing the latrines. Since about 95% of the nitrogen in human excreta is present in the urine, an even more attractive solution would be urine-separating latrines with surface near percolation of the urine in the root zone of the vegetation, utilising it for crop growth. Since such latrines are used elsewhere in the world the problem is not technical but social acceptability. Received: 27 February 1998 · Accepted 14 September 1998  相似文献   

Flow structure in large bedrock-channels: The example of macroturbulent rapids,lower Mekong River,Southeast Asia     

Paul A. Carling  He Qing Huang  Teng Su  Duncan Hornby 《地球表面变化过程与地形》2019,44(4):843-860

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基于6S模型的山区环境星影像大气校正研究     

韩杰  杨磊库  李家国  孟庆岩  李慧娜 《测绘信息与工程》2011,(5):4-7

针对山区地形复杂,高程变化较大的特点,利用6S辐射传输模型建立查找表,结合研究区DEM对影像进行了大气校正。试验结果表明,校正后的影像清晰度、对比度提高了,消除了大气对NDVI的负面影响。  相似文献   

The occurrence of obtuse junction angles and changes in channel width below tributaries along the Mekong River,south‐east Asia     

Christopher Hackney  Paul Carling 《地球表面变化过程与地形》2011,36(12):1563-1576

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侏罗纪末至白垩纪非海相介形类生物地层学:回顾与展望     

Benjamin SAMES  David J.HORNE 《地层学杂志》2012,(2):266-288

以非海相介形类为依据而建立的侏罗纪末至白垩纪的生物地层学,尤其是欧洲所谓"Purbeck-Wealden层段"(提塘阶顶部至巴列姆阶/阿普特阶底部)和全球同期沉积层的生物地层学建立已久,但这一生物地层学存有很多问题与局限性。本文对中生代晚期(聚焦于早白垩世)的非海相介形类生物地层学的基本原理、历史、目前进展、存在问题和前景进行了综述。因为介形类的繁殖、扩散与成种机制已有比较成熟的研究,所以介形类的生物地层学的应用潜力被认识已久。然而,全球不同地区中生代晚期的非海相介形类众多的研究积累已构成了一个丰富但常常混乱和矛盾的文献库。这些问题不仅存在于介形类的分类鉴定中,也见于关于古环境和系统发育的解释中。虽然地区性的盆地内的介形类生物地层学研究已产生了好结果,并可能能够用于局部地区的高精度对比。但是在进行地区间(盆地间至全球)的对比时,其实用性广遭怀疑。在过去的二十年间,许多学者采用了将今论古的古生物学研究方法,努力修订和更新中生代晚期的非海相介形类的生物地层学与古环境意义,从而促进了地区间生物地层学研究和对比的发展。古生物学家认识到,对于许多非海相介形类动物来讲,它们的分布和扩散不仅仅局限于单个的水系或较小的地理区域,而是和现生的非海相介形类一样,晚侏罗世至白垩纪的非海相介形类动物和它们的卵可被较大的动物或风长距离搬运,跨越迁移的屏障,进行扩散。鉴于以上事实,地区间的对比必须涉及两大内容:分类学的应用与古环境背景。缺乏适用于地区—全球的稳定和一致的分类学系统是进行正确对比的重要障碍。由于大量地方性分类命名、地方性特有动物的假设、与壳体特征相关的分类和生态型认识的混乱,以及对种内变异尺度的统一认识的缺乏,导致了对生物分异度的过高或过低的估量。非海相白垩纪介形类的地层记录受到诸多因素的影响:分类单元的演化与灭绝、扩散事件、当地的环境变化和地区性至全球的气候变迁。在生物地层学的应用中,我们可以通过不同手段去把握同时代的Cytheroidea,特别是Cypridoidea中具重要地层意义的Cypridea属及其亲近者(即CypridoideaMartin,1940)的分类单元的形态变异度。解释种内变异时需要格外谨慎。区分生物自生(内因)导致的变异(遗传的和形态的变异)和环境(外因)导致的变异(生态表型)是一大难题。比较保守的分类学观念(分类单元很少,但变异极大(分类单元中包含了多种生态表型))有助于不同古环境间的(生物地层)对比。另一方法是运用随着时间的古环境变化及其对介形类组合的组成的影响来进行(生物地层)对比。古生物工作者已在利用受环境控制的周期性介形类组合变化建立对比关系方面进行了大量有意义的尝试,但这些工作仍处在争议中。建立全球生物地层学方法,建立统一而持久的分类概念这一目标可以达到,但不可能在短期内实现。用现代的思想(概念)理解和研究非海相介形类的古生物学和古生物地理学及新资料将有助于修订工作的进展。尽管我们对中生代的非海相介形类的演化和分布的认识还很不全面,但目前我们已取得了可喜的进展。盆地间至大陆间的对比是否可行,早已不是问题。目前和未来的指导原则无疑是发展以介形类为基础,并与其他的年代地层学和地质年代学资料及方案相结合的从地区至全球范围的地层对比系统。因为我们正在迈向一个非海相晚中生代介形类生物地层学的重新解释和应用的新时代,我们必须承认我们还有许多东西需要学习。  相似文献   

A field‐based assessment of oxygen supply to incubating Atlantic salmon (Salmo salar) embryos     

Stuart Greig  David Sear  Paul Carling 《水文研究》2007,21(22):3087-3100

Oxygen fluxes through artificially created salmon redds within four UK rivers were quantified and assessed against survival to hatching of Atlantic salmon embryos. All sites recorded high spatial variability in survival. Minimum survival to hatching was zero at all sites. Maximum survival to hatching ranged from 35% to 91%. Mean survival to hatching ranged from 8·7% to 71%. Intra‐ and inter‐site variations in rates of oxygen supply were observed. Generally, interstitial dissolved oxygen concentrations declined over the incubation period from a maximum recorded directly after redd creation, although localized fluctuations were recorded. Similarly, interstitial flow velocities declined over the incubation period from a maximum directly after redd creation to a minimum at hatching. With respect to the causes of embryo mortalities, oxygen supply was shown to be a stronger determinant of survival than interstitial oxygen concentration or interstitial flow velocity. To improve delineation of potential causes of embryo mortalities in the field, the statistical analysis was integrated within mass transfer theory of the processes controlling respiration to determine the likely mechanisms inhibiting respiration. Based on this analysis, mortalities were assessed to have resulted from periods of lethal oxygen concentrations, from periods of interstitial flow velocities that were insufficient to remove metabolic waste, or from combinations of oxygen concentration and interstitial flow that did not support respiratory requirements. A set of oxygen‐supply‐related thresholds for assessing incubation habitat quality are proposed. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Peat slides in Teesdale and Weardale,northern pennines,july 1983: Description and failure mechanisms     

P. A. Carling 《地球表面变化过程与地形》1986,11(2):193-206

Peat landslides that occurred in Upper Teesdale and Weardale in 1983 are described. The slides occurred after thunderstorm rainfall of a very rare intensity and return period. The slope geomorphological features and the vegetation associated with the slide areas are detailed. Baseline geotechnical data are used in a simple retrospective stability analysis, treating the peat slides as shallow translational slips. The analysis demonstrates the probable important role played by open moor drains, natural soil pipes, and prior cracking of the peat (owing to dessication or slow mass movement) in the rapid transfer of water to the failure zone within an impervious sensitive clay beneath the peat. The frequency of peat landslides and the visual persistence of sites is considered briefly in relation to substratum and peat stability within a context of climatic change. It is suggested that there may be a gradation of type from the classic Irish bog-burst, through failures of intermediate character, to peat slips involving rigid peat blocks. Antecedent conditions and the mechanism of failure need not be similar for mass movements at either end of this spectrum.  相似文献   

An appraisal of the velocity-reversal hypothesis for stable pool-riffle sequences in the river severn,England     

P. A. Carling 《地球表面变化过程与地形》1991,16(1):19-31

The ‘velocity-reversal hypothesis’ is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool-riffle sequences in gravel-bedded streams. The literature in support of the hypothesis together with published adverse criticism is reviewed. It is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable. Continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow, high stage, and stable morphology. These observations are substantiated by a detailed study of the hydraulic geometry of stable pool-riffle sequences in the River Severn, England. Neither the sectionally-averaged velocity nor the near-bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow. Instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases. A detailed investigation of the three-dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles. Unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles. The hydraulic data are used to comment on the stability of the test reaches in the context of the development of the River Severn in the vicinity of Shrewsbury.  相似文献