Source and supply of sediment to a shoreline salient in a fringing reef environment     

Michael V.W. Cuttler  Jeff E. Hansen  Ryan J. Lowe  Julie A. Trotter  Malcolm T. McCulloch 《地球表面变化过程与地形》2019,44(2):552-564

Reef-associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef-fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef-associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (²³⁸U/²³⁰Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (>10³ years) source materials may be more resilient to climate change as present-day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef-associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.  相似文献   

黄东海间遗传连通性多物种案例分析与启示     

赵峰  王子涵  曹玲  曾聪 《海洋科学》2023,47(11):97-109

黄东海是太平洋重要的边缘海,拥有丰富的海洋生物多样性资源,但在气候变化及人类活动的双重胁迫下,黄东海面临生物多样性衰退等问题,亟需加强保护。保护区网络被认为可有效防止或减缓人类活动和气候变化对生物多样性的负面影响,但连通性作为保护区网络的重要参数却很难直接测量。因此,本研究希望通过梳理已发表的黄东海间遗传连通性文献来揭示黄东海区域内的保护区是否形成网络。通过搜集已发表的137篇文献,共获得175个研究案例。超过半数的案例(65.71%)认为黄东海之间具有显著的遗传分化,这也意味着跨生态区群体间具有较低的遗传连通性。在总结影响因素时发现长江冲淡水、生境异质性、空间距离、进化过程、生活史(较短的浮游幼体期)、洋流等6个因素阻碍了黄东海群体间的遗传连通性,而洋流、生活史(较长的浮游幼体期)等2个因素促进了遗传连通性。进一步分析发现黄东海群体间的遗传连通性与空间距离呈显著的负相关,而与浮游幼体期呈正相关。因此,根据本研究结果,建议未来保护区网络建设应针对黄、东海生态区分别构建网络,在网络设计时应考虑保护对象的扩散能力及保护区间的空间距离。本研究不仅为构建涵盖黄东海的海洋保护区网络提供理论基础,...  相似文献   

How well do indicator variograms capture the spatial connectivity of soil moisture?     

Andrew W. Western  Günter Blschl  Rodger B. Grayson 《水文研究》1998,12(12):1851-1868

Indicators are binary transforms of a variable and are 1 or 0, depending on whether the variable is above or below a threshold. Indicator variograms can be used for a similar range of geostatistical estimation techniques as standard variograms. However, they are more flexible as they allow different ranges for small and large values of a hydrological variable. Indicator geostatistics are also sometimes used to represent the connectivity of high values in spatial fields. Examples of connectivity are connected high values of hydraulic conductivity in aquifers, leading to preferential flow, and connected band-shaped saturation zones in catchments. However, to the authors' knowledge the ability of the indicator approach to capture connectivity has never been shown conclusively. Here we analyse indicator variograms of soil moisture in a small south-east Australian catchment and examine how well they can represent connectivity. The indicator variograms are derived from 13 soil moisture patterns, each consisting of 500–2000 point TDR (time domain reflectometry) measurements. Winter patterns are topographically organized with long, thin, highly connected lines of high soil moisture in the drainage lines. In summer the patterns are more random and there is no connectivity of high soil moisture values. The ranges of the 50^th and 90^th percentile indicator semivariograms are approximately 110 and 75 m, respectively, during winter, and 100 and 50 m, respectively, during summer. These ranges indicate that, compared with standard semivariograms, the indicator semivariograms provide additional information about the spatial pattern. However, since the ranges are similar in winter and in summer, the indicator semivariograms were not able to distinguish between connected and unconnected patterns. It is suggested that new statistical measures are needed for capturing connectivity explicitly. © 1998 John Wiley & Sons, Ltd.  相似文献   

颗粒形状对碎石料孔隙特性影响研究     

叶加兵  张家发  邹维列 《岩土力学》2018,39(12):4457-4467

颗粒形状是影响碎石料孔隙特性的主要因素之一,进而影响碎石料的渗透特性和力学行为。选取粒径为2~5 mm和5~10 mm的灰岩碎石颗粒填筑试样,同时与相同级配和孔隙率的玻璃球试样进行对比研究,采用CT扫描技术和图形处理软件获取多孔介质孔隙边界轮廓,选取0.5 mm开度阈值分割孔隙;每组试样选取3张扫描断面图像,取定量参数的平均值为研究对象,对孔隙特性进行定量分析。结果表明：玻璃球多孔介质孔隙形状的复杂性甚于碎石料;玻璃球多孔介质孔隙系统的连通度大于同粒组碎石料。  相似文献   

The effects of land consolidation on the ecological connectivity based on ecosystem service value: A case study of Da’an land consolidation project in Jilin province     

Jun WANG  Shenchun YAN  Yiqiang GUO  Junran LI  Guoqing SUN 《地理学报(英文版)》2015,25(5):603-616

Land consolidation has a profound impact on landscape patterns and ecological functions at various scales through engineering and biological measures. In recent years, China invests more than 100 billion RMB yuan on land consolidation each year. To understand how land consolidation affects landscape patterns and ecosystems, we investigated the ecosystem service value and the ecological connectivity in a consolidated area of Da’an city from 2008 to 2014 using a revised ecological connectivity index. The results indicated that land consolidation has certain negative influences on the ecosystem services in this area. The total ecosystem service value will decrease by nearly 30% in the late stage of consolidation. This decrease is caused by the loss of ecosystem service of the wetland and grassland, despite a sensible increase of cultivated land. In addition, land consolidation could change the ecological connectivity as well as the land use structure. Up to 85% of the entire area will be in low connectivity in the late stage of consolidation, representing a 6.23% increase in the total coverage compared to pre-consolidation. Finally, the different connectivity landscape and their key areas can be identified by the revised ecological connectivity index effectively. This study is helpful to trace out the relationships between landscape pattern and ecological process, and provides insights for ecological planning and designing of land consolidation in this area. We suggest that more attentions should be paid to improve the quality and ecosystem service value per unit area of the landscape, to establish ecological compensation mechanism of wetland losses, and to create the ecological corridors along the least accumulated impendence surface in the key areas during land consolidation.  相似文献   

A comparison of wetness indices for the prediction of observed connected saturated areas under contrasting conditions   总被引：1，自引：0，他引：1       下载免费PDF全文

Geneviève Ali  Christian Birkel  Doerthe Tetzlaff  Chris Soulsby  Jeffrey J. McDonnell  Paolo Tarolli 《地球表面变化过程与地形》2014,39(3):399-413

For lack of other widely available spatial information, topography is often used to predict water fluxes and water quality in mesoscale watersheds. Such data have however proven to be misleading in many environments where large and flat valley bottoms and/or highly conducive soil covers determine water storage and water transport mechanisms. Also, the focus is generally on the prediction of saturation areas regardless of whether they are connected to the catchment hydrographic network or rather present in isolated topographic depressions. Here soil information was coupled with terrain data towards the targeted prediction of connected saturated areas. The focus was on the 30 km² Girnock catchment (Cairngorm Mountains, northeast Scotland) and its 3 km² sub‐catchment, Bruntland Burn in which seven field surveys were done to capture actual maps of connected saturated areas in both dry and humid conditions. The 1 km² resolution UK Hydrology of Soil Types (HOST) classification was used to extract relevant, spatially variable, soil parameters. Results show that connected saturated areas were fairly well predicted by wetness indices but only in wet conditions when they covered more than 30% of the whole catchment area. Geomorphic indices including information on terrain shape, steepness, aspect, soil texture and soil depth showed potential but generally performed poorly. Indices based on soil and topographic data did not have more predictive power than those based on topographic information only: this was attributed to the coarse resolution of the HOST classification. Nevertheless, analyses provided interesting insights into the scale‐dependent water storage and transport mechanisms in both study catchments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modelling particle residence times in agricultural river basins using a sediment budget model and fallout radionuclide tracers   总被引：1，自引：0，他引：1       下载免费PDF全文

Hugh G. Smith  William H. Blake  Alex Taylor 《地球表面变化过程与地形》2014,39(14):1944-1959

Contemporary patterns in river basin sediment dynamics have been widely investigated but the timescales associated with current sediment delivery processes have received much less attention. Furthermore, no studies have quantified the effect of recent land use change on the residence or travel times of sediment transported through river basins. Such information is crucial for understanding contemporary river basin function and responses to natural and anthropogenic disturbances or management interventions. To address this need, we adopt a process‐based modelling approach to quantify changes in spatial patterns and residence times of suspended sediment in response to recent agricultural land cover change. The sediment budget model SedNet was coupled with a mass balance model of particle residence times based on atmospheric and fluvial fluxes of three fallout radionuclide tracers (⁷Be, excess ²¹⁰Pb and ¹³⁷Cs). Mean annual fluxes of suspended sediment were simulated in seven river basins (38–920 km²) in south‐west England for three land cover surveys (1990, 2000 and 2007). Suspended sediment flux increased across the basins from 0.5–15 to 1.4–37 kt y^‐1 in response to increasing arable land area between consecutive surveys. The residence time model divided basins into slow (upper surface soil) and rapid (river channel and connected hillslope sediment source area) transport compartments. Estimated theoretical residence times in the slow compartment decreased from 13–48 to 5.6–14 ky with the increase in basin sediment exports. In contrast, the short residence times for the rapid compartment increased from 185–256 to 260–368 d as the modelled connected source area expanded with increasing sediment supply from more arable land. The increase in sediment residence time was considered to correspond to longer sediment travel distances linked to larger connected source areas. This novel coupled modelling approach provides unique insight into river basin responses to recent environmental change not otherwise available from conventional measurement techniques. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

基于生产性服务业的长江三角洲城市网络   总被引：5，自引：1，他引：4  

王聪  曹有挥  陈国伟 《地理研究》2014,33(2):323-335

全球化进程中,城市网络的研究成为国内外学者关注的重要前沿。借鉴西方有关的研究工具,从城市网络的层级特征、网络模式、功能特征三个方面分析了长江三角洲地区的生产性服务业的城市网络发展特征。研究表明：基于生产性服务业的长三角城市网络具有显著的层级特征,与已有的城市等级体系特征并不完全一致,个别城市如昆山、义乌等城市承担了重要的网络联系中心的作用。同时,城市间的网络连接也呈现出明显的位序关系,三大核心节点城市（上海、南京、杭州）之间的联系形成了长三角地区城市间网络的最主要的联系。从影响范围来看,上海的网络指向性最强,涉及面也最广,但南京和杭州的影响不再仅仅局限于自身所在省份之内,扁平化发展的趋势愈发显著。网络联系的核心区域开始由传统的上海、南京、杭州、宁波所围合的“Z”字型区域向北部的南通、扬州以及南部的绍兴等地区扩散。根据不同类型的生产性服务业所形成的网络特征的不同,将11个部门分为完善型、扁平型、专业型等三种类型。  相似文献   

Structure and evolution of the submarine cable network of Chinese mainland     

Xie  Yongshun  Wang  Chengjin  Huang  Jie 《地理学报(英文版)》2022,32(5):932-956

Journal of Geographical Sciences - Submarine cable network is one of the most important connectivity infrastructures in the digital era. In the past 20 years, the submarine cable network of Chinese...  相似文献   

A new approach for linking event‐based upland sediment sources to downstream suspended sediment transport     

Peng Gao  James Puckett 《地球表面变化过程与地形》2012,37(2):169-179

In this study, we proposed a new approach for linking event sediment sources to downstream sediment transport in a watershed in central New York. This approach is based on a new concept of spatial scale, sub‐watershed area (SWA), defined as a sub‐watershed within which all eroded soils are transported out without deposition during a hydrological event. Using (rainfall) event data collected between July and November, 2007 from several SWAs of the studied watershed, we developed an empirical equation that has one independent variable, mean SWA slope. This equation was then used to determine event‐averaged unit soil erosion rate, Q_S/A, (in kg/km²/hr) for all SWAs in the studied watershed and calculate event‐averaged gross erosion E_ea (in kg/hr). The event gross erosion E_t (in kilograms) was subsequently computed as the product of E_ea and the mean event duration, T (in hours) determined using event hydrographs at the outlet of the studied watershed. Next, we developed two linear sediment rating curves (SRCs) for small and big events based on the event data obtained at the watershed outlet. These SRCs, together with T, allowed us to determine event sediment yield SY_e (in kilograms) for all events during the study period. By comparing E_t with SY_e, developing empirical equations (i) between E_t and SY_e and (ii) for event sediment delivery ratio, respectively, we revealed the event dynamic processes connecting sediment sources and downstream sediment transport. During small events, sediment transport in streams was at capacity and dominated by the deposition process, whereas during big events, it was below capacity and controlled by the erosion process. The key of applying this approach to other watersheds is establishing their empirical equations for Q_S/A and appropriately determining their numbers of SWAs. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献