Biogeomorphology of the Mediterranean Posidonia oceanica seagrass meadows

Here we review the multiple interactions between the endemic Mediterranean seagrass, Posidonia oceanica, and coastal geomorphologic processes as an outstanding example of biogeomorphology, taking into account recent advances in the field. Seagrass meadows are among the most important elements for the functioning of marine coastal ecosystems, and represent a major focus for research and conservation. Being considered a priority habitat, P. oceanica meadows are protected by several European Union directives and national laws. In this paper we examine: the role of sedimentary features in controlling the development of the meadows; the interplay between P. oceanica leaf litter (i.e. beached necromass) cast ashore and erosional‐depositional processes on the beaches; the interactions between meadows and nearshore hydrodynamics, and; possible linkages between geomorphological features of the seafloor and the architecture of meadows. Finally, we provide perspectives for future research on P. oceanica and other Mediterranean seagrass meadows in a biogeomorphological context with specific reference to climate change. Copyright © 2016 John Wiley & Sons, Ltd.     

Global distribution of coastal cliffs

Previous studies have estimated that coastal cliffs exist on about 80% of the global shoreline, but have not been validated on a global scale. This study uses two approaches to capture information on the worldwide existence and erosion of coastal cliffs: a detailed literature survey and imagery search, and a GIS-based global mapping analysis. The literature and imagery review show coastal cliffs exist in 93% of the combined recognized independent coastal states and non-independent coastal regions worldwide (total of 213 geographic units). Additionally, cliff retreat rates have been quantified in at least one location within 33% of independent coastal states and 15% of non-independent regions. The GIS-based mapping used the near-global Shuttle Radar Topography Mission 3 arc second digital elevation model and Arctic Coastal Dynamics Database to obtain near-global backshore coastal elevations at 1 km alongshore intervals comprising about 1,340,000 locations (81% of the world vector shoreline). Backshore coastal elevations were compared with the mapped distribution of European coastal cliffs to produce a model training set, and this relationship was extended globally to map the likelihood of coastal cliff locations. About 21% of the transects (17% of the world vector shoreline) were identified as mangroves and eliminated as potential cliff locations. The results were combined with estimates of cliff percentages for Greenland and Antarctica from the literature, extending the global coverage to estimate cliff occurrence across 89% of the world vector shoreline. The results suggest coastal cliffs likely exist on about 52% of the global shoreline. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Decadal behaviour of a washover fan,Skallingen Denmark

In this study, the decadal evolution of a washover fan on the west coast of Denmark is examined from its initial generation in 1990 until 2015. Since its inception, the bare and flat washover fan surface has recovered and accreted slowly due to re-activation by overwash during surges and due to aeolian activity and dune formation, stimulated by vegetation growth. The volume of sand on the washover has increased steadily at an average rate of about 23 m³/yr per unit length of shoreline, and a total of 175,000 m³ of sand is now deposited on the fan, while at the same time the shoreline has receded by some 250 m. The evolution can be divided into three stages: 1) An initiation phase when storm surge levels and energetic wave conditions caused a breach in the foredunes and overwash processes formed a washover fan with a relatively low elevation above mean sea level; 2) An initial recovery phase during which waves supplied sand to the fan during frequent overwash activity and winds transported this sand into marginal dunes surrounding the fan; and 3) A later recovery phase when the surface of the fan had accreted to a level where vegetation could survive and trap sediment into new foredune growth across the fan. The rate of accretion has been overall linear but scales with neither annual overwash frequency, nor with aeolian transport potential. Instead, the linear accretion is more closely related to the steady onshore migration of nearshore bars that weld to the beach and provide a sand supply for transfer to the fan. The fan evolution demonstrates the importance of washover fans in preserving barrier resilience during transgressional phases caused by increasing mean sea level. © 2019 John Wiley & Sons, Ltd.     

Coastal geomorphic chronosequences across broad spatiotemporal scales. Metrical observations from the Cape Verde hotspot

The study of the coastal landscapes of hotspot oceanic islands through comprehensive structural metrics and ecological estimators represents an opportunity to explore geomorphological transformations and broad spatiotemporal scale features of coastal evolution. As part of this approach, a new metrical comparative analysis is presented in this study, comprising four islands in different evolutionary stages. They belong to the Cape Verde archipelago, which forms a double insular chain in which an east–west gradient in age and evolution is particularly evident across the southern chain. A space-for-time (SFT) substitution approach is applied to the coasts of (1) Fogo, in the shield stage; (2) Santiago, in the early post-erosional stage; (3) São Vicente, in the advanced post-erosional stage; and (4) Boa Vista, in the last erosional stage. From the obtained spatial distributions and frequencies of landforms, the coastal landscapes of these islands are compared in relation to their (i) geomorphic composition, using similarity indices (Whittaker, β_w, Sorensen, C_s) and nestedness estimators (NOFD, WNODF), (ii) geomorphic abundance, using morpho-assembling densities (D_gm), and (iii) geomorphic diversity, using six alpha-diversity indices (Richness, S, Menhinick, D_MN, Simpson, D, Shannon, H', Berger-Parker, d, and Brillouin, HB). An advanced geomorphological taxonomy is implemented for areas with limited open-access data, including a set of planform features captured through scale-frequency decomposition. Photographic, cartographic and fieldwork data are used for landform identification at 1200 random sampling points, empirically determined by a bootstrap method. The results show a chronological ordering of the compared variables and a possible co-evolution towards an increase in organizational geomorphic complexity of coastal systems at broad space-timescales. The method proposed in this study can contribute, from a metrical perspective, to finding new long-term evolutionary features and constitutes an advance in the development of an integrated model of coastal evolution in oceanic islands. © 2019 John Wiley & Sons, Ltd.     

Effects of coastal erosion on landslide activity revealed by multi-sensor observations

Coastal erosion is becoming an increasingly serious consequence of climate change. This study demonstrates the effects of coastal erosion on landslide activity while considering the amount of erosion and changes in pore water pressure. To determine the factors related to landslide slip generation, we specifically measured the displacement, deformation, pore water pressure, and amount of erosion with high temporal resolution (1 s–1 h) for a coastal landslide in Hokkaido, north-eastern Japan, for 7 months. It has been determined that landslides occur simultaneously with high pore water pressure. Toe erosion events also occurred several times, while the landslide exhibited major displacement. Because toe erosion and the increase in pore water pressure occurred simultaneously, we tried to determine which of the two contributed majorly to the landslide displacement by conducting a stability analysis that incorporates the effects of the two factors. From the actual observed data, toe erosion and the increase in pore water pressure had comparable effects on the destabilization of the studied landslide. Specifically, the time series for the safety factor shows that the landslide in the case with toe erosion was destabilized more than that in the case with no erosion, with a difference of more than 5% in the safety factor. The model with toe erosion provided a better explanation for the landslide displacement. Furthermore, the inclination data suggested that erosion took place at least 1 month before the landslide displacement. This implied that coastal erosion played a role in the preparation and ongoing displacement of the coastal landslide. Inland landslides with toes that are subject to undercutting due to river incision or artificial construction have geomorphological settings that are similar to those of the studied landslide. The knowledge obtained here can contribute to the understanding of destabilization mechanisms and terrain changes related to such landslides. © 2020 John Wiley & Sons, Ltd.     

Effect of offshore waves and vegetation on the sediment budget in the Virginia Coast Reserve (VA)

The potential for rapid coastline modification in the face of sea-level rise or other stressors is alarming, since coasts are often densely populated and support valuable infrastructure. In addition to coastal submergence, nutrient-related water pollution is a growing concern for coastal wetlands. Previous studies found that the Suspended Sediment Concentration (SSC) of coastal wetlands acts as a first-order control of their sustainability, but SSC dynamics are poorly understood. Our study focuses on the Virginia Coast Reserve (VCR) Long Term Ecological Research (LTER) site, a shallow multiple tidal inlet system in the USA. We apply numerical modelling (Delft3D-SWAN) and subsequent analyses to determine SSC dynamics within the VCR. In particular, we consider two important controls on SSC in the system: vegetation (seagrass and salt marsh) and offshore waves. Our results show that vegetation colonies and increased wave energy lengthen water residence time. The reduction in the tidal prism decreases SSC export from the bay via tidal inlets, leading to increased sediment retention in the bay. We found that alongshore currents can enhance lagoon SSC by importing fine sediments from an adjacent inlet along the coastline. Our numerical experiments on vegetation seasonality can improve the understanding of wave climate impact on coastal bay sediment budget. Offshore waves increase sediment export from coastal bays, particularly during winter seasons with low vegetation density. Therefore, our study can help managers and stakeholders to understand how to implement restoration strategies for the VCR. © 2020 John Wiley & Sons, Ltd.     

秦皇岛地区海岸侵蚀及主要原因

本文根据实际调查资料对秦皇岛地区海岸侵淤活动进行了分析,论述了控制条件和对滨海资源环境的危害。得出近50多年来,秦皇岛123.5km长海岸发生过6种不同形式的侵淤活动,有82.69km岸段发生不同程度的侵蚀活动,占总岸段的67%.海岸侵蚀的原因除风暴潮影响外,主要是海岸带物质补给来源持续减少和人工采挖砂石。海岸侵蚀活动除威胁滨岸工程设施安全外,还严重破坏旅游资源和土地资源,加剧海水入侵活动。      

现代乌伦古湖滨岸沉积环境与沉积体系分布及其控制因素

通过现场实地踏勘、拍照、开挖探槽、利用卫星图解译等方法,对乌伦古湖环布伦托海区域和吉力湖北部乌伦古河现代三角洲地区的湖泊滨岸沉积环境和沉积体系进行了现代沉积调查。研究表明乌伦古湖滨岸沉积环境可以划分为基岩型湖岸、砾质湖岸、砂质湖岸、泥质湖岸等4种类型,发育山前基岩型湖岸、侵蚀基岩型湖岸、砾质冲积扇-扇三角洲、砾质辫状河三角洲、砾质滩坝、砂质滩坝、砂质三角洲、风成沙丘和泥质沼泽等9种滨岸沉积体系。山前基岩湖岸分布在布伦托海的北部,主要发育小型塌积扇、倒石锥和狭窄的湖滩。侵蚀型基岩湖岸位于布伦托海西岸和东北角地区,发育湖滩宽20~40 m。砾质冲积扇-扇三角洲沉积体系分布在布伦托海西北部25.8 km狭长区域,表现为一系列冲积扇-扇三角洲体系在山前形成裙边状展布的辫状平原,顺流向长5~15 km。砾质辫状河三角洲体系发育在布伦托海西部,砾质滩坝发育在砾质三角洲前缘,沉积物一般为中砾和粗砾,泥质含量低。现代乌伦古河三角洲位于吉力湖北部,沙丘广泛分布在布伦托海东部的三角洲平原。砂质滩坝发育在布伦托海东岸南部地区,滩坝带宽30~100 m,发育大量障碍痕、冰划痕。泥质沼泽占据湖岸总长度29.22 km,沼泽地带植物繁茂,水动力微弱,泥质和有机质含量高。根据卫星照片推测乌伦古湖水位可能发生过3次较大的下降,现代乌伦古河三角洲可能经过了4个发育阶段,但目前缺乏地质年代学证据。构造格局控制了湖泊边界的地形地貌特征,平行构造线走向容易形成规模较大的沉积体系,垂直构造走向形成的沉积体系规模较小。寒旱地区湖泊周缘入湖河流较少,具有季节性和暂时性特点,洪水泥石流、塌积扇等重力沉积体系比较发育。湖泊封冻是寒旱区湖泊区别于温暖地区湖泊的重要特征。在相同气候背景下,源汇地区的高差和河流的流程、流量决定了沉积物的供给总量和沉积体系的特征。湖盆边界形态影响沿岸流的发育,也影响湖泊风动力方向和强度。乌伦古湖滨岸沉积体系的多样性对研究古代湖泊滨岸沉积体系具有重要的启发,开展湖泊滨岸沉积环境和沉积体系调查对完善陆相湖盆沉积体系模式,对发现新的储层类型,对重建湖泊古地理环境具有重要的意义。     

辽宁省海岸带地质环境综合评价研究

对近20年来辽宁省海岸带地质环境调查成果进行全面的分析,系统梳理了辽宁省海岸带地质资源与环境条件及其变化,以及海岸带自然与人类活动引起的不良环境地质问题.根据地壳稳定性、活动断裂、地面沉降、地面塌陷等地质因素,对辽宁沿海6个城市进行了地质环境条件评价,结合国家政策与地方发展规划,为地质资源保护与开发利用提出建议.     

Distinction between the Storegga tsunami and the holocene marine transgression in coastal basin deposits of western Norway

Many coastal lakes were inundated by both the Storegga tsunami (7000 ¹⁴C yr BP) and the mid-Holocene sea-level rise (the Tapes transgression) in western Norway. The tsunami eroded lake bottoms and deposited graded and/or massive beds of sand, rip-up clasts, and coarse plant material. By contrast, when the rising sea entered the lakes, it deposited only gyttja, silt and fine sand, without causing much erosion of the underlying lake sediments. Storegga tsunami deposits in some coastal lakes were interpreted previously as ordinary marine sediments from the Tapes transgression. Our reinterpretation of these deposits shows that the transgression maximum phase was reached after 6500 yr BP, more than 1000 yr later than previously inferred for the coast of Sunnmøre. The new data cannot be combined in a shoreline diagram without showing the 6000 yr BP and 7000 yr BP shorelines as slightly warped. © 1998 John Wiley & Sons, Ltd.