Chronic offshore loss of nourishment on Nice beach,French Riviera: A case of over-nourishment of a steep beach?     

Edward J. Anthony  Olivier Cohen  Francois Sabatier 《Coastal Engineering》2011

The 4.5 km-long gravel beach fronting the exclusive resort of the city of Nice, on the French Riviera, in southeastern France, was artificially nourished from 1976 to 2005 to the tune of 558,000 m³, making this long-term operation one of the most significant for gravel beaches in the world. Nourishment has ranged from nil in certain years (1979, 1980, 1983–85, and 2001–2002) to a peak of over 97,000 m³ in 2000. Analyses of 50 transects covering the beach highlight no significant change in net beach width over this 30-year period of massive gravel nourishment. A Principal Components Analysis and a Cluster Analysis used to detect patterns in the 87 beach-width measurement dataset show no clear spatial trends in transect groups that can be interpreted in terms of the morphology of the beach and the steep inner shoreface. Significant wave height off Nice shows no change over the period 1979–2005. Since there is no possibility for alongshore gravel leakage on the strongly embayed Nice beach, the relative stability in beach width clearly implies loss of recharged gravel offshore. Gravel loss following nourishment is favoured by: (1) the steep inner shoreface inherited from the geological context of Nice beach at the flanks of the southern Alps, and (2) the practise of artificial beach widening through flattening, in summer, of a narrow (5–15 m-wide) mobile zone of the profile in order to enhance the ‘carrying’ capacity of this highly touristic beach. Beach widening and flattening following nourishment bring close to the very steep inner shoreface zone several cubic metres of gravel for each metre of beach that may be permanently lost downslope during autumn and winter storms. Recharged gravel is redistributed alongshore and offshore leakage is probably enhanced where small narrow submarine canyon heads impinge on the beach, resulting in a very narrow shoreface. Mean beach width shows an oscillating alongshore pattern that may be due to the influence of these canyons as pathways of gravel loss offshore. However, there is no correlation between mean beach width and distance to the 10-m isobath, used as a surrogate for inner shoreface width. Storms are associated with plunging waves that are particularly effective and concentrated, on this almost tideless shore, over the narrow mobile zone of the beach profile where a series of steep reflective berms are built during storms. The high dynamic pressures associated with this narrow zone of concentrated wave breaking, and energy reflection from the steepened profile, are deemed to contribute to the permanent downslope loss of gravel. This situation of long-term gravel loss is probably accepted by the beach management authority because of the low cost of obtaining nourishment material and the advantages derived from a temporarily wider beach in terms of recreational space.  相似文献   

Emerging coral diseases: a temperature‐driven process?          下载免费PDF全文

Aaron W. Miller  Laurie L. Richardson 《Marine Ecology》2015,36(3):278-291

In the last few decades there has been a surge in research focusing on coral disease. While climate change, specifically rising sea surface temperature, has been proposed as a major and growing driver of the emergence of marine diseases, to date a solid connection between disease epizootics and elevated sea surface temperature has not been established. However, a wealth of data now exists, compiled from many different perspectives, that may support such a connection. In this work we provide a comprehensive review targeting one coral disease, black band disease, that spans the infection process, pathobiology, and epizootiology, and links specific mechanisms of the disease process to increasing temperatures. This temperature‐driven pattern of infection can be expanded to include similar processes associated with other temperature‐related coral diseases. The conclusions presented here are based upon the results of many studies using a diverse suite of approaches that have been synthesized to argue that the emergence and continuing spread of black band disease is linked to warming sea surface temperatures. In summary, as global ocean temperatures increase seasonally and over decades, the environment shifts to become more favorable for the growth of potentially pathogenic microorganisms endemic to the immediate environment of the reef. The increase in the relative number of potential pathogens in the microbial community produces microenvironments conducive to the growth of other potential pathogens, leading to infection by a polymicrobial consortium. This consortium is easily perturbed by a (seasonal) temperature decrease, but remains associated with the coral host and can be reactivated with a subsequent seasonal increase in temperature, resulting in a cycle of temperature‐dependent disease emergence.  相似文献   

Are strandline meiofaunal assemblages affected by a once-only mechanical beach cleaning? Experimental findings     

Gheskiere T  Magda V  Greet P  Steven D 《Marine environmental research》2006,61(3):245-264

The increasing usage of sandy beaches as recreational resources has forced regional authorities of many tourist countries to remove all litter of fabricated origin and natural wrack from the beach. Consequently, a variety of heavy equipment has been developed during the last decades and is now used almost daily at many beaches. A field experiment, following a 'before-after-control-impact' (BACI) design, was conducted at the strandline of De Panne (Belgium) to investigate the impacts of mechanical beach cleaning on the strandline-associated meiofaunal assemblages, focussing on the free-living nematodes. Natural strandline assemblages were exposed to a one-off 5 cm deep mechanical beach cleaning and observed for 24 h. Differences between cleaned plots and those from control plots in terms of decreased percentage of organic matter, decreased total abundance and changed community structure were noticed from immediately after the experimental cleaning onwards and recovered to initial values after the following high water. Any impacts due to cleaning on species richness, Pielou's evenness and taxonomic diversity were shown to be minor in relation to the daily changes. Recolonization in the cleaned sediments is assumed to occur from the underlying sediments initiated by the elevated water table during the rising tide.  相似文献   

Determination of wave–shoreline dynamics on a macrotidal gravel beach using Canonical Correlation Analysis     

Amaia Ruiz de Alegría-Arzaburu  Adrián Pedrozo-Acuña  José M. Horrillo-Caraballo  Gerhard Masselink  Dominic E. Reeve 《Coastal Engineering》2010

This paper describes the application of Canonical Correlation Analysis (CCA) to derive forcing–response relations between the wave climate and shoreline position on a macrotidal gravel barrier located in the southwest of the U.K., and to develop a tool to determine shoreline positions from wave records. The data sequences comprise wave climate recorded by a nearshore directional wave buoy and video-derived shorelines over a time span of one year and a half. The hydrodynamic conditions are used to determine the probability density function of wave heights and alongshore energy fluxes. These are then related to shoreline change through a CCA analysis. The CCA analysis identifies patterns of behaviour of the wave conditions and the shoreline position, and the relation between both patterns is found to provide useful information about the beach response to wave action. The analysis shows that the movement of sediment is greater at the southern end of the study area and that there is an immediate shoreline response to the wave action. In the case of coastal management it is more often the case that wave forecasts are available on a routine basis. The ability of the CCA to provide useful estimates of shorelines from wave conditions was tested by using measured waves to calculate the corresponding shoreline position from additional data at the end of the sequences. Shoreline positions determined with the CCA agreed well with the measured ones. Thus, the CCA is found to be a useful tool to determine unknown shoreline positions and support effective coastal management if good quality hydrodynamic and morphological data are available to input into the initial set-up of the technique.  相似文献   

Is there a link between deep‐sea biodiversity and ecosystem function?     

Daniel Leduc  Ashley A. Rowden  Conrad A. Pilditch  Elizabeth W. Maas  P. Keith Probert 《Marine Ecology》2013,34(3):334-344

Studying the diversity‐ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity‐ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep‐sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity‐function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity‐ecosystem function relationship in the largest ecosystem on Earth.  相似文献   

Nourishment and disaster mitigation efficiency of feeding sand on the dry section of a dissipative beach     

Yazhuang Zhao  Hongshuai Qi  Shaohua Zhao  Feng Cai  Jianhui Liu  Pu Xu  Zheyu Xiao  Yanyu He  Zhiyong Zhang 《海洋学报(英文版)》2023,(7):138-148

To explore the nourishment effect and disaster reduction efficiency of a fully dissipative dry beach under the impact of storms, this paper uses the measured topography and hydrodynamic data to establish a onedimensional numerical model of the XBeach beach profile. By numerically modeling the change in the nourished profile for different dry beach widths under normal waves and storm conditions and the recovery process of the profile after the storm, the degree of response in dry beach nourishmen...  相似文献   

Using video imagery to reconstruct the 3D intertidal terrain along a beach with multiple cusps     

Feng Cai  Hang Yin  Hongshuai Qi  Jixiang Zheng  Yuwu Jiang  Zhubin Cao  Yanyu He 《海洋学报(英文版)》2023,(7):1-9

A high-frequency, high-resolution shore-based video monitoring system(VMS) was installed on a macrotidal(tidal amplitude >4 m) beach with multiple cusps along the Quanzhou coast, China. Herein, we propose a video imagery-based method that is coupled with waterline and water level observations to reconstruct the terrain of the intertidal zone over one tidal cycle. Furthermore, the beach cusp system(BCS) was precisely processed and embedded into the digital elevation model(DEM) to more effectiv...  相似文献   

Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain   总被引：4，自引：4，他引：0  

Emmanuel Poizot  Giorgio Anfuso  Yann Méar  Carlos Bellido 《Geo-Marine Letters》2013,33(4):263-272

An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higher-energy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management.