Marine erosive processes at the cliff foot

Erosion rates are 15–18.5 times higher in places where there is a beach at the cliff foot compared with those where there is no beach. The zone of intense erosion associated with a beach of sand and pebbles was below a height of about 10 cm above the surface, maximum erosion being at 14.5 cm below the surface. Erosion was by corrasion and wedging, a previously unrecognised process which is the quarrying of rock aided by fine-grained particles from the beach. Wedging, perhaps with some corrasion, had a median erosion rate of 11.05 · 10^?3 cm tide^?1 in Upper Lias shale while the rate for corrasion was 5.79 · 10^?3 cm tide^?1. A smooth, notched cliff foot may be produced by these processes. Where there was no beach, erosion of the cliff foot was by the sporadic quarrying of blocks of rock and the more continuous micro-quarrying of shale fragments. The cliff foot was dominated by structural planes and had a rough surface. The horizontal erosion rate due to quarrying at one cliff foot was 2.3 cm year^?1. Quarrying acts on the cliff foot above the intense zone of erosion at a beach surface. The median erosion rate for this quarrying was 0.91 · 10^?3 cm tide^?1.     

The biomass of macro- and interstitial fauna on clean and wrack-covered beaches in Western Australia

The benthic faunal spectrum including bacteria, protozoans, meiofauna, wrack epifauna and macrofauna, was quantitatively surveyed on two modally reflective, moderate energy, Western Australian beaches. The more exposed beach had coarser sand, no intertidal macrofauna and a poor interstitial fauna. The less exposed beach had a large deposit of wrack totalling 161 kg m^?1 dry mass concentrated on the lower shore. The amphipod Allorchestes compressa was abundant in the fresh wrack comprising most of the macrofauna. There were also fairly abundant small epifauna on the wrack. Dry biomass of macrofauna, epifauna, meiofauna, protozoans and bacteria was 0, 0, 15, 4 and 180 g m^?1 on the more exposed beach and 160, 3, 112, 9 and 901 g m^?1 on the less exposed beach with wrack. On the latter beach there was an inverse correlation between meiofaunal densities and the densities of protozoans and bacteria, suggesting grazing by the former on the latter. On both beaches meiofauna was concentrated in the mid- to upper beach, protozoans near the surface and bacteria in the mid- to lower beach. It is estimated that bacteria are responsible for most of the secondary production on both beaches.     

Erosive processes on the shore platform of northeast Yorkshire,England

Different processes erode the plane and ramp, the two morphological elements of the shore platform. On the plane, desiccation of the shale causes contraction of the clay lattices in intertidal periods but wetting by the flood tides produces expansion. These movements crack the shale bedding laminae into polygons about 2 cm in diameter which are removed by waves. Desiccation is enhanced in well-drained areas and there is a positive correlation between altitude and erosion rate producing the smooth-sub-horizontal plane. Erosion is highest during summer. It averages 0.1 cm year^?1 but ranges from 0.0 to 0.9 cm year^?1.Corrasion is the main erosive process on the ramp. It is most active during winter, the stormy season, but is influenced by beach depth and possibly grain size. A shallow sand and pebble beach less than 5 cm deep allows erosion at all times. Beach depth is the most important influence on corrasion if it brings the ramp within 5 cm of the surface at some times and buries it more than 13.5 cm deep at others. Wave energy is the most important variable if the beach is usually more than 13.5 cm deep. Erosion rates for the zones of 0–5 cm depth, 5–13.5 cm depth, and greater than 13.5 cm depth were respectively 3.94 · 10^?3 cm tide^?1, 3.26 · 10^?3 cm tide^?1 and 1.13 · 10^?3 cm tide^?1.     

Water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in Western Australia

Volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in Western Australia. The filtered volumes were large, 19 m³ m^?1 day^?1 and 73 m³ m^?1 day^?1 on two ‘clean’ beaches but only 0·4 m³ m^?1 per tidal cycle on a beach covered in kelp and seagrass wrack. The mean residence times of this water in the interstitial system and its percolation paths were both short, 1–7 h and 2–5 m respectively. Water input was greater across a beach cusp horn than across a cusp embayment. Most input occurred in the upper swash zone where the water table was less than 20 cm deep. Tidal variations in input volumes were evident even with tide ranges of only 20 cm. The inshore zone off these beaches filters on average 0·07 m³ m^?2 day^?1 at an average depth of 5·5 m under 0·4 m waves of 6·5 s duration. The importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore ‘lagoon ecosystem’ is estimated and discused.     

基于Argus图像的舟山东沙海滩对连续风暴的响应研究

海滩对风暴的响应是一个复杂的过程,尤其在连续风暴发生时。本研究利用Argus视频监测系统拍摄的连续图像,从海滩地貌、剖面、海滩滨线、海滩宽度等方面,定量分析了舟山东沙海滩对连续风暴"马勒卡"和"暹芭"的响应特征,并初步探讨了影响海滩地形地貌变化对连续风暴响应的因素。结果表明:(1)风暴"马勒卡"发生后海滩单宽体积变化量平均值为?73.75m3/m,风暴"暹芭"发生后海滩单宽体积变化量的平均值为?54.56m3/m,风暴"马勒卡"使整个海滩滨线平均后退14.75m,风暴"暹芭"使得海滩滨线相对于两次风暴前后退10.91m;(2)在海滩自身因素、外部动力因素以及人类活动等共同作用下海滩对连续风暴产生了复杂的响应。     

The distribution and behaviour of tar balls along the Israeli coast

A fortnightly sampling of tar balls on six beaches along the Israeli coastline between 14 April 1975 and 25 June 1976 showed that the mean content of tar during that period was 3625 g m^?1 of beach front. The northern and central parts of the coast were significantly more polluted than the southern part. Between July 1975 and February 1976 the mean tar quantity decreased continuously from 5635 to 1344 g m^?1.A comparison of tar quantities on the Israeli beaches with those of other beaches in the world showed that the Israeli beaches are more polluted than those of the west Atlantic coast, are as polluted as other beaches on the eastern coast of the Mediterranean Sea, and are less polluted than the beaches of Alexandria, Egypt, and Paphos, Cyprus. It is suggested that the tar content on the beach is related to the degree of oil pollution in the sea. The closer a beach is to an oil shipping lane or an oil dumping site, the heavier it is polluted.During storms, beach tar balls are pushed by the waves to the back of the beach or, in the case of a cliffed coast, are carried along the shore by the longshore current. When the tar balls reach a gap in the cliff (such as an estuary), they are carried inland by the storm waves. There the tar may become buried or dry, shrink and break into small particles which are then dispersed by the wind.     

Population Dynamics and Secondary Production of Emerita brasiliensis (Crustacea: Hippidae) at Prainha Beach, Brazil

Abstract. The secondary production and population dynamics of the mole crab Emerita brasiliensis Schmitt, 1935 (Decapoda: Hippidae) were studied by taking monthly samples from June 1993 to May 1995 at each of three intertidal transects at Prainha beach, Brazil. The lifespan was ca. 8 months for males and females, but females showed higher growth, mortality, secondary production, and turnover rate. The higher production in spring versus autumn and winter was related to intense recruitment during that period. The population production was estimated at between 39.86 and 46.88 g (AFDW) · m^?2 · a^?1 for the first year (June 93–May 94) and between 150.95 and 156.07 g (AFDW) · m^?2 · a^?1 for the second year (June 94–May 95); the mean annual biomass was 4.91 and 23.09 g (AFDW) · m^?2, respectively. High P/B rates, between ca. 6 and 9 · a^?1, reflected the fast growth, high mortality, and low lifespan of the population, characterized by a high percentage of recently recruited individuals.     

Runup estimations on a macrotidal sandy beach

This paper presents a methodological approach to calculate runup from the analysis of morphodynamic conditions on a macrotidal sandy beach. The method is based on measurements of the elevation of high-tide deposits and on the analysis of morphological and hydrodynamic changes. A series of measurements has been carried out on the beach of Vougot (Brittany, France) under different wave conditions. This allowed to assess runup formula effectiveness on a macrotidal sandy beach and to determine the best slope parameters to estimate runup. The results suggest that on that macrotidal sandy beach the slope of the active section of the upper beach should be used instead of the entire slope of the foreshore, the latter resulting in an underestimation of runup elevations when used in predictive equations from the literature. Results obtained with widely used equations are relatively well correlated with observed values (r² = 0.63). An analysis of the relationship between observed runup elevations and various variables has enabled the establishment of a runup estimation formula with a relatively good fit to the study site (r² = 0.86).     

In situ sampling reveals rapid uptake and depuration of polycyclic aromatic hydrocarbons by surf clams (Paphies subtriangulata) affected by the Rena oil spill

ABSTRACT

To investigate the uptake and depuration of polycyclic aromatic hydrocarbons associated with the Rena oil spill we sampled the surf clam Paphies subtriangulata at two open coast locations (6?km apart) just prior to oil coming ashore (7 October 2011), then at 1–3 week intervals for the next 4 months. Total polycyclic aromatic hydrocarbons (tPAH) increased at both sites from 1 to 96–124?µg?kg^?1 (wet weight) by 18 October before declining to low levels (<4?µg?kg^?1) by February 2012. Ongoing sampling throughout 2012–2014 included three additional sites to the north east (up to 30?km away) and a site 5?km to the south east revealing tPAH levels generally <10?µg?kg^?1 except in October 2013 where levels ranged between 39–45?µg?kg^?1 at all sites. A comparison of PAH component profiles with oil-contaminated beach sediment indicated that the high levels observed in surf clams between October–December 2011 were clearly associated with the Rena spill. However, the October 2013 peak had a PAH profile inconsistent with weathered Rena oil, suggesting an alternative source of contamination. Our results highlight the potential for P. subtriangulata as a PAH monitoring tool but recognise more study is needed to better quantify baseline levels and uptake and depuration dynamics.     

不同立地类型红树林修复效果评价——以深圳湾为例

为解明不同立地红树林生态修复效果,本研究以深圳湾滨海红树林修复工程为研究对象,选取植物生长状况、修复完成情况和沉积物环境参数3个标准层,以未修复区和裸滩区为对照,分析强风浪海滩、低潮带海滩和砾石质海滩立地条件下红树林修复后的植物群落结构特征和环境质量特征,并基于层次分析法(analytic hierarchy process, AHP)对其修复效果进行综合评价。结果表明：修复3年后,强风浪海滩和低潮带海滩红树植物的保存率明显高于砾石质海滩,均高于60%。沉积物有机质（TOM）、总磷（TP）、溶解无机氮（DIN）和硝酸盐（NO-3 N）含量提高,说明红树林修复对沉积物环境质量有改善作用。深圳湾红树林修复效果评分为：砾石质海滩(3.754)<低潮带海滩(4.397)<强风浪海滩(4.895)。总体而言,深圳湾滨海红树林修复工程的修复效果为优良。     

Beach erosion along the coastline of Alexandria, Egypt

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The effect of nitrite on the spectrophotometric determination of iodate in seawater

A widely used method for determining iodate in seawater involves reaction of the IO₃^? with excess I^?, under acid conditions, to form I₂ which is measured colorimetrically. It is known that when the acidification is by mineral acid, nitrite can interfere with the method by oxidising I^? to I₂ in an analogous way to IO₃^?. Some workers have used sulphamic acid for acidification since it is reported to destroy nitrite in solution.We have investigated the extent of nitrite interference in the colorimetric determination of iodate using both mineral acid and sulphamic acid for acidifying the reaction mixture. In seawater the extent of the interference is equivalent to 0.212 μM 1^?1 IO₃^? per μM 1^?1 NO₂^? with sulphuric acid, and 0.128 μM 1^?1 IO₃^? per μM 1^?1 NO₂^? with sulphamic acid. This means that for a seawater containing 0.31 μM 1^?1 (39 μg 1^?1) IO₃^?, the presence of 0.5 μM 1^?1 NO₂^? will lead to an error of 25% in the iodate determined colorimetrically in methods using sulphuric acid, and 15% in methods in which sulphamic acid is used.     

Formation of beach cusps in a wave tank

Beach cusps with a longshore spacing of 20 to 150 cm have been built by the continuous action of incident waves on a steep laboratory beach floor covered uniformly with a thin bed of glass beads. Breaking of incident waves was observed to induce vortices on the bed by interacting with swash motion along the beach face. Beach cusps formed when the value of a dimensionless parameter H_b/sgT_i² became smaller than 0.042; H_b is the breaking height of the incident waves, T_i their period, s the beach slope and g the acceleration due to gravity. This critical value occurred at a nearly central part of the generation region 0.003 < H_b/sgT_i² < 0.068 for plunging breakers presented by Galvin (1968). Breaking-wave-induced vortices rather than breaker types controlled the movement of bed material in the nearshore zone. Most of the measured spacings of beach cusps, including previous observations, were in good agreement with half a wavelength of the zero-mode subharmonic edge wave, which is generated on the beach by the refraction of incident waves and has twice the period of the waves. The role of edge waves at each stage of cusp formation still remains as an important problem to be clarified.     

Managing coastal erosion: A management proposal for a littoral cell in Todos Santos Bay,Ensenada, Baja California,Mexico

A diagnostic of coastal erosion and shoreline retreat occurring at a 7-km long sandy beach (Littoral Cell III) located in Todos Santos Bay (Baja California, Mexico) is performed trough the analysis of aerial photographs. Around 82,000 m² of this sandy beach have been lost in a 20 year period (1985–2005), at a beach loss rate of 2,100 m² per year. This indicates that coastal erosion is becoming a hazard to human lives and coastal infrastructure. Due to the latter, the implementation of a Shoreline Erosion Management Plan (SEMP) is proposed as the best management approach to deal with the problem. The Littoral Cell III SEMP considers four core policies, eight management strategies and a group of specific measures.     

Sediment oxygen consumption in semi-closed Korean coastal bays during summer

We used an oxygen microsensor for high-resolution measurements of pore water oxygen concentration in semi-closed coastal bays of the South Sea of Korea during summer. The oxygen penetration depths ranged from 0.60 to 3.65 mm. Oxygen consumption rates were estimated to be 9.1 to 59 mmol m^?2 d^?1 (average: 22.8 mmol m^?2 d^?1). At the sediment-water interface, the oxidation rates of organic carbon were estimated to be 84–545 mg C m^?2 d^?1 (average: 211 mg C m^?2 d^?1). Approximately 38% (～211 mg C m^?2 d^?1) of pelagic primary production was regenerated in the surface sediment, indicating the tight benthic-pelagic coupling in the coastal sea of the South Sea of Korea.     

基于Landsat影像的茅尾海河口地貌演变研究

为了揭示茅尾海河口1987~2015年间的地貌格局演变和冲於演变,基于Landsat TM/OLI等多期遥感影像,结合海图、波段比值线性水深反演模型,对28年来茅尾海河口面积变化、地貌类型转换趋势、地貌冲淤演变过程进行了分析。研究结果表明:在1987~2015年间河口面积逐渐缩小;地貌类型转换趋势方面主要表现为潮沟向淤泥滩、河口沙坝的转化,淤泥滩向红树林滩转化;地貌冲淤演变方面,红树林滩淤积面积较大,达20.78km²,淤泥滩的冲刷作用显著,冲刷面积达26.78km²。研究结果可为未来茅尾海资源的开发建设、整治保护提供理论依据。     

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

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.     

Contents of strontinm-90 and ruthenium-106 in beach and shallow water deposits of noto peninsula

⁹⁰Sr,¹⁰⁶Ru, natural strontium and major elements were studied in 12 samples of beach deposits from Togi, Fukuura and Shiga, and in 26 samples of shallow water sediments from sea off Fukuura, Noto Peninsula, Ishikawa Pref., Japan.The average contents of natural strontium and⁹⁰Sr in the beach deposits were 488 ppm ranging from 247 to 1,550 ppm and 45±9 pCi kg^–1-dry mud ranging from 18 to 72 pCi kg^–1-dry mud, respectively. While the average contents of natural strontium,⁹⁰Sr and¹⁰⁶Ru in the sediments were 234 ppm ranging from 136 to 415 ppm, 22±6 pCi kg^–1-dry sand ranging from 7 to 48 pCi kg^–1-dry sand and 0.6 ±0.2 nCi kg^–1-dry ranging from 0.3 to 1.2 nCi kg^–1-dry, respectively.The average contents of each natural strontium and⁹⁰Sr in the beach deposits were about two times higher than those in the shallow water sediments. But no obvious relation of natural strontium to⁹⁰Sr was found in all the samples. The enrichment of⁹⁰Sr and¹⁰⁸Ru in the beach deposits or tthe sediments were as high as 150320 and of 2,0003,000 compared with average contents of⁹⁰Sr and¹⁰⁶Ru in a liter of surface water from the Japan Sea. It is to be noticed that the average¹⁰⁶Ru to⁹⁰Sr ratio of 27 for the shallow water sediments is much higher than the average of 1.0 for surface sea water of the Japan Sea.As to major elements of the samples, the beach deposits are rich in silicon (Av. 70.89 ±0.92% SiO₂), but poor in iron (Av. 2.99±0.32% Fe₂O₃). Whereas the shallow water sediments are poor in silicon (Av. 52.96±10.33% SiO₂) and rich in iron (Av. 5.50±1.90% Fe₂O₃), calcium (Av. 9.64±9.22% CaO) and magnesium (Av. 2.83±1.58% MgO).     

A qualitative and quantitative assessment of the reproductive litter from Posidonia oceanica accumulated on a sand beach following a storm

The biomass of reproductive litter from Posidonia oceanica deposited on a 3.5 km stretch of beach in the north-western Mediterranean, as a consequence of a storm in May 2004, was quantified. The damage caused by this storm to the meadow from which fruits originated was evaluated in terms of loss of seed production. Intermediate fruits (i.e., developing fruits) were the most important reproductive component, followed by immature and damaged fruits. No fully mature fruits were found. No significant differences in the average number of fruits and biomass accumulated were detected among beach sections hundreds of metres apart. Extrapolation of the results at four beach sections indicated that about 1 million fruits were deposited on the entire (3.5 km) beach. This was equivalent to the seed production potential of about 313,217 inflorescences, or a flowered area of 1500 m². The organic input to the beach was 224 kg ash-free dry weight (AFDM). These results suggest that storms may provide an unpredictable source of seed mortality in P. oceanica. The reproductive material produced by storms, however, may constitute an important source of allochthonous organic matter to the beach.