Grain-size distribution and subsurface mapping at the Setiu wetlands,Setiu, Terengganu

A study was carried out around the lagoon and coastal area of Setiu wetlands to determine the general characteristics and grain-size distribution of their sediments. Sediment samples were collected from 39 stations of the lagoon area and 8 stations of the coastal area, and were analyzed for their sedimentological characteristics (mean, sorting, skewness and kurtosis). The sediment mean size ranged between 0.06–2.52 and 2.12–2.69 phi (Ø) for both lagoon and coastal sea-bottom sediments, respectively. Generally, the sediments in the study area consist mostly of coarse to fine particles. The major portions of the sediment are negatively skewed. This indicates that the study area is under the influence of the rather strong wave and current action. The study also encompassed the geophysical survey that was conducted near the coastal zone of the study area. The high-resolution seismic sub-bottom profiling technique is the standard method employed to map geological features and locate structures below the surface of the seafloor. Data obtained from seismic records were used to interpret the seismic reflectors. Three main reflectors (layers), which consist of the seabed and the seabed multiple, were traced using Sonar Web Pro software, and the results showed a uniform distribution pattern for all stations surveyed. It is envisaged that this method could be an effective way to image the marine subsurface structures; thus, its use is anticipated in the higher degrees of sedimentary research and marine resource exploration.     

Influence of friction on erosion and accretion processes in the Yavaros Bay,Gulf of California

A two-dimensional, vertically integrated, nonlinear numerical model was applied to investigate the tide-driven bed load transport of sediments and morphodynamics in the shallow coastal lagoon of Yavaros, located in the southeastern part of the Gulf of California, Mexico. Satellite imagery exposes strong sediment dynamics in this coastal region. The dynamics in the lagoon were forced by 13 tidal constituents at the open boundary. Tides are of a mixed character and they are predominantly semidiurnal. The calculations showed areas of intense tidal currents and considerable water exchange with the Gulf of California. Numerical experiments revealed an ebb-dominant tidal distortion and a net export of sediment from the lagoon to the Gulf of California. A simulation of 20 years showed that the lagoon exported about 1,600 m³ of sediment; however, the daily oscillating exchange of sediment reached values of around 8 m³. The daily averaged flux of export–import sediments oscillates principally with semiannual, monthly and fortnightly periods. By applying a threshold velocity, a variable friction coefficient and the calculated amplitude of tidal velocities, it was possible to determine that morphological changes occur in zones of sharp topographic gradients and to explain the effect of friction on the export–import process of sediments. A 10-year simulation revealed that accumulation of sediment (~20 cm) occurred in small areas, whereas erosion occurred in larger areas but with less intensity (~8 cm). Besides the importance for the morphodynamics, these kinds of erosion–accretion processes may be relevant for the marine ecology.     

Lagoon subsidence and tsunami on the West Coast of New Zealand

Sediment core and trench data from a coastal lagoon on the West Coast of the South Island, New Zealand are used to investigate evidence for co-seismic subsidence and associated tsunami inundation. Physical data are used to document a salt marsh soil buried  80 cm below the modern sediment surface that is locally covered by a gravelly sand bed. The sediment record also contains geochemical and biological (diatom and foram) evidence for abrupt changes in salinity of lagoon waters that link to subsidence, tsunami flooding and to the open versus closed state of the lagoon tidal entrance. At the local scale, these relationships allow for separation of tsunami evidence from other agents of environmental change in the lagoon. We also propose a conceptual connection between these local changes and regional drivers of landscape development, most notably major earthquakes and resultant pulses in sediment supply to the coast.     

Holocene sedimentation on the North Norfolk barrier coast in relation to relative sea-level change

Fourteen distinct sedimentary environments have been recognised in the surface sediments of the intertidal zone of the North Norfolk coast. Nine of these can be distinguished in borehole samples on the basis of sedimentological and micro-palaeontological characteristics. They comprise: gravel; channel sand; intertidal sand; intertidal silty sand; intertidal mud and marsh creek; lower salt marsh; upper salt marsh; dune sand; and peat. Sediment accumulations have been penetrated to a depth of ?8 m OD and basal peats dated by ¹⁴C back to 8410 ± 50 years BP. An overall rate of sediment accumulation (and subsidence) of about 1 m per thousand years is indicated. There is considerable persistence of sedimentary environments in the same areas during up-building, but some erosion and roll-over of the coastal barrier system has occurred. Evidence of positive and negative sea-level tendencies are present in the record, but the main development of the tract is determined by sediment supply to the beach and marshes; positive sea-level tendencies occur at c. 6610, 5970, 4630 and 2790 BP, negative sea-level tendencies occur at 4520 to 4450 and (possibly) 3470 BP.     

Environmental texture and geochemistry of the sediments of a subtropical mangrove ecosystem and surrounding areas,Red Sea Coast,Egypt

The textural and geochemical aspects of the sediments of subtropical mangrove ecosystem and surrounding areas have been studied and discussed. Forty sediment samples were collected from different areas of mangrove environment and surrounding areas along the Egyptian Red Sea coast. The sediments of each study areas are characterized by the abundance of sand with minor amounts of mud and gravel. The mean size of the sediments ranged from medium grained to fine grained at the study areas. Cluster analysis showed that the distribution of gravel, sand, and mud fractions is related to bottom facies and type of sediment source. Generally, sand fraction is the main category among the three constituents. Carbonate content recorded minor values in the study areas. The CaCo₃ content of the sediments ranged from 4.7 % at Hamata area to 64.9 % at Erier area. Terrigenous and biogenic components are the factor controlling of the carbonate content of studies sediments. The organic carbon content ranged from 1.10 at Hamata area to 3.1 % at Sharm el-Qibli and Erier areas, which is controlled by particle size of the sediments. Phosphorus content in the different studied localities is related to the sources of phosphorus to the area. Our observations provide evidence that there are no significant differences in environmental texture and geochemistry of the sediments of subtropical mangrove ecosystem and surrounding areas of the Egyptian Red Sea coast.     

Depositional environment in and around Tamiraparani estuary,and off Tuticorin,Tamil Nadu,India: clues from grain size studies

The sediments of the estuaries and offshore Tuticorin along the southern coast of Tamil Nadu were studied for their textural variation. Ninety sediment samples were collected from three sectors (river, estuary, offshore) on the basis of prevailing energy conditions and oceanographic parameters. Frequency curves show unimodal to bimodal in nature. Offshore samples also fall in bimodal with medium and fine sand where sediment is additionally deposited by the Tamiraparani River. The mean values ranging from 1.69 to 2.01 φ with medium to fine sand. The fine sand in the riverine region indicates the depositional nature of the sediments. In pre-monsoon, the standard deviation ranges from 0.29 to 0.81 φ, which falls in the very well sorted to moderately well sorted. Estuary ranges from 0.63 to 1.30 φ, with moderately sorted, whereas in the marine sediments ranges from 0.4 to 1.01 φ, with moderately to moderately well- sorted and some patches of poorly sorted is observed. In both monsoons, the grain size variations are mostly influenced in river and offshore samples compared to the estuaries. The CM pattern indicates the deposition of sediments in graded suspension. In estuary, the sediments are medium sand with moderately to poorly sorted, fine skewed which are indicative of denudation processes taking place there. In marine, the sediments are medium-to-fine, moderately-to-well sorted, and fine skewed to very fine skewed sediments, probably as a result of the influence of palaeo-sediments deposited by rivers from inland as well as by waves and currents from offshore. Further, the marine samples also highlight depositional processes.     

An Evaluation of Temporal Changes in Sediment Accumulation and Impacts on Carbon Burial in Mobile Bay,Alabama, USA

The estuarine environment can serve as either a source or sink of carbon relative to the coastal ocean carbon budget. A variety of time-dependent processes such as sedimentation, carbon supply, and productivity dictate how estuarine systems operate, and Mobile Bay is a system that has experienced both natural and anthropogenic perturbations that influenced depositional processes and carbon cycling. Sediments from eight box cores provide a record of change in bulk sediment accumulation and carbon burial over the past 110 years. Accumulation rates in the central part of the basin (0.09 g cm^?2) were 60–80 % less than those observed at the head (0.361 g cm^?2) and mouth (0.564 g cm^?2) of the bay. Sediment accumulation in the central bay decreased during the past 90 years in response to both anthropogenic (causeway construction) and natural (tropical cyclones) perturbations. Sediment accumulation inevitably increased the residence time of organic carbon in the oxic zone, as observed in modeled remineralization rates, and reduced the overall carbon burial. Such observations highlight the critical balance among sediment accumulation, carbon remineralization, and carbon burial in dynamic coastal environments. Time-series analysis based solely on short-term observation would not capture the long-term effects of changes in sedimentation on carbon cycling. Identifying these relationships over longer timescales (multi-annual to decadal) will provide a far better evaluation of coastal ocean carbon budgets.     

Stratigraphic evidence for anthropogenically induced coastal environmental change from Oaxaca, Mexico

Previous interdisciplinary paleoenvironmental and archaeological research along the Río Verde Valley of Oaxaca, Mexico, showed that Holocene erosion in the highland valleys of the upper drainage basin triggered geomorphic changes in the river's coastal floodplain. This article uses stratigraphic data from sediment cores extracted from Laguna Pastoría, an estuary in the lower Río Verde Valley, to examine changes in coastal geomorphology potentially triggered by highland erosion. Coastal lagoon sediments contain a stratigraphically and chronologically distinct record of major hurricane strikes during late Holocene times. Three distinct storm facies are identified from sediment cores obtained from Laguna Pastoría, which indicate that profound coastal environmental changes occurred within the region and are correlated with increased sediment supplied from highland erosion. The Chione/Laevicardium facies was deposited in an open bay while the Mytella/barnacle facies and sand facies were deposited in an enclosed lagoon following bay barrier formation. We argue that highland erosion triggered major geomorphic changes in the lowlands including bay barrier formation by 2500 cal yr B.P. These environmental changes may have had significant effects on human populations in the region. The lagoon stratigraphy further indicates an increase in mid–late Holocene hurricane activity, possibly caused by increased El Niño frequencies.     

河海交互作用沉积与平原地貌发育*

河流是搬运陆源泥沙的主要动力,对相邻的海岸海洋沉积动力有巨大影响。中国河流汇入海洋中的泥沙曾占全球入海泥沙的10 ％ ,现代中国边缘海大陆架在晚更新世时曾是海岸平原,河-海交互作用是形成海岸平原与浅海输积泥沙的主要因素。本文选择5个不同类型的河流展示其不同的泥沙运动与河口沉积的特性以及对相邻陆架之影响,包括: 1)强潮型动力的鸭绿江河口湾,形成从陆向海与从海向陆的双向水流交汇沉积,海岸形成潮流脊体系。 2)季风波浪为主导动力的滦河口,以泥沙的横向运动为主,形成沙坝环绕的双重海岸,沉积粒径自海向陆减小; 沿岸浪流携运泥沙向河口两侧分布,使沙坝具有沙咀状的复合特点。 3)弱潮型、多沙的黄河口,径流于两侧堆积指状沙咀,沙咀下风侧形成粉砂粘土淤泥湾,沿岸流携运泥沙向渤海湾延伸为淤泥舌。 4)径流与沿岸流组合作用的沉积模式,以长江口为代表,泥沙沿岸向南输运为主导,向海岸与向内陆架构成颗粒变细的带状沉积,外陆架出露残留砂。 5)充填河口湾的三角洲,以珠江为代表,河流分汊与会潮点泥沙堆积,悬移质扩散至湾外,被沿岸流携带沿海岸向SW运移,外陆架为残留砂沉积。20世纪80年代以来,上述河流均受到人为活动的改造影响,河流自然过程与河海交互作用效应均发生改变。本文主要以滦河三角洲为例阐述河-海交互作用与平原的地貌特征。     

Evidence for 17th-century tsunamis generated on the Kuril–Kamchatka subduction zone, Lake Tokotan, Hokkaido, Japan

In the seventeenth century, two tsunamis that were generated by earthquakes on the Kuril–Kamchatka subduction zone inundated the eastern coast of Hokkaido, northern Japan. Stratigraphic evidence for these two tsunamis and related land-level change in coastal Hokkaido consists of two landward-thinning sand layers in the sediments of Lake Tokotan, a coastal lagoon on the Hokkaido coast. The marine origin of these sand layers is indicated by the presence of brackish–marine diatoms. The rarity and high degree of fragmentation of diatom valves suggests that the sands were transported in a short time over a considerable distance. Tsunamis at this site were probably generated by great earthquakes along the Kuril–Kamchatka Trench. Volcanic ash deposits lying just above the sands suggest that tsunamis occurred in the late 17th century. Tsunamis during the historic period are not recorded in Lake Tokotan, which suggests that the sand layers were deposited by tsunamis substantially larger than historic tsunamis.     

Contemporary Rates of Carbon Sequestration Through Vertical Accretion of Sediments in Mangrove Forests and Saltmarshes of South East Queensland,Australia

Mangrove forests and saltmarshes are important habitats for carbon (C) sequestration in the coastal zone but variation in rates of C sequestration and the factors controlling sequestration are poorly understood. We assessed C sequestration in Moreton Bay, South East Queensland in mangrove forests and tidal marshes that span a range of environmental settings and plant communities, including mangrove forests and tidal marshes on the oligotrophic sand islands of the eastern side of Moreton Bay and on the nutrient enriched, western side of the bay adjacent to the city of Brisbane. We found that rates of C sequestration in sediments were similar among mangrove forests over the bay, despite large differences in the C density of sediments, because of different rates of vertical accretion of sediments. The C sequestration on the oligotrophic sand island tidal marshes, dominated by Juncus kraussii, had the highest rate of C sequestration in the bay while the western saltmarshes, which were dominated by Sarcocornia quinqueflora, had the lowest rate of C sequestration. Our data indicate C sequestration varies among different tidal wetland plant community types, due to variation in sediment characteristics and rates of sediment accretion over time.     

Sedimentological and geoenvironmental evaluation of the coastal area between Al-Khowkhah and Al-Mokha,southeastern Red Sea,Republic of Yemen

The increasing anthropogenic activities (e.g., constructing touristic resorts) have led to notable changes in the Yemeni Red Sea coastal regions. In this context, recent sediments have been investigated to infer possible natural and man-induced processes on these coastal areas. The target area lies between longitudes 43°13′–43°30′E and latitudes 13°15′–13°55′N. It extends about 90 km along the coastline as a part of the Tihama plain. Geomorphologically, it forms a long-curved stretch with pronounced headlands, embayments and bays. Generally, it is covered by recent sediments (wadi, lagoon, beach and spit deposits along with sabkha, coastal dunes and mangrove). Textural studies reveal that most of the studied sediments are mainly poorly to moderately sorted and are composed mainly of sandy fractions with few gravel and mud, mostly bimodal with minor unimodal patterns. The igneous (granites) as well as basic (basalt, andesite and andesitic pyroclastics) and acidic (dacite and rhyolite) volcanic rocks of Tertiary age, which are exposed to the east of the study area, are believed to be the source of pyroxenes, amphiboles, epidotes, biotite, sphene, zircon, tourmaline and rutile, in a decreasing order of abundance. Moreover, smectite, kaolinite, chlorite, illite and palygorskite are the predominant clay minerals, mainly of detrital origin. The total carbonate content fluctuates from 37.41% (lagoon sediments) to 53.74% (sabkha sediments). The high amount of sea grasses, which covers the tidal flat zone and relates to the fine-grained sediments, accounts for the high organic matter content. The mineralogy of the source rocks has controlled the general distribution of major elements (Fe, Mg, Na, K and Mn) in the beach sediments. In such sediments, the concentrations of the heavy metals (Cu, Zn, Cd, Ni, Pb and Co) may reflect the sediment pollution using different approaches. The enrichment factors (EFs) of the trace metals for most samples reveal values that are greater than 1, referring to three groupings, which are: moderate to moderately severe (Zn, Cu and Mn), minor to moderate (Pb and Co) and zero to minor (Cd and Ni) enrichment. The EFs for Pb, Cd, Ni and Co metals (<5) may be attributed to the crustal materials and/or natural weathering processes. But, those for Zn, Cu and Mn (>5), especially in Al-Khowkhah–Abu-Zahr, Moushij–Zahari–Ruays, Yokhtol and Mokha localities, are possible of anthropogenic contributions.     

Indications of an extreme event deposits along the west coast of India: evidences from GPR investigations

The ground-penetrating radar (GPR) was used to trace the subsurface details in the Palshet coastal zone (Maharashtra) as it exhibits an interesting array of geomorphological features. Furthermore, our main goal was to identify and locate features that might have formed during a reported extreme event and its effects on the flow of the nearby Sundri River. Two profiles (8 and 4 m depth) were collected across the beach and along the backshore, respectively. While the 8-m depth profile (west to east; across the beach) indicates a series of coastline regression in this area, the 4-m depth profile along the coastline (north to south) in the backshore zone reveals two significant incidents viz., (1) stages of development of the paleo-channels that indicate the migration of the Sundri River towards south and (2) huge sediment deposits up to 2.5-m thick in the backshore area. The erosional relict surface (~2.5 m depth) was traced along with various spells of sediments that perhaps occurred due to an extreme event. Sand samples were collected from two trial pits along the GPR profiles to understand the sedimentology and mineralogy in the backshore area. These data together with beach profiles and geomorphological maps suggest that the sands were deposited by an extreme event perhaps during the 1854 cyclonic storm. The sands were trapped in suitable geomorphological sites along the Palshet coast and these sand deposits of about 2.5 m thickness forced the River Sundri to shift its course towards the south. This new revelation facilitates a further study that could focus on the nearby coastal areas to document such extreme event deposits and their influence on the geomorphic set-up.     

白沙口海岸带沉积物的床面形态及层理构造

各种类型的沉积物床面形态及层理构造大量保存在沉积岩中,成为恢复古沉积环境和古地理的重要标志之一。1981年,作者在山东白沙口海岸,对海岸带不同地貌条件下的床面形态系列及层理构造进行了观测,并对其形成过程进行了探讨。     

An analysis of beach profile changes subsequent to the Colombo Harbor Expansion Project,Sri Lanka

Man-made coastal structures directly affect sediment balance and sediment dynamics on the surrounding beaches. The Colombo Harbor Expansion Project has created about 5-km-long breakwater nearly perpendicular to the beach. The present study is focused on quantitatively and qualitatively analyzing the effect of the Colombo Harbor Expansion Project on economically important beaches in and around Colombo city area. In this study, the authors measured monthly variations of beach width, beach profile and the mean grain-size of the sediments at mean sea level for complete annual monsoon cycle. Data were analyzed to establish site-specific erosion vulnerability. Monitoring results show that cumulative beach erosion has increased after the construction of the breakwater (rate = 0.7 m/year from May 2000 to April 2011 and rate = 28.2 m/year from April 2011 to June 2012). In addition, the cumulative and site-specific sand accretion and erosion patterns have a clear relationship with the monsoon seasonality. Beaches were narrower during the stormy southwestern monsoon, whereas beaches were wider during fair weather of northeast monsoon and inter-monsoon periods. In contrast, the constructed breakwater obstructs natural longshore sediment dynamics. For example, a significant amount of sediments from the Kelani-Ganga River were buried in the Colombo Harbor due to alteration of prominent longshore sediments transportation on the western coast of Sri Lanka. Therefore, this study shows enhancement of coastal erosion in the studied southern beaches due to a lack of sediment deposition.     

Carbonate sediment transport pathways based on foraminifera: case study from Frank Sound, Grand Cayman, British West Indies

Foraminifera can be used to determine the source(s) of carbonate sediment and the directions of sediment transport in shallow, coastal lagoons such as Frank Sound on the south-central coast of Grand Cayman. These determinations, based on the distribution of foraminiferal assemblages and ‘tracer species’ (numerically abundant species that live in known physiographic units and/or ecological conditions), show that the lagoonal sediments are a mixture of grains that originated in the lagoon and forereef. The variable proportions of these foraminifera throughout the lagoon reflects the dynamic processes that control lagoonal sedimentation. Amphistegina gibbosa, Discorbis rosea, and Asterigerina carinata lived in the forereef environment. The fact that these ‘tracer species’ are found throughout Frank Sound and in the beach sands, shows that they were transported across the reef crest and the lagoon. Abrasion-resistant Archaias angulatus, a‘tracer species’ indicative of a lagoonal setting, forms up to 50% of foraminiferal assemblages found in the lagoonal sediments. Preferential winnowing of small tests from these populations indicates sorting under high energy conditions. The vertical distribution of the forereef and lagoonal foraminifera in the sediment blanket that covers the floor of Frank Sound indicates that these processes are temporally persistent. Transportation of forereef foraminifera into and around the lagoon and sorting of the lagoonal foraminifera cannot take place under ‘normal’ conditions when the tranquil lagoon is characterized by weak currents. Storms and/or hurricanes, however, generate short-lived high-energy events that can move and sort the sediment and foraminifera. At the height of a storm, water and sediment are moved over the reef and then piled and held onshore by the onshore winds and the constant flow of water over the reef and across the lagoon. These currents can mix some of the lagoonal and forereef sediments. As a storm wanes, however, the ‘piled water’ flows offshore via strong rip currents that pass into the ocean through the channels which transect the reef. These currents winnow and/or strip sediment from the lagoon and may transport lagoonal sediments into the forereef area. As a result, residual lagoonal sediment is commonly characterized by larger and abrasion-resistant foraminifera.     

Temporal and spatial evolution of the coastal profiles along the Yellow River Delta over last three decades

The subaerial delta of the Yellow River has undergone a notable reshaping process with drastic changes in erosion and accretion patterns both temporally and spatially. These morphological changes not only have significant impact on the long-term evolution of delta but also pose severe threat to the existing infrastructures adjacent to the eroding delta lobe. This paper presents a data-based study of waves, currents, sediments and subaqueous bedforms including the application of Principal Component Analysis (PCA) to the measured coastal profiles in order to understand qualitative and quantitative processes that are responsible for the observed changes. The results demonstrated that the Yellow River Delta has recently been dominated by recession process due to the reduced sediment supply from the Yellow River in the recent decades. A critical threshold of river sediment discharge was formulated and used to explain the observed morphodynamic processes. It was found that the coast of the Yellow River Delta could be broadly divided into three geomorphic zones: the area near abandoned delta, the estuarine area, and Laizhou Bay. At the nearshore zone of the abandoned delta, waves are the main agent for bed erosion and sediments suspension. The tidal current is effective in transporting suspended sediments and exerts the main control on the depths of the erosion–accretion balance zone on the coastal profiles. The area near the present estuary has seen rapid deposition with the progradation rate being governed by the relative intensity of fluvial and marine processes while the coasts in Laizhou Bay are stable and the particular characteristics of the tidal current field prevent the sediments supplied by the Yellow River from reaching this area.     

Application of Plutonium Isotopes to the Sediment Geochronology of Coarse-Grained Sediments from Englebright Lake,California (USA)

The determination of sediment accumulation rates in environments with temporal variations in texture is challenging using traditional radioisotope methods, largely due to low activities associated with coarse sediments. This study used Englebright Lake, an impoundment in northern California, as a model system to examine the application of plutonium isotopes in lacustrine environments where the interlayering of coarse and fine sediments complicates the geochronology. Inductively coupled plasma mass spectrometry was used to quantify plutonium isotopes and low limits of detection allowed for the measurement of plutonium in sand, clay, and silt fractions. Although measurable levels of plutonium were found in sand fractions, over 75 % of the total plutonium activity was found in fine-grain-size fractions (<63 μm). Correlations between cesium-137 and plutonium activities in fine-grained sediments (r = 0.81–0.98, p < 0.005) suggest that plutonium isotopes may be substituted for cesium isotopes in coarse-grained sediments where cesium is typically below detectable levels. Sediment accumulation rates calculated from grain-size normalized plutonium activity profiles ranged from 6 to 145 cm year^?1 in Englebright Lake and identified a sediment depocenter at the delta front upstream of Englebright Dam. Progradation of the delta front reflected changes in sediment supply from the watershed in response to flood events, whereas average annual accumulation responded to human impacts. This study extends the application of plutonium isotopes for sediment geochronology to aquatic environments dominated by coarse sediments and provides new information that contributes to a better understanding of the processes influencing sediment deposition in Englebright Lake.     

Accumulation discrepancy of heavy metal and organic pollutants in three near-shore depositional environments, southeastern China

Heavy metal and organic pollutants in sediments along the coastal zone of southeastern China have been investigated. Sediment samples are retrieved from three depositional environments: coast, estuary, and tide-affected river mouth. The relative abundance of heavy metal and organic pollutants is related to their geochemical properties as well as depositional environments and anthropogenic discharge. Based on a sequential extraction method, it is revealed that anthropogenic Pb, Cr, Cu, and Cd are mainly bound to Fe–Mn oxides, suggesting that adsorption and co-precipitation of Fe–Mn oxides are in the control of their transfer processes from water column to sediment. Heavy metal bound to carbonates is also an important pool especially for Cd, Mn, and Pb. The main organic pollutants found in the study area include petroleum-related alkanes, phthalic acid ester, organic silicon, chlorophenol, phenyl ether, and amine. The accumulation of heavy metals and organics in surficial sediments has a decrease tendency from estuarine environment to coastal environment and to tide-affected river mouth.     

Impacts of relative sea level rise on the shoreface deposition,Shuidong Bay,South China

The influence of relative sea level rise on shoreface deposition helps to elucidate changes in beach and nearshore geomorphology in response to different forcing factors. In this study, two sets of sediment samples, one from 1982 and one from 2004, from the Shuidong Bay of South China were analyzed to determine the changes in shoreface depositions. An EOF (Empirical orthogonal function) method was used to examine how these depositions changed based on the relative sea level rise. The results show that shoreface sediments of Shuidong Bay are mainly composed of sand. Fine-grained sediments are distributed in the lower shoreface/offshore area, and coarse-grained sediments are mainly found in the upper shoreface/nearshore area. Due to the altered hydrological forcing caused by relative sea level rise, the sand fraction in sediments increased from 84.7 % in 1982 to over 90 % in 2004, and the clay and silt fractions decreased from 11.8 % in 1982 to 5.6 % in 2004. Grain-size parameters in sediments in 2004 became coarser, slightly more well sorted, less skewed and had lower kurtosis than those in 1982. In addition, the shoreface deposition of Shuidong in 1982 and 2004 is distinctly different: a polarized mode was described by the first eigenfunctions, and a homogenized mode was described by the second eigenfunctions. The former means that the sediment components developed towards the two opposite poles, undergoing both coarsening and refining processes. The second mode indicates that the secondary variation in sediment components was mostly in the three intermediate-grained sand components. In the future, the Shuidong Bay shoreface may be subjected to even further erosion because of increases in the energy of the environment resulting from rapid relative sea level rise.