Sediment characterisation of the 26 December 2004 Indian ocean tsunami in Andaman group of islands, bay of Bengal, India

The large tsunami, which was generated by an earthquake on 26 December 2004, affected most of the countries around the Indian Ocean. A total of 48 tsunamigenic surface sediments have been collected from various coastal geomorphological features such as beaches, estuaries/creeks and mangrove areas in the Andaman group of islands. These samples were analysed for sediment characteristics such as sediment texture, granulometric studies. The studied tsunamigenic sediments, deposited by the 26 December 2004 tsunami in the Andaman group of islands consist of poorly sorted, coarse sand to medium sands, and are similar to depositional effects of previously reported earthquake-generated tsunami waves. The tsunamigenic sediment consists of a coarse sand layer with abundant reworked shell and other carbonate fragments. The tsunami sediments were mainly composed of boulders of corals and sand which determines the high-energy environment throughout the study area. The variation in Ф mean size, therefore, reveals the differential energy conditions that lead to the deposition of these kinds of sediments in different locations. The tsunamigenic sediments were mainly poorly sorted, moderately well sorted and well sorted during the post-tsunami (2005) and whereas they were mainly moderately well sorted to well sorted during the post-monsoon (2008). The symmetry of the samples varies from strongly fine skewed to strongly very coarse skewed in the post-tsunami (2005) and post-monsoon (2008). The Kurtosis of the tsunami sediments were mainly Platykurtic, Mesokurtic and Lepokurtic during the post-tsunami (2005) and mainly Mesokurtic and Lepokurtic in post-monsoon (2008).     

Assessment of coastal dune characteristics using georadar imaging and sedimentological analysis: Odisha and Visakhapatnam, India

The East coast of India is subject to continuous changes by high energy events. We sought to assess the depositional conditions along the coast from the geophysical and sedimentological character of the dune sands of the Gopalpur and Paradeep coast of Odisha, and the Sagarnagar coast of North Visakhapatnam. Quartz layers of the heavy mineral-rich zone collected at a depth of ~2 m from the landward foot of the dunes in the Visakhapatnam and Odisha coast, gave the OSL age estimates as 1,050?±?50 and 260?±?10 years respectively, revealing that the age of the dunes in Visakhapatnam are older than those on the Odisha coast. Episodic high energy events have affected the coast. Evidence from ground penetrating radar data consists of three stratigraphic units. The upper unit consists of vague reflections, parallel to the ground in continuous manner, most probably formed by wind action. On the other hand, the middle layer shows high amplitude reflections of heavy mineral-rich massive layers, possibly the result of tsunami activity. The lower massive layer parallel to the ground surface shows a low reflection pattern. The GPR studies showed that the thickness of the heavy mineral layers is greater on the landward foot of the dune as compared to that on the seaward side. According to the grain size analysis, the dune is composed of both wind generated and tsunamigenic sediments. The scanning electron microscope studies revealed that the heavy minerals present in the dunes are mainly sillimanite, ilmenite, garnet, pyroxene, rutile, sphene, biotite, hornblende, zircon, monazite and magnetite. The study demonstrates the origin of sand dunes in different ages along the East Coast of India by the effect of various natural phenomena.     

Numerical simulation of the impacts of reflected tsunami waves on Pulo Raya Island during the 2004 Indian Ocean tsunami

There are numerous small populated islands near western Sumatra in Indonesia. The Weh, Banyak, Mentawai, and Enggano islands are home to many Indonesians. These small islands have been found to be effective at reducing tsunami wave energy on several occasions. At the same time, they are situated around Sumatras active subduction zone and are often among the areas most affected by tsunamisas in the case of Pulo Raya Island, in the western Aceh Jaya district about 800 m from Sumatra. Pulo Raya was devastated by the 2004 Indian Ocean tsunami. This study investigates the hydrodynamic processes of reflected tsunami waves and their impact on Pulo Raya, using a Cornell Multi-grid COupled Tsunami (COMCOT) model to simulate the tsunami wave runup and subsequent hydrodynamic processes. The simulation confirms eyewitness accounts that it was not the initial runup, but the reflected waves that devastated the worst-hit areas of the island. As a result, we can recommend that governments and communities on small islands need to anticipate the impacts of reflected waves following a tsunami, especially at lee side of of the island that was perceived to be a safer place by the island community before the 2004 Indian Ocean tsunami.     

Chromium geochemistry in coastal environment of the Western Harbour,Egypt: water column,suspended matter and sediments

The distribution of Cr between water, total suspended matter (TSM) and sediments in the maine harbour in Egypt (Western Harbour), has been studied in two surveys. Dissolved Cr displayed a negative association with salinity, indicating land sources outlets as a major source of inputs for it. The Harbour presents higher Cr concentrations in dissolved form above the background (0.17 μg/L) concentration for total dissolved Cr. The most important factors controlling the distribution of particulate Cr in the Western Harbour are the depositional from several activities inside the Harbour, as well as different charges from several landbased sources along its southern edge. Chromium was associated in decreasing amount in the: residual >oxidizable-organic >acid reducible >exchangeable fractions of the analyzed sediments. Therefore, the results indicate that Cr in sediments from W.H is not available for exchange and/or release into the marine environment.     

Froude scaling limitations in modeling of turbidity currents

The scaling problem associated with the modeling of turbidity currents has been recognized but is yet to be explored systematically. This paper presents an analysis of the dimensionless governing equations of turbidity currents to investigate the scale effect. Three types of flow conditions are considered: (i) conservative density current; (ii) purely depositional turbidity current; and (iii) mixed erosional/depositional turbidity current. Two controlling dimensionless numbers, the Froude number and the Reynolds number, appear in the non-dimensional governing equations. When densimetric Froude similarity is satisfied, the analysis shows that the results would be scale-invariant for conservative density current under the rough turbulent condition. In the case of purely depositional flows, truly scale-invariant results cannot be obtained, as the Reynolds-mediated scale effects appear in the bottom boundary conditions of the flow velocity and sediment fall velocity. However, the scale effect would be relatively modest. The Reynolds effect becomes more significant for erosional or mixed erosional/depositional turbidity currents as Reynolds-mediated scale effects also appear in the sediment entrainment relation. Numerical simulations have been conducted at three different scales by considering densimetric Froude scaling alone as well as combined densimetric Froude and Reynolds similarity. Simulation results confirm that although the scaling of densimetric Froude number alone can produce scale-invariable results for conservative density currents, variations occur in the case of turbidity currents. The results become scale invariant when densimetric Froude and Reynolds similarities are satisfied simultaneously.     

Geochemistry of heavy metals in bottom sediments from streams of the western coast of the rio de la plata estuary, Argentina

The fluvial system within the southwestern coastal sector of the Río de la Plata interacts with a very large and efficient mixing basin known as the Río de la Plata estuary. The region is a densely populated and productive sector of Argentina and is characterised by a temperate humid climate. The streams Carnaval, Martín, Del Gato and El Pescado of the study area drain two main geomorphologic units: a higher inner zone and the low lands of the coastal plain. In particular, the Del Gato stream receives heavily polluted discharges from agricultural, urban and industrial point and non-point sources of pollution, while the other streams collect a lower and variable discharge input. As a part of an initial assessment of the role of fluvial bottom sediments in the fate of metals through the stream ecosystems, the spatial distribution of trace and major elements related to particles in the accumulation areas was examined. Concentration of Cr, Ni, Cu, Zn, Cd, Hg, Pb, Fe and Mn, grain size, mineralogy (clay-X ray diffraction) and organic matter content were analysed in the four streams considering both geomorphologic units at different depositional time. Untreated and iron-normalised trace metal concentrations in the most polluted streams show higher levels in the upper layers of most contaminated sectors and accumulation areas associated to topographic low lands. The coastal plain sector behaves as a regional sink between the upstream area and the estuary.     

Field and GIS based post-tsunami assessment of Scleractinian coral cover in the Aerial Bay group of Islands, North Andaman, India

The Aerial Bay group of Islands are one of the diverse environments of Andaman & Nicobar Islands, where the coral reefs degraded much due to the natural calamity of tsunami on 26 December 2004. After this event, the entire North Andaman Islands got elevated, which resulted in the exposure of coral reefs during low tide, causing mass mortalities and destructions to this pristine environment. In order to understand the current status, bio-physical monitoring of coral reefs was carried out and compared with classified coral map of pre-tsunami period. A decline from 411.14 to 68.25 hectares (ha) of live coral area was observed in the Aerial Bay group of Islands. The dead corals and other abiotic factors (sand, mud and rubble) were observed to be 317.33 and 25.56 ha respectively, based on comparisons between ground truthed and classified pre-tsunami coral map (2004) processed in ArcGIS®. The detrended correspondence analysis of coral life form categories showed maximum cover of dead coral with algae, in comparison with the live corals. Bray-curtis cluster analysis revealed three different groups of study sites with 60 % similarity based on life-form categories within the coral reef environment.     

海洋风化溢油鉴别中特殊芳烃标志物的应用

对母质来源、沉积环境和成熟度各异的原油样品进行风化模拟实验,并对实验产物进行GC-MS分析,最后基于油气地球化学手段对多环芳烃风化溢油鉴别的可行性、原理、常用指标等进行探讨,结果表明,不同油样中同一芳烃生物标志化合物比值参数鼍值问有显著性差异;对同一油样的风化和未风化样品而言,同一烷基化多环芳烃特征比值参数的变异系数为6.51%-17.68%,而成熟度指标的变异系数通常小于8%;芳烃中烷基萘和"三芴"的分布特征、甲基萘指数、甲基菲指数和烷基化多环芳烃同系物的双比率可以作为重风化溢油鉴别的有效指标.     

The land-cover cascade: relationships coupling land and water

We introduce the land-cover cascade (LCC) as a conceptual framework to quantify the transfer of land-cover-disturbance effects to stream biota. We hypothesize that disturbance is propagated through multivariate systems through key variables that transform a disturbance and pass a reorganized disturbance effect to the next hierarchical level where the process repeats until ultimately affecting biota. We measured 31 hydrologic, geomorphic, erosional, and substrate variables and 26 biotic responses that have been associated with land-use disturbance in third- and fourth-order streams in the Blue Ridge physiographic province in western North Carolina (USA). Regression analyses reduced this set of variables to include only those that responded to land cover and/or affected biota. From this reduced variable set, hypotheses were generated that predicted the disturbance pathways affecting each biotic response following the land-cover-cascade design. Cascade pathways began with land cover and ended with biotic responses, passing through at least one intermediate ecosystem abiotic component. Cascade models were tested for predictive ability and goodness-of-fit using path analysis. Biota were influenced by near-stream urban, agricultural, and forest land cover as propagated by hydrologic (e.g., discharge), geomorphic (e.g., stream bank height), erosional (e.g., suspended sediments), and depositional streambed (e.g., substrate size) features occurring along LCC pathways, reflecting abiotic mechanisms mediating land-cover disturbance. Our results suggest that communities are influenced by land-cover change indirectly through a hierarchy of associated abiotic components that propagate disturbance to biota. More generally, the land-cover cascade concept and experimental framework demonstrate an organized approach to the generic study of cascades and the complex relationships between landscapes and streams.     

Sediment manganese and biogenic silica as geochemical indicators in estuarine salt marshes of coastal Georgia, USA

Salt-marsh estuarine sediments are not homogeneous. It is obvious that a steady state cannot be assumed if the depositional environments under which salt marshes accumulate change from subtidal through non-vegetated intertidal to vegetated intertidal state during their formation. In addition to these, the supply of sedimentary material depends on the tidal prism which changes as salt marshes are formed. Based on the study of cores collected in the estuarine region of Georgia, USA, it was found that the Mn/Al ratios in sediments of marsh cores change from subtidal through non-vegetated intertidal to vegetated intertidal. The relative variation of biogenic silica preserved in sediments of marsh core reflects the relative supply rate of organic carbon (phytoplankton) produced in the water column to the sediment surface at the time of deposition. In this paper it is proposed that sediment manganese and biogenic silica may be applied as geochemical indicators of changing depositional environments and organic carbon originating from phytoplankton in the estuarine salt marsh sediments.     

The potential impact of geological environment on health status of residents of the Slovak Republic

In order to assess the potential impact of the geological environment on the health of the population of the Slovak Republic, the geological environment was divided into eight major units: Paleozoic, Crystalline, Carbonatic Mesozoic and basal Paleogene, Carbonatic-silicate Mesozoic and Paleogene, Paleogene Flysch, Neovolcanics, Neogene and Quaternary sediments. Based on these geological units, the databases of environmental indicators (chemical elements/parameters in groundwater and soils) and health indicators (concerning health status and demographic development of the population) were compiled. The geological environment of the Neogene volcanics (andesites and basalts) has been clearly documented as having the least favourable impact on the health of Slovak population, while Paleogene Flysch geological environment (sandstones, shales, claystones) has the most favourable impact. The most significant differences between these two geological environments were observed, especially for the following health indicators: SMRI6364 (cerebral infarction and strokes) more than 70 %, SMRK (digestive system) 55 %, REI (circulatory system) and REE (endocrine and metabolic system) almost 40 % and REC (malignant neoplasms) more than 30 %. These results can likely be associated with deficit contents of Ca and Mg in groundwater from the Neogene volcanics that are only about half the level of Ca and Mg in groundwater of the Paleogene sediments.     

Beach erosion and geochemical factors: Influence on spawning success of horseshoe crabs (Limulus polyphemus) in Delaware Bay

Horseshoe crab spawning activity is spatially patchy within the Delaware Estuary. This study investigated the importance of geochemical and erosional factors to the selection of breeding beaches. Two sandy beaches in Cape May county, New Jersey, USA, were studied; one beach had been subjected to considerable erosion, exposing underlying peat; the second beach, less than 1 km away, had only traces of peat. Reduced sediments with high levels of hydrogen sulfide were correlated with the presence of peat, and significantly fewer crabs utilized sediments in the proximity of peat beds for reproduction. The lower spawning activity on the beach in the vicinity of exposed peat, suggests that crabs may detect, at a distance, the nature of sediments and the quality of beach for spawning activity. Active salt marsh and peat-bank sediments dominate the upper bay shore; these sediments are unsuitable, or at best marginal, for horseshoe crab reproduction. Extensive bulkheading of eroding sandy beach along several New Jersey shore communities has further restricted the availability of suitable spawning habitat, making the remaining stretches of optimal sandy beach critical to the reproductive success of this species.     

Effect of elevated CO2 on coarse-root biomass in Florida scrub detected by ground-penetrating radar

Growth and distribution of coarse roots in time and space represent a gap in our understanding of belowground ecology. Large roots may play a critical role in carbon sequestration belowground. Using ground-penetrating radar (GPR), we quantified coarse-root biomass from an open-top chamber experiment in a scrub-oak ecosystem at Kennedy Space Center, Florida, USA. GPR propagates electromagnetic waves directly into the soil and reflects a portion of the energy when a buried object is contacted. In our study, we utilized a 1500 MHz antenna to establish correlations between GPR signals and root biomass. A significant relationship was found between GPR signal reflectance and biomass (R2 = 0.68). This correlation was applied to multiple GPR scans taken from each open-top chamber (elevated and ambient CO2). Our results showed that plots receiving elevated CO2 had significantly (P = 0.049) greater coarse-root biomass compared to ambient plots, suggesting that coarse roots may play a large role in carbon sequestration in scrub-oak ecosystems. This nondestructive method holds much promise for rapid and repeatable quantification of coarse roots, which are currently the most elusive aspect of long-term belowground studies.     

Mercury distribution,speciation and potential ecological risk assessment in sediments from Lake Taihu,China

Abstract

Twenty-one surface sediments collected from seven surroundings areas of Lake Taihu in two different years were analyzed for total mercury (THg) concentrations, physicochemical characteristics and speciation using a sequential extraction method to assess spatial distribution, sources, and potential ecological risk. Surface sediments from Lake Taihu contained elevated levels of Hg in two sampling years with THg levels ranging from 77 to 346?ng/g (mean 145?ng/g) in October 2010 and ranging from 122 to 573?ng/g (mean 266?ng/g) in November 2012, respectively. The mean THg concentrations in all studied surface sediments exhibited an increasing trend over time. The oxidizable fraction (F3) and residual fraction (F4) were the predominant Hg species in sediments, while more mobile Hg phases of acid-soluble fraction (F1) and reducible fraction (F2) made up less than 0.5% THg. Significant relationships were found between total organic carbon (TOC) and THg and geochemical speciation indicating an important role for organic matter in affecting distribution, mobility, and bioavailability of Hg in sediments. As evidenced by Hakanson’s potential risk index the total ecological risk of Hg was low in the entire Lake Taihu in 2010 but considered moderate in Zhushan Bay, West Coast, and Meiliang Bay in 2012. These findings provide conservation managers with information needed to more effectively regulate the environment of Lake Taihu.     

菹草生长对沉积物间隙水中各形态磷浓度的影响

通过人工构建湖泊生态系统,用湖泊沉积物的上层泥和下层泥分别代表清淤前后的2种基质,研究菹草(Potamogeton crispus)生长对沉积物不同层次间隙水中各形态磷浓度的影响.垂直方向上,将2种基质中的间隙水分为表层、中层和底层3个层次.结果表明,菹草生长能够不同程度地降低各层间隙水中磷浓度,上层泥和下层泥2种基质均表现为表层间隙水溶解性总磷(DTP)和溶解性活性磷(SRP)含量降低幅度最大,DTP含量分别降低68.97％和83.09％,SRP含量分别降低54.57％和96.02％.菹草的吸收作用使得各层间隙水中磷浓度均低于无沉水植物的对照组.试验结束时,2种沉积物中TP含量降低幅度差异不显著,说明疏浚前后种植菹草均可有效控制湖泊内源磷污染.     

Resuspension and growth ofOstrea edulis: A field experiment

Field experiments withOstrea edulis L. were conducted to examine the effects of resuspension on subtidal oyster growth in a small cove in malifax County, Nova Scotia. Removable racks with strips of fixed juvenile oysters were placed at 4 and 30 cm above a coarse sandy bottom (2 m depth). Summer growth was assessed weekly for 7 wk (July to August 1985) using silhouette images to follow individual change in shell area, a correlate of change in wet weight. Daily measurements of temperature, erosion/deposition (buried plate depth) and sediment chlorophyll suggested that sediment transport partially controlled the standing stock of benthic microalgae. Relative oyster growth per week was positively correlated with temperature. In addition, relative growth initially increased as the transport regime went from erosional to depositional (maximum growth near zero net transport) but growth rate declined with continued deposition. The relationship of oyster growth to gross changes in sediment chlorophyll showed a similar parabolic trend. The shape of these curves is similar to those obtained in published laboratory feeding experiments, which suggest beneficial effects of resuspension as a bivalve food supplement, but inhibition at higher levels due to decreased ingestion or dilution of food with inorganics. It is postulated that sand bottoms may provide more suitable resuspension environments than mud due to lower suspended loads over coarse sediments. Resuspension may be a valuable supplement to water column production as food for cultured bivalves, a factor of value in grow-out site selection.     

An integrated GIS for sedimentological and geomorphological analysis of a lagoon environment. Barra de Cananéia inlet region, (Southeastern Brazil)

The aim of this work is to use GIS integration data to characterize sedimentary processes in a SubTropical lagoon environment. The study area was the Cananéia Inlet estuary in the southeastern section of the Cananéia Lagoon Estuarine System (CLES), state of S?o Paulo, Brazil (25°03′S/47°53′W). The area is formed by the confluence of two estuarine channels forming a bay-shaped water body locally called “Trapandé Bay”. The region is surrounded by one of the most preserved tracts of Atlantic Rain Forest in Southwestern Brazil and presents well-developed mangroves and marshes. In this study a methodology was developed using integrated a GIS database based on bottom sediment parameters, geomorphological data, remote sensing images, Hidrodynamical Modeling data and geophysical parameters. The sediment grain size parameters and the bottom morphology of the lagoon were also used to develop models of net sediment transport pathways. It was possible to observe that the sediment transport vectors based on the grain size model had a good correlation with the transport model based on the bottom topography features and Hydrodynamic model, especially in areas with stronger energetic conditions, with a minor contribution of finer sediments. This relation is somewhat less evident near shallower banks and depositional features. In these regions the organic matter contents in the sediments was a good complementary tool for inferring the hydrodynamic and depositional conditions (i.e. primary productivity, sedimentation rates, sources, oxi-reduction rates).     

长江口海域表层沉积物污染及其潜在生态风险评价

根据2004年8月份长江口海域表层沉积物的监测基础资料,采用单因子污染参数法和Hakanson前在生态风险指数法,通过分析长江口不同水域表层沉积物中典型污染要素PCB,Hg,Cd,Pb,As的质量分数,评价了长江口表层沉积物的质量状况。定量确定了长江口表层沉积物的潜在生态风险程度、主要污染因子和潜在生态风险因子;分析了近年来长江口表层沉积物总的潜在生态风险和单个污染要素的潜在生态风险的变化趋势。结果表明:长江口表层沉积物质量状况良好,各典型污染要素的质量分数值均小于背景值,典型污染要素的平均综合指数Cd为1.37,典型污染要素的污染程度由高至低顺序为As>Pb>Hg>PCB>Cd,As是主要环境污染因子;长江口各水域表层沉积物总的对水域均只具有低潜在生态风险,其由高至低的排列顺序为杭州湾北岸>长江口南支>长江口北支>长江口外;各典型污染物对水域也均只具有低潜在生态风险,其由高至低顺序为Hg>PCB>Cd>As>Pb,Hg是主要潜在生态风险因子;近年来,长江口表层沉积物总的潜在生态风险和单个污染物的潜在生态风险均呈现增加趋势。     

Fractionation of Heavy Metals in Surface Sediments of Taihu Lake, East China

The BCR (European Communities Bureau of Reference) three-step sequential extraction procedure was applied to fractionate heavy metals in the sediment of Taihu Lake. For the determination of total metal concentration of the sediments, sample digestion was achieved by using HF/H₂O₂/HNO₃(2/1/1) acid mixture in a microwave-irradiated closed vessel system. The concentrations of Cd, Ni, Cr, Zn, Cu and Pb in various extracts solutions were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The results obtained from the BCR three-step sequential extraction indicated relatively high mobility of Zn, Cu, Pb and Ni in the sediments while Cd and Cr were poorly mobile. Enrichment of heavy metals was found in the sediments collected in the northern parts of Taihu Lake. In the sediments collected in the southern and western sides of the Lake, heavy metal concentrations were relatively low. The relationship between total organic carbon (TOC) and heavy metals concentrations in the sediments is discussed.     

Fossil bog soils (‘<Emphasis Type="Italic">dwog</Emphasis> horizons’) and their relation to Holocene coastal changes in the Jade Weser region,southern North Sea,Germany

After the deceleration of the postglacial marine transgression, the German North Sea coast was subject to deposition of a complex pattern of subtidal to terrestrial facies. This study aims at reconstructing these facies changes in the ‘Land Wursten’ region (Lower Saxony) by focussing on so-called dwog horizons (incipient soil horizons of the pre-engineered salt marshes). We explore their implications for relative sea-level reconstructions and their indication for early settlement activities. Archive drilling data (1960, provided by the ‘Landesamt für Bergbau, Energie und Geologie’) were analysed to create five high-resolution stratigraphic cross sections. Three new drilling records were subjected to sedimentological and microfaunal investigations and interpreted to verify and calibrate the archive data. Two dwog horizons were found and ¹⁴C-AMS dated. We found basal salt marsh deposits inundated by a high-energy event and covered by tidal flat sediments. The thick tidal flat unit is again overlain by salt marsh deposits indicating the transition from a shallow marine to a terrestrial environment where dwogs were developed and covered by episodic marine incursions. The ages of the dwogs (1128–969 cal BC; cal AD 1426–1467) do not correlate with known layers of adjacent settlement sites and are critically discussed. However, we show that they correlate with phases of stagnant regional relative sea level (RSL) and can be used as RSL indicators. The combined archive and modern data provide valuable information for the RSL reconstruction and palaeoenvironmental changes. However, further research is recommended to accomplish more detailed information about coastal response during the Holocene sea-level changes and implications for settlement dynamics.