Muddy Sand Research Articles

Fishing ground mapping of static fishing gear in Lada Bay waters

Various types of fishing gear operated in Lada Bay waters. Data and information regarding fixed or static fishing gear (SFG) are minimal. This research aims to (1) determine the number and size of SFG; and (2) mapping the fishing ground of SFG in Lada Bay. The census method was conducted from August 2018 to April 2019. The identification of SFG and water characteristics were analyzed descriptively. Map of the fishing ground made with GIS. The number of SFG in Lada Bay was 123 units (45 units of fixed lift net and 78 units of the arrier). The fixed lift net sizes range from 10.6-12.7 m with bamboo and areca trees construction. The leader net of the barrier is 100 m, wings 37.5 m, body 10.5 m, and crib 4x4-4x5 m, with bamboo and nets construction. The fishing ground of the fixed lift net is from Tanjung Lesung to the north of Liwungan Island. While the barrier is from Tanjung Lesung to Ciseukeut River. Water characteristics for fixed lift net are temperature 27.2-29°C, pH 7.7-9, salinity 30-33 ppt, depth 11-16 m, and brightness 2.8-3.8 m. The water condition for barriers is temperature 27.3-30°C, salinity 30-34 ppt, current 0.1-0.3 m/s, and depth 1.3-7.7 m with the substrate of muddy sand and sandy coral.

Sound velocity characteristics of unconsolidated sediment based on high-resolution sub-bottom profiles in Jinzhou Bay, Bohai Sea of China

Accurate inversion of sound velocity in a Holocene stratum and a Quaternary stratum was achieved based on rich high-resolution sub-bottom profiles and boreholes in the Jinzhou Bay, Bohai Sea of China. The average value of the sound velocity is 1540.2 m/s in the Holocene stratum and 1764.7 m/s in the Quaternary stratum. The fitting analysis shows that there is an obvious positive linear correlation between the sound velocity and the burial depth of the stratum, with a gradient of 4.5 s−1. The method involving the solution of over-determined equations was innovatively put forward to explore the sound velocity characteristics of different types of sediments. The eigenvalues of the sound velocities of seven types of sediments and weathered rock in the study area are solved: the sound velocities of mud, muddy sand, muddy silty clay, muddy clay, silty clay, clay, silty sand, and strongly weathered rock are 1513.7 m/s, 1484.3 m/s, 1532.0 m/s, 1511.3 m/s, 1693.9 m/s, 1602.7 m/s, 1599.4 m/s, and 2137.7 m/s, respectively. And statistical analysis shows that the sound velocity of the sediment in the study area has obvious quadratic correlations with the void ratio and compressibility.

Defining a biogeochemical baseline for sediments at Carbon Capture and Storage (CCS) sites: An example from the North Sea (Goldeneye)

Injection of carbon dioxide (CO2) into subseafloor reservoirs is gaining traction as a strategy for mitigating anthropogenic CO2 emissions to the atmosphere. Yet, potential leakage, migration and dissolution of externally-supplied CO2 from such reservoirs are a cause for concern. The potential impact of CO2 leakage on the biogeochemistry of sediments and overlying waters in the North Sea was studied during a controlled subsurface CO2 release experiment in 2019 at a potential carbon capture and storage site (Goldeneye). This study describes the natural (unperturbed) biogeochemistry of sediments. They are classified as muddy sand to sandy mud with low organic carbon content (∼0.6 %). Distributions of dissolved inorganic carbon (DIC) and total alkalinity (TA) in sediment porewaters are reported in addition to in situ benthic fluxes of dissolved nutrients and oxygen between the sediments and the overlying water. Oxygen fluxes into the sediment, measured using benthic chambers and eddy covariance, were 6.18 ± 0.58 and 5.73 ± 2.03 mmol m−2 d-1, respectively. Diagnostic indicators are discussed that could be used to detect CO2 enrichment of sediments due to reservoir leakage at CCS sites. These include the ratio TA and ammonium to sulfate in sediment porewaters, benthic fluxes and chloride-normalized cation distributions. These indicators currently suggest that the organic carbon at Goldeneye has an oxidation state below zero and is mainly degraded via sulfate reduction. Carbonate precipitation is apparently negligible, whereas decreases in Mg2+ and K+ point toward ongoing alteration of lithogenic sediments by reverse weathering processes.

Fossil fish otoliths from the Chibanian Miyata Formation, Kanagawa Prefecture, Japan, with comments on the paleoenvironment

The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in the Middle-Late Pleistocene is known for its rich marine fauna that accommodated both the warm and cold water taxa brought by the Kuroshio and Oyashio Currents, respectively. However, little is known on the paleoichthyofauna in this area and the processes shaping the marine ichthyofauna of modern southern Kanto. We used fossil fish otoliths and teeth discovered in the Sha’ana Tuffaceous Sand Member belonging to the Chibanian Miyata Formation, exposed at Sha’ana-dai, Miura City, Kanagawa Prefecture, Japan, to reconstruct the paleoichthyofauna and its associated paleoenvironment and explore the content of fish assemblages during this period. The Sha’ana Tuffaceous Sand Member was composed of upper sandy mud and lower muddy sand horizons at the exposure. A total of 1,675 fish remains were collected from this site, of which 1,389 were assigned to 62 distinct taxa (20 orders, 31 families). The taxonomic composition revealed taxa from various environments, including shallow continental shelf, epi- to meso-pelagic settings, and the majority were from a generally temperate climatic zone. Paleoenvironmental analyses suggested that the fish assemblages were from the continental shelf (approximate depth of 100–200 m) in a temperate sea where both warm Kuroshio and cold Oyashio Currents had an influence on the biota. The analysis also showed that two boreal fishes, namely Clupea pallasii and Theragra chalcogramma, once had a wider distribution that extended to the southwestern areas of the Paleo-Tokyo Bay. This study provides a more complete view of the related paleobiogeography of marine fishes during the Chibanian and is essential for reconstructing the evolutionary processes of the rich ichthyofauna in the southern Kanto.

Recent Ostracoda from the shelf sediments of Southwestern part of Bay of Bengal: Implication on Microenvironments

A detailed study on Recent Ostracoda was carried out in twenty-six surface sediment samples collected from shelf region of the Southwestern part of Bay of Bengal. A total of 21 species of Ostracoda belonging to 18 genera have been identified, of which, seven species are abundant (>5%). The Q-mode and R-mode cluster analyses of the abundant species resulted in two assemblage defining different microenvironments. The shallowest assemblage (I) from 10 to 80 m water depth is characterised by Hemikrithe Orientalis, Pterygocythereis chennaiensis and Lankacythere multifora which are associated with sand to slightly muddy sand. The second assemblage (II) from 80 to 200 m water depth is associated by Keijella reticulata, Bairdoppilata paraalcyonicola, Actinocythereis scutigera and Stigmatocythere indica and the nature of sediments varies from slightly muddy sand to slightly sandy mud. The sediments from 50-100 m water depth are foundto contain higher concentration of organic matter (TOC and TN) suggesting the high productivity zone. The C/N ratio value ranges from 4 to 8 in 52% of sediment samples indicating both marine and terrestrial source. The shallower part of the seafloor up to 30 m depth is dominated by sandysediments, reflecting the occurence of high-energy conditions. The higher mud content in the deeper part is due to the prevalance of low energy condition. The carapace-valve ratio (1:9) indicates that the study area experiencing a slower rate of sedimentation. Our study results revealed that the distribution of Ostracoda in the Southwestern part of Bay of Bengal is controlled by the type of sediment, depth and physicochemical parameters of the bottom water.

Sedimentological, Geochemical and Hydrogeochemical Studies of Alluvial Fans for Mineral and Environmental Purposes (Case Study of Southwestern Iran)

The alluvial-fan sediments play a very important role in mineral reserves and underground water resources, though a comprehensive study on such sediments, especially from a geochemical point of view, is still lacking. In this research, a total of 22 particularly important alluvial fans across the Khuzestan Plain in the southwestern Iran were studied through field surveys, petrographic evaluations, and geochemical assessments. These investigations included particle size distribution studies, microscopic observation of 193 samples, subsurface study of 60 boreholes along 10 different sections, facies analysis on 46 different sections, and comprehensive geochemical studies through XRD, XRF, ICP Mass, and wet chemical analyses. Based on these studies, the sediments were found to be dominantly composed of gravel, muddy sand, silt, and clay. The sediments exhibited good roundness and good to fair sorting. The most abundant oxide in the study area being MgO followed by SiO2, Al2O3, and Fe2O3. According to the studies, most of the samples fell in the range of iron-bearing sandstones with rare cases of iron-bearing shales. Investigation of the geochemical indices showed the long sediment transport path from the source, humid climate, and moderate to extensive weathering of the deposit. The depositional setting was found to be dominantly an active continental margin and, to a lesser extent, a continental island arc. Investigating of the studied sediments provenance indicate a felsic to slightly basic source rock. The environmental studies were indicative of relatively low contamination of the region and abundance of rare earth elements including Y, Sc, Nd, La, and Ce, and the abundance of heavy elements including Cr, Zn, Pb, and Cd. Based on the mineralogical studies on the samples, the inter-grain cement in both gravel and conglomerate particles was found to be composed of calcite.

Application of PlanetScope-based Depth Invariant Index method in Seagrass Mapping: The study in Thi Nai Lagoon, Binh Dinh Province

The seagrass ecosystem is one of the most critical coastal and marine ecologies. The seagrass meadows can protect the seabed coastal erosion, absorb nutrients from coastal runoff and stabilize sediments, act as bio-filters, and provide a habitat for marine animals. Nevertheless, under the impact of socio-economic growth, seagrass in the Thi Nai lagoon has disappeared and been severely deteriorated. Therefore, mapping seagrass in this area is important in informing ecologists and economists to improve sustainable marine ecosystem management strategies. This study aims to detect seagrass in Thi Nai lagoon, Vietnam, by remote sensing method. PlanetScope (PS) satellite images have high spatial (3m) resolution that is applied to extract seagrass using Lyzenga's Depth Invariance Index technique for water column correction and Maximum Likelihood Classifier (MLC). After that, evaluate the accuracy of the results using field data collected from July 29, 2020, to August 1, 2021. The study results achieved high accuracy in isolating seagrass subjects with an overall accuracy of 85.09% and Cohen's Kappa value of 0.8. There are approximately 180 hectares of seagrass in the study area. Moreover, the results also show that seagrasses are mainly distributed on the sand, muddy sand, and sandy mud along the west shore of Thi Nai lagoon and dunes such as Con Chim, Con Trang, and Con Tau, with depths ranging from 1 to 2.5 meters (90.97 %).

Manifestation And Endoparacitic Intensity On Gonggong Conch (Laevistrombus turturella)

Habitat the gonggong conch (Laevistrombus turturella) also known as Dog conch is a species from the Gastropod class that can be found in shallow waters with muddy sand substrate. In Kepulauan Riau Province, these animals are hunted by fishermen to sell to consumers since gonggong conch is a favourite culinary in this province. The availability of conch in the market has only relied on natural catches. The high consumption and natural fluctuations have decreased the conch population. To maintain the sustainability of the dog conch, it is necessary to carry out the cultivation activities. The cultivation begins with the selection of quality broodstock. The gonggong conch of natural origin needs to be determined before cultivation, in order to prevent the entry of disease in the cultivation system i.e. parasites. This study includes the determination, prevalence and infection intensity of endoparasites in conch from Madong Bay, Tanjungpinang. The results showed that the total length of the conch shells ranged from 55.5 to 79.5 mm with an average length of 67.72 mm and a frequency mode of 64.6 mm. The sex ratio between male and female conch is 1:1.1 (not ideal) n=30. Two kinds of parasites were found in the digestive tract of gonggong conchs are conoidacid oocysts and trematode sporocysts. The number of endoparasites, prevalence and intensity in wild caught has high numbers involving conoidacid oocysts (prev=100%; I=48.23 ind/conch) and trematode sporocysts (prev=100%; I= 135.33 ind/conch). It was concluded that the level of endoparasites infection in the dog conch from the Madong Bay was categorized as moderate-to-severe.

Integrated geophysical investigation for the characterisation of valley bottom soil at Ilora, Southwestern Nigeria

ABSTRACT Hydromorphic soils have potential for sustainable agricultural production due to shallow water deposition, accumulation of organic matter and residual available moisture for farming during dry season. Integrated geophysical investigations comprising Ground Penetrating Radar (GPR) and Vertical Electrical Sounding (VES) were conducted on a valley bottom soil at Ilora, Southwestern Nigeria to determine subsurface geometry, lithology and water table in relation to its agricultural significance. Seventeen GPR profiles were established while twenty eight VES were conducted using Schlumberger array. Three test pits were excavated to a depth of 1 m for ground truth. Horizons revealed on the GPR are; sub-parallel reflections assumed to be fine muddy sand rich in organic matter, low amplitude and weak reflections indicating attenuated signal because of high moisture content and mutiple chaotic, non-parallel reflectors. The VES results show system of two to four geo-electric layers with average overburden thickness of about 7 m. The excavated pits show intercalation of clayey and loamy soil and revealed water level to be 0.8 m. The integrated geophysical approach applied has successfully identified the spatial pattern of clayey soil, overburden thickness and water level of the valley bottom soil which help retention of water during dry season.

SEDIMENTARY ARCHITECTURAL ELEMENTS AND SANDY BRAIDED FLUVIAL SUCCESSIONS IN AJALI SANDSTONE RIDGES, WESTERN AFIKPO BASIN, UTURU, NIGERIA

Lithofacies, bounding surfaces and sedimentary architectural elements exposed in two ridges at Uturu being quarried for construction sands were analysed to determine the paleoenvironment of deposition and the factors that control the deposition of sand units. Mainly outcropped is Ajali Formation overlying locally exposed Mamu Formation in Western Afikpo basin. Lithofacies identified include: Trough cross bedded medium- to coarse-grained (St), Planar cross bedded fine- to coarse-grained sandstone (Sp), Small scale planar cross bedded sandstone (SSp), Lenticular mudstone (Fm), Heterolithic sandstone/mudstone (Fsm), Horizontal stratified sandstone (Sh), Cross ripple laminated sandstone (Sr), Reddish muddy sand (Fl), Siltstone (SSm) and Shale (Fsh). The associations of lithofacies and bounding surfaces gave four fluvial and one marine architectural element. The fluvial elements which mainly characterized the Ajali Formation include: Channel-fill (CH), Macroforms Accretion (MA). Flood-Plain Fines (FF) and Channel Abandonment Fines (CAF). Offshore-shoreface fines (OSF) element defined marine Mamu Formation. The profiles of the ridges show dominance of MA followed by CH while FF is limited in occurrence and in some zones pinch-out to lenticular inter-bar mudstone. The MA is characterized by planar cross beddings, reactivation surfaces, internal grading, steep dipping ferruginized accretion surfaces and abrupt flat top which indicate mid-channel bars deposition in typical sandy braided fluvial depositional system. Generally, there is vertical aggradation/ amalgamation of channel deposits and dominance of sheet alluvial architecture. Low rate of channel avulsion, moderate rate of lateral migration and aggradation, variable discharge rate and high rate of sediment supply and subsidence were considered as factors that controlled the deposition and preservations of sand units. This study provided an understanding of mesoscopic heterogeneities and compartmentalization style inherent in hydrocarbon bearing sandy braided reservoirs which can be used as analog model for its development.

Sharing Electrons: An Extraordinary Friendship Between Bacteria

Did you know that iron is one of the most important elements on Earth? It is assumed that life evolved close to iron sources. This means that the earliest life forms—and therefore oldest creatures—were able to use iron to obtain energy the way we use food. These tiny organisms are called iron microorganisms and can occur in sediments, which are mainly muddy sand. But less was known about where iron microorganisms live in these sediments—are they located close to the water surface or deep in the sediment? In this study, a team from the University of Tübingen investigated the distribution and variety of iron microorganisms. The scientists discovered that iron microorganisms live independent from their favorite foods: iron, oxygen, and light! This independence might be explained by an unexpected extraordinary friendship with a “living cable.” Are you curious about what a living cable is?

Deep learning model for seabed sediment classification based on fuzzy ranking feature optimization

Accurate acquisition of information on seabed sediment distributions plays an important role in the construction of basic marine geographic databases. Although a multibeam echo-sounding system (MBES) can satisfy large-scale seafloor mapping with high precision and high resolution, the development of a consistent, stable, repeatable and validated seabed sediment classification method based on swath acoustic data is still in its infancy. To achieve accurate prediction and mapping of geographic seabed sediment information, this paper developed a deep learning model based on feature optimization. First, faced with high-dimensional features extracted from multibeam bathymetry and backscatter intensity measurement data, a fuzzy ranking (FR) feature optimization method was proposed. By combining the physical properties of actual sediment samples, the multidimensional features derived from terrain and intensity data are ranked and optimally selected according to the mean square error to eliminate redundant and irrelevant features. Second, the deep belief network (DBN) deep learning method was used to build a supervised seabed sediment classification model. The optimized features and actual sediment samples participate in model training, which further enhances the prediction ability of acoustic data to seabed sediments. Finally, to evaluate the performance of the DBN model, this experiment used large-scale multibeam survey data and ground-truth data (acquired by grabbers, core samplers, dredges, etc.) in the southern Irish Sea to achieve accurate prediction of 10 sediment types (slightly gravelly muddy sand, slightly gravelly sand, gravelly mud, gravelly muddy sand, gravelly sand, muddy sand, muddy sandy gravel, sand, sandy gravel and sandy mud). The experiment results show that by using the optimal feature combination based on FR, the overall classification accuracy and Kappa coefficient reached 86.20% and 0.834, respectively, which are significantly improved compared to the evaluation metrics of other feature selection methods. In addition, compared with the current five typical supervised classification methods (i.e., the random forests, BP neural network, support vector machine, maximum likelihood and decision trees methods), the proposed DBN classification model achieves a better performance, highlighting its application potential in seabed sediment detection and mapping.

Seagrass Potential as Supporting Ecotourism in Sibu Island, Subdistrict North Oba, North Maluku Province

Seagrass Ecotourism is a tourism activities based on the ecosystem of seagrass. Component of seagrass consist of vegetation and biota that associated with the seagrass. The purpose of this research is to understand the condition biophysics of seagrass (Types of seagrass, Cover of seagrass, fish, makrozoobenthos, types of substrat, water brightness, the depth of the seagrass) and to establish the suitability of seagrass to support nautical ecotourism. This research have been done in Sibu island, Guraping village, north oba district, Tidore city for 6 month from April – September 2020. The method that used is a survey method consist of direct measuring of types seagrass, cover of seagrass, fish, makrozoobenthos, types of substrat, water brightness, the depth of the seagrass. The data analysis includes percentage of cover seagrass and the suitability index of seagrass ecotourism. The result of the biophysical study were obtained are 8 types of seagrass, cover of seagrass (51,04- 92,71%), fish (12 types), makrozoobenthos (17 types), brightness (77-100%), substart (sand, muddy sand, mud) flow speed (0,01- 0,06 m/dt) and the depth of the seagrass (1-2,5 m). Sibu island could be developed as a region of Seagrass Ecotourism with index suitability tourism (IKW) station 1,3,4 and for the whole are located in category S1 (very suitable) and station 2 is in the suitable category.

Intertidal ecosystem engineer species promote benthic-pelagic coupling and diversify trophic pathways

Ecosystem engineering is a ubiquitous process by which the biological activity of a species shapes habitat diversity and often creates local biodiversity hotspots. The honeycomb-worm Sabellaria alveolata, an intertidal ecosystem engineer, actively builds reefs across Europe by aggregating sand. Here, we used carbon and nitrogen isotopic compositions measured on basal resources and bentho-demersal consumers (fish, mega- and macroinvertebrates) to empirically investigate how non-trophic interactions (ecosystem engineering) modify food web structure and functioning. Three sediment types corresponding to different substrata and species assemblages were sampled: a control soft sediment (medium to muddy sand, before the establishment of S. alveolata), the sediment engineered by S. alveolata (hardened 3D structures), and the soft sediment under the influence of S. alveolata (associated sediment). Using consumer community isotopic biplots (biomass-weighted), niche metrics (standard ellipse area), and mixing models, we found that S. alveolata, through the physical structure it creates, the stimulation of basal resources (microphytobenthos and Ulva), and the diversification of suspension-feeding species, promotes benthic-pelagic coupling and a habitat-wide form of ‘gardening,’ which further leads to trophic pathway diversification and limits trophic competition between the engineer species and associated suspension-feeders. Furthermore, our results help to refine the definition of S. alveolata reefs as the sum of the engineered and associated sediments since they are part of a single reef food web coupled by the stimulated basal resources and consumers. Finally, the non-trophic and trophic interactions mediated by S. alveolata and the associated macrofauna seem to promote the establishment of a temporally stable and probably highly resilient reef habitat.

Changes in particle sizes and geochemistry of Siyah Keshim lagoon sediment of Gilan province to determine origin and tectonic position of sediment

Useful information was obtained about the environmental condition of this region such as energy, sediment location, origin, sediment carrying path, pond evolutionary process, and tectonic conditions and origins of sediments by studying physical and geochemical sediment changes processes in place and time, distribution of sediments and elements in lagoon bed, and also identification the effective factors on sediment distribution model. In this regard, 59 sediment samples were taken from Siyah Keshim lagoon and were analyzed chemically and aggregation by XRF and ICP-MS technic. Adaptation of data by Folk diagrams showed that this region is placed in a range of sand, muddy sand, sand with a little gravel, muddy sand with a little gravel, and silty sand. Weak to medium sorting and negative tilting shows sediment in a coastal area. Geochemical evidence shows that SiO2/Al2O3 ratio in these sediments is 2.6-3.7. In addition, Na2O value shows relatively low sediment investigation for sediments of this lagoon. Moreover, determination of the weathering effect in origin place by the chemical index of alteration (CIA) and chemical weathering index (CWI) shows intensive chemical alternation on sediments. Index of combined variety was averagely 1.54 in the studied sediments and show that sediments resulted from the first cycle sediment. Using tectonic separating diagrams based on the primary and secondary oxidants percentage show the sediment in the active continent margin (ACM), continent-island arc (CIA), and oceanic island arc (OIA) and shows that the studied sediments are related to subduction margin.

Sedimentology and Geochemistry of Quaternary Sediments and Determination of Sediment Transport, Tectonic setting in the wetland of Saghalak-Sar Rasht

Wetlands as unique, rich, and fertile ecosystems are among the most vital environments in the world. Quaternary sediments of wetlands are the main components of our environment and an essential source of clastic, organic, and chemical substances that can be caused by natural processes and erosion or created by human intervention. This article broadly deals with the grain size and geochemistry of Quaternary sediments in Saghalak-Sar as one of the wetlands in Guilan province in the north of Iran. The 74 surface and subsurface samples (from 10 core) of the sediments were graded, and sedimentationparameters of the particles (Sorting, Skewness, and Kurtosis) were determined. Also, the frequency of elements oxides and subelements oxides were determined by ICP and XRF, respectively. The sediments were classified into eight sedimentary types including Slightly Gravelly Muddy Sand, Slightly Ggravelly Sandy Mud, Sandy Mud, Gravelly Muddy Sand, Gravelly Mud, Slightly Gravelly Sandy Mud, and Gravelly Sand. On the east of the wetland (core 1 to 8), the percentage of sand is less the mud, and on the south and west of the wetland (core 9 to13), the sand is higher, indicating more energy in the south and west. Sorting of sediments is poorly to moderately sorted and the Skewness in most samples is coarse Skewed. The number of sediment content is 2 to 3, but the sand content is the majority of the samples. According to these data, the sediments are transmitted to sedimentary basins by the river or muddy streams. The comparison of the oxide elements of the above samples with upper continental crust (UCC) indicated the mean value of SiO2 (63.1%) in the wetland sediments is slightly less than the average of this oxide in the upper continental crust (66.6%), the average of CaO (0.8) less than the average of upper continental crust (except the 12 core and surface sediments sw1) and the amount of Na2O (0.8) and K2O (2.1) are less than the upper continental that indicates the destruction of plagioclases as a result of chemical weathering in the source or during the transport process. The comparison of MgO, Fe2O3, TiO2 sediment samples at different depths and upper continental crust shows that the average of MgO (1.2) is lower than the upper continental crust ten but Fe2O3 ( 7.2), TiO2 (1.2) arehigher than the upper continental crust. The decrease of CaO, Na2O, and SiO2 and the increase of Al2O3 and Fe2O3 indicate an increase in weathering during the transport process and the production of clay and aluminum oxide and iron oxide due to the decomposition of complex clays and non-clay minerals. Matching sediment samples on the two-axial diagrams of the main elements oxides, i.e., (Fe2O3+ MgO) versus Al2O3/ SiO2 and TiO2 and log (K2O / Na2O) versus SiO2, as well as the triangular diagrams of the sub-elements Zr, Th, La, and Sc, indicate that the wetland sediments are more inclined towards the range of oceanic arc islands and continental arcs, and are composed of subduction rocks.

Mollusca’s Density and Distribution Pattern in Kalangan Mangrove Forest Ecosystem

Shellfish is one of the organisms that have habitat in mangrove forests because it has a muddy substrate. However, mangrove forests in the coastal area of Kalangan, Central Tapanuli Regency have suffered environmental damage. Therefore, a research on the density and pattern of shellfish distribution is needed to be a recommendation for optimal, sutainable mangrove forest management. This research was conducted in September 2020. The method used in determining the location of sampling is purposive sampling method using 1x1m2 plot on the surface of muddy sand substrate. The results showed that the population density of Anodentia edentula 32 ind/m2 at Point I with grouping distribution patterns; Cerithidea cingulata 74 ind/m2 at Point I (grouping), 156 ind/m2 in Point II (grouping), and 126 ind/m2 in Point III (grouping); Cerithidea quadrata 2 ind/m2 in Point I (uniform); Clypeomorus sp 12 ind/m2 at Point I (uniform); Nerites sp 178 ind/m2 at Point I (group), 94 ind/m2 at Point II (group), and 418ind/m2 at Point III (grouping); Donax trunculus 3 ind/m2 at Point I (uniform); Sulcospira testudinaria 1 ind/m2 at Point I (uniform), 79 ind/m2 at Point II (grouping), and 32 ind/m2 at Point III (random), and Telescopium telescopium 2 ind/m2 at Point I (uniform), and 1 ind/m2 at Point III (random). So it can be concluded that the biodiversity of mollusca in mangrove forest ecosystems in the coastal area of Kalangan, Central Tapanuli Regency, is of low value so that it needs to be maintained for the sake of ecosystem balance and the availability of germplasm for future generations.

An assessment of heavy metal contamination in the surface sediments of Ha Long Bay, Vietnam

Ha Long Bay is an attractive landscape and a center of dynamic economic activity; however, it is subject to negative impacts from tourism, activity in its harbor, mining, industry, and urbanization, which is evidenced by the presence of pollutants, including heavy metals, in surface sediment at the bay. To ascertain the extent of the anthropogenic impact, 48 surface sediment samples were collected and analyzed for grain size and the presence of heavy metals (Cu, Pb, Zn, As, Cd). Thirteen sediment types were identified in Ha Long Bay: sand, muddy sand, silty sand, sandy mud, mud, silt, sandy gravel, muddy sandy gravel, gravelly mud, gravelly muddy sand, slightly gravelly sandy mud, slightly gravelly sand, and sandy silt; of these, sandy silt and silty sand are the most common, while the others are less so. Regarding the concentration of heavy metals in the sediment, Cu concentration ranges from 3.80 to 41.72 mg/kg, with an average of 14.53 mg/kg; Pb ranges from 10.17 to 69.90 mg/kg, with an average of 30.39 mg/kg; Zn ranges from 6.34 to 119.21 mg/kg, with an average of 50.87 mg/kg; Cd ranges from 0.03 to 0.20 mg/kg, with an average of 0.08 mg/kg; As ranges from 1.78 to 13.71 mg/kg, with an average of 6.06 mg/kg. The concentrations of Cu, Pb, and As are higher than the Interim Sediment Quality Guideline (ISQG) levels at stations near the shoreline, and lower than the ISQG levels distributed throughout offshore stations.

Mangrove Community Structure in Papuan Small Islands, Case Study in Biak Regency

Mangrove plays the importance of roles for the small island sustainability, both physically and ecologically. In the high-risk Pacific Ocean’s islands, small islands in Biak face typhoons, earthquakes, high waves, and tsunami effects. The study was conducted at 100 10mx10m-quadratic-plots scattered on seven small islands in Biak-Numfor Regency. Research objectives were to investigate the mangrove community structure of each island, i.e., canopy coverage, density, and morphological size, and to analyze the correlation among those parameters. The result found that mangrove was in pristine condition, large individual size with low anthropogenic threats. They were covered by a medium and dense canopy from 61.32±3.04% in Pasi to 93.88±0.14% in Meos Mangguandi. Substrate significantly influenced the level of canopy coverage and the MDS ordination of species composition. Sonneratia alba tended to be dominant in rocky sand in Pasi, Owi, Padaidori, and Wundi, while Ceriops and Rhizophora were mostly occupied the muddy sand, or Bruguiera gymnorrhiza has the highest domination in sandy mud substrate in Auki, Pai, and Meos. The canopy coverage had a significant correlation only with total density but none with the others. The height of the tree (up to 21.2 m) was found highly related to the diameter size (max: 124 cm).

Ostrea edulis beds in the central North Sea: delineation, ecology, and restoration

Abstract Until the late 19th century, extensive beds of flat oyster Ostrea edulis populated the Central North Sea, which have vanished after intensive fisheries. At present, various initiatives are being carried out to investigate the potential to restore this former key species in the area. This historical ecological study contributes by delineating the former oyster bed area and through an assessment of its limits against known gradients in the North Sea. Extensive data from historical maps, texts, and ship-based surveys were used to synthesize our knowledge on the former beds. It was revealed that the area with oyster beds covered ∼6.2% of the total North Sea bottom, with a delineation that could partly be explained by hydrodynamic and temperature gradients. The position and extent of the area are notably different from the area that is used in recent feasibility studies on the restoration of North Sea oyster beds. The offshore oysters lived on muddy sand in relatively cold conditions, and there are several indications that their reproductive rate was low. The apparent disappearance of cold water adapted flat oysters will challenge restoration projects. This study provides indispensable information for the future restoration of flat oyster beds in the North Sea.