Muddy Sand Research Articles

Formation and Removal of a Coastal Flood Deposit

AbstractDuring floods, small mountainous rivers transport large sediment loads to the coastal ocean. This sediment often deposits near shore, and if conditions allow, various types of gravity flows (including hyperpycnal river plumes) can transport the sediment across the shelf within minutes to months of delivery. The stochastic and energetic nature of small‐mountainous‐river flood dispersal presents challenges to observations of transport processes and flood‐deposit formation during events, however. In this study, the removal of two dams on the Elwha River afforded an opportunity to closely monitor coastal sediment dispersal using boundary‐layer instrument systems during 4 years of intense sediment loading. A flood in March 2014 generated fluvial sediment concentrations of 14–20 g/L, coastal boundary‐layer concentrations of up to 14 g/L, and 23 cm of muddy sand deposition in a few days. Limited evidence exists for a gravity flow lasting <2 hr during slack tide, coinciding with the waning phase of the secondary flood peak. However, rapid sediment deposition over the 4‐day event period was dominated by advection of sediment in the boundary layer and by suspension settling from turbid river water, which never exceeded the well‐established 35–40 g/L required for hyperpycnal river plume formation. Within 3 weeks, the entire sandy flood deposit had been eroded by strong tidal currents. This system highlights the difficulty in forming hyperpycnal river plumes within tidally energetic systems, even from an extremely turbid river, and the conditions that can erase major sediment delivery events from the sedimentary record.

Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain)

Spatiotemporal distribution and growth pattern of Venus nux (Gmelin, 1791) in the Gulf of Cádiz (Southern Spain)

Permafrost and active layer research on James Ross Island: An overview

This study summarizes the current state of the active layer and permafrost research on James Ross Island. The analysis of climate parameters covers the reference period 2011–2017. The mean annual air temperature at the AWS-JGM site was -6.9°C (ranged from -3.9°C to -8.2°C). The mean annual ground temperature at the depth of 5 cm was -5.5°C (ranged from -3.3°C to -6.7°C) and it also reached -5.6°C (ranged from -4.0 to -6.8°C) at the depth of 50 cm. The mean daily ground temperature at the depth of 5 cm correlated moderately up to strongly with the air temperature depending on the season of the year. Analysis of the snow effect on the ground thermal regime confirmed a low insulating effect of snow cover when snow thickness reached up to 50 cm. A thicker snow accumulation, reaching at least 70 cm, can develop around the hyaloclastite breccia boulders where a well pronounced insulation effect on the near-surface ground thermal regime was observed. The effect of lithology on the ground physical properties and the active layer thickness was also investigated. Laboratory analysis of ground thermal properties showed variation in thermal conductivity (0.3 to 0.9 W m-1 K-1). The thickest active layer (89 cm) was observed on the Berry Hill slopes site, where the lowest thawing degree days index (321 to 382°C·day) and the highest value of thermal conductivity (0.9 W m-1 K-1) was observed. The clearest influence of lithological conditions on active layer thickness was observed on the CALM-S grid. The site comprises a sandy Holocene marine terrace and muddy sand of the Whisky Bay Formation. Surveying using a manual probe, ground penetrating radar, and an electromagnetic conductivity meter clearly showed the effect of the lithological boundary on local variability of the active layer thickness.

Environmental assessment of Lake Manzala inferred from diatom analysis of the lake surface sediments

The distribution patterns of diatoms in the surface sediments of Manzala Lake have been studied in detail. A total of 110 diatom species belonging to 48 genera have been identified from samples consist mainly of greenish gray mud with relatively some muddy sand sediments. The distribution pattern of the recorded diatom taxa displayed changes in the floristic composition due to changes in the ecological conditions such as salinity, pH, and some chemical elements, which are related to sea-level fluctuations, freshwater influences, waste discharge from the drains and climatic changes. Multivariate statistical techniques including hierarchical ascending clustering and Canonical correspondence analyses were used to identify ecological groups of diatoms and to estimate which environmental variables were important in diatom distribution. Five diatom ecological groups were identified and classified the lake into five distinct ecological zones.

How benthic habitats and bottom trawling affect trait composition in the diet of seven demersal and benthivorous fish species in the North Sea

Demersal and benthivorous fish depend on prey availability in benthic habitats for their diet. Prey availability may in turn be affected by bottom trawling. Our study attempted to link the prey consumed by fish directly to those available in the benthic environment. We test the hypothesis that bottom trawling significantly affected the trait composition of fish diets with a strong link to benthic habitats. Stomach content data were analysed for seven demersal and benthivorous fish species in the southern and central North Sea and were related to habitat fauna collected by grab and epi-benthic trawl data across the same spatial extent. Biological trait analysis was used to avoid taxonomic bias in large-scale comparisons across habitats and to quantify the effect of bottom trawling, which tends to shift prey diversity in favour of small, opportunistic and short-lived species and traits. The diets of two demersal omnivores (whiting, Merlangius merlangus and Atlantic cod, Gadus morhua) and two opportunistic benthivores (haddock, Melanogrammus aeglefinus and long-rough dab, Hippoglossoides platessoides) did not appear to reflect either infaunal or epifaunal traits that were abundant in the benthic environment. The diets of European plaice (Pleuronectes platessa) and Dover sole (Solea solea), however, showed strong links with infaunal prey trait composition in shallow sand to muddy sand habitats located in the eastern North Sea and the Dogger Bank. Such strong links were also observed for the diets of Common dab (Limanda limanda) and plaice in similar habitats in deeper waters. Plaice targeted small to medium sized infaunal burrowers and deeper dwelling infaunal species. Its diet was significantly affected by bottom trawling, which caused a reduction in prey biomass in their stomachs rather than a shift in trait composition. Our study showed that the diets of benthivorous fish across large spatial scales are strongly linked with the prey trait availability in their benthic habitats and that bottom trawling significantly affected the diet of plaice, a species with strong habitat-diet associations.

Seafloor mapping based on multibeam echosounder bathymetry and backscatter data using Object-Based Image Analysis: a case study from the Rewal site, the Southern Baltic

Abstract Seafloor mapping is a fast developing multidisciplinary branch of oceanology that combines geophysics, geostatistics, sedimentology and ecology. One of its objectives is to isolate distinct seabed features in a repeatable, fast and objective way, taking into consideration multibeam echosounder (MBES) bathymetry and backscatter data. A large-scale acoustic survey was conducted by the Maritime Institute in Gdańsk in 2010 using Reson 8125 MBES. The dataset covered over 20 km2 of a shallow seabed area (depth of up to 22 m) in the Polish Exclusive Economic Zone within the Southern Baltic. Determination of sediments was possible based on ground-truth grab samples acquired during the MBES survey. Four classes of sediments were recognized as muddy sand, very fine sand, fine sand and clay. The backscatter mosaic created using the Angular Variable Gain (AVG) empirical method was the primary contribution to the image processing method used in this study. The use of the Object-Based Image Analysis (OBIA) and the Classification and Regression Trees (CART) classifier makes it possible to isolate the backscatter image with 87.5% overall and 81.0% Kappa accuracy. The obtained results confirm the possibility of creating reliable maps of the seafloor based on MBES measurements. Once developed, the OBIA workflow can be applied to other spatial and temporal scenes.

Improving marine habitat mapping using high-resolution acoustic data; a predictive habitat map for the Firth of Lorn, Scotland

Habitat mapping is an important tool for marine spatial planning and is required for most ecosystem-based management approaches. The Firth of Lorn Special Area of Conservation (SAC), west Scotland, was originally designated for its rocky reef habitat but it is also an area of high importance for the Flapper skate (Dipturus intermedius) and Harbour porpoise (Phocoena phocoena). Here we present an improved predictive habitat map for the SAC utilising multibeam backscatter and bathymetry data collected as part of the Ireland, Northern Ireland and Scotland Hydrographic Survey Project.Backscatter, bathymetry and bathymetric derivatives were analysed using Principal Component Analysis (PCA) and acoustic signatures were created from drop-down video habitat location data. A predictive habitat map was created from Maximum Likelihood Classification using the PCA. Dominant habitat types identified included; moderate energy circalittoral rock (CR.MCR), sublittoral mixed sediment (SS.SMx) and sublittoral sand and muddy sand (SS.SSa). Drop down video showed variable accuracy with 0–100% correctly classified habitats due to the small sample size. The initial validation points were added and the model was rerun. In areas with no previous sea truthing points, some predictions changed to SS.SMx at depths > 100 m and SS.SSa in depths < 50 m, suggesting that the model can be improved with a greater depth-range of sea truthing data. Modern acoustic surveys undertaken for other purposes, such as navigational charting, can thus be used to generate broad-scale predictive habitat maps in a cost and time effective manner. Such maps have the potential for a wide range of use by marine stakeholders, in particular, for establishing environmental baselines for long term monitoring of benthic habitats. Given the high costs of surveying, such an approach supports the rationale of “Collect once and use many times”.

Molluscan benthic communities at Brijuni Islands (northern Adriatic Sea) shaped by Holocene sea-level rise and recent human eutrophication and pollution.

The effects of and the interplay between natural and anthropogenic influences on the composition of benthic communities over long time spans are poorly understood. Based on a 160-cm-long sediment core collected at 44 m water depth in the NE Adriatic Sea (Brijuni Islands, Croatia), we document changes in molluscan communities since the Holocene transgression ~11,000 years ago and assess how they were shaped by environmental changes. We find that (1) a transgressive lag deposit with a mixture of terrestrial and marine species contains abundant seagrass-associated gastropods and epifaunal suspension-feeding bivalves, (2) the maximum-flooding phase captures the establishment of epifaunal bivalve-dominated biostromes in the photic zone, and (3) the highstand phase is characterized by increasing infaunal suspension feeders and declining seagrass-dwellers in bryozoan-molluscan muddy sands. Changes in the community composition between the transgressive and the highstand phase can be explained by rising sea level, reduced light penetration, and increase in turbidity, as documented by the gradual up-core shift from coarse molluscan skeletal gravel with seagrass-associated molluscs to bryozoan sandy muds. In the uppermost 20 cm (median age <200 years), however, epifaunal and grazing species decline and deposit-feeding and chemosymbiotic species increase in abundance. These changes concur with rising concentrations of nitrogen and organic pollutants due to the impact of eutrophication, pollution, and trawling in the 20th century. The late highstand benthic assemblages with abundant bryozoans, high molluscan diversity, and abundance of soft-bottom epi- and infaunal filter feeders and herbivores represent the circalittoral baseline community largely unaffected by anthropogenic impacts.

Textures, provenances and structures of sediment in the inner shelf south of Shandong Peninsula, western South Yellow Sea

Although many studies have been performed on the mud wedge in the distal part of the Yellow River subaqueous delta, little is known about the southwestern terminus of the Yellow River mud wedge in the inner shelf of the Southern Yellow Sea (SYS). We use ∼3000 km of high-resolution subbottom seismic profiles, 147 surficial sediment samples, as well as 30 fluvial sediment samples to study sediment textures, provenance and structures in the inner shelf in western SYS. Our results show that sediment in the inner shelf south of Shandong Peninsula can be categorized into multiple types, including sand, silt, sandy silt, muddy sand, mud, gravel mud and others. About 60% of the study area is covered by silt and sandy silt. Assuming a finer texture of sediment from Yellow River and a relatively coarser one for sediment from local small rivers, our results reveal at least two contrasting sediment sources. East of the Laoshantou Headland, on the southern coast of the peninsula, the sediment is mainly from the Yellow River. Holocene sediment deposition reaches about 15 m thickness in water depths of ∼10 m. The homogeneous surficial sediment pattern is mainly controlled by the Yellow Sea Coastal Current, the Yellow Sea Warm Current, as well as local currents. However, west of Laoshantou Headland, sediment from local small rivers draining the peninsula plays a more important role. Over there the Holocene mud wedge is no more than 5-m thick, and is re-worked by strong tides and longshore currents. The seaward extension of Laoshantou Headland the southern peninsula seems to act as an effective sediment trap, aiding the accumulation of sediment carried by longshore currents. This new study delineates the western boundary of Yellow River subaqueous delta and helps better quantify sediment budget in the Yellow Sea. It also shed light on the sedimentation interplay of large rivers with local small rivers on many epicontinental shelves and passive margins around the world.

Sequential Extraction of Some Heavy Metals in Southwest Giza Soil, Egypt

The pollution of agriculture soil in southwest Giza, Egypt with As, Cd, Pb and Cr were assessed by the application of Index of Geoaccumulation (Igeo) and five steps sequential extractions technique. The results indicated that the soils are muddy sand, alkaline (pH ≈ 8.3), calcareous (CaCO3>5%) and have low organic matter (3.1%). Soil contains about 142.8, 1.7, 123.5 and 209.1 ppm of As, Cd, Pb and Cr, respectively. The Igeo indicated that the soils of the study area ranged from uncontaminated-moderately to extremely contaminated. The sequential extraction explained the incorporation of Pb and Cr in the residual fraction and the incorporation of As and Cd in the carbonate fraction. The exchangeable fraction contains 9, 7.9, 5.1 and 2.6% of As, Cd, Pb and Cr extracts, respectively. The environmental risk in the study area comes from the presence of 10.4 ppm As in the exchangeable fraction. The risk assessment code illustrated that Pb ranged from low to medium risk, Cr medium to high risk, As high to very high risk and Cd shows very high risk. These results reflect the mixed sources (geogenic and anthropogenic) of metals in the soil of the study area.

Heavy metal concentrations and chemical fractions in sediment from Swan Lagoon, China: Their relation to the physiochemical properties of sediment

This study was performed to determine the distribution and chemical fractions of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in sediment from three sampling areas in Swan Lagoon, and their relation to the physiochemical properties of sediment were explored. The results revealed that Cd in sediment from the sand part (SP), muddy sand part (MSP) and sand muddy part (SMP) were potentially highly susceptible and bioavailable since the exchangeable fractions were 21.0%, 27.4%, and 32.1%, respectively, of the total concentrations. A portion of Pb and Zn were observed as reducible fractions owing to their affinity to Fe-Mn; they were able to complex with Fe-Mn oxides and oxyhydroxides in the sediment. A large amount of Cu in the oxidizable fraction may be due to the fact that Cu can easily form stable complexes with organic matter. Cr was overwhelmingly found in the residual fraction, suggesting that Cr was strongly bound in mineral lattices. Enrichment factors (EF) indicated that Cd in three sampling areas suffered severe enrichment, whereas other metals were present in only minor amounts. In addition, Cd may pose a medium to high risk in the MSP and SMP based on risk assessment codes. According to the mean probable effects level quotient, the samples from the MSP and SMP had a 21% probability of toxicity. The multivariate statistical analysis suggested that sediment texture (d0.5, sand and silt), Fe-Mn, and the total organic carbon (TOC) influenced the distribution of the studied metals and their chemical fractions.

Elemental (C/N Ratios) Isotope Compositions (δ13CTOC and δ15NTN) of Surface Sediments from the Barrier Islands in the Nakdong River Estuary, South Korea

Lee, J.-H.; Jeong, K.-S.; Lee, D.-H.; Park, K.S., and Woo, H.J., 2018. Elemental (C/N Ratios) Isotope compositions (δ13CTOC and δ15NTN) of surface sediments from the barrier islands in the Nakdong river estuary, South Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 36–40. Coconut Creek (Florida), ISSN 0749-0208.The Nakdong River Estuary (NRE) in South Korea is a typical, artificially manipulated estuary that is blocked by two large dams. The estuary is characterized by a barrier-lagoon system with various subenvironments and a microtidal domain with a mean tidal range of 1.07–1.50 m. The stable isotopic values (δ13CTOC and δ15NTN) and elemental (C/N ratios) compositions of organic matter, including those of halophytes, from the barrier islands were investigated in the NRE. In May (n = 94) and August (n = 90) 2015, sediment samples were collected on and around three islands in the NRE. The mean grain size of the barrier island system in the NRE ranged from 1.1 to 8.9 Φ (average 3.9 Φ) and the sediment types included muddy sand, sandy mud, and mud. The relative low C/N ratios (average 5.88) imply that the deposited organic matter originated from autochthonous algae derived-sources. The δ13CTOC ranged from −28.2 to −16.8‰VPDB (average −22.5‰VPDB), with δ15NTN in the range 6.2–12.5‰AIR (average 9.4‰AIR). Two halophytes (Phragmites communis and Scirpus planiculmis) had δ13CTOC values that ranged from −29.0 to −25.3‰VPDB (average −26.5‰VPDB) at ES-R and ES-5. The isotope and elemental composition of sedimentary organic matter (δ13CTOC and δ15NTN) indicated the deposition of algae-derived organic matter with limited input from terrestrial organic matter. These results suggest that the microphytobenthos contribution was greater than the inflow of surrounding land vegetation and sediments to the north of the barrier islands had a marine origin. To the south, the effect was considered mixed. Further studies should determine the effects of end-member discrimination on the origins of the organic matter, such as the advance signature proxy. It is necessary to continue measuring sediments and water in the brackish water zone around the barrier system with on-site monitoring of dam discharge, tidal currents, waves, and, etc.

Sedimentary Processes of Barrier-Lagoon System in the Nakdong River Estuary, Busan, South Korea

Woo, H.J.; Lee, J.-H.; Kang, J., and Choi, J.U., 2018. Sedimentary processes of barrier-lagoon system in the Nakdong river estuary, Busan, South Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1–5. Coconut Creek (Florida), ISSN 0749-0208.The Nakdong River Estuary on the southeastern coast of the Korean Peninsula is enclosed by two large estuarine dams, one constructed in 1934, and one between 1983 and 1987. The estuary has been characterized as a barrierlagoon system with various subenvironments and micro-tidal ecosystem and a mean tidal range of 1.07 m. The monitoring short-term sedimentation rates and suspended sediment characteristics were investigated to understand sedimentary processes in the barrier-lagoon system of the Nakdong River Estuary. The surface sediments generally showed sand sediment was dominated along the seaward side of the barrier islands and muddy sand sediment was dominated within the lagoon. The short-term sedimentation rates for a year showed that deposition dominated the tidal flats between the mainland and Jinudo (JW-line) and the mainland and Sinjado (SJ-line), with net deposition rates of 10.09 and 12.38 mm/year, respectively. Erosion dominated the tidal flat for two years at the southern end of Eulsukdo (ES-line), which is located on the eastern side of the system, at an annual rate of −12.76 mm/year. Four 12.5-hour anchoring surveys conducted at the inlets and channel revealed that net suspended sediments were transported to the open sea during a tidal cycle in summer. The sedimentary processes of the Nakdong River Estuary showed that sediments were transported into the lagoon through inlets during floods and moved westward and/or northwestward; they were then deposited on the tidal flats and in channels near the dams under low energy conditions. Within the eastern side of the system, sediments flowed out of the sea with discharge from the Nakdong Dam during ebb conditions. The major control factors for seasonal variations in these sedimentary processes within the barrier-lagoon system were waves, tidal currents, and dam discharges.

Muddy sand and sandy mud on the distal Mississippi fan: Implications for lobe depositional processes

We used laser particle size analysis (LPSA) to quantitatively analyze grain-size characteristics from distal Mississippi submarine fan deposits (Gulf of Mexico) and relate them to established depositional models along the spectrum of sediment gravity flows. One hundred and seventy-nine (179) sediment samples from 22 beds were obtained from cores of Deep Sea Drilling Project Leg 96 Sites 614, 615, and 621. The sediment from Sites 614 and 615 was deposited in lobes ∼500 km downstream from the Mississippi canyon head. Most samples were described as sand from visual inspection of cores, containing >75% volume of sand grains, with clay content <5% based on LPSA. A muddy sand definition was given to sands comprising >20% silt and finer grains, with generally higher clay content (3%–16%). However, LPSA data show that facies assignments from visual core description overestimated the proportion of sand grains: 15% of samples initially interpreted as sand contain <75% sand grains; 40% of muddy sand samples have <50% sand. Samples from lobes at Sites 614 and 615 were compared to samples from Site 621, where beds are sandier with a relatively narrow distribution of grain sizes deposited in a more proximal channel setting, <250 km from the canyon head. We interpret the large proportion of silt and finer grains in the distal lobes to reflect diminished turbulence within sediment gravity flows as they expand from confined to unconfined settings downstream of channel conduits. Entrainment of finer-grained sediment at the channel-to-lobe transition could have also contributed to larger proportions of silt and finer grains in distal lobes.

Determining and mapping species sensitivity to trawling impacts: the BEnthos Sensitivity Index to Trawling Operations (BESITO)

Applying an ecosystem approach requires a deep and holistic understanding of interactions between human activities and ecosystems. Bottom trawling is the most widespread physical human disturbance in the seabed and produces a wide range of direct and indirect impacts on benthic ecosystems. In this work, we develop a new index, the BEnthos Sensitivity Index to Trawling Operations (BESITO), using biological traits to classify species according to their sensitivity to bottom trawling. Seventy-nine different benthic taxa were classified according to their BESITO scores in three groups. The effect of trawling on the relative abundance of each group (measured as biomass proportion) was analysed using General Additive Models (GAMs) in a distribution model framework. The distribution of the relative biomass of each group was mapped and the impact of trawling was computed. Species with the lowest BESITO score (group I) showed a positive response to trawling disturbance (opportunistic response) whereas species with values higher than 2 (group III) showed a negative response (sensitive response). Species with a BESITO score of 2 did not show a significant response to the pressure (tolerant response). Trawling disturbance reduced relative biomass of sensitive species by 31% across the study area. This value increased to 46% when shelf-break was considered in isolation and reached values of 59.6% in the most impacted habitat (deep-sea muddy sands). The new index classified successfully the analysed species according to their sensitivity to trawling allowing modeling the impact of trawling disturbance on sensitive species, without the masking effect of opposed responses.

Benthic foraminiferal distribution and biofacies in the shelf part of Bay of Bengal, east coast of India

The environmental conditions that determine the benthic foraminiferal biofacies in the shelf part of Bay of Bengal are identified in the present study. The possible variables such as water depth, nature of sediments and substrate, salinity, dissolved oxygen and hydrodynamic factors are evaluated. A total of 23 surface sediment samples were collected at different water depth from the study area and were subjected to foraminiferal analysis and sediment characterisation. Altogether, 147 species belonging to 59 genera and 6 orders are identified, only 22 species are abundant. Cluster (Q-mode and R-mode) analysis of the abundant species resulted in the identification of four distinct biofacies which are correlated with environmental variables. The shallowest biofacies from 0 to 38 m water depth is represented by Ammonia beccarii, Amphistegina radiata, Asterorotalia pulchella and Elphidium crispum, which are associated with sandy sediment. The second biofacies from 38 to 83 m water depth is characterised by Cibicides wuellerstorfi, Quinqueloculina seminula, Quinqueloculina lamarckiana, Quinqueloculina vulgaris, Quinqueloculina agglutinans, Rotalinoides compressiuscula and Textularia agglutinans and the nature of sediments varies from slightly muddy sand to muddy sand. The third middle shelf biofacies from 83 to 150 m water depth is composed of Asterorotalia dentata, Cassidulina laviegata, Cibicides subhaidingerii and Lenticulina thalmani that are found in muddy sand sediment. The fourth outer shelf biofacies consisting chiefly of Bolivina ordinaria, Brizalina spathulata, Bulimina aculeata, Cancris communis, Siphouvigerina proboscidea and Uvigerina parvula exists from the depth of 150–200 m and related to sandy mud sediment. Two Paleo strandlines are identified at the depths of 49 m and 105 m, respectively, from the occurrence of relic forms along with soft coral sclerites. The shallower part of the seafloor up to 30 m depth is dominated by sandy sediments, reflecting the prevalence of high-energy conditions. On the other hand, the deeper part contains sediments with more mud content formed in low-energy conditions. The spatial distribution of benthic foraminifera in this shelf region is chiefly controlled by the nature of sediments and the bathymetry. However, another factor, such as dissolved oxygen, salinity, temperature and hydrodynamic conditions, seems to have an influence on the composition of benthic foraminiferal biofacies.

Tidal Flat Depositional Response to Neotectonic Cyclic Uplift and Subsidence (1–2 m) as Superimposed on Latest-Holocene Net Sea Level Rise (1.0 m/ka) in a Large Shallow Mesotidal Wave-Dominated Estuary, Willapa Bay, Washington, USA

The late-Holocene record of tidal flat deposition in the large shallow Willapa Bay estuary (43 km in length), located in the Columbia River Littoral Cell (CRLC) system (160 km length), was investigated with new vibracores (n=30) and gouge cores (n=8), reaching 2–5 m depth subsurface. Reversing up-core trends of muddy sand to peaty mud deposits in marginal tidal flat settings demonstrate episodic submergence events resulting from cyclic tectonic uplift and subsidence (1–2 m) in the Cascadia subduction zone. These short-term reversals are superimposed on longer-term trends of overall sediment coarsening-up, which represent the transgression of higher-energy sandy tidal flats over pre-existing lower-energy tidal flat mud and peaty mud deposits in late-Holocene time. Fining-up trends associated with channel lateral migration and accretionary bank deposition occurred only infrequently in the broad intertidal flats of Willapa Bay. Vibracores and gouge cores were dated by 14C (n=16) and paleo-subsidence event contacts (n=17). Vibracore median probability 14C ages ranged from 0 to 6,992 yr BP and averaged 2,174 yr BP. Dated sample ages and corresponding depths of tidal flat deposits yield net sedimentation rates of 0.9–1.2 m ka-1, depending on the averaging methods used. Net sedimentation rates in the intertidal flat settings (~1.0 m ka-1) are comparable to the rate of net sea level rise (~1.0 m ka-1), as based on dated paleo-tidal marsh deposits in Willapa Bay. Reported modern inputs of river sand (total=1.77x104 m3 yr-1), from the three small rivers that flow into Willapa Bay, fall well short of the estimated increasing accommodation space (1.9x105 m3 yr-1) in the intertidal (MLLW-MHHW) setting (1.9x108 m2 surface area) during the last 3 ka, or 3.0 m of sea level rise. The under-supply of tributary sand permitted the influx of littoral sand (1.1x105 m3 yr-1) into Willapa Bay, as based on the net sedimentation rate (~1.0 m ka-1) and textural composition (average 60 % littoral sand) in analyzed core sections (n=179). The long-term littoral sand sink in Willapa Bay’s intertidal setting (55 % of total estuary area) is estimated to be about 5 % of the Columbia River supply of sand to the CRLC system, and about 30% relative to the littoral sand accumulated in barrier spits and beach plains during late-Holocene time. A 2.0 m rise in future sea level could yield a littoral sand sink of 2.2x108 m3 in the Willapa Bay intertidal setting, resulting in an equivalent shoreline retreat of 600 m along a 50 km distance of the barrier spit and beach plains that are located adjacent to the Willapa Bay tidal inlet. Willapa Bay serves as proxy for potential littoral sand sinks in other shallow mesotidal estuary-barrier-beach systems around the world following future global sea level rise.

The Abudance Of Makrozoobenthos On Different Break Water In Semarang And Demak Coastal Area

The coast of Semarang and Demak has suffered some damage to its coastal areas. This damage is caused by natural factors and also human activities. There are number of mitigation methods such as hard, soft and hybrid that available for mitigation erosion. In Semarang and Demak coastal area using hard and hybrid option as their mitigation erotion. Breakwater is one of the way beach structure that often used as mitigation erosion di coastal area. Breakwater will cause sediment deposits that will become the living place of various organisms such as makrozoobenthos. The aim of this research is compare the abudance of makrozoobenthos in different type breakwater in Semarang and Demak coastal area.This research held on December 2016 – January 2017 in five different location with different breakwater type. Hard structure in Mangkang (West Semarang), Morosari (Demak district) and Tambak Lorok (North Semarang) and the hybrid engineering in Morosari 2 (Demak district) and Timbulsloko (Demak district). The method used in this study is descriptive comparative. Makrozoobenthos has been found in each station and the highest indeks is in hybrid engineering location. Polychaeta is a genus that dominates at every location because muddy sand is its main habitat.

Unrecognized loss of seagrass communities based on molluscan death assemblages: historic baseline shift in tropical Gulf of Aqaba, Red Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 589:73-83 (2018) - DOI: https://doi.org/10.3354/meps12492 Unrecognized loss of seagrass communities based on molluscan death assemblages: historic baseline shift in tropical Gulf of Aqaba, Red Sea Ehud Gilad1,2, Susan M. Kidwell3, Yehuda Benayahu2, Yael Edelman-Furstenberg1,* 1Geological Survey of Israel, Jerusalem 95501, Israel 2Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel 3Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA *Corresponding author: yael@gsi.gov.il ABSTRACT: Anthropogenic stresses on the naturally oligotrophic Gulf of Aqaba over the last 50 yr are suspected to have had a strong impact on biota, but the status of benthic fauna on the extensive soft-sediment seafloors is unknown. This study represents the first research on possible anthropogenic impacts on benthic marine fauna other than corals in the Gulf of Aqaba, a region of exceptional biodiversity. Comparing the species and functional-group composition of the living bivalve community to dead-shell assemblages from the modern seabed (top 5 cm) at 15 and 30 m water depth, both proximal and distal to historic point sources of nutrients, reveals that the ecological baseline has shifted. Live-dead discordance is strongest in the area of former sewage outfall and fish farm operations where seagrass is now functionally absent, but molluscan trophic structure has changed significantly even at distal sites where seagrass is still moderately abundant. Chemosymbiont-bearing lucinid bivalves specialized to sandy seagrass dominate death assemblages but are scarce to absent in living assemblages, which are dominated instead by facultative deposit-feeding bivalves which prefer muddy sand or muddy seagrass, consistent with organic enrichment. Seagrass habitat has thus changed qualitatively even where it persists, and sites of seagrass loss have not recovered despite cessation of major pollution ≥10 yr ago. Although shells of dead-only species require geological age-dating to definitively establish human drivers, the documentation of significant habitat change and trophic restructuring makes a powerful case for adoption of paleontological analysis by environmental managers and conservation biologists. KEY WORDS: Live-dead analysis · Bivalves · Anthropogenic modification · Paleoecology · Gulf of Aqaba · Eutrophication Full text in pdf format Supplementary material PreviousNextCite this article as: Gilad E, Kidwell SM, Benayahu Y, Edelman-Furstenberg Y (2018) Unrecognized loss of seagrass communities based on molluscan death assemblages: historic baseline shift in tropical Gulf of Aqaba, Red Sea. Mar Ecol Prog Ser 589:73-83. https://doi.org/10.3354/meps12492 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 589. Online publication date: February 23, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Evaluation of Ruditapes spp. Clam Stock on the Western Coast of Cotentin (English Channel)

Evaluation of Ruditapes spp. Clam Stock on the Western Coast of Cotentin (English Channel) The Manila clam Ruditapes philippinarum (Adam and Reeve 1850) was introduced into France in the 1970s and now dominates the European clam Ruditapes decusattus (Linnaeus 1758) in the intertidal zone of the western Cotentin (English Channel). While it has successfully colonized a large variety of sediment habitats, from muddy sand to gravel, the densities remain< 20 ind. m-2. In this extensive intertidal zone, it is difficult to estimate the density as well as the stock of such dispersed species of clam. Our study has three main objectives: i) to determine a better sampling strategy to estimate the density of Ruditapes spp. clam populations; ii) to assess the spatial distribution of clams at the scale of the western coast of Cotentin (30 km of coastline from North to South), and iii) to evaluate the stock and annual quantities of clams fished by recreational and professional fishing in this area. For the estimation of densities and stock of Ruditapes spp., it is better to continue using a quadrat area of 1 m² for a large number of random sampling points (≥ 400) to estimate with the greatest possible spatial precision the local and regional abundance of such low-density populations. Sampling techniques with smaller quadrats and more sampling points lead to higher standard deviation of the mean densities. The species are distributed in four main patches covering between 0.54 to 3.14 km² out of a total of 10.47 km² (~ 10% of the intertidal zone). The 2015 stock (Ruditapes> 40 mm, legal catch size) in these four patches is estimated as 382 t (fresh weight with shell) for a total of harvest of 122 t (32% of the adult stock), which corresponds to a catch of 8 t by professional fishers and 113 t by recreational fishers.