Mud Fraction Research Articles

Baseline Inventory of Benthic Macrofauna in German Marine Protected Areas (2020-2022) before Closure for Bottom-Contact Fishing.

The response of benthic habitats and organisms to bottom-contact fishing intensity is investigated in marine protected areas (MPAs) of the German EEZ in the North and Baltic Seas. We examined the current state of macrofauna biodiversity in 2020-2022. Comparative analysis for macrofauna (in- and epifauna) inhabiting nine Natura 2000 MPAs constitutes a baseline to assess the effects of bottom-contact fishing exclusion in the future. Aspects of spatial and temporal variability are briefly summarized and discussed. We provide a species list for each region, including 481 taxa, of which 79 were found in both regions, 183 only in the North Sea, and 219 only in the Baltic Sea. The Baltic Sea dataset surprisingly included higher numbers of taxa and revealed more Red List species. The share of major taxonomic groups (polychaetes, bivalves and amphipods) in species richness showed peculiar commonalities between the two regions. In the North Sea, multivariate analysis of community structure revealed significantly higher within-similarity and stronger separation between the considered MPAs compared to the Baltic MPAs. Salinity, temperature and sediment fractions of sand were responsible for over 60% of the variation in the North Sea macrofauna occurrence data. Salinity, mud fraction and bottom-contact fishing were the most important drivers in the Baltic Sea and, together with other considered environmental drivers, were responsible for 53% of the variation. This study identifies aspects of macrofauna occurrence that may be used to assess (causes of) future changes.

Multivariate mapping of seabed grain size parameters in the Bay of Fundy using convolutional neural networks

High-resolution seabed sediment information is critical for a range of marine spatial planning applications in multi-use shelf environments. To establish this information for the Bay of Fundy, Canada, legacy seabed sediment measurements were obtained from regional data compilations, and eight parameters describing the grain size were modelled across the extent of the bay using high resolution acoustic seafloor mapping and oceanographic datasets. This was achieved using a purpose-made convolutional neural network configured for geospatial modelling of multivariate grain size parameters. Shared information between the response parameters enabled model training with partially complete observations from the varied legacy data sources, and an explicit multiscale model architecture ensured that environmental predictors were implemented at appropriate scales for modelling each parameter. This avoids typical exhaustive exploration and selection of scale-specific predictor sets that often precede model building. Compositional grain size parameters were additionally accommodated using appropriate output activation functions, providing an efficient alternative to compositional data transformation and imputation. Results agreed well with our current understanding of the surficial geology of the bay, and cross-validation was used to quantitatively evaluate map predictions. Of the eight predicted parameters, the mean grain size and mud (clay and silt) fractions were predicted with high accuracy (> 50% variance explained); the accuracy of grain size skewness was comparatively low (24% variance explained). Exploration of variable importance suggested that compiled acoustic backscatter was the most important environmental variable for predicting the grain size, but that geographic information describing the latitude and longitude within the bay was also highly useful. We hypothesize an interaction between these variables that enables location-specific prediction. Data layers of predicted grain size parameter values are made available for further sedimentological and ecological exploration, and for marine spatial planning activities within the bay.

Suspended sediment properties and visual clarity of the Manawatū River, New Zealand

ABSTRACT Studies of river suspended sediment typically focus on mass loads with little attention devoted to sediment properties such as particle size distribution (PSD) or light attenuation. However, environmental behaviour and ecological effects of suspended sediment vary greatly with particle properties. Visual clarity is a particularly important attribute of waters that is strongly affected by particle properties. We studied the relationship between visual clarity and suspended sediment in the Manawatū River – by combining event auto-sampling with long-term state-of-environment monitoring. We fractionated stormflow samples into sand and ‘mud’ (silt + clay) by wet-sieving at 63 μm, and the mud fraction was further analysed for organics, PSD and light beam attenuation (which controls visual clarity). Light beam attenuation correlated very closely with high-frequency field turbidity – providing an absolute optical calibration. The ratio of light beam attenuation to mass concentration (known as ‘optical cross-section’) averaged about 0.5 m2/g – somewhat higher than expected for silt particles in the measured size range, probably due to plate-shaped clays. The visual clarity regime, estimated from field turbidity, was consistent with monthly direct observations. Our study illustrates how certain sediment ‘quality’ metrics can usefully extend sediment monitoring applications, and we encourage closer integration of sediment and water quality monitoring.

Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds

In this study, we investigate the complex dynamics of multi-fractional suspended particle transport in a shallow water basin subjected to strong wind conditions. Our research focuses on understanding the interplay between wind-induced advection and particle settlement, and its implications for sediment redistribution.Through our analysis, we reveal the distinct behaviors of different sediment fractions. Clay particles, constituting the lowest fraction in sediment cores, remain suspended throughout the simulation due to their low settlement velocity, with relatively stable concentrations. Conversely, the dominant fraction, medium silt, is suspended during intense wind events but quickly settles to the bed due to its higher settling velocity. Wind stress exceeding 0.05 Pa triggers particulate matter erosion, leading to its presence in the water column.Additionally, we explore the 2D distribution of sediment characteristics, including thickness, dry density, and mud fraction, to identify areas prone to erosion and deposition. Our findings demonstrate that coastal areas of the Taganrog Bay experienced significant erosion following strong wind events, exhibiting the thinnest sediment thickness and the highest dry bulk density. Deposition areas, characterized by thicker sediment layers and lower dry density, were often found in proximity to erosion zones, indicating the influence of particle resuspension and settlement processes.Furthermore, we analyze the implications of our findings on the vulnerability of specific regions to erosion and deposition. The central part of the sea contains moderately thicker sediment layers with a moderately high mud fraction, representing a zone of fine sediment accumulation. These fine sediments, including fine silt and clay, remain suspended for longer durations and are redistributed over greater distances by currents.Overall, our study provides valuable understanding into the multi-fractional suspended particle pathways and their interaction with strong winds in shallow water basins. The results contribute to a better understanding of sediment dynamics, which has implications for coastal management, environmental monitoring, and the preservation of benthic ecosystems.

Distribution of individual mud fractions in a tidal basin of the East Frisian Wadden Sea (southern North Sea): affinities between sortable silts, aggregated particle suites, and calcium carbonate and organic matter contents

In the 1990s and early 2000s, it was recognized that marine muds consisted of sortable silt (63–8 µm) and aggregated (< 8 µm) particle suites and that these responded differentially to the hydraulic sorting process. Among the aggregated particle suite, the composition and hydraulic behavior of fecal pellets received the least attention. The present study focused on a tidal basin (~ 71 km2) of the East Frisian Wadden Sea (southern North Sea), in which the depositional patterns of both the sortable silt and aggregated mud fractions were compared with the aim of identifying similarities and/or dissimilarities. The results show essentially dissimilar trends, the sortable silt suite being characterized by two non-overlapping hydraulic populations, the aggregated particle suite by three overlapping populations with modal diameters separated by only a few microns. The depositional pattern of the latter is interpreted to suggest that the hydraulic populations relate to specific fecal pellet groups, each composed of a different discrete grain-size spectrum produced by different filter-feeding organisms. At the same time, it is demonstrated that the distribution of organic matter is closely linked to the aggregated (< 8 µm) particle suite. The CaCO3 content, by contrast, is linked to the mud fraction by a power relationship, the large data scatter suggesting multiple sources. Budget calculations show that the standing stock of mud in the uppermost 5 cm of the sediment in the tidal basin amounts to ~ 0.461 × 106 tons (9.78% of the total sediment), of which ~ 31.3 × 103 tons (0.67% of the total sediment) are contributed by organic matter.Graphical abstract

The effects of gas extraction under intertidal mudflats on sediment and macrozoobenthic communities

Abstract Land subsidence in intertidal environments may change the flooding regime and sediment composition, two drivers of the macrozoobenthic community. In the Dutch Wadden Sea, a UNESCO world heritage site, gas extraction has resulted in an average subsidence of intertidal mudflats of 2 mm year−1. These mudflats support an abundant macrozoobenthic community that offers important resources for birds and fish. The area is managed through the ‘hand on the tap’ principle, meaning that human activities should be halted if they affect the natural values. To what extent land subsidence affects sediment and macrozoobenthos remains unknown and is increasingly important given sea level rise. Taking advantage of a large‐scale monitoring program, we evaluated the effect of anthropogenically caused subsidence on sediment composition and macrozoobenthos. Nearly 4600 points were sampled yearly (2008–2020) across the Dutch Wadden Sea, allowing us to compare sediment composition and macrozoobenthos biomass within and outside the subsidence area while controlling for the main drivers of these variables. We also compared population trends within and outside the subsidence area for 31 species with different habitat use. Mud fraction was 3% higher within the subsided area and median grain size decreased at 1 μm year−1 while remaining constant in other mudflats. This had no effect on the total biomass of macrozoobenthos. Within the subsidence area, however, the biomass of species that use deeper areas increased compared to outside, and the opposite was true for species using shallower habitat. Policy implications: Land subsidence is related to changes in median grain size and macrozoobenthic community composition. However, because thresholds have not been defined, it is not clear if this requires management actions. For a successful implementation of the ‘hand on the tap’ principle in the Wadden Sea, it is necessary to define beforehand the relevant variables that represent the natural values, implement proper monitoring and define thresholds above which effects are not acceptable. We propose median grain size, mud fraction and macrozoobenthic composition as good measures of the natural values of the Wadden Sea, and the methods used here as a way for identifying anthropogenic effects on them.

Mineralogy and geochemistry of modern Red River sediments (North Vietnam): Provenance and weathering implications

Abstract This study illustrates the clay mineralogy and sedimentary geochemistry of the Red River and its major tributaries and distributaries in northern Vietnam and shows how these methods can be used to unravel grain size, provenance, hydraulic-sorting, and chemical weathering effects. All sand samples are SiO2-rich and consequently depleted in most chemical elements (but Sn and Pb) relative to the upper continental crust (UCC). The order of element mobility indicated by αAlE values, which estimate the degree of depletion in mobile element E relative to the UCC standard, is Ca ≥ Na &amp;gt; Sr &amp;gt; Mg &amp;gt; Ba ≥ K ≥ Rb. In mud fractions, SiO2 decreases, and other elements consequently increase. The grain size-dependent intrasample chemical variability of fluvial sediments reflects the grain size distribution of detrital minerals, which is strictly controlled in turn by the settling-equivalence principle. The 87Sr/86Sr ratio in Red River sands varies widely between 0.716 and 0.748, and εNd ranges from −8.5 to −13.8. The negative εNd values and high 87Sr/86Sr ratios point at a significant contribution from Precambrian crystalline basement, directly or through recycling of Triassic siliciclastic strata. Clay-mineral assemblages, dominated by illite and smectite with subordinate kaolinite and minor chlorite, suggest largely physical erosion in the upper catchment and stronger weathering in the monsoon-drenched lower catchment. Extremely intense weathering is demonstrated by a Quaternary soil sample from the Red River valley in northernmost Vietnam, which is a pure quartzose sand yielding a tourmaline-dominated heavy-mineral suite and a kaolinite-dominated clay-mineral assemblage. In the humid landscapes of northern Vietnam, no detrital mineral, excepting quartz, muscovite, tourmaline, prismatic sillimanite, anatase, and zircon, can resist even shallow early pedogenesis.

Effects of Mass Wasting on the Physiochemical Properties of Fluvial Sediments in Puerto Rico Following Hurricane Maria

AbstractMass wasting plays an important role in carbon cycling and sequestration by exposing fresh bedrock and delivering hillslope sediments to lowlands and fluvial systems. Chemical weathering signatures of landslide‐derived fluvial sediments can be used to understand linkages between hillslope and fluvial processes and thus to characterize spatiotemporal dynamics of sediments. However, chemical signatures of fluvial sediments derived by landslides are yet to be fully understood. Here, we compare the bulk chemistry, mineralogy, and grain size of fluvial sediments collected pre‐ and post‐Hurricane Maria in the Rio Guayanés and Rio Guayabo watersheds in southeastern Puerto Rico to help fill this knowledge gap. Comparison of the mud fraction (&lt;63 μm) of fluvial sediments collected before Hurricane Maria with similar mud fractions collected after the storm reveals that the post‐hurricane muds exhibit a wider range and higher average weathering index values, but coarser grain size modes. We infer that small landslides triggered by Hurricane Maria transported slope materials from shallow depths, including weathered topsoil and saprolite, as opposed to previous deep‐seated landslides, which likely sampled regolith and bedrock. Variances in weathering indices observed that pre‐ and post‐hurricanes do not necessarily reflect average climate signatures, but rather reflect subtle differences in a transport mechanism, which produce significant differences in weathering indices recorded by fluvial sediments. We propose that weathering indices provide a means to understand sediment dynamics in mountainous regions, particularly for sediment transported immediately after landslides triggered by extreme events, such as precipitation and earthquakes, and also provide important data sets required for mapping potential carbon sequestration across landscapes.

Temporal and spatial variations in calcium carbonate deposition in a mixed siliciclastic–carbonate deep marine system: the Ediacaran Deeside Limestone Formation, Aboyne, Scotland

The Deeside Limestone Formation (DLF), outcropping in western Aberdeenshire, comprises the eastern margin of a distinctive Upper Dalradian mixed siliciclastic–carbonate system of Ediacaran age which may be correlated southwestwards for more than 400 km to County Donegal in Ireland. A reconstructed stratigraphic column suggests three broad vertical sequences (S1–S3), each comprising a general upward proportionate increase in calcium carbonate with respect to quartz, locally capped by metalimestones (L1–L3). A simple explanation for this upward change lies in the differing physical response of the two heterolithic components under the same hydrodynamic process, with the heavier quartz grains preferentially enriching the bedload and the finer carbonate mud fraction, the suspended load. The three metalimestone intervals are observed only in central/eastern parts of the field area, suggesting a lateral facies variation. The predominance of calcareous–siliciclastic bed-scale compositional mixing within the DLF suggests sedimentation on the Dalradian shelf comprised contemporaneous mixing of the siliciclastic and carbonate fractions prior to subsequent re-mixing during transportation downslope into the deep water, punctuated by pulses of point-sourced siliciclastic input.

Contribution of mineral filler to the fatigue damage behaviour of bituminous mastic

The objective of this research was to quantify the contribution of mineral filler to the linear shear strain amplitude sweep-based fatigue behaviour of mastic. Mastics with different volume fractions of mud (RM), marble dust (MD), and limestone dust (LS) fillers were tested in intermediate temperature domain, while the mechanical responses throughout the test sequence were compared to that of bitumen. The conspicuously high contribution of the RM filler indicated its comprehensive interaction with bitumen. The threshold of this contribution by approaching the ultimate particle interlocking was identified at the volume fraction of the RM filler of 20 %. On the contrary, the contributions of the common MD and LS fillers were moderate. The transition of the mechanical properties throughout the test sequence showed a characteristic dependency on the type of filler, its volume fraction, and test temperature. A more advanced characterisation of this transition in the zone of failure would have a considerable potential for the quantitative assessment of the type of failure, critical for the relevance of the results.

Modeling the Morphodynamic Response of Estuarine Intertidal Shoals to Sea‐Level Rise

AbstractIntertidal shoals are key features of estuarine environments worldwide. Climate change poses questions regarding the sustainability of intertidal areas under sea‐level rise (SLR). Our work investigates the SLR impact on the long‐term morphological evolution of unvegetated intertidal sandy shoals in a constrained channel‐shoal system. Utilizing a process‐based model (Delft3D), we schematize a short tidal system in a rectangular (2.5 × 20 km) basin with a high‐resolution grid. An initial, mildly sloping, bathymetry is subjected to constant semidiurnal tidal forcing, sediment supply, and small wind‐generated waves modeled by SWAN. A positive morphodynamic feedback between hydrodynamics, sediment transport, and morphology causes the emergence of large‐scale channel‐shoal patterns. Over centuries, tide‐residual sediment transport gradually decreases leading to a state of low morphological activity balanced by tides, waves, and sediment supply. Tidal currents are the main driver of the SLR morphodynamic adaptation. Wave action leads to wider and lower shoals but does not fundamentally change the long‐term morphological evolution. SLR causes increased flood dominance which triggers sediment import into the system. Shoals accrete in response to SLR with a lag that increases as SLR accelerates, eventually causing intertidal shoals to drown. Seaward shoals near the open boundary sediment source have higher accretion rates compared to landward shoals. Similarly, on a shoal‐scale, the highest accretion rates occur at the shoal edges bounding the sediment suppling channels. A larger sediment supply enhances the SLR adaptation. Waves help distribute sediment supplied from channels across shoals. Adding mud fractions leads to faster, more uniform, accretion and muddier shoals under SLR.

Modelling seabed sediment physical properties and organic matter content in the Firth of Clyde

Abstract. High-quality quantitative maps of seabed sedimentary physical and geochemical properties have numerous research and conservation applications, including habitat and ecosystem modelling, marine spatial planning, and ecosystem service mapping. However, such maps are lacking for many ecologically and economically important marine areas. Using legacy data supplemented by measurements from recent benthic surveys, modelled hydrodynamic variables, and high-resolution bathymetry, quantitative maps for the top 10 cm of seabed sediment were generated via a combination of statistical and machine-learning techniques for the Firth of Clyde, a semi-enclosed coastal sea on the west coast of Scotland. The maps include sediment fractions of mud, sand, and gravel; whole-sediment median grain size; sediment permeability and porosity; rates of natural seabed abrasion; and sediment particulate organic carbon and nitrogen content. Properties were mapped over an unstructured grid so that very high resolutions were achieved close to the coastlines, where sediments may be expected to be spatially heterogeneous. Overall, the maps reveal extensive areas of very low sediment permeability coupled with low rates of natural seabed disturbance. Moreover, muddy sediments in the inner Firth of Clyde, Inchmarnock Water, and the sea lochs are enriched in organic carbon and nitrogen relative to the sediments of the outer Firth of Clyde. As a demonstration of the value of these maps, the standing stock of organic carbon and nitrogen in the surficial sediments of the Clyde was calculated. The Clyde stores 3.42 and 0.33 million t of organic carbon and nitrogen in the top 10 cm of seabed sediment, respectively, substantially contributing to Scotland's coastal and shelf blue carbon stocks. Data products are available from https://doi.org/10.15129/2003faa2-ee93-4c11-bb16-48485f5f136d (Heath and Pace, 2021).

Red Sea Holocene carbonates: Windward platform margin and lagoon near Al-Wajh, northern Saudi Arabia

ABSTRACTAnalysis of Holocene sedimentary seascape is focused on the Red Sea windward Al-Wajh platform margin, its central lagoon, and nearby isolated platforms based on data that include mapped ecological facies (habitats), water depths, grain sizes, and allochem types and abundances determined from thin sections. On this basis, a depositional model applicable to Red Sea Plio-Pleistocene and other ancient icehouse carbonate platforms is presented. The model highlights favorable reservoirs in analogous ancient systems to include coral crests and columnar framework habitats with primary porosity developed in boundstone lithologies and windward platform margins to contain considerable open pore space, including cavernous openings, of which not all should be anticipated to be occluded with marine cements and sediments. Meteoric diagenesis is expected to be minor as limited freshwater is available due to extreme aridity, but may play a role during glaciation.Most habitats have potential for secondary (enhanced) porosity resulting from dissolution of aragonite skeletons, particularly mollusk shells and calcareous coral (Scleractinia) endoskeletons. Central-lagoon habitats are expected to have the least favorable reservoir potential of environments considered because they are dominated by peloids. Central-lagoon sediment differs from other published localities, having higher peloid abundances, greater peloid distribution, and little or no association with Halimeda and quartz grains. Under the likely scenario that platform-interior sediments are completely bioturbated and comprise peloid-rich, grain-dominated fabrics, with many smaller peloids (most of them likely fecal pellets) at or near 4 μm in size (i.e., mud fraction), it is possible that grain size will control pore size once the considered deposits are lithified. If so, platform-interior sediments will lithify as mudstones, wackestones, or very fine-grained grainstones, an outcome which might otherwise be unexpected given the abundance of coarse peloid grains.The Al-Wajh platform is compared with 15 Holocene analogs and found to be unique with respect to rift-margin type, restricted-marine circulation, in having a lagoon with high peloid content, and lack of karst. In further comparison with ancient reservoir analogs, two greenhouse and four icehouse, it compares favorably to icehouse platforms deposited in rift basins with respect to mineralogy of deposition, meter-scale cycle thicknesses, and general peloid content and distribution. It provides a snapshot as to how an icehouse platform might have nucleated and attached along an active rift margin; it is a broadly applicable carbonate analog for the Red Sea Plio-Pleistocene and similar icehouse, rift basins.

Diatoms of the intertidal environments of Willapa Bay, Washington, USA as a sea-level indicator

An understanding of the modern relationship between diatom species and elevation is a prerequisite for using fossil diatoms to reconstruct relative sea level (RSL). We described modern diatom distributions from seven transects covering unvegetated subtidal environments to forested uplands from four tidal wetland sites (Smith Creek, Bone River, Niawiakum River, and Naselle River) of Willapa Bay, Washington, USA. We compared our diatom dataset (320 species from 104 samples) to a series of environmental variables (elevation, grain-size, total organic carbon (TOCSOM), and porewater salinity) using hierarchical clustering and ordination. While no single variable consistently explains variations in diatom assemblages at every site, elevation, salinity, and substrate (mud fraction and TOCSOM) are variables affecting diatom distribution along our transects. Elevation was the major environmental control of diatom variability (explained 27–39% variance) at four transects (Bone River Transect 1, Niawiakum River Transect 2, Naselle River Transect 1 and 2). Salinity and substrate were the major environmental controls (explained 12–32% variance) of diatom variability at three transects (Niawiakum River Transect 1: salinity; Smith Creek Transect and Bone River Transect 2: TOCSOM). Analyses of a combined regional dataset of all transects suggest that elevation is the driver of regional diatom variability in Willapa Bay, with salinity and substrate co-varying along an elevation gradient. We identify species with narrow elevation tolerances that can serve as indicator species of specific environments. Despite the site-specific variability of our modern diatom distribution, the regional dataset provides an important dataset that can be used to reconstruct RSL in Willapa Bay.

Phosphorous fractionation distribution in surface sediments of the Jobokuto Bay

Phosphorus (P) is an essential nutrient that can limit primary productivity in waters. Phosphorus has significant impact on the biogeochemical cycle in marine ecosystems. Surface sediments play an important role in the nutrient dynamics. Riverine input is sources of P to the ocean and sediment plays an important role as a source or sink of P in the coloumn of water. Phosphorous (P) availability is regarded as the most important factor for determining the water quality in coastal waters. However, not all of the P fractions can be released from the sediment. This study was conducted to identify the distribution of phosphorus (P) fractionation in the sediment surface of Jobokuto Bay. Samples were collected from ten locations. Percentage of sedimentary parameters such as sand, silt, clay, and organic carbon were analyzed to find out their relation with various P fractions. The sediment found was mostly sand at the station near to the coast and mud (silt and clay) at offshore stations. The results showed that Ca-P dominant (56.03%) and percentages of Fe-P, OP, and Ads-P were 23.43, 17.41, and 3.2% respectively. Terrestrial inputs and biological deposits cause Ca-P dominant. The bioavailability of P fractions were ranged from 34.45 to 56.1% of the total P (TP) content. The high concentrations of the Ads-P was found in the mud fraction and located at offshore stations. The order of abundance of the major forms of P in the surface sediments of Jobokuto bay is as follows: Ca-P &gt; Fe-P &gt; OP &gt; Ads-P

Source‐to‐sink analysis for the mud and sand in the late‐Quaternary Qiantang River incised‐valley fill and its implications for delta‐shelf–estuary dispersal systems globally

AbstractThe Changjiang (i.e. the Yangtze River) debouches a huge amount of sediment to the East China Sea and exerts a significant effect on the evolution of the down‐drift Qiantang River system. This study quantitatively documents the temporal change in the import of Changjiang sand and mud to the late Quaternary Qiantang River incised valley by establishing separate mixing models based on zircon U‐Pb ages for the sand and trace‐element compositions of the mud fraction. Results indicate that the Qiantang River provided all of the sediment to its valley before ca 8.0 cal kyr bp. However, its sediment proportion decreases upward due to the onset of export of sediment from the Changjiang after its delta had prograded sufficiently. Changjiang mud, a major component (ca 87%) of the Changjiang‐derived sediment, is considered to be primarily supplied through the resuspension and landward transportation of sediment from the inner‐shelf mud wedge in the East China Sea by flood‐tidal currents and waves. Changjiang sand, which arrived in the Qiantang River valley later than the mud, is interpreted to be derived from the reworking of older deposits on the East China Sea shelf and along the northern margin of the Qiantang River estuary. In the later part of the valley fill, Qiantang River sediment is only ca 9% of the Changjiang contribution, although Qiantang River mud has begun to be exported recently. The Changjiang contribution to the Qiantang River system constitutes ca 50% of the total sediment load discharged by the Changjiang during the 8–6 cal kyr bp period, but &lt;4% since 6 cal kyr bp. This study illustrates the need to exercise caution when interpreting compositional data from linked coastal‐shelf sediment‐dispersal systems with significant along‐coast transport, and is expected to be applicable in a general way to other linked river–coastal‐shelf systems.

Trace elements in the shoreline and seabed sediments of the southern Caspian Sea: investigation of contamination level, distribution, ecological and human health risks, and elemental partition coefficient.

This study assesses the occurrence of trace elements (TEs) in sediments of the southern Caspian Sea. A total of 16 shoreline sediment samples and 15 seabed sediment samples along five coastal transects were studied. The mean concentration of TEs follows the order of Zn > V > Cr > Ni > Cu > Pb > Co > As > Sb > Mo > Cd. The TEs had an uneven, heterogeneous distribution within the shoreline and seabed sampling sites. This is due to that the study area comprises a large number of different pollution sources, also different sediment physicochemical characteristics. Levels of individual TEs within the seabed sediment transects were higher where their shoreline sites had higher concentrations, reflecting that the coastal sites play an important role in diffusing the contaminants towards the sea. The main anthropogenic source of TEs in this highly populated region, especially in the western part, is likely a large number of discharge points of greywater entering the sea. In addition, dominant fishing industry, tourism, intense agriculture, and textile and paper industry, as well as several other commercial activities, contribute significantly to the overall loading of TEs. Based on the statistical analyses, the organic matter and mud fraction had a strong explanatory value for the spatial variation of Cu, while oxyhydroxides of Fe and Mn had good explanatory factors to govern the spatial variation of other TEs. Pb and Zn had a relatively high partition coefficient (Kd), reflecting the affinity of these elements to be sorbed to the sediment phase. Cd and Sb had lower Kd, tending to remain in the aqueous phase. Geochemical indices indicated high enrichment of Cd, Sb, Zn, and Pb at a number of sampling sites, reflecting potential local sources of contamination. The Sisangan recreational area was identified as the most contaminated site. From a public health perspective, the non-carcinogenic risk of TEs was significant only at this site. The carcinogenic risks of Pb(II) and As(III) in adults, and Pb(II), Cd(II), and As(III) in children, were tolerable.

Relation Macrozoobenthos with Sediment Organic Material in the Intertidal Zone in Selat Baru Beach, Bengkalis Regency, Riau Province

Selat Baru Village was one of several beaches on Bengkalis Island which was located in the northern part of Bengkalis Island. Selat Baru Beach is a tourist spot that has the most visitors every day, especially during the Eid holidays. In addition, there are rivers, ports, and boat crossings also taking place on Selat Baru Beach. The purpose of this study was to determine the content of sediment organic matter, the type and abundance of macrozoobenthos, and to determine the relationship between the organic matter of sediment and the abundance of macrozoobenthos in the New Strait coastal waters. The method used was a survey method, where the data collected was primary data which was then analyzed statistically and discussed descriptively. The results of measurements of oceanographic parameters from the research location have an average temperature of 28,67 oC, and pH of 7, a salinity of 26,33 ‰, transparency of 24,33 cm, and a current velocity of 0,1 m/s. The average sediment content obtained at station 1 was 1,42%, station 2 was 0,77%, and station 3 was 7,34%. The percentage of sand fraction has the highest percentage at station 1 substation 3 (95,56%) and the lowest at station 3 substation 3 (39,78%), while the highest percentage of mud fraction was at station 3 substation 3 (54,19%) and the lowest found at station 2 substation 1 (4,15%). The macrozoobenthos found were from the Bivalvia class (Corbicula sp, Lucinidae sp, Anomia sp) and the Gastropod class (Nucella sp, Rabdotus sp, Cerithidea sp) and the Malacostraca class (Hermigrapsus sp). The average abundance of macrozoobenthos found at station 1 was 4,22 ind/m2, station 2 was 4,22 ind/m2, and station 3 was 10,67 ind/m2. The result shows the effect of the sludge sediment fraction on the abundance of macrozoobenthos has a coefficient of determination (R2) with a value of 0,9015 and a correlation coefficient (r) with a value of 0,9495 meaning that 90,15% of macrozoobenthos abundance was influenced by sediment fraction and the rest was influenced by other environmental factors

Enrichment and distribution of metals in surface sediments of the Thanh Hoa coastal area, Viet Nam

Thirty-two surface sediment samples were collected in the Thanh Hoa coastal area, from the shore to a depth of 30 m. Grain sizes and the contents of 14 major and trace metals were measured with the goal of assessing the impact from the mainland to the coastal area of Thanh Hoa.The sand fraction ranged from 0.5 to 82.7%, and the mud fraction ranged from 17.3 to 99.5%.The contents of major and trace elements – namely, Fe, Cu, Pb, Zn, As, Cr, Co, Ni, Mn, Cd, Mo, Li, V, and Sn – in the sediments were assessed by comparison with Canadian environmental quality guidelines and indices. The concentrations of Cu, Pb, Zn, As, and Cr were higher than the interim marine sediment quality guidelines (ISQGs) benchmark but lower than the probable effect levels (PELs). The geo-accumulation (Igeo) indexes of As and Pb indicated moderate pollution; the enrichment factor (EF) indexes of Cu, Pb, Zn, Cd, As, Li, and Mn indicated minor to moderate enrichment; the contamination factor (CF) indexes of Fe, Cu, Pb, Zn, Cd, As, Co, Li, and Mn indicated moderate to considerable contamination, the CF showed considerable contamination for As and Pb in particular; the ecological risk factor (ER) indexes of Cd and As were moderate; and the degree of contamination (CD) of all 14 elements was high.On the basis of this preliminary environmental risk evaluation, the levels of some trace elements indicated potential issues for the Thanh Hoa coastal area, particularly near river mouths and the northern zone, where concentrations were higher. Thus, appropriate monitoring plans based on sound scientific knowledge are imperative for safe and sustainable development.

Unmixing water and mud: Characterizing diffuse boundaries of subtidal mud banks from individual satellite observations

Mapping of subtidal banks in mud-dominated coastal systems is crucial as they influence not only shoreline and ecosystem dynamics but also economic activities and livelihoods of local communities. Due to associated spatiotemporal variations in suspended particulate matter concentrations, subtidal mudbanks are often confined by diffuse and rapidly changing boundaries. To avoid inaccurate representations of these mudbanks in remote sensing images, it is necessary to unmix distinctive reflectance signals into representative landcover fractions. Yet, extracting mud fractions, in order to characterize such diffuse boundaries, is challenging because of the spectral similarity between subtidal- and intertidal features. Here we show that an unsupervised decision tree, used to derive spatially explicit and spectrally coherent image endmembers, facilitates robust linear spectral unmixing on an image-to-image basis, enabling the separation of these coastal features. We found that resulting abundance maps represent cross-shore gradients of vegetation, water and mud fractions present at the coast of Suriname. Furthermore, we confirmed that it is possible to separate land, water and an initial estimate of intertidal zones on individual images. Thus, spectral signatures of end-member candidates, determined from relevant index histograms within these initial estimates, are consistent. These results demonstrate that spectral information from well-defined spatial neighbourhoods facilitates the detection of diffuse boundaries of mudbanks with a spectral unmixing approach.