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This study provides an in-depth analysis of the relationship between radionuclide and particle size-class abundance through an investigation of radionuclide distribution in finer sediments within surface core samples collected from two contaminated upper saltmarsh areas of the Dee estuary and Biggar marsh in north-west England. The particle size fractionation (PSF) analysis was carried out following gravitational settling and pipette method to separate all samples into six size-fractioned groups ranging from 63 to <2 µm (very coarse silt to clay), and radioactivity analysis was performed using a well-type High Purity Germanium (HPGe) detector. The highest 241Am and 137Cs activities in PSF samples were found to be 291 ± 5 and 2071 ± 16 Bq kg−1, respectively, for the Dee estuary saltmarsh and 3832 ± 14 and 4840 ± 23 Bq kg−1, respectively, for Biggar saltmarsh and found in the clay fractions for both sites. Correlation of radioactivity concentration data of three size groups ranging from 63 to <2 µm (very coarse silt to clay) confirms a strong and increasing association of radioactivity with fine particles from coarse to fine clay-size particles. Also, examination of textural and radionuclide data of all bulk core and size-fractioned samples revealed that upper saltmarshes are made up of both contaminated and uncontaminated sediments. Furthermore, the annual outdoor external effective dose range for all short core data (0.001–0.11 mSv y−1) and for PSF sample data (0.001–0.08 mSv y−1) reveal that some values exceed the world average value of 0.07 mSv y−1as reported in UNSCEAR [43], for outdoor, which are non-negligible. Thus, the total annual external effective dose associated with existing contaminated saltmarsh sediments represents a possible health risk to saltmarsh users and coastal populations living nearby these saltmarshes. [ABSTRACT FROM AUTHOR]

The genesis, facies conditions of sedimentation, degree of organic matter transformation in the bottom sediments and march soils of the southwestern coast of the Barents Sea are characterized based on results of a GC-MS study of the composition and distribution of hydrocarbons (n-alkanes, isoprenoids, steranes, hopanes, polycyclic aromatic hydrocarbons (PAHs), and their alkyl homologues). The effects of the toxicity levels of polyarenes on the biota inhabiting the tidal zones of the coast was assessed, and areas of elevated anthropogenic load were identified (littoral of the eastern Tana Fjord, the village of Kiberg, Abram Cape, the village of Mishukovo, the mouth of the Kulonga River, the apex part of Yarnyshnaya Bay, and Oscar Bay), indicating an unfavorable ecological state of the tidal zones of the Barents Sea coast. [ABSTRACT FROM AUTHOR]

The paper discussed the influence of the forms of sediment accumulation on the surface of glaciers on their chemical and physicochemical properties. The materials sampled from the surface of five glaciers of the Svalbard Archipelago was analyzed. We studied such forms of sediment accumulation as dirt cones - the ice core covered with sediments and cryoconite holes - hollows on the glacier surface containing cryoconite material. Parameters such as total organic carbon content, microbiological activity, pH, the content of mobile forms of potassium and phosphorus, and concentrations of heavy and trace metals were studied. Also, mesomorphological studies were carried out and the polydisperse composition of the sediments was determined. According to the results of this work, it was found that the content of organic carbon in the material selected from dirt cones and cryoconite holes can be up to 2.5%, but the content of clay particles in it is mainly at the 10–15% level. Potassium concentrations are up to 250 mg/kg, and phosphorus is up to 800 mg/kg. The content of metals is typical or lower than in the previously published data. The main influence on the chemical composition of materials has a geographical factor of the sampling site, rather than the form of material accumulation. [ABSTRACT FROM AUTHOR]

The paper presents the results of a comprehensive analysis of bottom sediment samples taken in 2020 during the Roshydromet marine scientific research in Stepovoi and Litke bays of the Novaya Zemlya archipelago and in the coastal zone of the Kara Sea near Amderma village. All sediment samples were analyzed for the concentration of radionuclides 137Cs, 90Sr, 238Pu, 239 + 240Pu, and some samples were analyzed for the content of toxic chemicals: heavy metals, persistent organochlorine compounds, and aliphatic hydrocarbons. The analysis of the results showed that the levels of radionuclides and toxic chemicals in bottom sediments of Stepovoi Bay are generally consistent with the data of similar surveys in previous years. [ABSTRACT FROM AUTHOR]

Global research is showing that coastal blue carbon ecosystems are vulnerable to climate change driven threats including accelerated sea-level rise and prolonged periods of drought. Furthermore, direct anthropogenic impacts present immediate threats through deterioration of coastal water quality, land reclamation, long-term impact to sediment biogeochemical cycling. These threats will invariably alter the future efficacy of carbon (C) sequestration processes and it is imperative that currently existing blue carbon habitats be protected. Knowledge of underlying biogeochemical, physical and hydrological interactions occurring in functioning blue carbon habitats is essential for developing strategies to mitigate threats, and promote conditions to optimise C sequestration/storage. In this current work, we investigated how sediment geochemistry (0–10 cm depth) responds to elevation, an edaphic factor driven by long-term hydrological regimes consequently exerting control over particle sedimentation rates and vegetation succession. This study was performed in an anthropogenically impacted blue carbon habitat along a coastal ecotone encompassing an elevation gradient transect from intertidal sediments (un-vegetated and covered daily by tidal water), through vegetated salt marsh sediments (periodically covered by spring tides and flooding events), on Bull Island, Dublin Bay. We determined the quantity and distributions of bulk geochemical characteristics in sediments through the elevation gradient, including total organic carbon (TOC), total nitrogen (TN), total metals, silt, clay, and also, 16 individual polyaromatic hydrocarbon's (PAH's) as an indication of anthropogenic input. Elevation measurements for sample sites were determined on this gradient using a LiDAR scanner accompanied by an IGI inertial measurement unit (IMU) on board a light aircraft. Considering the gradient from the Tidal mud zone (T), through the low-mid marsh (M) to the most elevated upper marsh (H), there were significant differences between all zones for many measured environmental variables. The results of significance testing using Kruskal–Wallis analysis revealed, that %C, %N, PAH (µg/g), Mn (mg/kg), TOC:NH4+ and pH are significantly different between all zones on the elevation gradient. The highest values for all these variables exists (excluding pH which followed a reverse trend) in zone H, decreasing in zone M and lowest in the un-vegetated zone T. TC content is 16 fold higher overall in vegetated (3.43 -21.84%) than uninhabited (0.21–0.56%) sediments. TN was over 50 times higher (0.24–1.76%), more specifically increasing in % mass on approach to the upper salt marsh with distance from the tidal flats sediments zone T (0.002–0.05%). Clay and silt distributions were greatest in vegetated sediments, increasing in % content towards upper marsh zones The retention of water, metals, PAHs, mud, chloride ions, NH4+, PO43− and SO42− increased with elevated C concentrations, concurrently where pH significantly decreased. Sediments were categorized with respect to PAH contamination where all SM samples were placed in the high polluted category. The results highlight the ability of Blue C sediments to immobilise increasing levels of C, N, and metals, and PAH with over time and with both lateral and vertical expansion. This study provides a valuable data set for an anthropogenically impacted blue carbon habitat predicted to suffer from sea-level rise and exponential urban development. Summarized results from this study demonstrating the geochemical changes through an elevation gradient, with a transect encompassing intertidal sediments through supratidal salt marsh sediments within Bull Island's blue carbon lagoon zones. [ABSTRACT FROM AUTHOR]

Salt marsh vegetation, mudflat and salt production are common features in worldwide coastal areas; however, their influence on microbial community composition and structure has been poorly studied and rarely compared. In the present study, microbial community composition (phospholipid fatty acid (PLFA) profiling and 16S rRNA gene sequencing (bacterial and archaeal)) and structure, enzymatic activities and abundance of functional genes in the sediments of salt ponds (crystallizer, condenser and reservoir), mudflat and vegetated mudflat were determined. Enzyme activities (β-glucosidase, urease and alkaline phosphatase) were considerably decreased in saltpan sediments because of elevated salinity while sediment of vegetated mudflat sediments showed the highest enzyme activities. Concentrations of total microbial biomarker PLFAs (total bacterial, Gram-positive, Gram-negative, fungal and actinomycetes) were the highest in vegetated mudflat sediments and the lowest in crystallizer sediments. Nonmetric-multidimensional scaling (NMDS) analysis of PLFA data revealed that the microbial community of crystallizer, mudflat and vegetated mudflat was significantly different from each other as well as different from condenser and reservoir. The most predominant phyla within the classified bacterial fractions were Proteobacteria followed by Firmicutes, Bacteroidetes and Planctomycetes, while Euryarchaeota and Crenarchaeota phyla dominated the classified archaeal fraction. Cyanobacterial genotypes were the most dominant in the condenser. Mudflat and vegetated mudflat supported a greater abundance of Bacteroidetes and Actinobacteria, respectively. The results of the present study suggest that salt ponds had significantly decreased the microbial and enzyme activities in comparison to mudflat and vegetated mudflat sediments due to very high salinity, ionic concentrations and devoid of vegetation. The present study expands our understanding of microbial resource utilization and adaptations of microorganisms in a hypersaline environment. [ABSTRACT FROM AUTHOR]

Long-term anthropogenic nitrate (NO3−) enrichment is a serious threat to many coastal systems. Nitrate reduction coupled with the oxidation of reduced forms of sulfur is conducted by chemolithoautotrophic microbial populations in a process that decreases nitrogen (N) pollution. However, little is known about the diversity and distribution of microbes capable of carbon fixation within salt marsh sediment and how they respond to long-term NO3− loading. We used genome-resolved metagenomics to characterize the distribution, phylogenetic relationships, and adaptations important to microbial communities within NO3−-enriched sediment. We found NO3− reducing sulfur oxidizers became dominant members of the microbial community throughout the top 25 cm of the sediment following long-term NO3− enrichment. We also found that most of the chemolithoautotrophic genomes recovered contained striking metabolic versatility, including the potential for complete denitrification and evidence of mixotrophy. Phylogenetic reconstruction indicated that similar carbon fixation strategies and metabolic versatility can be found in several phylogenetic groups, but the genomes recovered here represent novel organisms. Our results suggest that the role of chemolithoautotrophy within NO3−-enriched salt marsh sediments may be quantitatively more important for retaining carbon and filtering NO3− than previously indicated and further inquiry is needed to explicitly measure their contribution to carbon turnover and removal of N pollution. [ABSTRACT FROM AUTHOR]

Salt marshes are recognized as blue carbon ecosystems for their ability to rapidly sequester organic carbon (OC) via sedimentation. For this reason, there is growing interest in managing these systems to help mitigate climate change. However, in order for sediment accretion to offset ongoing CO2 emissions, organic matter undergoing burial must be derived from contemporary primary production. To investigate the provenance of OC sequestered by salt marshes, we analyzed the concentration and isotope composition (δ13C and Δ14C) of sedimentary OC in two minerogenic marshes in San Francisco Bay, California, USA. Data from the low marsh dominated by Spartinaspp. show that autochthonous OC is entering the sediment matrix and may in part be stabilized through incorporation into the mineral‐bound pool. However, the sedimentary OC stock as a whole is dominated by material with low values of δ13C (~ −20 to −25‰) and Δ14C (~ 100 to −300‰) indicating a preponderance of allochthonous OC that was retained in other OC reservoirs for 102 to 103 years prior to deposition in the marsh. Diagenetic modeling of OC and its δ13C values further shows that autochthonous OC is lost from the sediment profile at a much faster rate than allochthonous OC. The rapid turnover of contemporary autochthonous OC ("fast carbon") relative to the apparent stability of old allochthonous OC ("slow carbon") suggest that carbon burial at these sites is largely decoupled from ongoing CO2 emissions. [ABSTRACT FROM AUTHOR]

In situ persistence of salt marshes in the face of sea-level rise relies on their ability to maintain substrate elevation through sufficient vertical accretion of sediment. However, sedimentation rates in salt marshes vary spatially and temporally, which complicates the assessment of their ability to keep up with sea-level rise. Here, we explore the spatial and temporal variation in sediment accumulation in a single back-barrier salt marsh site. Using one-time in situ measurements at the landscape scale, we obtained synoptic information of elevation and sediment thickness over the entire salt marsh in a chronosequence over centuries. Repeated measurements along short elevation transects (0.3–0.9 m +MHT) revealed decadal changes, complementing the broader marsh data with detailed information on elevation, thickness of the marsh deposits and accumulation rates. Thickness of the deposits was largely related to the elevation gradient: the sediment layer was thinner at the higher marsh (near the dunes and far away from the intertidal flats), and thicker at the lower marsh (near the intertidal flats). Moreover, the thickness of the layer increased with salt marsh age along the chronosequence, and age accounted for 72 % of variability in sediment accumulation. The rate of sediment accumulation was higher than the local rate of sea-level rise in the younger marsh, whereas it was equal to the rate of sea-level rise in the older marsh. In the older salt marsh, sediment accumulation was lower, possibly due to autocompaction in the thicker, older layers. Both at the landscape scale and along short elevation transects within individual drainage basins, sediment accumulation decreased with distance to sediment supply routes. However, their relative importance depended on the scale of observation. Distance to creeks accounted for 17 % of the variability in sediment accumulation at the landscape scale, compared to 4 % at the smaller scale. Similarly, the influence of distance to intertidal flats varied from 1 % at the landscape scale to 13 % at the smaller scale. Our main findings indicate that lower-elevation older marshes and higher-elevation younger marshes far away from sediment sources are at risk of not keeping pace with the local rate of sea-level rise and are potentially vulnerable to increased flooding. • Spatial and temporal scales are combined to understand salt-marsh sedimentation. • Marsh age is an important factor for sedimentation rates; other factors depend on spatial scale. • Low-elevation old marshes and high-elevation young marshes more at risk with sea-level rise. [ABSTRACT FROM AUTHOR]

Blue carbon stored in coastal wetlands can be highly impacted by extreme events, such as typhoons. However, the sediment carbon accumulation capacity in this circumstance, remains unclear. In this study, a field site crossing the bare mudflat-saltmarsh interface was established in Southern Hangzhou Bay, to investigate the geomorphological and subsequent sediment carbon accumulation changes during the typhoon season (2 months) and the succeeding calm weather period (10 months). Surface Elevation Tables (SETs) were used, together with GPS-RTK and UAV-LiDAR surveys, to observe surface elevation changes at different spatial scales. The elevation and sediment organic carbon density data were used to estimate the gain/loss of sediment carbon pool under the impact of two successive typhoons, "In-Fa" and "Chanthu". This revealed that during the typhoon season, 6.3 cm of surface erosion occurred on the bare mudflat whilst rapid depositions of 6.1 and 12.3 cm occurred in Scirpus mariqueter and Spartina alterniflora habitats, respectively. In the gap between the two typhoon events, the bare mudflat experienced deposition of 4.2 cm, signalling recovery from erosion, but deposition within the saltmarsh front slowed. During the calm weather period, sediment deposition increased landward, with magnitudes of 13.1 cm, 16.4 cm, and 18.2 cm. Sediment carbon budget estimates indicated that during the typhoon season, the bare mudflat lost ~3.4 Mg C ha−1 but saltmarshes gained ~4.9 Mg C ha−1 in their sediment organic carbon pools. These changes in sediment carbon accumulation rates over the typhoon season accounted for >30 % of annual change in the study area, and may be associated with tidal creek dynamics. This study suggests the important role of typhoons in mediating the sediment carbon pool across the mudflat-saltmarsh interface. With future climate change, increasingly frequent catastrophic events could cause considerable changes in coastal blue carbon sequestration capacity. • Sediment carbon accumulation rates were recorded at the mudflat-saltmarsh interface. • Differing patterns of carbon accumulation were found during typhoon and calm periods. • Typhoons caused a sediment carbon loss in mudflat but a gain in saltmarsh. • Typhoons accounted for >30 % of the annual change in the sediment carbon pool. • Tidal creeks could be crucial in mediating sediment carbon pools in typhoon season. [ABSTRACT FROM AUTHOR]

Dongting Lake is one of the most important inland freshwater lakes in China. To investigate the spatial distribution and seasonal variation characteristics of heavy metals (Cr, Co, Cu, Zn, Cd, and Pb) in the lake, 53 surface sediment samples were collected in the East Dongting Lake (ED Lake) in the wet and dry seasons. Results show Cr, Co, Cu, Zn, Cd, and Pb contents were 1.7 (1.9), 1.8 (2.0), 2.9 (3.0), 1.9 (1.9), 11.7 (13.1), and 2.0 (2.2)-fold of their geochemical soil background values of Hunan province (China) in the wet (dry) season. Spatial and seasonal heterogeneity could be found in the distribution of Cr, Co, Cu, Zn, and Pb in the surface sediments. The enrichment factor (EF) suggested that Cd has reached severe enrichment in the sediment. The result of the geo-accumulation index ( I geo ) indicated that Cr, Co, Cu, Zn, and Pb were at levels corresponding to low contamination, and moderately to highly polluted with Cd. Multivariate statistical analysis including pearson correlation analysis and principal component analysis was used for the identification of potential sources of the heavy metals in the sediments. The results showed that Cu, Zn, and Pb from the sediments of the East Dongting Lake in the wet and dry seasons were possibly anthropogenic sources, such as emissions from mining and smelting while Al, Fe, and Cr are attributed for natural sources. Cd enrichment in the sediments is influenced by both natural factors, and human activities in local areas. [ABSTRACT FROM AUTHOR]

The article focuses on the challenges faced by tidal marshes due to sediment austerity and rising sea levels. Topics discussed include insufficient sediment for marsh accretion, the importance of sediment in coastal resilience, and the need for creative coastal planning to address these issues in the face of inevitable change.

Meiofaunal assemblages are often overlooked, yet they are important ecological components of estuarine ecosystems. To evaluate variations in meiofaunal communities in estuarine habitats, we conducted a comprehensive analysis of meiofaunal density, distribution and relationships with environmental parameters in a mangrove-dominated ecosystem at Mangawhai, Northern New Zealand, in summer (March) and winter (October), 2013. Five habitat types were studied including mangrove stands, pneumatophore zones, sandflats, mudflats and saltmarshes. In addition, data were recorded for sediment grain size, organic content, and primary benthic productivity (chlorophyll a). Twelve major taxa were identified, with meiofaunal densities ranging between 269 and 8090 ind. 10 cm−2. Highest abundances were found in fine-grained organic-rich sediments compared to coarse-grained organically poor sediments; the former were generally associated with mangroves stands and pneumatophore zones. Nematodes dominated all observed habitats. Foraminifera ranked second in fine-grained organically rich sediments, whereas copepods ranked second in coarser-grained sediments. Results suggest that meiofaunal taxonomic abundance and distribution are highly sensitive to local physical and biological parameters (e.g. sediment grain size, organic content, benthic primary productivity). The findings revealed that environmental characteristics have an important influence within this temperate estuary. [ABSTRACT FROM AUTHOR]

The surface salt marsh sediments from marine ecosystems in the Bay of Bengal, Bangladesh was assessed for trace elements like iron (Fe), calcium (Ca), titanium (Ti), potassium (K), strontium (Sr), rubidium (Rb), zirconium (Zr), zinc (Zn), copper (Cu) and lead (Pb), their potential sources, and associated ecological risks. The range of trace elements in sediment (mg/kg) followed the decreasing order: Fe (25020–35176) > Ca (8679–16323) >Ti (2678–3340) > K (23680–16770) > Sr (138.32–209.64) > Rb (124–186.57) > Zr (96.21–161.35) > Zn (37.71–44.95) > Cu (36.51–51.66) > Pb (1.35–10.42). The concentrations of trace elements were under the average shale values of metals in sediment except for Fe, Cu and Rb, which can occasionally be associated with adverse biological effects. Contamination level and ecological risk were evaluated using contamination factor (CF), enrichment factor (EF), geo-accumulation index (Igeo), pollution load index (PLI), and potential ecological risk index (PERI). Multivariate statistical technique was used to classify the metal sources. The results showed that Fe was significantly enriched in the sediments. Ecological risk factors illustrated a pollution-free condition of the salt marsh ecosystem in Bangladesh. [ABSTRACT FROM AUTHOR]

Interspecific interactions between plants influence plant phenotype, distribution, abundance, and community structure. Each of these can, in turn, impact sediment biogeochemistry. Although the population and community level impacts of these interactions have been extensively studied, less is known about their effect on sediment biogeochemistry. This is surprising given that many plants are categorized as foundation species that exert strong control on community structure. In southern California salt marshes, we used clipping experiments to manipulate aboveground neighbor presence to study interactions between two dominant plants, Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica). We also measured how changes in cordgrass stem density influenced sediment biogeochemistry. Pickleweed suppressed cordgrass stem density but had no effect on aboveground biomass. For every cordgrass stem lost per square meter, porewater ammonium increased 0.3–1.0 µM. Thus, aboveground competition with pickleweed weakened the effects of cordgrass on sediment biogeochemistry. Predictions about plant–soil feedbacks, especially under future climate scenarios, will be improved when plant–plant interactions are considered, particularly those containing dominant and foundation species. [ABSTRACT FROM AUTHOR]

Creeks are essential for salt marshes by conveying water and sediment through this geomorphic system. In this paper, we investigate the mechanisms that determine the residual sediment flux using measurements conducted in tidal creeks in salt marshes of the Yangtze Estuary. A main creek and a secondary creek were studied to explore whether the mechanisms determining residual sediment fluxes through the main creek differ from those in the secondary creek. Measurements in creeks were carried out over 5 years, spanning different months. Sediment import was found during most tides, both in the main creek and the secondary creek, implying that creeks in Chongming generally function as a conveyor belt of sediment into the marsh. However, sediment export can occur during certain overbank tides. When comparing the role of creeks in drainage and sediment delivery, the main creek functions more in delivering sediment while the secondary creek primarily serves as a drainage conduit. To better understand the mechanisms behind sediment fluxes, the residual sediment flux was compared with the residual discharge and the sediment differential (differences in sediment concentration between flood and ebb). Overbank tides generally lead to a net outward discharge as more water from saltmarshes can be concentrated into the marsh creek during ebb tides. This net outward discharge tends to export more sediment during ebb tides. However, due to the sediment abundance during the flood phase in the turbid environment, sediment import can be expected even with the residual export of water. Export of sediment was only found for the few tides with a net outward discharge and a small positive sediment concentration differential. Large negative sediment differentials (larger averaged suspended sediment concentration during ebb tides) have not been observed because the sediment supply during ebb is limited. This paper unravels how the sediment differential and residual discharge contribute to the residual sediment flux, providing a better understanding of sediment dynamics in marsh creek systems. • The relative importance of asymmetries in sediment concentration and in flow for residual sediment fluxes was explored. • The main creek is mainly a conduit for sediment delivery whereas the secondary creek is mainly a drainage conduit. • Sediment supply limitation can even occur in a turbid system like Chongming. [ABSTRACT FROM AUTHOR]

The concentrations of Cu, Fe, Mn, Ni, Zn, Cr, Pb, and Cd in 37 samples collected from surface sediments from the Inner Mongolia section of Yellow River, China were discussed in order to estimate their distribution and pollution level. The measured metals in the sediments were found be in the range of Cu 10.28~45.54, Fe 18, 460.00~41, 880.00, Mn 448.90~919.83, Ni 8.52~67.39, Zn 60.93~149.40, Cr 65.69~149.67, Pb 0.50~19.98 and Cd 0.23~4.36 mg kg–1. The mean values of the heavy metal contents were arranged in the following decreasing order: Fe > Mn > Cr > Zn > Ni > Cu > Pb >Cd. Significant positive correlations were observed between the concentrations of Cu, Fe, Mn and Zn. Common sources and the identical behavior are observed in these heavy metals. PCA extracted two components with eigenvalues explaining 62.190% of the total variance. Cu, Fe, Mn, Zn, Cr had the natural origin controlled by the first factor. Anthropogenic causes are major sources of Pb and Cd. Ni could be affected by natural geological background and human activity. The higher values of Geo-accumulation index, enrichment factor, and PLI of Cr were attributed principally to anthropogenic activities. Fe and Zn did not lead to pollution. The Sediment contamination grade from the Inner Mongolia section in upstream of Yellow River was 0~1, belonging to from unpolluted to moderately polluted. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation is a long-term process with various risks, such as reduction of storage capacity, hydropower generation and flood control functions throughout a reservoir's lifespan. For reservoirs facing loss of function with severe deposition, sediment flushing is an approach to preserving long-term storage. Here, submerged vanes combined with pressure flushing operations are proposed to facilitate scouring of such deposition. Experiments with various submerged vane heights, inclination angles on the flow direction, spacing, and divergent and convergent arrangements were conducted to investigate the scour cone volume and removal efficiency. Results showed that two divergent submerged vanes at an angle of 20° on the flow direction and optimum vane spacing ratios removed the deposited sediment significantly. In the presence of the submerged vanes, final sediment flushing volume and efficiency increased by a factor of 48 compared to the reference test. Using the experimental results, three equations were proposed to estimate the scour cone dimensions (length, width and depth). Additionally, a non-dimensional equation was developed for estimating the scour cone volume, using a polynomial correlation with vane spacing. The results of this study recommend the best installation of submerged vanes for releasing deposited sediments in the region near the bottom outlets of reservoirs. [ABSTRACT FROM AUTHOR]

Tidal marshes have been recognized globally for their ability to sequester "blue carbon" but there is still a need for studies investigating the marsh response to restoration, particularly in the Pacific Northwest United States. Here we report carbon stocks and accumulation rates for restored and natural tidal marshes in the Stillaguamish River estuary in Puget Sound, Washington, where a 60-hectare marsh was reintroduced to the tidal regime from its previous use as diked and drained farmland. We found that the restoration not only maximized carbon accumulation but also enhanced resilience to rising sea levels. Four years after restoration, mean sediment carbon stocks in the upper 30 cm within the restored marsh (4.43 kg C m-2) were slightly lower than those measured in the adjacent natural marshes (5.95 kg C m-2). Mean carbon accumulation rates, however, were nearly twice as high in the restored marsh (230.49 g C m-2 yr-1) compared to the natural marshes (123.00 g C m-2 yr-1) due to high rates of accretion in the restored marsh (1.57 cm yr-1). Mean elevation change rates were nearly twice that of corresponding 210Pb accretion rates, but all were greater than the current rate of sea level rise. [ABSTRACT FROM AUTHOR]

Summary: We surveyed Spartina saltmarsh sediment rhizosphere fungal communities at three saltmarshes and two timepoints in coastal Nova Scotia. Based on ITS2 Illumina miSeq rDNA data and multivariate analysis, neither sediment zone nor collection period correlated with fungal ASV richness, but collection site did. However, Shannon diversity indicated that sediment zone played a significant role in fungal diversity. For unweighted and weighted UniFrac distance, site was the major factor driving beta‐diversity, with sediment zone and collection period having smaller roles. Sediment type and saltmarsh plant species may play important roles in structuring rhizosphere fungal assemblages, here dominated by ascomycetes. To our knowledge, our study is the first to assess fungal sediment communities in saltmarshes in Atlantic Canada using metabarcoding. It provides a biodiversity analysis of sediment fungi in a poorly studied but highly important ecosystem and points to their roles in nutrient cycling, blue carbon, coastal stability and coastal restoration. Our work will inform ongoing saltmarsh restoration in Atlantic Canada. [ABSTRACT FROM AUTHOR]

Summary: Coastal salt marshes are key sites of biogeochemical cycling and ideal systems in which to investigate the community structure of complex microbial communities. Here, we clarify structural–functional relationships among microorganisms and their mineralogical environment, revealing previously undescribed metabolic activity patterns and precise spatial arrangements within salt marsh sediment. Following 3.7‐day in situ incubations with a non‐canonical amino acid that was incorporated into new biomass, samples were resin‐embedded and analysed by correlative fluorescence and electron microscopy to map the microscale arrangements of anabolically active and inactive organisms alongside mineral grains. Parallel sediment samples were examined by fluorescence‐activated cell sorting and 16S rRNA gene sequencing to link anabolic activity to taxonomic identity. Both approaches demonstrated a rapid decline in the proportion of anabolically active cells with depth into salt marsh sediment, from ~60% in the top centimetre to 9.4%–22.4% between 2 and 10 cm. From the top to the bottom, the most prominent active community members shifted from sulfur cycling phototrophic consortia, to putative sulfate‐reducing bacteria likely oxidizing organic compounds, to fermentative lineages. Correlative microscopy revealed more abundant (and more anabolically active) organisms around non‐quartz minerals including rutile, orthoclase and plagioclase. Microbe–mineral relationships appear to be dynamic and context‐dependent arbiters of biogeochemical cycling. [ABSTRACT FROM AUTHOR]

Understanding the control mechanisms of carbon dioxide (CO 2) emissions in intertidal wetland sediments is beneficial for the concern of global carbon biogeochemistry and climate change. Nevertheless, multiple controls on CO 2 emissions from intertidal wetland sediments to the atmosphere still need to be clarified. This study investigated the effect of tidal action on CO 2 emissions from salt marsh sediments covered by Spartina alterniflora in the Jiaozhou Bay wetland using the static chamber method combined with an infrared CO 2 detector. The results showed that the CO 2 emission fluxes from the sediment during ebb tides were higher than those during flood tides. The whole wetland sediment acted as a weak source of atmospheric CO 2 (average flux: 24.44 ± 16.80 mg C m−2 h−1) compared to terrestrial soils and was affected by the cycle of seawater inundation and exposure. The tidal influence on vertical dissolved inorganic carbon (DIC) transport in the sediment was also quantitated using a two-end member mixing model. The surface sediment layer (5–15 cm) with maximum DIC concentration during ebb tides became the one with minimum DIC concentration during flood tides, indicating the DIC transport from the surface sediment to seawater. Furthermore, aerobic respiration by microorganisms was the primary process of CO 2 production in the sediment according to 16 S rDNA sequencing analysis. This study revealed the strong impact of tidal action on CO 2 emissions from the wetland sediment and provided insights into the source-sink pattern of CO 2 and DIC at the land-ocean interface. [Display omitted] • The strong impact of tidal flooding on CO 2 emissions from wetland sediments. • DIC in surface sediments would diffuse into seawater under tidal inundations. • Microbial aerobic respiration was the primary process of CO 2 production in sediments. [ABSTRACT FROM AUTHOR]

Coastal marshes offer natural solutions for adapting to and mitigating the effects of climate change and sea level rise. However, the resilience of the marsh physical system and, with it, the ecosystem services that it provides, is largely site specific. This calls for the increase in the spatial cover of coastal marsh studies in order to assess the controlling factors of marsh evolution, and their long-term carbon storage capacities. Here, we study the spatio-temporal variations in sedimentation rates and organic carbon (OC) sequestration capacity of the macrotidal minerogenic saltmarshes in Aiguillon Bay, belonging to one of the largest French coastal marshes. Supported by aerial photographs and satellite image analysis, we first show that saltmarshes of the Aiguillon Bay have prograded at very high rates, up to 14 m yr−1 since 1950. Sediment accumulation rates (SAR) were estimated at both multi-annual to multi-decadal scales based on two approaches: (i) LiDAR-based digital elevation models from multiple acquisition dates (2010–2021); and (ii) depth profiles of 210Pb in excess and 137Cs in sediment cores collected along cross-shore transects in the saltmarshes. Long-term SAR range from 0.8 to 2.2 cm yr−1 and are among the highest reported worldwide for equivalent systems. The positive accretion balance (accretion rate minus local sea-level rise rate) provides important clues on marsh resilience suggesting that the Aiguillon Bay is currently able to adapt to rising sea level. Despite relatively low organic carbon content (1.3–6.0%), high SAR leads to high carbon sequestration rates (99–345 gC m−2 yr−1; or a mean value of 2.5 Mg C ha−1 yr−1). The isotopic signature of sediment OC reveals a significant and rapid decomposition of organic material in surface cores, while allochthonous sediment of marine origin dominates the signature of chemically-stable OC of marsh sediments. This implies that the carbon sequestration capacity of minerogenic saltmarshes, such as those of the Pertuis Charentais, also depends upon the wealth of adjacent coastal environments through high sediment supply and primary productivity. [Display omitted] • Saltmarshes prograde and aggrade at very high rates, keeping up with sea level rise. • Sediment source proximity and accommodation space explain SAR spatial variability. • Organic carbon accumulation rates are highly variable at the scale of a bay. • Allochthonous C of marine origin prevails in long-term C sequestration. [ABSTRACT FROM AUTHOR]

Salt marshes are ecosystems with significant economic and environmental value. However, the accelerating rate of sea-level rise is a significant threat to these ecosystems. Storms significantly contribute to the sediment budget of salt marshes, playing a critical role in salt marsh survival to sea-level rise. There are, however, uncertainties on the extent to which storms contribute sediments to different areas of marsh platforms (e.g., outer marsh vs marsh interior) and on the sediment sources that storms draw on (e.g., offshore vs nearshore). This study uses field analyses from an eight-month field campaign in the Ribble Estuary, North-West England, to understand storms' influence on the sediment supply to different marsh areas and whether storms can deliver new material onto the salt marsh platform which would otherwise not be sourced in fair-weather conditions. Field data from sediment traps indicate that storm activity caused an increase in inorganic sediment supply to the whole salt marsh platform, especially benefitting the marsh interior. Geochemistry and particle size distribution analysis indicate that the majority of the sediment supplied to the salt marsh platform during the stormy periods was generated by an increase in erosion and resuspension of mudflat and tidal creek sediments, while only a minimal contribution was given by the sediments transported from outside the intertidal system. This suggests that, in the long term, storms will promote salt marsh vertical accretion but might simultaneously reduce the overall larger-scale sediment availability with implications for the marsh lateral retreat. • Storms contribute significantly to salt marsh sediment budget. • There are uncertainties as to what extent this contribution benefits the marsh platform. • Field data showed that storms benefit marsh vertical accretion but limit lateral expansion. [ABSTRACT FROM AUTHOR]

Salt marshes are key ecosystems for biogeochemical cycling of nutrients in coastal areas, providing essential sequestration of contaminants and elemental organic forms while recycling these last to more bioavailable forms. Extracellular phosphatase-mediated phosphorus biogeochemical cycling acquires this way a reinforced role. In terms of speciation, salt marsh sediments exhibited a large pool of P in a bioavailable form (> 60%), being this pool characterized by being readily accessible to plants by weak chemical reactions. Regarding phosphatase activity, the acid isoform was found to be the most abundant pH-isoform present in salt marsh rhizosediments. A positive correlation could be found between humic acid bound P and total and acid phosphatase activities, possibly driven by the action of acid phosphatase on the acidic molecules of humic acids, using organic P as substrate, and releasing inorganic P into the desorbable P-pool. This process is more evident during the cold seasons, where the largest necromass input is observed entering the sediments, due to seasonal plant senescence. It could also be observed a positive correlation between inorganic phosphorus forms and phosphatase activity, consistent with phosphatases-driven inorganic phosphorus production from the recycling of organic forms, and thus a possible direct effect of phosphatase, as it was described for other ecosystems. This biogeochemical cycling is key for the ecosystem nutrient recycling, while passive remediator of eutrophication, but also for maintaining the salt marsh areas high primary productivity and their role as habitat, shelter and feeding ground of many animal species. • Salt marsh sediments exhibited a large pool of P in a bioavailable form. • Acid phosphatase was the most abundant isoform present in salt marsh sediments. • Acid phosphatase activity is responsible for releasing inorganic P into the desorbable P-pool. • This process is more active during the cold seasons due to higher necromass input. [ABSTRACT FROM AUTHOR]

As the first effort in literature, this paper conducts pore scale modeling on the methane hydrate dissociation and transportation in the reconstructed three-dimensional models of the MH-bearing sediment. The porous MH sample is synthesized using excess-gas method and imaged by micro-CT, which is used as input for the reconstructed mesh models. The real-time distribution of MH & water & methane, velocity and temperature is investigated. The effects of the temperature, pressure and flow rate of the injected water on MH dissociation and transportation are simulated and discussed. The results indicate that: 1) The hydrate generated by the excess - gas method is mainly cementing and mineral-coating on the sands surface, and occupies the small pores firstly. 2) The heterogeneity of the porous MH sediments is one of the key factors which influences the dissociation and the transportation process of the MH. 3) A lack of heat supply will restrict the dissociating rate of the MH reaching the maximum under the given PT conditions. 4) The gathering of the gas will decrease the flowing capacity of both water and methane. This study provides a new method to predict the multiple physicochemical and thermodynamical properties of the porous MH bearing sediments. • Pore scale MH dissociation and transportation in the real-shape porous media is modeled. • Real-time phase-change, multiphase flow, heat & mass transfer in porous media are studied. • Absolute and dynamic permeability of water & methane in the MH samples are predicted. • New method to predict petrophysical-thermal properties of MH sediments is provided. [ABSTRACT FROM AUTHOR]

Artificial coastal dykes have been widely built to prevent erosion, or to accelerate sedimentation processes in saltmarshes. To investigate the sediment dynamic changes induced by construction of dykes, three observation stations were set around a dyke within an expanding Scirpus mariqueter saltmarsh, in southern Hangzhou Bay. The hydrodynamics of the study area was dominated by tidal currents. The presence of dyke, in combination with the adjacent tidal creek, altered the hydrodynamic boundary conditions, thereby affecting the flow field. When the tidal flows approaching the dyke, the speed was accelerated at the head of the dyke and then decreased at the rear, due to the narrowing effect of the dyke head. Turbulence intensity around the dyke showed a similar pattern to that of the tidal flows. The net sediment input behind the dyke is approximately 2.3 times of that at the dyke head, illustrating sediment deposition in the back region of the dyke. As a result, flows entrained the sediments and then deposited behind the dyke to cause a local accretion to promote saltmarsh vegetation succession. The construction of dykes should be taken into account for future coastal wetland management. • In situ sediment dynamic observation was conducted around a dyke in saltmarsh. • Dyke altered tidal flows and caused sediment transport towards the rear region. • Construction of the dyke drove vegetation succession in the saltmarsh. [ABSTRACT FROM AUTHOR]

Thin layer application (TLA) of dredged sediments has emerged as an adaptive management option for marshes that are not increasing in elevation fast enough to keep pace with local relative sea level rise. While there have been multiple previous demonstrations of TLA, there is limited pre-and post-application monitoring data available from past projects to develop guidance concerning optimal siting, design and implementation of projects. To address this gap, we conducted a controlled TLA experiment in a Spartina alterniflora marsh adjacent to the Atlantic Intracoastal Waterway in central North Carolina. The project was informed by the results of a long-term marsh monitoring and research program which had identified the project area as particularly vulnerable to sea level rise. The experimental design included triplicate meso-scale (24m2) treatment and control cells and quarterly (during the first year) to annual monitoring efforts to document trends in marsh surface elevation and vegetative biomass. In addition, sampling was conducted to characterize porewater chemistry and sediment characteristics. Thin layer application of dredged sediments resulted in an average elevation gain of 6 cm in treatment plots. Monitoring results indicate that the gains in elevation achieved by TLA have been maintained over five growing seasons. The response of vegetative biomass to the added elevation was well-predicted by the elevation-biomass relationship of the surrounding marsh platform. Treatment cells exhibited continued increases in surface elevation after placement, while control cell elevation remained constant. These data illustrate the potential of TLA as a tool for increasing the resilience of low-lying marshes to sea level rise and illustrate the value of the surface elevation-marsh biomass relationship for providing guidance for its use in S. alterniflora -dominated marshes. • The impact of adding a thin layer of dredged sediments to a low-lying coastal salt marsh was assessed. • Increasing the elevation of the marsh platform by 6 cm resulted in a doubling of vegetative biomass • Increased biomass led to increased ability to build further elevation after sediment application was completed. • Thin layer sediment application provides a mechanism for enhancing marsh resilience to future sea level rise. [ABSTRACT FROM AUTHOR]

Salt marshes provide diverse ecosystem services including coastal protection, habitat provision and carbon sequestration. The loss of salt marshes is a global scale phenomenon, of great socio-economic concern due to the substantial benefits that they provide. However, the causes of spatial variability in marsh loss rates are inadequately understood for the purposes of predicting future ecosystem distributions and functions under global environmental change. This study investigated the relationship between the presence of different saltmarsh plants and the mechanical properties of the underlying substrate that relate to its vulnerability to erosion. Relationships between three halophytes (Puccinellia spp. , Spartina spp. and Salicornia spp.) and sediment stability were assessed and compared to unvegetated substrates using in-situ and laboratory tests of substrate geotechnical properties and sediment characteristics. Sampling was conducted at two UK sites with contrasting sedimentology, one sand-dominated and one clay-rich. Sediment samples, collected simultaneously with measurements of shear strength, were analysed for moisture content, particle size and organic, carbonate and mineral compositions. These data were then used to explore the contribution of plant type, alongside the sedimentological parameters, to measured shear strength. Shear strength of the sediment varied between and, to a lesser extent, within sites, with the four cover types having a similar effect on shear strength within sites relative to each other. Sediments covered by Puccinellia spp exhibit the highest shear strength, while bare sediments exhibit the lowest. The effect of vegetation type on shear strength was greater in the coarser sediments of Warton Sands. Surface cover type made a significant contribution to exploratory statistical models developed for the prediction of sediment shear strength. The findings support existing recognition that vegetation can enhance sediment shear strengths but extend the insight to reveal differences in this effect that show generality between sedimentological settings. Further, the combination of methods provides insight into the fundamental mechanics by which various measures of sediment stability may be affected by different surface cover types. Cohesion appears to be a more appropriate descriptor of sediment erodibility than shear strength or friction angle and is most greatly enhanced by the presence of a fine, fibrous root system such as that of Puccinellia. A more detailed understanding of the multi-scale mechanisms by which plants confer strength to substrates is needed to better anticipate their impact on sediment erodibility, and therefore salt marsh vulnerability. • Relationships are established between geotechnical properties of salt marsh sediments and the plant species growing on them. • Plant species effect is stronger in coarser sediments but shear strength alone is an inadequate descriptor of erodibility. • Mapping plant distributions may help to understand within-site variability in salt marsh vulnerability to erosion. [ABSTRACT FROM AUTHOR]

Sub-bottom sediment classifications have been widely used in marine science and engineering to obtain high-resolution information on types of sediments; however, these are often plagued by inaccuracies. Classification difficulties arise from the inability to effectively filter multiple reflections, extract representative lithology characteristic parameters, identify sub-bottom layer interfaces, extract image samples, control sample quality, optimise characteristic parameters, etc. To generate a highly accurate sub-bottom profile sediment map, a five-step classification method that considers two key lithology characteristic parameters of sub-bottom profile acoustic data was proposed. First, multiple reflections were filtered from the sea surface and sub-bottom layer interfaces of the primary signal. Second, two key characteristic parameters (relative backscattering intensity difference and attenuation compensation residual) were calculated. These reflect the relative differences in backscattering intensity and the attenuation compensation between adjacent interfaces based on the sound intensity attenuation model of a sub-bottom profile. Third, a combined method based on the sediment quality factor and peak trough of the echo signal loss level curve was employed to identify the actual interfaces between layers. An additional technique was proposed to determine the image sample width and preferred characteristic parameters. The resulting high-quality image samples and preferred characteristic parameters not only resulted in a faster convergence rate and increased ability of self-aggregation and identification, but also ensured that the training results met the convergence accuracy requirement. Ultimately, the preferred image samples were trained to classify the overall sub-bottom map of a selected test area of approximately 36 km2 in Bahai Bay, China. Compared with traditional methods, a considerably higher sediment identification accuracy was obtained. The experimental results indicate that the contribution rate of the two key lithology characteristic parameters was 65.49% according to principal component analysis, and the internal and external compatibilities were 97.98% and 84.76% for the training image samples, respectively. The total identification accuracy for the sub-bottom profile map was 98.2%. The two key characteristic parameters accurately captured the acoustic characteristics of sub-bottom sediments, significantly improving sediment classification. These results show that this method could be used to help refine the distributional estimates of submarine mineral resources. • A combined filtering method using predictive deconvolution and iterative feedback was proposed. • Two key parameters were derived from sound intensity attenuation model of sub-bottom profile. • Sample width selection and characteristic parameter preferred-selection method were proposed. • Experimental result indicated that identification accuracy for sub-bottom profile map was 98.2%. [ABSTRACT FROM AUTHOR]

Thin Layer Placement (TLP) is an increasingly used management technique to promote coastal resilience to accelerated sea level rise, but it is unclear how differential thickness of dredged sediment application alters plant-soil carbon dynamics in northeastern Atlantic coast salt marshes. We initiated a field experiment in a microtidal Spartina alterniflora (smooth cordgrass) dominated salt marsh in Connecticut (USA) to examine how a silt-loam dredge applied at different thicknesses (low: +5 cm, medium: +10 cm, and high: +15 cm) altered biological and biogeochemical responses. Over two growing seasons we monitored plant responses (above and belowground biomass, stem height, stem density, leaf area) and soil-biogeochemical parameters (EC, pH, redox, NH 4 +, sulfides, C:N, decomposition, bulk density, carbon fluxes). We found adding 5–7 cm of dredged sediment promoted rapid revegetation, alleviated phytotoxic sulfides, enhanced CO 2 uptake, and reduced CH 4 emissions. Low treatments reached similar vegetation cover to controls after one growing season, though sediment treatments greater than 10-cm thick showed delayed growth. Low levels of sediment addition stimulated the highest root biomass in the underlying soil, promoting CO 2 efflux, but this was offset by aboveground biomass productivity, promoting net CO 2 uptake. Phytotoxic sulfides were reduced in all sediment addition treatments, but our data indicate that coastal managers aiming to promote rapid vegetative recovery while increasing elevation in the short term should target conservative depths (< 10 cm) when using fine-grained dredged material. Collectively, our work will guide wetland managers as they develop restoration specifications for perpetuating coastal marshes in the face of rising seas. [Display omitted] [ABSTRACT FROM AUTHOR]

Saltmarsh restoration is described as a cost-effective response to coastal biodiversity loss and flood management, although, to date such conservation practices yield different characteristics than natural marshes, such as in plant communities and sediment properties. The outcome of these differences is thought to be influenced by the initial conditions set within the first year of marsh re-establishment, which are often overlooked or neglected as part of the restoration process. Therefore, our study aimed to address this gap by examining the spatial and temporal variations in sediment characteristics of a newly (<15 months) realigned saltmarsh in Essex, UK and the effects of previous land use (arable and pasture). Sediment properties (bulk density, nutrients and pH) were sampled monthly from the realigned site as well as from an adjacent reference natural marsh. After 14 months from initial inundation the two realigned marsh regions (arable and pasture) behaved similarly despite different starting points in terms of pH, water content, bulk density and nutrient load. Physical aspects of the realigned sediments (bulk density and water content) matched those of the reference natural marsh within 14 months post-breach in the 0–5 cm depth range. By contrast, the lower depth sediments within realigned sites remained more dense and drier compared to natural marsh sediments. Chemical properties of the realigned sediments matched those of the natural marsh throughout the sediment profile 14 months post-breach. Success of restoration is measured in the ability of the site to provide the desired ecosystem services and short-term recoveries and set goals may not imply long term sustainability as these observed differences may have ramifications for future biological community development and the success of a restoration. • Old agricultural relic sediment remains unchanged in realigned saltmarshes. • Pre-restoration land-use can affect the structure of restored salt marshes. • Functional measures often reveal a significant lag of ecological processes recovery. [ABSTRACT FROM AUTHOR]

The distribution and accumulation of rare earth elements (REE) in the labile fraction of sediment cores collected from salt marshes in the Patos Lagoon estuary from southern Brazil were investigated. Sediment cores (ca. 40 cm) were obtained from three locations within the estuary to capture possible changes in REE content across the salinity gradient (i.e., where saline, brackish, and freshwater dominate). Salt marsh sediments from all three coring locations were enriched in the light REE (LREE) over the heavy REE (HREE) when normalized to the North American shale composite (NASC). Shale normalized values for the LREE of marsh sediments from sites M2 and M3 in the mid- and upper estuary commonly approximates unity indicating these sediments chiefly exhibit a terrigenous signature. In contrast, all 14 naturally occurring REE are depleted in the sediments from the M1 coring location in the lower estuary compared to shale. Sediments from the mid-estuary (M2 core location) where typical salinity values are ca. 10 practical salinity units, exhibit the greatest shale normalized LREE enrichments. The higher LREE contents of the M2 sediments likely reflect preferential removal of LREE from the water column owing to salt-induced coagulation of river-borne colloids that occurs during estuarine mixing processes. Sediments samples collected from the salt marsh in the lower estuary nearer the Atlantic Ocean (i.e., M1), have substantially lower REE contents than salt marsh sediments from sites M2 and M3 in the mid- and upper estuary, respectively. The more sand-rich lower estuary sediments are exposed to higher salinity water from the South Atlantic compared to the generally finer grained sediments from the mid- and upper estuary, which are dominated by brackish and freshwater conditions, respectively. Negative Ce-anomalies (i.e., Ce/Ce* < 1) in marsh sediments from depths generally greater than 27 cm support the occurrence of early diagenetic reactions consistent with suboxic to anoxic conditions whereby reductive dissolution of ferromanganese oxide/oxyhydroxide carrier phases, and/or Ce(IV) phases, release Ce(III) to the marsh pore waters. The negative Ce anomalies suggests that a suboxic or anoxic environment predominates to a depth of 9 cm, and then again below 27 cm depth in sediments from the M2 salt marsh core, and below a depth of 13 cm in the upper estuary marsh sediments (i.e., M3). In contrast, positive Ce anomalies (Ce/Ce* > 1) for much of the sediment from the M1 core, the mid depths of core M2 (i.e., 9 cm to 27 cm), and shallower than 13 cm in sediments from core M3 support oxic conditions where Ce is enriched in sediments from these depths by preferential scavenging from pore waters onto Fe/Mn oxides/oxyhydroxides. These trends in Ce/Ce* with depth in each sediment core are also consistent with known bioturbation that occurs within these marsh sediments. The relatively high REE contents of the sediments from location M3 are also related to the fact that these sediments are dominantly composed of clay-silt deposits that are enriched in organic matter. Finally, we find no conclusive evidence that the studied salt marsh sediments have been impacted by addition of REE from the local fertilizer manufacturing industry. • ƩLREE/ƩHREE ratios were generally lower in saltmarshes sediments closer to the sea. • REE enrichment in freshwater dominate part of the estuary is due to high fine-grained and organic contents. • Positive Ce-anomalies are supported by oxic conditions in salt marsh sediment. [ABSTRACT FROM AUTHOR]

Estuaries are considered one of the most dynamic ecosystems in the world, ensuring high production and transfer of large quantities of organic matter (OM) from continents to the ocean. Despite the large influence of estuaries in the functioning of coastal ecosystems, our understanding of OM dynamics in these buffering coastal environments remains fragmented. In this frame, our study was carried out to describe and understand the main drivers of OM distribution in two estuaries (Canche, Authie) of the eastern English Channel, based on descriptive and quantitative approaches. For this purpose, in February and March 2018, surface sediments were sampled at low tide along cross-shore transects in the intertidal zone of each estuary. Analysis of sediment grain size, porosity, proportion of aggregated particles, total carbonate content and organic geochemical characteristics (total OM content, atomic TOC/TN ratio, δ13C value) of surface sediments allowed identifying four biosedimentary facies: sand flat, mud flat, low and high salt marshes. In parallel, the elemental and isotopic characterization of the suspended particulate OM inputs by the rivers, the surface biofilms and the halophytic vegetation was performed to trace the three major sources contributing to sedimentary OM in both estuaries. Spatial distribution of OM in surface sediments (ranging between 0.6 and 26.9% dry weight) evidenced higher contents along marsh platforms than in sand and mud flats. and the OM pool was mainly constituted of a mixing of C 3 terrestrial vascular plants, marine and riverine phytoplankton. The comparison between both estuaries highlighted that the geomorphology impacted by natural and anthropic factors plays a preponderant role in the distribution and the sources of sedimentary OM by influencing vegetation communities and hydrodynamic processes. In the context of sea level rise, an improved understanding of the OM dynamics within each biosedimentary facies is crucial to better constrain and assess the role of macrotidal estuaries in carbon cycle. • Field observation and physico-chemical analyses of exhaustive surface sediment samples used for determining biosedimentary facies. • Source of sedimentary organic matter defined by elemental and isotopic proxies. • Influence of the structure and texture of surface sediments on OM distribution. • Principal Components Analysis highlighted two contrasted geomorphological stages. [ABSTRACT FROM AUTHOR]

• Biomarker data were combined with PCA-MLR to estimate sedimentary OC contributions. • The OC contribution of C 4 plants was equal to C 3 plants. • The study area was universally affected by the petroleum and sewage pollution. • The OC contributions of anthropogenic activities were 77.6% in the Dagu River. Land-ocean interactions play an important role in transporting and accumulating organic carbon (OC) in marine sediments. Understanding sources (terrestrial, marine and anthropogenic contributions) of sedimentary OC are important to better evaluate the processes controlling the OC distribution in coastal zones. In this study, we present bulk parameters of total organic carbon (TOC), total nitrogen (TN), stable carbon isotopic composition (δ13C org) and biomarker contents in surface sediments from the Dagu River-estuary-marine system in the Jiaozhou Bay. Comparison between OC/N ratios and δ13C org indicated significant C 4 plant contribution to the sedimentary OC, which was approximately equal to C 3 plant contribution in this study. Generally, terrestrial biomarkers contents were high in the river and showed a decreasing trend towards the estuary and inner bay. Marine biomarkers displayed opposite spatial distribution patterns with terrestrial biomarkers except for the brassicasterol that also has a terrestrial/fluvial source. The universal detection of petroleum and sewage biomarkers revealed the significant anthropogenic influence on the sedimentary OC in our study. Principal component analysis-multiple linear regression (PCA-MLR) was performed to quantitatively estimate the OC contributions in the Jiaozhou Bay, showing that anthropogenic activities contributed 77.6% and 29.9% to the sedimentary OC in Dagu River and outside the Dagu River (the estuary and the inner Bay), respectively. Further studies need to be carried out to test this approach in broader regions. [ABSTRACT FROM AUTHOR]

Salt marshes are important ecosystems but their resilience to sea-level rise and possible increases in storm intensity is largely uncertain. The current paradigm is that a positive sediment budget supports the survival and accretion of salt marshes while sediment deprivation causes marsh degradation. However, few studies have investigated the combined impact of sea-level rise and increased storm intensity on the sediment budget of a salt marsh. This study investigates marsh resilience under the combined impact of various storm surge (0 m, 0.25 m, 0.5 m, 1.0 m, 2.0 m, 3.0 m and 4.0 m) and sea-level (+0 m, +0.3 m, +0.5 m, +0.8 m and +1.0 m) scenarios by using a sediment budget approach and the hydrodynamic model Delft3D. The Ribble Estuary, North-West England, whose salt marshes have been anthropogenically restored and have a high economic and environmental value, has been chosen as test case. We conclude that storm surges can positively contribute to the resilience of the salt marsh and estuarine system by promoting flood dominance and by triggering a net import of sediment. Conversely, sea-level rise can threaten the stability of the marsh by promoting ebb dominance and triggering a net export of sediment. Our results suggest that storm surges have a general tendency to counteract the decrease in sediment budget caused by sea-level rise. The timing of the storm surge relative to high or low tide, the duration of the surge, the change in tidal range and vegetation presence can also cause minor changes in the sediment budget. • Storm surges can positively contribute to the resilience of salt marshes. • Sea-level rise can threaten the stability of salt marshes. • Intense storms can counteract the negative impact of sea-level rise. [ABSTRACT FROM AUTHOR]