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As a consequence of anthropogenic activities and climate change, accelerated terrestrial sediment runoff is causing the gradual mudification of soft sediment estuarine habitats worldwide. Increased sediment mud content (< 63 µm) has been recognised to alter seagrass morphology and cause declines in primary production in unvegetated habitats. However, the effect of increased mud content on primary production in seagrass meadows remains largely unknown. To address this, primary production in intertidal seagrass meadows (Zostera muelleri) and adjacent unvegetated habitats was measured in situ using benthic incubation chambers across an existing sedimentary gradient (nine sites spanning 5–33% mud content). An additional two unvegetated mudflat sites (39–49% mud content) were also sampled to expand the gradient. Seagrass net (NPP) and gross primary production (GPP) was greater than in the adjacent unvegetated habitat and did not vary with mud content, even after standardising GPP by photosynthesising biomass (i.e. photosynthetic efficiency). In contrast, in the adjacent unvegetated habitat, photosynthetic efficiency declined with increasing mud content. Inclusion of the additional mudflat sites negatively impacted NPP, GPP, and photosynthetic efficiency in the unvegetated habitat. Thus, while primary production in seagrass meadows may have some resilience to future increases in mud content (up to ~33%), further degradation and loss of seagrass habitats could result in the expansion of unvegetated habitats and ultimately lead to production losses, likely to be most acute in areas with high mud content (≥ 39%). [ABSTRACT FROM AUTHOR]

Marsh lateral expansion and retreat are often attributed to sediment availability, but a causal link is difficult to establish. To shed light on this problem, we analyzed changes in salt marsh area along the ~ 200-km-long Georgia coast (USA) from the 1850s to 2010s in relation to total suspended sediment (TSS) and to proxies for river sediment input and local sediment resuspension. Marsh area is characterized by large gains and losses (up to 200 m2/m/yr), but relatively small net change (-50 to 50 m2/m/yr or -0.1 to 0.1%/yr). This has resulted in a general loss of marsh area, except close to the mouths of major rivers, where there is net gain. Net expansion rates decreased in the Savannah Estuary but increased in the Altamaha Estuary from the 1850s–1930s period to the 1930s–2010s period, which are consistent with observed decreases and likely increases in sediment discharge in the two estuaries, respectively. To explain the spatial patterns in the 1930s–2010s marsh area change, we estimated TSS from satellite measurements (2003 to 2020). Along the northern part of the Georgia coast, net marsh gain is positively correlated to the average TSS within the estuarine region. However, this correlation breaks down in more southern areas (Cumberland Sound). Coast-wide, there is a better correlation between TSS associated with new input from the rivers, estimated as the TSS difference between high-discharge (Jan–Mar) and low-discharge (Sept–Nov) months. To identify the effect of wave resuspension in the nearshore, we consider the TSS difference between high-wave, low-discharge (Sept–Nov) and low-wave, low-discharge periods (Jun–Aug). Wave resuspension is relatively uniform along the coast and does not explain spatial patterns of marsh area change. Sediment input from the nearshore is likely contributing to the estuarine sediment budget in Georgia, but it is not sufficient to prevent marsh lateral retreat. To identify the role of tidal resuspension and advection, we consider differences in TSS between low and high tide. This differential is relatively constant along most of the coast, but it is much lower in the southern part of the coast, suggesting a lower tidal action in this region. Sediment resuspended by tides is likely originating from internal recycling (i.e., erosion) within the estuary, and thus does not contribute to marsh lateral expansion. The proposed approach to partition TSS is a general demonstration and could be applied to other coastal regions. [ABSTRACT FROM AUTHOR]

Asymmetric tidal dynamics are of great significance for material transport and morphological evolution in estuaries. The tidal dynamics of the macro-tidal Hangzhou Bay (HZB) are characterized by flood-ebb asymmetries, spring-neap asymmetries, surface-bottom asymmetries, and up-downstream asymmetries. The mechanisms of spatio-temporal asymmetric tides and lateral flows in HZB were studied through a fully calibrated three-dimensional numerical model. The results show that tidal tides, tidal currents, and tidal asymmetry in HZB varied specially and temporally. In general, the bay was mostly flood-dominant. Temporally, tidal duration asymmetry in the bay fluctuated between spring and neap tides, with larger skewness during spring tides and smaller skewness during neap tides. The locally produced overtides are the primary sources of shallow-water tides in the bay, and the interaction between the lunar semi-diurnal tide M2 and the solar semi-diurnal tide S2 generates shallow-water overtides and deforms tidal asymmetries. The dissipated tidal energy may consumed by the bottom friction, with less passed to the generated shallow water overtides M4 and M6 tides (AM4 = 12.07 cm, AM6 = 3.91 cm) when comparing with the experiments that open boundary is purely forced by M2 tide (AM4 = 13.63 cm, AM6 = 6.31 cm). The increased depth reduces the bottom friction and the convergence of volume, resulting in skewness values close to zero (γTDA = 0.220, γM2-M4 = 0.141, γM2-M4-M6 = −0.002, γM2-S2-MS4 = 0.105). The changes of tidal duration asymmetry caused by the increased channel convergence, reduced bay width, and reclaimed intertidal zone spatially vary in different parts. The bottom friction contributed to the generation of the shallow-water tides and asymmetries in the bay (the RVRs for M4 and M6 are −73.5% and −92.5%), while the Coriolis force (the RVRs for M4 and M6 are 4.8% and 8.9%) and nonlinear advection (the RVRs for M4 and M6 are −17.3% and − 21.8%) are minor factors. The findings of the study provide hydrodynamic foundations for the research of sediment transport and estuarine evolution in similar macro-tidal turbid estuaries worldwide. [ABSTRACT FROM AUTHOR]

Weird horizontal shapes of branches, in large branching estuaries, often cause significant flood risks and environment-related problems. People usually resort to engineering methods to improve the horizontal shape of the weird branches and solve related issues. The responses of the riverbed evolution of a branching estuary to anthropogenic activity are complicated because of complex estuarine hydrodynamics and sediment transports, especially when the project locates specially (e.g., at estuary outlets). The North Branch of the Yangtze Estuary has a narrow upper reach which is almost orthogonal to the South Branch and has a trumpet-shaped lower reach with a wide outlet. The weird horizontal shape of the North Branch brings significant flood risks to cities along this branch, the shrinkage of its entrance, and other problems. In this study, a regulation of the North Branch, which is launched at Guyuan Sand (GYS) just outside the exit of the North Branch, is taken as an example. The GYS regulation aims to improve the weird horizontal shape of the North Branch by building new layouts of outlets, by which people decrease the flood risk of the surrounding cities. The GYS regulation is studied using a 2D numerical model. The riverbed evolution of the Yangtze Estuary in a typical hydrological year is simulated, while the water/sediment fluxes at cross-sections of branches in the estuary during a spring/neap tide are quantitatively calculated. It is found that the regulation changes the rotational flows near the shore, and further reshapes the estuarine circulations of mass inside the outlets, especially exchanges of water/sediment between different branches. The regulation directly changes the riverbed evolution at the outlet of the North Branch, and meanwhile has significant indirect influences on the riverbed evolution of the entrance of the North Branch. The varying riverbed evolution at the entrance of the North Branch and the varying water/sediment fluxes, under different designs of regulations, are related and analyzed. An essential improvement for the weird horizontal shape of the North Branch by an engineering method is shown to be possible, while the regulation mechanism of the engineering method and the response of estuarine riverbed evolution to the regulation are clarified. This study provides a new insight for improving estuarine branches with weird horizontal shapes, by reshaping the tidal processes and the accompanying sediment transports in a branching estuary. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate bottom sediments quality in 32 stations at Santos Estuarine Channel, home to one of the main international ports in South America, and to the Cubatão industrial complex, the most important petrochemical and metallurgical area in Brazil. Sediment quality was approached through contamination (mCd), ecological (PEI, SQG-Q, PLI) and geoaccumulation (Igeo) indices. Phosphorus Enrichment Index (PEI) revealed phosphorus enrichment, with potential risk to biota regarding eutrophication effects. Index of geoaccumulation (Igeo) revealed accumulation of Pb, Cu, Zn, Ni, Cr, Cd and As, all reaching class 6 of contamination, pointing to extreme contamination. Contamination index revealed null to moderate contamination for most stations. Pollution Load Index (PLI) revealed no contamination, and Sediment Quality Guideline (SQG-Q) pointed to moderate impact, suggesting risk to benthic biota. The mud content of the samples did not correlate with arsenic, phosphorus and trace metals. Organic matter seemed to be the main carrier of these elements in the system. Results revealed accumulation of trace metals and As in bottom sediments of Santos estuarine channel, which can be used to develop guidelines for monitoring these pollutants in anthropogenic activities along the harbor area. [ABSTRACT FROM AUTHOR]

River floods and human activities would impact land‐to‐sea sediment transport, which is essential for understanding the evolution of the global sediment cycle in the Anthropocene era. This study focused on investigating how river floods and a dike constructed in 2005 along a river channel influence sediment transport from the Ou River Estuary to the East China Sea. A validated three‐dimensional sediment transport model based on the Finite Volume Community Ocean Model was utilized for this study. The presence of the dike obstructs alongshore currents and fish migrations, leading to negative effects on marine ecology. Therefore, selective dismantling and ecological restoration measures are deemed necessary. Three scenarios were considered in this study: no‐dike, dike‐constructed, and dike‐partially‐removed conditions, along with various types of river floods. The findings indicate that the monthly sediment flux to the sea decreased by 7.7% from 8.11 × 106 to 7.49 × 106 t following dike construction, while the proportion of cross‐shore sediment flux to the total flux increased from 37% to 59%. The dike consistently has a greater impact than river floods in their interactions. However, partially removing the dike reduces its influence and restores sediment transport to pre‐dike levels, the effectiveness of which is more pronounced with more frequent floods, larger volumes, and rising sea levels. This study provides valuable insights into the interplay between river floods and dikes on sediment transport, thereby enhancing our understanding of the repercussions of human interventions on sediment dynamics. Plain Language Summary: Global warming is expected to cause an increase in sea levels and a rise in the frequency and volume of river floods, which will change the delivery of riverine sediment to the ocean. Human construction of dikes for various purposes has also changed modern estuarine sediment transport patterns. These alterations are significant as they affect the natural sediment cycling of the Earth, influencing marine geology and marine ecosystems. Through a case study of the Ou River Estuary in southeastern China, numerical sensitivity tests have shown that dikes constructed along river channels disrupt natural flow patterns, resulting in decreased sediment transport to the sea and redirection toward deeper oceanic areas. The presence of dikes is crucial in their interaction with river floods on sediment transport. However, removing sections of dikes can help restore sediment transport to conditions without dikes. The increasing frequency, larger volumes, and faster discharge rates of river floods, as well as dam‐controlled river floods and rising sea levels, may all play a role in restoring natural sediment transport dynamics. This study examines how floods and dikes collectively impact sediment transport in estuaries with drainage areas larger than the estuary area. Key Points: A dike redirects sediment transport from the alongshore to the cross‐shore from the Ou River to the East China SeaMetrics are proposed to quantify the interaction between various river flood conditions and dike configurations on sediment transportFrequency, pattern, and duration of river floods, as well as partial dike removal and sea‐level rise, impact the interaction [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen (N) mineralization and immobilization are two important N biogeochemical processes in estuarine and coastal sediments. However, the changes of those two processes in sediment following Spartina alterniflora (S. alterniflora) invasions into mangrove wetlands under aerobic and anaerobic conditions remain limited. Methods: We used a 15N stable isotope dilution technique to investigate sediment gross N mineralization (GNM) and NH4+ immobilization (GAI) under aerobic and anaerobic conditions in mangrove communities, mangrove communities mixed with S. alterniflora, and pure S. alterniflora communities in the Zhangjiang Estuary, China. Results: GNM and GAI rates varied spatially and seasonally. Summer N mineralization and immobilization rates under aerobic and anaerobic conditions were both significantly higher than those in winter, and the high rates were observed mainly in mangrove sediments and decreased with S. alterniflora invasion. GNM rates in aerobic conditions were significantly higher than those in anaerobic conditions, while GAI rates in aerobic conditions were less than those in anaerobic conditions. GNM and GAI rates were related closely to temperature, water content and organic matter. S. alterniflora invasion can weaken GNM and GAI rates by reducing organic matter accumulation, and S. alterniflora invasion could have reduced sediment N mineralization (2.10 × 103 t N yr−1) and immobilization (1.46 × 103 t N yr−1) in mangrove wetlands of China from 1980 to 2020. Conclusions: Our results highlight the importance of S. alterniflora invasion and hydrological conditions in controlling N mineralization and immobilization processes in mangrove sediments and are essential for the evaluation of N-balance in this N-limited ecosystem. [ABSTRACT FROM AUTHOR]

Widespread sediment resuspension and transport processes on continental margins can modify deposits and influence the preservation of particulate organic carbon (POC) in marine sediments. However, it remains unclear how post‐depositional processes interact with physical mineral protection to affect the transport and fate of terrestrial POC along the river‐estuary‐shelf paths. Here, we synthesized literature data and newly obtained results from multiple analyses of sedimentology, mineralogy, and inorganic and organic geochemical tracers. Our goal was to quantitatively evaluate the impact of sediment reworking on the redistribution and further transformations of terrestrial POC at the Yangtze River‐ocean interface. Our results reveal that sediment resuspension resulting from physical forces along with mineral protection of phyllosilicates plays a crucial role in regulating the recycling and fate of terrestrial POC during its transport across the coastal ocean continuum. Physical processes lead to the resuspension of sequestered POC from suboxic/anoxic muddy sediments into the overlying water column. Concurrently, the interplay of energetic forcing and elevated oxygen levels has the potential to disrupt the organo‐mineral associations. The decrease in mineral‐carbon stabilization increases the likelihood that reactive POC inclusion/aggregation with minerals becomes accessible to surrounding microorganisms, making it susceptible to microbial/oxidative degradation. Consequently, mostly phyllosilicate‐protected 14C‐depleted POC (primarily soil‐derived) in <63 μm suspended sediment (>90% of the total mass) remains available for export and reburial in continental shelf sediments. The lateral transport of resuspended sediments from estuaries, previously underestimated, represents a potential contributor to the remobilized millennial‐aged POC components involved in active biogeochemical cycling on continental margins. Plain Language Summary: River‐dominated Ocean Margins (RiOMar) play a crucial role in the global biogeochemical cycling of organic carbon (OC) because they receive substantial riverine inputs of particulate matter and bound organic materials. Among the present‐day oceans, the largest repositories for OC burial are found in large river‐dominated estuaries and deltas. When disturbed, OC deposited in seafloor sediments can be converted to dissolved inorganic carbon—either releasing it as carbon dioxide into the atmosphere or sequestering it within marine sediments. This study found that sediment reworking and remobilization by physical forces within the Yangtze River Estuary contribute to the degradation and aging of particulate OC (POC). Such disturbed processes may reduce the potential for carbon storage in marine sediments. Repeated cycles of sediment setting and resuspension enhance the significance of residual aged terrestrial POC associated with phyllosilicate minerals. This alteration affects the distribution and quantity of fluvial POC before it reaches the coastal oceans. As estuaries are highly vulnerable to human pressures and widespread climate change, the resuspension of estuarine sediments is expected to be an essential factor influencing the long‐term preservation of OC in marine sediments. Key Points: Disruption of organo‐mineral associations by sediment reworking enhances the respiration and aging of terrestrial biosphere carbonDynamic resuspension/deposition loops in energetic estuaries modify the quality and quantity of riverine organic carbonRepeated cycles of particle deposition/resuspension within the estuary leave unreactive terrestrial carbon buried in the shelf depocenter [ABSTRACT FROM AUTHOR]

Plastic pollution poses a worldwide environmental challenge, affecting wildlife and human health. Assessing the biodegradation capabilities of natural microbiomes in environments contaminated with microplastics is crucial for mitigating the effects of plastic pollution. In this work, we evaluated the potential of landfill leachate (LL) and estuarine sediments (ES) to biodegrade polyethylene (PE), polyethylene terephthalate (PET), and polycaprolactone (PCL), under aerobic, anaerobic, thermophilic, and mesophilic conditions. PCL underwent extensive aerobic biodegradation with LL (99 ± 7%) and ES (78 ± 3%) within 50–60 days. Under anaerobic conditions, LL degraded 87 ± 19% of PCL in 60 days, whereas ES showed minimal biodegradation (3 ± 0.3%). PE and PET showed no notable degradation. Metataxonomics results (16S rRNA sequencing) revealed the presence of highly abundant thermophilic microorganisms assigned to Coprothermobacter sp. (6.8% and 28% relative abundance in anaerobic and aerobic incubations, respectively). Coprothermobacter spp. contain genes encoding two enzymes, an esterase and a thermostable monoacylglycerol lipase, that can potentially catalyze PCL hydrolysis. These results suggest that Coprothermobacter sp. may be pivotal in landfill leachate microbiomes for thermophilic PCL biodegradation across varying conditions. The anaerobic microbial community was dominated by hydrogenotrophic methanogens assigned to Methanothermobacter sp. (21%), pointing at possible syntrophic interactions with Coprothermobacter sp. (a H2-producer) during PCL biodegradation. In the aerobic experiments, fungi dominated the eukaryotic microbial community (e.g., Exophiala (41%), Penicillium (17%), and Mucor (18%)), suggesting that aerobic PCL biodegradation by LL involves collaboration between fungi and bacteria. Our findings bring insights on the microbial communities and microbial interactions mediating plastic biodegradation, offering valuable perspectives for plastic pollution mitigation. [ABSTRACT FROM AUTHOR]

A total of 21 surface sediment samples collected from Arasalar River are subjected to sediment texture (sand-silt-clay ratio), trace elements, organic matter, and CaCO3 studies to understand the accumulation dynamics of sediments. To assess the impact of metal pollution in estuarine sediments, the essential parameters should be done by checking the sediment characteristics, spatial distribution of heavy metal sources, sediment dynamics, and geochemical analysis. To evaluate the contamination level of metal pollution, a basic standard reference is required to decipher the values ranging from natural to anthropogenic contribution. From this research analysis, it is observed that the study area predominantly comprises silty sand and sand silty nature. The calcium carbonate content in the sediment is found to be proportional to the presence of shell fragments, whereas the organic matter (OM) is derived from riverine and coastal input which acts as a primary source. The obtained results confessed the average contents (mg/g) for the following selected eight elements in the order of Fe (35249–49068) > Mn (286–519) > Ni (107–279) > Cu (78.30–155.70) > Cr (50–99) > Zn (38.70–91.90) > Pb (39.90–62.40), and Co (12.6–29.1) by using an atomic absorption spectrophotometer (AAS) are utilized for this analysis. Multivariate analysis of heavy metals affirms geogenic sources (weathering of parent rocks) for Fe, Mn, Cr, Co, and Zn, whereas Cu, Ni, and Pb originated from anthropogenic activities (urban and industrial activities). The pollution load index, sediment pollution index, Igeo index, and PERI are categorized as under polluted, low to moderate polluted, and low potential environmental risk variety. Constant inspection and guidance are needed to prevent effluences from various agriculture and industrial activities in the nearby regions. The findings from this research may support and help the government to follow the suitable remediation on the better management of river and coastal areas. [ABSTRACT FROM AUTHOR]

The site AERONET-OC Bahía Blanca (BB-AERONET-OC) is located at the mouth of the Bahía Blanca Estuary, Argentina (Southwestern Atlantic Ocean), a coastal system defined by its high suspended loads and relatively low colored dissolved organic matter. The typically high turbidity of these waters makes the BBAERONET-OC distinctive within the AERONET-OC network stations, providing exceptional opportunities not only for the validation of atmospheric correction algorithms but also for the development of regional algorithms for coastal complex waters. A SeaWiFS Photometer Revision for Incident Surface Measurements (SeaPRISM) instrument was deployed in January 2020 in the upper rail of a Mareograph Tower, a 15 m tall structure, located 10 miles away from the coast in optically deep waters. In this work we used the remote sensing reflectance (Rrs) derived from the BB-AERONET-OC measurements along with in situ hyperspectral radiometric data to classify optical water types (OWTs). We assigned each Rrs(λ) spectra to one of the five OWTs defined by Tran et al., and OWTs were further characterized with the concentrations of optically significant components (chlorophyll-a and suspended particulate matter) and inherent optical properties (absorptions of phytoplankton, non-algal particles, and dissolved organic matter), retrieved from water samples obtained simultaneously with radiometric spectra. Based on a match-up exercise with in situ data, different schemes of atmospheric correction methods were applied to Sentinel-3 Ocean and Land Colour Instrument (OLCI) images. The operational product OLCI Level 2 European Space Agency (ESA) standard (hereafter referred to as “Standard Neural Network (NN)”) proves to be the most suitable atmospheric correction algorithm, which was then used to describe spatial patterns and temporal variability of the different OWTs in the region. The BB-AERONETOC site is located in a sharp transition between estuarine and coastal waters that present contrasting optical conditions: OWT 4 dominates over time (73.72% of the observations), followed by OWT 3 (24.74%) and OWT 5 (1.53%). OWTs 4 and 5 are associated with turbid waters of the Bahía Blanca Estuary, especially OWT 5, which typifies the very turbid waters from the inner estuary, with the particulate load dominated by mineral sediments and detritus. OWT 3, in turn, depicts the eutrophic coastal waters of the inner shelf. The variability of OWTs and the relative contribution of organic and inorganic compounds to the suspended material would be mostly related with the prevalence of northwest winds in the area, which would drive the export of estuarine sediments to the shelf. [ABSTRACT FROM AUTHOR]

The formation and dynamics of individual estuarine turbidity maximum (ETM) in the Pearl River estuary (PRE) have been investigated but the temporal variability of the ETMs and interconnections among them remain poorly understood. To address these open questions, the distribution and transport of suspended particulate matter (SPM) in the PRE for the period of 2017-2020 are investigated by numerical modeling. The simulated sediment transport flux is decomposed into several major components associated with specific physical processes. Then, the relative contribution of each component to the formation of the ETMs is evaluated. Results suggest the coexistence of three prominent ETMs in the Lingding Bay of the PRE. They are formed by different physical mechanisms and characterized by remarkable seasonality in the spatial extension. In the two ETMs located at the west shoal and middle shoal, advection dominates the sediment transport flux, whilst tidal pumping plays a crucial role in maintaining the ETMs. A sharp bathymetric gradient leads to an entrapment of sediment flux within the bottom layer in the west channel ETM, a phenomenon referred to as topographical trapping. The interconnection analysis shows that the sediment transport between the ETMs varies with seasons, which is attributed to the variation of stratification driven by the monsoon-mediated river runoff. Our results provide new insights into the physical dynamics and interconnections of the ETMs in the PRE, which can serve as scientific base for estuarine sediment management and engineering. [ABSTRACT FROM AUTHOR]

Environmental development and water level changes in the south-western part of the Curonian Lagoon are reconstructed based on the results of bottom sediment investigations, including data on lithology, diatoms, pollen, and radiocarbon dating. Three stages have been identified in the ~ 10000-year history of the lagoon's development. The diatoms suggest that in the Early Holocene, the southern part of the Curonian Lagoon was a shallow freshwater basin, mainly fed by run-off from the continent. During the Middle Holocene, the study area was a marshy coastal zone. Due to a change in hydrological conditions at the beginning of the Late Holocene, it became an open-water part of the lagoon. [ABSTRACT FROM AUTHOR]

The manuscript investigates the sediment textures, heavy metals, and magnetic susceptibility analysis of the Cauvery and Vettar core sediments to affirm the pollution status by coupling environmental magnetism and geochemical studies. Pollution indices such as the Geoaccumulation Index, enrichment factors, and contamination factors were used to evaluate the pollution status. Fastidious inspection of the textural characteristics of the core sediments implies that the Cauvery core chiefly comprises sand and silt, whereas Vettar core sediments consist of silt and clay compositions. The magnetic susceptibility of the Vettar sediments implies higher magnetic contents than the Cauvery sediments. Notably, the profound inquisition illustrates the mean concentration of the studied heavy metal concentrations (Fe, Cu, Cr, Zn, Pb, Ni) for both core sediments did not exceed the mean world sediments and the Earth's crust standards. Employing the pollution indices reflects the concentration of heavy metals in both core sediments, which infers environmental contamination. The result implies that the Vettar estuarine sediments show a mixed nature of magnetic grains (maghemite minerals) coupled with clay and silt composition, followed by the Cauvery estuarine sediments showing slighter magnetic susceptibility, which reflects that the Cauvery core sediments are less prone to pollution. However, the non-superparamagnetic grains indicate primarily sand and minor silt composition, reflecting ferromagnetic lithogenic minerals such as magnetite and hematite magnetic components. The statistical techniques establish the relationship between the magnetic susceptibility of χlf value higher in the core sediments depending on the heavy metal contents, clay, and organic matter. [ABSTRACT FROM AUTHOR]

Regular release of sediment from reservoir has been increasingly adopted as a strategy for sustainable management. Here, we use a process‐based morphodynamic model to simulate the estuarine sediment dynamics impacted by turbidity current venting implemented by the Shihmen Reservoir during three typhoon events in 2008. Upon validation with the post‐event bathymetries, the model hindcasts reveal that mud releasing can be effective in mitigating reservoir siltation, yet may be a suboptimal strategy for alleviating coastal sediment deficit. A vast majority of the released muds were delivered through the estuary and exported to offshore by flood advection, wave dispersion, and tidal flushing. The flood‐driven sands, sourced mainly from downstream tributaries, were instead the major contributor to coastal sediment budget. However, mud mantling (covering and immobilizing sand deposits by the reservoir‐released muds) reduced sand availability and thus sand delivery to the coast. For the present case, 25% of the released muds were deposited along the way, presence of these mud covers reduced sand delivery by 15%, compared to a hypothetical scenario of clear‐water flood releases. The relative sand transport deficit is found to increase linearly with the degree of bed mud saturation, 1–D/R, with D/R the ratio of single‐event mud deposit to release. Given broad relevance to global reservoirs encountering the problems of siltation and coastal sediment deficit, our findings highlight that sustainable management needs to look beyond just a bulk amount of sediment, but it is critical to consider how different sediment fractions are interacting and impacted by human activities. Key Points: Increasingly adopted mud release strategy is effective to mitigate reservoir siltation yet suboptimal to alleviate coastal sediment deficitFlood‐driven tributary‐sourced sands dominate supply to coastal sediment budget yet sand delivery is reduced by mantling of released mudsSand delivery deficit (relative to sand delivery of clear‐water flood release scenario) increases linearly with degree of bed mud saturation [ABSTRACT FROM AUTHOR]

Paleovegetation studies require understanding the relationship between vegetation dynamics and the processes controlling pollen deposition. This article investigates the mechanisms of pollen deposition and the associated vegetation patterns within the hydrographic basin of Guanabara Bay, a region of considerable ecological diversity and complexity situated in southeastern Brazil. Fifty-six surface sediment samples were collected from several Guanabara Bay hydrographic basin locations. Palynological analysis was used together with multivariate methods, such as Non-Metric Multidimensional Scaling (NMDS) and cluster analysis, were used to identify patterns of similarity between the samples. Furthermore, Statistical tests, including ANOSIM, were employed to assess significant differences in taxon composition among the study areas. The palynological analysis identified a high frequency of shrub and herbaceous pollen types, mainly represented by Poaceae. The mangrove vegetation, represented by Avicennia and Rhizophora, was recorded primarily on samples near the intertidal zone. This research contributes to a better understanding of pollen-vegetation relationships and the mechanisms governing pollen transport within estuarine sediments. The findings provide valuable insights into the potential pollen sources in Guanabara Bay, aiding in assessing ecological changes and environmental preservation efforts. Further studies are necessary to expand the knowledge of pollen transport dynamics and vegetation patterns in large basins with complex vectors, such as the Guanabara Bay watershed. [ABSTRACT FROM AUTHOR]

The quantification of the erodibility of cohesive sediments is fundamental for an advanced understanding of estuarine sediment transport processes. In this study, the surface erosion threshold tc for cohesive sediments collected from two sites in the area of the Port of Hamburg in the River Elbe is investigated in laboratory experiments. An improved closed microcosm system (C-GEMS) is used for the erosion experiments, which allows the accumulation of suspended sediment concentration (SSC) over an experimental run. A total of 34 erosion experiments has been conducted with homogenized samples and bulk densities between 1050 kg/m³ and 1250 kg/m³. The covered range of bulk densities is seen to represent the values commonly exhibited by freshly deposited cohesive sediments. Two approaches to derive tc based on the erosion rate (e-method) and the SSC (SSC-method) were elaborated and compared. For both approaches, only one parameter has to be set in order to facilitate transferability to other devices. The results show a better performance of the SSC-method in terms of lower uncertainties, especially at the upper application limits of the utilized C-GEMS. The application of the SSCmethod yields values for tc between 0.037 N/m² and 0.305 N/m², continuously increasing with bulk density. Repetition tests proved the repeatability of the experimental procedure and utilized methods to derive tc. The derived data for tc is used to fit two mathematical models: i) a highly empirical model relating tc to dry bulk density and ii) a recently proposed model relating tc to the physical properties of the sediment-mixture. While the derived parameters for the first model vary widely for the two sampling sites, the fit-parameter for the lattermodel is virtually independent of the investigated site, suggesting the superiority of this approach. [ABSTRACT FROM AUTHOR]

Coastal and marine areas have huge ecosystem values. However, intensive anthropogenic activities have largely changed coastal landscapes. In this research investigation, sediment and water samples were collected to clarify the distribution patterns and sources of heavy metals in the rapid growing urbanization areas of Haizhou Bay in China's Jiangsu Province. The physical and chemical properties of the water and sediment were tested. Meanwhile, the ecological toxicity levels of heavy metals were also examined using the Igeo accumulation index, and the potential ecological risk index (PERI), respectively. The results revealed that the water and sediments of the marine ecosystems had an unpolluted status, with the element concentrations not exceeding the threshold effect levels. In terms of the spatial distribution patterns of the heavy metal concentrations in the water samples, it was determined that the Cd concentration was only 0.10 µg/L in the western area, and the highest concentration value was found in the northeastern area. The concentration levels of As in the sediments exhibited higher concentrations mainly in the southern area of Haizhou Bay. The results obtained in this study can help increase the awareness of the mitigating actions that coastal areas naturally provide against pollution and also provide valuable information for the design of future plans and policies that will progress toward a more sustainable development of the such areas. [ABSTRACT FROM AUTHOR]

The anomalous variation in the diversion of flow and sediment at the major bifurcation nodes of the Pearl River network in recent years has been generally recognised and accepted, yet the underlying mechanisms have not been revealed. In this study, a large‐scale two‐dimensional flow‐sediment numerical model of the Pearl River estuary was constructed using the TELEMAC‐MASCARET modelling system. Additionally, synchronous field surveys from the dry season of 2016 and wet season of 2017 were used to validate the model. The complex branches system of the Pearl River network was generalised. The theoretical models for calculating the water diversion ratio (WDR) of complex estuarine river networks were proposed. The WDR at each river network node is related to Manning's roughness coefficient, the average cross‐sectional water depth, the water surface slope, the length of the branches and the average cross‐sectional area from the river network nodes to the main estuary outlets. Specifically, the average cross‐sectional water depth is the main driver of the formation of the WDRs at the nodes in the Pearl River network. The sediment SDRs at the primary and secondary lateral branching nodes are significantly higher than the WDRs in the dry season, which explains the uneven distribution of flow and sediment. Sediment mining and reclamation are the main factors that have affected the variation in flow and SDRs in the Pearl River network over recent decades. [ABSTRACT FROM AUTHOR]

Atmospheric concentrations of nitrous oxide (N2O), a potent greenhouse gas that is also responsible for significant stratospheric ozone depletion, have increased in response to intensified use of agricultural fertilizers and other human activities that have accelerated nitrogen cycling processes. Microbial denitrification in soils and sediments is a major source of N2O, produced as an intermediate during the reduction of oxidized forms of nitrogen to dinitrogen gas (N2). Substrate availability (nitrate and organic matter) and environmental factors such as oxygen levels, temperature, moisture, and pH influence rates of denitrification and N2O production. Here we describe the role of physicochemical perturbation (defined here as a change from the ambient environmental conditions) on denitrification and N2O production. Changes in salinity, temperature, moisture, pH, and zinc in agricultural soils induced a short-term perturbation response characterized by lower rates of total denitrification and higher rates of net N2O production. The N2O to total denitrification ratio (N2O : DNF) increased strongly with physicochemical perturbation. A salinity press experiment on tidal freshwater marsh soils revealed that increased N2O production was likely driven by transcriptional inhibition of the nitrous oxide reductase (nos) gene, and that the microbial community adapted to altered salinity over a relatively short (within one month) timeframe. Perturbation appeared to confer resilience to subsequent disturbance, and denitrifiers from an environment without salinity fluctuations (tidal freshwater estuarine sediments) demonstrated a stronger N2O perturbation response than denitrifiers from environments with more variable salinity (oligohaline and mesohaline estuarine sediments), suggesting that the denitrifying community from physicochemically stable environments may have a stronger perturbation response. These findings provide a framework for improving our understanding of the dynamic nature of N2O production in soils and sediments, in which changes in physical and/or chemical conditions initiate a short-term perturbation response that promotes N2O production that moderates over time and with subsequent physicochemical perturbation. [ABSTRACT FROM AUTHOR]

To study the processes that govern the post-depositional mobility of metals in the estuarine sediment, five sediment cores were sampled in the Krka River estuary (Croatia). The obtained concentration ranges in the pore water were 0.057–49.7 μM for Fe, 0.310–100 μM for Mn, 0.068–26.8 nM for Co, 0.126–153 nM for Cu, 11.5–2793 nM for Zn, 0.222–31.3 nM for Pb, 4.09–59.4 nM for U, 38.8–2228 nM for Mo, and 0.065–2.29 nM for As. The vertical distribution of metals in the dissolved and solid fraction of the sediment, coupled with other diagenetic tracers (e.g., dissolved sulphide), demonstrate the importance of early diagenetic reactions, in particular Fe and Mn oxyhydroxide and sulphate reduction, for the cycling of metals in the sediment. The redox zonation in the sediment was compressed, and the suboxic zone occurs immediately below the sediment–water interface. The estimated benthic fluxes in the estuary were 5220 kg y−1 for Fe, 27,100 kg y−1 for Mn, 6.00 kg y−1 for Co, 20.5 kg y−1 for Cu, 5.16 kg y−1 for Pb, 111 kg y−1 for Mo, and 87.3 kg y−1 for As. The riverine input was more important than the benthic flux, except in the case of Mn and Fe. [ABSTRACT FROM AUTHOR]

Estuarine sediment transport is driven by the combined action of a multitude of influencing factors, including astronomical tides, waves dynamics, and river discharges. This study focuses on the effects of wave forces on sediment transport patterns in micro-tidal estuaries near Wanbao Beach, China. Numerical simulations are carried out using Delft3D. Modeling scenarios are configured using different wave characteristics, spanning from typical waves to those with a return period of 50 years. Results show that waves have a positive effect on landward sediment transport, resulting a larger active range of sediment. By comparing the spatial geomorphic variations under varying wave conditions, we find that modifications in significant wave height (Hs) primarily impact the position of erosion and deposition zones, whereas alterations in spectral peak period (Tp) predominantly influence the magnitude of these changes. The finding is further demonstrated by a comparison of residual currents under different wave intensities. Analysis of sediment transport rates in different transects indicates that the sediment transport rate is highest at the mouth transects and lowest at the alongshore transects. Moreover, variations in sediment transport rates exhibit distinctive patterns between the two outlet transects, even when subjected to identical wave conditions. The disparities are attributed to differences in runoff and the topographical features in proximity to the estuaries. Additionally, we find the sediment transport rate becomes insensitive to the variations in Hs when Hs is larger than a threshold value. The threshold decreases with increasing Tp. [ABSTRACT FROM AUTHOR]

The existence of coastal ecosystems depends on their ability to gain sediment and keep pace with sea level rise. Similar to other coastal areas, Northeast Florida (United States) is experiencing rapid population growth, climate change, and shifting wetland communities. Rising seas and more severe storms, coupled with the intensification of human activities, can modify the biophysical environment, thereby increasing coastal exposure to storm-induced erosion and inundation. Using the Guana Tolomato Matanzas National Estuarine Research Reserve as a case study, we analyzed the distribution of coastal protection services-expressly, wave attenuation and sediment control-provided by estuarine habitats inside a dynamic Intracoastal waterway. We explored six coastal variables that contribute to coastal flooding and erosion-(a) relief, (b) geomorphology, (c) estuarine habitats, (d) wind exposure, (e) boat wake energy, and (f) storm surge potential-to assess physical exposure to coastal hazards. The highest levels of coastal exposure were found in the north and south sections of the Reserve (9% and 14%, respectively) compared to only 4% in the central, with exposure in the south driven by low wetland elevation, high surge potential, and shorelines composed of less stable sandy and muddy substrate. The most vulnerable areas of the central Reserve and main channel of the Intracoastal waterway were exposed to boat wakes from larger vessels frequently traveling at medium speeds (10-20 knots) and had shoreline segments oriented towards the prevailing winds (north-northeast). To guide management for the recently expanded Reserve into vulnerable areas near the City of Saint Augustine, we evaluated six sites of concern where the current distribution of estuarine habitats (mangroves, salt marshes, and oyster beds) likely play the greatest role in natural protection. Spatially explicit outputs also identified potential elevation maintenance strategies such as living shorelines, landform modification, and mangrove establishment for providing coastal risk-reduction and other ecosystem-service co-benefits. Salt marshes and mangroves in two sites of the central section (N-312 and S-312) were found to protect more than a one-quarter of their cross-shore length (27% and 73%, respectively) from transitioning to the highest exposure category. Proposed interventions for mangrove establishment and living shorelines could help maintain elevation in these sites of concern. This work sets the stage for additional research, education, and outreach about where mangroves, salt marshes, and oyster beds are most likely to reduce risk to wetland communities in the region. [ABSTRACT FROM AUTHOR]

Understanding the geochemical behavior of the Mo isotopes in estuarine systems is essential for determining the isotopic composition of riverine inputs to the ocean and for assessing the historical oxidation state of Earth's ancient oceans. However, the extent and mechanisms of Mo isotope fractionation during estuarine processes are not yet fully understood. This study systematically investigated the seasonal and spatial variations in aqueous and particulate δ98Mo values within the Pearl River Estuary (PRE). Our research found that aqueous δ98Moaque. values in both summer and winter deviated significantly from the theoretical mixing line for the PRE. Based on the geochemical characteristics of the water column, particulate matter, and pore water in the PRE, we first propose that diagenesis release from sediments is the predominant factor resulting in lower than anticipated aqueous δ98Moaque. values. Given the prevalence of suboxic and anoxic sediments in estuarine and coastal areas, such diagenetic release may substantially decrease the global riverine influx of aqueous Mo isotopes to the ocean. Additionally, particulate δ98MoSPM values exhibit an increasing trend (from 0.02 to 1.62‰) with increasing salinity in both seasons, suggesting that the terrestrial input particulate δ98MoSPM value would be heavier than the mean value for UCC. We hypothesize that the adsorption and desorption processes involving Fe (hydro) oxides predominantly influence this trend. This study advances our understanding of the mechanisms of aqueous and particulate Mo isotopic fractionation in estuarine systems and would be helpful in constraining Mo isotopic compositions of rivers and oceans. Plain Language Summary: The reliability of using Mo isotopes to trace historical shifts in global ocean redox depends heavily on precise constraints of the Mo isotopic composition of riverine inputs to the ocean. Estuaries, serving as dynamic interfaces between terrestrial and marine environments, can substantially alter the Mo isotopic composition of riverine inputs to the ocean. To more accurately constrain the Mo isotopic composition of riverine inputs to the ocean, understanding the extent and mechanisms of Mo isotope fractionation during estuarine processes is crucial. Addressing this knowledge gap, our study investigates the seasonal and spatial variations in δ98Mo values of aqueous and particulate Mo in the Pearl River Estuary (PRE), China. Our findings reveal that aqueous δ98Moaque. values are markedly lower than the theoretical mixing‐line values in both summer and winter seasons, whereas particulate δ98MoSPM values demonstrate a distinct increasing trend from the upper to lower reaches of the PRE. This suggests that estuaries can profoundly modify the Mo isotopic composition of riverine inputs to the ocean. In conclusion, we propose that the reductive release from sediments likely explains the lower aqueous δ98Moaque. values, while the adsorption and desorption of Fe (hydro) oxides primarily drive the observed increase in particulate δ98MoSPM values. Key Points: Aqueous δ98Mo values in different seasons were substantially lower than theoretical mixing‐line values in the Pearl River Estuary (PRE)Reductive release from sediments is responsible for the aqueous δ98Mo values being lower than theoretical levelsFe (hydro) oxides are the dominant factors controlling the increasing trend in the particulate δ98Mo values with salinity [ABSTRACT FROM AUTHOR]

• Surface Fe (oxyhydr)oxides mediated electron transfer to promote HO• production. • Corrosion of surface oxides and quenching of HO• by Cl− inhibited HO• production. • Formation of surface Fe(II)-CO 2 complexes increased average rate of HO• production. • Photoelectrons generated by UV irradiation promoted extensive production of HO•. Pyrite is widely distributed in estuarine sediments as an inexpensive natural Fenton-like reagent, however, the mechanism on the hydroxyl radical (HO·) production by pyrite under estuarine environmental conditions is still poorly understood. The batch experiments were performed to investigate the effects of estuarine conditions including aging (in air, in water), seawater anions (Cl−, Br− and HCO 3 −) and light on the HO· production by pyrite oxidation. The one-electron transfer dominated the process from O 2 to HO· induced by oxidation of pyrite. The Fe (oxyhydr)oxide coatings on the surface of pyrite aged in air and water consumed hydrogen peroxide while mediating the electron transfer, and the combined effect of the two resulted in a suppression of HO· production in the early stage of aging and a promotion of HO· production in the later stage of aging. Corrosion of the surface oxide layers by aggressive anions was the main reason for the inhibition of HO· production by Cl− and Br−, and the generation of Cl· and Br· may also play a role in the scavenging of HO·. HCO 3 − increased the average rate of HO· production through surface-CO 2 complexes formed by adsorption on the surface of pyrite. The significant enhancement of HO· production under light was attributed to the formation of photoelectrons induced by photochemical reactions on pyrite and its surface oxide layers. These findings provide new insights into the environmental chemical behavior of pyrite in the estuary and enrich the understanding of natural remediation of estuarine environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Uplift of the overriding plate at a subduction zone denotes interseismic strain accumulation, which is subsequently released during a megathrust earthquake. Although most interseismic strain is thought to be released elastically, observations of uplifted coastal regions at subduction zones worldwide indicate that some strain may result in permanent uplift. The Grays Harbor and Willapa Bay (Washington, USA) coastal region of the Cascadia subduction zone hosts flights of marine terraces testifying to late Pleistocene rock uplift. Our new detailed mapping of the marine terraces recognizes nine new units, including estuarine and fluvial sediments. Luminescence dating, relative age based on soil maturity and terrace elevation, and an evaluation of previous ages from fossil shells collectively constrain the probable ages of three estuarine units to sea-level high stands during Marine Isotope Stages 5a, 5c, and 5e. We estimate an average uplift rate of 0.4 ± 0.1 mm/yr for the terraced estuarine units, consistent with other Pleistocene uplift and incision rates in Cascadia. When compared with observed interseismic vertical deformation, these rates suggest that about one-tenth of interseismic strain may become permanent. The values are permissible within the uncertainties of uplift based on regional estimates of interseismic vertical strain rates and of coseismic subsidence. [ABSTRACT FROM AUTHOR]

The Fundão dam failure in 2015 severely impaired the economy, the lives of riverine communities, and the aquatic ecosystems of the Rio Doce basin in southeast Brazil. Several contaminants, including polycyclic aromatic hydrocarbons (PAHs), were transported downstream, deposited in the estuary, and released into the Atlantic Ocean. The high concentration of PAHs in estuarine sediments may pose ecological risks and deleterious effects to benthic organisms, so here we aimed at determining the source and fate of these compounds before and after the tailings' arrival. The mean concentration of the analyzed Σ16PAHs increased from 34.05 µg kg−1 in the prefailure period to 751.77 µg kg−1 one year after the arrival of the tailing. The classification of the sediment quality changed from low to moderate contamination. Our results suggest that there was PAHs remobilization by mine tailings along the Rio Doce basin. The target analytes exhibited mostly a pyrolytic profile from fossil fuel and biomass burning. In addition to other contaminants deposited in the estuary after the arrival of the tailings, this study revealed that the profile change of PAHs in the estuary region is a consequence of the mud's erosive power. Integr Environ Assess Manag 2024;20:169–178. © 2023 SETAC Key Points: One year after the tailings arrived at the mouth, the average concentration of polycyclic aromatic hydrocarbons (PAHs) in the estuary increased 20 times.Sediment quality changed significantly from low to moderate and/or high contamination.The sources that contributed to the input of PAHs also changed over time, at first characterized by burning fossil fuels prior to arrival and transitioning to a mixed pyrolytic profile after the tailings arrived at the river's mouth.The compounds carried by the mud appear to be trapped in the estuary, creating a source of chronic contamination for the mouth and adjacent coastal areas. [ABSTRACT FROM AUTHOR]

Nutrient fluxes from fine-grained, organic-rich sediments in estuaries can hasten the onset and progression of eutrophication and harmful algal blooms. Targeted efforts to manage degraded sediments and improve estuarine water quality require a better understanding of physicochemical controls and the relative importance of benthic fluxes. Toward that end, we determined fluxes from organic-rich, high porosity sediments deposited during the past 5-6 decades along 60kmof the Indian River Lagoon, a barrier island lagoon in Florida, USA. Highly bioavailable ammonium and phosphate were the predominant chemical forms of interstitial nitrogen and phosphorus in these highly-reducing sediments. Median fluxes of ammonium and phosphate were 320 µmol m-2 h-1 and 11 µmol m-2 h-1, respectively. Fluxes were 3-10 times greater when sediment temperatures were >28°C and interstitial sulfide concentrations were >1 mM. Temperature-compensated fluxes of ammonium and phosphate were significantly correlated with sediment organic matter content; total organic carbon averaged 5.3 ± 2.4% and the maximum was 12.4% for the sediments studied. Fine-scale physical probing, plus lidar data, showed that these organicrich sediments covered <10% of our study area; however, fluxes from these sediments were estimated to supply 20-40% of internal + external annual loads of nitrogen and phosphorus. Furthermore, 60% of nitrogen and phosphorus fluxes fromsediments in the northern Indian River Lagoon came from just 22% of the total surface area. Lagoon segments with high benthic fluxes overlapped in part with areas prone to harmful algal blooms. Effective strategies to manage degraded sediments in the Indian River Lagoon depend on knowing the relative magnitude of internal loading of nutrients as well as appropriate techniques to mitigate sediment fluxes. [ABSTRACT FROM AUTHOR]

Microorganisms play a major role in the degradation of organic matter in sediments. However, the spatiotemporal variation and factors affecting these communities are not clearly understood. At the same time, conventional hydrographic and geochemical parameters do not offer an accurate assessment of transitional ecosystems. PLFA biomarkers which are specific to different taxonomic groups of microorganisms are able to provide a detailed assessment of the community composition in an environment and reflect a more direct assessment of the biological health of transitional ecosystems. We, therefore, conducted a comparison of PLFA biomarkers at four stations (Barmouth, B; Vaduthala, V; Munambam, M; and Arookutty, A) during three seasons (pre-monsoon, PRE; monsoon, MON; and post-monsoon, POST) in the Cochin estuary (CE). Each of the stations represented either a reference point (B), high pollution (V), high salinity (M), or low pollution (A). The communities determined using PLFA profiles could be categorized into six major groups with each group capable of reflecting the state of the ecosystem which correlated with the conventional parameters. The six groups were: G + ve Bacillota (formerly Firmicutes) and G-ve anaerobes (G-I), G-ve aerobic prokaryotes (G-II), ectomycorrhizal fungi (G-III), arbuscular mycorrhizae (G-IV), type-I methanotrophs (G-V), and microeukaryotes (G-VI). The prokaryotes were predominant in sediments amounting to over 78% of the total PLFAs detected, followed by the microeukaryotes. The freshwater-influenced stations were partially anaerobic in nature during PRE and MON and were mainly affected by both marine and terrestrial organic matter inputs, at times prominent in sewage matter. During POST season, CE behaves uniformly, especially in station M. Salinity and DO of BW and texture and organic matter of the sediment were the driving forces for microbial community structure. The reduced presence of cyclopropane fatty acids suggested that the CE was not under any stress during the study period. Our results using PLFA-based community profiling not only provide the fundamental information required to quickly access the impact of stress and other environmental inputs on the CE but also offer a more robust and realistic assessment of the nature of microbial communities in the ecosystem. A periodic and systemic assessment of PLFA profiles at these stations in CE throughout the year will enable the generation of enough metadata enabling a better understanding of this ecosystem and its efficient management in the long term. [ABSTRACT FROM AUTHOR]

The treatment and beneficial use of polluted or contaminated environmental matrices have become major issues, especially as the world strives toward a zero-waste policy. In this regard, dredged sediments need to be treated before they can be used in an environmentally safe and sustainable manner. Therefore, this work aims to treat estuarine sediments and, more importantly, use physicochemical, mineral, organic, and chemical information to understand the reactions that occur upon treatment. Dredged estuarine sediments were collected from Tancarville (Seine River estuary, France) and subjected to electrokinetic (EK) remediation using a 128-L laboratory-scale reactor. The sediments were treated 8 h per day for 21 days. The electric (voltage and current) and physicochemical (pH and electric conductivity) parameters were monitored during treatment. Sediments were collected from various sections in the reactor at the end of the experiment (lengthwise, widthwise, and depthwise). The spatial variation was investigated in terms of organic, mineral, and metal contents. Statistical analyses proved that the variation occurred only in the lengthwise direction. Furthermore, three main phases described the treatment, which were mainly linked to carbonate dissolution and pH variation. The results also showed that the trace elements Ni and Zn were reduced by 21% and 19%, respectively, without a direct link to pH, while Ca and Mg were only redistributed. The buffering capacity of the anodic sediment was reduced due to carbonate dissolution. The treated sediments showed reduced contents in trace metals without affecting major elements that can be useful in agriculture (i.e., Ca and Mg). [ABSTRACT FROM AUTHOR]

Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to "re-suspend" and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as "self-digging". The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and "re-suspension", which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC "tails" appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of "self-digging" induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the "self-digging" problem to a certain extent and ensure the safety of OWFs. [ABSTRACT FROM AUTHOR]

Headwater tidal creeks are a primary link between estuarine and upland habitats, serving as conduits for runoff. They are sentinel habitats, providing early warning of potential harm, thus ideal systems to evaluate the effects of coastal suburban and urban development on environmental quality. Estuarine sediments have concentrations of metals, polycyclic aromatic hydrocarbons (PAHs), pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) that are associated with human activity. High concentrations of contaminants can impair faunal communities, habitat quality, and ecosystem function. Forty-three headwater creeks were sampled between 1994 and 2006 to assess contaminants, and 18 of these were sampled again in 2014/2015. Watersheds were classified as forested, forested to suburban, suburban, or urban land. These values are based on their percent impervious cover (IC) levels and change in IC from 1994–2014. Analyses of temporal data resulted in significant relationships between IC and select metals, PAHs, pesticides, PCBs, and PBDEs. In addition, 11 of the creeks sampled in 2014/2015 have paired data from 1994/1995, allowing for change analysis over the 20 years. Results indicated increasing chemical contamination occurring with increasing levels of development, although only PAHs and total dichloro-diphenyl-trichloroethane (DDT) exhibited a statistically significant increase over time; PAHs also exhibited significantly higher concentrations in developed creeks. Additionally, several metals were deemed enriched in developed creeks based on reference conditions. These results expand our knowledge of how these systems respond to urban development and can inform managers about how human population growth along coastlines may predict altered tidal creek health. [ABSTRACT FROM AUTHOR]

Holocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of ca 50 m. Detailed data on textural and lithofacies variations, grain‐size analysis, environmental magnetism and accelerator mass spectrometry 14C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high‐resolution record extending back to 10 ka has been reconstructed from the top ca 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub‐tidal, intertidal and supra‐tidal environments. The sediment accumulation rate is highest in the sub‐tidal to intertidal facies (1.9 cm year−1) and decreases towards the supra‐tidal facies to 0.09 cm year−1. Environmental magnetic analysis, χlf coupled with the S‐ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi‐arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S‐ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub‐tidal (Unit 3), is attributed to sea‐level transgression followed by regressive intertidal (Unit 4) to supra‐tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level. [ABSTRACT FROM AUTHOR]

The hydrodynamics and grain size distributions of sediment in estuarine and coastal environments provide important information on the material source, environmental events, and so forth. According to our knowledge, there is no research on the sediment characteristics of the entire Sebou estuary (Morocco), particularly, on the correlation between hydrodynamics and sediment properties. Grain-size analysis of estuary sediments along Sebou estuary (Morocco) has been carried out to reveal the depositional environment condition, energy and hydrodynamic conditions, as well as the mode of transportation along the study area. Linear discriminate analysis technique and bivariate plotting of grain size parameters are used to explain and understand the environment of sediment deposition. Hydrodynamic processes working during the deposition of sediments have been identified by CM plotting. As the mean grain size increased, sorting improved, and skewness became more positive and leptokurtic to very leptokurtic nature was observed in both periods. The spatial distribution indicates majority of sample fall in silt and clay category in both periods (i.e., spring and neap). Based on the CM pattern it was inferred that the sediment fall in rolling and suspension field. The sediments may be derived from offshore and catchment area deposits of the clay and silt, and evidence was found to suggest that these deposits are being eroded by tidal currents. [ABSTRACT FROM AUTHOR]

The impact of coastal acidification on sediment nitrous oxide (N2O) and methane (CH4) fluxes is largely unknown. We exposed temperate estuarine sediments to moderate (pH 7.3) and extreme (pH 6.3) acidification. Sediments were collected from two sites—one exposed to high and the other to low nitrogen loading. We demonstrate that low pH has a strong effect on greenhouse gas fluxes. The response, in terms of both magnitude and direction, was site specific. Sediments from the high nitrogen loading site exhibited increased N2O fluxes and decreased CH4 fluxes under moderate and extreme acidification. In contrast, sediments from the low nitrogen loading site exhibited decreased N2O fluxes under moderate and extreme acidification while CH4 fluxes both decreased (moderate) and increased (extreme). This study highlights the dynamic response of sediment N2O and CH4 fluxes to low pH and emphasizes the need for deeper understanding of ofcoastal acidification impacts on sediment biogeochemistry. [ABSTRACT FROM AUTHOR]

A decline of the fluvial sediment supply leads to coastal erosion and land loss. However, the fluvial sediment load may influence not only coastal morphodynamics but also estuarine hydrodynamics and associated saltwater intrusion. Previous studies revealed that suspended sediments influence estuarine hydrodynamics through various flow–sediment interactions. In this contribution, we systematically investigate how changes in fluvial sediment load and other climate‐change‐induced environmental change influence estuarine hydrodynamics and sediment dynamics. For this purpose, we utilize a well‐calibrated fully coupled model in which hydrodynamics, saltwater intrusion, and sediment transport interact with each other, to explore saltwater intrusion in the Yangtze Estuary in response to a decline in the sediment load, modified discharge, and sea‐level rise. Model results suggest that a 70% decline in the suspended sediment load weakens the impact of sediments on salinity‐induced stratification and thereby reducing saltwater intrusion. Sea‐level rise or discharge peak reduction increases saltwater intrusion. However, a fully coupled model accounting for sediment effects predicts a much larger increase in saltwater intrusion compared to noncoupled models. Whether this effect is important depends on estuarine sediment concentrations and therefore the potential role of sediments should be carefully investigated before applying a noncoupled model. This work highlights not only the relevance of a suspended sediment decline but also the use of fully coupled models for predicting saltwater intrusion in turbid estuaries and has broad implications for freshwater resource management in turbid estuarine systems influenced by human interventions and climate change. Plain Language Summary: Saltwater intrusion is strongly influenced by river flow, tides, and morphology in estuaries. In highly turbid estuaries, high suspended sediment concentrations interact with salinity, which also plays an important role in saltwater intrusion and freshwater resources. However, many of these estuaries are suffering from a reduction in sediment supply, leading to reduced sediment concentration in recent decades. In this study, we employ a fully coupled three‐dimensional numerical model to investigate the effect of reduced sediment supply on saltwater intrusion. The fully coupled model predicts a much larger increase in saltwater intrusion in response to sea‐level rise or modulation of the river discharge compared to noncoupled models. In contrast, a decline in riverine sediment supply weakens sediment–turbulence interaction, thereby decreasing saltwater intrusion. These findings are important for the management of sediment and freshwater resources in turbid estuaries. Key Points: A decline in riverine sediment supply weakens sediment–fluid interactions, thereby decreasing saltwater intrusionSaltwater intrusion may be as much influenced by a sediment load reduction as by changes in river discharge distribution or sea‐level risePredicting saltwater intrusion in highly turbid estuaries requires evaluation of the role of sediments before applying a noncoupled model [ABSTRACT FROM AUTHOR]

In the estuarine sediment, the nitrite oxidation process mediated by bacteria significantly influences nitrification. Nitrospira is the most widely distributed nitrite-oxidizing bacteria (NOB) and can adapt to various environments. In this study, the Nitrospira-specific primer nxrB 169F-638R was used to analyze the microbial communities in the sediments of low-, middle-, and high-level zones in the Luan River estuary. The structure of the microbial community and its response to environmental factors were also assessed. The abundance and diversity of Nitrospira were the highest in the low-level zone and lowest in the high-level zone. Lineage II and lineage IV were the dominant Nitrospira at 43.58% and 32.09%, respectively. The distribution pattern of Nitrospira was also affected by complex environmental factors, such as the concentration of NH4+, Fe, and Cu cations. This study provides novel insights into the niche differentiation and adaptation strategies of Nitrospira in an estuarine sediment environment and will help to facilitate single-step nitrification. [ABSTRACT FROM AUTHOR]

Thirty surface sediment samples collected from Ariyankuppam (N =12) and Chunnambar estuaries (N = 18) located along the coast of Pondicherry, India, are analyzed to understand the nature of weathering and provenance. The granulometric study reveals that sediments are poorly sorted, positively skewed and platykurtic to leptokurtic in nature. The abundance and inverse relationship of SiO2 with other major oxides signify the detention of silica within quartz. The Index of Chemical Variability (ICV) suggests that sediments are compositionally immature and are derived from less weathered source rock. The weathering indices such as the Chemical Index of Alteration (CIA); Chemical Index of Weathering (CIW); Plagioclase Index of Alteration (PIA), and A-CN-K diagram also suggest less intense weathering of parent rocks. The major and trace element ratios viz. Al2O3/TiO2, TiO2/Zr, Cr/V and Y/Ni and discrimination diagrams indicate that estuarine sediment is derived from felsic and intermediate provenance. [ABSTRACT FROM AUTHOR]

This study deals with the relations of sediment texture and depositional conditions to the organic carbon (OC) and carbon (C) stock distribution, and estimates C sequestration in the coastal estuaries of the Naf River and Maheshkhali Channel of Bangladesh. In this study, the average OC percentages were 0.65% and 0.55%, the C stocks were calculated as 9.02 t/ha and 9.87 t/ha, and the conversion of C stock to total C sequestration became 33.35 t CO2/ha and 36.54 t CO2/ha, with the monetary values $1000.42 and $1096.26 per hectar of the Naf River and Maheshkhali Channel estuaries, respectively. The distribution of OC and C stock mostly depends on the sedimentary depositional conditions and sediment texture, as well as on the existence of mangrove and salt marsh along the banks of the estuaries. Low energy and velocity conditions and unidirectional fluvial settings tend to increase the concentration of OC and C stock, and also moderate grain-size with poorly sorted sediment contains high OC and C stock. Transportation mode with two populations (traction and saltation) increases the concentration of OC and C stock by more than three populations. There is some effect from the mixing environment and heavy mineral concentration on the OC and C stock distributions. [ABSTRACT FROM AUTHOR]

Estuaries, in particular freshwater estuaries, provide valuable economic, social, and ecological services, but their ecosystems are often heavily stressed. Located in the Laurentian Great Lakes basin, Green Bay is a large freshwater estuary and a prominent example of a degraded ecosystem due to intensive human interventions and rapid development. Excessive amounts of contaminants and nutrients were discharged to the bay by inflowing tributaries for almost half a century, while in contrast Green Bay's seasonal‐, morphological‐, and physically‐restricted mixing is unable to export a significant portion of those materials out of the bay, that is, Green Bay behaves as an efficient retention basin for the Lake Michigan. Consequently, several environmental and public health‐related issues have risen in Green Bay and turned the lower bay into an area of environmental concern since the 1980s. To address these challenges, restoration programs were developed, including the development of monitoring programs, scientific research, and remedial action plans. There is a consensus that accelerated loading rates of contaminated and nutrient‐rich sediments are a major driver of the environmental crisis in the bay, yet the fate and transport patterns of Green Bay sediments are not clearly understood. While field observations in Green Bay are season‐limited and costly, advanced computing techniques provided opportunities to refine our understanding of sediment dynamics in this estuarine system. This review of existing knowledge on Green Bay sediment processes can help to better understand the interplay between sediments, and physical/biogeochemical activities in estuarine systems and contributes conceptually to the restoration of degraded aquatic ecosystems. This article is categorized under:Science of Water > Hydrological ProcessesScience of Water > Water QualityWater and Life > Stresses and Pressures on Ecosystems [ABSTRACT FROM AUTHOR]

The scientific and reasonable evaluation of heavy metals pollution in estuarine sediments is crucial for characterizing the environmental quality of the lake, however, it is still unavailable due to the lack of local geochemical baseline concentrations (GBCs) and thus applying background values of soils. In this study, the statistical method of cumulative frequency was employed to obtain the GBCs, which were applied as reference standards for the pollution assessment of heavy metals and source apportionment in estuary sediments of northwestern Taihu Lake. The results showed that the GBCs of Cd, Cu and Zn were higher than soil background values in Jiangsu Province while Ni and Pb displayed a small gap between GBCs and background values. Cd, Ni and Zn presented a degree of moderate pollution or moderate to strong pollution according to geo-accumulation index (Igeo). The pollution load index (PLI) showed that 75% of samples ranged from non-pollution to moderate pollution level while 2.94% of samples exhibited a moderate to high pollution level. The possible sources of heavy metals in the estuary sediments were quantitatively identified by positive matrix factorization (PMF), including agricultural source (23%), the combined contribution of natural sources and traffic emissions (36%) and industrial source (41%). [ABSTRACT FROM AUTHOR]

Jackson, K.; Wang, P.; Pluckhahn, T.J.; Rogers, J.A., and Thompson, V.D., 2023. Stratigraphic framework, paleoenvironments, and Indigenous terraforming of inshore estuarine subbasins in Tampa Bay, Florida, U.S.A. Journal of Coastal Research, 39(5), 779–815. Charlotte (North Carolina), ISSN 0749-0208. Tampa Bay is a karst-controlled estuary system on Florida's central peninsular Gulf of Mexico coast. Although previous work has reconstructed late-Pleistocene environments (ca. 20–11.5 kya) and early marine influence (ca. 8–5.5 kya) in deeper central portions of the bay, the estuarine development of the shallow inshore subbasins remains poorly understood. Across the late Holocene, Indigenous societies terraformed the coastal strand with large volumes of estuarine mollusk shell, and these anthropogenic landforms constitute coastal barriers that partially enclose marginal tidal bayous. This study integrates sediment coring and archaeological excavations to reconstruct the Holocene estuarine evolution of four inshore subbasins within Tampa Bay. This study synthesizes sedimentological, macrofossil, and archaeological data to describe and differentiate seven sedimentary facies and 18 subfacies representing weathered Miocene limestone at the base, overlain by late-Pleistocene freshwater wetland deposits, followed by Holocene estuarine sediments and late-Holocene shell-terraformed settlements. Four stratigraphic cross-sections and >100 radiocarbon assays are utilized to interpret the sequences of inshore estuary development, situate ancient shell-bearing Native settlements within a geologic and paleoenvironmental framework, and resolve elements of mid- and late-Holocene sea-level history. [ABSTRACT FROM AUTHOR]

Barakar Formation (Early Permian) in Peninsular India contains a thick sandstone-shale-coal succession. Petrographic study of the Ramnagar seam (BR 6) from Ramnagar colliery within the Barakar succession, Raniganj Basin, reveals alternating dull and bright bands of durain, duroclarian, and clarodurain, with lensoidal occurrences of fusain and rounded clastic mineral matter. Geochemical study such as MgO/Al2O3 vs K2O/Al2O3 plot of associated and overlying sandstones and mudrocks of Ramnagar coal seam indicates sedimentation from marine source. Higher concentration of Ba within the sedimentary rocks indicates a transitional environment whereas few readings above standard value of marine sediments indicate estuarine condition. High values for the Tissue Preservation Index (TPI) and Gelification Index (GI), abundance of mineral matter, detrital macerals like liptodetrinite, detrovitrinite, and inertodetrinite, and absence of in situ plant preservation indicate transported, allochthonous origin for the coal. Change from a vitrinite-liptinite dominated coal to inertinite dominated coal indicates transition from wet, swamp phase depositional conditions to semi-arid condition with tidal influence, while mutually exclusive abundances of detrovitrinite and semifusinite signify successive wet and dry phases within the peat forming brackish water (estuarine) setting. [ABSTRACT FROM AUTHOR]

We evaluated fundamental characteristics of bacteria attached onto microplastics (MPs) in aquatic environments. Twenty-four strains were isolated from the estuarine sediments in Tokyo Bay by enrichment culture using polystyrene (PS) pellets and were found to belong to various genera, one of which was identified as an opportunistic pathogen, Brevundimonas diminuta. The ability of most of them to form biofilm on PS was high, and the PS-attached strains were selected based on the phylogenetic diversity to examine characteristics such as antibacterial susceptibility, enzymatic activity, and degradation ability of high-molecular-weight compounds. Antibacterial susceptibility tests using thirteen antibacterial compounds showed that all the selected strains were susceptible to tetracycline, but none of them were susceptible to kanamycin. All the strains were also susceptible to several antibacterial compounds on the basis of different mechanisms of action. Concerns have been raised over the pathogenic and/or antibiotic-resistant bacteria enriched on MPs in studies using high-throughput sequencing analysis; however, this study suggests that relationships between MPs and pathogenic and antibiotic-resistant bacteria should be continuously considered as ecological risk, which may be limited. In addition, PS-attached bacteria showed several activities, as shown by the results of enzymatic activity and hydrolysis of high-molecular-weight compounds, and were diverse biochemically. [ABSTRACT FROM AUTHOR]

Port and industrial activities often cause contamination of estuarine sediments, yet information on sediment metal contamination in Richards Bay Harbour is limited. This study examined the extent and ecological relevance of metal contamination using sediment quality guidelines, pollution indices, macrobenthic community structure and the biotic index M-AMBI. Sediment samples for metal and macrobenthic analyses were collected quarterly at seven sites during 2016−2017 using a Van Veen sediment grab sampler. Sediment samples were acid digested using a microwave digester and analysed for metal concentrations using ICP-OES. Highest metal concentrations (Cd, Cr, Cu, Ni and Zn) were associated with areas most affected by industrial activities, while concentrations of most metals at the remaining sites were low. Pollution indices confirmed significant enrichment of Cd, Cr and Cu in bulk terminal sediment. Sediment quality guidelines revealed potential toxicity associated with Cu, Cr and Ni. The dominant taxa were Halmyrapseudes digitalis (two sites), Mediomastus capensis (three sites) and Sigambra parva (two sites). A significant inverse correlation existed between pollution indices and M-AMBI scores, confirming the adverse effect of metals on habitat quality. The need for a biomonitoring programme incorporating relevant biotic and abiotic indices is emphasised to assess the long-term effects of sediment contamination on aquatic communities in South African estuarine environments. [ABSTRACT FROM AUTHOR]

In this study, the abundance of microplastics (MPs) in the Uppanar and Gadilam estuaries in Cuddalore, on the southeast coast of India, is reported. In the estuarine sediments, MP abundance ranged from 36.3 ± 3.39 to 51.6 ± 2.05 particles/Kg dw. Different types of MP shapes, such as fibers (41.7–47.9%), films (21.2–27.2%), and fragments (18.3–25.5%) were observed in the size range of 100–1000 µm. Diverse colours of MPs were observed, among which red (30.1–34.5%) was predominantly noticed in the estuarine sediments. Six polymers were identified by µ-FTIR, among which LDPE (39%) and PP (35%) were dominant. MPs pollution in these estuaries is composed of domestic, industrial, and fishing wastes. Risk assessments show that the area falls under hazard categories I to III, indicating low to high risk. This study improves knowledge on MPs contamination in Uppanar and Gadilam estuaries and provides impetus for further research to identify the actual sources and impacts of MPs on aquatic systems along the east coast of India. [ABSTRACT FROM AUTHOR]

Sulfate-reducing bacteria (SRB), a diverse taxonomic group of anaerobic microorganisms that oxidize sulfur compounds as terminal electron acceptors, drive the key biogeochemical process of sulfate reduction. However, little is known about the diversity of SRB in tropical coastal habitats. Thus, the goal of this study is to explore and compare the community diversity of the Ashtamudi and Vembanad estuaries and evaluate the sedimentary sulfate reduction rate. The microbiome profiling of SRB was carried out using Next Generation Sequencing (NGS) techniques (Illumina sequencing) based on gene amplification of the dissimilatory sulfate reductase (dsr) enzyme to confirm the diversity and dominant taxa of SRB. The diversity of SRB represented by the Shannon alpha diversity index of the Ashtamudi estuary (6.55) was two-fold that of the Vembanad estuary. In the Vembanad estuary, the marine zone (4.09) harboured more diversity than the freshwater zone (1.825). Higher diversity and lower abundant taxa in the Ashtamudi estuary pointed out the presence of a rare biosphere that has not yet been studied. It was interesting to note that both estuaries have the same SRB phylum diversity. At the level of species, however, there was a noticeable difference. This differential diversity of SRB has an apparent influence on methane production during the breakdown of organic matter in addition to sulfate reduction. Several species of SRB have an important role in the biodegradation of persistent pollutants and the removal of heavy metals.

The development of stable barium (Ba) isotope measurements provides a novel tool to investigate the geochemical cycling of Ba in the ocean and its sediments. In sediment pore waters, gradients of dissolved Ba concentrations result from various diagenetic processes. The distribution and fractionation of Ba isotopes in the pore waters are expected to further improve our understanding of these early diagenetic control mechanisms. Here, we present pore water profiles of dissolved stable Ba isotopic signatures (δ138Bapw) from shallow water sediments covering the entire Pearl River Estuary (PRE) in Southern China. We find pronounced depth‐dependent Ba isotope variations generally showing a shift from heavy to light δ138Bapw signatures from the sediment surface down to 15 cm depth. These gradients are well reproduced by a diffusion‐reaction model, which generates an apparent fractionation factor (138ε) of −0.60 ± 0.10‰ pointing to preferential removal of low‐mass Ba isotopes from the pore water during solution‐solid phase interactions. Consequently, the combined diagenetic processes induce the highest δ138Bapw values of +0.5 to +0.7‰ in the pore waters of the topmost sediment layer. Although the detrital fraction dominates the Ba content in the PRE surface sediments, the determined gradients of pore water Ba isotopes, together with concentration variations of Ba and other redox‐sensitive elements such as manganese (Mn), show that non‐detrital excess Ba carriers including Mn oxides and authigenic barite clearly affect the post‐depositional Ba dynamics. Stable Ba isotopes are thus a potentially powerful tracer of Ba geochemistry during early sediment diagenesis in estuarine depositional environments. Plain Language Summary: Dissolved barium (Ba) concentrations change with depth in sediment pore waters because of various chemical reactions involving the formation and dissolving of manganese (Mn) and barite (BaSO4) minerals. The development of stable Ba isotope measurements provides a novel tool to better understand these reactions in sediment pore waters. Here, we measured the dissolved stable Ba isotopic compositions in sediment pore waters near the bottom of the Pearl River Estuary, China. Pore water Ba isotopic signatures generally decrease from the sediment surface downward. The change of Ba concentrations and isotopic compositions measured in the field is well reproduced by a chemical model including diffusion and mineral formation/dissolving processes. This change in pore water Ba isotopes results from a combination of different processes including Ba sticking to sediment particles formed during the cycling of Mn minerals and the formation of BaSO4 minerals, which preferentially remove lighter Ba isotopes from the pore water into the solids. This is significant because it allows pore water Ba isotopes to be used to trace chemical reactions during Ba cycling in freshwater and marine sediments. Key Points: We present a data set of dissolved stable Ba isotopic compositions in surface sediment pore waters of a large river estuaryPore water Ba isotope values generally decrease with increasing sediment depth, reflecting post‐depositional Ba isotope fractionationA diffusion‐reaction model predicts the distribution and fractionation of stable Ba isotopes in the sediment pore waters well [ABSTRACT FROM AUTHOR]

The upper part of the Krka River estuary and Prokljan Lake are a specific example of a well-stratified estuarine environment in a submerged river canyon. Here, we reconstructed the geomorphological evolution of the area and classified the data gathered in the study, integrating multibeam echosounder data, backscatter echosounder data, side-scan sonar morpho-bathymetric surveys, and acoustic sub-bottom profiling, with the addition of ground-truthing and sediment analyses. This led to the successful classification of the bottom sediments using the object-based image analysis method. Additional inputs to the multibeam echosounder data improved the segmentation of the seafloor classification, geology, and morphology of the surveyed area. This study uncovered and precisely defined distinct geomorphological features, specifically submerged tufa barriers and carbonate mounds active during the Holocene warm periods, analogous to recent tufa barriers that still exist and grow in the upstream part of the Krka River. Fine-grained sediments, classified as estuarine sediments, hold more organic carbon than coarse-grained sediments sampled on barriers. A good correlation of organic carbon with silt sediments allowed the construction of a prediction map for marine sedimentary carbon in this estuarine/lake environment using multibeam echosounder data. Our findings highlight the importance of additional inputs to multibeam echosounder data to achieve the most accurate results. [ABSTRACT FROM AUTHOR]

Vibrio parahaemolyticus(VP) is a common gram-negative bacterium, mainly distributed in marine, estuary and estuarine sediments, which can cause acute gastroenteritis, wound infection and sepsis in humans, and endanger aquatic product aquaculture. Food poisoning incidents caused by this bacterium occur frequently all over the world, and this bacterium is considered to be one of the main pathogens of microbial food poisoning. The virulence factors that affect the pathogenicity of VP include hemolysin, adhesion factor, secretion system, etc., especially in the secretion systems, Type Ⅲ Secretion Systems (T3SS) and Type Ⅵ Secretion Systems (T6SS). It is closely related to the pathogenicity of VP. T3SS is a multi-subunit needle-like structure that injects secreted proteins directly into the recipient cytoplasm through the donor cytoplasm; T6SS is a contact-dependent protein secretion apparatus that injects toxins directly into target cells. By sorting out the research progress of T3SS and T6SS, starting from the structure of these two secretion systems, and analyzing and comparing their functions and regulatory mechanisms, it was pointed out that the two are involved in effector proteins and regulatory mechanisms. The difference in the production of toxins, the relationship between the two and the colonization of VP were found out, in order to further understand the pathogenic mechanism of VP through the connection between the two, and provide scientific guidance for the prevention and treatment of the bacteria. [ABSTRACT FROM AUTHOR]