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

Ocean acidification in nitrogen‐enriched estuaries has raised global concerns. For decades, biotic and abiotic denitrification in estuarine sediments has been regarded as the major ways to remove reactive nitrogen, but they occur at the expense of releasing greenhouse gas nitrous oxide (N2O). However, how these pathways respond to acidification remains poorly understood. Here we performed a N2O isotopocules analysis coupled with respiration inhibition and molecular approaches to investigate the impacts of acidification on bacterial, fungal, and chemo‐denitrification, as well as N2O emission, in estuarine sediments through a series of anoxic incubations. Results showed that acidification stimulated N2O release from sediments, which was mainly mediated by the activity of bacterial denitrifiers, whereas in neutral environments, N2O production was dominated by fungi. We also found that the contribution of chemo‐denitrification to N2O production cannot be ignored, but was not significantly affected by acidification. The mechanistic investigation further demonstrated that acidification changed the keystone taxa of sedimentary denitrifiers from N2O‐reducing to N2O‐producing ones and reduced microbial electron‐transfer efficiency during denitrification. These findings provide novel insights into how acidification stimulates N2O emission and modulates its pathways in estuarine sediments, and how it may contribute to the acceleration of global climate change in the Anthropocene. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to develop a new and rapid sample digestion procedure for metal extraction using ultrasonic energy together with a combination of an ionic liquid and mineral acids as extractants. Methods: A fixed mass of sediment (about 0.50 g) was extracted with a combination of low volumes of NaHCO3, HCl, HNO3, HF and the ionic liquid Bmim[BF4]. Afterwards, the mixture was sonicated for 20 min. After neutralizing the hydrofluoric acid excess, the extracts were filtered and measured by ICP OES where Cd, Cr, Cu, Ni, Pb and Zn were determined. Results: The recoveries in certified reference materials ranged from 92 to 102% for LGC-6137, from 88 to 98% for IAEA SL-1 and from 81 to 98% for MURST-ISS-A1, with a good precision (relative standard deviation (RSD) < 10.0% for all the certified reference materials). The new digestion procedure was successfully applied to the determination of metals in estuarine sediment samples, with a satisfactory precision (RSD < 9.5%). The results showed no significant statistical differences compared to those obtained by the conventional digestion procedure (with an α-error of 0.05). Conclusion: This approach has led to satisfactory results in the determination of the total metal concentrations for most of the elements studied using shorter analysis times than the conventional procedure, and small volumes of hydrofluoric acid. The new pretreatment method made it possible to satisfactorily assess the total metal concentrations in estuarine sediments. [ABSTRACT FROM AUTHOR]

Pharmaceutical drugs have emerged as major micropollutants in aquatic ecosystems. Their presence has been systematically reported in monitoring surveys, and their wide distribution and constant presence in the wild is a direct consequence of their massive use, in both human and veterinary therapeutics. Drugs used to treat parasitic infections in livestock are major contaminants, given the amounts in which they are administered, and reach the aquatic compartment in high amounts, where they may affect non target species. Some of these drugs are prone to find their final deposit in sediments of estuarine areas, exerting their toxic effects preferentially at these locations. Sediment dwelling organisms of coastal areas, such as polychaetas, are especially prone to have their major physiological functions compromised after being exposed to pharmaceutical drugs. Ivermectin is one of the most used antiparasitic drugs, and its effects are not limited to biochemical traits, but also behavioral features may be compromised considering their neurotoxic actions. Despite these putative effects, little is known about their toxicity on polychaetas. The present study aimed to characterize the toxicity of realistic levels of ivermectin on the polychaeta Hediste diversicolor, in biochemical and behavioral terms. The obtained results showed that low levels of ivermectin are capable of causing significant disturbances in mobility and burrowing activity of exposed worms, as well as alterations of metabolic and anti-oxidant defense efficacy of exposed animals, suggesting that its environmental presence may mean a major environmental concern. [ABSTRACT FROM AUTHOR]

Coastal systems such as estuaries are threatened by multiple anthropogenic stressors worldwide. However, how these stressors and estuarine hydrology shape benthic bacterial communities and their functions remains poorly known. Here, we surveyed sediment bacterial communities in poorly flushed embayments and well flushed channels in Sydney Harbour, Australia, using 16S rRNA gene sequencing. Sediment samples were collected monthly during the Austral summer-autumn 2014 at increasing distance from a large storm drain in each channel and embayment. Bacterial communities differed significantly between sites that varied in proximity to storm drains, with a gradient of change apparent for sites within embayments. We explored this pattern for embayment sites with analysis of RNA-Seq gene expression patterns and found higher expression of multiple genes involved in bacterial stress response far from storm drains, suggesting that bacterial communities close to storm drains may be more tolerant of localised anthropogenic stressors. Several bacterial groups also differed close to and far from storm drains, suggesting their potential utility as bioindicators to monitor contaminants in estuarine sediments. Overall, our study provides useful insights into changes in the composition and functioning of benthic bacterial communities as a result of multiple anthropogenic stressors in differing hydrological conditions. [ABSTRACT FROM AUTHOR]

Currently, little is known about the distribution of metal resistance genes (MRGs) in estuarine sediments. In this study, we used the high-throughput quantitative real-time polymerase chain reaction (HT-qPCR) to determine the distribution of MRGs in the sediments of an estuary system and the associated key impact factors. The relative abundance of the detected MRGs showed a decreasing trend from the river inlet toward the sea and a decrease from the middle area of the estuary to the near-shore areas on both sides; these decreases were higher in the summer than in the winter. In the estuary system during the summer, the abundance of Zn- and Cu-MRGs from the river inlet to the sea decreased by 99.5% and 93.6%, whereas those of Hg- and Cd-Zn-Co-MRGs increased by 51.5% and 16.7%, respectively. Moreover, the abundance of Zn- and Cu-MRGs in the winter decreased by 88.6% and 97.7%, respectively, whereas that of Cd-Bi-Zn-Pb-MRGs increased by 729.6%. Furthermore, the abundances of MRGs and mobile genetic elements (MGEs) were significantly positively correlated with the levels of antibiotic residues and heavy metals as well as with the particle size and total organic carbon content of the sediment; however, they were significantly negatively correlated with seawater salinity and the oxidation and reduction potential (Eh) and pH of the sediment. The abundance of MGEs was significantly positively correlated with the abundance of MRGs in the sediment. Our findings suggest that antibiotic residues facilitated the proliferation and propagation of MRGs by promoting MGEs in estuarine sediments. [ABSTRACT FROM AUTHOR]

As the key link connecting the earth's spheres, continental weathering plays an important role in regulating the global biogeochemical cycle and long-term climate change. Siliciclastic sediments derived from large river basins can record continental weathering and erosion signals, and are thus widely used to investigate weathering processes. However, sediment grain size, hydrodynamic sorting and sedimentary recycling complicate the interpretation of sediment weathering proxies. This study presents elemental and lithium isotope compositions of estuarine surface sediments (SS) and suspended particulate matters (SPM) collected from the Changjiang (Yangtze River) Estuary. Based on a simple mass balance model, the proportions of different end-members (i.e., igneous rocks, modern weathering products and inherited weathering products) in sediments were quantitatively calculated and thus the silicate weathering process can be estimated. Overall, the sediments in the Changjiang Estuary are mainly eroded from un-weathered rock fragments (>60%), while modern weathering products account for less than 40%. The fine-grained SPM contain more shale components (52–66%), and the modern weathering products account for 21–40%. Comparatively, the coarse-grained surface sediments contain more un-weathered igneous rock fragments (63–84%) and less modern weathering products (only 4–18%). The comparison of δ7Li values with the weathering proxy (Chemical Index of Alteration, CIA) suggests that sediment weathering intensity declines with increasing proportion of un-weathered igneous rock fragments. Additionally, the occurrence of inherited weathering products (i.e., shale) in modern sediments makes it a challenge to simply use CIA and δ7Li as indicators of weathering intensity. This study confirms that fine-grained particles are more suitable for tracing contemporary weathering process, albeit with the influence of sedimentary recycling. Lithium isotopes combining with the mass balance model can quantitatively constrain the continental weathering processes in large river basins. [ABSTRACT FROM AUTHOR]

Purpose: The quality of organic matter influencing sediment nitrate (NO3−) reduction processes in estuarine zones is not well understood. This study aimed to assess the denitrification (DNF), anaerobic ammonium oxidation (ANA), and dissimilatory reduction of nitrate to ammonium (DNRA) in estuarine zones of South Africa, and to understand the effects of organic matter fractions and degradation states on anaerobic NO3− reduction processes. Materials and methods: We measured the anaerobic NO3− reduction process rates using 15N isotope-tracing techniques in Knysna Estuary, South Africa. Total hydrolyzable amino acids and fractions and geochemical parameters were also measured. The correlation analysis and structural equation model were used to evaluate the key environmental factors driving NO3− reduction processes. Results and discussion: Potential DNF, ANA, and DNRA rates in Knysna Estuary varied from 3.59 to 16.62, 0.28 to 1.16, and 1.52 to 8.38 nmol g−1 h−1, respectively, with a large spatial variation. The variations in NO3− reduction process rates can largely be explained by sediment water content, dissolved organic carbon, and amino acid–based degradation index, while the total organic carbon and inorganic nitrogen contents were not related to the NO3− reduction processes. The DNF process contributed 47.28–79.34% total NO3− reduction, as compared to 17.59–47.58% for DNRA and 2.53–5.76% for ANA. The retention of reactive nitrogen (N) attributed to the DNRA process was approximately 42 t N km−2 year−1. Conclusions: This study reported the first simultaneous investigation of the anaerobic NO3− reduction processes in estuarine areas of South Africa, implying that the qualities of substrate were more important in regulating NO3− reduction processes than substrate quantities and highlighting that DNRA played an important role in reactive N retention. [ABSTRACT FROM AUTHOR]

Anammox bacteria have been detected in various ecosystems, but their occurrence and community composition along the shipping channels have not been reported. In this study, anammox bacteria were recovered by PCR-amplified biomarker hzsB gene from the genomic DNA of the sediment samples. Phylogenetic tree revealed that Candidatus Scalindua and Ca. Brocadia dominated the anammox community of the Hong Kong channels; Ca. Scalindua spp. was present abundantly at the sites farther from the shore, whereas Ca. Jettenia and Ca. Kuenenia were detected as the minor members in the estuarine sediments near the shipping terminals. The highest values of Shannon–Wiener index and Chao1 were identified in the sediments along the Urmston road (UR), suggesting the highest α-diversity and species richness of anammox bacteria. PCoA analysis indicated that anammox bacterial communities along UR and Tai Hong (TH) channel were site-specific because these samples were grouped and clearly separated from the other samples. The maximum diversity of anammox bacteria was detected in UR samples, ranging from 6.28 × 105 to 1.28 × 106 gene copies per gram of dry sediment. A similar pattern of their transcriptional activities was also observed among these channels. Pearson's moment correlation and redundancy analysis indicated that NH4+-N was a strong factor shaping the community structure, which showed significant positive correlation with the anammox bacterial abundance and anammox transcriptional activities (p < 0.01, r > 0.8). Also, NH4+-N, (NO3− + NO2−)-N, and NH4+/NOX were additional key environmental factors that influenced the anammox community diversity and distribution. This study yields a better understanding of the ecological distribution of anammox bacteria and the dominant genera in selective niche. [ABSTRACT FROM AUTHOR]

In natural habitats, the diversity of anaerobic ammonia-oxidizing (anammox) bacteria could be affected by multiple environmental variables. In this study, we investigated the distribution of the anammox bacterial community in surface sediment from the Dongjiang River (riverine sediment, DJ) to the Pearl River Estuary (estuarine sediment, PRE) and then to the South China Sea (coastal sediment, SCS). The results revealed evident differences in the structural diversity of anammox bacteria in three different habitats. Candidatus Brocadia accounted for approximately 90% of the total anammox bacteria in DJ, conversely, Ca. Scalindua dominated in the SCS. Nevertheless, Ca. Scalindua, Ca. Brocadia and Ca. Kuenenia coexisted in the PRE. The qPCR results indicated that anammox bacterial 16S rRNA gene abundance ranged from 2.23 × 105 to 1.19 × 107 copies g−1 of wet weight, but no significant correlation was found between the abundances and environmental variables (p > 0.05). The relative abundances of Ca. Brocadia gradually decreased with increasing salinity, and Ca. Scalindua showed the opposite trend, suggesting that salinity was a crucial factor in sculpturing the community composition of anammox bacteria in natural environments. Ca. Brocadia should be able to live in freshwater ecosystems, but it can also tolerate a certain level of salinity. Ca. Scalindua was halophilic anammox bacterium and exists only in saline environments. Ca. Kuenenia could adapt to a wide range of salinity and preferred to live in high DIN level conditions according to our search. The distribution pattern of anammox bacteria may be the result of microbial migration and long-term adaptation to salinity. [ABSTRACT FROM AUTHOR]

How an estuary responds to sea level rise (SLR) is complex and depends on energy drivers (e.g., tides and river inflows), estuarine geometry (e.g., length and depth), intrinsic fluid properties (e.g., density), and bed/bank roughness. While changes to the tidal range under SLR can impact estuarine sediment transport, water quality, and vegetation communities, studies on the altered tidal range under SLR are often based on case studies with outcomes applicable to a specific site. As such, this study produced a large ensemble of estuarine hydrodynamic models (>1800) to provide a systematic understanding of how tidal range dynamics within different estuary types may change under various SLR and river inflow scenarios. The results indicated that SLR often amplifies the tidal range of different estuary types, except for short estuaries with a low tidal range at the mouth where SLR attenuates the tides. SLR alters the location of the points with minimum tidal range and overall tidal range patterns in an estuary. Variations in tidal range were more evident in converging estuaries, shallower systems, or in estuaries with strong river inflows. These findings provide an indication of how different estuary types may respond to estuaries and may assist estuarine managers and decision makers. [ABSTRACT FROM AUTHOR]

The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large‐scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large‐scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood‐ and ebb‐oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune‐induced directional bed roughness in numerical models of estuarine and tidal environments. [ABSTRACT FROM AUTHOR]

Numerical models of sediment transport in estuarine systems rely on parameter values that are often poorly constrained and can vary on timescales relevant to model processes. The selection of parameter values can affect the accuracy of model predictions, while environmental variation of these parameters can impact the temporal and spatial ranges of sediment fluxes, erosion, and deposition in the real world. We implemented a numerical model of San Pablo Bay, an embayment within San Francisco Bay, California, for November–December 2014, and compared model outputs to observations of water level, velocity, wave parameters, salinity, and suspended sediment concentration (SSC) in the shallow regions. Idealized model runs show that wind timing relative to the phase of the tides is the strongest control on sediment fluxes and bed erosion. We varied sediment erodibility in the outflow of the Petaluma River; while this causes erosion and deposition to vary strongly through the shallows system, total export from the shallows does not change. Model runs with realistic winds show that wind likely resuspends faster settling particles or allows for more particle flocculation; particle settling velocity controls system‐wide sediment accumulation. At the margins of the system, the magnitude of SSC is closely tied to wind direction when winds occur during flood tide, but sediment deposition is less connected: Both bed evolution and SSC need to be considered in the prediction of marsh fate. Spatial patterns of light attenuation due to SSC is strongly tied to assumed settling velocity. Plain Language Summary: Numerical models rely on a number of input values, or parameters, to make predictions about sediment movement and accumulation through estuarine systems, yet often the values are poorly known. Selection of parameter values can impact the effectiveness of numerical models; meanwhile, real‐world variation in the parameters also impacts sediment transport. We implemented a three‐dimensional numerical model in San Pablo Bay, part of San Francisco Bay, California, to predict water level, water velocity, waves, salinity, and suspended sediment concentration to explore these two questions. Our modeling reveals that the timing of winds relative to tidal phase has the strongest impact on spatial patterns of bed erosion and deposition, stronger than wind direction, sediment settling velocity, spring‐neap cycle, or spatial variation in bed erosion parameters. When winds are known, settling velocity, coupled with the erosion rate parameter, can impact the spatial distribution of light attenuation, which is important for protecting estuarine systems from phytoplankton blooms. Under our model, a near‐shore region will attenuate more light than a near‐channel region under low winds only when settling velocity is smaller; that is, model parameter values impact our interpretation of model outputs. Key Points: The timing of wind events relative to the tidal cycle most strongly dictates bed evolution in a shallow estuarySettling velocity controls system‐wide sediment accumulationWindy periods are better represented by faster settling particles [ABSTRACT FROM AUTHOR]

Estuarine tidal dynamics are influenced by changes in morphology and friction. In this work, we quantified changes in tidal damping in the Yangtze Estuary and explored the impact of morphology and friction using a numerical model. In‐depth analyses of tidal data reveal a strong reduction in tidal damping from 1990 to 2010, followed by a slightly enhanced damping from 2010 to 2020 in the South Branch. The reduced tidal damping in the South Branch from 1990 to 2010 is controlled by sediment decline which induces an increase in water depth (erosion), thereby strongly amplifying tides. However, the effective bottom roughness (Manning coefficient) is increased by 60%, which is probably related to the ∼80% decrease in the suspended sediment concentration (SSC). Such an effect may enhance tidal damping, which counteracts the contribution of water depth increase on amplifying tides by ∼75%. From 2010 to 2020, the tides in the South Branch became more damped, suggesting a dominance of the decrease in SSC over the morphological changes. In the mouth zone, tidal dissipation is enhanced from 1997 to 2010, which is mainly caused by an overall increase in effective bottom roughness. Local structures dominate the increase in effective bottom roughness; however, fluid mud formation may contribute to a decrease after 2010. Overall, we argue that estuarine morphological and sedimentary changes in response to riverine sediment decline and local engineering works control the tidal evolution in the Yangtze Estuary, which is important for evaluation of human activities and estuarine management. Plain Language Summary: In many estuaries, human interventions have strongly influenced bed levels and sedimentary features (e.g., sediment concentration, sediment grain size), which led to consequent changes in tidal dynamics. In this study, we investigated decadal changes in the tidal propagation in the Yangtze Estuary from field data and explored the mechanisms responsible for these changes using a numerical model. This study suggests that tidal damping is weakened in the South Branch and enhanced in the mouth zone of the Yangtze Estuary. Local structures enhance tidal damping, whereas a reduction in riverine sediment supply has a more complex response by influencing bed roughness and bed levels. These findings are important for understanding and management of morphodynamic changes in strongly engineered estuaries. Key Points: Tidal damping was stronger in the mouth zone of the Yangtze Estuary since 1997, mainly due to an increase in the effective bottom roughnessThis increase in the effective bottom roughness in the mouth zone is mainly the result of local engineering worksReduced sediment supply amplified tides in the South Branch via its effects on morphology but weakened tides through its effect on friction [ABSTRACT FROM AUTHOR]

Estuarine sediments are increasingly contaminated by heavy metals as a result of urbanization and human activities. Continuous multi-heavy metal accumulation in the ecosystem can provoke new effects on top of the complex environmental interactions already present in estuarine ecosystems. It is important to study their integrated influence on imperative microbial communities to reflect on the environmental and ecological risks they may impose. Inductively coupled plasma optical emission spectroscopy analysis for five metals Cd, Cr, Cu, Pb, and Zn showed that Cr and Cu concentrations in intertidal sediments of the urbanized Yangtze River estuary in China have consistently exceeded respective threshold effect concentration (TEC) levels. The geo-accumulation and potential ecological risk index results of the five metals showed that all sampling sites were weakly to moderately polluted, and at considerable to high ecological risk, respectively. Redundancy and correlation analyses showed that Zn followed by Cr in the ecosystem were explanatory of the shifts in recorded microbial community structures. However, the spatial variation in metal concentrations did not correspond to the selection of metal resistance genes (MRGs). Unlike many other dominant bacterial taxa, most of the sulfate-reducing bacteria (SRB) and associated sulfate respiration as the dominant microbially contributed ecological function were found to negatively correlate with Zn and total heavy metal pollution. Zn concentration was proposed to be a potent indicator for heavy metal pollution-associated microbial community compositional shifts under urbanized estuarine conditions. The associations between heavy metals and estuarine microbial communities in this study demonstrate the influence of heavy metals on microbial community structure and adaptations that is often overshadowed by environmental factors (i.e., salinity and nutrients).

Nutrient loads delivered to estuaries via submarine groundwater discharge (SGD) play an important role in the nitrogen (N) budget and eutrophication status. However, accurate and reliable quantification of the chemical flux across the final decimeters and centimeters at the sediment–estuary interface remains a challenge, because there is significant potential for biogeochemical alteration due to contrasting conditions in the coastal aquifer and surface sediment. Here, a novel, oxygen‐ and light‐regulated ultrasonic seepage meter, and a standard seepage meter, were used to measure SGD and calculate N species fluxes across the sediment–estuary interface. Coupling the measurements to an endmember approach based on subsurface N concentrations and an assumption of conservative transport enabled estimation of the extent of transformation occurring in discharging groundwater within the benthic zone. Biogeochemical transformation within reactive estuarine surface sediment was a dominant driver in modifying the N flux carried upward by SGD, and resulted in a similar percentage of N removal (~ 42–52%) as did transformations occurring deeper within the coastal aquifer salinity mixing zone (~ 42–47%). Seasonal shifts in the relative importance of biogeochemical processes including denitrification, nitrification, dissimilatory nitrate reduction, and assimilation altered the composition of the flux to estuarine surface water, which was dominated by ammonium in June and by nitrate in August, despite the endmember‐based observation that fixed N in discharging groundwater was strongly dominated by nitrate. This may have important ramifications for the ecology and management of estuaries, since past N loading estimates have generally assumed conservative transport from the nearshore aquifer to estuary. [ABSTRACT FROM AUTHOR]

Estuarine sediments make an important contribution to the global carbon cycle, but we do not know how this will change under a future climate, which is expected to have lower pH oceans and frequent high‐temperature days. Six combinations of warming and partial pressures of CO2 (pCO2) were chosen to investigate the combined and individual effects of short‐term pressures on the diel metabolic response of shallow unvegetated sediments ex‐situ. Whereas warming significantly increased respiration, making sediments more heterotrophic, high‐pCO2 increased net primary productivity, resulting in less heterotrophic sediments. As a result, warming decreased the carbon burial potential of estuarine sediments and high‐pCO2 had the opposite effect. High‐pCO2 mitigates the negative effects of warming on benthic metabolism under the combined scenario, with carbon burial similar to that expected under high‐pCO2 conditions alone. Climate scenarios also changed the diurnal pCO2 variation, with ranges increasing by 33% with warming, and almost doubling under high‐pCO2 conditions. An additive response in pCO2 variability was observed under the combined scenario, increasing to 2.3× the current diel‐pCO2 range, highlighting the reduced buffering capacity of the water associated with a high CO2 climate. Future carbon burial and export under increased frequencies of unseasonably warm days projected for mid and end of century (30% and 50% of days‐per‐year, respectively) were estimated with and without ocean acidification. By 2100, warming alone could decrease annual estuarine sediment burial potential by 25%. However, ocean acidification could mitigate the negative effects of more frequent high‐temperature days and increase carbon burial potential over current conditions by ~18%. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) provides carbon substrates and energy sources for sediment microbes driving benthic biogeochemical processes. The interactions between microbes and DOM are dynamic and complex and require the understanding based on fine-scale microbial community and physicochemical profiling. In this study, we characterized the porewater DOM composition in a 300-cm sediment core from the Pearl River estuary, China, and examined the interactions between DOM and archaeal and bacterial communities. DOM composition were highly stratified and associated with changing microbial communities. Compared to bacteria, the amplicon sequence variants of archaea showed significant Pearson correlations (r ≥ 0.65, P < 0.01) with DOM molecules of low H/C ratios, high C number and double bond equivalents, indicating that the distribution of archaea was closely correlated to recalcitrant DOM while bacteria were associated with relatively labile compounds. This was supported by the presence of auxiliary enzyme families essential for lignin degradation and bcrABCD, UbiX genes for anaerobic aromatic reduction in metagenome-assembled genomes of Bathyarchaeia. Our study demonstrates that niche differentiation between benthic bacteria and archaea may have important consequences in carbon metabolism, particularly for the transformation of recalcitrant organic carbon that may be predominant in aged marine sediments. [ABSTRACT FROM AUTHOR]

The Southeast Asia and Melanesia region has extensive nickel (Ni)‐rich lateritic regoliths formed from the tropical weathering of ultramafic rocks. As the global demand for Ni continues to rise, these lateritic regoliths are increasingly being exploited for their economic benefit. Mining of these regoliths contributes to the enrichment of coastal sediments in trace metals, especially Ni. The present study used high‐throughput sequencing (metabarcoding) to determine changes in eukaryote (18s v7 recombinant DNA [rDNA] and diatom‐specific subregion of the 18s v4 rDNA) and prokaryote (16s v4 rDNA) community compositions along a sediment Ni concentration gradient offshore from a large lateritized ultramafic regolith in New Caledonia (Vavouto Bay). Significant changes in the eukaryote, diatom, and prokaryote community compositions were found along the Ni concentration gradient. These changes correlated most with the dilute‐acid extractable concentration of Ni in the sediments, which explained 26, 23, and 19% of the variation for eukaryote, diatom, and prokaryote community compositions, respectively. Univariate analyses showed that there was no consistent change in indices of biodiversity, evenness, or richness. Diatom richness and diversity did, however, decrease as sediment acid extractable‐Ni concentrations increased. Threshold indicator taxa analysis was conducted separately for each of the 3 targeted genes to detect changes in taxa whose occurrences decreased or increased along the acid extractable‐Ni concentration gradient. Based on these data, 46 mg acid extractable‐Ni/kg was determined as a threshold value where sensitive species began to disappear. In the case of the estuarine sediments offshore from lateritized ultramafic regolith in New Caledonia, this is recommended as an interim threshold value until further lines of evidence can contribute to a region‐specific Ni sediment quality guideline value. Environ Toxicol Chem 2021;40:1894–1907. © 2021 SETAC [ABSTRACT FROM AUTHOR]

In order to measure the contamination of dredged and beach sediments and the applicability of sediment quality guidelines in a wet subtropical region of southern Brazil, the areas surrounding both the Paranaguá and Babitonga estuaries were studied, including their harbour zones and adjacent beaches. Investigation of the sampled sediments comprised optical and electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and physicochemical and toxicological analyses. Additionally, data provided by the harbours administrations on dredged volumes, sedimentology, and coastal dynamics were compared. It was determined that the studied sediments, especially the ones from both tidal deltas, have similar characteristics, including physical and chemical parameters. It was also confirmed that tidal deltas are depositional areas with low potential to accumulate pollutants. Therefore, the current disposal of this scarce sandy material during dredging might not be beneficial, considering the significant sand removal amount from the coastal depositional system. [ABSTRACT FROM AUTHOR]

This investigation evaluated the bioaccumulation potential of the tropical estuarine bivalve Anomalocardia flexuosa for trace metals. To this aim, chemical and sedimentological analyses and bioaccumulation tests were performed. The sediments were mainly composed by fine-sands and mud, with variable levels of organic matter and CaCO3. Muddy sediments from a depositional site (P2) presented the highest concentrations of metals, despite SEM/AVS not indicating bioavailability. Bioaccumulation factors showed high ratios for Cd, Ni, and Zn, while associations between the contents of mud, organic matter, CaCO3 and metals in sediments and tissues of A. flexuosa were indicated by a principal component analysis. The SEM/AVS was not effective to predict the bioavailability through dissolved metals. The results showed that contaminants were bioavailable, while the performed bioaccumulation test proved to be a reliable technique for assessing sediment contamination in estuarine regions. Moreover, A. flexuosa was considered an adequate test organism for bioaccumulation studies. [ABSTRACT FROM AUTHOR]

This study aimed to understand the key surfaces and the sedimentary filling pattern of the Coreaú incised valley (CIV) system (NE Brazil) using high-resolution seismic stratigraphy. Six key surfaces (Ss) and five seismic units (SUs) were identified. The difference in the basal reflector (S1) and the paleointerfluve (modern sea floor) was verified to be up to 40 m of incision, of which only 20 m are filled. S1 (sequence boundary—SB) was associated with the acoustic basement (Tibau Formation/Barreiras Group) and presented strong control (antecedent topography) in the incision (re-incisions in the Pleistocene lowstands) and sedimentary stacking pattern. The CIV fill showed lowstand system tract, LST (chaotic facies)–transgressive system tract, TST (horizontal layers to chaotic facies)–highstand system tract, HST (chaotic facies) from the base to top. Thin fluvial deposits above SB correspond to LST. Overlapping this system tract is the first marine flooding surface—transgressive surface. Afterwards, the largest seismic unit (lateral and vertical) with sub-parallel and parallel (onlap) seismic facies, interpreted as related to a low energy system, with shallow gas, and vertical accretion (central basin of estuary) occurred. This environment is related to the drowning of the shelf from the shelf break (a decrease in gradient). A tide ravinement surface truncated the top of SU3 and favored coastal to shallow marine deposition. The transgressive system tract (TST) is thicker in the middle (mainly) and outer sectors in the fluvial troughs (depocenter). The maximum flooding surface appears near the sea floor and favored the development above of carbonate sedimentation in the HST. These seimostratigraphic stacking patterns showed a strong influence of semi-arid climate and antecedent topography/structural inheritance. Thus, it is evident that the filling of the CIV differs from other valleys on semi-arid systems and/or influenced by paleotopography (e.g., South Africa and Texas Shelf), which demonstrates the importance of local settings. The great influence of estuarine to coastal sediments in the valley infilling is also observed in the modern Coreaú coastal plain incised valley. [ABSTRACT FROM AUTHOR]

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Floods are extreme weather events that can rapidly change water quality in receiving estuaries. The delivery of nutrients to the coastal zone via floods may stimulate productivity; however, in urban areas, the degradation of water quality and influx of contaminants can negatively affect inhabiting biota. Determining flood effects on inhabiting biota is important for informing catchment management practices. We investigated the body condition response of a commercially important prawn species, the brown tiger prawn Penaeus esculentus, to a large cyclone-driven flood in an urbanized subtropical coastal bay. Prawns were caught 10 days before the flood, 11 days after the flood, and 53 days after the flood in bare substrate areas of central Moreton Bay in Australia. Stable isotopes (δ15N and δ13C) were determined for prawn muscle tissue, and lipid content and a length-weight (Fulton's K) index were used to assess prawn body condition. There were two distinct isotope signatures of tiger prawns living in either riverine or marine influenced areas, suggesting different residency areas within the bay. A flood signal (lower δ13C values post-flood) was detected in prawns in the southern area closest to the Logan River. Condition indices showed a short-term increase in condition of prawns in these southern sites, with no apparent condition change in prawns at other sites. A concurrent pulse in benthic primary productivity (chlorophyll a biomass) was measured in this southern area. Our results suggest that nutrients from the flood stimulated benthic primary production that was transferred through the food web, with positive impacts on prawn nutrition at southern sites. With an expected increase in unpredictable weather, including floods, under a changing climate, understanding short- and long-term ecosystem responses in modified catchments is important for mitigating sediment erosion and estuarine and coastal infilling effects, while maintaining productivity benefits to fisheries in receiving estuaries. [ABSTRACT FROM AUTHOR]

• Fine particles control the exchangeable silica mobilization in the river. • Current sediment in the estuary contain less reactive silica than historical level. • Increased fine particle fraction affect silica sediment with forms variation in estuary. Changes in riverine sediment transport are an important part of land-sea geochemical cycling and further impact geochemical element fluxes in turbid rivers. However, as a vital nutrient element supporting primary productivity, silica mobilization from drainage in turbid rivers is overlooked. The turbid Yellow River has a strong ability to adsorb reactive silica, thereby exerting a substantial impact on the estuarine deposition of silica. Through an integration of monitoring databases, field sampling and historical hydrological data, we concluded that riverine fine particles control the exchangeable silica in the river and its estuary under soil erosion. Indoor simulation further revealed that the adsorbed content of exchangeable silica (ex-Si) in fine sediment constituted 35 % of total sediment matter. In addition, the transport of phosphorus and ex-Si was jointly regulated by fine sediment in global fluvial sediment transport, thereby exerting additional influence on the trophic structure of estuarine ecosystems. Against the backdrop of sediment budget deficit in the estuary, the heightened content of fine particles is depleting the silica storage from estuarine sediments. [Display omitted] [ABSTRACT FROM AUTHOR]

Spartina alterniflora invasion is considered a critical event affecting sediment phosphorus (P) availability and stock. However, P retention and microbial phosphate solubilization in the sediments invaded with or without S. alterniflora have not been fully investigated. In this study, a sequential fractionation method and high-throughput sequencing were used to analyze P transformation and the underlying microbial mechanisms in the sediments of no plant (NP) zone, transition (T) zone, and plant (P) zone. Results showed that except for organic phosphate (OP), total phosphate (TP), inorganic phosphate (IP), and available phosphate (AP) all followed a significant decrease trend from the NP site to the T site, and to the P site. The vertical decrease of TP, IP, and AP was also observed with an increase in soil depth. Among the six IP fractions, Fe–P, Oc–P, and Ca 10 –P were the predominant forms, while the presence of S. alterniflora resulted in an obvious P depletion except for Ca 8 –P and Al–P. Although S. alterniflora invasion did not significantly alter the alpha diversity of phosphate-solubilizing bacteria (PSB) harboring phoD gene, several PSB belonging to p_Proteobacteria , p_Planctomycetes , and p_Cyanobacteriota showed close correlations with P speciation and IP fractions. Further correlation analysis revealed that the reduced soil pH, soil TN and soil EC, and the increased soil TOC mediated by the invasion of S. alterniflora also significantly correlated to these PSB. Overall, this study elucidates the linkage between PSB and P speciation and provides new insights into understanding P retention and microbial P transformation in the coastal sediment invaded by S. alterniflora. An overview of the linkage between soil phosphorus retention and phosphate-solubilizing bacteria under Spartina alterniflora invasion. [Display omitted] • P retention and transformation in the sediments invaded with or without S. alterniflora were studied. • S. alterniflora invasion decreased P stock in the sediments of estuarine wetland. • S. alterniflora invasion significantly altered P speciation and PSB composition. • p_Proteobacteria , p_Planctomycetes , and p_Cyanobacteriota predominantly contributed to P transformation and retention. [ABSTRACT FROM AUTHOR]

This study investigates the sedimentation behaviors of microplastics (MPs) within a typical meso-scale river estuary, the Yalu River Estuary (YRE) and its riverine reservoir. It analyzes sediment cores in two habitats of Yalu River, revealing changing MPs abundance over time. Results highlight significant differences in riverine and estuarine MPs deposition. Reservoir sample contains more MPs in fragments. Color variations are notable in estuarine samples but minimal in reservoir sample. After 1980, estuarine cores show an increase in coarser MPs, likely due to growth of aquaculture activities. Although sediment accumulates at 1/10 of the rate in reservoir compared to estuary, MPs in reservoir sediments exceeds estuarine level by over threefold. A possible mechanistic framework is then proposed to discuss the varying MPs behaviors in the two habitats, indicating reservoirs accumulate MPs at a higher rate due to the barrier effect of an upper-stream reservoir, stable hydrodynamics, and weak salinity-induced buoyancy. • Historical sedimentary behaviors of microplastics (MPs) were studied from sediment core samples in a meso-scale coastal region. • The results revealed distinct patterns of MPs deposition between riverine reservoir and estuarine environments in the study area. • MPs in the reservoir have the highest accumulation rate, driven by the barrier effect of an upper-stream reservoir, hydrodynamics, and salinity-induced buoyancy. • A mechanistic framework was proposed in this study, demonstrating the different MPs behaviors in the two habitats. [ABSTRACT FROM AUTHOR]

Knowledge about the effects of sediment contamination on estuarine benthos has come mainly from observational studies and spiking experiments. There is a lack of experimental studies with field-contaminated sediments, especially those assessing the combined effects of contamination and other environmental stressors. Here we investigated the biomarker responses of ragworms Hediste diversicolor to contaminated sediments and warming. Ragworms were exposed to sediments with different contamination levels from the Oder estuary (German-Polish border) at 10 and 20 °C for three weeks. The most contaminated sediments induced dicarbonyl stress, but did not result in enhanced detoxification, significant oxidative stress, or impaired energy balance. Warming altered antioxidant defense in ragworms and increased their energy reserves. The effects of contamination and warming were generally mild, and the interactive effects were absent. This study suggests the relatively high resilience of H. diversicolor to multiple stressors. [Display omitted] • Experimental study with contaminated sediments from the Oder estuary. • Combined effects of contamination and warming were assessed. • Mild effects observed on biomarker responses of ragworms. • No interaction found between the two stressors. [ABSTRACT FROM AUTHOR]

Macrofaunal species inhabiting intertidal mudflats and performing intense bioturbation are considered as ecosystem engineers, since they profoundly influence their physical, chemical, and biological environments. Nowadays, to complete our knowledge on the effect of bioturbation processes on the surrounding environment, interdisciplinary approach is essential to unravel their complex intertwined effects on intertidal mudflats. In this study, the effects of bioturbators on sediment properties, biogeochemical variables, and microbial dynamics (microphytobenthos, bacteria and archaea) were investigated. To this end, manipulation experiments were carried out in an intertidal mudflat of the Seine Estuary (France) by revamped the abundance of the two dominant bioturbators, Scrobicularia plana and Hediste diversicolor , in winter and late summer. Results showed that the presence of H. diversicolor in winter had a significant effect, with a significant increase in bed level accretion and microbial nitrate reduction rates. In contrast, the presence of S. plana showed no significant impact on sediment properties, most likely due to a reduced bioturbating activity at low temperature. In summer, both ecosystem engineers strongly influenced their surrounding environment but with opposite effects. The intense reworking of the sediment surface by S. plana limited microbial growth and enhanced erosion processes. Conversely, the presence of H. diversicolor favoured sediment accretion and enhanced microbial growth. Overall, this interdisciplinary study confirms the importance of these two ecosystem engineers in temperate estuarine mudflats by highlighting their simultaneous and intertwined effects on the sedimentary, physicochemical, and biological features. This confirms the importance of actively considering ecosystem engineers when restoring the natural habitats of tidal flats to cope with the different vulnerability risks related to global warming (sandification of estuarine sediments, disappearance of productive mudflats, sea level rise, vulnerability to storms and erosion). • Ecosystem engineers in mudflat simultaneously influence sediment properties, biogeochemical variables, and microbial dynamics • During winter, the bivalve species S. plana has minimal impact on the surrounding environment due to low temperature • During summer, the intense sediment reworking by S. plana limits biogeochemical and microbial processes • H. diversicolor enhances sediment stability, biogeochemistry, and microbial dynamics, via mucous secretion and bioirrigation [ABSTRACT FROM AUTHOR]

We report the first empirical confirmation of the co-occurrence of organophosphate esters (OPEs) additives and microplastics (MPs) in benthic compartments from the Loire estuary. Higher median concentrations of MPs (3387 items/kg dw), ∑ 13 tri-OPEs (12.0 ng/g dw) and ∑ 4 di-OPEs (0.7 ng/g dw) were measured in intertidal sediments with predominance of fine particles, and under higher anthropogenic pressures, with a general lack of seasonality. Contrarily, Scrobicularia plana showed up to 4-fold higher ∑tri-OPE concentrations in summer (reaching 37.0 ng/g dw), and similar spatial distribution. Polyethylene predominated in both compartments. Tris(2-ethylhexyl) phosphate (TEHP), its degradation metabolite (BEHP) and tris-(2-chloro, 1-methylethyl) phosphate (TCIPP) were the most abundant OPEs in sediments, while TCIPP predominated in S. plana. The biota-sediment accumulation factors suggest bioaccumulation potential for chlorinated-OPEs, with higher exposure in summer. No significant correlations were generally found between OPEs and MPs in sediments suggesting a limited role of MPs as in-situ source of OPEs. [Display omitted] • TEHP, BEHP and TCIPP most abundant OPEs in sediments, TCIPP predominated in S. plana. • Different spatial-temporal trends of OPEs in sediments and S. Plana in the estuary. • Limited role of MPs as effective in-situ source of OPEs in estuarine sediments. • No significant role of tri-OPEs as environmental source of di-OPEs in sediments. • BSAFs suggest bioaccumulation of TDCIPP, and higher exposure in summer. [ABSTRACT FROM AUTHOR]

The contents of metals, total carbon, total nitrogen (TN), total organic carbon (TOC), and stable isotope composition (δ13C org and δ15N) of sediment organic matter (SOM) were investigated to explore the sources and spatial distribution of metals and SOM in the surface sediments (Kaohsiung Port, Taiwan). Results showed that TOC and metals in estuarine sediments are high, gradually decreasing toward the port entrances. The δ13C org , δ15N, and TOC/TN ratios indicate that SOM comes mainly from terrestrial sources. This study proposes a befitting model between metal pollution and toxicity risk index and SOM sources in port sediments by combining stable isotope composition, correlation matrix, and multiple linear regression analysis. The model indicates that the degree of metal pollution and toxicity risk in sediments are mainly affected by TOC terr content and SOM source. The results help to understand the influence of organic matter sources in port sediments on metal concentration distribution. [Display omitted] • The sediment organic matter (SOM) in port sediments mainly originated from land. • The sources and distribution patterns of SOM and metals are similar. • Estuarine sediments are enriched with metals and pose high toxicity risks. • The TOC terr , δ13C org and TOC/TN are the main factors affecting metal distribution. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is a conspicuous and persistent global pollutant. Ionic Hg can be methylated into noxious methylmercury (CH 3 Hg), which biomagnifies in marine tropic webs and poses a health risk to humans and organisms. Sediment Hg methylation rates are variable, and the output flux of created CH 3 Hg are dependent on sediment characteristics and environmental factors. Thus, uncertainties remain about the formation and flux of CH 3 Hg from sediment, and how this could contribute to the bioaccumulative burden for coastal organisms in shallow ecosystems. Cores were collected from 3 estuarine locations along the Eastern USA to examine how sediments characteristics influence the introduction of Hg and CH 3 Hg into the base of the food chain. Stable isotopes of inorganic 200Hg and CH 3 199Hg were injected into sediments of individual cores, with cultured diatoms constrained to overlying waters. Five different treatments were done on duplicate cores, spiked with: (1) no Hg isotopes (control); (2) inorganic 200Hg; (3) CH 3 199Hg; (4) both 200Hg and CH 3 199Hg isotopes, (5) both 200Hg and CH 3 199Hg into overlying waters (not sediment). Experimental cores were incubated for 3 days under temperature and light controlled conditions. These results demonstrate that upper sediments characteristics lead to high variability in Hg cycling. Notably, sediments which contained abundant and peaty organic material (∼28 %LOI), had the highest pore water DOC (3206 μM) and displayed bands of sulfur reducing bacteria yielded the greatest methylation rate (1.97 % day−1) and subsequent diatom uptake of CH 3 200Hg (cell quota 0.18 amol/cell) in the overlying water. [Display omitted] • Mercury methylation in sediment rapidly transported into water and diatoms. • CH 3 Hg flux was highest for sediments with higher sulfide and organic content. • Mineral and compressed sediment released minor Hg and CH 3 Hg. • Higher sediment Hg species flux does not correlate with high sediment content. • Stable isotope incubations provide substantial insight to environmental Hg cycling. [ABSTRACT FROM AUTHOR]

Identification of key As mobilization processes in estuarine sediments is challenging due to the transitional hydrodynamic condition and the technical restriction of obtaining fine-scale results. Herein, high-resolution (μm to mm) and in situ profiling of As with associated elements (Fe, Mn, and S) by the diffusive gradients in thin-film (DGT) technique were applied and coupled with pore water and solid phase analysis as well as microbial high-throughput sequencing, to ascertain the driving mechanisms of As mobilization in the sediments of Pearl River Estuary (PRE). Significant diffusion fluxes of As from sediment to water were observed, particularly in the upper estuary. With the seaward increase of salinity, the driving mechanism of As mobilization gradually shifted from microbial-induced dissimilatory Fe reduction to saltwater-induced ion exchange. Correspondingly, the dominant Fe-reducing bacteria (FeRB) in sediments changed from the genera Clostridium_sensu_stricto_1 and Bacillus to Ferrimonas and Deferribacter. The presence of dissolved sulfide in deeper sediments contributes to As removal through the formation of As-S precipitates as supported by theoretical calculations. Fine-scale findings revealed seaward changes of As mobilization mechanism in the sediments of a human-impacted estuary and may benefit the understanding of As biogeochemical behavior in estuaries worldwide. [Display omitted] • Significant efflux of As from upper estuarine sediments to water was observed. • Dissimilatory Fe reduction drives As mobilization in upper estuarine sediments. • Seawater-induced ion exchange drives As mobilization in lower estuarine sediments. • Functional Fe-reducing bacteria in sediments varied along the salinity gradient. • Precipitation as sulfides was a major burial process of As in estuarine sediments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optical spectroscopy, FT-ICR MS and microbial sequencing were employed to analyze DOM. • Sediment DOM, DON and DOS showed reduced molecular diversity but enhanced reactivity seaward. • Contribution of terrestrial OM to sediment DOM transformation decreased seaward. • Microbial consumption of labile DON and DOS components alters their properties. • Anthropogenic inputs can enhance DOM bio-reactivity by increasing DON and DOS fractions. Dissolved organic matter (DOM) constitutes the most active fraction in global carbon pools, with estuarine sediments serving as significant repositories, where DOM is susceptible to dynamic transformations. Anthropogenic nitrogen (N) and sulfur (S) inputs further complicate DOM by creating N-bearing DOM (DON) and S-bearing DOM (DOS). This study delves into the spatial gradients and transformation mechanisms of DOM, DON, and DOS in Pearl River Estuary (PRE) sediments, China, using combined techniques of UV–visible spectroscopy, Excitation–emission matrix (EEM) fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and microbial high-throughput sequencing. Results uncovered a distinct spatial gradient in DOM concentration, aromaticity (SUV A254), hydrophobicity (SUVA 260), the content of substituent groups including carboxyl, carbonyl, hydroxyl and ester groups (A 253 /A 203) of chromophoric DOM (CDOM), and the abundances of tyrosine/tryptophan-like protein and humic-like substances in fluorophoric DOM (FDOM). These all decreased from upper to lower PRE, accompanied by a decrease in O 3 S and O 5 S components, indicating seaward reduction in the contribution of terrestrial OM, especially anthropogenic inputs. Additionally, sediments exhibited a reduction in molecular diversity (number of formulas) of DOM, DON, and DOS from upper to lower PRE, with molecules tending towards a lower nominal oxidation state of carbon (NOSC) and higher bio-reactivity (MLB L), molecular weight (m / z) and saturation (H/C). While molecular composition of DOM remained similar in PRE sediments, the relative abundance of lignin-like substances decreased, with a concurrent increase in protein-like and lipid-like substances in DON and DOS from upper to lower PRE. Mechanistic analysis identified the joint influence of terrestrial OM, anthropogenic N/S inputs, and microbial processes in shaping the spatial gradients of DOM, DON, and DOS in PRE estuarine sediments. This study contributes valuable insights into the intricate spatial gradients and transformations of DOM, DON, and DOS within human-impacted estuarine sediments. [ABSTRACT FROM AUTHOR]

The present investigation is the first of its kind which aims to study the characteristics of microbial consortium inhabiting one of the natural high background radiation areas of the world, Chavara Coast in Kerala, India. The composition of the microbial community and their structural changes were evaluated under the natural circumstances with exorbitant presence of radionuclides in the sediments and after the radionuclide's recession due to mining effects. For this purpose, the concentration of radionuclides, heavy metals, net radioactivity estimation via gross alpha and beta emitters and other physiochemical characteristics were assessed in the sediments throughout the estuarine stretch. According to the results, the radionuclides had a significant effect in shaping the community structure and composition, as confirmed by the bacterial heterogeneity achieved between the samples. The results indicate that high radioactivity in the background environment reduced the abundance and growth of normal microbial fauna and favoured only the growth of certain extremophiles belonging to families of Piscirickettsiacea, Rhodobacteriacea and Thermodesulfovibrionaceae, which were able to tolerate and adapt towards the ionizing radiation present in the environment. In contrast, communities from Comamondacea, Sphingomonadacea, Moraxellacea and Erythrobacteracea were present in the sediments collected from industrial outlet, reinforcing the potent role of radionuclides in governing the community pattern of microbes present in the natural environment. The study confirms the presence of these novel and unidentified bacterial communities and further opens the possibility of utilizing their usefulness in future prospects. [Display omitted] • Microbial community analyses reveal heterogeneity between bacterial samples before and after mining. • Communities of proteobacteria, actinobacteria and Bacteroidetes were abundant and resistant to radiation. • Radionuclides concentration exerted a significant role in influencing the microbial structure and pattern. • These novel communities can be used for bioremediation & for their extremolytes. [ABSTRACT FROM AUTHOR]

Tropical estuarine areas present microbial and geochemical conditions that have been pointed out as important conditions to trigger the mechanisms of mercury methylation improving its bioavailability to higher trophic levels. Despite the potential risk of these mechanisms to human health, few studies have reported in situ analysis in costal subtropical ecosystems, relating bacterial activity and mercury concentrations. In the present work we analyse the relationship between some relevant environmental parameters that may stimulate the bacterial activity and control mercury concentrations in the sediments of a tropical mangrove tidal flat. Forty-four samples were collected and analysed for total organic carbon, bacterial organic carbon, lipids, proteins, esterase activity and mercury concentrations and SEM/AVS. The redox potential, temperature and pH were also measured in situ. The results showed intense bacterial activity and increasing mercury levels when compared with local backgrounds. The use of SEM/AVS indicator recommended by USEPA as a criterium to check the sediment quality, did not show enough accuracy to predict the ecological bioavailability risk in sediments with high organic matter content. This methodology requires new approach to help decision making.

Summary: Steroidal oestrogens are often accumulated in urban estuarine sediments worldwide at microgram per gram levels. These aromatic steroids have been classified as endocrine disruptors and group 1 carcinogens. Microbial degradation is a naturally occurring mechanism that mineralizes oestrogens in the biosphere; however, the corresponding genes in oestrogen‐degrading actinobacteria remain unidentified. In this study, we identified a gene cluster encoding several putative oestrogen‐degrading genes (aed; actinobacterial oestrogen degradation) in actinobacterium Rhodococcus sp. strain B50. Among them, the aedA and aedB genes involved in oestrogenic A‐ring cleavage were identified through gene‐disruption experiments. We demonstrated that actinobacterial oestrone 4‐hydroxylase (AedA) is a cytochrome P450‐type monooxygenase. We also detected the accumulation of two extracellular oestrogenic metabolites, including pyridinestrone acid (PEA) and 3aα‐H‐4α(3'‐propanoate)‐7aβ‐methylhexahydro‐1,5‐indanedione (HIP), in the oestrone‐fed strain B50 cultures. Since actinobacterial aedB and proteobacterial edcB shared < 40% sequence identity, 4‐hydroxyestrone 4,5‐dioxygenase genes (namely aedB and edcB) could serve as a specific biomarker to differentiate the contribution of actinobacteria and proteobacteria in environmental oestrogen degradation. Therefore, 4‐hydroxyestrone 4,5‐dioxygenase genes and the extracellular metabolites PEA and HIP were used as biomarkers to investigate oestrogen biodegradation in an urban estuarine sediment. Interestingly, our data suggested that actinobacteria are active oestrogen degraders in the urban estuarine sediment. [ABSTRACT FROM AUTHOR]

Environmental degradation in estuaries may lead to a serious threat to marine life and may trigger human health risk with the help of the food web. This study was conducted to evaluate the concentration, distribution, sources, pollution status, and potential risk of contamination of five trace metals (Cd, Cu, Pb, Zn, and Fe) in estuarine surface sediment of ten different estuaries with their physicochemical parameters in the Kelantan State of Malaysia. The heavy metal concentrations in the estuarine surface sediment differ from one estuary to another following the order of: Fe (39.08%) > Zn (37.02 μg/g) > Pb (20.78 μg/g) > Cu (6.68 μg/g) > Cd (3.69 μg/g). The cluster analysis and source identification study indicated that almost all the estuaries are more or less polluted by anthropogenic activities. The Geo-accumulation index (Igeo) showed that all estuaries of the Kelantan Coastline were moderately polluted by Fe and strongly polluted by Cd which was also confirmed by enrichment factor (EF) and integrated potential ecological risk value (RI) assessment. The higher Pollution load index (PLI) values (PLI>1) revealed that all estuaries were polluted by studied trace metal contamination at a different level of magnitude. [ABSTRACT FROM AUTHOR]

Manakudy estuary is located in the southernmost tip of the Indian sub‐continent, which is essential to study the sediment geochemistry as it receives limited input of sediments during the rainy season from its catchment zones. The elemental geochemical variation of sediments is to understand the mechanism influencing the estuarine environment, and it becomes baseline data to assess the environmental impact in the near future. Twenty surface sediments samples were collected at different seasons, and the grain size results showed that the estuary sediments were carpeted by the mixture of sand, silt, clay, organic matter (OM), and CaCO3. The seasonal variation of elements is slightly more in the pre‐monsoon than in the post‐monsoon season. Fe showed maximum variation, while Cd showed minimum variation in total heavy metal concentrations of detrital sediments. The order of abundance of metals based on their mean values is as Fe > Mn > Cr > Zn > Cu > Pb > Ni > Co > Cd in pre‐monsoon and Fe > Mn > Zn > Cr > Ni > Co > Cu > Pb > Cd > in post‐monsoon, respectively. Different elemental ratios and enrichment factors were used to assess the abundance of major and trace elements in both seasons. The ecological risk assessment clearly shows the higher concentration of a few metals in the estuarine sediments during post‐ monsoon. Correlation and factor analysis show that from geogenic along with the anthropogenic input of industrial effluents, agriculture, urban, municipal wastes and slum sewage are the major sources for derived metals in the estuarine sediments. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) in estuaries is becoming a global concern, and may affect microbial characteristics in estuarine sediments. Bacterial communities in response to acidification in this habitat have been well discussed; however, knowledge about how fungal communities respond to OA remains poorly understood. Here, we explored the effects of acidification on bacterial and fungal activities, structures and functions in estuarine sediments during a 50-day incubation experiment. Under acidified conditions, activities of three extracellular enzymes related to nutrient cycling were inhibited and basal respiration rates were decreased. Acidification significantly altered bacterial communities and their interactions, while weak alkalization had a minor impact on fungal communities. We distinguished pH-sensitive/tolerant bacteria and fungi in estuarine sediments, and found that only pH-sensitive/tolerant bacteria had strong correlations with sediment basal respiration activity. FUNGuild analysis indicated that animal pathogen abundances in sediment were greatly increased by acidification, while plant pathogens were unaffected. High-throughput quantitative PCR-based SmartChip analysis suggested that the nutrient cycling-related multifunctionality of sediments was reduced under acidified conditions. Most functional genes associated with nutrient cycling were identified in bacterial communities and their relative abundances were decreased by acidification. These new findings highlight that acidification in estuarine regions affects bacterial and fungal communities differently, increases potential pathogens and disrupts bacteria-mediated nutrient cycling. [ABSTRACT FROM AUTHOR]

An estuarine turbidity maximum (ETM) is a region of elevated suspended sediment concentration (SSC) resulting from residual transport mechanisms driven by river flow, tides, and salinity‐induced density gradients (SalDG). However, in energetic and highly turbid environments such as the Yangtze Estuary, SedDG may also substantially contribute to the formation and maintenance of the ETM. Since this mechanism is relatively poorly understood, we develop a three‐dimensional model to explore the effect of SedDG on tidal dynamics and sediment transport. By running sensitivity simulations considering SalDG and/or SedDG, we conclude that the longitudinal SedDG leads to degeneration and landward movement of the ETM. Moreover, two effects of the vertical SedDG are identified to be responsible for sediment trapping: One by enhancing the vertical sediment concentration gradients, and another by additionally affecting hydrodynamics including the water levels, velocities and salinities. The longitudinal and vertical SedDG leads to seasonal and spring‐neap variations of upstream migration of the salt wedge: Vertical SedDG is more pronounced at neap tides in the wet season due to stronger stratification effects, whereas longitudinal SedDG is more pronounced at intermediate tides in the dry season due to weaker mixing and limited deposition. These findings imply that the SedDG contributes substantially to channel siltation and salt intrusion in highly turbid systems, and need to be accounted for when numerically modeling such phenomena. Plain Language Summary: In highly turbid estuaries, estuarine turbidity maximum (ETM) with high suspended sediment concentrations (SSC) influences the water quality and ecological system. These high SSCs interact with salinity, and the salinity and sediment transport influence siltation of navigation channels, freshwater resources and so on. In this study, we employ a three‐dimensional numerical model to investigate the effect of sediment‐induced density gradients (SedDG) on sediment transport and salt intrusion. The effects of the longitudinal and vertical SedDG weaken and promote the ETM (respectively), and influence salt intrusion. These findings are important for the management of sediment and freshwater resources in turbid estuaries. Key Points: SSC‐induced longitudinal density gradients cause longitudinal dispersion of the salinity‐induced turbidity maximumSSC‐induced vertical density gradients strengthen the salinity‐induced horizontal density currents and associated sediment trappingLongitudinal and vertical SSC density gradients are significant under weaker and stronger salinity stratification conditions, respectively [ABSTRACT FROM AUTHOR]

Climate and human pressures can influence the evolution of estuarine sediment dynamics concurrently, but the understanding and quantification of their cause–effect relationships are still challenging due to the occurrence of complex hydro‐morpho‐sedimentary feedbacks. The Garonne Tidal River (GTR, upper Gironde Estuary, France) is a clear example of a system stressed by both anthropogenic and climate change, as it has been subject to decreasing river discharges, natural morphological changes, and gravel extraction. To understand the relative effect of each hydrological and geomorphological pressure on the turbidity maximum zone (TMZ), the sediment dynamics in the GTR over the last six decades was evaluated using the width‐averaged idealized iFlow model. Model results show a gradual increase in tidal amplitude and currents over the decades that has led to the upstream shift of the landward sediment‐transport capacity components (external M4 tide, spatial settling lag, and tidal return flow). The upstream displacement of the TMZ between the 1950s and the 2010s was estimated to be at least 19 km, of which about three fourth was induced by geomorphological changes and one fourth by hydrological changes. Concerning the geomorphological changes, the natural evolution of the lower Gironde morphology was the main pressure inducing the displacement of the TMZ in the GTR. Anthropogenic and natural changes in morphology and bed roughness in the GTR itself also contributed to this evolution. The natural geomorphological changes were, in turn, probably promoted by the evolution of sediment dynamics, so this study reveals the closed circle that governs the intensification of the TMZ. Plain Language Summary: According to local managers, the Garonne Tidal River has experienced an increase of sediment concentration between the 1960s and the 2010s. During this period, the tidal river was subject to decreasing river discharges, morphological changes controlled by natural boundary conditions, and gravel extraction. To test this hypothesis and to better understand the influence of climate and human pressures on the estuarine sediment dynamics, this study evaluates the evolution of sediment‐transport patterns in the Garonne Tidal River over the last six decades. In the absence of historical observations of sediment concentration, we applied the idealized model iFlow to different scenarios of river discharge and morphology. Model results show a gradual increase in the landward transport of sediment over the decades. The natural evolution of the morphology was the main pressure inducing the upstream shift of the maximum concentrations. The model uses simplified descriptions of physical mechanisms, allowing for a systematic analysis of the underlying physical processes that contributed to the multidecadal evolution of sediment transport. Key Points: Morphological and hydrological changes contributed to the upstream shift of the turbidity maximum zone over the last six decadesThis shift is explained by an enhanced sediment import driven by the external M4 tide, tidal return flow, and spatial settling lag effectsClimate‐induced morphological changes were the main pressure inducing the displacement and intensification of the turbidity maximum zone [ABSTRACT FROM AUTHOR]

The formation of wetland channel networks on coastal river floodplains is affected by spatial transitions in tidal‐fluvial processes. This study evaluated sedimentation patterns in tidal marshes on the 147‐km tidal Columbia River and its 87‐km estuary and characterized the cross‐sectional geometry and planform morphometry of tidal wetlands along the estuarine to riverine gradient. Tidal marshes were predominantly depositional (median 0.7 cm yr−1, primarily silt), consistent with late‐Holocene rates. Marsh sediment accretion rate increased with annual maximum 7‐day average daily maximum water depth. Elevation was negatively correlated with accretion rate in the tidal river and positively correlated with total organic carbon (TOC%) in the tidal river and estuary. TOC% was greater in the estuary and, like percent fines, greater farther from the main‐channel Columbia River. For four single‐channel and six channel‐network planforms of tidal marsh, shrub‐dominated, and forested wetlands: (1) Spatial patterns of cross‐sectional morphology conformed to typical coastal wetland morphology in estuarine reaches up to the tidal river. (2) Reach‐based and common slope linear models for channel perimeter on wetland area were predictive in the estuary (R2 > 0.81) and differed between island (n = 144) and mainland (n = 164) wetlands. No planform linear models were predictive for the entire study area or the tidal river. No models for channel outlets were acceptable. (3) Channel perimeter, surface area, and outlets were all highly variable within and among estuarine–riverine reaches. Analyses of sediment, cross‐section, and planform support the use of a "natural network paradigm" for wetland‐restoration design on tidal river floodplains. Key Points: A new metric, the annual maximum of the 7‐day average daily maximum water depth, explains much variability of tidal river floodplain sedimentation rateIn the estuary, up to the tidal river, cross‐sectional morphology and planform channel network perimeter tend to conform to coastal processesOrganic carbon is positively correlated with elevation and with distance from the main river channel. It is highest in the estuary [ABSTRACT FROM AUTHOR]

Anammox is a cost‐effective and sustainable process for nitrogen removal; however, the production of a physiologically stable inoculum is a critical point in the start‐up process. In this work, estuarine sediments were used as incubation seeds to obtain cultures with stable anammox activity. Assays were performed in batch cultures fed with stoichiometric amounts of ammonium and nitrite, analyzing physiological response variables and the microbial community. Estuarine sediments showed a stable anammox process after 90 days, consuming ammonium and nitrite simultaneously with concomitant generation of N2 and nitrate in stoichiometric amounts. In kinetic assays, substrates were fully consumed after 210 hr, exhibiting N2 and nitrate yields of 0.85 and 0.10, respectively. The microbial community analysis using PCR‐DGGE indicated the presence of uncultured anammox bacteria and members of the genus Candidatus Jettenia. The results evidenced the achievement of anammox cultures, although their start‐up and kinetic characteristics were less favorable than those recorded in man‐made systems. Practitioner points: Estuarine sediments were used as incubation seeds to obtain cultures with stable anammox activity.The sediments were fed with stoichiometric amounts of ammonium and nitrite, analyzing the physiological response variables and the microbial community.Sediments showed a stable anammox process after 90 days, converting the substrates into N2 and nitrate according to stoichiometry.Anammox cultures were achieved although their start‐up and kinetic characteristics were less favorable than those recorded in man‐made systems.Microbial community analysis using PCR‐DGGE indicated the presence of uncultured anaerobic ammonia‐oxidizing bacterium and members of genus Candidatus Jettenia. [ABSTRACT FROM AUTHOR]

Summary: ANME‐1 archaea subsist on the very low energy of anaerobic oxidation of methane (AOM). Most marine sediments shift from net AOM in the sulfate methane transition zone (SMTZ) to methanogenesis in the methane zone (MZ) below it. In White Oak River estuarine sediments, ANME‐1 comprised 99.5% of 16S rRNA genes from amplicons and 100% of 16S rRNA genes from metagenomes of the Methanomicrobia in the SMTZ and 99.9% and 98.3%, respectively, in the MZ. Each of the 16 ANME‐1 OTUs (97% similarity) had peaks in the SMTZ that coincided with peaks of putative sulfate‐reducing bacteria Desulfatiglans sp. and SEEP‐SRB1. In the MZ, ANME‐1, but none of the putative sulfate‐reducing bacteria or cultured methanogens, increased with depth. Our meta‐analysis of public data showed only ANME‐1 expressed methanogenic genes during both net AOM and net methanogenesis in an enrichment culture. We conclude that ANME‐1 perform AOM in the SMTZ and methanogenesis in the MZ of White Oak River sediments. This metabolic flexibility may expand habitable zones in extraterrestrial environments, since it enables greater energy yields in a fluctuating energetic landscape. [ABSTRACT FROM AUTHOR]

Surface sediments from estuarine and coast of CanGio wetland (CGW) of Hochiminh City, Vietnam, were investigated to identify the spatial and temporal variations of polycyclic aromatic hydrocarbons (PAHs). The total PAHs showed wide variation but similar to patterns observed (F = 0.901, p = 0.46) in LongTau (31 ± 77 ng/g dry weight, n = 13), SoaiRap (53 ± 81, n = 4), ThiVai (60 ± 62, n = 10) estuaries, and coastal areas (112 ± 211, n = 9). A decreasing trend in the wet season (F = 8.8, p = 0.01) reflected that inland sources such as wastewater discharged and atmospherically transported contaminants contributed to PAHs in sediments. The risk posed by the PAHs in the coastal and estuarine areas of CGW is still negligible. The present study provides baseline data, which can be used for regular monitoring and future strategy of environmental protection for the study area. [ABSTRACT FROM AUTHOR]

Relative to their surface area, estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of temperature change (from Δ- 3 to Δ+ 5 ∘ C compared to ambient mean temperatures) and ocean acidification (OA, ∼ 2 × current CO 2 partial pressure, p CO 2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake; sediments became net sinks of DOC (3.5 to 8.8 mmol C m -2 d -1) at warmer temperatures (Δ+ 3 and Δ+ 5 ∘ C, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (up to 4 × greater than under current p CO 2 conditions). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, we find that the future climate of warming (Δ+ 3 ∘ C) and OA may decrease estuarine export of DOC by ∼ 80 % (∼ 150 Tg C yr -1) and have a disproportionately large impact on the global DOC budget. [ABSTRACT FROM AUTHOR]

Intertidal systems are complex and dynamic environments with many interacting factors influencing biochemical characteristics and microbial communities. One key factor are the actions of resident fauna, many of which are regarded as ecosystem engineers because of their bioturbation, bioirrigation and sediment stabilising activities. The purpose of this investigation was to elucidate the evolutionary implications of the ecosystem engineering process by identifying, if any, aspects that act as selection pressures upon microbial communities. A mesocosm study was performed using the well characterised intertidal ecosystem engineers Corophium volutator, Hediste diversicolor, and microphytobenthos, in addition to manual turbation of sediments to compare effects of bioturbation, bioirrigation and stabilisation. A range of sediment functions and biogeochemical gradients were measured in conjunction with 16S rRNA sequencing and diatom taxonomy, with downstream bacterial metagenome function prediction, to identify selection pressures that incited change to microbial community composition and function. Bacterial communities were predominantly Proteobacteria, with the relative abundance of Bacteroidetes, Alphaproteobacteria and Verrucomicrobia being partially displaced by Deltaproteobacteria, Acidobacteria and Chloroflexi as dissolved oxygen concentration and redox potential decreased. Bacterial community composition was driven strongly by biogeochemistry; surface communities were affected by a combination of sediment functions and overlying water turbidity, and subsurface communities by biogeochemical gradients driven by sediment reworking. Diatom communities were dominated by Nitzschia laevis and Achnanthes sp., and assemblage composition was influenced by overlying water turbidity (manual or biogenic) rather than direct infaunal influences such as grazing. [ABSTRACT FROM AUTHOR]