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The radioactive concentrations of 40K, 232Th and 226Ra in 11 intertidal sediment cores in the Red River Delta were determined, and radiological hazard indices for environmental risk were assessed. The values of 40K, 232Th and 226Ra activity were 656 Bq/kg, 49.8 Bq/kg and 37.0 Bq/kg, respectively. The values of radiological hazard indices such as radium equivalent activity (Raeq), absorbed dose rate (ADR), equivalent annual effective dose (AEDE), representative gamma index (Iγr), index active use, external hazard index (Hex), annual gonadal equivalent dose (AGDE) were 158.7 Bq/kg, 74.5 nGy/h, 0.09 mSv/year, 1.18, 1.0, 0.40, and 496.4 µSv/year, respectively. The results obtained of this study showed that eleven sediment cores can be divided into two groups, of which the radioactive concentrations of 40K, 232Th and 226Ra in group 2 were higher than in group 1, and the concentration of radionuclides in sediments was higher than the global average, except for 226Ra in group 1. The ADR, AEDE, Iγr and AGDE indices were above UNSCEAR's recommended levels for both groups. The results of this study show that sediments have the potential to impact organisms in the intertidal zone and are safe for use as construction materials. [ABSTRACT FROM AUTHOR]

The intertidal zone is an important pathway for the transport of dissolved carbon across the land–ocean interface. Quantifying carbon transformation and export from the intertidal zone remains large uncertainties due to the natural heterogeneity and various driving mechanisms. Here, we used the 224Ra/228Th disequilibrium method to quantify porewater exchange and dissolved carbon export from intertidal sandy and muddy sediments, two main intertidal wetland types in the coast. Porewater exchange fluxes from sandy sediments ranged from 1.4 ± 0.1 to 1084 ± 53 L m−2 h−1, which gradually increased in the landward direction. Porewater exchange fluxes from mangrove muddy sediments ranged from 0 to 4.4 ± 0.7 L m−2 h−1. Advective porewater exchange was recognized as the dominant solute transport process in sandy sediments, whereas bioturbation may be the key process in mangrove muddy sediments. Furthermore, marine dissolved organic carbon (DOC) was removed in sandy sediments, indicating that the sandy sediment acted as a sink of DOC, likely via aerobic remineralization. DOC consumption fluxes ranged from 3.7 ± 0.2 to 206 ± 9 mmol C m−2 d−1. The total consumption flux of DOC in the entire sandy beach was one order of magnitude higher than the globally maximum DOC removal flux in the upper ocean. Porewater-derived dissolved inorganic carbon (DIC) export fluxes from sandy sediments ranged from 5.6 ± 0.3 to 883 ± 43 mmol C m−2 d−1. Nearly 50% of DIC export originated from the consumption of DOC. The rate constants for DOC transformation ranged from 0.009 to 0.155 h−1. In comparison, porewater-derived DOC and DIC export fluxes from muddy sediments were 25 ± 4 and 206 ± 30 mmol C m−2 d−1, respectively. Porewater-derived DIC export from sandy sediments was comparable or even higher than those from muddy sediments. These results showed that sandy sediments acted as a fast lane for marine DOC remineralization. Overall, both organic-poor sandy and organic-rich mangrove muddy sediments play important roles in the delivery of dissolved carbon to the ocean. [ABSTRACT FROM AUTHOR]

Bacteria from coastal habitats exposed to challenging environmental conditions constitute a promising source of enzymes with novel catalytic properties for the depolymerization of complex carbohydrates of terrestrial and marine origins. In this work, we investigated the sequence and structural diversity of putative enzymes related to the glycoside hydrolase family 51 (GH51) identified in a metagenomic dataset of intertidal sediments from a subantarctic environment. The majority of the characterized members of the GH51 family are α-L-arabinofuranosidases (EC 3.2.1.55), enzymes with important industrial applications that catalyze the hydrolysis of side chains from arabinose-substituted polysaccharides. The 28 sequences identified in the metagenome were highly diverse and were assigned to the Bacteroidota, Planctomycetota, Chloroflexota, Pseudomonadota, and Kiritimatiellaeota phyla, with four sequences remaining unassigned. In a sequence similarity network, most GH51 homolog sequences clustered with uncharacterized members of the GH51 family or were highly divergent. Three-dimensional models of the putative enzymes showed distinctive structural characteristics, including a highly variable length of the loop located between β-strand 2 and α-helix 2 and the absence in some of the sequences of a highly conserved Trp residue in this loop. Important differences in the predicted surface electrostatic potential in models of closely related GH51 homologs suggest various levels of adaptation to the prevailing environmental conditions. This work provides an insight into the characteristics of putative enzymes related to the GH51 family from intertidal sediment bacteria, from taxa that are relevant in the marine environment but remain poorly characterized due to the difficulties in their cultivation. [ABSTRACT FROM AUTHOR]

Coastal sediments filter and accumulate organic and inorganic materials from the terrestrial and marine environment, and thus provide a high diversity of microbial niches. However, sediment-based analyses typically examine bulk samples and seldom consider variation at a scale relevant to changes in environmental conditions, due to the lack of mid-long term field data which can cover both the seasonal and sediment depth variations. In this study, microbial production and bacterial community structure were determined together with grain parameters over 10 months of intertidal silty sands on Jiangsu Coast, China. We demonstrated that the microbiological effects did not merely present on the surface, but greatly varied and stratified in both physical and biological contexture within the top 4 cm layer. Bacterial community structure showed a clear vertical variation with higher operational taxonomic unit (OTU) numbers at 1~2 cm depth than in the top 2 mm, probably because of the decreasing disturbance by hydrodynamic forces. However, the microbial production rates and metabolic activities, represented by the production of extracellular polymeric substances (EPS), were always higher in the top. Seasonal changes were strongly reflected in the vertical patterns of EPS but could not explain the variation across sites. The overall EPS secretion in spring and summer was generally at high level than that in autumn and winter, with the maximum value of 5~6 times higher. Interestingly, the stratification of biological and physical properties followed a fixed relationship, where with the decrease of the grain size D50, the EPS content increased exponentially, and this relationship was independent of temporal or spatial variation. Despite the significant seasonal variation of microbial activity and sedimentary grain size individually, the basic function between EPS content and D50 however did not alter. Filling these knowledge gaps will not only help to decipher the fate of grain-biofilm aggregates and organic matter burial under global changes, but also provide field evidence for the development of sediment transport models as well as blue carbon models incorporating microbial processes.

Intertidal coastal sediments are important centers for nutrient transformation, regeneration, and storage. Sediment resuspension, due to wave action or tidal currents, can induce nutrient release to the water column and fuel primary production. Storms and extreme weather events are expected to increase due to climate change in coastal areas, but little is known about their effect on nutrient release from coastal sediments. We have conducted in-situ sediment resuspension experiments, in which erosion was simulated by a stepwise increase in current velocities, while measuring nutrient uptake or release in field flumes positioned on intertidal areas of a tidal bay (Eastern Scheldt) and an estuary (Western Scheldt). In both systems, the water column concentration of ammonium (NH4+) and nitrite (NO2−) increased predictably with greater erosion as estimated from pore water dilution and erosion depth. In contrast, the phosphate (PO43−) dynamics were different between systems, and those of nitrate (NO3−) were small and variable. Notably, sediment resuspension caused a decrease in the overlying water PO43− concentration in the tidal bay, while an increase was observed in the estuarine sediments. Our observations showed that the concentration of PO43− in the water column was more intensely affected by resuspension than that of NH4+ and NO2−. The present study highlights the differential effect of sediment resuspension on nutrient exchange in two contrasting tidal coastal environments.

Darwin Harbour is a working port and the most populated city in the Northern Territory of Australia. This macrotidal estuary is located in the wet–dry tropics of Northern Australia and notwithstanding mounting development pressures in the region, is largely unmodified. The prevailing oligotrophic condition of estuarine waters suggest that biogeochemical cycling in sediments remain active, buffering the influence of anthropogenic inputs. We tested the hypothesis that nutrient hotspots exist in depositional low-velocity zones, with a gradient of high to low nitrogen processing from the upper to outer reaches of the estuary. A number of factors were examined for their influence on the effectiveness of denitrification in these depositional zones, a putative key process driving nitrogen removal, with particular emphasis on carbon-loading extremes in tidal creeks, spatial gradients along the estuary and the influence of seasonality. There were significant differences in process rates between hypereutrophic/eutrophic tidal creeks that receive the largest proportion of treated sewage loads in the region and the mesotrophic/oligotrophic tidal creeks that were comparatively undisturbed. Net benthic nutrient fluxes and dinitrogen efflux rates were more than an order of magnitude higher and lower, respectively, in degraded (hypereutrophic/eutrophic) tidal creek systems where denitrification efficiency (DE%) was < 40%. Denitrification (Dinitrogen efflux) rates in tidal creeks (mesotrophic/oligotrophic) and broader estuarine sites were high (~ 8 mmol N m−2 day−1) and denitrification efficiency remained > 65%, particularly during the wet season. On a whole-of-estuary basis, denitrification in conjunction with mechanisms such as burial could feasibly make a substantial impact, abating the influence of anthropogenic inputs. Although considerable variability was encountered, particularly across seasons, the hypothesis of elevated denitrification rates as nutrient hotspots in depositional zones along the estuary was not convincing. More influential are tidal creeks as potential 'reactors' for N cycling and removal, but their capacity can be degraded by overloading with nutrients. [ABSTRACT FROM AUTHOR]

The exploration of sediment pollution caused by PAHs and its impact on microbial communities can provide valuable insights for the remediation of sediments. The spatial distribution of PAHs and their impact on the microbial community within the Pearl River Estuary were investigated in this study. The findings revealed that the total concentration ranges of 16 PAHs were between 24.26 and 3075.93 ng/g, with naphthalene, fluorene, and phenanthrene potentially exerting adverse biological effects. More PAHs were found to accumulate in subsurface sediments, and their average accumulation rates gradually decreased as the number of rings in PAHs increased, ranging from 180 % for 2-ring to 36 % for 6-ring. The phyla Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi were found to dominate both surface and subsurface sediments The correlation between microbial genera and PAHs contents was weak in sediments with low levels of PAHs contamination, while a more significant positive relationship was observed in sediments with high levels of PAHs contamination. The physicochemical properties of sediments, such as pH, soil structure and Cu significantly influence bacterial community composition in highly contaminated sediments. Additionally, the network analysis revealed that certain bacterial genera, including Novosphingobium , Robiginitalea and Synechococcus_CC9902 , played a pivotal role in the degradation of PAHs. These findings are significant in comprehending the correlation between bacterial communities and environmental factors in intertidal ecosystems, and establish a scientific foundation for bioremediation of intertidal zones. [Display omitted] • Nap, Flu and Phe may have harmful effects on intertidal sediments. • More PAHs accumulated in subsurface sediments. • Microbial assembly primarily responds to PAHs, pH, sediment structure and Cu. • Cyanobacteriota, Proteobacteria, and Bacteroidota can degrade PAHs. [ABSTRACT FROM AUTHOR]

Migratory shorebirds are notable consumers of benthic invertebrates on intertidal sediments. The distribution and abundance of shorebirds will strongly depend on their prey and on landscape and sediment features such as mud and surface water content, topography, and the presence of ecosystem engineers. An understanding of shorebird distribution and ecology thus requires knowledge of the various habitat types which may be distinguished in intertidal areas. Here, we combine Sentinel-1 and Sentinel-2 imagery and a digital elevation model (DEM), using machine learning techniques to map intertidal habitat types of importance to migratory shorebirds and their benthic prey. We do this on the third most important non-breeding area for migratory shorebirds in the East Atlantic Flyway, in the Bijagós Archipelago in West Africa. Using pixel-level random forests, we successfully mapped rocks, shell beds, and macroalgae and distinguished between areas of bare sediment and areas occupied by fiddler crabs, an ecosystem engineer that promotes significant bioturbation on intertidal flats. We also classified two sediment types (sandy and mixed) within the bare sediment and fiddler crab areas, according to their mud content. The overall classification accuracy was 82%, and the Kappa Coefficient was 73%. The most important predictors were elevation, the Sentinel-2-derived water and moisture indexes, and Sentinel-1 VH band. The association of Sentinel-2 with Sentinel-1 and a DEM produced the best results compared to the models without these variables. This map provides an overall picture of the composition of the intertidal habitats in a site of international importance for migratory shorebirds. Most of the intertidal flats of the Bijagós Archipelago are covered by bare sandy sediments (59%), and ca. 22% is occupied by fiddler crabs. This likely has significant implications for the spatial arrangement of the shorebird and benthic invertebrate communities due to the ecosystem engineering by the fiddler crabs, which promotes two vastly different intertidal species assemblages. This large-scale mapping provides an important product for the future monitoring of this high biodiversity area, particularly for ecological research related to the distribution and feeding ecology of the shorebirds and their prey. Such information is key from a conservation and management perspective. By delivering a successful and comprehensive mapping workflow, we contribute to the filling of the current knowledge gap on the application of remote sensing and machine learning techniques within intertidal areas, which are among the most challenging environments to map using remote sensing techniques. [ABSTRACT FROM AUTHOR]

Chemical measures combined with biological data (biomarkers) are recommended in monitoring programs of marine environments. In the present research, the use of multiples biogeochemical indicators allowed interrelating different environmental measurements to deepen the knowledge of the quality/status of the intertidal flat from Puerto Rosales (Bahía Blanca estuary, Argentina) subjected to anthropogenic pressure. The sediments from this site presented a eutrophic status and high organic matter concentration with high nutritional value for the benthic community. The TPR/TCH ratio (~ 10) would evidence the untreated sewage discharge contribution and increments in protein content due to the complexation of nitrogen during phytodetritus accumulation and degradation. Trace metals levels in the fine sediments were lower than those recommended by international guides for uncontaminated sites. In the sediments, except Cu, all metals analyzed were rarely associated with adverse biological effects. Finally, metallothioneins levels in the burrowing crab Neohelice granulata were lower than those found in the literature and significantly higher in females than in males. Even though the different analyses and indices performed indicate that this intertidal flat is in good environmental condition, the wastewater discharge influenced it. Thus, it is advisable to continue with this kind of study by applying multi-combined proxies in this and other impacted tidal flats. [ABSTRACT FROM AUTHOR]

Microbial communities are important indicators of aquatic ecosystem health, responsible for functional roles sustaining the ecosystem such as nutrient cycling, as well as environmental problems. Urbanized estuaries are vulnerable intersections between terrestrial and marine ecosystems and are susceptible to pressure and perturbation from both natural processes and human activities over time. The response by microbial communities toward changes in the environment should be closely monitored and studied. In this study, microbial communities in brackish intertidal sediments, sampled seasonally over a year along the coast of Yangtze River estuary, were analyzed using 16S rRNA gene sequencing. Potential compositional and functional changes in microbial communities resulting from temporal variation and associated physiochemical gradients in the environment were studied and notable patterns were observed over time. Summer season was recorded with the lowest microbial community α-diversity. For β-diversity, spatiotemporal differentiation in community structures was recorded with seasonal clustering. Proteobacteria was recorded as the most dominant phylum among all sampling sites throughout the year but its relative abundance showed no temporal changes. Instead, relative abundances of phyla Actinobacteria, Chloroflexi, and Verrucomicrobia were found to differ significantly over time, generally favoring the wet Spring and Summer. In contrast, temporal variation was observed for the class Deltaproteobacteria and some of the corresponding sulfate/sulfur-reducing bacterial genera, favoring the dry Autumn and Winter. However, there were no major temporal changes in ecological functions contributed by microbial communities throughout the study period. While results from redundancy analysis showed that the subtle changes in pH in the environment had the greatest impact on microbial community composition, the variation it explained remained relatively low. Alternatively, precipitation, distinguishing the dry and wet seasons of the subtropical monsoon climate zone, was suggested to be another potential key factor influencing microbial community composition and their relative abundances. The present study provides new data and insights on the impact of temporal variation on microbial community composition and ecological function in an urbanized estuarine ecosystem.

Hyper-DRELIO (Hyperspectral DRone for Environmental and LIttoral Observations) is a custom, mini-UAV (unmanned aerial vehicle) platform (® and a field spectrometer, allowing performance of an initial calibration of the sensor in order to correct “vignetting effects” and a field standardization to convert digital numbers (DN) collected by the hyperspectral camera to reflectance, taking into account the time-varying illumination conditions. Radiometric corrections are applied to a subset of a dataset collected above mudflats colonized by pioneer mangroves in French Guiana. The efficiency of the radiometric corrections is assessed by comparing spectra from Hyper-DRELIO imagery to in situ spectrometer measurements above the intertidal benthic biofilm and mangroves. The shapes of the spectra were consistent, and the spectral angle mapper (SAM) distance was 0.039 above the benthic biofilm and 0.159 above the mangroves. These preliminary results provide new perspectives for quantifying and mapping the benthic biofilm and mangroves at the scale of the Guianese intertidal mudbanks system, given their importance in the coastal food webs, biogeochemical cycles, and the sediment stabilization.

Illumina high-throughput sequencing was applied to study the microbial community structure and seasonal variations in the mudflat sediments of Sansha Bay, China. Significant seasonal differences of microbial communities were observed, and pH, total P, total N, and organic carbon concentration were important factors affecting the microbial communities. A total of 52 bacterial phyla were detected in the sediments, dominated by γ-Proteobacteria (27.78%), δ-Proteobacteria (20.16%) and Bacteroidetes (10.58%). A total of 717 bacterial genera were detected, and among the top 100 genera with the highest abundances, 48 genera changed significantly (p <0.05) with seasons. The microbial community structure in summer was significantly different from others, and the environmental factors driving the changes were mainly temperature, organic carbon and total N concentration. The bacteria with higher abundances in summer were mainly attached bacteria, thermophilic bacteria, anaerobic bacteria, and those involved in carbon and nitrogen cycling, while in other seasons, those with higher abundances were mainly aerobic bacteria, which could adapt to low temperatures and are involved in the degradation of cellulose and chitosan. However, the physicochemical indexes didn't change significantly, which indicated that the bacterial communities are more sensitive and can serve as a good sentinel for environmental changes. [ABSTRACT FROM AUTHOR]

Primary production of microphytobenthos (MPB) contributes significantly to the total production in shallow coastal environments. MPB is a diverse community in which diatoms are usually the main microalgal group. Diatoms require N, P, and other nutrients as with other autotrophs, but in addition require silicate to create their outer cell wall. Therefore, dissolved silica (DSi) might be a potential limiting factor for benthic primary production in areas with reduced freshwater input. To test this hypothesis, a microcosm experiment was conducted using intact sediment cores collected from an intertidal mudflat in the Bay of Cádiz and supplied with increasing concentrations of DSi (0, 5, 10, 25, and 45 μmol • L-1). After 7 d of enrichment, we determined chlorophyll a and c (Chl a, c) contents, metabolic rates (Net [Pn] and Areal Gross [PgA] Production and Light [RL] and Dark [RD] Respiration), as well as fluxes of inorganic nutrients across the sediment-water interface. Chl a and c contents increased significantly with respect to the initial conditions but no differences between treatments were found. Both Pn and Pg A showed a saturating-like pattern with silicate concentration, reaching maximum rates at a DSi concentration of 45 μmol • L-1. The addition of DSi also resulted in an increase of DSi and ammonium uptake by the sediment, which was significantly higher in light than in darkness. Our results clearly show that water column DSi concentrations have a direct impact on benthic primary production, also controlling other related processes such as inorganic nutrient fluxes. [ABSTRACT FROM AUTHOR]

Three new species of Fallacia, F. miyajimensis sp. nov., F. nodulifera sp. nov., and F. similigemmifera sp. nov. are described from intertidal sediments in Japan. Their morphologies are studied with light, scanning and transmission electron microscopy. Fallacia miyajimensis differs from congeners in the presence of an apical pore, a finely porous conopeum possessing finger-shaped extensions with uniseriate rows of pores and a thick layer adjacent to the raphe with isolated depressions with small pores inside. Fallacia nodulifera differs from congeners in the presence of a unique asymmetric internal central nodule. It can also be distinguished by the combination of stria density, conopeum with short extensions, and centrally convex lateral sterna. Fallacia similigemmifera differs from congeners by its lanceolate valve outline, more or less straight, distinct lateral areas and the presence of a rectelevatum on internal central nodule. We suggest that the structural combination of the structure of the conopeum and the lateral sterna is a stable feature in species discrimination and could be used to define species groups. The cingulum of F. similigemmifera comprises a wide open valvocopula and two linear bands with different ligulae. This type of cingulum structure is also present in F. tenera, F. hodgeana, and probably in F. litoricola and F. fracta as well, and likely occurs commonly in Fallacia. [ABSTRACT FROM AUTHOR]

Abstract The frequent rainfall during the low tide would erode and transport the surface sediment and microphytobenthos (MPB) in the intertidal flat. In order to quantify the rainfall effects on the erodibility of sediment and MPB at the salt marsh and mixed flat, a series of erosion experiments have been conducted with a Gust erosion microcosm system. Surface sediments were sampled for analyzing algal biomass (Chl- a) and primary production (PP) during three typical weather (without rain, rain, and post-rain) conditions. The results of erosion experiment, in both salt marsh and mixed flat, showed that the sediment erodibility under rain condition was higher than that under without rain condition, with increased total eroded mass by 37–86%. It indicated that the rainfall effects caused to significantly disturb the surface sediment. After the rainfall events, the removal of highly-erodible sediments resulted in the reduction in eroded mass. The MPB erodibility under rain condition was lower than that under without rain condition, with decreased total eroded Chl- a by 29%. At the mixed flat, the rainfall effects caused to significantly decrease biological activities of MPB (biomass and PP) associated with surface sediment. The surface Chl- a concentration under post-rain condition decreased by 73%, compared to that under rain condition. At the salt marsh, in contrast, the rainfall effects were barely shown when the biological activities of MPB were rather stable. This implied that the eroded MPB induced by rainfall was retained within the marsh system due to vegetation canopy. Graphical abstract Image 1 Highlights • Rainfall effects on the erodibility of sediment and MPB were investigated at tidal flat. • Under rain condition, sediment erodibility increased by 86%, and MPB erodibility decreased by 29%. • Rainfall effects on salt marsh were barely shown when MPB biomass was rather stable. [ABSTRACT FROM AUTHOR]

Abstract Concentrations of heavy metals in sediments and seawaters from the intertidal zone are analyzed along with cage-bred fish in the Sandu Bay of Fujian Province in China. Elements measured are As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. The concentrations of Cu and Ni found in the sediments do not meet the first standard of the Chinese National Criteria for Marine Sediment Quality. The results of I geo , EF, and CF index calculations for the sediment samples clearly prove anthropogenic causes of contamination. The water quality standard for fisheries was exceeded by As, Hg, and Cu. Cage-bred fish show increased levels of As, Cr, and Zn. Significant associations are found for As Cu and Ni Zn. These findings can be related to coal and crude oil combustion and processes associated with the production of batteries, steel, and alloys. The results point to industrial source locations along discharging rivers north and northwest of the Sandu Bay. Highlights • Main contaminants in the sediments and seawater are As, Cr, Cu, Hg, Ni, Pb, and Zn. • The contamination with heavy metals is of anthropogenic origin. • Fish, cage bred in the bay, exceed Chinese food safety standards for As, Cr and Zn. • Processes of heavy industry and maritime ship traffic can be considered as sources. [ABSTRACT FROM AUTHOR]

Distribution characteristics, potential sources, and possible biological hazards of polycyclic aromatic hydrocarbons (PAHs) were examined in intertidal surface sediments of Zhelin Bay, the biggest mariculture base of eastern Guangdong Province, Southern China. The total PAH concentrations ranged from 8.05–51.32 ng/g (dry weight) with an average of 29.23 ng/g, which is beneath the documented concentrations in intertidal sediments gathered from various bays across the globe. The composition of PAHs was distinguished by high molecular weight (HMW, 4–6 rings) PAHs, with phenanthrene (PHE), fluoranthene (FA), and benzo(b)fluoranthene (BbFA) established as predominant components. Principle component analysis along with multivariate linear regression discovered that liquid fossil fuel combustion and coal/wood combustion contribute to 60.23% and 39.77% of PAHs in Zhelin Bay's intertidal sediments, respectively. Overall, surface sediments of Zhelin Bay have an 8% increased incidence of adverse biological effects due to PAH contamination, based on the mean probable effect level quotient. [ABSTRACT FROM AUTHOR]

Intertidal surface sediments collected from Zhelin Bay, the largest mariculture base of eastern Guangdong Province of China, were analyzed for total metal concentrations and chemical speciation. Average total metal concentrations (mg/kg) were 0.063 (Cd), 35.69 (Pb), 23.07 (Cr), 7.50 (Ni), 7.95 (Cu), 74.95 (Zn), and 751.32 (Mn). Concentrations of Cd, Cu, Zn, and Mn were significantly higher than the corresponding background values of Zhelin Bay. All studied metals were dominated by residual fractions, whereas the second relatively higher average portions of Cd (24.10%) and Mn (15.17%) were strongly associated with the acid-soluble fraction. Overall, the intertidal surface sediments of Zhelin Bay were only slightly polluted based on the pollution load index (PLI), with a 21% probability of toxicity based on the mean effects range–median quotient. The metals Cd and Mn posed medium to high risk levels based on the method of risk assessment code (RAC). [ABSTRACT FROM AUTHOR]

Intertidal sediments of Tagus estuary regularly experiences complex redistribution due to tidal forcing, which affects the cycling of mercury (Hg) between sediments and the water column. This study quantifies total mercury (Hg) and methylmercury (MMHg) concentrations and fluxes in a flooded mudflat as well as the effects on water-level fluctuations on the air-surface exchange of mercury. A fast increase in dissolved Hg and MMHg concentrations was observed in overlying water in the first 10 min of inundation and corresponded to a decrease in pore waters, suggesting a rapid export of Hg and MMHg from sediments to the water column. Estimations of daily advective transport exceeded the predicted diffusive fluxes by 5 orders of magnitude. A fast increase in dissolved gaseous mercury (DGM) concentration was also observed in the first 20–30 min of inundation (maximum of 40 pg L − 1 ). Suspended particulate matter (SPM) concentrations were inversely correlated with DGM concentrations. Dissolved Hg variation suggested that biotic DGM production in pore waters is a significant factor in addition to the photochemical reduction of Hg. Mercury volatilization (ranged from 1.1 to 3.3 ng m − 2 h − 1 ; average of 2.1 ng m − 2 h − 1 ) and DGM production exhibited the same pattern with no significant time-lag suggesting a fast release of the produced DGM. These results indicate that Hg sediment/water exchanges in the physical dominated estuaries can be underestimated when the tidal effect is not considered. [ABSTRACT FROM AUTHOR]

Intertidal sediments of the inner and middle zone from the Bahía Blanca estuary were sampled for geochemical and environmental assessment of metals (Cd, Cu, Pb, Zn, Mn, Ni, Cr and Fe). Results indicate that both the organic matter content and the sediment grain size plays an important role in controlling the differential concentrations of the metals found in sediments from both zones. For most of the elements (except Mn), sediment metal concentrations were greater in the middle zone, although the concentrations did not exceed the maximums for quality of marine sediments. In this sense, anthropogenic impact (i.e., sewage drain) appears to be a key factor in the distribution of metals within the estuarine system. Comparing the levels obtained with quality levels (LEL and SEL), except Cu that showed levels slightly above the LEL, the rest of the concentrations of metals were lower to those levels. The low metal concentrations obtained within this highly impacted estuarine system suggest that the great volume of water that flooding the extensive flats in each tidal cycle has much importance. Although the potential risks of metals to the estuarine environment were low, taking into account the toxicity of some of these metals, continuity of monitoring is highly recommended. [ABSTRACT FROM AUTHOR]

Behavioural decisions are often context-dependent, where information from immediate experience is incorporated into an individual's decision-making, particularly in complex environments. To test whether such mechanism is adopted by foragers in heterogeneous environments, we investigated the foraging behaviour of the deposit-feeding sand-bubbler crab, Scopimera intermedia. An individual-based model was constructed, based on an optimal-patch selection criterion, which implicitly assumed that individuals adjust foraging decisions based on immediate past experience. The model's predictions were tested on the shore by manipulating the location of food patches, where the crab showed a strong context-dependent foraging pattern. When resources were randomly distributed, the crab responded by spending 56% of time in enriched patches compared with only 28% in the same area when patches were composed of natural sediments. Shore manipulations varying resource distribution supported the underlying principles of the model mechanism, and highlighted the benefits of such a strategy in heterogeneous environments such as intertidal sediments where food resources vary at different spatial and temporal scales. The proposed model therefore provides a mechanistic process, based on optimal foraging, to predict foraging decisions and movement patterns of animals feeding in heterogeneous landscapes. [ABSTRACT FROM AUTHOR]

The Fildes Peninsula has a maritime Antarctic climate and has attracted the interest of scientists for decades. The soil bacterial community and the environmental factors shaping it have been well documented. However, the bacterial community of intertidal sediments, which has been determined to play crucial roles in biogeochemical cycles in temperate regions, has been comparatively neglected. Here, the diversity and abundance of bacteria in intertidal sediments represented by 18 samples from the Fildes Peninsula were revealed by 16S rRNA gene pyrosequencing and qPCR. The results showed distinct bacterial community structure, and lower diversity and abundance relative to low-latitude areas. Proteobacteria, Bacteroidetes, and Actinobacteria were the predominant phyla, accounting for ~90 % of the total community. Among the measured environmental factors, chlorophyll a (Chl a), total organic matter (TOM), and standard deviation ( σ) of sediment grain size explained the bacterial community variation in the redundancy analysis across all samples, and had consistent relationship with bacterial diversity and abundance. Granulosicoccus, the most abundant genus within Chromatiales Gammaproteobacteria in this study, showed positive correlation with standard deviation of sediment grain size. The present study demonstrated a distinct bacterial community different from temperate regions and provided insights into the potential ecological roles of specific taxa in the Antarctic environment. [ABSTRACT FROM AUTHOR]

Marine magnetotactic bacteria were collected from the intertidal sediments of Yuehu Lake (China), where their abundance reached 10-10 ind./cm. Diverse morphotypes of magnetotactic bacteria were observed, including cocci and oval, vibrio-, spirillum-, rod-, elliptical-, handle- and bar-shaped forms. The magnetococci were the most abundant, and had flagella arranged in parallel within a bundle. The majority of magnetosomes were arranged in one, two or multiple chains, although irregular arrangements were also evident. All the results of high-resolution transmission electron microscopy (HRTEM) analysis show that magnetosome crystals were composed of FeO, and their morphology was specific to particular cell morphotypes. By the 16S rRNA gene sequence analysis, we found fourteen operational taxonomic units (OTUs) which were related to magnetotactic bacteria. Among these, thirteen belonged to the Alphaproteobacteria and one to the Gammaproteobacteria. Compared with known axenic and uncultured marine magnetotactic bacteria, the 16S rRNA gene sequences of most magnetotactic bacteria collected from the Yuehu Lake exhibited sequence identities ranging from 90.1% to 96.2% (<97%). The results indicate that microbial communities containing previously unidentified magnetotactic bacteria occur in the Yuehu Lake. [ABSTRACT FROM AUTHOR]

The study of inorganic nutrients dynamics in shallow sediments usually focuses on two main pools: the porewater (PW) nutrients and the exchangeable (EX) ammonium and phosphate. Recently, it has been found that microphytobenthos (MPB) and other microorganisms can accumulate large amounts of nutrients intracellularly (IC), highlighting the biogeochemical importance of this nutrient pool. Storing nutrients could support the growth of autotrophs when nutrients are not available, and could also provide alternative electron acceptors for dissimilatory processes such as nitrate reduction. Here, we studied the magnitude and relative importance of these three nutrient pools (PW, IC and EX) and their relation to chlorophylls (used as a proxy for MPB abundance) and organic matter (OM) contents in an intertidal mudflat of Cadiz Bay (Spain). MPB was localized in the first 4 mm of the sediment and showed a clear seasonal pattern; highest chlorophylls content was found during autumn and lowest during spring-summer. The temporal and spatial distribution of nutrients pools and MPB were largely correlated. Ammonium was higher in the IC and EX fractions, representing on average 59 and 37% of the total ammonium pool, respectively. Similarly, phosphate in the IC and EX fractions accounted on average for 40 and 31% of the total phosphate pool, respectively. Nitrate in the PW was low, suggesting low nitrification activity and rapid consumption. Nitrate accumulated in the IC pool during periods of moderate MPB abundance, being up to 66% of the total nitrate pool, whereas it decreased when chlorophyll concentration peaked likely due to a high nitrogen demand. EX-Nitrate accounted for the largest fraction of total sediment nitrate, 66% on average. The distribution of EX-Nitrate was significantly correlated with chlorophyll and OM, which probably indicates a relation of this pool to an increased availability of sites for ionic adsorption. This EX-Nitrate pool could represent an alternative nitrate source with significant concentrations available to the microbial community, deeper in the sediment below the oxic layer.

Retroreflective glass microbeads used in road markings have been characterised and subsequently identified in urban coastal sediments. Clear or translucent silica beads range in diameter from about 30 to 700 μm and readily break from the matrix of detached or damaged markings on abrasion. At an urban location close to the city centre of Plymouth, southwest England, and in an estuary below a large road bridge, microbeads were detected in nearly all intertidal sediments analysed (n = 18) and at concentrations up to about 550 kg−1 dw. At a location not immediately impacted by major roads, beads were entirely absent from sediments (n = 9). With a size range and density similar to silt-sand, glass beads appear to accumulate in sediment subject to road runoff and act as persistent proxies for traffic-related contamination. Although beads are unlikely to be inherently toxic, they may serve as indicators of more harmful chemicals in road dust. • Glass road marking microbeads identified and counted in urban coastal sediments • Microbeads are clear-translucent silica with diameters ranging from 30 to 700 μm. • Close to stormwater effluents and major road bridge concentrations reach 550 kg−1 dw. • Outside a country park not serviced by marked roads microbeads entirely absent • Glass microbeads serve as a proxy for road-related contamination of sediments. [ABSTRACT FROM AUTHOR]

The estuarine nitrogen cycle can be substantially altered due to anthropogenic activities resulting in increased amounts of inorganic nitrogen (mainly nitrate). In the past, denitrification was considered to be the main ecosystem process removing reactive nitrogen from the estuarine ecosystem. However, recent reports on the contribution of dissimilatory nitrate reduction to ammonium (DNRA) to nitrogen removal in these systems indicated a similar or higher importance, although the ratio between both processes remains ambiguous. Compared to denitrification, DNRA has been underexplored for the last decades and the key organisms carrying out the process in marine environments are largely unknown. Hence, as a first step to better understand the interplay between denitrification, DNRA and reduction of nitrate to nitrite in estuarine sediments, nitrogen reduction potentials were determined in sediments of the Paulina polder mudflat (Westerschelde estuary). We observed high variability in dominant nitrogen removing processes over a short distance (1.6 m), with nitrous oxide, ammonium and nitrite production rates differing significantly between all sampling sites. Denitrification occurred at all sites, DNRA was either the dominant process (two out of five sites) or absent, while nitrate reduction to nitrite was observed in most sites but never dominant. In addition, novel nitrate-to-ammonium reducers assigned to Thalassospira, Celeribacter and Halomonas, for which DNRA was thus far unreported, were isolated, with DNRA phenotype reconfirmed through nrfA gene amplification. This study demonstrates high small scale heterogeneity among dissimilatory nitrate reduction processes in estuarine sediments and provides novel marine DNRA organisms that represent valuable alternatives to the current model organisms.

Odontophora is a globally distributed marine nematode genus common in intertidal and subtidal sediments. Odontophora is one of the most diverse genus of the family Axonolaimidae with over 30 valid species described to date; however, the last revision of the genus was made over four decades ago. In addition, limited molecular sequence data are available for the Axonolaimidae and relationships among axonolaimid genera have not yet been investigated using molecular tools. Here, an updated list of species and a key for the identification of all 34 valid species is provided, and preliminary analyses of phylogenetic relationships within the Axonolaimidae are conducted using SSU and D2-D3 of LSU molecular sequences. Odontophora atrox sp. n. is described from intertidal sediments of Wellington, North Island of New Zealand, and is characterised by cephalic setae 1.1-1.5 corresponding body diam. long, 12 subcephalic setae, eight of which are slightly shorter and four of which are markedly shorter than the cephalic setae, excretory pore located slightly posterior to the amphids, and nerve ring located at two-thirds to three-quarters of pharynx length from anterior. Males are characterised by weakly arcuate spicules and tapering gubernacular apophyses, 9-10 small tubular precloacal supplements, cloacal aperture flanked by two sets of heavily cuticularised and eversible spines, and two elongated laterodorsal setae near the tail tip. Preliminary analyses of phylogenetic relationships within the Axonolaimidae provide some support for the monophyly of Odontophora, but drawing more solid inferences about relationships within the Axonolaimidae will require more molecular sequence data of accurately (and verifiably) identified species. [ABSTRACT FROM AUTHOR]

The spectral features of intertidal sediments are all influenced by the same biophysical properties, such as water, salinity, grain size or vegetation and therefore they are hard to separate by using only multispectral sensors. This could be shown by a previous study of Jung et al. (2015) . A more detailed analysis of their characteristic spectral feature has to be carried out to understand the differences and similarities. Spectrometry data (i.e., hyperspectral sensors), for instance, have the opportunity to measure the reflection of the landscape as a continuous spectral pattern for each pixel of an image built from dozen to hundreds of narrow spectral bands. This reveals a high potential to measure unique spectral responses of different ecological conditions ( Hennig et al., 2007 ). In this context, this study uses spectrometric datasets to distinguish between 14 different sediment classes obtained from a study area in the German Wadden Sea. A new feature selection method is proposed (Jeffries-Matusita distance bases feature selection; JMDFS), which uses the Euclidean distance to eliminate the wavelengths with the most similar reflectance values in an iterative process. Subsequent to each iteration, the separation capability is estimated by the Jeffries-Matusita distance (JMD). Two classes can be separated if the JMD is greater than 1.9 and if less than four wavelengths remain, no separation can be assumed. The results of the JMDFS are compared with a state-of-the-art feature selection method called ReliefF. Both methods showed the ability to improve the separation by achieving overall accuracies greater than 82%. The accuracies are 4%–13% better than the results with all wavelengths applied. The number of remaining wavelengths is very diverse and ranges from 14 to 213 of 703. The advantage of JMDFS compared with ReliefF is clearly the processing time. ReliefF needs 30 min for one temporary result. It is necessary to repeat the process several times and to average all temporary results to achieve a final result. In this study 50 iterations were carried out, which makes four days of processing. In contrast, JMDFS needs only 30 min for a final result. [ABSTRACT FROM AUTHOR]

The study of inorganic nutrients dynamics in shallow sediments usually focuses on two main pools: porewater (PW) nutrients and exchangeable (EX) ammonium and phosphate. Recently, it has been found that microphytobenthos (MPB) and other microorganisms can accumulate large amounts of nutrients intracellularly (IC), highlighting the biogeochemical importance of this nutrient pool. Storing nutrients could support the growth of autotrophs when nutrients are not available, and could also provide alternative electron acceptors for dissimilatory processes such as nitrate reduction. Here, we studied the magnitude and relative importance of these three nutrient pools (PW, IC, and EX) and their relation to chlorophylls (used as a proxy for MPB abundance) and organic matter (OM) contents in an intertidal mudflat of Cadiz Bay (Spain). MPB was localized in the first 4 mm of the sediment and showed a clear seasonal pattern; highest chlorophylls content was found during autumn and lowest during spring-summer. The temporal and spatial distribution of nutrients pools and MPB were largely correlated. Ammonium was higher in the IC and EX fractions, representing on average 59 and 37% of the total ammonium pool, respectively. Similarly, phosphate in the IC and EX fractions accounted on average for 40 and 31% of the total phosphate pool, respectively. Nitrate in the PW was low, suggesting low nitrification activity and rapid consumption. Nitrate accumulated in the IC pool during periods of moderate MPB abundance, being up to 66% of the total nitrate pool, whereas it decreased when chlorophyll concentration peaked likely due to a high nitrogen demand. EX-Nitrate accounted for the largest fraction of total sediment nitrate, 66% on average. The distribution of EX-Nitrate was significantly correlated with chlorophyll and OM, which probably indicates a relation of this pool to an increased availability of sites for ionic adsorption. This EX-Nitrate pool could represent an alternative nitrate source with significant concentrations available to the microbial community, deeper in the sediment below the oxic layer. [ABSTRACT FROM AUTHOR]

Coastal marine sediments, where important biological processes take place, supply essential ecosystem services. By their location, such ecosystems are particularly exposed to human activities as evidenced by the recent Deepwater Horizon disaster. This catastrophe revealed the importance to better understand the microbial processes involved on hydrocarbon degradation in marine sediments raising strong interests of the scientific community. During the last decade, several studies have shown the key role played by microorganisms in determining the fate of hydrocarbons in oil-polluted sediments but only few have taken into consideration the whole sediment’s complexity. Marine coastal sediment ecosystems are characterized by remarkable heterogeneity, owning high biodiversity and are subjected to fluctuations in environmental conditions, especially to important oxygen oscillations due to tides. Thus, for understanding the fate of hydrocarbons in such environments, it is crucial to study microbial activities, taking into account sediment characteristics, physical-chemical factors (electron acceptors, temperature), nutrients, co-metabolites availability as well as sediment’s reworking due to bioturbation activities. Key information could be collected from in situ studies, which provide an overview of microbial processes, but it is difficult to integrate all parameters involved. Microcosm experiments allow to dissect in-depth some mechanisms involved in hydrocarbon degradation but exclude environmental complexity. To overcome these lacks, strategies have been developed, by creating experiments as close as possible to environmental conditions, for studying natural microbial communities subjected to oil pollution. We present here a review of these approaches, their results and limitation, as well as the promising future of applying ‘omics’ approaches to characterize in-depth microbial communities and metabolic networks involved in hydrocarbon degradation.

The estuarine nitrogen cycle can be substantially altered due to anthropogenic activities resulting in increased amounts of inorganic nitrogen (mainly nitrate). In the past, denitrification was considered to be the main ecosystem process removing reactive nitrogen from the estuarine ecosystem. However, recent reports on the contribution of dissimilatory nitrate reduction to ammonium (DNRA) to nitrogen removal in these systems indicated a similar or higher importance, although the ratio between both processes remains ambiguous. Compared to denitrification, DNRA has been underexplored for the last decades and the key organisms carrying out the process in marine environments are largely unknown. Hence, as a first step to better understand the interplay between denitrification, DNRA and reduction of nitrate to nitrite in estuarine sediments, nitrogen reduction potentials were determined in sediments of the Paulina polder mudflat (Westerschelde estuary). We observed high variability in dominant nitrogen removing processes over a short distance (1.6 m), with nitrous oxide, ammonium and nitrite production rates differing significantly between all sampling sites. Denitrification occurred at all sites, DNRA was either the dominant process (two out of five sites) or absent, while nitrate reduction to nitrite was observed in most sites but never dominant. In addition, novel nitrate-to-ammonium reducers assigned to Thalassospira, Celeribacter, and Halomonas, for which DNRA was thus far unreported, were isolated, with DNRA phenotype reconfirmed through nrfA gene amplification. This study demonstrates high small scale heterogeneity among dissimilatory nitrate reduction processes in estuarine sediments and provides novel marine DNRA organisms that represent valuable alternatives to the current model organisms. [ABSTRACT FROM AUTHOR]

Aims To investigate the potential to degrade polycyclic aromatic hydrocarbons ( PAHs) of yet-to-be-cultured bacterial populations from chronically polluted intertidal sediments. Methods and Results A gene variant encoding the alpha subunit of the catalytic component of an aromatic-ring-hydroxylating oxygenase ( RHO) was abundant in intertidal sediments from chronically polluted subantarctic and temperate coastal environments, and its abundance increased after PAH amendment. Conversely, this marker gene was not detected in sediments from a nonimpacted site, even after a short-term PAH exposure. A metagenomic fragment carrying this gene variant was identified in a fosmid library of subantarctic sediments. This fragment contained five pairs of alpha and beta subunit genes and a lone alpha subunit gene of oxygenases, classified as belonging to three different RHO functional classes. In silico structural analysis suggested that two of these oxygenases contain large substrate-binding pockets, capable of accepting high molecular weight PAHs. Conclusions The identified uncultured micro-organism presents the potential to degrade aromatic hydrocarbons with various chemical structures, and could represent an important member of the PAH-degrading community in these polluted coastal environments. Significance and Impact of the Study This work provides valuable information for the design of environmental molecular diagnostic tools and for the biotechnological application of RHO enzymes. [ABSTRACT FROM AUTHOR]

Denitrification plays a critical role in nitrogen removal in estuarine and coastal ecosystems. In this study, the community composition, diversity, abundance, and distribution of cytochrome cd1-type nitrite reductase gene ( nirS)-harboring denitrifiers in intertidal sediments of the Yangtze Estuary were analyzed using polymerase chain reaction (PCR)-based clone libraries and quantitative PCR techniques. Clone library analysis showed that the nirS-encoding bacterial biodiversity was significantly higher at the lower salinity sites than at the higher salinity sites. However, there was no significant seasonal difference in the nirS gene diversity between summer and winter. Phylogenetic analysis revealed that the nirS-harboring denitrifier communities at the study area had distinctive spatial heterogeneity along the estuary. At the lower salinity sites, the nirS-harboring bacterial community was co-dominated by clusters III and VII; while at the higher salinity sites, it was dominated by cluster I. Canonical correspondence analysis indicated that the community compositions of nirS-type denitrifiers were significantly correlated with salinity, ammonium, and nitrate. Quantitative PCR results showed that the nirS gene abundance was in the range of 1.01 × 10 to 9.00 × 10 copies per gram dry sediment, without significant seasonal variation. Among all the environmental factors, the nirS gene abundance was only significantly related to the change of salinity. These results can extend our current knowledge about the composition and dynamics of denitrification microbial community in the estuarine ecosystem. [ABSTRACT FROM AUTHOR]

Coastal sediments are important sources of dissolved iron (dFe) that make the coastal ocean iron replete, and contribute an important supply of dFe to the photic regions of the adjacent open ocean. The biogeochemical processes that dictate sedimentary dFe flux are a complex interplay of microbial activities related to reduction-oxidation condition, Fe and S cycling, and sediment bio-mixing and bio-irrigation by benthic fauna. We investigated the effect of bottom water oxygen concentration on iron dynamics in laboratory mesocosms in the presence and absence of the common polychaete Nereis diversicolor. Mesocosms were established using sediment obtained from a local intertidal mudflat, maintained with varying levels of hypoxia (defined as <63 μM dissolved O 2), and monitored for changes in iron biogeochemistry. At the end of the experiment, subcores were taken to measure solid phase Fe species and microbial community analysis via 16S rDNA gene sequencing. Bioturbation played an important role in increasing the quantity of poorly crystalline Fe(III)-oxides within the sediments, but decreasing the flux of Fe(II) across the sediment-water interface. These results further demonstrate the importance of bioturbation for sedimentary Fe-cycling and show a complex response to hypoxia involving both animal behavior and microbial response. • The biogeochemical effects of hypoxia on benthic fauna are poorly understood. • Increasing hypoxia reduced accumulation of reactive iron oxides in animal burrows. • Short-term bioturbation minimally impacted microbes involved in Fe–S cycling. • Increased hypoxia can disrupt the marine sedimentary iron cycle. [ABSTRACT FROM AUTHOR]