Coastal Sediments Research Articles

Natural Variations in the Benthic Environment and Bacterial Communities of Coastal Sediments around Aquaculture Farms in South Korea.

The online version contains supplementary material available at 10.1007/s12088-023-01067-8.

Responses of coastal sediment organic and inorganic carbon to habitat modification across a wide latitudinal range in southeastern China

Coastal wetlands are important to the global carbon (C) budget and climate regulation. Plant invasion and aquaculture reclamation have drastically transformed China’s coastal wetlands, but knowledge of the effects on sediment carbon remains limited. We sampled top layer sediments (0–20 cm) in 21 coastal wetlands in southeastern China across the tropical-subtropical climate gradient, that have experienced the same sequence of habitat transformation from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to aquaculture ponds (APs). We measured the sediment carbon contents and ancillary physicochemical parameters. Landscape change from MFs to SAs increased sediment organic carbon (SOC) but decreased sediment inorganic carbon (SIC) content, whereas conversion of SAs to APs resulted in the opposite changes. Based on stepwise regression analysis, ammonium concentration and particle size distribution were the common factors that affected changes in SOC between habitat types, whereas for SIC it was ammonium and chloride concentrations. Habitat change affected SOC to a larger degree than SIC. Overall, invasion of MFs by SAs increased total carbon storage in the top sediment by 22%, or 6.6 × 106 g C ha−1; conversion of SAs to APs decreased it by 9.7%, or 3.5 × 106 g C ha−1. Our results showed the differential effects of different habitat modification scenarios on the sediment carbon pools and help assess how landscape-scale change affects terrestrial carbon budget and emission in the context of global climate change.

Metagenomes from Coastal Sediments of Kuwait: Insights into the Microbiome, Metabolic Functions and Resistome.

Coastal sediments in the proximity of wastewater and emergency outfalls are often sinks of pharmaceutical compounds and other organic and inorganic contaminants that are likely to affect the microbial community. The metabolites of these contaminants affect microbial diversity and their metabolic processes, resulting in undesirable effects on ecosystem functioning, thus necessitating the need to understand their composition and functions. In the present investigation, we studied the metagenomes of 12 coastal surface sediments through whole genome shot-gun sequencing. Taxonomic binning of the genes predicted about 86% as bacteria, 1% as archaea, >0.001% as viruses and Eukaryota, and 12% as other communities. The dominant bacterial, archaeal, and fungal genera were Woeseia, Nitrosopumilus, and Rhizophagus, respectively. The most prevalent viral families were Myoviridae and Siphoviridae, and the T4 virus was the most dominant bacteriophage. The unigenes further aligned to 26 clusters of orthologous genes (COGs) and five carbohydrate-active enzymes (CAZy) classes. Glycoside hydrolases (GH) and glycoside transferase (GT) were the highest-recorded CAzymes. The Kyoto Encyclopedia of Genes and Genomes (KEGG) level 3 functions were subjugated by purine metabolism > ABC transporters > oxidative phosphorylation > two-component system > pyrimidine metabolism > pyruvate metabolism > quorum sensing > carbon fixation pathways > ribosomes > and glyoxalate and dicarboxylate metabolism. Sequences allying with plasmids, integrons, insertion sequences and antibiotic-resistance genes were also observed. Both the taxonomies and functional abundances exhibited variation in relative abundances, with limited spatial variability (ANOVA p > 0.05; ANOSIM-0.05, p > 0.05). This study underlines the dominant microbial communities and functional genes in the marine sediments of Kuwait as a baseline for future biomonitoring programs.

Protracted dynamicity of microplastics in the coastal sediment of the Southeast Black Sea

This study provided the first evaluation of microplastic abundance, features, risk assessment, and decade-changing status in sediment along the southeastern Black Sea coast. Sediment samples were collected from thirteen stations in the Southeast Black Sea in 2012 and 2022. >70 % of the detected microplastics had a length of up to 2.5 mm and consisted of fragments and fibers in shape. The average microplastic abundance in the sediment samples was 108 MP/kg. The composition in the sediment (particles/kg) was dominated by polyethylene (PE) (44.9 %), polyethylene terephthalate (PET) (27.2 %), and polypropylene PP (15.2 %). Remarkable results for contamination factors, polymeric risk assessment and contamination risk indices. The sharp rise in MPS highlighted the heavily populated stations and stream discharge locations. The data shed light on anthropogenic and basal microplastic pollution in the Southeast Black Sea, assisting in developing effective policies for preserving and managing the Black Sea environment.

Marine Fungi Select and Transport Aerobic and Anaerobic Bacterial Populations from Polycyclic Aromatic Hydrocarbon-Contaminated Sediments.

The organization of microbial communities in marine sediment relies on complex biotic and abiotic interactions. Among them, the interaction between fungi and bacteria plays a crucial role building specific microbial assemblages, resulting in metabolic networks adapted to environmental conditions. The fungal-bacterial interaction (FBI) includes bacterial translocation via fungal mycelia, allowing bacterial dispersion, and ecological niche colonization. In order to demonstrate that the translocation of bacteria through fungal mycelia involves bacterial selection, the mycelia of two fungi isolated from marine coastal sediment, Alternaria destruens F10.81 and Fusarium pseudonygamai F5.76, showing different strategies for uptake of polycyclic aromatic hydrocarbon (PAH), homogenous internalization and vacuole forming respectively, were used to translocate bacteria through hydrophobic hydrocarbon contaminated sediments. A. destruens F10.81 selected four specific bacteria, while bacterial selection by F. pseudonygamai F5.76 was not evident. Among the bacteria selected by A. destruens F10.81, Spirochaeta litoralis, known as strictly anaerobic bacterium, was identified, indicating that A. destruens F10.81 selects and transports both aerobic and anaerobic bacteria. Such a result is consistent with the observed formation of anoxic micro-niches in areas surrounding and affected by fungal hyphae. Our findings provide new insights on the selection and dispersion of bacterial communities by fungi, which are crucial for the organization of microbial communities and their functioning in coastal PAH-contaminated sediments. IMPORTANCE The study provides advances for understanding fungal-bacterial relationships, particularly on the selection and dispersion of bacterial communities by fungi, which are crucial for the organization of microbial communities and their functioning in coastal PAH-contaminated sediments. The transportation of bacteria via fungal hyphae (fungal highway) results in bacterial selection; in particular, fungal hyphae offer adequate conditions for the transport of both aerobic and anaerobic bacteria through hydrophobic patches for the colonization of novel niches.

Identifying and protecting macroalgae detritus sinks toward climate change mitigation.

Harnessing natural solutions to mitigate climate change requires an understanding of carbon fixation, flux, and sequestration across ocean habitats. Recent studies have suggested that exported seaweed particulate organic carbon is stored within soft-sediment systems. However, very little is known about how seaweed detritus disperses from coastlines, or where it may enter seabed carbon stores, where it could become the target of conservation efforts. Here, focusing on regionally dominant seaweed species, we surveyed environmental DNA (eDNA) from natural coastal sediments, and studied their connectivity to seaweed habitats using a particle tracking model parameterized to reproduce seaweed detritus dispersal behavior based on laboratory observations of seaweed fragment degradation and sinking. Experiments showed that seaweed detritus density changed over time, differently across species. This, in turn, modified distances traveled by released fragments until they reached the seabed for the first time, during model simulations. Dispersal pathways connected detritus from the shore to the open ocean but, importantly, also to coastal sediments, and this was reflected by field eDNA evidence. Dispersion pathways were also affected by hydrodynamic conditions, varying in space and time. Both the properties and timing of released detritus, individual to each macroalgal population, and short-term near-seabed and medium-term water-column transport pathways, are thus seemingly important in determining the connectivity between seaweed habitats and potential sedimentary sinks. Studies such as this one, supported by further field verification of sedimentary carbon sequestration rates and source partitioning, are still needed to help quantify the role of seaweed in the ocean carbon cycle. Such studies will provide vital evidence to inform on the potential need to develop blue carbon conservation mechanisms, beyond wetlands.

Regional-scale site characterization mapping in high impedance environments using soil fundamental resonance (f0): New England, USA

In this work, we develop regional-scale site characterization maps of New England, a glaciated region in the Eastern United States, using site fundamental frequency (f0). Due to the strong impedance contrast that creates strongly resonant site response behavior in New England, f0 is the preferred site response proxy for the region and best characterizes spatial variability in soil amplification. We first develop a database of 1577 f0 values collected from the literature (1313) and picked from HVSR curves collected during an additional field campaign (487). Using the surficial geologic units from the conterminous US surficial geology map, we compute distributions of f0 for each of the surficial geologic units mapped in New England. We find that the thick glaciofluvial ice-contact sediments and thick proglacial sediments of Cape Cod and Long Island are characterized by f0 distributions with the lowest medians (1.06 and 1.03 Hz respectively) and narrowest interquartile ranges (0.23 and 0.28 Hz respectively) in New England, which we interpret as being the thickest sediments in the region. The f0 distribution of the thin, proglacial sediments, mostly fine-grained in the Boston Basin, the coast of Lake Champlain and the Maine coast has a relatively low median (2.70 Hz), however it has high variability (3.65 Hz interquartile range) since the sediment thickness varies widely in this geologic unit. The f0 distribution of the thin alluvial sediments of the Connecticut River Valley also has a low f0 median (1.83 Hz) however, it has less variability than the proglacial sediments, mostly fine-grained thin (1.59 Hz). We present maps of the median and interquartile range of the f0 distributions and their corresponding Vs30 distribution approximations. Vs30 distributions are developed for each of the surficial geologic units by assuming a layer-over-halfspace model for site response and establishing estimates of sediment average shear-wave velocity (Vsavg) for each of the units based on a limited number of shear wave velocity profiles from the region. We compare our results against two existing site characterization maps for the region, Wald and Allen (2007) and Becker et al. (2011) and find that our updated maps result in median Vs30 values that tend to be higher than Becker et al. (2011) except in geologies with consistently deep profiles, and lower than Wald and Allen (2007) median values, with the exception of coastal zone sediments.

Are seafloor habitats influencing the distribution of microplastics in coastal sediments of a Marine Protected Area?

The marine environment is affected by the increasing presence of microplastics (MPs; < 5 mm), and the seafloor acts as a sink for these particles. Locations with different predominant seafloor habitat and protection level applied were selected from Cabrera Marine-Terrestrial National Park (henceforth, Cabrera MPA) (western Mediterranean Sea) with the aim to assess the distribution of MPs along the sediments of this Mediterranean MPA. A total of 37 samples were collected. A high diversity of sediment between locations was detected according to the Udden-Wentworth classification and locations were clustered into two main groups according to the predominance of different particle size fractions. The identification of MPs was carried out according to the sediment particle size classification. A total of 1431 MPs and a mean value (± SD) of 314.53 ± 409.94 items kg−1 D.W. were identified, and 70% of the particles were fibers. Statistically higher abundances of MPs were found in sediments collected from sandy habitats, with a mean value of 630.80 ± 636.87 items kg−1 D.W., compared to the abundances of MPs found in locations with different predominant seafloor habitats, that ranged from 136.79 ± 156.33 items kg−1 D.W. in habitats with similar predominance of seagrass and sand to 223.02 ± 113.35 items kg−1 D.W. in habitats with similar predominance of rocks and sand. The abundance of MPs regarding each sediment particle size fraction differed between years and locations, and the abundance of MPs according to each identified shape differed between sampling years, particle size fraction, and predominant seafloor habitat. The present study highlights the ubiquitous presence of MPs in seafloor sediments from a MPA. Furthermore, the results suggest that the predominant seafloor habitat can modulate the presence of MPs in marine environments in both general abundances and shape of items.

Environmental radioactivity assessment of the Brunei Darussalam coastline of the South China Sea

Radioactivity levels of naturally occurring radionuclides at the coast of Brunei Darussalam were evaluated along with their dose rates. Twenty-six berm and intertidal sediment samples were measured using gamma-ray spectrometry. The mean activity concentrations of 226Ra, 232Th and 40K in berm sediments were 10.07 ± 1.02 Bq/kg, below the minimum detectable activity, and 21.44 ± 1.23 Bq/kg, respectively, whereas for intertidal sediments they were 7.01 ± 0.87, 1.67 ± 0.15 and 4.99 ± 0.42 Bq/kg, respectively. With respect to the radiological health risk, the average hazard indices, absorbed gamma dose rate, effective dose equivalent, and excess lifetime cancer risk were found to be less than the global average. Calculation of the activity ratio showed that 40K is the main source of radiation in the coastal sediments. Furthermore, the difference in radioactivity levels between the berm sediments and intertidal sediments collected at the same location was investigated. Finally, a standard geological terminology of the littoral zone profile is proposed for describing coastal samples for universal communication among researchers.

The dispersal of fluvially discharged and marine, shelf-produced particulate organic matter in the northern Gulf of Mexico

Abstract. Rivers play a key role in the global carbon cycle by transporting terrestrial organic matter (TerrOM) from land to the ocean. Upon burial in marine sediments, this TerrOM may be a significant long-term carbon sink, depending on its composition and properties. However, much remains unknown about the dispersal of different types of TerrOM in the marine realm upon fluvial discharge since the commonly used bulk organic matter (OM) parameters do not reach the required level of source- and process-specific information. Here, we analyzed bulk OM properties, lipid biomarkers (long-chain n-alkanes, sterols, long-chain diols, alkenones, branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs and isoGDGTs)), pollen, and dinoflagellate cysts in marine surface sediments along two transects offshore the Mississippi–Atchafalaya River (MAR) system, as well as one along the 20 m isobath in the direction of the river plume. We use these biomarkers and palynological proxies to identify the dispersal patterns of soil–microbial organic matter (SMOM), fluvial, higher plant, and marine-produced OM in the coastal sediments of the northern Gulf of Mexico (GoM). The Branched and Isoprenoid Tetraether (BIT) index and the relative abundance of C32 1,15-diols indicative for freshwater production show high contributions of SMOM and fluvial OM near the Mississippi River (MR) mouth (BIT = 0.6, FC321,15 &gt; 50 %), which rapidly decrease further away from the river mouth (BIT &lt; 0.1, FC321,15 &lt; 20 %). In contrast, concentrations of long-chain n-alkanes and pollen grains do not show this stark decrease along the path of transport, and especially n-alkanes are also found in sediments in deeper waters. Proxy indicators show that marine productivity is highest close to shore and reveal that marine producers (diatoms, dinoflagellates, coccolithophores) have different spatial distributions, indicating their preferred niches. Close to the coast, where food supply is high and waters are turbid, cysts of heterotrophic dinoflagellates dominate the assemblages. The dominance of heterotrophic taxa in shelf waters in combination with the rapid decrease in the relative contribution of TerrOM towards the deeper ocean suggest that TerrOM input may trigger a priming effect that results in its rapid decomposition upon discharge. In the open ocean far away from the river plume, autotrophic dinoflagellates dominate the assemblages, indicating more oligotrophic conditions. Our combined lipid biomarker and palynology approach reveals that different types of TerrOM have distinct dispersal patterns, suggesting that the initial composition of this particulate OM influences the burial efficiency of TerrOM on the continental margin.

Nitrogen cycling activities during decreased stratification in the coastal oxygen minimum zone off Namibia.

Productive oxygen minimum zones are regions dominated by heterotrophic denitrification fueled by sinking organic matter. Microbial redox-sensitive transformations therein result in the loss and overall geochemical deficit in inorganic fixed nitrogen in the water column, thereby impacting global climate in terms of nutrient equilibrium and greenhouse gases. Here, geochemical data are combined with metagenomes, metatranscriptomes, and stable-isotope probing incubations from the water column and subseafloor of the Benguela upwelling system. The taxonomic composition of 16S rRNA genes and relative expression of functional marker genes are used to explore metabolic activities by nitrifiers and denitrifiers under decreased stratification and increased lateral ventilation in Namibian coastal waters. Active planktonic nitrifiers were affiliated with Candidatus Nitrosopumilus and Candidatus Nitrosopelagicus among Archaea, and Nitrospina, Nitrosomonas, Nitrosococcus, and Nitrospira among Bacteria. Concurrent evidence from taxonomic and functional marker genes shows that populations of Nitrososphaeria and Nitrospinota were highly active under dysoxic conditions, coupling ammonia and nitrite oxidation with respiratory nitrite reduction, but minor metabolic activity toward mixotrophic use of simple nitrogen compounds. Although active reduction of nitric oxide to nitrous oxide by Nitrospirota, Gammaproteobacteria, and Desulfobacterota was tractable in bottom waters, the produced nitrous oxide was apparently scavenged at the ocean surface by Bacteroidota. Planctomycetota involved in anaerobic ammonia oxidation were identified in dysoxic waters and their underlying sediments, but were not found to be metabolically active due to limited availability of nitrite. Consistent with water column geochemical profiles, metatranscriptomic data demonstrate that nitrifier denitrification is fueled by fixed and organic nitrogen dissolved in dysoxic waters, and prevails over canonical denitrification and anaerobic oxidation of ammonia when the Namibian coastal waters and sediment-water interface on the shelf are ventilated by lateral currents during austral winter.

End-member characteristics of sediment grain size in modern Yellow River delta sediments and its environmental significance

IntroductionThe sediments of the Yellow River delta record the environmental changes in the Yellow River basin on a long time scale and are sensitive to the river diversion and sedimentary environment evolution.MethodsIn this study, cores YDC and YDG in the delta near the estuary of the Yellow River since 1976 were taken as the research object, and the parameterized end-member analysis model was used to analyze the grain-size data of the cores.ResultsThe results show that: The main sediments were silty and sand (58% and 77.9%). The grain-size parameters showed opposite changes with wide grain-size ranges and mixed sizes obviously. End member 1 (EM1) and end member 2 (EM2) were composed of clay and fine silt with fine particle sizes of 0.04 mm and 9.8 mm, respectively, and were deposited under weak hydrodynamic conditions during long-distance transport along the Yellow River. End member 3 (EM3) and end member 4 (EM4) were coarse silt with mode particle sizes of 40.14 mm and 66.89 mm, respectively. These were deposited by waves and tidal currents under strong dynamic conditions.DiscussionAccording to the channel changes and the sedimentary facies data of the modern Yellow River delta, before the Yellow River was diverted in 1996, the cores YDC and YDG were both in the estuary-front bar sedimentary environment. In 1996, the Yellow River was diverted to the Qing 8 course. Subsequently, the core YDC changed to the delta-plain sedimentary facies, and the core YDG changed to the delta-front facies. The sediment sources of the two cores changed from the Yellow River sediments to coastal sediment erosion and resuspension. The sedimentary environment changed from siltation to erosion. The results of this study are of great practical significance for estuary management and coastal engineering construction in the modern Yellow River delta and can provide a scientific basis for ecological protection and high-quality development of the Yellow River basin.

Sources identification and distribution of aliphatic and aromatic hydrocarbons in coastal sediments of Arica Bay – Chile

ABSTRACT This study assesses the first approach regarding the origin, level of contamination, and spatial and vertical distribution of aliphatic and polycyclic aromatic hydrocarbons in coastal sediments of Arica’s Bay. Twenty-seven aliphatic hydrocarbons (AHs) and eighteen polycyclic aromatic hydrocarbons (PAHs) were studied at three depths in sediment cores collected from six locations in the coastal bay. The spatial distribution pattern of the molecular composition of aliphatic and aromatic hydrocarbons is consistent with the directions of the ocean currents from the northeast to the southwest. PAHs are mainly correlated with anthropogenic input sources to the bay. The total aliphatic hydrocarbons showed a wide concentration range from 112.07 to 2,382.43 ng·g−1 dry wt. while total PAHs ranged from 8.01 to 85.40 ng·g−1 dry wt. The vertical distribution of the total AHs shows a tendency to concentrate between 10–20 and 20–30 cm depth. Specific diagnostic characterisation ratios suggest that the bay sediments mainly consist of a mixture of autochthonous, predominantly marine sources composed of marine bacteria (n-C16, n-C18, and C20) and terrestrial plant derivatives (n-C29 and n-C31) and with a contribution of petrogenic hydrocarbons masked by biogenic hydrocarbons. The vertical distribution of the total polycyclic aromatic hydrocarbons is dominated by low molecular weight (LMW) PAHs of two and three rings, such as fluoranthene (FLT), phenanthrene (PHE), pyrene (PYR), and the highest concentrations are found between 10 and 20 cm depth of the sediment column. The PAH diagnostic ratios revealed a mixture of pyrogenic hydrocarbons (biomass and coal combustion) with petrogenic compounds from the Port of Arica and its neighbouring areas. According to the guidelines of UNEP for AHs and PAHs categorisation, the bay’s sediments may be classified from harmless to harmful due to AHs composition and low PAHs pollution.

Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn2+ or Mg2+. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. 57Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.

Potentially toxic elements (PTEs) in coastal sediments of Bandar Abbas city, North of Persian Gulf: An ecological risk assessment

ABSTRACT The concentration of potentially toxic elements (PTEs; Lead (Pb), Nickel (Ni), and Cadmium (Cd) Pb, Ni, and Cd), using flame atomic absorption spectrometry (FAAS) was measured in fifty surface coastal sediment samples collected from 5 points coastal sediment of Bandar Abbas city, Iran besides the potential ecological risk index (RI) estimated the environmental health risk. The rank order of PTEs was Pb (52.090 ± 4.113 mg/kg dry weight) > Ni (34.940 ± 8.344 mg/kg dry weight) > Cd (2.944 ± 0.013 mg/kg dry weight). RI due to PTEs in sediments for A, B, C, D, and E points were 187.655, 190.542, 191.079, 189.496, and 192.053, respectively. RI for sampling points A to E was at moderate risk (150 ≤ RI < 300). Therefore, it is recommended to carry out control programs to reduce the amount of PTEs in the coastal sediment of the Persian Gulf.

Seasonal variations in textural characteristics and depositional environment of foreshore sediments along Kerala Coast, India

The study investigates textural characteristics of foreshore sediment along the central Kerala coast. The selected beaches extend from Ponnani in the north to Alleppey in the south along the west coast of India. Samples were collected from foreshore zone at 22 selected locations to assess sediment grain size distribution and its seasonality. Statistical parameters such as mean (M), standard deviation (SD), skewness (Sk), and kurtosis (K) were used to evaluate the textural characteristics. The purpose of the present study was to examine the textural behaviour of coastal sediments in different seasons from November 2014 to October 2015. Textural characteristics show that the sediment samples are unimodal and bimodal with medium and fine grain sand. The standard deviation (sorting) reveals the sediment samples are very well sorted to moderately sorted with a range of 0.24 phi to 1.03 phi, while the skewness values of the sediment samples range from −0.55 phi to 0.32 phi. The CM plot depicts that the foreshore sediments are transported by tractive currents and transporting the sediments by rolling, bottom suspension with rolling. The analysis of Linear Discriminant Function (LDF) illustrates that the sediment samples are accumulated by aeolian or coastal and shallow turbulent environments.

Increased Nitrogen Loading Facilitates Nitrous Oxide Production through Fungal and Chemodenitrification in Estuarine and Coastal Sediments.

Estuarine and coastal environments are assumed to contribute to nitrous oxide (N2O) emissions under increasing nitrogen loading. However, isotopic and molecular mechanisms underlying N2O production pathways under elevated nitrogen concentration remain poorly understood. Here we used microbial inhibition, isotope mass balance, and molecular approaches to investigate N2O production mechanisms in estuarine and coastal sediments through a series of anoxic incubations. Site preference of the N2O molecule increased due to increasing nitrate concentration, suggesting the changes in N2O production pathways. Enhanced N2O production under high nitrate concentration was not mediated by bacterial denitrification, but instead was mainly regulated by fungal denitrification. Elevated nitrate concentration increased the contribution of fungal denitrification to N2O production by 11-25%, whereas it decreased bacterial N2O production by 16-33%. Chemodenitrification was also enhanced by high nitrate concentration, contributing to 13-28% of N2O production. Elevated nitrate concentration significantly mediated nirK-type denitrifiers structure and abundance, which are the keystone taxa driving N2O production. Collectively, these results suggest that increasing nitrate concentration can shift N2O production pathways from bacterial to fungal and chemodenitrification, which are mainly responsible for the enhanced N2O production and have widespread implications for N2O projections under ongoing nitrogen pollution in estuarine and coastal ecosystems.

Glass microbeads in coastal sediments as a proxy for traffic-related particulate contamination

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.

Characteristics of metal pollution and multi-isotopic signatures for C, Cu, Zn, and Pb in coastal sediments from special management areas in Korea

The concentrations and isotopic compositions of carbon (C), copper (Cu), zinc (Zn), and lead (Pb) in coastal sediments were analyzed to identify potential pollution sources. High concentrations of total organic carbon (TOC) and metals were found close to cities and industrial areas. The isotopic compositions of C, Cu, Zn, and Pb tended to decrease as their concentrations increased. Bi-plots between δ65Cu and δ66Zn showed that the isotopic compositions in most coastal sediments, except sediments around a smelter, were similar to the isotopic compositions of road dust in urban and industrial areas of Korea. Our results suggest that heavy metal pollution in coastal sediments is greatly influenced by the pollution source, such that most metals originate from traffic and industrial activities in the urban environment. This analysis of multiple isotopes provides insights concerning the transport mechanisms and clarifies potential sources of metal contamination in coastal environments.

Contamination and Risk Assessment of Potentially Toxic Elements in Coastal Sediments of the Area between Al-Jubail and Al-Khafji, Arabian Gulf, Saudi Arabia

Coastal environments need continuous environmental risk assessment, especially with increasing coastal development and human activities. The present work evaluates the distribution, contamination, and environmental risk of potentially toxic elements (PTEs) in coastal sediments between Al-Jubail and Al-Khafji cities along the Arabian Gulf, Saudi Arabia, and documents the influence of background references applied in pollution indices. Thirty-two sediment samples were collected for analysis of Ni, Cu, Cr, As, Zn, Pb and Hg using ICP-AES. The ranges of PTEs (mg/kg) were in the following order: Cr (3.00–20.0), Ni (2.00–32.0), Zn (2.00–14.0), As (2.00–4.00), Pb (1.50–5.00), Cu (1.00–5.00), and Hg (0.50–1.00). The coastal sediments show severe enrichment with As and Hg, and no to minor enrichment and a low contamination with Cr, Cu, Cr, Zn, and Pb. Based on sediment quality guidelines, concentrations of Cu, Pb, Zn, As, and Cr do not represent a concern for benthic communities, while Ni and Hg show a risk for benthic communities in four and 17 sampled areas, respectively. Multivariate analysis indicated a geogenic source for Zn, Cr, Cu, Ni, and Pb, mixed natural and anthropogenic sources for As, and an anthropogenic source for Hg, mostly from oil pollution, sewage, and industrial effluents spreading near Al-Jubail industrial city.