This study was carried out to evaluate the present-day chemical properties of methylmercury in surface sediment in Minamata Bay where a dredging project was completed 28years ago. Present-day sediment from Minamata Bay consists of sandy silt, and the average loss-on-ignition in surface sediment was 7.0±2.3%. The average methylmercury concentrations in the upper sediment layers were significantly higher than those in the lower sediment layers. Currently, the concentrations in sediments in Minamata Bay do not exceed the Japanese regulatory standard value for mercury. The average concentration of methylmercury in Minamata Bay surface sediment was 1.74±1.0ng/g on a dry weight basis (n=107). The methylmercury concentration in Minamata Bay surface sediment was almost 16 times higher than that in surface sediment from Isahaya Bay surface sediment, which was 0.11±0.045ng/g on a dry weight basis (n=5).

Investigations carried out on surface sediments collected from the Anaximander mud volcanoes in the Eastern Mediterranean Sea to determine sedimentary and geochemical properties. The sediment grain size distribution and geochemical contents were determined by grain size analysis, organic carbon, carbonate contents and element analysis. The results of element contents were compared to background levels of Earth’s crust. The factors that affect element distribution in sediments were calculated by the nine push core samples taken from the surface of mud volcanoes by the E/V Nautilus. The grain size of the samples varies from sand to sandy silt. Enrichment and Contamination factor analysis showed that these analyses can also be used to evaluate of deep sea environmental and source parameters. It is concluded that the biological and cold seep effects are the main drivers of surface sediment characteristics from the Anaximander mud volcanoes.

Baseline data on anthropogenic seafloor debris contamination in the year 2000 is provided for 24 submersible video transects at depths of 80–900m, off the Dutch ABC-islands (Aruba, Bonaire, Curaçao), in the southeastern Caribbean Sea. In total, 202 objects were documented from a combined 21,184m of transect, ranging from sandy lower island-slope to rocky upper island-slope habitat. Debris densities differed significantly with depth. Highest debris accumulation (0.459 items 100m−2 or 4590 items per km2) occurred at depths of 300–600m on more shallow-sloping (20–30°) sand and silt bottoms. The overall average debris density was 0.27 objects per 100m2 (or 2700 items per km2), which is an order of magnitude higher than most other deepwater debris studies. What we describe may be representative for other small, populated, steep volcanic Caribbean islands. Food and beverage-related items were the single largest usage category identified (44% of objects; mostly glass beverage bottles).

The microbial community and the nirS- and nirK-encoding denitrifiers in the intertidal sediments along Laizhou Bay in China were studied using pyrosequencing and real-time quantitative PCR (qPCR), respectively. There were three primary intertidal zones: Laizhou (La), Weifang Harbor (We), and Dongying (Do). Significant differences in composition and abundances at the different taxonomic levels were observed among the three bacterial communities. The qPCR results indicated that the nirS gene abundance varied from 8.67×105 to 5.68×106copies/gwet weight (ww), whereas the nirK gene abundance varied from 1.26×105 to 1.89×106copies/gww. The canonical correlation analysis (CCA) indicated that the sand percentage was the most important factor in shaping the bacterial community followed by silt percentage, NO2−, TOC, DO, pH, and clay percentage, whereas the clay percentage, pH, NO3−, DO, NO2−, TOC, silt percentage, and sand percentage were the most important factors associated with regulating the abundance of nirS- and nirK-encoding denitrifiers.

The extreme 2010–2011 wet season resulted in highly elevated Burdekin River discharge into the Great Barrier Reef lagoon for a period of 200days, resulting in a large flood plume extending >50km offshore and >100km north during peak conditions. Export of suspended sediment was dominated by clay and fine silt fractions and most sediment initially settled within ∼10km of the river mouth. Biologically-mediated flocculation of these particles enhanced deposition in the initial low salinity zone. Fine silt and clay particles and nutrients remaining in suspension, were carried as far as 100km northward from the mouth, binding with planktonic and transparent exopolymer particulate matter to form large floc aggregates (muddy marine snow). These aggregates, due to their sticky nature, likely pose a risk to benthic organisms e.g. coral and seagrass through smothering, and also by contributing to increased turbidity during wind-induced resuspension events.

Surface sediments from intertidal Bohai Bay were sampled for the geochemical and environmental assessment of six trace metals (Cd, Cr, Cu, Ni, Pb and Zn). Results indicate that sediment grain size plays an important role in controlling the distribution and fractionation of them. Metal concentrations in clayey silt sediments are all clearly higher than in sand and silty sand ones. Cd and Pb in clayey silt sediments are more mobile than in sand and silty sand ones. Two sediment quality guidelines and two geochemical normalization methods (index of geoaccumulation and enrichment factor) were used to judge the potential risk and accumulation of metals. According to the mean probable effects level quotient, the combination of studied metals may have a 21% probability of being toxic. The sediments with high fraction of clay and silt have been contaminated by trace metals to various degrees, among which Cr contributes the most to contamination.

Ten surficial sediment samples (up to a depth of 3 cm) were randomly collected during the pre-monsoon and analyzed for nine heavy metals using an atomic absorption spectrophotometer (AAS) to assess the distribution, contamination levels, and potential sources of heavy metals. The particle size distribution of the sediments was also investigated using a laser particle size analyzer. The mean concentration (mg/kg) of the analyzed metals followed a decreasing order of Fe (4706.24) > Mn (95.20) > Cu (36.97) > Zn (20.65) > Ni (9.26) > Cr (7.20) > Pb (5.63) > Co (5.52) > Cd (0.29). Surficial sediment of the Island was low to moderately contaminated by Cd and, to a laser extent by Cu in terms of enrichment factor (EF), geo-accumulation index (Igeo), and contamination factor. Ecologically, the Nijhum Dweep area was at low to moderate risk, where Cd was the most potential ecological risk factor. The Pearson correlation analysis revealed a significant positive correlation among Cr, Pb, Zn, Mn, Cd, Fe, Co, Ni, and silt particles, whereas a negative correlation with sand particles. No correlation was found with Cu and other metals except clay particles.

This work presents the structural and functional traits of benthic amphipods in the Saudi waters of the Arabian Gulf. Sixty-two species belonging to 37 genera and 17 families were recorded. Sensitive species such as Grandidierella bonnieroides, G. exilis, Gammaropsis atlantica and Caprellidea indet., were mostly dominant. The average values of richness, density and diversity (H′ log₂) were 11 ± 1, 512 ± 232 ind. m-2 and 3.1 ± 0.1 respectively. The density decreased with increased in depth (nearshore (NS) - 784 ± 445 and offshore (OS) - 222 ± 28, p = 0.023), while evenness (NS – 0.93 and OS -0.94) and diversity (NS – 3.10 and OS - 3.18) were unaffected by depth. Interstitial space dwellers (56.76%) and surface deposit feeders (60.16%) were dominant in the nearshore sand substratum. However, domicolous (72.2%) with suspension and surface deposit feeders (71.7%) were more in offshore silt sediments. The combination of depth, pH and TPH (p = 0.249) influenced the distribution of amphipods.

Ten surface sediments collected from Joanes River, Bahia, Brazil in rainy and drought periods in 2019 were evaluated according to the enrichment factor (EF), potential ecological risk index (RI), potential contamination index (PCI), pollution load index (PLI), and index of geoaccumulation (Igₑₒ). Initially the dry sediment was subjected to granulometric analysis and determination of the concentration of organic matter. Then, the samples were digested in HNO₃ and analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) to determine the metals cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb) and zinc (Zn). Zn and Cu were classified in that order as the most contaminated elements in most sediment. Comparison of the total metal concentrations with the threshold (TELs) and probable (PELs) effect levels in sediment quality guidelines suggested a more worrisome situation for Zn (648.83–1415.90 μg g⁻¹; PELZₙ = 315 μg g⁻¹), of which concentrations were occasionally associated with adverse biological effects in four sediments, followed by Cu in five sediments during dry and rainy periods; while adverse effects were rarely associated with Cd, Cr, Ni, and Pb. In another evaluation, Cd, Cu, Cr, and Zn could be considered the most dangerous in the entire river, as they were classified in the high levels of contamination by the PCI, associated with serious adverse effects in most samples. In an assessment regarding the ecological risks in the study environment, the sediment samples remained below the limit established by the risk index (IR). The Zn presented moderately severe enrichment (6.78–11.83) in all the collection stations in the dry and rainy periods, followed by the Cd that presented moderate enrichment (2.23–4.17), whose values exceeded almost 1000 times the background at one site. Through the PCA it was possible to evidence the existing correlation between metals, organic matter, and silt and clay fraction. The results obtained in the PCA represented more than 80% of the variance between the data. The environmental risk assessment revealed a significant increase in the risk associated with metals during the rainy season. This is probably due to the greater supply of organic matter from the leaching of the margins.

To investigate the effects of the water-sediment regulation on the spatial variations of metals in the surface sediments of the Yellow River Estuary (YRE), sampling sites were set in 2015 (51 sites in June and 33 in October). The content of Cu, Pb, Cd, Cr, Zn, Ni and Mn was determined using inductively coupled plasma spectrometry and of Hg and As atomic fluorescence spectrometry. The results showed that the concentrations of metals in the sediments of YRE were lower after the regulation, while that of most metals increased in the tidal areas of the current estuary with fine particles. Environmental pollution and ecological risk of metals were mainly from Hg and Cd. Metals carried with the silt of the river should be focused. The findings were expected to update the current status of metal pollution of YRE and be helpful for the delicacy management of the regime and silt-laden rivers.