The origins of sediment organic matter (SOM) and their contributions were studied in three contrasting wetlands (mudflat, estuarine and mangrove) of Daya Bay, South China Sea. Lower sediment δ13C but higher δ15N values were observed in coastal wetland than in offshore water of the bay. Greater terrigenous organic matter (TOM) contribution to SOM was observed in lower tidal area in mudflat and estuarine wetland. Higher concentrations of total organic carbon and total nitrogen in the three wetlands, as well as lower sediment δ13C, were found in the wet season. Extremely lower sediment δ15N with higher seawater ammonia were observed in estuarine wetland than in mudflat and mangrove, which was caused by the input of 15N-depleted ammonia from petrochemical industrial wastewater. Mangrove contributed substantially to SOM, with a larger contribution in mangrove area than in non-mangrove area. The mean contribution of TOM to SOM was lower in mangrove than in mudflat.

Ocean acidification is known to affect primary producers differentially in terms of species and environmental conditions, with controversial results obtained under different experimental setups. In this work we examined the physiological performances of the coccolithophore Gephyrocapsa oceanica that had been acclimated to 1000 μatm CO₂ for ~400 generations, and then exposed to multiple drivers, light intensity, light fluctuating frequency, temperature and UV radiation. Here, we show that increasing light intensity resulted in higher non-photochemical quenching and the effective absorption cross-section of PSII. The effective photochemical efficiency (Fv′/Fm′) decreased with increased levels of light, which was counterbalanced by fluctuating light regimes. The greenhouse condition acts synergistically with decreasing fluctuating light frequency to increase the Fv′/Fm′ and photosynthetic carbon fixation rate. Our data suggest that the coccolithophorid would be more stressed with increased exposures to solar UV irradiances, though its photosynthetic carbon fixation could be enhanced under the greenhouse condition.

We present a study of small microplastic particles (S-MPPs) in the sediments of mangrove ecosystem of Khor-e- Khoran, a Ramsar site in Iran. The spatial distribution of S-MPPs (<1 mm) in mangrove surface sediments were investigated, which provided new insights into the detection and composition of S-MPPs in the study area. S-MPPs were extracted via the air-induced overflow (AIO) extraction procedure, and then they were counted and categorized according to the particle shape, color and size. The mean number of S-MPPs at the five sampling sites ranged from 19.5 to 34.5 particles per kg dry sediment in Bandar Gelkan and Bandar Lengeh, respectively. In general, microfibres followed by fragments were the most common type of S-MPPs isolated in each site (>56% and ~35%, respectively). Sewage discharge is probably the main source of extracted fibres in almost all the sites. The observed S-MPPs were classified into two size groups (10–300 μm and 300–1000 μm). The majority of S-MPPs fell into the smallest size group which accounted for 70–97% of the total S-MPPs. Fourier transform infrared (FTIR) analysis of some subsamples showed that polyethylene (PE) was the most common recovered polymer. Some non-plastic particles were also isolated from plastic-like particles of suspected S-MPPs in the mangrove sediments using a Scanning Electron Microscope (FE-SEM). This study provided the first evidence of S-MPPs contamination in the mangroves of the Iranian coast of the Persian Gulf. Long-term studies are required to understand, monitor and prevent further microplastics pollution in the region.

The temporal and spatial distributions of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi), and their long-term changes were investigated in Bohai Bay (BHB) in spring, summer, and autumn (2013–2014). The high DIN values were consistently distributed in the western inshore waters, mainly determined by terrestrial factors, e.g., riverine input, while DIP and DSi were mostly distributed in the southern coastal waters, the central BHB, or near the sea port Caofeidian in northern BHB, largely related to non-terrestrial factors, e.g., sediment release. Based on the nutrient distribution, BHB could be partitioned into western and eastern parts, with −15 m depth as the separation. The long-term variations of nutrients since 2000 showed an increase in DIN and decreases in DIP and DSi. Relatively slow changes in DIN and DIP and a rapid decrease in DSi were exhibited in summer, which was associated with precipitation and sediment release.

Biodegradation is important for the fate of oil spilled in marine environments, yet parameterization of biodegradation varies across oil spill models, which usually apply constant first-order decay rates to multiple pseudo-components describing an oil. To understand the influence of model parameterization on the fate of subsurface oil droplets, we reviewed existing algorithms and rates and conducted a model sensitivity study. Droplets were simulated from a blowout at 2000 m depth and were either treated with sub-surface dispersant injection (2% dispersant to oil ratio) or untreated. The most important factor affecting oil fate was the size of the droplets, with biodegradation contributing substantially to the fate of droplets ≤0.5 mm. Oil types, which were similar, had limited influence on simulated oil fate. Model results suggest that knowledge of droplet sizes and improved estimation of pseudo-component biodegradation rates and lag times would enhance prediction of the fate and transport of subsurface oil.

The objective was to compare the different effects of essential element Cu and non-essential element Hg on antioxidant and inflammatory responses in the liver of large yellow croaker Larimichthys crocea. Fish were exposed to Cu stresses (72 and 288 μg L−1) and Hg stresses (14 and 56 μg L−1) for 96 h. High-dose Cu increased metallothioneins (MTs) levels and immune defenses in response to elevated reactive oxygen species (ROS), but low-dose Cu had no effect on ROS. High-dose Hg reduced antioxidant and inflammatory responses, which contributed to the increment of ROS. MTs may be a suitable biomarker to assess Cu contamination, but no relationship was observed between MTs levels and Hg content. Furthermore, NFE2-related nuclear factor 2 (Nrf2) and nuclear transcription factor κB (NF-κB) were positively related to their respective target genes in the Cu-exposed groups. In conclusion, Cu and Hg induced some differences in antioxidant and inflammatory responses, which providing some novel insights into toxicological effects of Cu and Hg stresses.

Microbial communities in wetland soils play vital roles in biogeochemical cycling of nutrients. In this study, the soil samples were collected from Suaeda, reed and Suaeda-reed hybrid zones in Shuangtaizi River Estuary, Northeast China, and the rhizosphere bacterial communities were compared using Illumina MiSeq sequencing. The microbial richness, diversity and structure of bacterial communities varied greatly in reed and Suaeda. Canonical correspondence analysis and Mantel test indicated that pH was the most significant factor (P < 0.05) in bacterial community assembly. Proteobacteria was the most dominant phylum, accounting for 45.7–58.0% of the total sequences. Thioprofundum, Thiohalomonas and Exiguobacterium were the predominant genera in Suaeda, while Exiguobacterium, Gillisia, Desulfomonile, Citrobacter, Thioprofundum and Acinetobacter were the core species in reed. PICRUSt analysis revealed similar functional profiles of rhizosphere microbiota in reed and Suaeda. Nitrate reduction related genes were abundant for nitrogen metabolism, whereas assimilatory sulfate reduction was the major process for sulfur metabolism.

Total metal concentrations and acid-volatile sulfide (AVS) measurements coupled with simultaneously extracted metals (SEM) were determined in heterogeneous sediments from Maluan Bay, China. Zn was the predominant component of SEM, while Cd was the least. In sediment cores, AVS increased with sediment depth, followed by a decrease with large variation, while SEM fluctuated. Multiple empirical sediment quality guidelines (SQGs) and equilibrium partitioning (EqP) approaches were applied to assess the contamination degree, sediment quality and potential risks associated with bioavailable metals, indicating that not all sediments with [SEM]-[AVS] > 0 were capable of causing toxicity because TOC is also an important metal-binding phase. In order to screen out the physicochemical variability and the complexity and large variance of datasets, multivariate statistical techniques were utilized to comprehensively reveal pollution status by visualized factor scores. Collectively, this study favors the integrative utilization of multifarious methods to scientifically diagnose the pollution characterization for sustainable coastal management.