Phytoplankton community structure and environmental factors during the outbreak of Crown-of-Thorns Starfish in Xisha Islands, South China Sea.

The "larval starvation hypothesis" proposed that the growing frequency of Crown-of-Thorns Starfish (CoTS) outbreaks could be attributed to increased availability of phytoplankton. However, comprehensive field investigation on the living environment of CoTS larvae and the availability of phytoplankton are still lacking. A cruise was conducted in June 2022 in Xisha Islands, South China Sea, to study the interaction between environmental conditions and phytoplankton communities during CoTS outbreak period. The average concentrations of dissolved inorganic phosphorus (0.05 ± 0.01 µmol L-1), dissolved inorganic nitrogen (0.66 ± 0.8 µmol L-1) and chlorophyll a (0.05 ± 0.05 µg L-1) suggested that phytoplankton may be limited for CoTS larvae in Xisha Islands. Microscopic observation and high-throughput sequencing were used to study the composition and structure of the phytoplankton communities. Bacillariophyta predominated in phytoplankton communities with the highest abundance and species richness. 29 dominant species, including 4 species with size-range preferred by CoTS larvae, were identified in Xisha Islands. The diversity index of all stations indicated a species-rich and structure-stable phytoplankton community in Xisha Islands during the period of CoTS outbreak, which may contribute to CoTS outbreak. These findings revealed the structure of phytoplankton community and environmental factors in the study area during CoTS outbreak, providing the groundwork for future research into the causes and processes of CoTS outbreak.

Characterization, source identification, risk assessment of potentially toxic elements (PTEs) in the surface water and sediment of the Beibu Gulf, China.

The concentrations, distribution, and risk of seven potentially toxic elements (PTEs), including As, Cd, Cr, Cu, Hg, Pb, and Zn, in seawater and sediment from the eastern Beibu Gulf of China were studied using national standard methods. Results showed that the concentrations of PTEs in seawater exhibited significant spatial and seasonal variations, resulting in tolerable non-carcinogenic and carcinogenic health risks for both adults and children. The sediment concentrations of PTEs were generally lower than historical values, indicating an acceptable pollution level and ecological risk, except for Hg. Granularity was found to be an important factor in regulating the distribution. Furthermore, principal component analysis (PCA) and positive matrix factorization (PMF) model simulation revealed that the sources of PTEs in sediment were primarily of natural origin, with the exception of Hg, which was predominantly of anthropogenic origin. The parent rock of As was different from that of other PTEs.

Potentially hazardous metals in the sediment of a subtropical bay in South China: Spatial variability, contamination assessment and source apportionment.

Potentially hazardous metals (PHMs) in the coastal environment have become a great concern due to their easy bioaccumulation, poor biodegradability and high toxicity. Surface sediment samples were collected in a subtropical bay in South China to analyse the spatial variations, contamination level and potential sources of PHMs. The results indicated that the order of average contents of PHMs in Qinzhou Bay sediment was Zn > Pb > Cr > Cu > As > Hg > Cd. The most important potential ecological risk factor was Hg pollution in the Qinzhou Bay sediments. The positive matrix factorization (PMF) model results indicated that Cu, Pb, Zn, Cd and Cr mainly originated from natural sources while Hg and As were related to coal fired industrial inputs and petroleum production activities. The results could provide a basis for marine management to formulate relevant pollution prevention and control measures.

Radium and Lead Radioisotopes Composition of Sediment and Its Biogeochemical Implication in Polymetallic Nodule Area of Clario-Clipperton Zone.

Radioactivity levels of 210Pb and 226Ra were detected in a sediment core obtained using a multi-corer from the polymetallic nodule area inside the Clarion-Clipperton Zone (CCZ), a contract area of the China Ocean Mineral Resources Association (COMR) in the eastern Pacific Ocean. The profile of excess 210Pb (210Pbex) shows that the specific activity of 210Pbex has three parts with different distributions at depths of 0-16 cm (I), 17-36 cm (II), and 37-48 cm (III). When the I section of nonlocal mixing was excluded, using a steady-state diffusion mode, the bioturbation coefficients of the core were estimated to be 24.2 cm2/a at 17-36 cm deep and 5.9 cm2/a at 37-48 cm deep, which were greater compared to previously published results. This is most likely owing to bioturbations caused by various organism species in the two sections.

Assessment of manta trawling and two newly-developed surface water microplastic monitoring techniques in the open sea.

The ubiquitous microplastic (MP) pollution across the waterways, sediments, biota, and atmosphere has amplified concerns at a global scale. Unfortunately, harmonized MP monitoring protocols are absent for accurate evaluation on MP pollution. Few large-scale MP sampling programs involving different designs have been implemented in the open sea. In this study, a manta trawling and two newly custom-built pump filtration systems, namely, a trawl-underway pump combination system coupled in conjunction with an in-situ filtration device (Y-shaped filter, New Type I) and a stationary onboard pumping coupled to Y-shaped filter (New Type II), were evaluated for MP pollution in the mid-North Pacific Ocean. The trawling-based systems (manta trawl and New Type I) collected samples covering a large area, whereas New Type II operated at a fixed site. The new systems achieved fractionated filtration of MPs on site and prevented airborne contamination. The electronic fuel meter installed in the New Type II yielded a more accurate volume. Results showed that the average MP abundance of the aforementioned sampling techniques were 0.65, 2.56, and 7.48 items m-3, respectively. The abundances in the same particle size range (0.3-5.0 mm) from the new systems were higher. The recovered MPs from all systems were mainly white and polypropylene. Note that the MPs from the manta trawl were primarily fragments; however, they were mainly fibers from the new systems. This corroborated the capability of new systems in harvesting small items (0.1-0.3 mm) and fibers. The cost analysis showed that the new systems beat the manta trawl concerning price performance. The study results provide alternatives for future MP sampling, which will ultimately aid in the method harmonization and standardization of MP sampling.

Distribution, source and risk assessment of heavy metals in the seawater, sediments, and organisms of the Daya Bay, China.

Cu, Pb, Zn, Cd, Cr, Hg and As in seawater, sediment and organisms of the Daya Bay, Guangdong province, China were measured to acquire the comprehensive understanding on distribution, sources and risk assessment of heavy metals (HMs) in the marine ecosystem. The concentrations were relatively ideal, and the Pb was the major pollutant in the seawater and sediment. The contents of HMs were highest in spring; the concentrations near the sewage outlet and shore were noticeable. Submarine pipeline sewage, atmospheric deposition and runoff were the main sources of HMs in coastal waters. Studied HMs were preferentially retained by liquid phase; Cd, Cu and Zn were the most accumulated elements in the organisms from the surrounding environment. Cd in shellfish deserved particular attention, but the health risks including non-carcinogenic and carcinogenic risks of all elements were within acceptable limits. The potential health risks of Pb have been confirmed by molecular docking.

Pollution, ecological risk, and source identification of potentially toxic elements in sediments of a landscape urban lagoon, China.

Given the great importance of Yundang lagoon (China), a detailed evaluation and source identification of multiple potentially toxic elements (PTEs) is required. Low concentrations of the PTEs were found in the Diversion canal, while high in the Main canal, Inner lagoon, and Outer lagoon. Evaluation results indicated that the pollution of PTEs was widespread, and that the extremely high eco-risks and evident toxicity were owing to the great contributions of Hg and Cd. Positive matrix factorization model demonstrated that the PTEs were from both natural and different types of anthropogenic sources. TOC played a critical role in the PTEs. It was also found that the limited environmental carrying capacity and the poor hydrological condition of the lagoon may still accumulate the pollution in a progressive fashion. These findings provide a detailed information on making effective strategies of new directions for long-term prevention of PTEs pollution in the landscape urban lagoon.

Distribution, source identification and environmental risk assessment of potentially toxic elements (PTEs) in the surface sediment of Sanmen Bay, Zhejiang Province, China.

In this paper, the distribution, degree of pollution and sources of Cu, Pb, Zn, Cd, Cr, As, Co, Ni and Hg in the surface sediment of Sanmen Bay were studied. The average concentrations of the identified potentially toxic elements (PTEs) were in the following order: Zn > Ni > Cr > Cu > Pb > Co > As>Cd > Hg. Almost all PTEs had a significant positive correlation with TOC, clay and Al; Cr had no significant correlations. Apart from Hg, the contamination levels of 8 PTEs were at those considered to be low-to-no pollution. Comparatively, the contamination level of Hg was much higher than the background value, which indicated moderate pollution. The source of this pollution may have included industrialization, urbanization and/or transport of industrial waste materials. Both geoaccumulation index (Igeo) and potential ecological risk (RI) values suggested that Hg was the major contributor to the ecological risk posed by the selected PTEs.

Distribution of mercury isotope signatures in Yundang Lagoon, Xiamen, China, after long-term interventions.

Isotope signatures of mercury (Hg) were determined for Hg fractions in seawater, sediments, porewaters, core sediments and fish from the Yundang Lagoon, Xiamen, China. Sequential extraction was used to extract Hg fractions in sediments and the purge-trap method was used to preconcentrate Hg in seawater. A large variation in mass dependent fractionation (δ202Hg: -2.50‰ to -0.36‰) was observed in the lagoon. Seawater and fish samples showed positive mass-independent fractionation (Δ199Hg: -0.06‰-0.45‰), while most of sediment and porewater samples displayed insignificant mass-independent fractionation (Δ199Hg: -0.10‰-0.07‰). Ancillary parameters (total organic carbon, sulfide, pH, Eh, water content and grain size) were also measured in the sediments to investigate correlations with Hg isotopes. Three sources (domestic sewage, sediments and atmospheric deposition) were identified as the main sources of Hg in the lagoon seawater. Photochemical reaction was the main process causing isotope fractionation in seawater. Through Hg partitioning and deposition, light isotopes were enriched from dissolved Hg to particulate Hg, then to sediments, and then to porewaters. Finally, Hg isotope signatures were used to identify the Hg sources and fractionation processes in core sediments from different depths. Our results demonstrate that Hg isotopes are powerful tools for tracing Hg sources and arriving at a better understanding of Hg biogeochemical cycling in the lagoon after long-term interventions.

Microplastic pollution and ecological risk assessment in an estuarine environment: The Dongshan Bay of China.

Microplastic (MP) pollution has spurred a wide range of concerns due to its ubiquity and potential hazards to humans and ecosystems, yet studies on MP abundance, distribution, and ecological impacts on the small-scale local estuarine systems are insufficient. We conducted the first study of MP pollution in surface water of Dongshan Bay in southern China. A total of six water samples were collected using a Manta trawl (length = 3 m, width = 1 m, height = 0.6 m, and mesh size = âˆ¼330 µm). The abundance, type, shape, color, and size, were measured using light microscopy and micro-Raman spectroscopy. Our results showed that MPs spanned from 0.23 to 4.01 particles m-3 with an average of 1.66 particles m-3. 75% of the MPs were PP, PE, and PS that may be explained by the widespread application of PE, PP, and PS foam in local fishing and aquaculture within the bay. Foam, white, and 1.0-2.5 mm were dominant shape, color, and size of MPs, respectively. Both indices of MPs-induced risk (Hestuary = 13.7) and pollution load (PLIestuary = 14.2) yielded a Hazard Level II for MPs pollution in the Dongshan Bay. The potential ecological risk from combined MPs polymers (RIestuary = 21.5) ended up at a minor risk. Our findings established the first set of baseline data on MPs pollution in Dongshan Bay and provided preliminary quantitative measures on the scale of ecological risk, which would improve the understanding of MP fate, transport, and ecological impacts in the estuarine environment.

Heavy metal pollution and ecological risk assessment in the Maowei sea mangrove, China.

The level and ecological impact of heavy metal pollution in the Maowei Sea mangrove are poorly understood. This work first investigated the distribution and ecological risk of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in Maowei Sea mangrove sediments. The results showed that heavy metals were mainly concentrated in the top 10 cm of mangrove stands, declined up to 20 cm deep, and were constant afterwards. Exceptionally, Mn concentration increased significantly with depth in the mudflat. Multiple environmental risk indices indicated that the investigated area was broadly contaminated by heavy metals and that Cd was the dominant contributor to potential ecological risks. However, the biological toxicity posed by these metals was negligible. Multivariate analyses implied that Cd, Co, Cr, Cu, Ni, Pb, and Zn originated mainly from anthropogenic sources, whereas Mn was primarily from natural processes. These findings could provide insightful information for future management of this mangrove.

Riverine microplastic pollution matters: A case study in the Zhangjiang River of Southeastern China.

Microplastics have pulled the alarm for its far-reaching impacts in the environment and potential risks to human health. Here, we first investigated the microplastic pollution in the Zhangjiang River of southeastern China. Water samples were collected across a river catchment using bulk sampling method. The abundance, distribution, and characteristics of microplastics were analyzed using stereomicroscopy and micro-Raman spectroscopy. The results indicated that microplastic abundance ranged from 50 to 725 items m-3 with an average of 246 items m-3. PP and PE were the major polymers and accounted for ~75%. The dominant shape, color, and size of microplastics are fragment, white, and 0.5-1 mm, respectively. The findings established the baseline information on the microplastic pollution in the Zhangjiang River, which may improve the knowledge of sources of microplastic debris to the local watershed and future evaluation on the role of river catchments in transporting microplastics to the estuary and beyond into the ocean.

Environmental implications of microplastic pollution in the Northwestern Pacific Ocean.

Microplastics (MPs) contamination has been recognized as one of major threats to coastal marine environments. Although studies evidenced severe MPs contaminations to the Pacific Ocean, environmental implications of MPs concentrations, distributions, and characteristics have not been evaluated in sufficient detail. Here, we report on the distribution, abundance, and characteristics of MPs at the surface of the Northwestern Pacific Ocean, from which environmental implications are assessed. A manta trawl with a mesh size of ~330 µm and a rectangular net opening of 0.45 × 1 m was used to collect MPs samples on May 11-June 3, 2018. The MPs samples were sequentially isolated, digested, filtered, and characterized using an optical microscope, micro-Raman spectroscopy, and scanning electron microscopy. The results indicate the heterogeneity in abundance, shapes, color, and sizes of MPs. The study provides strong environmental implications such as sources, environmental degradation, residence time, transportation routes, and biological interactions.

Prevalence of microplastic pollution in the Northwestern Pacific Ocean.

People are increasingly aware of ubiquitous microplastic (MP) pollution in the world's ocean due to its far-reaching harmful impacts on marine ecosystem and potential hazards to human health, yet surprisingly comparatively limited studies about the abundance, source, transport, and fate of MPs in the Northwestern Pacific Ocean are available. We conducted the field survey of MPs pollution at the surface of the Northwestern Pacific Ocean between August 25 and September 26, 2017. MPs were collected from 18 sampling stations in the Northwestern Pacific Ocean using a manta trawl net with a mesh size of ∼330 µm and a rectangular net opening of 0.45 × 1 m. The abundance, shape, color, size, chemical composition, and surface morphology were characterized using light microscopy, µ-Raman spectroscopy, and scanning electron microscopy (SEM). The results show surface MPs at concentrations ranging over two orders of magnitude (6.4 × 102 to 4.2 × 104 particles km-2) and a mean abundance of 1.0 × 104 particles km-2. The most concentrated MPs were found at XTJ3-9, which may be associated with the convergence of surface currents collectively affected by the Kuroshio and its extension, adjacent eddies, and flow regimes. Polyethylene accounts for 57.8% of enumerated MPs, followed by polypropylene (36.0%) and nylon (3.4%). Pellets, sheets, lines, and films are major forms which may be linked to the breakdown of larger particles, aging processes, and movement over long distances by prevailing currents. Four possible MPs migration pathways were proposed based on the source-specific distribution, chemical fingerprints, size distribution patterns, and the observed physical oceanographic parameters.

Microplastics in the Northwestern Pacific: Abundance, distribution, and characteristics.

Prevalence of microplastics (MPs) throughout the world's oceans has raised growing concerns due to its detrimental effects on the environment and living organisms. Most recent studies of MPs, however, have focused on the estuaries and coastal regions. There is a lack of study of MPs pollution in the open ocean. In the present study, we conducted field observations to investigate the abundance, spatial distribution, and characteristics (composite, size, color, shape and surface morphology) of MPs at the surface of the Northwestern Pacific Ocean. Samples of MPs were collected at 18 field stations in the Northwestern Pacific Ocean using a surface manta trawl with a mesh size of ~330 µm and width of 1 m from August 25 to September 26, 2017. The MPs were characterized using light microscopy, Micro-Raman spectroscopy, and scanning electron microscopy (SEM). Our field survey results indicate the ubiquity of MPs at all stations with an abundance from 6.4 × 102 items km-2 to 4.2 × 104 items km-2 and an average abundance of 1.0 × 104 items km-2. The Micro-Raman spectroscopic analysis of the MPs samples collected during our field survey indicates that the dominant MPs is polyethylene (57.8%), followed by polypropylene (36.0%) and nylon (3.4%). The individual chemical compositions of MPs from the stations within the latitude range 123-146°E are comparable with each other, with PE being the dominating composition. Similar chemical fingerprints were observed at these field stations, suggesting that the MPs originated from similar sources. In contrast, the major MPs at the field stations adjacent to Japan is polypropylene, which may originate from the nearby land along the coast of Japan. Physical oceanography parameters were also collected at these stations. The spatial distribution of MPs is largely attributed to the combined effects of flow pattern, adjacent ocean circulation eddies, the Kuroshio and Kuroshio Extension system.

Total mercury flux and offshore transport via submarine groundwater discharge and coal-fired power plant in the Jiulong River estuary, China.

A mass balance of total mercury (HgT, dissolved+particulate) is constructed for China's Jiulong River estuary based on measured HgT concentrations in the surface water, sediment, porewater, and groundwater for May, August, and November 2009, combined with data from the literature. The HgT mass budget results show that the dominant source (39-55%) is desulfurized seawater discharged from the Songyu coal-fired power plant. Submarine groundwater discharge (SGD)-derived HgT flux into the estuary is equivalent to 8-58% of the HgT input from the Jiulong River, which is remarkable when compared with SGD-derived HgT fluxes reported in coastal systems worldwide. Hence, SGD is a significant pathway for the transport of HgT into the Jiulong River estuary. The primary HgT sinks is export to the Taiwan Strait (53-88%), which has important environmental implications on the Hg cycling and marine ecosystems in marginal seas.