Riverine carbon (C) composition and export are closely related to changes in the coastal environment and climate. Excessive C inputs from rivers to seas and their subsequent decomposition could result in harmful algal blooms and ecosystem degradation in the coastal sea. In this study, we explored the C transportation and composition in the 24 major rivers of the Bohai Sea (BS) Rim based on the investigation of dissolved organic carbon (DOC), carbon stable isotopes (δ¹³CDOC) and chromophoric dissolved organic matter (CDOM). The results showed that the riverine DOC concentrations were high (10.6 ± 6.04 mg/L) in the BS Rim compared with the DOC levels in the main rivers in Eastern China (4.98 ± 2.45 mg/L). The δ¹³CDOC ranged from −28.29‰ to −25.32‰ in the rivers of the BS Rim, suggesting that the DOC mainly originated from riverine plankton, soil organic matter mainly induced by C3 plants, and sewage. The excitation-emission matrix fluorescence spectroscopy of the CDOM indicated that a soluble, microbial by product-like material accounted for the largest proportion (approximately 40%) of CDOM in these rivers and that CDOM mainly originated from autochthonous riverine sources with high protein-like components. The rivers in the BS Rim transported approximately 0.55 Tg C of DOC to the BS each year, with more than 70% of reactive C based on the CDOM composition. The DOC yields in terms of unit drainage area transported from the small rivers to the BS were higher compared to those of the larger rivers in the world, which indicated that the small rivers in the Bohai Rim could be an important source of the C in the BS. This study would enrich our understanding of environmental evolution in coastal areas with numerous small rivers.

Airborne fine particles can affect climate change and human health; moreover, they can be transported over significant distances. However, studies on characteristics of individual particles and their morphology, elemental composition, aging processes, and spatial distribution after long-range transport over the Yellow Sea are limited. Therefore, in this study, we conducted shipborne measurements of fine particulate matter of less than 2.5 μm in diameter (PM₂.₅) over the Yellow Sea and classified the individual particles into seven types based on their morphology and composition. Overall, the percentage of organic-rich particles was the highest, followed by that of sea spray, sulfur-rich, dust, metals, fly ash, soot, and other particles. Near Shandong, China, the percentage of fly ash and sulfur-rich particles increased, while an increased percentage of only sulfur-rich particles was observed near the Korean Peninsula. In the open sea, the PM₂.₅ concentrations were the lowest, and sea spray particles predominated. During the cruises, three types (Types 1, 2, and 3) of events with substantially increased PM₂.₅ concentrations occurred, each with different dominant particles. Type 1 events frequently featured air masses from northern China and Mongolia with high wind speeds and increased dust particles. Type 2 events involved air masses from China with high wind speeds; fly ash, soot, organic-rich particles, and the sulfate percentage in PM₂.₅ increased. Type 3 events displayed stagnant conditions and local transport (from Korea); soot, dust particles, and the secondary sulfate and nitrate percentages in PM₂.₅ increased. Thus, different types of transport affected concentrations and dominant types of fine particles over the Yellow Sea during spring.

Around the world, green tides are happening with increasing frequency because of the dual effects of increasingly intense human activity and climate change; this leads to significant impacts on marine ecology and economies. In the last decade, the world's largest green tide, which is formed by Ulva/Enteromorpha porifera, has become a recurrent phenomenon every year in the southern Yellow Sea (China), and it has been getting worse. To alleviate the impacts of such green tide outbreaks, multiple measures need to be developed. Among these approaches, biotechnology plays important roles in revealing the outbreak mechanism (e.g., molecular identification technology for algal genotypes), controlling and preventing outbreaks at the origin sites (e.g., technology to inhibit propagation), and utilizing valuable algal biomass. This review focuses on the various previously used biotechnological approaches that may be applicable to worldwide seaweed blooms that result from global climate change and environmental degradation.

Organophosphates (OPEs) are manmade organic pollutants that are widely used as flame retardants, plasticizers, and antifoaming and hydraulic agents. In this study, seven OPEs in seawater and sediment from the Yellow Sea and East China Sea were determined to study the distribution and diffusion behavior, and to evaluate the environmental risks. The ΣOPEs in the seawater and sediments ranged from below the method detection limit (<MDL) to 497.40 ng/L and from < MDL to 66.50 ng/g dw, respectively. Tri-n-butyl phosphate (TnBP), tris-(1, 3-Dichloro-2-Propyl) phosphate (TDCPP), and tri-meta-cresyl phosphate (TmCP) were the dominant OPEs in the seawater and sediments. OPEs were mainly distributed in coastal areas and the South Yellow Sea, indicating that they are mainly affected by land-based pollution and ocean currents. Fugacity analysis shows that tri-para-cresyl phosphate (TpCP) was in a state of equilibrium, while TDCPP, TnBP, and TmCP other OPEs tended to diffuse from sediment to water. The diffusion behavior of OPEs is mainly affected by their chemical properties. Hazard quotient (HQ) values of TmCP and TpCP in sediment samples were >1.0, indicating high ecological risks to aquatic organisms.

As reservoirs for pollutants transported via the Yangtze and Yellow Rivers, the Bohai Sea (BS) and Yellow Sea (YS) play an important role in transporting microplastics (MPs) to the Pacific Ocean. The fate, sources and mass budget of MPs in the BS and the YS were investigated by Pearson correlation, principal component analysis-multilinear regression analysis (PCA-MRLA) and a mass balance model to sedimentary MPs data. Average MP abundances were 137 and 119 items kg⁻¹ in the Bohai and Yellow Seas, respectively. MPs <1000 μm exhibited similar distribution patterns to total organic carbon and fine-grained sediments, while MPs >1000 μm were confined in the BS and exhibited a strong positive correlation with chlorophyll-a and polyethylene terephthalate, suggesting that larger MPs might deposit faster due to biofouling or when comprised of high density polymers. PCA-MLRA analysis indicated land-based inputs (packing materials, textile material and daily commodities) were dominant in the BS, while maritime activities (fishing and mariculture) were the main source of MPs in the YS. The mass balance model revealed that the total MP input and output to the BS and the YS was 3396.92 t yr⁻¹ and 3814.81 t yr⁻¹, respectively. The major input pathway of MPs to the BS and the YS were river discharge and air deposition, respectively. Notably, 94% of MPs in the BS and the YS were deposited to sediments. This study revealed that BS and YS sediments play an important role in preventing MPs from being further transported to the Pacific Ocean, thus more attention should be paid to local ecological risk assessment.

The physico-chemical properties of submicron aerosols were measured in the spring of 2018 and 2019 over the Yellow Sea onboard the Gisang 1 research vessel. Aerosol number concentrations in 2019 were slightly higher than those in 2018, and the mean number concentrations of particles larger than 10 nm and cloud condensation nuclei (CCN) at 0.6% supersaturation (S) in spring 2019 were 7312 ± 3807 cm⁻³ and 4816 ± 1692 cm⁻³, respectively. Aerosol concentrations in June were lower than those in April and May, which was considered to be due to the East Asian summer monsoon. Aerosol number concentrations and size distributions were significantly influenced by meteorological conditions, such as wind and relative humidity. Aitken and accumulation mode particles dominated the aerosol number size distributions over the Yellow Sea. A distinct new particle formation (NPF) and growth event was observed, the spatial extent of which was estimated to cover at least 200 km × 400 km of the Yellow Sea. The general characteristics of NPF and growth over the Yellow Sea were similar to those in rural areas. Aerosol number concentrations below 1000 cm⁻³ were recorded on extremely clean days. A CCN closure experiment conducted using previous measurement data showed good results, indicating that CCN concentrations can be estimated with good accuracy, and the hygroscopicity over the Yellow Sea was similar to that of aged continental aerosols.

Dechlorane Plus (DP), which has severe effects on marine ecosystems, has been proposed for listing under the Stockholm Convention as a persistent organic pollutant (POPs). This study was the first comprehensive investigation of the concentration and fate of DP in the Bohai Sea (BS) based on determination of river estuary water, river estuary sediment, surface seawater, bottom seawater, and sea sediments samples. The highest water DP levels were found in river estuary in Tianjin in North China due to the huge usage of DP in recent years, and spatial distribution analysis indicates it was mainly affected by regional high urbanization and emission of E-waste. The spatial distribution of DP in the BS was mainly affected by a combination of coastal hydrodynamics and land anthropogenic activities. On the basis of multi-box mass balance, simulations of DP in seawater showed an increase from 2014 to 2025, before leveling off at 184 pg L ⁻¹ by a constant DP input to the BS. Riverine discharge almost contributed to the total input (∼99%) and dominated the DP levels in the BS. Degradation of DP accounted for 55.3% and 78.1% of total DP output in seawater and sediment, respectively, indicating that degradation mainly affected decline of DP in the environment.

Plastics are globally distributed in oceans and can pose a threat to the environment and organisms. In this study, plastic pollution in surface water and sediments of the Bohai Sea was assessed based on plastic abundance, distribution and characteristics (shape, polymer, size and color). Water and sediment samples were collected across the sea using a plankton net (330 μm) and a grab sampler, respectively. The following conclusions were reached. 1) In surface water, large plastics were less abundant (0.14 items/m³) and showed less diverse characteristics than microplastics (0.79 items/m³) but did not significantly differ in spatial distribution. 2) Microplastics in water were more abundant (1.95 items/m³) with more diverse characteristics in Liaodong Bay than in other regions of the sea (0.26–0.59 items/m³). Plastic waste from highly concentrated agricultural, industrial and fishery activities could make large contributions to microplastics in Liaodong Bay. Additionally, low hydrodynamics and long distance to Bohai Strait are unfavorable for diffusion of particles, facilitating the retention of microplastics and increasing the abundance in this bay. 3) Microplastics in sediments were smaller in terms of dominant sizes (<0.5 mm) with less diverse characteristics than particles in water (0.5–1.5 mm). Specifically, fragments, foams and lines dominated among the microplastics in water, whereas fibers and fragments were dominant particles in sediments; alkyd resin, polyethylene, polystyrene and polypropylene (PP) predominated among the particles in water, but rayon, cellulose and PP were dominant particles in sediments. 4) Neither abundance nor size of microplastics in the two media was proportionally correlated and showed low similarity indexes of polymer (0.16), shape (0.29) or color (0.38). This could be related to mismatch in spatiotemporal distributions and variations in the characteristics, fate and behavior of microplastics in the two media. The findings provide knowledge for tracing the sources of plastics in the Bohai Sea.

The spatial distributions, fluxes, and environmental effects of non-methane hydrocarbons (NMHCs) were investigated in the Yellow Sea (YS) and the East China Sea (ECS) in spring. The average concentrations of ethane, propane, i-/n-butane, ethylene, propylene and isoprene in the seawater were 18.1 ± 6.4, 15.4 ± 4.7, 6.8 ± 2.9, 6.4 ± 3.2, 67.1 ± 26.7, 20.5 ± 8.7 and 17.1 ± 11.1 pmol L⁻¹, respectively. The alkenes in the surface seawater were more abundant than their saturated homologs and NMHCs concentrations (with the exception of isoprene) decreased with carbon number. The spatial variations of isoprene were consistent with the distributions of chlorophyll a (Chl-a) and Chaetoceros, Skeletonema, Nitzschia mainly contributed to the production of isoprene, while the others’ distributions might be related to their photochemical production. Observations in atmospheric NMHCs indicated alkanes in the marine atmosphere decreased from inshore to offshore due to influence of the continental emissions, while alkenes were largely derived from the oceanic source. In addition, no apparent diurnal discrepancy of atmospheric NMHCs (except for isoprene) were found between daytime and night. As the main sink of NMHCs in seawater, the average sea-to-air fluxes of ethane, propane, i-/n-butane, ethylene and propylene were 31.70, 29.75, 18.49, 15.89, 239.6, 67.94 and 52.41 nmol m⁻² d⁻¹, respectively. The average annual emissions of isoprene accounted for 0.1–1.3% of the global ocean emissions, which indicated that the coastal and shelf areas might be significant sources of isoprene. Furthermore, this study represents the first effort to estimate the environmental effects caused by NMHCs over the YS and the ECS and the results demonstrated contributions of alkanes to ozone and secondary organic aerosol (SOA) formation were lower than those of the alkenes and the largest contributor was isoprene.

Freshwater systems serve as important sources and transportation routes for marine microplastic pollution, and inadequate attention has been paid to this situation. Data on microplastic pollution of typical seagoing rivers in northern China are lacking. In the current study, we investigated the distribution and characteristics of microplastics in the main stream of the Haihe River, which flows through a metropolis with a high population density and level of industrialization and then flows into the Bohai Sea. The microplastic samples were collected by manta trawls with pore sizes of 333 μm, and the microplastic concentrations ranged from 0.69 to 74.95 items/m³. Fibers dominated in the surface water of the Haihe River; their shapes that were categorized as fibers, film, foam, fragments, and spheres, and contributed 17.4–86.7% of the total microplastics studied. The size distribution of the microplastics was concentrated in a range of 100–1000 μm, with 54.7% of the total sizes corresponding to the 333-μm trawl. Micro-Fourier transform infrared (μ-FT-IR) spectra showed that the main components were polyethylene, poly(ethylene-propylene) copolymer, and polypropylene. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) measurements revealed scratches, micropores, and cracks on the surfaces of the microplastics due to mechanical friction, chemical oxidation and degradation processes. The results of this study confirmed the high abundance and high diversity of microplastics in an urban river and indicated appreciable impacts from point-source inputs on the microplastic pollution, such as effluents from wastewater treatment plants (WWTPs).