Typhoon-induced stormwater drives nutrient dynamics and triggers phytoplankton blooms in Laizhou Bay, China

In this study, we investigated the hydrological and ecological impacts of heavy rainfall caused by the storm Rumbia and Typhoon Lekima on Laizhou Bay (LZB) through land‒sea synchronous field surveys, online remote sensors, and simulated enclosure experiments. Within two weeks of Rumbia, approximately 9% and 16% of the annual riverine total nitrogen (TN) and total phosphorus (TP) fluxes, respectively, were transported to the LZB and the proportions were 17% and 35%, respectively, for Lekima. The land use on the watersheds increased the rates of land-derived nutrient loading and altered their biogeochemical forms. Consequently, the average concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the LZB increased by 2.6 and 1.0 times post-Rumbia and by 3.5 and 1.3 times post-Lekima, respectively. Relatively lower salinity and temperature, sudden increases in DIN, and strengthened coastal currents stimulated the growth of highly adaptable and small diatoms, resulting in the first diatom blooms. Subsequently, a bloom of Noctiluca scintillans formed.

Spatiotemporal distribution and particle-water partitioning of polycyclic aromatic hydrocarbons in Bohai Sea, China

The Bohai Sea is one of the most polluted marine areas in China with polycyclic aromatic hydrocarbons (PAHs) due to its unique hydrological and geographical environment. To investigate differences in PAH concentrations, composition, and particle-water partitioning before and after the rainy reason, water samples were collected during two surveying voyages covering most of the area of the Bohai Sea. Total and dissolved PAH concentrations were higher during the June voyage (total PAHs: 32.29 ± 15.18 ng/L, dissolved PAHs: 31.25 ± 15.26 ng/L) than the August voyage (total PAHs: 15.98 ± 6.39 ng/L, dissolved PAHs: 11.21 ± 5.59 ng/L). The opposite trend was observed for particulate PAHs (June: 1.04 ± 1.01 ng/L, August: 4.78 ± 2.96 ng/L). Among particulate PAHs, an unusually high proportion (65.07%) of low-molecular-weight (LMW) PAHs was observed during the August voyage, which was significantly higher than the proportion during the June voyage (21.86%). This high proportion was inconsistent with the general distribution of PAHs in the aquatic environment according to their physicochemical properties. The excess LMW PAHs adsorbed on suspended particulate matter arose mainly from soil affected by the petrochemical industry of the Bohai Economic Rim, and were carried with particles on runoff into the Bohai Sea during the rainy season. An estimated 5.49 t of LMW PAHs transitioned from the particulate phase to the dissolved phase during the rainy season. This transfer of LMW PAHs from coastal soil to the water column may be an important source of PAHs in the Bohai Sea.

Evaluating the effectiveness of coastal environmental management policies in China: The case of Bohai Sea

With marine pollution issues becoming serious and widespread, a series of coastal environmental managemental policies are being carried out worldwide, the effectiveness of which requires comprehensive evaluation. Taking the Bohai Sea (BS) of China as an example, which has been plagued by serious ecological and environmental issues for decades due to terrestrial pollution discharge, this study explored and quantified, for the first time to our best knowledge, the variability of water quality after initiating a dedicated 3-year pollution control action (Uphill Battle for Integrated Bohai Sea Management, UBIBM, 2018-2020) implemented by China's central government, with two water quality indexes of water color (Forel-Ule index, FUI) and transparency (Secchi disk depth, Z_SD, m) from satellite observations. During the UBIBM, a significant improvement in water quality was detected, characterized by a clearer and bluer BS, with Z_SD and FUI improved by 14.1% and 3.2%, respectively, compared with the baseline period (2011-2017). In addition, an abrupt drop in the long-term record (2011-2022) of the coverage area of highly turbid waters (Z_SD≤2 m or FUI≥8) was found in 2018, which coincided with the start of the UBIBM, indicating that the water quality improvement may be attributed to the pollution alleviation of the UBIBM. Independent data of land-based pollution statistics also supported this deduction. (3) Compared with the previous two pollution control actions in the first decade of 21st century, UBIBM was proved to be the most successful one in terms of the achieved highest transparency and lowest FUI during the past two decades. Reasons for the achievement and implications to future pollution control are discussed for a more sustainable and balanced improvement in the coastal environment. This research provides a valuable example that satellite remote sensing can play a vital role in the management of coastal ecosystems by providing effective evaluation of pollution control actions.

Vibrio paucivorans sp. nov. and Vibrio qingdaonensis sp. nov., two marine bacteria

Two Gram-stain-negative, facultatively anaerobic, motile, rod-shaped and flagellated marine bacteria, designated strains DBSS07^T and ZSDZ65^T, were isolated from the surface sediments of the Bohai sea and Qingdao coastal seawater, respectively. Phylogenetic analysis based on 16S rRNA genes, multilocus sequence analysis (MLSA), phylogenomic analysis of single-copy gene families and whole-genome data placed DBSS07^T and ZSDZ65^T within the genus Vibrio. DBSS07^T was most closely related to Vibrio aestivus M22^T, with 97.51 % sequence similarity, whereas ZSDZ65^T was most closely related to Vibrio variabilis R-40492^T with 97.58 % sequence similarity. DBSS07^T grew with 1-7 % (w/v) NaCl (optimum 3 %), at 16-37 °C (optimum 28 °C) and at pH 6.0-9.0 (optimum pH 7.0); whereas ZSDZ65^T grew with 1-5 % (w/v) NaCl (optimum 2 %), at 16-32 °C (optimum 28 °C) and at pH 6.0-9.0 (optimum pH 8.0). Both strains shared the same major fatty acid components (more than 10 % of total fatty acids) of summed feature 3 (C_16 : 1ω7c or/and C_16 : 1ω6c), with different proportions. The DNA G+C contents of DBSS07^T and ZSDZ65^T were 44.7 and 44.3 %, respectively. On the basis of the results of polyphasic analysis, DBSS07^T and ZSDZ65^T are considered to represent novel species within the genus Vibrio, for which the names V. paucivorans sp. nov. (type strain, DBSS07^T = KCTC 82896^T= MCCC 1K06284^T) and V. qingdaonensis sp. nov. (type strain, ZSDZ65^T = KCTC 82893^T = MCCC 1K06289^T) are proposed, respectively.

Tar ball pollution under the influence of ocean circulation in the Bohai Sea, China

The deposition of tar balls of unknown sources on the coast poses a great threat to the fishery, tourism and coastal biodiversity in the Bohai Sea. This work aimed to identify the sources of tar balls by using oil fingerprint technique. Tar ball samples were collected from the seashore of two islands of the western Bohai Sea and divided into two groups (Group I and Group II). Principal component analysis showed that although Caofeidian oilfield was one of the closest oilfields to the sampling area it was not a source. Fingerprints of characteristic hopanes and steranes showed that samples of Group I were similar to the crude oils from the nearby Jidong oilfield, and samples of Group II were similar to the Penglai-19-3 crude oils. Combined with cross-plots of the samples and the reference oils, it indicated that Group I may come from Jidong and Group II may come from Penglai-19-3. The weathering characteristics of alkanes and polycyclic aromatic hydrocarbons showed that the samples were affected by natural weathering processes (e.g., evaporation, photooxidation and biodegradation). It revealed that oil pollution from the nearby oilfields can also affect other areas under the influence of ocean circulation. It is the first study on source identification of tar balls from the Bohai Sea and the effects of ocean circulation on the tar ball transport. This study can considerably help to further understand the evolution of tar balls and consequently determine their sources.

Brown tides linked to the unique nutrient profile in coastal waters of Qinhuangdao, China

Brown tides caused by the pelagophyte Aureococcus anophagefferens have frequently occurred in the Bohai Sea since 2009 and have led to a dramatic collapse of the local scallop culture. To determine why brown tides occurred in the Bohai Sea rather than in other eutrophic coastal waters of China, phytoplankton communities and nutrients were evaluated and nutrient addition experiments were conducted in the Qinhuangdao coastal area. The concentration of dissolved organic nitrogen (DON) was nearly five times higher than that of dissolved inorganic nitrogen (DIN) during brown tides. High levels of phytoplankton biomass and nutrients were observed in the inshore waters, and the patterns of different nutrients were heterogeneous, which could be due to the uneven distribution of pelagophytes and non-brown tide phytoplankton populations (NBTP). The nutrient enrichment results indicated that the growth of the phytoplankton community was nitrogen-limited. Enrichment of DON, especially urea, could promote the growth of pelagophytes during the development stages of the brown tide. In brief, the results of this study imply that the unique nutrient profile (rich in DON but deficient in DIN) could support the outbreak of brown tides in the inshore waters of Qinhuangdao.

A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

The largest semi-enclosed sea of China, the Bohai Sea, serves as an important sink of microplastics (MPs) originated from terrestrial and marine sources. This study summarized potential sources and migration pathways of MPs in the Bohai Sea and reviewed the abundance and characteristics of MPs in water, sediments, and organisms. Coastal anthropogenic activities (i.e., plastic production, agricultural activities, and industrial and domestic sewage discharge) and marine origins (i.e., aquaculture, marine litters, and transportation) might accelerate the MPs enrichment in the Bohai Sea. The abundance of MPs ranged from 0.07 to 5200 items/m³ in the seawater, mainly influenced by the application of different trawl nets/sieves with different sizes (0.005-0.33 mm). Sediments of coastal rivers contained the MPs ranging from 56.7 to 1795 items/kg, significantly higher than that of the Bohai Sea (6.24-461.6 items/kg). Among organisms, the average abundance of MPs was the lowest in zooplanktons (0.03 items/animal), significantly lower than that in invertebrates (1.39 items/animal) and fish (2.12 items/animal), but no biomagnification of MPs was observed. The preliminary risk assessment indicated that seawater in the Liaodong Bay had medium ecological risk of MPs while other bays of the Bohai Sea had minor risks. To make the ecological risk of MPs quantifiable and comparable, future research priorities are recommended to focus on more frequent field surveys, standardization of sampling methods, and establishment of toxicity database of common polymer types of MPs in the Bohai Sea.

Derivation of copper water quality criteria in the Bohai Sea of China considering the effects of multiple environmental factors on copper toxicity

Copper has become one of the most important heavy metal pollutants in the environment because of its wide application and high toxicity, but research on water quality criteria (WQCs) on copper is limited, especially the derivation of seawater WQC. In addition, the toxicity of copper in the seawater system is affected by various environmental factors. Therefore, establishing a WQC that meets the characteristics of the regional environment is a top priority. The correlations between four factors of temperature, salinity, pH, dissolved organic carbon (DOC) and the toxic effect values of copper were analyzed in this study, and the temperature was determined as the most influential factor among the four factors in the Bohai Sea. A specific correlation between temperature and the toxic effects of copper was identified, and WQCs were derived based on the identified correlation and the variations of the Bohai Sea's temperature in different seasons by species sensitivity distribution (SSD) method. Under the condition of the winter, spring, autumn, and summer with an average water temperature of 0.09, 15.96, 17.83, and 24.87 °C, the obtained short-term water quality criteria (SWQCs) were 44.29, 4.70, 4.31, and 3.33 μg/L; the long-term water quality criteria (LWQCs) were 18.14, 1.93, 1.77 and 1.36 μg/L. The findings indicated the importance of introducing specific environmental conditions during the derivation process. This work could provide valuable information for pollution prevention and aquatic life protection in the Bohai Sea and provide a valuable reference for the derivation of criteria in other regions alike.

Distribution of Aureococcus anophagefferens in relation to environmental factors and implications for brown tide seed sources in Qinhuangdao coastal waters, China

Brown tides caused by Aureococcus anophagefferens have occurred along the Qinhuangdao coastline in the Bohai Sea (BS) in recent years. Little is known about the spatio-temporal distribution of A. anophagefferens, particularly its profile distribution and the effects of environmental controls. In this study, four surveys were conducted in Qinhuangdao coastal waters during the brown tide from June to July 2013; another survey was conducted to cover a larger region in the BS in May 2016. Temperature, salinity, nutrients, and chlorophyll a were analyzed; and the density of A. anophagefferens was detected by a sensitive qPCR method. The intensive brown tide only occurred in Qinhuangdao inshore waters at temperatures ranging from 21.5 to 23.2 °C and relatively high salinity (> 29). Redundancy analysis indicated that the low dissolved inorganic nitrogen limited the growth of other pico- and nano-algal species; high dissolved organic nitrogen and low inorganic nutrients were suitable for the development of brown tides in Qinhuangdao coastal waters, which also contained a thermocline during the brown tide. At the early stage of the brown tide, a high abundance of A. anophagefferens appeared at the bottom of offshore waters characterized by low temperature and high salinity. The A. anophagefferens cells were speculated to originate from water mass located in a depression between the central ridge and the Qinhuangdao coastal area. In brief, this study reported the spatio-temporal variation of brown tides based on the abundance of A. anophagefferens and environmental forces and implied that A. anophagefferens could be transported from the bottom of offshore waters to promote brown tides in inshore waters of Qinhuangdao.

Microplastic Pollution in Nearshore Sediment from the Bohai Sea Coastline

Microplastics are recognized as an emerging global issue in marine environments. In this study, microplastic pollution in subtidal sediments from nine typical stations in the Bohai Sea was investigated. The mean concentration was 458.6 ± 150.0 items/kg of dry weight, varying from 280.0 to 773.4 items/kg. All of the microplastics were categorized according to shape, color and size. Among these microplastics, fiber (77.1%), white/blue/black (85.0%) and small microplastics (< 1500 μm) (82.9%) were the most abundant types. Seven polymer types were identified and were, in decreasing order of abundance, rayon > PE > PS > PP > PET > ABS > PA. The microplastics abundance was of the same order of magnitude as that of other similar areas. The microplastic characteristics suggest that tourism, maritime activities and sewage discharge are possible sources. Our results provide useful information for performing an environmental risk assessment of microplastic pollution in this area.

Spatiotemporal distribution, source apportionment and combined pollution of antibiotics in natural waters adjacent to mariculture areas in the Laizhou Bay, Bohai Sea

The spatiotemporal distribution, source apportionment and combined pollution of 14 antibiotics in natural waters adjacent to mariculture farms of Laizhou Bay in the Bohai Sea were studied. The contribution proportion and quantity of each potential pollution source to antibiotics in natural water bodies were quantitatively described. The correlations between heavy metals and antibiotics and their underlying mechanisms in natural and aquaculture water environment were analyzed. Fourteen antibiotics were detected in natural water and sediment in the coastal area of Laizhou Bay. The maximum concentrations of sulfamethazine and trimethoprim in water reached tens or even hundreds of μg/L in winter. Trimethoprim was the main antibiotic in natural water bodies in winter and summer, and enrofloxacin was the principal antibiotic in sediments. Enrofloxacin, ciprofloxacin and oxytetracycline were detected in all underground water samples; thus, control of these antibiotics needs to be made a priority to mitigate groundwater contamination. PCA-MLR revealed that the potential sources of antibiotics in natural waters of Laizhou Bay include the mariculture wastewater (18.3%), the domestic sewage (63.3%) and the livestock wastewater (18.4%). Therefore, the antibiotic burden of Laizhou Bay was principally from the domestic sewage. In natural water, the concentration of Cu was positively correlated with antibiotics, which might be related to the common sources, the competitive adsorption in sediments and the easy complexation characteristic of Cu and antibiotics. Positive correlations among antibiotics and heavy metals were observed in mariculture sediments, while negative relationships were observed in natural sediments.

Potential threat of SARS-CoV-2 in coastal waters

A novel coronavirus (SARS-CoV-2) has caused more than 150 million confirmed infections worldwide, while it is not clear whether it affects the coastal waters. This paper proposed a biophysical model based on 16 scenarios with different virus half-life parameters to assess potential viral contamination from 25 municipal sewage outfalls into the Bohai Sea. Viral concentration maps showing spatial and temporal changes are provided based on a biophysical model under multiple scenarios. Results demonstrate that adjacent sea areas can become exposed to SARS-CoV-2 via water-borne transport from outfalls, with a higher risk in winter, because SARS-CoV-2 can be highly stable at low temperature. As coastal waters are the ultimate sink for wastewater and the epidemic will last for long time, this work is of great importance to raise awareness, identify vulnerable areas for marine mammals, and avoid the risk of exposure of tourists at bathing beach.

Dual-isotope-based source apportionment of nitrate in 30 rivers draining into the Bohai Sea, north China

Excessive nitrate (NO₃^-) in rivers can lead to water quality deterioration, and can also be directly input into estuaries and oceans, thus posing a serious threat to the stability of their ecosystems. In this study, the concentration, isotopes and sources of NO₃^- in 30 rivers discharging into the Bohai Sea were comprehensively investigated. The mean concentration of NO₃^--N was 2.24 ± 2.11 mg L^-1, with obvious seasonal and spatial variations. In total, 104.24 kt of NO₃^--N was discharged into the Bohai Sea annually, to which the Yellow River Basin and Liao River Basin made the largest contributions. The range of δ¹⁵N-NO₃^- was -1.1‰ to +33.2‰ (mean value, +11.4 ± 5.0‰), with no significant seasonal or spatial differences; the mean value of δ¹⁸O-NO₃^- was +9.4 ± 7.2‰, with much higher values seen in June. Based on the MixSIAR model, manure (24.3 ± 7.5%) and sewage (19.1 ± 14.5%) were the primary sources of NO₃^- in the 30 rivers, followed by NO₃^- fertilizers (16.3 ± 12.5%), soil N (15.5 ± 11.9%), atmospheric deposition of NO₃^- (13.5 ± 5.7%) and NH₄⁺ fertilizers (11.4 ± 8.9%). This finding highlights the vital roles of sewage and manure management in riverine NO₃^-. Using a mathematical method, the contributions of various sources to each river were simulated. The results indicated that management of the Yellow River, Daliao River, Liao River, and Xiaoqing River is more urgently needed than that of other rivers to control Bohai NO₃^- pollution. We believe that this finding will provide guidance for scientific management of NO₃^- pollution in these 30 rivers and the Bohai Sea.

Spatial-temporal characteristics of mercury and methylmercury in marine sediment under the combined influences of river input and coastal currents

Mercury, especially in the form of methylmercury (MeHg), is a global pollutant, and aquatic products are considered the main sources of Hg exposure to humans. The Bohai and Yellow seas are two important epicontinental seas for marine fisheries and aquaculture in China. A decreasing trend of the THg in the Yellow River Estuary toward the outer edge was reported according to 83 surface sediments (27.3 ± 15.0 ng g^-1) and 3 sediment cores from the Bohai Sea and Yellow Sea. The relatively higher THg levels in the central Yellow Sea can be primarily attributed to higher organic carbon levels and finer-grained sediment sizes and partly to the particulates from the riverine input of the Yellow River driven by the currents. An increasing trend in THg levels since industrialization in north China around the Bohai and Yellow seas, and a decreasing trend of Yellow River THg input in recent years were recorded by sediment cores. The spatial distribution pattern of surface sediments MeHg (161 ± 130 pg g^-1) was different from that of THg. A higher MeHg content and MeHg/THg ratio were found in the Bohai and Yellow seas compared to the East China Sea, and extremely high MeHg levels (714 pg g^-1) were found in the Yellow Sea Cold Water Mass (YSCWM) area, which is considered an important region for fishery and marine breeding, suggesting that more attention should be paid to the potential ecological and human health risks in the region due to mercury exposure.

Source, fate and budget of Dechlorane Plus (DP) in a typical semi-closed sea, China

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.

Improving the understanding of central Bohai Sea eutrophication based on wintertime dissolved inorganic nutrient budgets: Roles of north Yellow Sea water intrusion and atmospheric nitrogen deposition

The Bohai Sea is a shallow-water, semi-enclosed marginal sea of the Northwest Pacific. Since the late 1990s, it has suffered from nutrient over-enrichment. To better understand the eutrophication characteristics of this important coastal sea, we examined four survey datasets from summer (June 2011), late autumn (November 2011), winter (January 2016), and early spring (April 2018). Nutrient conditions in the Bohai Sea were subject to seasonal and regional variations. Survey-averaged N/P ratios in estuarine and nearshore areas were 20-133. In contrast, the central Bohai Sea had mean N/P ratios of 16.9 ± 3.4 in late autumn, 16.1 ± 3.0 in winter and 13.5 ± 5.8 in early spring, which are close to the traditional N:P Redfield ratio of 16. In summer, both dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) were used up in the surface waters of the central Bohai Sea, suggesting that the biological consumption of DIN and DIP may also follow the Redfield ratio. Wintertime nutrient budgets of the central Bohai Sea water were then established based on a mass balance study. Our results suggest that the adjacent North Yellow Sea supplied additional DIP to the central Bohai Sea via wintertime water intrusion, balancing terrigenous excess DIN that was introduced in summer. A water-mixing simulation combining these two nutrient sources with atmospheric nitrogen deposition suggests that eutrophication in the central Bohai Sea will likely be enhanced by the large-scale accumulation of anthropogenic nitrogen in adjacent open oceans. Such changes in nutrients may have fundamentally contributed to the recent development of algal blooms and seasonal hypoxia in the central Bohai Sea.

Environmental impact and recovery of the Bohai Sea following the 2011 oil spill

The 2011 spill at platforms B and C of the Penglai 19-3 oil field in the Bohai Sea has been the worst oil spill accident in China. To assess long-term effects, a comprehensive monitoring program of chemical and biological variables (within a 2.2 km radius of the spill site) was conducted five years after the spill. Comparison of nutrient, Chl-a and oil concentrations in seawater, TOC, PAHs, heavy metals concentrations within the sediments, and the abundance and biomass of macrobenthic organisms to values obtained before and after the oil spill in previous studies indicate habitat recovery has occurred within the Bohai Sea following the episodic oil release. Observed elevated oil concentration in the water column and higher concentrations of two heavy metals, five PAHs, TOC, TOC/TN and lower values of δ¹³C, together with a reduction in macrobenthic biomass in near-field samples, suggest the influence of contaminants from chronic releases of oil and operational waste discharges within the vicinity of the oil platforms.

Heavy metal contamination in surface sediments: A comprehensive, large-scale evaluation for the Bohai Sea, China

Heavy metal contamination in the Bohai Sea (China) has been the focus of many studies, but most of them only focused on local pollution levels and thus lacked high spatial resolution for the whole sea. In this study, heavy metals (i.e., As, Cr, Cu, Cd, Pb, Zn, and Fe) in surface sediments were analyzed to assess the spatio-temporal pollution conditions of the Bohai Sea, an important coastal environment consisting of Bohai Bay, Laizhou Bay, and Liaodong Bay. The results indicated that the heavy metal concentration in the sediments was in the range of 6.43-32.18 mg/kg for As, 14.90-58.07 mg/kg for Cr, 3.90-27.19 mg/kg for Cu, 0.04-0.27 mg/kg for Cd, 11.09-30.95 mg/kg for Pb, 18.76-65.58 mg/kg for Zn, and 0.78%-2.55% for Fe. The distribution of heavy metals revealed that the concentrations were relatively low in Laizhou Bay, very high in the northwest coastal region of the Bohai Sea, and decreased from near-shore to off-shore areas. Moreover, both the enrichment factor and geo-accumulation index demonstrated that there was no contamination to be found for Cr, Cu, Zn in the region and a slight to moderate pollution of As, Cd, and Pb. Cd and As presented considerable potential ecological risk as a result of their high toxicity. The potential ecological risk index (RI) suggested that a third of the areas (northwest coastal area of the Bohai Sea) has moderate ecological risk. The risk area was generally decreased as offshore distance increased, which suggested that the contamination and risk of heavy metals are influenced by anthropogenic activities.

Nutrients and heavy metals mediate the distribution of microbial community in the marine sediments of the Bohai Sea, China

The Bohai Sea, one of the largest marginal seas in China, is extensively influenced by human and industrial activities. The pollutant loads from anthropogenic activities have induced severe ecological problems. The study investigates the physicochemical characteristics of seawater and sediments in Bohai Bay and Laizhou Bay of the Bohai Sea. The diversity and composition of microbial community in sediments are analyzed by 16S rRNA gene amplicon sequencing. The sequencing results present 16 phyla and 31 classes from the samples. Proteobacteria constituted a dominant phylum, of which the classes of Gamma-, Delta-, and Epsilon-are predominant sub-divisions. Nitrogen, phosphorus, and sulfur cycling related microbes present high abundance in both bays. The metabolism of organic matters is the main factor that influences the distribution of microbial communities in Bohai Bay, while the inflow of Yellow River is the dominant factor that influences the distribution of microbial communities in Laizhou Bay. Sulfur oxidizing process is expected to be positively influenced by heavy metals, while ammonia (NH₄⁺) oxidizing process is prone to be negatively affected by heavy metals in both bays. Microbial communities in the offshore sediments of Laizhou Bay and the majority microbial communities in Bohai Bay sediments are subject to similar predominant controlling factors. This phenomenon is likely ascribed to ocean circulation. The results of this study can provide constructive guidelines on ecosystem management of marginal seas in Bohai and elsewhere.

Distribution of dissolved gaseous mercury (DGM) and its controlling factors in the Yellow Sea and Bohai Sea

Elemental mercury (Hg⁰) is the major form of mercury (Hg) emitted into the environment via anthropogenic activities, resulting in the distribution of Hg worldwide via atmospheric transport. Hg⁰ in oceans plays an important role in global Hg cycling, mainly by affecting the oceanic-atmospheric exchange of Hg. Due to the large amounts of Hg that are released into Chinese coastal seas from rivers and other sources, Chinese coastal seas are thought to be important sources of Hg in open oceans and in the atmosphere. There have been some studies on the distribution of dissolved gaseous mercury (DGM) in Chinses coastal seas and their controlling factors. However, most of these studies were focused on the surface seawater. There is still a lack of comprehensive study on the DGM through the entire water column in Chinese coastal seas. In this study, two cruises were conducted in August 2017 and in December 2017 to January 2018 to identify the distribution of DGM and its controlling factors in the Yellow Sea (YS) and the Bohai Sea (BS). The concentrations of DGM were higher in summer (167.5 ± 121.4 pg/L) than in winter (41.5 ± 25.5 pg/L), reflecting a significant seasonal variation in DGM. DGM concentrations in the BS and the YS were higher than in open oceans and lower than in some coastal regions. DGM concentrations were generally highest in the BS, followed by the northern YS and the southern YS in summer, whereas the reverse trend was observed in winter. DGM in seawater presented a complicated spatial distribution pattern, with high DGM concentration areas present both nearshore and offshore areas. This result indicates that both terrestrial input and in situ production may play important roles in controlling the DGM distribution. Correlation and multiple regression analyses suggested that temperature (T) and wind speed may be important factors affecting the seasonal variation in DGM in the YS and the BS, and reactive Hg (RHg), dissolved Hg (DHg), dissolved oxygen (DO) and suspended particulate matter (SPM) play important roles in controlling the spatial distribution of DGM.

Occurrence and spatial distribution of antibiotic resistance genes in the Bohai Sea and Yellow Sea areas, China

Rapid development of Bohai and Yellow Sea Economic Rim has led to the concern of emerging contamination of marine environments. This study investigated the spatial distribution of antibiotic resistance genes (ARGs) in Bohai and Yellow Sea areas. A large scale sampling from Bohai Sea, Yellow Sea and the major cities along the coastline from the mouth of Yalu River to the Yangtze River was performed. The spatial distribution of target ARGs based on the absolute abundances was in the trend of river water ≈ coastal water > the Bohai Sea > the Yellow Sea, inshore > offshore and inner bay > bay mouth. The total absolute abundances of selected ARGs in the coastal waters (1.23 × 10⁴-3.94 × 10⁵ copies/mL) were about 1-4 orders of magnitude higher than those in the sea (21.1-8.00 × 10³ copies/mL). The abundances of ARGs fluctuated greatly in the Yellow Sea and the coastal areas. Sulfonamide resistance genes hold the highest abundances in the Bohai and Yellow Sea (up to 2.13 × 10³ copies/mL of sul1 and 6.23 × 10³ copies/mL of sul2), followed by tetracycline and quinolone resistance genes, while qnrA hold the highest abundances in coastal areas (up to 3.66 × 10⁵ copies/mL). The distribution coefficients of target genes between sediments and corresponding water samples were more than 1.0 in the majority of different aquatic systems. According to the principle component analysis and redundancy analysis, water samples collected from the sea clustered together while those from the coastal zone and rivers were separated. Ammonium and nitrate played important roles in the distribution and variation of ARGs. Co-occurrence network analysis revealed that the potential multi-antibiotics resistant bacteria were detected with higher abundances in the Yellow Sea than in the Bohai Sea. These observations provided a comprehensive new insight into the pollution status of ARGs in the Bohai and Yellow Sea areas.

Presence and environmental risk assessment of selected antibiotics in coastal water adjacent to mariculture areas in the Bohai Sea

The presence and concentrations of 25 antibiotics in Dalian coastal water of the Bohai Sea were investigated using solid-phase extraction coupled with high-performance liquid chromatography tandem mass spectrometry. Results showed that antibiotics were widely detected in this region with total concentration ranging from 22.6 to 2402.4 ng/L. Enrofloxacin and trimethoprim were 100% detected followed by sulfamethoxazole with a detection rate of 90.9%. No significant correlations were found between antibiotics concentrations and sample parameters such as dissolved organic carbon, salinity, and distance from the coast, suggesting that concentrations and distributions of the antibiotics in this area were source-dependent. Antibiotic concentration in the sample from an offshore cage-culture area was the highest. Based on composition profiles, mariculture was supposed to be an important source of antibiotics. According to the assessment, individual antibiotic posed low to moderate risk, while the antibiotic mixture presented high risk. Enrofloxacin, clarithromycin and sulfamethoxazole, the top three contributors to the mixture risk quotients for each site, need priority control in this area. Besides, levels of enrofloxacin were high enough to exert a selective pressure on bacteria that may lead to an increase in the prevalence of resistance.

Contamination status of lipophilic marine toxins in shellfish samples from the Bohai Sea, China

Lipophilic marine toxins in shellfish pose significant threats to the health of seafood consumers. To assess the contamination status of shellfish by lipophilic marine toxins in the Bohai Sea, nine species of shellfish periodically collected from five representative aquaculture zones throughout a year were analyzed with a method of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Lipophilic marine toxins, including okadaic acid (OA), dinophysistoxin-1 (DTX1), pectenotoxin-2 (PTX2), yessotoxin (YTX), homo-yessotoxin (homo-YTX), azaspiracids (AZA2 and AZA3), gymnodimine (GYM), and 13-desmethyl spirolide C (13-DesMe-C), were detected in more than 95 percent of the shellfish samples. Toxins PTX2, YTX, 13-DesMe-C and GYM were predominant components detected in shellfish samples. Scallops, clams and mussels accumulated much higher level of lipophilic marine toxins compared to oysters. Toxin content in shellfish samples collected from different sampling locations showed site-specific seasonal variation patterns. High level of toxins was found during the stages from December to February and June to July in Hangu, while from March to April and August to September in Laishan. Some toxic algae, including Dinophysis acuminata, D. fortii, Prorocentrum lima, Gonyaulax spinifera and Lingulodinium polyedrum, were identified as potential origins of lipophilic marine toxins in the Bohai Sea. The results will offer a sound basis for monitoring marine toxins and protecting the health of seafood consumers.

The biogeochemical characteristics of phosphorus in coastal sediments under high salinity and dredging conditions

The geochemistry of phosphorus (P) can usually be related to prevailing environmental conditions. To investigate sedimentary P cycling mechanism and biogeochemical characteristics under high salinity and dredging conditions in polluted coastal sediments, thirty-three surface sediment samples were collected from the Jiehe River (JH), Jiaolai River (JL) and their estuarine and offshore areas in the Bohai Sea. Analyses included the Standards, Measurements and Testing method (SMT), Ivanoff organic P (OP) fractionation, and nuclear magnetic resonance (³¹P-NMR) of soluble P and indicated that HCl-P was the dominant fraction in sediments under high salinity stress. However, under dredging conditions in freshwater river sediments, NaOH-P was the dominant fraction. The potential activity of the OP fraction was reactive in freshwater river sediments, while it was unreactive under high salinity conditions. NaOH-P and HCl-P were found to be mainly derived from anthropogenic inputs, whereas both in-situ biological and anthropogenic inputs were important sources of the OP fractions. High salinity had the potential to increase NaOH-P content in acidic river sediments, resulting in the OP being relatively stable with a low risk level. Sediment dredging potentially increased the regeneration of P from HCl-P and OP and increased the potential activity of OP and IP. Seawater was found to induce removal of the NaOH-P and OP from offshore sediments, resulting in the regeneration of the remaining P at a low level.

Occurrence of microplastics in the water column and sediment in an inland sea affected by intensive anthropogenic activities

Microplastics may lose buoyancy and occur in deeper waters and ultimately sink to the sediment and this may threaten plankton inhabiting in various water layers and benthic organisms. Here, we conduct the first survey on microplastics in the water column and corresponding sediment in addition to the surface water in the Bohai Sea. A total of 20 stations covering whole Bohai Sea were selected, which included 6 stations specified for water column studying. Seawater was sampled every 5 m, with maximal depth of 30 m in the water column using Niskin bottles coupled with a ship-based conductivity, temperature and depth sensor (CTD) system and surface sediment samples were collected using box corer. The results indicated that higher microplastic levels accumulated at a depth range of 5-15 m in the water column in some stations, suggesting the surface water survey was not sufficient to reflect microplastics loading in a water body. Fibers predominated microplastic types in both seawater and sediment of the Bohai Sea, which accounted for 75%-96.4% of the total microplastics. However the relatively proportion of the fibers in the deeper water layers and sediment was lower than that in the surface water. Microplastic shapes are more diverse in the sediment than in the seawater in general. The microplastic sizes changed with depth in the water column and the proportion of the size-fraction < 300 μm increased with depth, probably as a result of rapid biofouling on the small microplastics due to their higher specific surface area. Such depth distribution also implied that sampling with manta net (>330 μm) that commonly used in the oceanographic survey might underestimate microplastics abundance in the water column. Further studies are recommended to focus on the sinking behavior of microplastics and their effects on marine organisms.

Flux and source-sink relationship of heavy metals and arsenic in the Bohai Sea, China

This study conducted a field campaign to collect atmospheric deposition samples of heavy metals and arsenic, a metalloid element with typical chemical-physical characteristics (HMA), from 12 sampling sites and water samples from 37 rivers across the Bohai Sea (BS) and North Yellow Sea (NYS) in China. The HMA budgets in the BS and NYS were quantified by a budget model, which was developed based on the HMA inputs from atmospheric deposition and riverine discharge, sequestration to sediment, and interexchange among the BS's four subareas and the NYS. Statistical analyses of 76 deposition samples and 109 water concentration samples showed that atmospheric deposition was a main pathway of Pb entering the BS and NYS, whereas riverine discharge dominated the input of Cr, Cu, Zn, Cd, and As into the marine environment. Modeled results showed that the fractions of HMA in the water bodies compared with their total burdens were 86.6 ± 4.55% in the Liaodong Bay, 60.5 ± 10.5% in the Bohai Bay, 20.9 ± 9.05% in the Laizhou Bay, 95.1 ± 2.06% in the Central BS, and 94.3 ± 1.93% in the NYS. The lowest fraction of HMA in the Laizhou Bay was attributed to high sedimentation rates and higher suspended particulate matter concentrations due to inputs from the Yellow River. The modeled 1-, 10- and 100- year mass budgets indicated that the Liaodong Bay in the north of the BS was a sink of HMA, the Bohai Bay and Laizhou Bay in the west and south of the BS acted as sources, and the Central BS and NYS were a transition area for most HMA.

Environmental occurrence and distribution of organic UV stabilizers and UV filters in the sediment of Chinese Bohai and Yellow Seas

Organic UV stabilizers and UV filters are applied to industrial materials and cosmetics worldwide. In plastics they prevent photo-induced degradation, while in cosmetics they protect human skin against harmful effects of UV radiation. This study reports on the occurrence and distribution of organic UV stabilizers and UV filters in the surface sediment of the Chinese Bohai and Yellow Seas for the first time. In total, 16 out of 21 analyzed substances were positively detected. Concentrations ranged from sub-ng/g dw to low ng/g dw. The highest concentration of 25 ng/g dw was found for octocrylene (OC) in the Laizhou Bay. In the study area, characteristic composition profiles could be identified. In Korea Bay, the dominating substances were OC and ethylhexyl salicylate (EHS). All other analytes were below their method quantification limit (MQL). Around the Shandong Peninsula, highest concentrations of benzotriazole derivatives were observed in this study with octrizole (UV-329) as the predominant compound, reaching concentrations of 6.09 ng/g dw. The distribution pattern of UV-329 and bumetrizole (UV-326) were related (Pearson correlation coefficient r > 0.98, p « 0.01 around the Shandong Peninsula), indicating an identical input pathway and similar environmental behavior.

Extensive study of potential harmful elements (Ag, As, Hg, Sb, and Se) in surface sediments of the Bohai Sea, China: Sources and environmental risks

This study analyzed 405 surface sediment samples, obtained from across the Bohai Sea, for concentrations of five potentially harmful elements (Ag, As, Hg, Sb, and Se) and several ancillary parameters (Al, Fe, Mn, total organic carbon (TOC), and grain size). Statistically, the spatial distributions of these elements were correlated positively with Al, Fe, TOC, and grain size, indicating natural sources for these elements or common accumulation mechanisms. The assessment of potential environmental risk with empirical sediment quality guidelines showed that a significant proportion of the samples had As and Sb concentrations that exceeded the effects range low (ERL) or T₂₀ values in the Bohai Sea, indicating the potential for adverse biological effects. However, the assessment results differed when using evaluation methods that considered background values. Based on the geoaccumulation index (I_geo), Hg and Ag were found to have the highest percentages (35% and 60%, respectively) in samples that were moderately contaminated. The estimated contamination degree (C_d) suggested higher contamination levels for the entire area, with 69% of the samples being moderately contaminated. Generally, except for some local hotspots, such as Jinzhou Bay, the contamination levels of these elements in the Bohai Sea were established as slight to moderate. Samples from the Jinzhou Bay area had concentrations that were 10-100 times higher than in the rest of the Bohai Sea, indicating severe contamination.

Hexabromocyclododecanes (HBCDDs) in surface soils from coastal cities in North China: Correlation between diastereoisomer profiles and industrial activities

Hexabromocyclododecane (HBCDD) is a brominated flame retardant with a wide range of industrial applications, although little is known about its patterns of spatial distribution in soils in relation to industrial emissions. This study has undertaken a large-scale investigation around an industrialized coastal area of China, exploring the concentrations, spatial distribution and diastereoisomer profiles of HBCDD in 188 surface soils from 21 coastal cities in North China. The detection frequency was 100% and concentrations of total HBCDD in the surface soils ranged from 0.123 to 363 ng g(-1) and averaged 7.20 ng g(-1), showing its ubiquitous existence at low levels. The spatial distribution of HBCDD exhibited a correlation with the location of known manufacturing facilities in Weifang, suggesting the production of HBCDD as major emission source. Diastereoisomer profiles varied in different cities. Diastereoisomer compositions in soils were compared with emissions from HBCDD industrial activities, and correlations were found between them, which has the potential for source identification. Although the contemporary concentrations of HBCDD in soils from the study were relatively low, HBCDD-containing products (expanded/extruded polystyrene insulation boards) would be a potential source after its service life, and attention needs to be paid to prioritizing large-scale waste management efforts.