Bohai Sea Research Articles

Dramatic loss of seagrass Zostera marina L. suitable habitat under projected climate change in coastal areas of the Bohai Sea and Shandong peninsula, China

Seagrass is an important foundational species in marine ecosystems that plays an important role in providing ecosystem services. However, seagrass distribution and suitable habitat have rapidly declined in recent decades because of climate change and human-mediated disturbances. To achieved better conservation and management of the seagrass Zostera marina, an important representative seagrass in northern China, studies must investigate how this species responds to climate change. Here, we used an ensemble species distribution model to forecast the potential distribution and future suitable habitat change for the eelgrass Z. marina in coastal areas of the Bohai Sea and Shandong Peninsula, China. Two future climate scenarios, RCP 4.5 and RCP 8.5, were considered, which represent stable and high levels of greenhouse gas emissions, respectively. The ensemble model accurately predicted the current Z. marina distribution and performed better than the single-algorithm methods of random forest, generalized boosting model and maximum entropy according to performance matrices (AUC and TSS). The distance to land (78.50 ± 3.51%) and the maximum sea surface temperature (11.90 ± 0.25%) were the most important variables determining the distribution of Z. marina, while the contributions of other variables, maximum sea surface current velocity (3.80 ± 0.33%), minimum surface salinity (2.15 ± 0.22%) and water depth (1.74 ± 0.24%) were relatively low. Under future climate scenarios, the suitable habitat of Z. marina was predicted to decrease by more than half by the 2050s, whereas under the pessimistic greenhouse gas emission scenario (RCP 8.5), suitable Z. marina habitat was predicted to decrease by nearly 80% by the end of this century. The loss of Z. marina seagrass beds will have important ecological effects on the marine ecosystem. Our results not only provide valuable information to assist in identifying potential Z. marina meadows, but also have important implications for guiding conservation and management of Z. marina in the northern coastal region of China.

Three-dimensional spatial interpolation for chlorophyll-a and its application in the Bohai Sea

Assessing the health of coastal ecosystems is crucial for maintaining ecological balance. One significant indicator of water eutrophication is the distribution of chlorophyll-a (Chl-a), which makes obtaining a complete three-dimensional spatial distribution of Chl-a essential for assessment. This study utilized the linear radial basis function (RBF-Linear) method to obtain a comprehensive and reasonable spatial distribution of Chl-a. The method was applied to obtain the three-dimensional spatial field of Chl-a concentration in the Bohai Sea in March, May, August, and October from 2016 to 2018. The distribution pattern of Chl-a concentration in the Bohai Sea displayed characteristic spatial and temporal variations. Spatially, high Chl-a concentration was most concentrated in coastal waters, particularly in estuaries and mariculture areas. Temporally, there were two peaks in March and August. The total Chl-a and areas with high Chl-a concentration in four sub-regions of the Bohai Sea were also calculated to enable a comprehensive assessment of the marine ecological environment. By analyzing the temporal and spatial variation of Chl-a in the Bohai Sea and evaluating the marine ecological environment, we confirmed the feasibility and rationality of RBF-Linear. Our findings have the potential to contribute to improve the accuracy of ecological models and assessment of the satellite products.

Sediment settling process revealed by a bottom-tethered sediment trap at the east tip of the Shandong Peninsula

This paper investigates sediment settling process during summer seasons based on in-situ observation and sediment analysis at the east tip of the Shandong Peninsula, which is a pathway for sediments from the Bohai Sea and the North Yellow Sea to enter the South Yellow Sea in China. Bottom-tethered sediment traps, together with platforms equipped with current profilers/meters and temperature/salinity and turbidity sensors, were deployed for approximately 10 days in August 2017 over an elongated deposit off the coast of the Shandong Peninsula. A computed tomography (CT) scan and grain size and 210Pb analyses of trap sediment were carried out to determine the settling process of suspensions at the study site. Twenty-three couplets were found in the CT images of the trap, the time series of which was established using intervalometer disks. Quantitative characterization of rhythmites using a hounsfield unit indicates that the period of couplets is approximately quarter-diurnal, and the settling process could be divided into three stages during Aug. 21st – 27th. Current, wave, wind, and SSC data illustrate that the diversion of the bottom current leads to the formation of couplets, and the thickness of the couplet is controlled by the vertical current velocity and wind direction. Northerly winds enhance the difference in settlement between flood and ebb tides, whereas southerly winds smoothen the difference. The gale event inhibited the settlement of the suspended matter, and the source of the suspensions was converted from local to remote after the event, as evidenced by 210Pb data. No evident erosion can be detected in the sediment traps. The results are of significance to better understand the sedimentary dynamics near the Shandong clinoform and inspire the practical efficiency of bottom-tethered sediment traps in the settling process in coastal areas.

Responses of the Sea Surface Temperature and Suspended Matter Concentration to ENSO Events in the Bohai Sea

Responses of the Sea Surface Temperature and Suspended Matter Concentration to ENSO Events in the Bohai Sea

Feasibility of Oil Mud Reinjection from Offshore Platforms in Bohai Oilfield

Sludge produced by offshore oilfields can be difficult to treat. thus, it is necessary to explore the feasibility of its reinjection into reservoirs for environmental protection and economic benefits. In this study, oil sludge produced from an oilfield in the Bohai Sea was ground and refined, and a reinjection system using a polymer solution was developed. To determine the feasibility of the reinjection system, we analysed its stability, solution performance, injection performance, and oil displacement effect. The experiment results indicate that when the particle concentration of the system is ≤ 200mg/L, the system dispersion, anti-shearing, and anti-ageing stability can be enhanced. When he particle concentration is ≤100 mg/L, the system can easily manage the viscous nature of the solid particles, thereby achieving optimal stability. At a particle concentration of 100mg/L, the system can run with optimal performance and achieve good oil displacement efficiency. Therefore, a system with a particle concentration of 100mg/L can be used for long-term reinjection of offshore platforms in the Bohai oil reservoir, achieving environmentally friendly treatment of produced sludge while further enhancing the oil recovery rate of the reservoir.

Forel-Ule index extraction and spatiotemporal variation from MODIS imagery in the Bohai Sea of China.

In large-scale water quality evaluation, traditional field-measured data lack spatial-temporal representativeness, and the role of conventional remote sensing parameters (SST, Chla, TSM, etc.) is controversial. By calculating and grading the hue angle of a water body, a Forel-Ule index (FUI) can be obtained, which provides a comprehensive statement of water condition. Using MODIS imagery, hue angles are extracted with better accuracy than the literature's method. It is found that FUI changes in the Bohai Sea have correlated consistently with water quality. The decreasing trend of non-excellent water quality areas in the Bohai Sea was highly correlated with FUI (R2 = 0.701) during the government-dominated land-based pollution reduction program (2012-2021). FUI can monitor and evaluate seawater quality.

Winter and summer sedimentary dynamic process observations in the sea area off Qinhuangdao in the Bohai Sea, China

Sedimentary processes in marginal seas play an important role in the biology, physics, and geochemistry as well as ecology of coastal environments and contain abundant information about the material transfer from land to ocean and the regional circulation. Due to the huge sediment discharge of the Yellow River, the Bohai Sea, China is one of the areas with the highest suspended sediment concentration (SSC) in the world. Interestingly, the SSC at the west of the Bohai Sea is low all year round. Thus, it is of great significance to examine the sedimentary dynamic process in this area for better understanding the circulation structure, material exchange and regional environment of the Bohai Sea. Using seabed base observation platform measurements obtained in February 2017 and August 2019, this study examines the winter and summer hydrography and suspended sediment concentration in the sea area off Qinhuangdao located to the west of the Bohai Sea. In summer, the relatively weak residual currents flowed northeastward and showed little correlation with the wind field, especially in the middle layer of the water column. In winter, the residual currents were strengthened, flowing to the northeast during strong wind periods, and predominantly to the southwest during intermittent periods. Moreover, driven by the pressure gradient force associated with the wind-induced sea surface height variations, the winter current was closely related to the wind speed, with correlation coefficients ranging from 0.4 to 0.6 and a time lag of 10 h. The summer SSC was lower and mainly controlled by the tidal current, whereas in winter, owing to the enhanced Reynolds stress and turbulent kinetic energy, strong wind bursts triggered significant sediment resuspension and led to a higher SSC. For the suspended sediment flux (SSF), the advection terms contributed more than 80% in the winter and summer, while the vertical circulation terms contributed 13% in winter, and approximately half that much in summer. Generally, the suspended sediment is transported back and forth, with a little net northward and northeastward motions in winter and summer, respectively. This may explain the low SSC sustaining in coastal Qinhuangdao all year round. These results provide a reference for sedimentary studies conducted in other coastal waters, especially in monsoon-dominating shelf seas.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

The temporal and spatial distribution of sea fog in offshore of China based on FY-4A satellite data

Satellite remote sensing is an important instrument of sea fog monitoring. In order to study the temporal and spatial distribution characteristics of sea fog and the influence of sea surface temperature (SST) on the sea fog, based on sea fog monitoring and SST products from FY-4A satellite, the monthly variation of sea fog and monthly average SST in five typical sea areas (including Bohai Sea, Yellow Sea, East China Sea, Taiwan Strait and South China Sea) are statistically analyzed. The results show that the sea fog in offshore has strong regional and seasonal characteristics. From winter to autumn, the sea fog first appears in the Beibu Gulf of the South China Sea, the sea fog extends from South China Sea to East China Sea, and then to Yellow Sea, finally to Bohai Sea. Sea fog is related to sea surface temperature. By comparing the sea fog with the SST distribution, the optimal SST is from 7 °C to 25 °C when the sea fog happens.

A modified sea ice area empirical prediction model based on multi-source satellite remote sensing data for Liaodong Bay of the Bohai Sea, China

Liaodong Bay is located in the north of the Bohai Sea, China. It experiences ice conditions of different degrees every year for about 3 months. Accurate prediction of sea ice area is of great significance for various marine activities. An empirical models based on the cumulative freezing temperature and cumulative melting temperature have been proposed in the past studies. This model can well describe the freezing and melting trend during each ice age, but it lost its accuracy for the prediction of short-term drastic change of sea ice area. In the present study, a modified empirical model considering sea surface temperature and wind besides cumulative freezing temperature and cumulative melting temperature is proposed. The coefficients of the modified model are fitted by the matched sea ice area of Liaodong Bay extracted from the multivariate satellite remote sensing images and the hydro-meteorological data from 2015, 2016, 2018 and 2019, while the data of 2020 are used for verification. Results show that the modified model can better adapt to the dramatic changes of sea ice area caused by short-term weather processes. The average absolute error is 685.71 km2 and the relative error is 23%. Finally, the influence of sea ice area on the time lag of temperature response and other factors such as water depth are discussed.

China's marine economic efficiency: A meta-analysis

With the rapid growth of the global economy and the depletion of land-based resources, the demand for the ocean as a major driver of economic development is increasing. In China, the marine economy has been a significant “blue engine” for national economic growth; hence, it is crucial to evaluate marine economic efficiency to understand China's marine industry's input-output status and development level. Based on 559 independent observations presented in 49 empirical primary studies, we conducted a meta-analysis to quantitatively explore the differences in measurement results and identify the factors influencing marine economic efficiency. The notable results were fourfold. (1) Significant heterogeneity is evident among the findings of the primary studies. Based on the random-effect model, China's overall marine economic efficiency is 0.720, indicating that considerable potential remains for improving economic efficiency in the marine sector. (2) The data types, estimation methods, evaluation indicators, publication types, and publication years of primary studies significantly affect marine economic efficiency estimation results. (3) At the temporal level, marine economic efficiency generally demonstrates an upward trend with the increase in the sample data years. At the spatial level, the marine economic efficiency of the Circum Bohai Sea region is significantly higher than that of the Pan-Pearl River Delta region, whereas it does not significantly differ from the Yangtze River Delta region. (4) The level of marine science and technology, as well as the marine industry structure, exerts a significant positive impact on marine economic efficiency, whereas the gross ocean product negatively impacts marine economic efficiency. Accordingly, the following insights were obtained. In terms of marine economic development policies, policymakers should intensify scientific and technological innovation, balance marine resource use and marine environmental conservation, so that power a shift of the marine economy from resource-dependent growth to the orientation of better quality and benefit. In addition, priority must be given to the synergistic development of coastal regions and marine industry structure optimization and upgrading. Future studies should use long-term panel data, focus on using the parametric stochastic frontier analysis method, and assess negative environmental impacts by constructing a green evaluation index system.

Sedimentary record of a late Holocene storm event in Laizhou Bay, Bohai Sea, China

Sedimentary record of a late Holocene storm event in Laizhou Bay, Bohai Sea, China

Organophosphate esters in the seawater of the Bohai Sea: Environmental occurrence, sources and ecological risks

Organophosphate esters (OPEs) are widely distributed in surface water systems, but limited information was available on the spatial occurrence and ecological risks of OPEs in the Bohai Sea. In this study, 89 water samples in the Bohai Sea and the five surrounding rivers were investigated for the determination of 15 OPEs. The concentration of ∑15OPEs ranged from 373.20 to 2931.27 ng·L−1 in the river water and 137.81 to 2641.30 ng·L−1 in the seawater, with high levels of OPEs in Liaodong Bay. Tris(2-chloroethyl) phosphate (TCEP, 10– 92 %) and triethyl phosphate (TEP, 5– 64 %) were dominant for OPEs. The correlation analysis, principal component analysis and hierarchical cluster analysis suggested the conjunction of municipal wastewater via river input and maritime shipping was the main source of OPEs in the Bohai Sea. The ecological risk assessment indicated that the individual OPEs arise low ecological risks in the Bohai Sea, while medium ecological risks of ∑15OPEs are in minority river samples.

Description of a new nematode species, Chromadorinacommunis sp. nov. (Nematoda, Chromadoridae), from Changdao Island, China and phylogenetic analysis of Chromadorida based on small subunit rRNA gene sequences.

Chromadorinacommunissp. nov. is described from Changdao Island at the confluence of the Yellow and the Bohai seas. The new species is characterized by its medium-sized body; finely striated cuticle with homogeneous punctations; absence of ocelli; buccal cavity with three equal-sized, solid teeth; four cephalic setae; oval amphidial fovea which is positioned between cephalic setae; curved spicules with tapered distal ends; simple, boat-shaped gubernaculums; five or six cup-shaped precloacal supplements; and conical tail with a very short spinneret. A phylogenetic analysis of small subunit rRNA gene sequences using maximum-likelihood and Bayesin inference confirmed the taxonomic position of Chromadorinacommunissp. nov. within Chromadorinae. Tree topology in Chromadorida shows six morphological families clustered into a monophyletic clade and verifies the taxonomic position of the family Neotonchidae based on morphological and molecular analysis.

Projection of future long-term Aurelia coerulea biomass variability by regional moderate-temperature-duration approach in the Bohai and Yellow Seas

As temperature is regarded as a significant environmental factor affecting the intensity and frequency of jellyfish blooms, the projection of jellyfish peak biomass variation under global warming becomes essential for disaster prevention and mitigation on long-term time scales. The jellyfish Aurelia coerulea is distributed in worldwide oceans, particularly in the Bohai and Yellow Seas (BYSs), which are productive regions with substantial economic and climatic significance and have been suffered from A. coerulea blooms. Based on the theory of how A. coerulea reacts to various experimental temperature circumstances, recent studies have been proposed to determine the qualitative trends of A. coerulea blooms in response to climate change. However, the quantitative study of future A. coerulea biomass variability is a challenging task due to the uncertainty in the numerical relation between temperature and the biomasses of A. coerulea and the difficulty in determining the biomass considering the high mobility of jellyfishes. In this paper, we develop a moderate-temperature-duration approach to solve these two problems. The temperature suitability for all key life stages of A. coerulea during pelagic and benthic processes is involved in this approach, and we identify the major life stage that determines the peak biomass variation. The projection of future peak biomass of A. coerulea in BYSs is performed based on this approach and utilizing the long-term projection results of temperature changes by 2100 using the MPI-ESM-MR model from phase 5 of the Coupled Model Intercomparison Project (CMIP5) under the RCP4.5 scenario. The results indicate that global warming can certainly lead to the increase in A. coerulea biomass in some degree. The steady state of the highest peak biomass will be achieved during 2075∼2080, with an increase of 8.4%, 5.0%, and 11.5% in the Bohai Sea, the North Yellow Sea, and the South Yellow Sea, respectively, compared to the first steady state starting in 2020 detected by the regime shift. However, the result also shows that global warming cannot consistently lead to the increase of A. coerulea peak biomass. As the temperature rises to a large extent, the duration of moderate temperature ranges for strobilation and growth may be reduced, and thus resulting in the decrease of peak biomass instead.

Spatio‐temporal pattern and driving mechanisms of land use conflicts changes (2010–2018) in the Bohai Rim transition zone

AbstractWith the rapid development of society and economy in the coastal regions, conflicts between ecological protection and human exploitation are inevitable. However, previous studies on the Spatio‐temporal evolution of conflicts in the coastal transition zone are insufficient, and the majority ignore the dependence of data on space. This study constructed a multi‐objective evaluation model from three angles (ecological, agriculture, and construction). It evaluated the dynamics of land use conflicts (LUCs) in the Bohai Rim transition zone for 2010, 2015, and 2018 at 30 m2 spatial resolution using the multi‐factor superposition method. The driving mechanism of LUCs was explored from the perspectives of natural and socio‐economic by applying the spatial econometric method. Major findings of this study indicated that there was a critical Spatio‐temporal mismatch in the spatial distribution of three types of land suitability around the Bohai Sea from 2010 to 2018. On the grid scale, an estimated LUCs area in 2010 was 1.21 × 105 km2, which decreased to 1.20 × 105 km2 in 2018. On the country scale, the conflict index displayed a polarized spatial distribution of “high in the south and low in the north,” and its spatial disparity showed a narrowing trend. Moreover, LUC types showed different change characteristics along the sea‐land direction. It ought to be noticed that the spatial clustering pattern of LUCs resulted from the combined action of various factors. This study's logical framework and outcomes could be utilized for formulating reasonable land use patterns to reduce the LUCs in the coastal transition zone.

Characteristics, seasonal variations, and dry deposition fluxes of carbonaceous and water-soluble organic components in atmospheric aerosols over China's marginal seas

A total of 37 atmospheric aerosol samples were collected over the Yellow and Bohai Seas (YBS) during four cruises in autumn, winter, spring and summer from 2017 to 2018. The concentrations of organic carbon (OC) and water-soluble organic carbon (WSOC) ranged from 1.04 to 15.43 μg m−3 and 0.77–5.49 μg m−3, respectively, with higher values in autumn and winter than in spring and summer. WSOC contributed 68.49 % to OC in summer and 34.55 % in winter and was affected by temperature and relative humidity. Dicarboxylic acid showed a predominance of oxalic acid followed by malonic and then succinic acids. The contributions of secondary sources to OC and WSOC were 54 % and 65.3 %, respectively, indicating the importance of secondary aging in improving the water solubility of OC. The dry deposition flux of WSOC over the YBS was estimated to be 0.87 mg m−2 d−1, which might play a potential role in the marine carbon cycle.

Physical structure and summer bottom oxygen depletion dynamics in the Bohai Sea

Physical structure and summer bottom oxygen depletion dynamics in the Bohai Sea

Large-scale assessment of exposure to legacy and emerging per- and polyfluoroalkyl substances in China's shorebirds

Emerging per- and polyfluoroalkyl substances (PFAS) have become more widely applied, whereas legacy PFAS such as PFOS continue to distribute ubiquitously in the environment. Large-scale assessment of wildlife exposure to both emerging and legacy PFAS plays a key role in effective biomonitoring to better discriminate regional contamination patterns and provide early warnings. Using eggs of two closely-related shorebird species collected across China during the breeding season in 2021, we constructed contrasting PFAS levels and profiles in coastal versus inland populations. The highest ∑PFAS concentrations were found in two Kentish plover (Charadrius alexandrinus) populations from the Bohai Sea, a semi-enclosed shallow bay located in northeast China. These two populations showed exceptionally high PFOA concentrations (mean: 94 and 121 ng/g wet weight; West and North Bohai Sea, respectively) dominating the overall PFAS profile (66% for both). This pattern is characteristic, compared to that of other seabird eggs worldwide. By comparison, PFAS profile in the white-faced plover (Charadrius dealbatus) population at the South China Sea coast was dominated by PFOS (46%), which showed similar levels to those at the North Bohai Sea coast (mean: 29 and 20 ng/g, respectively). PFAS concentrations of Kentish plovers from the remote Qinghai Lake were lower compared to the three coastal populations, and were dominated by PFNA (mean: 2.6 ng/g, 29%) and PFOS (mean: 2.5 ng/g, 27%). None of the eggs analyzed in the present study exceeded estimated toxicity reference values for PFOS or PFOA. Additionally, the emerging 6:2 Cl-PFESA was detected in eggs from all regions, while its concentrations were highest in the Bohai Sea populations, and short-chain PFBS was only detected in the North Bohai Sea population. Our results indicate intensive local emissions of PFOA and emerging PFAS at the Bohai Sea region, and warrant further investigation and monitoring.

Laboratory Experiment and Application Evaluation of a Bio-Nano-depressurization and Injection-Increasing Composite System in Medium-Low Permeability Offshore Reservoirs.

Given the high injection pressure and insufficient injection volume in the offshore oilfield, Bohai Oilfield has developed a bio-nano-depressurization and injection-increasing composite system solution (bio-nano-injection-increasing solution) composed of bio-surfactants, hydrophobic nano-polysilicon particles, and dispersant additives. In response to the current problems, a new type of bio-nano-depressurization and injection enhancement technology has been studied, which has multiple functions such as nano-scale inhibition and wetting reversal. The new technology has the technical advantages of efficient decompression, long-term injection, and wide adaptation. However, there is still a lack of optimization schemes and application effect prediction methods, which hinder the further popularization and application of the bio-nano-composite system solution. To solve this problem, this paper takes Well A1 in the Bohai Sea as an example to optimize the injection volume, concentration, and speed of the bio-nano-augmentation fluid and evaluates the application effect by using the proposed well testing, water absorption index, and numerical simulation methods. The research results show that the bio-nano-injection fluid can effectively improve the reservoir permeability and reduce the injection pressure. The application effect evaluation method proposed is reliable and can provide some reference for similar depressurization and injection-increasing technologies.