Impacts of inland pollution input on coastal water quality of the Bohai Sea

Phosphorus depletion is exacerbated by increasing nitrogen loading in the Bohai sea

Phosphorus (P) is an essential nutrient for algal growth in nearshore ecosystems. In recent years, there has been a shift in nutrient dynamics in nearshore areas, leading to an exacerbation of P limitation, although the underlying mechanisms remain unclear. This study analyzed the P species and budget in the Bohai Sea (BS) from 2011 to 2020, aiming to explore the intrinsic mechanisms of P limitation in the BS. The results show that the main external source of P in the BS was river transport (89%), and the primary fate of P was burial (96%) into the sediment. Due to excessive nitrogen (N) input and biological processes in the BS, the P budget in the BS is unbalanced, resulting in an increase in the N/P ratio, particularly in nearshore areas. Nearshore areas typically have lower concentrations of dissolved inorganic P (DIP) in the water and higher concentrations of reactive P (Reac-P) in the sediments. This pattern is particularly evident in Bohai Bay and the northwest nearshore region, where harmful algal blooms occur frequently. To cope with enhanced P limitation, the biologically driven P regeneration and cycling processes within the BS are accelerated. From 2011 to 2020, the concentration of DIP in the BS during autumn increased, while the content of Reac-P in sediments slightly decreased. Historical data indicate that P depletion in the BS is intensifying and expanding, primarily due to N enrichment and algal production. N enrichment alters the structure and composition of primary production, potentially exacerbating P depletion in the BS. Excessive N may have significant impacts on the P pool, potentially influencing the stability of future coastal ecosystems.

Seasonal and anthropogenic influences on bacterioplankton communities: ecological impacts in the coastal waters of Qinhuangdao, Northern China

Marine bacterioplankton play a crucial role in the cycling of carbon, nitrogen, and phosphorus in coastal waters. And the impact of environmental factors on bacterial community structure and ecological functions is a dynamic ongoing process. To systematically assess the relationship between environmental changes and bacterioplankton communities, this study delved into the spatiotemporal distribution and predicted metabolic characteristics of bacterioplankton communities at two estuarine beaches in Northern China. Coastal water samples were collected regularly in spring, summer, and autumn, and were analyzed in combination with environmental parameters and bacterioplankton community. Results indicated significant seasonal variations in bacterioplankton communities as Bacteroidetes and Actinobacteria were enriched in spring, Cyanobacteria proliferated in summer. While Pseudomonadota and microorganisms associated with organic matter decomposition prevailed in autumn, closely linked to seasonal variation of temperature, light and nutrients such as nitrogen and phosphorus. Particularly in summer, increased tourism activities and riverine inputs significantly raised nutrient levels, promoting the proliferation of specific photosynthetic microorganisms, potentially linked to the occurrence of phytoplankton blooms. Spearman correlation analysis further revealed significant correlations between bacterioplankton communities and environmental factors such as salinity, chlorophyll a, and total dissolved phosphorus (TDP). Additionally, the metabolic features of the spring bacterioplankton community were primarily characterized by enhanced activities in the prokaryotic carbon fixation pathways, reflecting rapid adaptation to increased light and temperature, as well as significant contributions to primary productivity. In summer, the bacterial communities were involved in enhanced glycolysis and biosynthetic pathways, reflecting high energy metabolism and responses to increased light and biomass. In autumn, microorganisms adapted to the accelerated decomposition of organic matter and the seasonal changes in environmental conditions through enhanced amino acid metabolism and material cycling pathways. These findings demonstrate that seasonal changes and human activities significantly influence the structure and function of bacterioplankton communities by altering nutrient dynamics and physical environmental conditions. This study provides important scientific insights into the marine biological responses under global change.

Nitrate transformation and source tracking of rivers draining into the Bohai Sea using a multi-tracer approach combined with an optimized Bayesian stable isotope mixing model

Excessive levels of NO3- can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO3- sources, while limited studies have utilized optimized Bayesian models for NO3- tracing in the coastal rivers. The Bohai Rim is highly susceptible to ecological disturbances, particularly N pollution, and has emerged as a critical area. Therefore, identification the N fate and understanding their sources contribution is urgent for pollution mitigation efforts. In addition, understanding the influenced key driven factors to source dynamic in the past ten years is also implication to environmental management. In this study, water samples were collected from 36 major river estuaries that drain into the Bohai Sea of North China. The main transformation processes were analyzed and quantified the sources of NO3- using a Bayesian stable isotope mixing model (MixSIAR) with isotopic approach (δ15N-NO3- and δ18O-NO3-). The overall isotopic composition of δ15N-NO3- and δ18O-NO3- in estuary waters ranged from -0.8-19.3‰ (9.3 ± 4.6‰) and from -7.1-10.5‰ (5.0 ± 4.3‰), respectively. The main sources of nitrate in most river estuaries were manure & sewage, and chemical fertilizer, while weak denitrification and mixed processes were observed in Bohai Rim region. A temporal decrease in the nitrogen load entering the Bohai Sea indicates an improvement in water quality in recent years. By incorporating informative priors and utilizing the calculated coefficients, the accuracy of sourcing results was significantly improved. This study highlighted the optimized MixSIAR model enhanced its accuracy for sourcing analysis and providing valuable insights for policy formulation. Future efforts should focus on improving management strategies to reduce nitrogen into the bay.

Marine ecological security shelter in China: Concept, policy framework, mechanism and implementation obstacles

Building a marine ecological security shelter (MESS) has become the main strategy to adapt marine ecological threats in China. As China's marine policy lacks a robust framework document, it is necessary to consider whether the policy system can effectively support the construction of MESS. However, the linkage between the construction measures of MESS and related policies is not clear. Therefore, the purpose of this paper is to clarify the concept of MESS and its connection with policy, by adopting the policy content analysis method to analyze the evolution process of MESS-related policy system. The legislative shortcomings and implementation obstacles of the MESS-related policy system are then summarized and discussed. The results show that from 1981 to 2021 the MESS-related policy system has been continuously improved. However, the policy system's support and guarantee capacity for building MESS still needs to be improved. (1) Due to the lack of basic laws and special laws, the coordination among governance subjects and among policies lacks legislative guarantee. (2) The construction of MESS continues the inter-regional and inter-department administrative barriers in collaborative governance of marine environment. To establish an effective collaborative governance model, it is essential to improve the governance structure and mechanism. (3) The government-led governance pattern faces the problem of mechanism failure. The command and control instrument accounts for more than 82%, and the public and enterprises lack strong policy guarantees to participate in marine governance. (4) The policy system's adaptability to emerging threats must be improved. Marine policies rarely involve emerging threats such as climate change and new pollutants. Meanwhile, the real-time supervision and monitoring mechanism is weak. The real-time supervision is only accounting for about 10%. Generally speaking, as a complex and long-term system engineering, the construction of MESS will inevitably encounter contradictions in politics, culture, and economy. China should deepen the construction of marine ecological civilization and form a governance concept based on ecosystems. Overall, this paper helps to understand the internal connection between MESS and policy comprehensively and provides a new perspective for improving China's marine governance capacity.

Nutrient dynamics in the Bohai and North Yellow seas from seasonal to decadal scales: Unveiling Bohai Sea eutrophication mitigation in the 2010s

The eutrophication status in the central Bohai Sea tends to be mitigated in recent years. To explore the recent nutrient status, seasonal surveys were carried out from 2018 to 2021, covering both the Bohai Sea and the adjacent North Yellow Sea. In recent cold seasons, both dissolved inorganic nitrogen concentration (DIN) and the ratio of DIN to soluble reactive phosphorus were lower than those in 2016. In warm seasons, the variations in nutrients and apparent oxygen utilization were correlated with each other, roughly following the traditional Redfield ratio of N:P:O2 of approximately 16:1:(-138). When historical data for N*, which is the excess DIN related to soluble reactive phosphorus, was collated, the Bohai Sea showed a decreasing trend for N* at a rate of -0.64 ± 0.12 μmol N* kg-1 a-1 between 2011 and 2021. During the same period, the North Yellow Sea N* concentrations (i.e., the oceanic end-member of the Bohai Sea N* dynamics) and the local atmospheric nitrogen (N) deposition (atmospheric end-member) were estimated to decline at rates of -0.22 ± 0.04 μmol N* kg-1 a-1 and - 0.93 ± 0.34 kg N ha-1 a-2, respectively. Consequently, the oceanic and atmospheric changes accounted for 25.7 % ± 28.4 % and 69.0 % ± 42.6 %, respectively, of the Bohai Sea eutrophication mitigation in 2011-2021. On the long-term changes of the Bohai Sea eutrophication, the terrestrial nutrient source has only minor (likely <10 %) impacts, although it certainly affects the spatial distribution of nutrients. This study has implied that coastal eutrophication is a dynamic process that is subject to sea-land-air interactions, and its mitigation needs both local pollution controls and regional environment management. The latter contains the understanding of oceanic changes and external effects of the air pollution control.

Comparative assessment of the environmental pollution and marine economic growth of Guangxi and China by using the environmental Kuznets curve fitting model

This study examined the nexus between per capita gross ocean product (GOP) growth and total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) discharged from land-based sources in Guangxi and China. Multiple pollution indicators, such as red tide area (RTA), seawater quality area (SWQA), and eutrophication area (EA), were used as marine environmental quality indicators, and annual time series data during the period 2010-2019 were employed. The data were analyzed using the environment Kuznets curve fitting model. Results showed that the average annual growth rates of the GOP and gross domestic product (GDP) of China were 9.88% and 10.79%, respectively, and those of Guangxi were 13.62% and 10.02%, respectively. The average annual GOP ratio in GDP for Guangxi and China was 6.59 and 9.47, respectively. The marine tertiary industry was the most dominant marine industry; it accounted for 41.12-50.01% (mean: 46.12%) of Guangxi's GDP and 47-60% (mean: 52.47%) of China's GDP. The TP, COD, SWQA, and EA of Guangxi and the TP, TN, COD, SWQA, and EA of China displayed inverted U-shaped GOP growth. These findings indicate that the marine economic growth and marine environmental quality of Guangxi and China are harmonious. However, TN increased synchronously with marine economic growth in Guangxi. Therefore, the industrial structure must be further optimized, pollutant discharge management must be strengthened, and the harmonious development of Guangxi's marine economy and marine environment needs to be promoted.

Co-occurrence of toxic metals, bacterial communities and metal resistance genes in coastal sediments from Bohai bay

Sediment heavy metal contamination poses substantial risks to microbial community composition and functional gene distribution. Bohai Bay (BHB), the second-largest bay in the Bohai Sea, is subject to severe anthropogenic pollution. However, to date, there have been no studies conducted to evaluate the distribution of metal resistance genes (MRGs) and bacterial communities in the coastal sediments of BHB. In this study, we employed high-throughput sequencing based on 16S rRNA genes and real-time quantitative PCR (qPCR) to provide a comprehensive view of toxic metals, MRGs, and bacterial communities in BHB's coastal sediment samples across two seasons. We detected high levels of Cd in the summer samples and As in the autumn samples. The metal content in most autumn samples and all summer samples, based on ecological indices, indicated low ecological risk. Proteobacteria dominated all samples, followed by Desulfobacterota, Bacteroidota and Campilobacterota. Bacterial community variability was higher between autumn sampling sites but more stable in summer. We detected 9 MRG subtypes in all samples, with abundances ranging from 4.58 × 10-1 to 2.25 copies/16S rRNA copies. arsB exhibited the highest relative abundance, followed by acr3, czcA and arrA. The efflux mechanism is a common mechanism for sediment resistance to metal stress in Bohai Bay. Procrustes analysis indicated that bacterial community composition may be a determinant of MRGs composition in BHB sediments. Network analysis suggested that eight classes could be potential hosts for six MRGs. However, this type of correlation requires further validation. To summarize, our study offers preliminary insights into bacterial community and MRG distribution patterns in heavy metal-exposed sediments, laying the groundwork for understanding microbial community adaptations in multi-metal polluted environments and supporting ecological restoration efforts.

Terrestrial inputs and physical processes control the distributions of potentially toxic elements (PTEs) in the seawater of the large-range Beibu Gulf, the northern South China Sea

The potentially toxic elements (PTEs), Cu, Pb, Zn, Cd, Cr, Hg and As in the water from the Beibu Gulf, were investigated to reveal the contaminant characteristics and assess the risks to human health. The results showed that the concentration of PTEs in the Beibu Gulf varies significantly both seasonally and spatially, with higher concentrations in summer and in the northern and southern gulf. Terrestrial inputs and local anthropogenic discharge are responsible for the higher level in the northern gulf, and the transportation of water masses is also an important factor for the higher concentrations in the southern gulf. Ecological risk assessment suggested that Hg is the main ecological risk factor. The health risk assessment revealed that dermal exposure to PTEs in the gulf presents potentially carcinogenic health effects for humans. This study provides new insight into the transport of PTEs over a large area of the Beibu Gulf.

Seasonal dynamics of coastal pollution migration in open waters with intensive marine ranching

Mariculture activities have been recognized as one of the major sources of contamination for marine pollutants, such as the excessive discharging of nitrogen and phosphate. The fully understanding of the pollutants emission and transportation is crucial for coastal environment management. However, the influence of such highly dynamic coastal process on the pollutant migration remain unclear, such as the effects of coastal seasonal hydrodynamics on the dissolved pollutant transportation, especially under intensive marine ranching activities in open waters. This study investigated the seasonal transport mechanisms of pollutants released from three typical mariculture methods (floating raft, cage and bottom pond) in the Wangjia Island (WJ), Yellow Sea, China. We have conducted three field surveys to monitor the coastal dynamics and measure the distribution of dissolved pollutants in the ranching area. Results from these field surveys show that the WJ and adjacent area experienced significant degradation in terms of water quality with the development of regional marine ranching. The average of calculated index for eutrophication Ei increases from 0.12 in the non-farming area to 0.78 in the farming area. In order to delineate the impacts area of pollutant transport associated with these highly dynamics of water exchange, a Eulerian passive tracer-tracking module is applied to simulate the pollutant transport processes based on a field scale three-dimensional Finite Volume Coastal Ocean Model (FVCOM). Then after, the impacts of barotropic and baroclinic coastal dynamics on the migration of dissolved pollutants were evaluated. The transport of pollutants was greatly influenced by the different farming modes. The travel distance of pollutants released from the bottom pond farming mode was limited, whereas pollutants from the surface-farming methods were transported over a longer distance. In this study, there are three folders of finding: 1) The migration direction varies with seasons, with a landward direction in winter and an offshore direction in summer; 2) In winter, strong wind (wind speed over 10 m/s) is the dominant factor for water exchange, which is conducive to the dispersion of pollutants in the study area. However, in summer, the thermal stratification controls pollutant migration; 3) The results of breakthrough time illustrate that the pollutants travelled slower during summer, especially for pollutants discharged from the bottom pond farming method. In summary, this study demonstrates that even in open waters with stronger water exchange capacity, the pollutants from intensive marine ranching can still increase the risk of eutrophication. The finding of this study has important implications for the management and regulation of offshore aquaculture activities, particularly for mitigating pollutants from marine ranching.

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.

Hindcasting harmful algal bloom risk due to land-based nutrient pollution in the Eastern Chinese coastal seas

Harmful algal blooms (HABs) have been increasing in frequency, areal extent and duration due to the large increase in nutrient inputs from land-based sources to coastal seas, and cause significant economic losses. In this study, we used the "watershed-coast-continuum" concept to explore the effects of land-based nutrient pollution on HAB development in the Eastern Chinese coastal seas (ECCS). Results from the coupling of a watershed nutrient model and a coast hydrodynamic-biogeochemical model show that between the 1980s and 2000s, the risk of diatom blooms and dinoflagellate blooms increased by 158% and 127%, respectively. The spatial expansion of HAB risk caused by dinoflagellates is larger than that of diatoms. The simulated suitability of the habitat for bloom of Aureococcus anophagefferens, a pico-plankton of non-diatom or dinoflagellate, in the Bohai Sea is consistent with observations spatially and temporally. To halt further nutrient accumulation in the ECCS, reductions of dissolved inorganic nitrogen (DIN) (16%) and dissolved inorganic phosphorus (DIP) (33%) loading are required. To improve the situation of distorted DIN:DIP ratios, even larger reductions of DIN are required, especially in the Bohai Sea. Our approach is a feasible way to predict the risk of HABs under the pressure of increasing anthropogenic nutrient pollution in coastal waters.

Interannual variations in the nutrient cycle in the central Bohai Sea in response to anthropogenic inputs

In recent decades, there has been growing concern regarding the effects of human activities on the coastal nutrient cycle. However, interannual variations in the coastal nutrient cycle in response to anthropogenic nutrient input have rarely been quantified. In this study, a hydrodynamic-ecological model capable of describing the nitrogen and phosphorus cycles was used to analyze interannual variations in the nutrient cycle in the central Bohai Sea, a typical semi-enclosed sea in the Northwest Pacific. The results showed an increasing trend of dissolved inorganic nitrogen and particulate nitrogen from 1998 to 2017, whereas different forms of phosphorus showed no obvious interannual variations. The annual nutrient budgets were also quantitatively estimated from 1998 to 2017. This indicates that atmospheric nitrogen deposition plays an important role in interannual variations in the nitrogen cycle. A large amount of nitrogen from anthropogenic inputs was mainly removed by sedimentation processes instead of increasing the standing stock of nitrogen in the sea. With the reduction of anthropogenic inputs, the model showed that a variety of forms of nitrogen concentration decreased linearly, whereas phosphorus concentration increased slightly. Therefore, although environmental governance can effectively alleviate water eutrophication, it is necessary to avoid the situation where the dissolved inorganic nitrogen concentration in the sea becomes too low for phytoplankton to grow, which may determine the primary productivity and eventually affect fishery resources.

Utilization of water-based drilling cuttings from offshore oil development to manufacture lightweight aggregates: a case study in the Bohai oil field, China

Offshore water-based drilling cuttings (OWDC) are by-products of offshore oil-well drilling, whose effective management has become an urgent environmental and engineering issue. This study investigated the feasibility of recycling OWDC from the Bohai oilfield in China as a raw material for manufacturing lightweight aggregates (LWA). The effects of OWDC content (0-50%), preheating temperature (300-500 °C), and sintering temperature (1050-1200 °C) on the physical-mechanical performance of the resulting LWA were investigated through single-factor experiments. The microstructural and expansion mechanism analyses were determined based on X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectrometric microanalysis. The results showed that under the optimum preparation conditions (mass ratio of OWDC and fly ash at 50:50, preheating at 400 °C for 30 min, and sintering at 1150 °C for 30 min), the OWDC-based LWA could meet the requirements of Chinese standard GB/T 17431.1-2010. The incorporation of OWDC lowered the aggregate melting points and promoted dense structure formation inside the aggregates due to the presence of flux agents (e.g., Na₂O and K₂O). Besides, OWDC additions promoted the formation of the liquid phase and gases inside the pellets, which was beneficial to the expansion behavior and lightweight performance of the aggregates. However, OWDC also had a negative effect on the compressive strength of the aggregates owing to the formation of enlarged pores. Furthermore, the results of the environmental performance tests indicated that the LWA were safe for the environment. This study provides a reference for recycling water-based drilling cuttings from offshore oilfields and contributes to the circular economy.

Spatiotemporal dynamics of suspended particulate matter in the Bohai Sea, China over the past decade from the space perspective

Suspended particulate matter (SPM) concentration is an important biogeochemical parameter for water quality assessment and morphodynamic studies. In this study, the four recent SPM retrieval models developed for Bohai Sea were evaluated using in situ datasets, and the best performing model was selected to investigate the spatiotemporal dynamics of SPM in Bohai Sea from 2011 to 2021 based on 1164 satellite imageries. The results indicated that the satellite-derived SPM concentrations had a high accuracy (R² = 0.86, relative percentage difference = 33.71 %). The SPM concentrations in the Bohai Sea demonstrated a significant decadal decreasing trend (0.503 mg/L/yr), and the distribution area with low SPM (<30 mg/L) increased by 3.29 % annually. The southern Bohai Sea declined observably, involving the Bohai Bay (2.07 mg/L/yr), Laizhou Bay (1.916 mg/L/yr), and central Bohai Sea (-0.661 mg/L/yr). Monthly SPM was characterized by significant seasonality. The SPM circulation pattern in the Bohai Strait was generally northerly inflow and southerly outflow. Significant wave heights (Hs) dominated the SPM variations and explained 58.9 % of monthly SPM changes in the Bohai Sea. The strong waves reduction was the main reason for the decadal decline of SPM concentrations. Wind waves associated with monsoons controlled seasonal variations of SPM and promoted the output in winter through the southern Bohai Strait. Storms could cause a sharp increase in SPM concentrations, especially in Bohai Bay and Laizhou Bay which were highly sensitive to northerly winds and strong waves. After the storm ended, the effects of short-duration storm might fade away within a few hours, while that of long-duration storm could last for 2-3 days. High sediment transport from Yellow River (>500 × 10⁴ t/M) controlled 74.8 % of monthly SPM variations within 3-km area off the estuary, 45 % of that within 5-km area, and 28.4 % of that within 10-km area.

Water quality shifts the dominant phytoplankton group from diatoms to dinoflagellates in the coastal ecosystem of the Bohai Bay

In this study, we conducted two cruises in the Bohai Bay (China) focusing on phytoplankton community and relation to water quality. The evaluation revealed that most of the open area was non-eutrophic, whereas the river inlet had severe eutrophication. Phytoplankton populations respond differently to different aquatic environments and are controlled by more than two factors, as revealed by aggregated boosted tree analysis. Notably, a shift in the phytoplankton community structure was observed during the seasonal transition, from the dominance of diatoms to the co-dominance of diatoms-dinoflagellates. However, the relative abundance of dinoflagellates increased by 14 % in autumn, when the harmful algae species Akashiwo sanguinea exclusively predominated; this was primarily linked to the nutrient ratios, temperature, and dissolved oxygen. The eutrophication and organic pollution had direct effects on phytoplankton abundance. Overall, our findings may provide further insights into the impacts of eutrophic environments on phytoplankton community structure in coastal systems.

Species and functional diversity of marine macrobenthic community and benthic habitat quality assessment in semi-enclosed waters upon recovering from eutrophication, Bohai Bay, China

This study investigated the structure and function of macrobenthic community in Bohai Bay upon improvement of water quality due to pollution abatement. A total of 166 species were collected in the summer and autumn sampling, with an increase in sensitive species recorded as compared to data from previous studies. While historical variations in species richness indicated signs of improvement in community structure, results of functional diversity indices revealed that the macrobenthic community in Bohai Bay was still in an early stage of recovery. From BIO-ENV analysis, habitat instability may hinder how community responded to water quality improvement. Results of the benthic habitat quality assessment also indicated that the ecological status in most areas of Bohai Bay was classified as good, while a few estuarine regions were categorized in a poor status.

Prediction of Wave Energy Flux in the Bohai Sea through Automated Machine Learning

The rational assessment of regional energy distribution provides a scientific basis for the selection and siting of power generation units. This study, which focused on the Bohai Sea, set 31 research coordinate points in the Bohai sea for assessing the potential/trends of wave energy flux (WEF). We applied a point-to-point time series prediction method which modelled the different geographical coordinate points separately. Subsequently, we evaluated the performance of three traditional machine learning methods and three automated machine learning methods. To estimate WEF, the best model was applied to each research coordinate points, respectively. Then, the WEF was calculated and predicted based on the data of MWP, SWH, and water depth. The results indicate that, for all coordinates in the Bohai Sea, the H2O-AutoML algorithm is superior to the other five algorithms. Gradient boosting machine (GBM), extreme gradient boosting (XGBoost), and stacked ensemble models yielded the best performance out of the H2O algorithms. The significant wave height (SWH), the mean wave period (MWP), and the WEF in the Bohai Sea tended to be concentrated in the center of the sea and dispersed in the nearshore areas. In the year 2000, 2010, 2020, and 2030, the maximum annual average WEF at each research coordinate in the Bohai Sea is around 1.5 kW/m, with a higher flux in autumn and winter. In summary, the results provide ocean parameter characterization for the design and deployment of wave energy harvesting devices. Moreover, the automated machine learning introduced herein has potential for use in more applications in ocean engineering.

Three-Phase Three-Dimensional Electrochemical Process for Efficient Treatment of Greywater

Water shortages around the world have intensified the search for substitute sources. Greywater can serve as a solution for water requirements. Compared to two-dimensional electrochemical processes for water treatment, the addition of particle activated carbon enhances the conductivity and mass transfer or the adsorption of pollutants in a three-dimensional (3D) electrochemical process. The large specific surface areas of these particles can provide more reactive sites, resulting in a higher removal efficiency. In this study, the treatment of greywater by the electro-Fenton (E-Fenton) method was carried out in a 3D electrolytic reactor. The effects of the operating conditions, such as electrode spacing, applied voltage, treatment time, and activated carbon loading, on the efficacy of the E-Fenton process were investigated, and the corresponding optimum conditions were found to be 7 cm, 9 V, 2 h, and 10 g. The results showed that CODCr removal of greywater treated using the 3D electrochemical process was 85%. With the help of the Box–Behnken experiment design and the response surface methodology, the parameters were optimized to determine the optimal conditions. The results of the response surface analysis were consistent with the experimental results. The above findings illustrate that the proposed three-phase 3D electrochemical process is feasible for the efficient treatment of greywater.

Waste preserved wood derived biochar catalyst for promoted peroxymonosulfate activation towards bisphenol A degradation with low metal ion release: The insight into the mechanisms

The rational disposal of waste preserved wood is of great significance since its embedded metals (Cu, As, and Cr) pose potential threat to environment and human health. In this study, a biochar catalyst derived from waste preserved wood (PWB) was prepared for the degradation of bisphenol A (BPA) via peroxymonosulfate (PMS) activation. The PWB exhibited prominent catalytic degradation capability towards BPA compared with common wood derived biochar (CWB). Further tests and analysis elucidated that both radical species (OH) and non-radical species (¹O₂) were generated by the PWB/PMS system, whereas only ¹O₂ was detected in CWB/PMS system. Specifically, the metal compounds, especially metallic Cu in the PWB activated PMS via radical pathway, and the CO groups in the biochar generated the non-radical pathway, the coexistence of which resulted in higher BPA degradation rate in PWB/PMS system. It was also demonstrated that the heavy metal ion leaching (As and Cr) in PWB/PMS system was negligible. Furthermore, the biochar could effectively inhibit the leakage of oxidized Cu ions. This study provides a novel approach to prepare high-efficient carbocatalysts for organic pollutant degradation in water, which also enables the waste preserved wood with an environmental nondestructive mode of dispatch.

Effects of COVID-19 lockdown and unlock on health of Bhutan-India-Bangladesh trans-boundary rivers

The COVID-19 pandemic significantly destructs the rhythm of global modern human civilization but worldwide lockdown radically recovers the health of the total environment. The Himalayan trans-boundary rivers provide huge provisional, regulatory and cultural ecosystem services to millions of people throughout the year but in the recent years the water quality is being deteriorated due to multiple reasons. In the last decade, India-Bangladesh political relationship has been slightly broken down due to water sharing and environmental flow of rivers.The COVID-19 lockdown offered a great scope to execute the comparative study among pre, lockdown and unlock phase. The research attempts to investigate the spatiotemporal water quality of trans-boundary rivers through WAWQI and irrigation water quality indices such as Sodium absorption ratio, Soluble sodium percentage, Potential salinity, Magnesium hazard and Kelly's index considering eighteen water quality parameters (pH, EC, TDS, TSS, Ca²⁺, Mg²⁺, Na²⁺, K⁺, F-, Cl-, NO3-, SO₄²-, PO 4 3 -, DO, T, TUR, COD and BOD). The result shows the strong positive correlation between EC and TDS during three phases. Significant reduction of BOD, COD and TUR has been noticed almost 70% stations during lockdown compared with prelockdown while augmentation of DO has been recorded around 40% stations. WQI of most of the stations shows around 80% improvement of water quality during lockdown period. Moreover, worst kind of WQI was found in the Mathabhanga-Churni river followed by Mahananda. During lockdown, the striking results show that SAR and MH were significantly amplified in most of the stations due to agricultural run-off.

Concentrations and health risks of heavy metals in five major marketed marine bivalves from three coastal cities in Guangxi, China

Seafood consumption provides essential elements to humans while also posing risks to human health. A total of 2610 individuals of five edible marine bivalve species (Ruditapes philippinarum, Paphia undulata, Meretrix meretrix, Sinonovacula constricta and Meretrix lyrata) were randomly sampled from six farmer markets in three cities (Beihai, Qinzhou and Fangchenggang) in the southernmost coastal region of China. The concentrations of heavy metals (Cu, Pb, Zn, Cd, Cr, Hg and As) were determined by inductively coupled plasma mass spectrometry (ICP-MS). The estimated daily intake (EDI), target hazard quotient (THQ), total hazard index (HI), and target cancer risk (TR) were calculated to evaluate potential human health risks from bivalve consumption. The mean concentrations of metals in the tissues of bivalves descended in the order Zn > Cu > As > Cd > Cr >Pb > Hg in descending order, and the concentrations varied substantially among the five bivalves. Heavy metal concentrations in edible tissues of most bivalve samples were below the safety limits set by national and international regulations, and there were significant correlations between certain metal concentrations. The EDI values for each metal in each bivalve were significantly lower than the corresponding PTDI (provisional tolerable daily intake) values. Health risk assessment showed that although there is no noncarcinogenic health risk for local residents exposed to individual or combined metals from these bivalves, there is a carcinogenic risk from Cd and Cr exposure. Thus, in the long term, monitoring and controlling bivalve consumption will be important. Although current accumulation levels of bivalves are safe, continued and excessive lifetime consumption over 70 years may pose a target cancer risk.

Strong Precipitation and Human Activity Spur Rapid Nitrate Deposition in Estuarine Delta: Multi-Isotope and Auxiliary Data Evidence

The intensive development of the Yellow River Delta has caused huge transportation of non-point pollutants into the Bohai Sea through source river estuaries and thus poses a considerable threat to eco-environmental security in the region. Long-term irrigation in the Yellow River basin, with occasional heavy rainfall and the related effects of ensuring hydrological processes and human activities in terms of nitrate N transport via surface water systems, is unclear. Using stable isotope (δ2H-H2O and δ18O-H2O, δ15N-NO3− and δ18O-NO3−) and auxiliary geographic data, the ISO source model was run to quantitatively analyze the supply relationship of river systems and the rapid change in the spatial pattern of nitrate N due to heavy rainfall in the estuarine delta. This analysis made clear the dominant contribution of agricultural activities and urbanization to NO3−-N emission, on which basis refined management measures were proposed to deal with NO3− in surface water from the “source-process”. The results of the study show that: (1) The relationship of surface water replenishment in the Yellow River Delta was affected not only by rainfall, irrigation, and other water conservancy measures but also the proportion of water from Yellow River flow declined from the source to estuary; (2) To a certain extent, rainfall diluted the concentration of nitrate N in the river and increased instantaneous flux of nitrate N into the sea, where nitrate N flux continuously increased from upstream to downstream; (3) The rapid deposition of nitrate in the estuary delta was driven by heavy rainfall and human activities such as excessive use of nitrogen fertilizers, rapid urbanization, and livestock waste discharge, and; (4) Scientific measures were needed to realize the interactive effect of the output of non-point source pollutants and the carrying and absorption capacity of coastal fragile ecosystems of the exogenous inputs.