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A power law velocity profile for engineering application was obtained based on the field data set of flow velocity and sediment concentration in coastal areas of Jinzhou, Nantong, and Zhoushan. Using theoretical analyses, van Rijn's formula for sediment concentration profile was modified. Tests of the new power-law velocity profile and the modified formula of suspended sediment concentration against a large data set were performed. The results show a good fit to the data and that these two formulae could demonstrate the basic principles of vertical distribution of flow velocity and suspended sediment concentration, respectively. [ABSTRACT FROM AUTHOR]

As is known, most of the discovered oil and gas fields in Azerbaijan are associated with terrigenous deposits; thus, the successful discovery of new fields largely depends on determining the genesis of terrigenous formations. Determining the genesis of reservoir deposits allows apetroleum geologist to more accurately predict the reservoir’sshape and change its main parameters in both lateral and vertical directions.This information also allows us to choose a rational drilling operationsystem in the field. Comprehension of the genesis of the productive stratum deposits is also important in developing oil and gas fields. The research of the genesis of deposits of productive series is of great interest given the acceleration of exploration and evaluation of their oil and gas potential. In this regard, using the ««qualitative logging facies models» proposed by V.S. Muromtsev in the article, the sections of the wells of the Garbi Absheron, Shimali Absheron, Khazri, and Arzu structures of the North Absheron zone of the uplift PS suites «Fasila», «Upper Kirmaky Clayey» (UKC) and on the sedimentary rocks of the «Upper Kirmaky Sandy» (UKS) formation, a lithofacial analysis of sedimentary rocks was carried out, the genesis of sedimentary rocks was established, and an explanation of the results obtained was given. Geophysical logging data of the borehole potential curve of intrinsic polarisation were used to build spatial models and 3D models. The constructed models allow us to attribute various shapes of the well potential curve (WP) to deposits of a defined facies composition. In the research work, the total thickness of facies for the UKC and UKS suites was calculated, three-dimensional spatial models were built considering the variation in their thickness by structuresof the North Absheron zone of the uplift, and 3D models were built by the structures located on them.The facies composition of the sediments of the layers in the «Fasila», «UKC» and «UKS» formations was determined based on created models selected by their appearance and forms of display from WP diagrams of well sections in the Garbi Absheron, Shimali Absheron, Khazri, and Arzu structures. These models are major for accurately calculating oil and gas reserves in the area, for drilling and designing new wells, and refining the operation scheme.

This article proposes to apply long-short-term memory (LSTM) deep learning models to transform Sentinel-1 A/B interferometric wide (IW) swath image data into the wave density spectrum. Although spectral wave estimation methods for synthetic aperture radar data have been developed, similar approaches for coastal areas have not received enough attention. Partially, this is caused by the lack of high-resolution wave-mode data, as well as the nature of wind waves that have more complicated backscattering mechanisms compared to the swell waves for which the aforementioned methods were developed. The application of the LSTM model has allowed the transformation of the Sentinel-1 A/B IW one-dimensional image spectrum into wave density spectra. The best results in the test dataset led to the mean Pearson's correlation coefficient 0.85 for the comparison of spectra and spectra. The result was achieved with the LSTM model using $VV$ and $VH$ polarization spectra fed into the model independently. Experiments with LSTM neural networks that classify images into wave spectra with the Baltic Sea dataset demonstrated promising results in cases where empirical methods were previously considered.

Eutrophication-driven hypoxia is one of the reasons for the deterioration of coastal waters, especially those adjacent to densely inhabited urban cities. Thus, effective hypoxia management is urgently needed, and quantitative knowledge of factors controlling hypoxia is required. A case in point is the coastal water around Hong Kong, a megacity that has over 7.5 million residents and is located downstream of the large and nutrient-rich Pearl River. The Victoria Harbour (VH) is the core area of Hong Kong water and has been suffering from marine environment deterioration for years because of external biogeochemical influxes from adjacent waters and internal physical and biogeochemical responses. Three channels orienting from south to north (C1), southeast to northwest (C2), and west to east (C3) connect the VH to adjacent waters and serve as the primary exchange pathways for water mass and biogeochemical substances. Using observational data and a coupled physical–biogeochemical model, we showed that the northward transport of low dissolved oxygen (DO) water from the coastal transition zone by the shoreward bottom current mainly through C1 directly contributes to the hypoxia formation in VH. The external influx of anthropogenic nutrients and organic matter through C2 further enhances the bottom water hypoxia in VH by stimulating phytoplankton bloom and microbial consumption of oxygen in water columns and sediments. Although the horizontal oxygen influx to VH is weak, the comparatively strong vertical mixing in C3 facilitates the replenishment of bottom water in the VH, mitigating bottom hypoxia. Locally in the VH, sediment oxygen demand is the dominant biogeochemical contributor (~93%) to hypoxia formation, while the contribution of water column remineralization is relatively minor (~6-7%). In general, vertical diffusion serves as the largest source (~57%) of DO in the VH because of the strong vertical DO gradient, whereas vertical motion ranks the second largest source of DO (~24%) and serves as a critical physical factor regulating the oxygen budget of the entire VH. In the spatial constriction area where the vertical DO gradient is weak, the magnitude of vertical motion exceeds vertical diffusion to become the largest source of DO (~48%).

Studying how natural phytoplankton adjust their photosynthetic properties to the quantity and quality of underwater light (i.e. light climate) is essential to understand primary production. A wavelength-dependent photoacclimation strategy was assessed using a multi-color pulse-amplitude-modulation chlorophyll fluorometer for phytoplankton samples collected in the spring at 19 locations across the English Channel. The functional absorption cross section of photosystem II, photosynthetic electron transport (PETl) parameters and non-photochemical quenching were analyzed using an original approach with a sequence of three statistical analyses. Linear mixed-effects models using wavelength as a longitudinal variable were first applied to distinguish the fixed effect of the population from the random effect of individuals. Population and individual trends of wavelength-dependent PETl parameters were consistent with photosynthesis and photoacclimation theories. The natural phytoplankton communities studied were in a photoprotective state for blue wavelengths (440 and 480 nm), but not for other wavelengths (green (540 nm), amber (590 nm) and light red (625 nm)). Population-detrended PETl values were then used in multivariate analyses (partial triadic analysis and redundancy analysis) to study ecological implications of PETl dynamics among water masses. Two wavelength ratios based on the microalgae saturation parameter Ek (in relative and absolute units), related to the hydrodynamic regime and underwater light climate, clearly confirmed the physiological state of microalgae. They also illustrate more accurately that natural phytoplankton communities can implement photoacclimation processes that are influenced by in situ light quality during the daylight cycle in temporarily and weakly stratified water. Ecological implications and consequences of PETl are discussed in the context of turbulent coastal ecosystems. [ABSTRACT FROM AUTHOR]

Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. To investigate the role of coastal TEPs in sinking carbon from the upper layer, samples were collected in the spring and summer of 2011 in the Changjiang River (Yangtze River) Estuary, a typical coastal water. The concentrations and sinking rates of TEPs were measured, and potential sedimentation flux of TEPs was estimated. TEPs concentrations ranged from 40.00 µg/L to 1 040.00 µg/L (mean=(209.70±240.93) µg/L) in spring and 56.67 µg/L to 1 423.33 µg/L (mean=(433.33±393.02) µg/L) in summer, and they were higher at bloom stations than at non-bloom stations during both cruises. A significant positive correlation between TEPs concentration and chlorophyll a (Chl a) concentration was detected, suggesting that phytoplankton was the primary source of TEPs in this area. TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of (0.28±0.14) m/d in spring and 0.10 m/d to 1.08 m/d with a mean of (0.34±0.31) m/d in summer. The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d) to 29.40 mg/(m2·d) with a mean of (14.66±8.83) mg/(m2·d) in spring and 6.80 mg/(m2·d) to 30.45 mg/(m2·d) with a mean of (15.71±8.73) mg/(m2·d) in summer, which was ∼17.81% to 138.27% (mean=65.15%±31.75%) of sedimentation flux of phytoplankton cells in the study area. Due to the increase of TEPs concentrations and their sinking rates, sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises. This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary, especially during bloom events, and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea. [ABSTRACT FROM AUTHOR]

A Gram-stain-negative, rod-shaped, obligately aerobic, nonflagellated, and chemoheterotrophic bacterium, designated IMCC3088T, was isolated from coastal seawater of the Yellow Sea. The 16S rRNA gene sequence analysis indicated that this strain belonged to the family Halieaceae which shared the highest sequence similarities with Luminiphilus syltensis NOR5-1BT (94.5%) and Halioglobus pacificus S1-72T (94.5%), followed by 92.3–94.3% sequence similarities with other species within the aforementioned family. Phylogenetic analyses demonstrated that strain IMCC3088T was robustly clustered with Luminiphilus syltensis NOR5-1BT within the family Halieaceae. However, average amino acid identity (AAI), percentages of conserved proteins (POCP), average nucleotide identity (ANI), and alignment fraction (AF) between strain IMCC3088T and Luminiphilus syltensis NOR5-1BT were 54.5%, 47.7%, 68.0%, and 16.5%, respectively, suggesting that they belonged to different genera. Whole-genome sequencing of strain IMCC3088T revealed a 3.1 Mbp genome size with a DNA G + C content of 51.7 mol%. The genome encoded diverse metabolic pathways including sulfur oxidation, phenol degradation, and proteorhodopsin phototrophy. Mono-unsaturated fatty acids were found to be the predominant cellular fatty acid components in the strain. Phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol were the primarily identified polar lipids, and ubiquinone-8 was identified as a major respiratory quinone. The taxonomic data collected herein suggested that strain IMCC3088T represented a novel genus and species of the family Halieaceae, for which the name Aequoribacter fuscus gen. nov., sp. nov. is proposed with the type strain (= KACC 15529T = NBRC 108213T). [ABSTRACT FROM AUTHOR]

• Yellow River PAH input & sea currents determined PAH spatial distribution in the sea. • Yellow River alluvial loess solid dilution effect led to lower PAH levels in the sediment. • Yellow River & Yellow Sea water dilution effect led to lower PAH levels in the water. • PAH properties decided its partitions in surface/bottom water & bottom water/sediment. • PAH ecological risks in both water and sediment were negligible or acceptable. The marginal Bohai Sea, connected to the northwestern Pacific Ocean, is threatened by human activity. The Yellow River, the second largest river in China, drains large amounts of water, silts, and polycyclic aromatic hydrocarbons (PAHs) into the southern Bohai Sea; however, to what extent the Yellow River inputs influence the spatial distributions and partitions of PAHs in the southern Bohai Sea is not well known. Therefore, this study collected surface water, bottom water, and sediment samples from the southern Bohai Sea and analyzed them to examine the spatial distributions and partitions of 15 priority PAHs. The results showed that PAH concentrations ranged from 26.9 to 50.1 ng L–1 in surface water, 18.8 to 44.1 ng L–1 in bottom water, and 7.4 to 143.9 ng g–1 in sediment, with higher proportions of four-, five-, and six-ring PAHs in sediment than in water. PAH inputs from the Yellow River and sea coastal currents determined the spatial distribution of PAH concentrations in water and sediment, with an overall decrease from the estuary to the southeast. However, the solid dilution effect of input silts from the Yellow River and the liquid dilution effect of water from the Yellow River and Yellow Sea led to lower PAH concentrations in the water and sediment of the southern Bohai Sea than those in other areas of the Bohai Sea. PAH exchange between the atmosphere and seawater led to significantly higher individual PAH concentrations (except for acenaphthylene) in the surface water than in the bottom water, with ratios significantly related to the PAH n-octanol-water partition coefficient, organic carbon-water partition coefficient, and Henry's law constants. These parameters also determined PAH partitioning between the bottom water and sediment. Individual and total PAH concentrations in the sediment were significantly correlated with organic matter, clay, and silt contents. Therefore, the partitions and spatial distributions of PAHs in the southern Bohai Sea comprehensively depend on PAH properties, PAH inputs from the Yellow River and the atmosphere, sea currents, and seawater and sediment properties. The ecological risks posed by individual PAHs in both water and sediment were negligible or acceptable. [Display omitted] [ABSTRACT FROM AUTHOR]

Ocean satellites provide accurate and precise data across various scales, making them a vital tool for investigating the association between global change and ocean processes. However, low-quality data creates unavoidable gaps in satellite data, diminishing its usefulness and continuity. These deficiencies can be resolved by implementing machine learning techniques as valuable tools. This paper details a new satellite data prediction tool titled "SatelliteFixer". The SatelliteFixer model, utilizing a custom-built random forest structure, can generate dependable data with enhanced temporal-spatial continuity. This model has demonstrated feasibility with diverse satellite data sources and light bands, and outperforms the basic machine learning approach. The juxtaposition of model data with in-situ cruise sampling results allows for widespread analysis of the movement and dispersion of suspended sediment. The above entails the inversion of long-term events and the observation of short-term events, which enables accurate seasonal analysis using continuous data without the influence of uneven data volume distribution and outliers, and is also the first-time satellite data has tracked the entire process of pulsed artificial flooding. SatelliteFixer provides a fresh outlook for detailing the varying trends on consecutive timescales and successional spaces among ocean processes. • A data-driven model for ocean satellite missing data prediction is established based on a specially designed machine learning structure. • The feasibility and availability of model result are demonstrated with MODIS Aqua and GOCI visible light data. • As an example of application, SatelliteFixer data are used with in-situ cruise data to analyze the transportation and distribution of suspended sediment. • SatelliteFixer data enables the accurate seasonal analysis and the first tracking of the entire process on pulsed artificial flooding. [ABSTRACT FROM AUTHOR]

Bed sediment characteristics and distribution is one of the important parameters in determining the management plan and utilization of estuarine and coastal waters. The objective of this study was to analyze sediment distribution and determine dominant oceanographic factors controlling the distribution of bed sediment in river estuary and coastal sea of Malili. Sediment samples were collected using a grab sampler at ten stations, namely four stations in the river estuary and six stations in the adjacent coastal sea for grain size and sediment organic content analysis. The results showed that the bed sediment along the river estuary consisted of silt, very fine sand, fine sand, and medium sand with organic content varying from 1.31 to 7.18 %. In the coastal sea, bed sediment was dominated by silt with a higher organic content of 2.25 - 7.31%

Optically active substances (i.e. chromophoric dissolved organic matter (CDOM), total suspended matter (TSM), chlorophyll-a (Chl-a)) and other physico-chemical parameters were measured in the coastal sea off Indian Sundarban during October 2016–January 2017. The present study, firstly, portrayed the vertical distribution of optically active substances (OAS) in the study zone. The salinity ranged from 18.2–32.1 and 18.3–30.1 in the surface water as well as bottom water respectively. Higher values of CDOM were observed near the Hugli River confluence in both surface and bottom water and a gradual decrease towards the offshore was observed except in January. The aCDOM(440) varied between 0.1031–0.4321 m−1 and 0.0265–0.4221 m−1 in the surface water and bottom water, respectively, during the study period. Moreover, CDOM decreased towards the bottom of the water column in all three stations throughout the study periods except in October in the inshore sampling station (A1). CDOM also showed a significant temporal variation in the inshore in parity with the dynamics of TSM. Average Chl-a concentration was higher (<2 mg m−3) in the surface water than the bottom water (<1 mg m−3). During January, when favourable conditions for photosynthetic activity prevailed at the water surface, an increase in Chl-a was observed in the offshore along with a concurrent mild increase in CDOM but there was no similar trend in the bottom water. Overall, vertical distribution of OAS variability in this study area is principally dominated by the freshwater flow of the Hugli River. [ABSTRACT FROM AUTHOR]

Chlorophyll (chl a) concentration in coastal seas exhibits variability on various spatial and temporal scales. Resuspension of particulate matter can somewhat limit algal growth, but can also enhance productivity because of the intrusion of nutrient-rich pore water from sediments or bottom water layers into the whole water column. This study investigates whether characteristic changes in net phytoplankton growth can be directly linked to resuspension events within the German Bight. Satellite-derived chl a were used to derive spatial patterns of net rates of chl a increase/decrease (NR) in 2003 and 2004. Spatial correlations between NR and mean water column irradiance were analysed. High correlations in space and time were found in most areas of the German Bight (R2 > 0.4), suggesting a tight coupling between light availability and algal growth during spring. These correlations were reduced within a distinct zone in the transition between shallow coastal areas and deeper offshore waters. In summer and autumn, a mismatch was found between phytoplankton blooms (chl a > 6 mg m−3) and spring-tidal induced resuspension events as indicated by bottom velocity, suggesting that there is no phytoplankton resuspension during spring tides. It is instead proposed here that frequent and recurrent spring-tidal resuspension events enhance algal growth by supplying remineralized nutrients. This hypothesis is corroborated by a lag correlation analysis between resuspension events and in-situ measured nutrient concentrations. This study outlines seasonally different patterns in phytoplankton productivity in response to variations in resuspension, which can serve as a reference for modelling coastal ecosystem dynamics.

Graphical abstract Highlights • GCA is produced through coal fly ash from coal thermal electric power stations. • The removal rate of hydrogen sulfide was investigated by the GCA. • The GCA could remove hydrogen sulfide under both anaerobic and aerobic conditions. • Hydrogen sulfide was removed due to the multiplier effect under aerobic conditions. Abstract Annual emissions of fly ash from the burning of coal have increased to approximately 750 million tons. It is hoped that new applications utilizing by-products from coal-fired power plants will contribute to further waste reduction and set the standard for industrial-scale recycling. The purpose of this study was to evaluate the removal rate of hydrogen sulfide by a new recycled material called granulated coal ash, which is produced from coal fly ash from coal thermal electric power stations and blast furnace cement. A batch experiment was carried out to evaluate the removal rate of hydrogen sulfide by granulated coal ash under both anaerobic and aerobic conditions. The granulated coal ash could remove hydrogen sulfide under both anaerobic and aerobic conditions. However, the maximum removal of hydrogen sulfide by granulated coal ash was only 5.1 mg-S g−1 under anaerobic conditions because the manganese oxide which oxidizes hydrogen sulfide to sulfur could not be regenerated under anaerobic conditions. In contrast, the rate constant for hydrogen sulfide under aerobic conditions was high due to the multiplier effect attributed to both increasing Eh and the regeneration of manganese oxide by dissolved oxygen. [ABSTRACT FROM AUTHOR]

The Baltic Sea is an enclosed basin that experienced a number of different salinity phases during the Holocene corresponding to the establishment of a connection with the North Sea. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) in surface sediments and Holocene sedimentary successions from the Gotland and Arkona Basins were analyzed to examine their potential applicability as indicators for soil organic matter input, as well as their suitability for paleoclimate reconstructions. Our results show a marked change in brGDGT distributions and the branched and isoprenoid tetraether (BIT) index. The transition of the Ancylus Lake (fresh) to the Littorina Sea (brackish) phase is revealed by a large drop in the BIT index and an increase in the MBT′ 5Me , which reveals a large shift in provenance of the sedimentary brGDGTs. During the lake phase, brGDGTs are presumed to be primarily produced by in situ production in the water column. During the brackish phase, in situ brGDGT production in the alkaline pore waters of the surface sediments (as revealed by their high degree of cyclization) was predominant although there was evidence of occasional input of soil-derived brGDGTs. The predominant aquatic autochthonous production of brGDGTs does not allow the use of brGDGTs for continental air temperature reconstructions but they can be used for bottom water and lake temperature reconstructions during some intervals. The results from this study demonstrate that geological changes and concomittant salinity variations can be revealed by the provenance of brGDGTs. [ABSTRACT FROM AUTHOR]

Coastal seas are composed of relatively independent ecosystems, such as estuaries, rocky shores, mangroves, and coral reefs. Such individual ecosystems (IEs) are linked closely to each other by the dispersal and circulation of nutrients and organic matter and the movement of organisms, and form a coastal ecosystem complex (CEC). The CEC is understood as a unit of structure and function of coastal seas. It is characterized by a high degree of species diversity and it plays a large role in fishery and aquaculture production, as it provides important marine services for humans. This special volume compiles recent ecological studies of target species and IEs, to facilitate the conservation of coastal seas and the sustainability and production of their fisheries and aquaculture based on our understanding of the structure and function of the CEC in these environments. [ABSTRACT FROM AUTHOR]

Since the environmental levels of selenium (Se) can moderate the bioaccumulation and toxicity of mercury (Hg) in marine organisms, their interactions were studied in seawater, sediments, plankton and the benthic (Bull ray Pteromylaeus bovinus, Eagle ray Myliobatis aquila) and the pelagic (Pelagic stingray Dasyiatis violacea) rays, as apex predators in the Gulf of Trieste (Northern Adriatic Sea). Male and female rays showed no difference in the Se contents in muscle tissue. Pelagic species contained higher Se levels in muscle but slightly lower levels in the livers of both genders. The Hg/Se ratios in seawater dissolved and colloidal fractions, plankton and sediment were <0.5, while those in particulate matter were <1.3. In benthic ray species, a parallel increase in Se and Hg in muscle was observed, so that an increased in Hg (MeHg) bioaccumulation results in Se coaccumulation. The Hg/Se ratios (molar) in muscle and liver of pelagic and benthic rays were <1.4 and <0.7, respectively. The low levels of Hg in muscle and liver in all the ray species corresponded to low Hg/Se ratios and increases in muscle and liver to 1 at 7 µg/g, dry weight (dw) and 5 µg/g dw, respectively, i.e., about 1.6 µg/g wet weight (ww). [ABSTRACT FROM AUTHOR]

Abstract: High inputs of nutrients and organic matter make coastal seas places of intense air‐sea CO2 exchange. Due to their complexity, the role of coastal seas in the global air‐sea CO2 exchange is, however, still uncertain. Here, we investigate the role of phytoplankton stoichiometric flexibility and extracellular DOC production for the seasonal nutrient and CO2 partial pressure (pCO2) dynamics in the Gulf of Bothnia, Northern Baltic Sea. A 3‐D ocean biogeochemical‐physical model with variable phytoplankton stoichiometry is for the first time implemented in the area and validated against observations. By simulating non‐Redfieldian internal phytoplankton stoichiometry, and a relatively large production of extracellular dissolved organic carbon (DOC), the model adequately reproduces observed seasonal cycles in macronutrients and pCO2. The uptake of atmospheric CO2 is underestimated by 50% if instead using the Redfield ratio to determine the carbon assimilation, as in other Baltic Sea models currently in use. The model further suggests, based on the observed drawdown of pCO2, that observational estimates of organic carbon production in the Gulf of Bothnia, derived with the 14 C method, may be heavily underestimated. We conclude that stoichiometric variability and uncoupling of carbon and nutrient assimilation have to be considered in order to better understand the carbon cycle in coastal seas. [ABSTRACT FROM AUTHOR]

Although the influence of benthic fauna on estimating the nutrient upward fluxes from the coastal sediments are a concern, there are few comprehensive studies. We conducted monthly observations in a coastal embayment to examine the effect of benthic fauna on measuring the nutrient flux. Nutrient fluxes were measured by the core incubation method and the densities of organisms in benthic communities were also measured. Numerical composition of benthic communities, according to taxonomic group, was dominated by Polychaeta composed of a few Capitellida and Spionidae species. A negligible effect of the benthic communities on measuring nutrient fluxes was demonstrated. [ABSTRACT FROM AUTHOR]

Coastal areas can represent an ecological transition zone with the function of biodiversity conservation, and good water quality is fundamental to maintaining this function. In this study, we analyzed data from 2011 to 2020 to reveal the variation in dissolved oxygen (DO) and the aquatic biological response in China's coastal seas. Results showed that DO in coastal waters exhibited an upward trend from 2011 to 2020 because of reduction in terrestrial anthropogenic pollutant (TAP) input. In comparison with DO in other seas, the DO content in the East China Sea was lower owing to higher TAP input, i.e., the proportion of DO of <5 mg L−1 accounted for approximately 60% of the total. Species numbers, density, and the species diversity index of phytoplankton, zooplankton, and macrobenthos were different in the different sea areas because phytoplankton, zooplankton, and macrobenthos have different responses to changes in DO. In comparison with the species numbers of zooplankton and macrobenthos, the species numbers of phytoplankton were more significantly related to DO, and showed a negative linear relationship with a better DO environment (DO ≥ 5 mg L−1; r2 = 0.39, p < 0.01) and positive correlation with a poor DO environment (DO < 3 mg L−1; r2 = 0.52, p < 0.01). A better DO environment is conducive to increased density of macrobenthos. Studies have shown that a good DO environment contributes to coastal ecosystem health, and continuous control of TAP input is an effective means of ensuring DO recovery. [Display omitted] • DO in the coastal seas has improved from 2011 to 2020. • East China Sea has worse DO than that in other seas due to more TAP input. • The responses of aquatic organisms to DO changes were different. • Further control TAP input benefit for DO recovery and coastal ecosystem protection. [ABSTRACT FROM AUTHOR]

We explored picophytoplankton in the surface (0 m) and bottom (2.3–8.7 m) layers of a shallow (<10 m) eutrophic coastal system (Isahaya Bay, Japan). We found that picophytoplankton (principally Synechococcus) constituted the major phytoplankton in spring and summer. The chlorophyll a (chl. a) concentration in the 0.7–2.0-μm picophytoplankton fraction (hereinafter 'pico-sized chl. a ') and picophytoplankton abundance in Isahaya Bay were higher than those in other eutrophic coastal waters. The pico-sized chl. a concentration and the picophytoplankton abundance counted with an epifluorescence microscope was up to 49.31 μg L−1 and 1.9 × 106 cells mL−1, respectively. Higher contributions of pico-sized chl. a to the total chl. a were evident in summer (up to 63.5%), relative to spring (up to 32.1%), at both depths. Picophytoplankton abundance and the pico-sized chl. a concentration was positively correlated with water temperature and dissolved inorganic phosphorus (DIP) concentrations. Thus, both temperature and DIP may be major controllers of picophytoplankton in Isahaya Bay. The pico-sized chl. a concentration and picophytoplankton cell number at the bottom layer were positively correlated with those in the surface layer, suggesting that picophytoplankton in bottom layers may have sunk from the surface layers. The results imply that the picophytoplankton affects the biogeochemical processes in the bottom of Isahaya Bay more than previously thought. This may be true not only for this estuary but also for other eutrophic coastal seas. • Picophytoplankton contributed considerably to the total phytoplankton biomass in spring and summer of a shallow, eutrophic coastal sea. • Higher contributions of pico-sized chl. a to the total chl. a were evident in summer (up to 63.5%), relative to spring (up to 32.1%), at both depths. • High amount of picophytoplankton may sink from the surface to accumulate in near-bottom layers. [ABSTRACT FROM AUTHOR]