Yangtze River Estuary Research Articles

Fronts affect fish community structure in the Yangtze River estuary and its adjacent area

Dispersal, a critical factor in the viability of marine organisms, is strongly influenced by the physical dynamics of the ocean. Fronts, as a common phenomenon in ocean dynamics, can theoretically impact the dispersal of organisms and ultimately cause spatial homogeneity or heterogeneity of marine communities. However, there is relatively limited understanding concerning whether frontal formation hinders the connectivity between communities and thus results in differences in community structure. To verify whether the formation of fronts caused differences between communities, 60 eDNA samples and their environmental parameters were collected from 32 sites in the Yangtze River estuary and its adjacent area, and four groups, the Yangtze River front-inner group (YRI), the Yangtze River front-outer group (YRO), the Zhejiang costa front-inner group (ZCI), and the Zhejiang coast front-outer group (ZCO), were compared to examine the differences in fish communities between the sides of the front. The results showed that there was a significant difference between YRI and YRO, suggesting that the front affected the community structure. There was no significant difference in fish communities between ZCI and ZCO, indicating that fronts could only hinder dispersal at high intensities. The difference between YRI and YRO possibly resulted from dramatic changes in temperature, salinity, and turbidity related to the front. Fronts also separated water masses with different environmental characteristics and thereby attracted fish to their optimal habitats. Overall, fronts appear to be ecologically significant for fish dispersal and community differentiation.

Morphological and Molecular Analysis Identified a Subspecies of Crassostrea ariakensis (Fujita, 1913) along the Coast of Asia.

Crassostrea ariakensis (Fujita, 1913) is one of the most important economic and ecological oysters that is naturally distributed along the coast of Asia, separated by the Yangtze River estuary. They are usually compared as different populations, while there is no consensus on whether C. ariakensis in northern and southern areas should be considered as two species or subspecies. Here, we analyzed morphological characteristics, COI, 16s rRNA, mitogenome sequences, and species delimitation analysis (ASAP and PTP) to resolve the intraspecific taxonomic status of the C. ariakensis. Phylogenetic and ASAP analysis highlight that C. ariakensis was divided into N-type and S-type. PTP was unable to differentiate between the two types of C. ariakensis. The divergence time of N-type and S-type C. ariakinsis is estimated to be 1.6 Mya, using the relaxed uncorrelated lognormal clock method. Additionally, significant morphological differences exist between the two groups in terms of the adductor muscle scar color. Despite these differences, the COI (0.6%) and 16S rRNA (0.6%) genetic distance differences between N-type and S-type C. ariakensis has not yet reached the interspecific level. These results suggest that N-type and S-type C. ariakensis should be treated as different subspecies and renamed as C. ariakensis ariakensis subsp. nov and C. ariakensis meridioyangtzensis subsp. nov.

Temporal and spatial variation of typhoon-induced surges and the impact of rainfall in a tidal river

The Huangpu River, which flows into the Yangtze Estuary, runs through Shanghai Municipality in China. During the flood season, typhoon-induced surges result in extremely high water levels in the Huangpu River, which is the main factor threatening flood control safety in Shanghai. Based on observations of water levels at three stations along the Huangpu River from 2008 to 2021, together with wind and rainfall, this paper investigates: the trends of the annual highest storm surges; the differences in periodic variation and magnitude of surges during the spring-neap cycle; the longitudinal variation of surges; and the impact of rainfall. The results show that the annual highest surges at three stations all show a significant increasing trend, which is caused by the increasing wind speed, and the intensity and duration of rainfall during typhoon events, induced by the increasing frequency of landfall and close-to-YE (Yangtze Estuary) typhoon events, and strong and very strong typhoon events. The periodic variation and magnitude of surges show clear differences during the spring-neap cycle, resulting from the largest nonlinear surge-tide interaction during spring tide and the smallest during neap tide. Heavy rainfall can reduce the probability of 6–7 h and 2.7–3.3 h periods, and change the phase of the periodic variation, inducing partial main peaks and maximum surges during ebb or low tide. The longitudinal variation of storm surge along the Huangpu River can be divided into three types: decreasing upstream, first increasing then decreasing, and increasing upstream. Heavy and long-duration rainfall increases the water discharge from the basin to the river, amplifying the surge, with the largest impact in the upper reach and the smallest in the lower reach, which is the main factor inducing the latter two types, particularly the third type.

Wave, flow, and suspended sediment dynamics under strong winds on a tidal beach

Tidal beaches are shaped by intense wave-current interactions, leading to dynamic sediment erosion and accretion, which can be further complicated by strong winds. In this study, field observations were conducted on a tidal beach at the junction of Yangtze Estuary and Hangzhou Bay (China), to investigate the dynamics of wave, flow, and suspended sediment under strong winds. Observations were carried out synchronously at two sites on the middle and lower intertidal beach covering 4 semidiurnal tides (52 h) including a ∼20 h-long strong wind period. During the strong wind period, wave motions and flood currents were significantly enhanced, leading to a high combined wave-current bed shear stress (τcw). The wave-induced bed shear stress (τw) greatly exceeded current-induced bed shear stress (τc). Breaking waves generated turbulence at the surface and amplified the near-bed turbulent Reynolds stress (−u′w′‾ and −v′w′‾) at the shallow, middle intertidal beach. The intense hydrodynamics and turbulence kept sediments in suspension and hindered any settling, resulting in net erosion of the intertidal beach. These findings provide valuable insights into the complex interplay among waves, currents, and sediment dynamics under short-duration strong winds on tidal beaches. A key emphasis is placed on the significant role of breaking waves, underscoring the critical importance of their contribution to near-bed turbulence.

Analysis of influencing factors of seawater intrusion in the Yangtze River Estuary and control for water supply security

Seawater intrusion poses a significant threat to the water supply of coastal cities both presently and in the future. It is crucial to identify the controllable factors influencing seawater intrusion, both natural and anthropogenic, in order to ensure water supply security. This study examined seawater intrusion characteristics using monitoring data from 1994 to 2019. Factors such as daily flow rate, duration of intrusion, water quality, and tidal level were analyzed to establish correlations and identify the primary influencing factors in the Yangtze River Estuary. The findings reveal that seawater intrusion in this area is most prevalent from November to April, peaking in February and March. The key controllable factors affecting chloride levels at the intake are the daily flow rate at Datong Station and the tidal range at Xuliujing Station. Additionally, the study proposes control methods to safeguard water supply, including providing daily flow rate values for flushing seawater intrusion at Datong Station under different tidal ranges and intrusion durations. These research results provide valuable guidance for the emergency operation of the Three Gorges-centered reservoir group against seawater intrusion.

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

Long-term reclamation of tidal flats of Chongming Island and ecological security of Yangtze estuary, China

Variations of the soil macrofauna community and corresponding influencing factors in the newly reclaimed coastal area: A case study in Yangtze Estuary, China

Intensive reclamation activity has reshaped global coastal ecosystems. Soil macrofauna, an effective proxy for ecosystem health, has the potential to predict coastal reclamation ecological impact. Previous studies have primarily focused on the long-term (≥ 30 years) soil macrofaunal succession in reclaimed areas. However, composition of the soil macrofauna and its environmental drivers in newly reclaimed areas (< 30 years) remain uncertain. We selected Hengsha Dongtan in the Yangtze Estuary to conduct the study, and four different regions (reclaimed for 13, 8, 4, and 1 year, respectively) were employed to investigate soil macrofaunal composition and corresponding environmental drivers. The results showed that: (1) Terrestrial species millipedes (Paradoxosomatidae sp.), chinch bugs (Dimorphopterus spinolae), and wolf spiders (Pirata subpiraticus) were dominant. Millipedes, chinch bugs, wolf spiders, ants (Myrmecina sp.), and rove beetles (Stenus melanarius and Paederus fuscipes) were major species contributing to the average dissimilarity among regions. (2) The taxonomic composition of soil macrofauna varied over time after reclamation, which showed that the number of species, density, and biomass of soil macrofauna in region 1 (reclaimed for 13 years) was higher than that in regions 2, 3, and 4 (reclaimed for 8, 4, and 1 year). (3) The functional composition of soil macrofauna varied over time after reclamation. The number of species, density, and biomass of the phytophagous and saprophagous groups increased over time, whereas those of the predatory group decreased gradually. (4) Soil pH and total organic carbon content, together with land use, appeared to be key factors that determine soil macrofaunal composition. Overall, our study illustrates the response of soil macrofauna to changes in environmental factors and land use in newly reclaimed areas. Future studies should expand the range of potential factors and comprehensively analyze the mechanisms that maintain soil macrofaunal diversity in reclaimed areas.

Anthropogenic eutrophication and stratification strength control hypoxia in the Yangtze Estuary

Many large estuaries are threatened by intensifying hypoxia. However, due to the limited duration of available observations, uncertainties persist regarding the level of contemporary hypoxia intensity in a longer-term context and the relative contributions of climate versus human factors. Here we present sediment records for the hypoxia intensity and associated environmental parameters in the Yangtze Estuary over the past three centuries. The results show that the hypoxia intensity has been increasing during the last half century due to anthropogenic eutrophication, but the current hypoxia condition is not as severe as some preindustrial periods due to weaker stratification in the water column. Our findings suggest that if anthropogenic and climatic forcing coincide in the foreseeable future, the hypoxia intensity of the Yangtze Estuary may reach unprecedented levels.

Seasonal coupling of iron (hydr-) oxides and organic carbon across elevations in Phragmites marshes of Yangtze Estuary

As sea levels rise, coastal tidal wetlands are increasingly threatened by flooding and salt stress, highlighting the importance of iron (Fe) (hydr-) oxides in soil for stabilizing organic carbon (OC). This study focuses on Phragmites australis, common in the Yangtze River Estuary, exploring the interplay between OC and Fe (hydr-) oxides in the rhizosphere of P. australis across various seasons and elevations. It also examines microbial community shifts in the Fe oxidation–reduction cycle. Results show that in the non-growing season (January), Fe (hydr-) oxides and total organic carbon (TOC) levels in the rhizosphere soil of high-tide P. australis are significantly higher than during the growing season (August), with a notable increase in Fe oxide-bound OC (Fe-OC). The content of Fe-OC in tidal wetland soil fluctuates with plant growth stages and elevation. Notably, during the growing season, the Fe-OC content in the rhizosphere of low-tide P. australis is markedly higher than in high-tide areas, reversing in the non-growing season. The presence of P. australis roots is found to significantly enhance the accumulation and coupling of Fe (hydr-) oxides and OC, especially in low-tide areas compared to bare flats. This coupling is affected by the organic matter contributed by roots, microbial metabolism, and redox conditions of the soil. The study also highlights how plant and microbial metabolism regulate the response of rhizosphere Fe-OC across different tidal flat elevations. In low-tide environments during the non-growing season, the prevalence of Fe-reducing bacteria results in decreased Fe-OC content, while in high-tide areas, increased organic matter input boosts complexed Fe-OC formation. Overall, this study emphasizes the significance of plant metabolism in understanding the impact of sea level rise on Fe-OC stores in tidal wetlands, a vital factor for comprehending C cycling mechanisms and assessing C sequestration potential under future climate change scenarios.

Short-term evolution pattern in salt marsh landscapes: the importance of physical constraints

ContextSalt marsh landscapes at the land-sea interfaces exhibit contrasting spatiotemporal dynamics, resulting from varying physical constraints that limit new marsh establishment. The expansion of salt marsh landscapes towards the sea or their retreat towards the land is determined by patch-level changes, relying on the balance of power between the intrinsic biota traits and external physical disturbances.ObjectivesExamine how marsh dynamics respond to physical constraints, and clarify the pathway from coupled physical processes involving hydrodynamic forces, sediment transport, and morphological changes to rapid patch evolution and landscape changes.MethodsWe defined and distinguished four types of marsh changes based on patch proximities from five-month drone images in two typical marsh pioneer zones of the Yangtze Estuary, China: outlying expansion, edge expansion, infilling expansion, and retreat. Hydrodynamics and sediment transport were synchronously measured and compared near the two marsh edges, and morphological changes were generated by drone-derived digital elevation models (DEMs).ResultsWe identified distinct seasonal patterns of net marsh expansion at the accretion-prone site, that is: Net marsh expansion started from the outlying expansion in spring, followed by edge expansion in summer and infilling expansion in autumn. However, at the erosion-prone site that experienced high bed shear stress, low sediment availability and high seaward sediment transport, we only observed limited infilling and edge expansion in spring. This suggests that the potential for long-distance patch formation beyond the initial marsh edges is diminished in areas subjected to intensive physical disturbances.ConclusionsPatch evolution dynamics in response to site-specific physical constraints drive state differentiation of salt marsh landscape changes. Consequently, the heterogeneous evolution in salt marsh landscapes should be taken into account in restoration practice.

Ecophysiological responses of Phragmites australis populations to a tidal flat gradient in the Yangtze River Estuary, China.

Phragmites australis is a prevalent species in the Chongming Dongtan wetland and is capable of thriving in various tidal flat environments, including high salinity habitats. P. australis population displays inconsistent ecological performances, highlighting the need to uncover their survival strategies and mechanisms in tidal flats with diverse soil salinities. Upon comparing functional traits of P. australis at multiple tidal flats (low, middle, and high) and their responses to soil physicochemical properties, this study aimed to clarify the salt-tolerant strategy of P. australis and the corresponding mechanisms. These results showed that leaf characteristics, such as specific leaf area and leaf dry matter content, demonstrated more robust stability to soil salinity than shoot height and dry weight. Furthermore, as salt stress intensified, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxisome (POD) in P. australis leaves at low tidal flat exhibited an increased upward trend compared to those at other tidal flats. The molecular mechanism of salt tolerance in Phragmites australis across various habitats was investigated using transcriptome sequencing. Weighted correlation network analysis (WGCNA) combined with differentially expressed genes (DEGs) screened out 3 modules closely related to high salt tolerance and identified 105 core genes crucial for high salt tolerance. Further research was carried out on the few degraded populations at low tidal flat, and 25 core genes were identified by combining WGCNA and DEGs. A decrease in the activity of ferroptosis marker gonyautoxin-4 and an increase in the content of Fe3+ in the degenerated group were observed, indicating that ferroptosis might participate in degradation. Furthermore, correlation analysis indicated a possible regulatory network between salt tolerance and ferroptosis. In short, this study provided new insights into the salt tolerance mechanism of P. australis population along tidal flats.

Severe flood modulates the sources and age of dissolved organic carbon in the Yangtze River Estuary

Floods in global large rivers modulate the transport of dissolved organic carbon (DOC) and estuarine hydrological characteristics significantly. This study investigated the impact of a severe flood on the sources and age of DOC in the Yangtze River Estuary (YRE) in 2020. Comparing the flood period in 2020 to the non-flood period in 2017, we found that the flood enhanced the transport of young DOC to the East China Sea (ECS), resulting in significantly enriched Δ14C-DOC values. During the flood period, the proportion of modern terrestrial organic carbon (OC) was significantly higher compared to the non-flood period. Conversely, the proportion of pre-aged sediment OC was significantly lower during the flood period. The high turbidity associated with the flood facilitated rapid transformation and mineralization of sedimentary and fresh terrestrial OC, modifying the sources of DOC. The flux of modern terrestrial OC transported to the ECS during the flood period was 1.58 times higher than that of the non-flood period. These findings suggest that floods can modulate the sources and decrease the age of DOC, potentially leading to increased greenhouse gas emissions. Further research is needed to understand the long-term impacts of floods on DOC dynamics in global estuaries.

Prokaryotic community assembly patterns and nitrogen metabolic potential in oxygen minimum zone of Yangtze Estuary water column

It is predicted that oxygen minimum zones (OMZs) in the ocean will expand as a consequence of global warming and environmental pollution. This will affect the overall microbial ecology and microbial nitrogen cycle. As one of the world's largest alluvial estuaries, the Yangtze Estuary has exhibited a seasonal OMZ since the 1980s. In this study, we have uncovered the microbial composition, the patterns of community assembly and the potential for microbial nitrogen cycling within the water column of the Yangtze Estuary, with a particular focus on OMZ. Based on the 16 S rRNA gene sequencing, a specific spatial variation in the composition of prokaryotic communities was observed for each water layer, with the Proteobacteria (46.1%), Bacteroidetes (20.3%), and Cyanobacteria (10.3%) dominant. Stochastic and deterministic processes together shaped the community assembly in the water column. Further, pH was the most important environmental factor influencing prokaryotic composition in the surface water, followed by silicate, PO43−, and distance offshore (p < 0.05). Water depth, NH4+, and PO43− were the main factors in the bottom water (p < 0.05). At last, species analysis and marker gene annotation revealed candidate nitrogen cycling performers, and a rich array of nitrogen cycling potential in the bottom water of the Yangtze Estuary. The determined physiochemical parameters and potential for nitrogen respiration suggested that organic nitrogen and NO3− (or NO2−) are the preferred nitrogen sources for microorganisms in the Yangtze Estuary OMZ. These findings are expected to advance research on the ecological responses of estuarine oxygen minimum zones (OMZs) to future global climate perturbations.

Potential risk assessment and occurrence characteristic of heavy metals based on artificial neural network model along the Yangtze River Estuary, China.

Pollution from heavy metals in estuaries poses potential risks to the aquatic environment and public health. The complexity of the estuarine water environment limits the accurate understanding of its pollution prediction. Field observations were conducted at seven sampling sites along the Yangtze River Estuary (YRE) during summer, autumn, and winter 2021 to analyze the concentrations of seven heavy metals (As, Cd, Cr, Pb, Cu, Ni, Zn) in water and surface sediments. The order of heavy metal concentrations in water samples from highest to lowest was Zn > As > Cu > Ni > Cr > Pb > Cd, while that in surface sediments samples was Zn > Cr > As > Ni > Pb > Cu > Cd. Human health risk assessment of the heavy metals in water samples indicated a chronic and carcinogenic risk associated with As. The risks of heavy metals in surface sediments were evaluated using the geo-accumulation index (Igeo) and potential ecological risk index (RI). Among the seven heavy metals, As and Cd were highly polluted, with Cd being the main contributor to potential ecological risks. Principal component analysis (PCA) was employed to identify the sources of the different heavy metals, revealing that As originated primarily from anthropogenic emissions, while Cd was primarily from atmospheric deposition. To further analyze the influence of water quality indicators on heavy metal pollution, an artificial neural network (ANN) model was utilized. A modified model was proposed, incorporating biochemical parameters to predict the level of heavy metal pollution, achieving an accuracy of 95.1%. This accuracy was 22.5% higher than that of the traditional model and particularly effective in predicting the maximum 20% of values. Results in this paper highlight the pollution of As and Cd along the YRE, and the proposed model provides valuable information for estimating heavy metal pollution in estuarine water environments, facilitating pollution prevention efforts.

Study on Factors Contributing to Severity of Ship Collision Accidents in the Yangtze River Estuary

Abstract The Yangtze River estuary in China is characterized by a complex maritime geographical environment and presents significant challenges to ship maneuvering and control, thereby increasing the risk of ship collision accidents. Based on the 2013–2022 shipwreck investigation report published by Shanghai and Zhejiang Maritime Safety Administration, this paper analyzes the primary factors responsible for ship collision accidents severity in the Yangtze River estuary from four aspects, namely ship, environment, human, and management. Utilizing accident severity as the dependent variable and 24 factors, including ship type, gross tonnage, wind speed, and operational errors, as independent variables, the study employed a stepwise regression approach to filter the variables. Subsequently, an ordered probit regression model was constructed based on the ten most influential variables, followed by a marginal effect analysis. The findings indicate that a ship's gross tonnage, wind speed, ocean current speed, offshore distance, and day/night conditions significantly influence the likelihood of different accident levels. Specifically, wind speed, offshore distance, and ocean current speed have a negative impact on minor and general accidents while positively affecting major and severe accidents. Gross tonnage and daytime/nighttime have a positive impact on minor and general accidents but negatively impact major and severe accidents. Moreover, general accidents exhibit the most pronounced marginal effect for each explanatory variable. The findings can help the shipping authorities to identify the causes of ship collision accidents and take effective measures to reduce such accidents, thereby enhancing the safety of ship navigation in the area.

Typical antibiotic resistance genes and their association with driving factors in the coastal areas of Yangtze River Estuary.

The massive use of antibiotics has led to the escalation of microbial resistance in aquatic environment, resulting in an increasing concern regarding antibiotic resistance genes (ARGs), posing a serious threat to ecological safety and human health. In this study, surface water samples were collected at eight sampling sites along the Yangtze River Estuary. The seasonal and spatial distribution patterns of 10 antibiotics and target genes in two major classes (sulfonamides and tetracyclines) were analyzed. The findings indicated a high prevalence of sulfonamide and tetracycline resistance genes along the Yangtze River Estuary. Kruskal-Wallis analysis revealed significant seasonal variations in the abundance of all target genes. The accumulation of antibiotic resistance genes in the coastal area of the Yangtze River Estuary can be attributed to the influence of urban instream runoff and the discharge of effluents from wastewater treatment plants. ANISOM analysis indicated significant seasonal differences in the microbial community structure. VPA showed that environmental factors contribute the most to ARG variation. PLS-PM demonstrate that environmental factors and microbial communities pose direct effect to ARG variation. Analysis of driving factors influencing ARGs in this study may shed new insights into the mechanism of the maintenance and propagation of ARGs.

Improvement in Storm Surge Numerical Forecasting Based on Wave Buoys Data

The maximum wind speed radius of a strong typhoon making landfall is an important factor influencing the numerical forecasting of storm surges. A method for inverting the maximum wind speed radius of typhoons based on wave buoys data was designed to significantly reduce the error in 24 h storm surge forecasting in this paper, and an operation scheme was proposed to enhance the storm surge numerical forecasting system based on this method. Hangzhou Bay and the Yangtze River Estuary, which have been frequently impacted by typhoons over the past five years, were selected as the research area. Common schemes for the maximum wind speed radius were analyzed, and five ladder schemes (10, 15, 20, 25, and 30 km) were established for wave and storm surge numerical model verification of Typhoon Muifa in 2022. Based on a comparison of the wave hindcast results and wave buoys observation data, the wave hindcast result of the commonly used scheme (30 km) was significantly greater than that of the observation data, and the optimal scheme (15 km) closest to the observation data could be determined during the 48 h warning period. Moreover, it was difficult to identify the optimal scheme during the 48 h warning period based on the storm surge hindcast results. A 24 h storm surge numerical forecasting test was performed with the commonly used scheme (30 km) and the optimal scheme (15 km). The results showed that the root mean square error (RMSE) of the optimal scheme (15 km) was 34% lower than that of the commonly used scheme (30 km), while the maximum storm surge error was also reduced from 47.7% for the commonly adopted scheme (30 km) to 11.8% for the optimal scheme (15 km). The maximum storm surges under the optimal scheme (15 km) along Hangzhou Bay and the Yangtze River Estuary ranged from 1.9 to 2.2 m, which were closer to the observation data, and the maximum storm surge under the commonly used scheme (30 km) was 0.8~1.2 m greater than that under the optimal scheme (15 km).

Analysis of emission characteristics associated with vessel activities states in port waters

This study investigates AIS data from March 2019 to February 2020 in Shanghai Port waters. The ship activities of berthing, waiting, and ingress/egress are extracted in detail to elucidate the emission characteristics of ships in Shanghai Port, differentiating emissions patterns across various ship activity. The findings reveal that the top three pollutants within Shanghai Port are CO2, NOX, and SO2. Container ships have the highest emissions, followed by bulk carriers. Berthed container ships and oil tankers exhibit the highest emission. Waiting container ships emit the most, followed by oil tankers and bulk carriers. Among ships entering and leaving the port, low-speed navigation produces the most emissions, followed by maneuvering and steady-speed navigation. Emission hotspots include the Yangtze River Estuary Anchorage and the main navigation channel into and out of the port. This study offers robust data support for an in-depth understanding and evaluation of ship emission characteristics in Shanghai Port.

Pollution characteristics, distribution and risk level of heavy metals in sediments of the Yangtze River estuary

Pollution characteristics, distribution, risk and sources of 7 heavy metals in sediments of Yangtze River Estuary were investigated. Total concentration ranges of As, Cr, Cu, Cd, Pb, Zn and Ni were [0, 16.5], [1.48, 51.3], [2.66, 318], [0, 0.99], [35.6, 992], [8, 91.3] and [1.88, 108] mg/kg, respectively. Based on the potential ecological risk index and Geoaccumulation index, it was determined that Pb is the most polluted heavy metal. According to class I standard of “Marine sediment quality” of China, mean baseline levels multiples were Pb (8.34) > Cu (0.57) > Cr (0.37) > Zn (0.355) > Ni (0.352) > As (0.28) > Cd (0.00). The study also found the heavy metal content of Pb is the most serious, but most of the Pb content comes from the residual state, which has minimal impact on the environment. The East Nanhui Shoal was identified as the most polluted sub-area in terms of Pb pollution, followed by other specific locations. Considering the pollution level and transport costs, the study concluded that dredge soils of the Yangtze River Estuary Deepwater Channel are not suitable for the restoration of East Hengsha Shoal.

Water masses influence the variation of microbial communities in the Yangtze River Estuary and its adjacent waters.

The Yangtze River estuary (YRE) are strongly influenced by the Kuroshio and terrigenous input from rivers, leading to the formation of distinct water masses, however, there remains a limited understanding of the full extent of this influence. Here the variation of water masses and bacterial communities of 58 seawater samples from the YRE and its adjacent waters were investigated. Our findings suggested that there were 5 water masses in the studied area: Black stream (BS), coastal water in the East China Sea (CW), nearshore mixed water (NM), mixed water in the middle and deep layers of the East China Sea (MM), and deep water blocks in the middle of the East China Sea (DM). The CW mass harbors the highest alpha diversity across all layers, whereas the NM mass exhibits higher diversity in the surface layer but lower in the middle layers. Proteobacteria was the most abundant taxa in all water masses, apart from that, in the surface layer masses, Cyanobacterium, Bacteroidota, and Actinobacteriota were the highest proportion in CW, while Bacteroidota and Actinobacteriota were the highest proportion in NM and BS; in the middle layer, Bacteroidota and Actinobacteriota were dominant phylum in CW and BS masses, but Cyanobacterium was main phylum in NM mass; in the bottom layer, Bacteroidota and Actinobacteriota were the dominant phylum in CW, while Marininimicrobia was the dominated phylum in DM and MM masses. Network analysis suggests water masses have obvious influence on community topological characteristics, moreover, community assembly across masses also differ greatly. Taken together, these results emphasized the significant impact of water masses on the bacterial composition, topological characteristics and assembly process, which may provide a theoretical foundation for predicting alterations in microbial communities within estuarine ecosystems under the influence of water masses.