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Summary: The gut microbiota plays a crucial role in foodwebs, carbon cycling, and related elements. Exopalaemon annandalei and Exopalaemon carinicauda are two important forage species in the Yangtze River estuary with extremely similar living habits andmorphological characteristics. Exploring the microorganisms in the guts of these two shrimp species can help us understand the survival status of forage species and gut microbiota in the Yangtze River estuary. Therefore, this study analyzed the similarities and differences in the intestinal flora of E. annandalei and E. carinicauda through high-throughput sequencing of 16S rRNA gene amplicons. The results showed that the dominant bacteria in the intestinal flora of E. annandalei and E. carinicauda at the phylum level were Proteobacteria and Firmicutes, respectively. At the genus level, the intestinal flora had higher concentrations of Psychrobacter, Bacillus, Pseudomonas, Acinetobacter, and Macrococcus. In both shrimp species, the contents of Acinetobacter and Macrococcus were higher in spring than in winter. The most important potential functions of the intestinal microbiota were amino acid metabolism and purine metabolism. Additionally, the functions of metabolismand diseases in the intestinal microbiota of E. annandalei were greatly influenced by the season. Furthermore, the experimental results indicated that a lower ratio of Firmicutes to Bacteroidetes was associated with a larger body weight in shrimp. Overall, this study provides a theoretical reference for understanding the intestinal bacterial community of shrimp in estuaries and the healthy cultivation of E. annandalei and E. carinicauda. [ABSTRACT FROM AUTHOR]

The non-uniform suspended sediment flowing into the Yangtze River Estuary (YRE) has a substantial impact on riverbed evolution and the ecological environment. Conducting a numerical simulation can provide missing measurement data and act as an important support for river management. In this study, we developed a formula for determining the non-uniform suspended sediment-carrying capacity (SCC) based on the statistical theory of sediment transport. The formula was applied to a river network model domaining the tidal section of the lower reaches of the Yangtze River (LYR) to simulate the non-uniform suspended sediment flowing into the YRE. The verification results showed that the model accurately simulated fine-grained sediments with a high measurement accuracy. The simulation results for coarsegrained sediments were consistent with riverbed evolution thatmanifests as erosion. Owing to the sediment transport complexity in natural rivers, we propose a method for optimizing calculations of the SCC that providesmore accuratemodeling results and can be adapted when the observational measurement accuracy is improved in the future. These findings provide support for simulations and measurements of non-uniform suspended sediment transported in the LYR. [ABSTRACT FROM AUTHOR]

Coilia nasus are an important fish resource in the Yangtze River, and the Yangtze River Estuary is a crucial migration pathway for them. In this study, we used otolith microchemistry to analyze the strontium/calcium (Sr/Ca) ratios and Sr contents in the sagitta otolith of C. nasus from the south branch (SB) and north branch (NB) of the Yangtze River Estuary and obtained the diversity of migration patterns and spawning ground distribution for C. nasus. The results indicate that C. nasus from both branches include two types of habitat history: freshwater (F)–brackish water (B) (Type I) and F-B seawater (S) (Type II), with Type I being dominant at 62.50% in both branches. The C. nasus from the SB comprise six migration patterns, while that from the NB has seven migration patterns. The C. nasus from both branches hatch in F habitats. At the time of capture, the C. nasus from the SB predominantly remain in F, accounting for 62.5%, while C. nasus from the NB primarily stay in B, accounting for 87.5%. Throughout the migration process, C. nasus from both branches switch between different habitats, with C. nasus from the NB exhibiting more frequent transitions between F and B, showing a greater reliance on the estuarine brackish habitat. The radius of the first blue region near the core (Lf) and freshwater coefficient (Fc) of the otolith for C. nasus from both branches are divided into three groups: long-distance freshwater dependence (LD), medium-distance freshwater dependence (MD), and short-distance freshwater dependence (SD), with the LD only appearing in the SB, while the NB is primarily represented by MD. There is a correlation between the differences in Lf among different groups of C. nasus and the differences in the distance from the spawning grounds of C. nasus in different sections of the Yangtze River to the estuary (DYRE), reflecting the distribution pattern of C. nasus spawning grounds in different sections of the Yangtze River. This study provides theoretical guidance for the protection of migration pathways and maintenance of spawning grounds for C. nasus, which have significant practical value in the precise management of C. nasus resources in the Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

Saltwater intrusion is a common issue in the Yangtze River estuary (YRE), significantly affecting the nearshore ecological environment and human activities. Using 20 years of runoff data, a high-resolution Finite-Volume Coastal Ocean Model (FVCOM) is constructed to simulate the lower reaches and estuary of the Yangtze River. This model is employed to analyze full-depth current and salinity characteristics and to explore the influence of factors such as runoff, wind, tides, and riverbank morphology on saltwater intrusion in the YRE. The model's accuracy is validated by comparing its output with current speed and salinity observations and comparing long-term salinity variations with reanalysis data. The comparison shows that the model well reproduces the saltwater intrusion in the YRE. Over the long term, the salinity pattern exhibits a "high–low–high" variation. Analyzing the vertical structure of the intrusion, it is observed that during summer, surface waters are heated, resulting in stronger stratification, weaker mixing, and a more pronounced saltwater intrusion in the YRE. Using power spectrum and correlation analyses, runoff is identified as the factor having the greatest impact on saltwater intrusion, followed by meridional wind and changes in riverbank morphology. This study of the variations in long-term saltwater intrusion has important reference value for the protection of freshwater resources in the YRE. [ABSTRACT FROM AUTHOR]

The estuarine system functions as natural filters due to its ability to facilitate material transformation, planktonic bacteria play a crucial role in the cycling of complex nutrients and pollutants within estuaries, and understanding the community composition and assembly therein is crucial for comprehending bacterial ecology within estuaries. Despite extensive investigations into the composition and community assembly of two bacterial fractions (free-living, FLB; particle-attached, PAB), the process by which bacterioplankton communities in these two habitats assemble in the nearshore and offshore zones of estuarine ecosystems remains poorly understood. In this study, we conducted sampling in the Yangtze River Estuary (YRE) to investigate potential variations in the composition and community assembly of FLB and PAB in nearshore and offshore regions. We collected 90 samples of surface, middle, and bottom water from 16 sampling stations and performed 16S rRNA gene amplicon analysis along with environmental factor measurements. The results unveiled that the nearshore communities demonstrated significantly greater species richness and Chao1 indices compared to the offshore communities. In contrast, the nearshore communities had lower values of Shannon and Simpson indices. When compared to the FLB, the PAB exhibit a higher level of biodiversity and abundance. However, no distinct alpha and beta diversity differences were observed between the bottom, middle, and surface water layers. The community assembly analysis indicated that nearshore communities are predominantly shaped by deterministic processes, particularly due to heterogeneous selection of PAB; In contrast, offshore communities are governed more by stochastic processes, largely due to homogenizing dispersal of FLB. Consequently, the findings of this study demonstrate that nearshore and PAB communities exhibit higher levels of species diversity, while stochastic and deterministic processes exert distinct influences on communities among near- and offshore regions. This study further sheds new light on our understanding of the mechanisms governing bacterial communities in estuarine ecosystems. [ABSTRACT FROM AUTHOR]

Chinese sturgeon (Acipenser sinensis) is an endangered species, and the Yangtze River Estuary is an important migration channel for this species. With the scale of Chinese sturgeon restocking along the Yangtze River gradually increasing, an increasing number of artificially bred Chinese sturgeon will come to the estuary. It is urgent to make the first insights about the distribution characteristics and migration strategy of the endangered Chinese sturgeon in the Yangtze River Estuary available. So, to balance the need for information about this endangered species and its conservation, a total of 14 Chinese sturgeons were released in the waters near Chongming Island on 9 April 2021 and 20 October 2022, and 50% of them have been successfully recovered. The data demonstrated that Chinese sturgeon had a good migration ability in the Yangtze River Estuary and its adjacent waters. One sturgeon returned to the freshwater area of the estuary after spending approximately 46 days in the sea at a maximum depth of 54.5 m, and two sturgeons returned to the Yangtze River mainstream within 3.5 days after release. We propose that the Northern Channel of the estuary may be the main passway for Chinese sturgeon to undertake the river–sea migration. The bycatch data of Chinese sturgeon showed that this species may prefer the southern area of the estuary. We hypothesize that the food resources and salinity regime are the main factors that promote Chinese sturgeon to enter the shoals around the coast of Chongming Island. The ocean currents, river runoff, salinity, and food resource may affect the distribution of Chinese sturgeon along the Chinese coast. Future work on the conservation of Chinese sturgeon should focus on the marine life history and continuously enrich the research data to improve conservation strategies. [ABSTRACT FROM AUTHOR]

Introduction: In this study, the seasonal differences in the intestinal microbiota of Chinese mitten crab (Eriocheir sinensis) larvae were investigated at different sites in the intertidal zone of the Yangtze River Estuary. Methods: 16S rRNA high-throughput sequencing technology was used to compare and analyze the microbial community structure in the intestines of juvenile crab from different seasons. Results: The results showed that the main microbial phyla in all seasons and sites were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria, which accounted for 97.1% of the total microbiota. Composition analysis revealed that the relative abundance of Proteobacteria decreased from summer to winter at each station, whereas Bacteroidetes showed the opposite trend. Alpha diversity analysis showed that species richness increased from summer to winter at the upstream site (P < 0.05), but decreased at the downstream site (P < 0.05), with no significant differences observed in other comparisons. Biomarker species analysis showed that juvenile crab exhibited a more specialized microbial community in summer compared with autumn and winter. Co-occurrence network analysis revealed that microbial interaction network complexity was lower in autumn compared with summer and autumn. Functional prediction analysis showed that the microbial community only exhibited seasonal differences in amino acid biosynthesis, cofactor, prosthetic group, electron carrier, and vitamin biosynthesis, aromatic compound degradation, nucleotide and nucleoside degradation, and tricarboxylic acid cycle pathways. Discussion: The results indicated that the microbiota did not significantly differ among sites, and seasonal variation was a main factor influencing the differences in intestinal microbiota of Chinese mitten juvenile crab. Moreover, the microbial community was more complex in summer compared with autumn and winter. [ABSTRACT FROM AUTHOR]

Dimethyl sulfide (DMS), an organic volatile sulfide produced from Dimethylsulfoniopropionate (DMSP), exerts a significant impact on the global climate change. Utilizing published literature data spanning from 2005 to 2020, a BP neural network (BPNN) model of the surface seawater DMS in the Yellow and East China Sea (YECS) was developed to elucidate the influence of various marine factors on the DMS cycle. Results indicated that the six parameters inputted BPNN model, that include the time (month), latitude and longitude, sea-surface chlorophyll a (Chl-a), sea-surface temperature (SST), and sea-surface salinity (SSS), yielded the optimized simulation results (R2 = 0.71). The optimized estimation of surface seawater DMS in the YECS were proved to be closely aligned with the observed data across all seasons, which demonstrated the model’s robust applicability. DMS concentration in surface seawater were found to be affected by multiple factors such as Chl-a and SST. Comparative analysis of the three environmental parameters revealed that Chl-a exhibited the most significant correlation with surface seawater DMS concentration in the YECS (R2 = 0.20). This underscores the pivotal role of chlorophyll in phytoplankton photosynthesis and DMS production, emphasizing its importance as a nonnegligible factor in the study of DMS and its sulfur derivatives. Furthermore, surface seawater DMS concentration in the YECS exhibited positive correlations with Chl-a and SST, while displaying a negative correlation with SSS. The DMS concentration in the YECS show substantial seasonal variations, with the maximum value (5.69 nmol/L) in summer followed in decreasing order by spring (3.96 nmol/L), autumn (3.18 nmol/L), and winter (1.60 nmol/L). In the YECS, there was a gradual decrease of DMS concentration from the nearshore to the offshore, especially with the highest DMS concentration concentrated in the Yangtze River Estuary Basin and the south-central coastal part off the Zhejiang Province. Apart from being largely composed by the release of large amounts of nutrients from anthropogenic activities and changes in ocean temperature, the spatial and temporal variability of DMS may be driven by additional physicochemical parameters. [ABSTRACT FROM AUTHOR]

The non-uniform suspended sediment flowing into the Yangtze River Estuary (YRE) has a substantial impact on riverbed evolution and the ecological environment. Conducting a numerical simulation can provide missing measurement data and act as an important support for river management. In this study, we developed a formula for determining the non-uniform suspended sediment-carrying capacity (SCC) based on the statistical theory of sediment transport. The formula was applied to a river network model domaining the tidal section of the lower reaches of the Yangtze River (LYR) to simulate the non-uniform suspended sediment flowing into the YRE. The verification results showed that the model accurately simulated fine-grained sediments with a high measurement accuracy. The simulation results for coarse-grained sediments were consistent with riverbed evolution that manifests as erosion. Owing to the sediment transport complexity in natural rivers, we propose a method for optimizing calculations of the SCC that provides more accurate modeling results and can be adapted when the observational measurement accuracy is improved in the future. These findings provide support for simulations and measurements of non-uniform suspended sediment transported in the LYR.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Environmental flow (e-flow) is the water demand of one given ecosystem, which can become the flow regulation target for protection and restoration of river or estuarine ecosystems. In this study, an e-flow assessment based on the flow-ecological health index (EHI) relation model was conducted to improve ecosystem health of the Yangtze River Estuary (YRE). Monitoring data of hydrology, biology, and water environment in the last decades were used for the model establishment. For the description of the YRE ecosystem, an EHI system was developed by cumulative frequency distribution curves and adaption of national standards. After preprocessing original flow values into proportional flow values, the generalized additive model and Monte Carlo random sampling were used for the establishment of the flow-EHI relation model. From the model calculation, the e-flow assessment results were that, in proportional flow values, the suitable flow range was 1.05–1.35, and the optimum flow range was 1.15–1.25 (flows in Yangtze River Datong Station). For flow regulation in two crucial periods, flows of 42,630–65,545 m3/s or over 14,675 m3/s are needed for the suitable flow of YRE in summer (June–August) or January, respectively. An adaptive management framework of ecological health–based estuarine e-flow assessment for YRE was contrived due to the limitation of current established model when facing the extreme drought in summer, 2022. The methodology and framework in this study are expected to provide valuable management and data support for the sustainable development of estuarine ecosystems and to bring inspiration for further studies at even continental or global levels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The protection and utilization of the Hengsha area at the mouth of the Yangtze River has been a hot topic in recent years. This article summarizes and reviews the land formation process of Hengsha Island and Hengsha Xinzhou, as well as the recent evolution characteristics of shoals. Based on national strategies and previous utilization ideas, it proposes the current disasters faced by the Hengsha area and the constraints that need to be demonstrated for future utilization. Hengsha Island was demarcated and formed into land in 1958, while Hengsha Xinzhou (Dongtan) was formed in 2021 under the influence of historical floods, waterway engineering, and siltation promoting enclosure. Currently, the Hengsha Shallow Beach is in a state of shrinking evolution, with no growth in height; The article is based on the national strategy of “protecting the Yangtze River” and summarizes some utilization ideas proposed by predecessors. It is believed that it is necessary to comprehensively study and judge the protection and utilization mode of the Hengsha area; At present, the Hengsha area is mainly facing the problem of shallow beach erosion caused by low sediment transport in the basin and rising sea levels. It is recommended to combine the dredging soil resources of the surrounding waterways with sand fixation and beach protection projects. In the future, it is also necessary to conduct in-depth research on the ecological protection, foundation stability, waterway erosion and sedimentation, saline intrusion, and extreme climate carrying capacity issues in the Hengsha area. [ABSTRACT FROM AUTHOR]

The fishery resources in the Yangtze River Estuary (YRE) have declined drastically because of overfishing and environmental changes, leading to ecosystem degradation of the YRE, and bringing numerous rare fish species to the brink of extinction. As a new technology with great prospects for popularization and application, environmental DNA (eDNA) technology has been utilized and proven by many studies to have high potential in revealing the various species' biodiversity. In this study, we analyzed the species composition and diversity of the Yangtze River Estuary using a combination of eDNA technology and bottom trawling approaches, and later, the comparison of both methods. The results showed that combining eDNA technology and bottom trawling, 30 fish species from 7 orders and 11 families were identified. Among the 30 fish species, a total of six species of fish could be observed in catches from both methods. Perciformes were the most abundant and Coilia mystus was the dominant species. According to diversity indices, the eDNA technology reveals significant differences in fish community richness and diversity in the Yangtze River Estuary compared to the bottom trawl. In summary, the eDNA technology is feasible for monitoring fishery resources in the waters of the Yangtze River Estuary, thereby serving as a valuable supplementary tool for conducting comprehensive surveys in this region. Moreover, it holds significant implications and promising prospects for conserving the diverse ecosystem of the YRE in future conservation efforts.

Saltwater intrusion is a common issue in the Yangtze River estuary (YRE), significantly affecting the nearshore ecological environment and human activities. Using 20 years of runoff data, a high-resolution Finite-Volume Coastal Ocean Model (FVCOM) is constructed to simulate the lower reaches and estuary of the Yangtze River. This model is employed to analyze full-depth current and salinity characteristics and to explore the influence of factors such as runoff, wind, tides, and riverbank morphology on saltwater intrusion in the YRE. The model’s accuracy is validated by comparing its output with current speed and salinity observations and comparing long-term salinity variations with reanalysis data. The comparison shows that the model well reproduces the saltwater intrusion in the YRE. Over the long term, the salinity pattern exhibits a “high–low–high” variation. Analyzing the vertical structure of the intrusion, it is observed that during summer, surface waters are heated, resulting in stronger stratification, weaker mixing, and a more pronounced saltwater intrusion in the YRE. Using power spectrum and correlation analyses, runoff is identified as the factor having the greatest impact on saltwater intrusion, followed by meridional wind and changes in riverbank morphology. This study of the variations in long-term saltwater intrusion has important reference value for the protection of freshwater resources in the YRE.

Coilia nasus are an important fish resource in the Yangtze River, and the Yangtze River Estuary is a crucial migration pathway for them. In this study, we used otolith microchemistry to analyze the strontium/calcium (Sr/Ca) ratios and Sr contents in the sagitta otolith of C. nasus from the south branch (SB) and north branch (NB) of the Yangtze River Estuary and obtained the diversity of migration patterns and spawning ground distribution for C. nasus. The results indicate that C. nasus from both branches include two types of habitat history: freshwater (F)–brackish water (B) (Type I) and F-B seawater (S) (Type II), with Type I being dominant at 62.50% in both branches. The C. nasus from the SB comprise six migration patterns, while that from the NB has seven migration patterns. The C. nasus from both branches hatch in F habitats. At the time of capture, the C. nasus from the SB predominantly remain in F, accounting for 62.5%, while C. nasus from the NB primarily stay in B, accounting for 87.5%. Throughout the migration process, C. nasus from both branches switch between different habitats, with C. nasus from the NB exhibiting more frequent transitions between F and B, showing a greater reliance on the estuarine brackish habitat. The radius of the first blue region near the core (Lf) and freshwater coefficient (Fc) of the otolith for C. nasus from both branches are divided into three groups: long-distance freshwater dependence (LD), medium-distance freshwater dependence (MD), and short-distance freshwater dependence (SD), with the LD only appearing in the SB, while the NB is primarily represented by MD. There is a correlation between the differences in Lf among different groups of C. nasus and the differences in the distance from the spawning grounds of C. nasus in different sections of the Yangtze River to the estuary (DYRE), reflecting the distribution pattern of C. nasus spawning grounds in different sections of the Yangtze River. This study provides theoretical guidance for the protection of migration pathways and maintenance of spawning grounds for C. nasus, which have significant practical value in the precise management of C. nasus resources in the Yangtze River Estuary.

The physicochemical properties of suspended sediment affect the adsorption of heavy metals. Based on scanning electron microscopy-energy dispersive X-ray spectrometry and Image Pro Plus, we detected the physicochemical properties of suspended sediment in Yangtze Estuary. The following results were observed: (1) The graphical diameter (GD), roundness (RO) and fractal dimension (FD) of suspended sediment all presented normal distribution. According to Kolmogorov-Smirnov (K-S) test, the RO of suspended sediment of the ShiDongkou station at sewage outlet was 1.31, which was significantly higher than that of other points. (2) According to the K-S test, there was no significant difference in elements among various points in the Yangtze River Estuary. (3) Compared to the chemical properties of suspended sediment, its physical characteristics had a greater impact on heavy metal absorption. The physical characteristics had the least impact on the Cu adsorption, while the chemical properties had the least impact on the Cr absorption. This study deepens the understanding of suspended sediment in the Yangtze Estuary and provides comprehensive data for the numerical simulation of suspended sediment dynamics. [ABSTRACT FROM AUTHOR]

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Marine fungi are essential for the ecological function of estuarine ecosystems. However, limited studies have reported on the structure and assembly pattern of the fungal communities in estuaries. The purpose of this study is to reveal the structure and the ecological process of the fungal community in the Yangtze River Estuary (YRE) by using the amplicon sequencing method. Phyla of Ascomycota, Basidiomycota, and Chytridiomycota were dominant in the seawater and sediment samples from YRE. The null model analysis, community-neutral community model (NCM), and phylogenetic normalized stochasticity ratio (pNST) showed that the stochastic process dominated the assembly of fungal communities in YRE. Drift and homogeneous dispersal were the predominant stochastic processes for the fungal community assembly in seawater and sediment samples, respectively. The co-occurrence network analysis showed that fungal communities were more complex and closely connected in the sediment than in the seawater samples. Phyla Ascomycota, Basidiomycota, and Mucoromycota were the potential keystone taxa in the network. These findings demonstrated the importance of stochastic processes for the fungal community assembly, thereby widening our knowledge of the community structure and dynamics of fungi for future study and utilization in the YRE ecosystem. [ABSTRACT FROM AUTHOR]

Simple Summary: The Japanese eel, a high-valued commercial fish species in the Yangtze River ecosystem, faces a significant decline in the resource. In the present study, we reported our 11-year investigation to track the migratory patterns of glass eels of Anguilla japonica into the Yangtze estuary. We identified two distinct annual peak arrival times which coincide with cooler water temperatures, i.e., the first peak at 6–8 °C and the second at 10–12 °C, both in sync with the strong spring tides of the lunar cycle. Despite rebounded population in a few years, an auto-regressive integrated moving average model analysis reveals a concerning trend: since 2016, rising temperatures have been associated with delayed recruitment. This change poses a threat to their migratory routes and life cycle stability. Underlining the critical nature of our research, our findings call for immediate conservation efforts to counteract the impact of climate change on the eel and to safeguard the biodiversity of the river ecosystem, a valuable asset to society. The decline of Japanese eel (Anguilla japonica) populations in the Yangtze River estuary represents a critical conservation concern. Eleven-years of daily catch data during recruitment periods (i.e., January–April, 2012–2022) indicate that annual catch averaged from 153 to 1108 eels, and show a bimodal pattern in glass eel arrivals. Utilizing seasonal-trend decomposition and generalized additive models, we demonstrated a strong correlation between catch abundance, optimal water temperatures, and lunar cycles. An auto-regressive integrated moving average (ARIMA) model predicts an increase in glass eel numbers for 2023–2024 but also points to a concerning trend of delayed recruitment timing since 2016, attributable to the 0.48 °C per decade rise in sea surface temperatures. This delay correlates with a significant decrease in the average body weight of glass eels, suggesting potential energy deficits that may hinder successful upstream migration. This study not only furthers our understanding of glass eel recruitment dynamics but also underscores the urgent need for targeted conservation measures. Additionally, it highlights the importance of sustained, detailed monitoring to mitigate the detrimental effects of climate change on these eels, vital for preserving the Yangtze River's ecological integrity. [ABSTRACT FROM AUTHOR]

In order to understand the fish community structure in Qingcaosha Reservoir in the Yangtze River estuary, the fish resources investigation and community structure analysis were carried out in 2021. A total of 3209 individuals were collected, identified and classified into 9 orders, 13 families, 36 genera and 46 species. The freshwater carnivorous fish species are the largest. The Index of Relative Importance, IRI of Hypophthalmichthys molitrix, Aristichthys nobilis, Hemibarbus maculatus, Carassius auratus, Coilia nasus, Culter alburnus, Saurogobio dumerili and Lateolabrax japonicus were more than 1 000 and all were dominant species. The niche analysis of dominant species showed that carnivorous and omnivorous fish had higher niche overlap in food resources and living environments. The population expansions of the two groups of fish should be more limited by food, space and other resources than the low niche overlap groups. The niche overlap among Silver carp, Bighead carp and other fish is lower, and the competitions for food, space and other living resources in the reservoir are also lower. In 2021, the Margalef species richness index（D） was 5.70, the Shannon-Wiener diversity index（H'） was 3.01, the Pielou evenness index（J） was 0.78, and the Simpson dominance index（C） was 0.81. Compared with the results of fish diversity and the community structure from 2015 to 2019 in the Reservoir, the diversity index is increasing significantly. The ABC curve analysis showed that the community structure was less disturbed by external factors. [ABSTRACT FROM AUTHOR]

In order to ascertain the fish community structure in the southern waters of the Yangtze River Estuary, 12 stations were set up in the North Port, the North Channel and the South Channel of the Yangtze River Estuary in April （spring） and September （autumn） of 2020, and two voyages of fishery resource surveys were conducted using single bag trawls （minimum mesh size 25 mm）. By calculating individual, weight resource density, relative importance index, α-diversity index, combined with multiple factor regression analysis and canonical correspondence analysis （CCA）, we could determine the spatio-temporal change rule of the community and the impact of environmental factors on the distribution. In this study, 49 species of fish were collected, belonging to 16 orders, 25 families and 41 genera. All of them are warm temperature and warm water fish. The majority of them are estuarine fish, while the narrow salt fish are less and distributed regionally. The resource density in spring is higher than that in autumn, while the weight resource density in autumn is higher than that in spring. Coilia mystus, Coilia nasus, Collichthys lucidus and Miichthys miiuy were dominant species in both seasons. In spring, Miichthys miiuy's individual resource density has the highest contribution rate to the total density and the most significant impact. In autumn, the contribution rate of the individual resource density of Harpadon nehereus is the highest, but the influence of the individual resource density of Coilia nasus is the most significant. The results of individual and weight diversity index showed that H', J' and D' in autumn were higher than those in spring, while the average value of C' in spring was higher. The surface salt temperature of the water surface in the study area is affected by many dynamic factors and there is a large seasonal change. The resource density plane distribution map and the ranking map reveal that certain groups have a life habit of tending to temperature and salt. [ABSTRACT FROM AUTHOR]

Antibiotics have attracted global attention due to the ecological risks to environment. In this paper, solid-phase extraction and ultra-performance liquid chromatography triple quadrupole mass spectrometry (LC–MS/MS) were utilized to analyze the fugitive characteristics of 10 antibiotics of sulfonamides (sulfadiazine, sulfamethazine, sulfadimidine, sulfathiazole, sulfapyridine, sulfamethoxazole) and tetracyclines (tetracycline, oxytetracycline, chlortetracycline and doxycycline) in the coastal waters and surfece sediments of the Yangtze River Estuary and the ecological risks of antibiotics in water were estimated using ecological risk assessment method. The results have showed that 7 of the 10 antibiotics were detected in the water, with total concentrations ranging from 0.652 to 434.47 ng/L. 8 antibiotics were detected in the sediment, with total concentrations ranging from 0.091 to 499.23 ng/g. The main antibiotic species detected in the sediment and water varied seasonally. Higher concentrations in spatially distributed areas where rivers meet and where human activities have a more significant impact. The ecological risks were found to be higher in spring and autumn than those in winter and summer. Spatial variation in individual microbial communities was not evident in the sediments. The relationship between antibiotics and microorganisms in the environment was predominantly positive. Physical and chemical factors were significantly correlated for both antibiotics and microbial communities. This study can provide research ideas for other types of antibiotics and provide a basis for the prevention of antimicrobial resistance (AMR). [ABSTRACT FROM AUTHOR]

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.

This data article aimed to evaluate the influencing mechanisms of the nutrients and the level of eutrophication in the Yangtze River estuary. The seasonal characteristics of nutrients (dissolved inorganic nitrogen (DIN), SiO32−–Si, and PO4 3–P) in the seawater of the Yangtze River estuary were analyzed by conducting surveys in spring and summer of 2019. The findings revealed that the concentrations of all nutrient at the surface and bottom layers were lower in spring compared to summer. NO3 −–N was typically the major form of DIN. Runoff was identified as the primary source of DIN and SiO3 2−–Si, while PO4 3−–P originated from a various sources.The SiO32−–Si/PO43−–P and DIN/PO43−–P values in the surface and bottom layers during the spring and summer were higher than the Redfield values, indicating an imbalanced nutrient distribution. Furthermore, discrepancies were observed in the distributions of DIN/PO4 3−–P, SiO3 2−–Si/DIN, and SiO3 2−–Si/PO4 3−–P in the Yangtze River estuary. Through an examination of the ratio of DIN/PO4 3−–P absorbed by phytoplankton, PO4 3−–P was identified as a potential limiting factor for nutrition in the sea area of the Yangtze River estuary during spring and summer. The Eutrophication Index (E) values for both spring and summer were found to be higher than the eutrophication threshold, indicating severe eutrophication in the studied sea area.

Chinese sturgeon (Acipenser sinensis) is an endangered species, and the Yangtze River Estuary is an important migration channel for this species. With the scale of Chinese sturgeon restocking along the Yangtze River gradually increasing, an increasing number of artificially bred Chinese sturgeon will come to the estuary. It is urgent to make the first insights about the distribution characteristics and migration strategy of the endangered Chinese sturgeon in the Yangtze River Estuary available. So, to balance the need for information about this endangered species and its conservation, a total of 14 Chinese sturgeons were released in the waters near Chongming Island on 9 April 2021 and 20 October 2022, and 50% of them have been successfully recovered. The data demonstrated that Chinese sturgeon had a good migration ability in the Yangtze River Estuary and its adjacent waters. One sturgeon returned to the freshwater area of the estuary after spending approximately 46 days in the sea at a maximum depth of 54.5 m, and two sturgeons returned to the Yangtze River mainstream within 3.5 days after release. We propose that the Northern Channel of the estuary may be the main passway for Chinese sturgeon to undertake the river–sea migration. The bycatch data of Chinese sturgeon showed that this species may prefer the southern area of the estuary. We hypothesize that the food resources and salinity regime are the main factors that promote Chinese sturgeon to enter the shoals around the coast of Chongming Island. The ocean currents, river runoff, salinity, and food resource may affect the distribution of Chinese sturgeon along the Chinese coast. Future work on the conservation of Chinese sturgeon should focus on the marine life history and continuously enrich the research data to improve conservation strategies.

Suspended sediment plays a major role in estuary morphological change and shoal erosion and deposition. The impact of storm waves on sediment transport and resuspension in the Yangtze River Estuary (YRE) was investigated using a 3D coupling hydrodynamic-wave model with a sediment transport model during Typhoon Ampil. This model has been validated in field observations of water level, current, wave, and sediment concentration. The model was run for tide only, tide + wind, tide + wind and wave forcing conditions. It was found that: (1) typhoons can increase the suspended sediment concentration (SSC) by enhancing bed shear stress (BSS), especially in the offshore area of the YRE, and there is hysteresis between SSC and BSS variation; (2) exponential and vertical-line types are the main vertical profile of the SSC in the YRE and typhoons can strengthen vertical mixing and reconstruct the vertical distribution; and (3) waves are the dominating forcing factor for the SSC in the majority of the YRE through wave-induced BSS which releases sediment from the seabed. This study comprehensively investigates the spatio-temporal variation in SSC induced by Typhoon Ampil in the main branch of the YRE, which provides insights into sediment transport and resuspension during severe storms for estuaries around the world.

Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to "re-suspend" and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as "self-digging". The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and "re-suspension", which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC "tails" appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of "self-digging" induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the "self-digging" problem to a certain extent and ensure the safety of OWFs. [ABSTRACT FROM AUTHOR]

Microplastics are widespread in the oceans as a new type of pollutant. Due to the special geographical environment characteristics, the Yangtze River estuary region become hotspot for microplastics research. In 2017 and 2019, surface seawater microplastics samples were collected from five stations off the Yangtze River estuary during four seasons (spring, summer, autumn, and winter). The abundance and characteristics of microplastics in seawater were researched. The results showed that microplastics widely existed in surface seawater; the average abundance of microplastics in seawater was (0.17 ± 0.14) items/m3 (0.00561 ± 0.00462) mg/m3; and accounting for 80% of the total plastic debris, the abundance of microplastics was at moderately low levels compared to national and international studies. The particle size of most microplastics was between 1 mm to 2 mm, accounting for 36.1% of the total microplastics. The main shapes of microplastics were fiber, flake, and line, accounting for 39.5%, 28.4%, and 20.8%, respectively. Polypropylene, polyethylene terephthalate, and polyethylene were the main components of microplastics, accounting for 41.0%, 25.1%, and 24.9%, respectively. Yellow, green, black, and transparent were the most common colors, accounting for 21.9%, 19.6%, 16.5%, and 15.7%, respectively. This study shows that the spatial distribution of microplastics in the surface waters off the Yangtze River estuary shows a decreasing trend from nearshore to farshore due to the influence of land-based inputs, hydrodynamics, and human activities; the distribution of microplastics has obvious seasonal changes, and the level of microplastic pollution is higher in summer. The potential ecological risk of microplastics in the surface waters off the Yangtze River estuary is relatively small. [ABSTRACT FROM AUTHOR]

Complex hydrocultural conditions in the estuary affect the migration and transformation of mercury. Using two voyages in July and October 2018, Dissolved Gaseous Mercury (DGM) and Reactive Mercury (RHg) were determined to explore the source, transformation and influence of DGM content in the adjacent waters of Yangtze River Estuary in summer and autumn. The results showed the contents of DGM and RHg in summer were higher than those in autumn, and both of them were higher than those in open sea. In summer and autumn, the Yangtze River brought a higher concentration of DGM, and different flow direction and runoff resulted in differences in the high value region of the surface. The emergence of low-oxygen zones in summer was conducive to the production of DGM. In autumn, windy weather allowed seawater disturbances to promote the release of mercury from the underlying sediments, especially in shallow sea in northwest. RHg showed a higher concentration in the offshore than in the open sea in summer, but there was no such trend in autumn, reflecting the influence of less runoff input. DGM is the main product of RHg reduction, and there was a significant positive correlation between DGM and RHg in summer (r = 0.356, P <0.05), while the correlation between DGM and RHg was not significant in autumn due to the influence of light intensity, wind speed and nutrients. The exchange flux of mercury in the adjacent waters of the Yangtze River Estuary was higher than that in the open sea. There was no significant difference of the release flux of mercury in summer and autumn. This article highlighted that the input of mercury from the Yangtze River runoff promotes the release of mercury in seawater, and the hypoxic zone caused by eutrophication is conducive to the production of DGM. [ABSTRACT FROM AUTHOR]

In order to investigate the species composition and diversity of larvae and juvenile fish in Chongming Dongtan and its surrounding waters, 14 stations were set up in Chongming Dongtan and its surrounding waters from November 2020 to August 2021, and surface horizontal trawling surveys were conducted quarterly with large larvae and juvenile fish nets (diameter 1.3 m, mesh 0.5 mm) for four voyages at each station. A total of 4 556 larvae and juveniles were collected, belonging to 8 orders, 14 families and 48 species. The species composition of dominant species is obvious, of which Coilia mystus (25.09%) was the dominant fish. This was followed by Stolephorus commersonnii (20.12%) and Salanx ariakensis (17.11%). The results showed that the species number and density of larvae and juvenile fishes in spring and summer were significantly higher than those in autumn and winter, and the highest density was 0.658 ind./m³ in summer. The number of species in spring was 28, and the number of species in winter was the least. The species richness index, diversity index and evenness index showed the same trend between seasons, with the highest in spring and the lowest in winter. The density of larvae and juveniles was higher in the north branch than in the south branch in spring and summer, and higher in the south branch than in the north branch in autumn and winter. The results of cluster analysis showed that larvae and juvenile fishes can be divided into freshwater group, estuarine group I and estuarine group II in spring. Summer can be divided into estuarine group and marine group, the larvae and juveniles in Chongming Dongtan of Yangtze River estuary in autumn could be divided into freshwater group, estuarine group and marine group. The species and number of fish larvae and juveniles in winter are very small. Pearson correlation index analysis showed that the richness index, diversity index and evenness index in summer were correlated with salinity, but not with water temperature. The temporal and spatial distribution characteristics of dominant species and communities of larvae and juvenile fish in Chongming Dongtan and the environmental factors affecting their distribution were also discussed. The results will provide important analysis data for the sustainable development and protection of fishery ecological resources in Chongming Dongtan, Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

This paper examines the application of the erosion- deposition law to the multilevel bifurcating system of Yangtze River Estuary under dam-induced runoff flattening. The spatiotemporal pattern of erosion- deposition change and associated hydrodynamic mechanism are identified by analyzing water- sediment, terrain and engineering data from 1950 to 2021 in terms of a runoff intensity index Da(i. e., multiyear average days of runoff discharge ≥60 000 m 3 / s), tracked positions of stagnation points, and estimates of restored erosion- deposition volume of the north passage according to navigation dredging data. It is found that the ebb partition ratios of the north and south branching channels tend to increase and decrease, respectively, as Da grows; this aggravates erosion and impedes deposition in the north branching channels while facilitating deposition and restraining erosion in the south branching channels. Meanwhile, depo- centers in north and south branching channels move downstream and upstream. The foregoing changes in erosion- deposition are driven by hydrodynamic inertia and the flow- deflecting effect of nodes along the south bank. More specifically, the ebb flow axis swings either northward or southward as the runoff discharge varies, forming a linkage mechanism for the lateral- longitudinal erosion- deposition pattern between the north and south branching channels. As the runoff process becomes continuously flattened owing to upstream dam regulation activities, the north branching channels and their upper sub- reaches are likely to maintain a trend of deposition aggravation and erosion impediment, whereas their lower sub- reaches maintain a trend of erosion aggravation and deposition impediment. Conversely, the south branching channels are likely to witness an opposite trend in erosiondeposition. The critical runoff discharge for migration of the stagnation point between upper and lower sub-reaches in the north passage is 35 000 m 3 / s. At such a situation, additional deposition is expected to occur in the upper subreach, and timely maintenance adjustments would be required along key segments of the navigational channel. [ABSTRACT FROM AUTHOR]

This study investigated microplastic distribution characteristics by collecting surface seawater from sea areas to the south of Jeju Island in August 2020. The average microplastic abundance was 0.46 ± 0.27 particles/L (n = 23), and PE had a high ratio, averaging 53%. The levels of fragments and fibers were observed to be 69% and 31% on average, respectively. The most common size of the microplastics was on average 0.02–0.30 mm at a level of 69%. We found a higher abundance of microplastics in the study area than in other open waters such as the Arctic Central Basin and the Atlantic Ocean, whereas the abundance was lower than that in previous studies on coastal areas. We studied an area of open sea connecting China, Japan, and the Pacific Ocean, and, in this region, the microplastic distribution varies depending on sea currents in the surrounding areas. In the summer, the western and central regions of the study sea area have low salinity levels due to discharge from China's Yangtze River. This generally indicates that high-density plastic deposits are found in the Yangtze River estuary, and low-density plastics are found in the study area. Furthermore, this implies that low- and high-density plastics are transported in water for long periods of time due to the Taiwan Warm Current and because the eastern sea area has high salinity. [ABSTRACT FROM AUTHOR]

An indoor simulation test system with a mud (sediment) water mass ratio of about 1:1 and a period of 56 days was adopted. Six concentration gradient test groups, including the control group, were set up to study the change characteristics of total organic carbon (TOC) content in sediments caused by different levels of exogenous phosphorus input. At the same time, UV-Vis absorption spectroscopy was used to study the effect of phosphorus containing substances on the structural changes of dissolved organic matter in sediments. The experimental results showed that the TOC content in the sediment of each experimental group decreased by 3.60%, 7.08%, 8.09%, 9.33% and 11.80% respectively compared with the control group on the 56th day, indicating that the decomposition of TOC in the sediment of the Yangtze Estuary accelerated with the increase of exogenous phosphorus input. During the test period, the maximum humification degree and aromatization degree of dissolved organic matter in sediments were positively correlated with the input of phosphorus. The molecular weight and aromatic ring structure of dissolved organic matter were positively correlated with the input of exogenous phosphorus, indicating that the increase of exogenous phosphorus input could accelerate the change of dissolved organic matter in sediments. With the increase of test time, the humification degree and aromatization degree of dissolved organic matter with different phosphorus levels increased first, and then began to decline; The molecular weight of dissolved organic matter gradually decreased with the increase of time, and the substituents on its aromatic ring substituents were gradually replaced by more active functional groups. It shows that humus is formed during the reduction of organic carbon content in sediments. As humus continues to decompose, the degree of humification decreases, and the degree of humification is the same as that of aromatization. [ABSTRACT FROM AUTHOR]

Chinese sturgeon Acipenser sinensis is an anadromous migratory fish species, which inhabits the Chinese coastal continental shelf areas and breeds in the Yangtze River Basin. The Yangtze River Estuary is an important migration passage of Chinese sturgeon. The Chinese sturgeon population is endangered, which has been listed as a top-level protected animal in List of key protected wild animals in China and a critically endangered species in IUCN Red List of Threatened Species. Since 2013, the abnormal interruption of natural spawning behavior of wild Chinese sturgeon has brought great challenges to the protection and restoration of Chinese sturgeon population. Based on the survey data of juvenile Chinese sturgeon resources in the Yangtze River estuary from 2004 to 2020, this study analyzed the population characteristics and migration habits of juvenile Chinese sturgeon in the Yangtze River estuary following the abnormal natural spawning behavior. The results show that:(1) Since natural spawning behavioral interruption of Chinese sturgeon, juvenile Chinese sturgeon was not detected in the Yangtze River estuary in 2014, 2016, 2018, 2019 and 2020. The recruitment of juvenile Chinese sturgeon population in the Yangtze River estuary showed an interannual continuous fracture. (2) The migration habits of juvenile Chinese sturgeon changed significantly, it showed that the first occurrence time was advanced to mid-April, and the final occurrence time was delayed to late October, and the occurrence time span was extended by 118 days. (3) The biological indexes of juvenile Chinese sturgeon were lower than the same period in history; Their minimum body length and minimum body weight were 7. 0 cm and 4. 9 g respectively. To sum up, the juvenile Chinese sturgeon recruitment decreased year by year. The migration habit shows that the earlier the first occurrence time, the later the final occurrence time in the Yangtze River estuary. The results of this study will provide an important scientific reference for the protection of rare and endangered species of Chinese sturgeon. [ABSTRACT FROM AUTHOR]

Benzotriazoles (BTRs), benzothiazoles (BTHs), and benzotriazole ultraviolet absorbers (BUVs) are common products in plastic rubber and personal care products. Due to their toxicity and bioaccumulation, they have been identified as emerging contaminants (ECs) in the environment. Solid-phase microextraction (SPME) and solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC–MS) were used for the enrichment and detection of the contaminants in seawater and sediment, respectively. The conditions of SPE and SPME were optimized in terms of material, temperature, time, pH, ionic strength, extraction solvent, and elution solvent. Although SPME requires a small sample volume, it is not reliable for the extraction efficiency and reproducibility of BTHs, BTRs, and BUVs in seawater. However, the precision of SPE-GC–MS for the determination of BTHs, BTRs, and BUVs was around 10%, with recoveries of 67.40–102.3% and 77.35–101.8% in seawater and sediment, respectively. The limits of detection of 14 contaminants in seawater and sediment were 0.03–0.47 ng/L and 0.01–0.58 ng/g, respectively. Secondly, BTHs, BTRs, and BUVs were detected with low ecological risk when SPE-GC–MS was applied to the analysis of seawater and sediment samples from the Yangtze estuary and its adjacent areas. The SPE-GC–MS was highly precise with lower detection limits relative to previous studies and thus was able to meet the requirements for the detection of BTHs, BTRs, and BUVs in seawater and sediments. [ABSTRACT FROM AUTHOR]

The decline of Japanese eel (Anguilla japonica) populations in the Yangtze River estuary represents a critical conservation concern. Eleven-years of daily catch data during recruitment periods (i.e., January–April, 2012–2022) indicate that annual catch averaged from 153 to 1108 eels, and show a bimodal pattern in glass eel arrivals. Utilizing seasonal-trend decomposition and generalized additive models, we demonstrated a strong correlation between catch abundance, optimal water temperatures, and lunar cycles. An auto-regressive integrated moving average (ARIMA) model predicts an increase in glass eel numbers for 2023–2024 but also points to a concerning trend of delayed recruitment timing since 2016, attributable to the 0.48 °C per decade rise in sea surface temperatures. This delay correlates with a significant decrease in the average body weight of glass eels, suggesting potential energy deficits that may hinder successful upstream migration. This study not only furthers our understanding of glass eel recruitment dynamics but also underscores the urgent need for targeted conservation measures. Additionally, it highlights the importance of sustained, detailed monitoring to mitigate the detrimental effects of climate change on these eels, vital for preserving the Yangtze River’s ecological integrity.

An estuary plays an important role in material and energy exchange between the land and sea, where complex physical, chemical, and biological processes occur. Here, we investigated the assembly processes of free‐living (FL) and particle‐associated (PA) bacterial communities in two seawater layers at five stations in the Yangtze River Estuary (YRE) by using 16S rRNA sequencing methods. The results indicated that Proteobacteria was the most abundant phylum in the YRE. The α‐diversity of PA community was significantly higher than FL community, and analysis of similarity showed significantly different (Global R = 0.2809, p < 0.005). RDA revealed that phosphate (PO43−) was significantly correlated with PA bacterial community abundance (p < 0.05). An ecological null model showed that both PA and FL bacterial communities were mainly influenced by stochastic processes (PA: 100%, FL: 70%), which PA attached to nutrient particles and are less affected by environmental filtration. Dispersal limitation (50%) was the main assembly process of the PA community, while homogeneous selection (30%) and drift (30%) were important processes in the FL community assembly. The available substrate for colonization limits the transformation from FL to PA bacteria. This study would improve our understanding of FL and PA bacterial community structure and factors affecting assembly process in estuarine environments. [ABSTRACT FROM AUTHOR]

• AAs and their TPs were prevalent in water and sediments across the YRE. • DPG, DPA, and DChA were the most abundant AA congeners. • Human impacts, hydrodynamics, and (bio)degradation shaped AAs' behaviors. • Partitioning of AAs was determined by their hydrophobicity and biostability. • AAs might pose moderate to high ecological risks to the YRE ecosystem. Aniline accelerators and antioxidants (AAs) are high-production-volume industrial additives that have recently attracted emerging concern given their ubiquity in environmental compartments and the associated (eco)toxic effects. Nonetheless, available information on the multi-media behavior of AAs and their transformation products (TPs) remains scarce. Therefore, we determined the residues of twenty-four AA(TP)s in paired dissolved phases (i.e., filtered water), suspended particulate matter (SPM), and sediment samples collected from the Yangtze River Estuary (YRE), a highly urbanized estuary in the East China. The median total concentrations of targeted compounds were 0.73 ng/g dw, 34.4 ng/L, and 39.6 ng/L in sediments, surface and bottom water, respectively. Diphenylamine (DPA) was the most abundant congener in SPM, while 1,3-diphenylguanidine (DPG) and dicyclohexylamine (DChA) dominated in the dissolved phases and sediments. Various anthropogenic emissions and (a)biotic degradation may collectively shape the matrix-specific accumulation patterns and spatial trends of these compounds across the YRE. However, the vertical patterns of AA(TP)s were obscure, probably due to the estuarine hydrodynamics and/or the modest sample size. The SPM fractions of AA(TP)s in water (Ф: 7.9–100%) and the sediment sorption coefficients (K OC : 0.01–6.56) both positively correlated with their hydrophobicity as indicated by the octanol-water partition coefficient (K OW). Moreover, risk quotients implied moderate to high aquatic toxicity posed by several AA(TP)s at certain YRE sites. The estimated total annual fluxes of our analytes transported via water and sediments towards the East China Sea were 5.90–365.5 tons and 4.23–1,100 kg, respectively. This work provides a systematic investigation of multi-media processes and ecological risks of AA(TP)s in a highly-urbanized estuary, contributing to holistic comprehension of these emerging contaminants in estuarine environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Coilia nasus was once an economically important fish in the Yangtze River estuary, but overfishing and other anthropogenic factors have severely depleted its population. To conserve and restore C. nasus , there is an urgent need to determine its precise spatiotemporal distribution. However, as a typical anadromous species, C. nasus seasonally uses estuarine habitats, resulting in a very high proportion of nulls in some seasons and posing a great challenge to predicting abundance. This study compared three commonly used tree methods (gradient boosting machine (GBM), random forest (RF), and conditional random forest (CRF)) to predict the abundance of C. nasus in the Yangtze River estuary using trawl resource monitoring survey data from 2013 to 2018. Based on the survey data, 16 explanatory variables, including temperature, salinity, pH, and chemical oxygen demand, were used as predictors, and the coefficient of determination (R2), root mean square error (RMSE), and root mean square logarithmic error (RMSLE) were used to evaluate the performance of the three tree methods. Three metrics were used to assess the performance difference between interpolation and extrapolation for the three tree methods when modeling by season and combining seasons. The results showed that (1) compared with combined modeling, seasonal modeling could accurately determine the high- and low-abundance regions in interpolation, and the quarterly model greatly improved the extrapolation prediction accuracy. (2) Almost all metrics indicated that the interpolation RF model had the best performance, while CRF and GBM were significantly worse than other methods for some indicators, and the RF model had better robustness and could be applied to the abundance of all seasons. (3) The model performance in extrapolation was significantly lower than that of interpolation, RF was also the best method, and RF could still identify high-abundance areas when the amount of data was much smaller than that used for interpolation. The findings of our study can be generalized to species distribution modeling of other migratory species in the Yangtze River estuary or estuarine ecosystems in the Northwest Pacific Ocean. • Seasonally zero-inflated abundance data are derived from differences in species ecology. • Seasonal modeling is more suitable for anadromous species that use estuaries periodically. • RF demonstrated superior performance in both interpolation and extrapolation. • Accurate spatiotemporal distribution predictions of C. nasus improve the evaluation of estuarine protected areas. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) frequently threaten the health of marine environments and ecosystems in the adjacent waters of the Yangtze River Estuary (YRE) in summer. To better understand the spatiotemporal distribution, variation characteristics, and major influencing factors of algal bloom-prone zones in the adjacent waters of the YRE in summer, the present study used Geostationary Ocean Color Imager (GOCI) chlorophyll-a (Chl-a) data from 2011 to 2020. The Chl-a concentration threshold for summer algal blooms in the adjacent waters of the YRE was determined to be 16 mg/m3, based on which the monthly and interannual distribution characteristics of algal blooms were further clarified, and the influence of runoff and sea surface temperature (SST) on algal blooms was analyzed. The results showed that the area of the algal bloom-prone zones was the largest in July, at 1337 km2, which was approximately 2.8-fold greater than that in June (474 km2) and 1.3-fold greater than that in August (1028 km2); the algal bloom-prone zones were mainly distributed in the eastern sea area of the YRE, and the spatial distribution of the algal blooms showed significant interannual variation. In 2020, the distribution range of the algal bloom-prone zones was the largest, and the maximum probability was >20%. Runoff had a significant positive effect on the algal bloom index (BI) (r = 0.89, p < 0.05), the correlation between BI and SST was weak (r = 0.50, p = 0.14), and the algal bloom probability had a significant negative correlation with SST (r = −0.71, p < 0.05), implying that above a certain range of temperatures, algal growth rates may decrease with increasing temperature. The research results can provide a scientific basis for the early prevention, control, and emergency response of disasters, which is conducive to the sustainable and healthy development of marine resources and has significant scientific and management significance. • Chlorophyll-a concentration threshold method can be used to identify algal blooms. • The area of algal bloom-prone zones in the YRE is the largest in July in summer. • Spatial distribution of algal blooms shows significant interannual variability. • Yangtze River runoff has a significant positive effect on the bloom intensity. • Temperature has a significant negative effect on the algal bloom probability. [ABSTRACT FROM AUTHOR]

Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to “re-suspend” and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as “self-digging”. The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and “re-suspension”, which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC “tails” appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of “self-digging” induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the “self-digging” problem to a certain extent and ensure the safety of OWFs.

Microplastics are widespread in the oceans as a new type of pollutant. Due to the special geographical environment characteristics, the Yangtze River estuary region become hotspot for microplastics research. In 2017 and 2019, surface seawater microplastics samples were collected from five stations off the Yangtze River estuary during four seasons (spring, summer, autumn, and winter). The abundance and characteristics of microplastics in seawater were researched. The results showed that microplastics widely existed in surface seawater; the average abundance of microplastics in seawater was (0.17 ± 0.14) items/m3 (0.00561 ± 0.00462) mg/m3; and accounting for 80% of the total plastic debris, the abundance of microplastics was at moderately low levels compared to national and international studies. The particle size of most microplastics was between 1 mm to 2 mm, accounting for 36.1% of the total microplastics. The main shapes of microplastics were fiber, flake, and line, accounting for 39.5%, 28.4%, and 20.8%, respectively. Polypropylene, polyethylene terephthalate, and polyethylene were the main components of microplastics, accounting for 41.0%, 25.1%, and 24.9%, respectively. Yellow, green, black, and transparent were the most common colors, accounting for 21.9%, 19.6%, 16.5%, and 15.7%, respectively. This study shows that the spatial distribution of microplastics in the surface waters off the Yangtze River estuary shows a decreasing trend from nearshore to farshore due to the influence of land-based inputs, hydrodynamics, and human activities; the distribution of microplastics has obvious seasonal changes, and the level of microplastic pollution is higher in summer. The potential ecological risk of microplastics in the surface waters off the Yangtze River estuary is relatively small.

In addition to nutrients and light, temperature plays a crucial role in marine biogeochemical processes. In this study, the sensitivity of the growth rate of phytoplankton to temperature was systematically studied by using a two-level nested physical–biogeochemical coupled model for the Yangtze River estuary of the East China Sea. The physical component of the coupled model is configured from the Regional Ocean Modeling System (ROMS) with the highest horizontal resolution of 3 km. The biogeochemical component of the coupled model is based on the carbon, silicon and nitrogen ecosystem model (CoSiNE). Five specific growth rate of phytoplankton equations with different relation to temperature were tested with the objective of reproducing the temporal evolution of chlorophyll concentration as observed by SeaWiFS. Our results indicate that the specific growth rate of phytoplankton equation which is from Geider's work, reaches a maximum at 22 °C and remains constant with higher temperature, can reproduce the seasonal variation of chlorophyll very well, and may be suitable for application in the physical–biogeochemical coupled model (ROMS-CoSiNE) of the Yangtze River estuary. [ABSTRACT FROM AUTHOR]

The gut microbiota plays a crucial role in food webs, carbon cycling, and related elements. Exopalaemon annandalei and Exopalaemon carinicauda are two important forage species in the Yangtze River estuary with extremely similar living habits and morphological characteristics. Exploring the microorganisms in the guts of these two shrimp species can help us understand the survival status of forage species and gut microbiota in the Yangtze River estuary. Therefore, this study analyzed the similarities and differences in the intestinal flora of E. annandalei and E. carinicauda through high-throughput sequencing of 16S rRNA gene amplicons. The results showed that the dominant bacteria in the intestinal flora of E. annandalei and E. carinicauda at the phylum level were Proteobacteria and Firmicutes, respectively. At the genus level, the intestinal flora had higher concentrations of Psychrobacter , Bacillus , Pseudomonas , Acinetobacter , and Macrococcus . In both shrimp species, the contents of Acinetobacter and Macrococcus were higher in spring than in winter. The most important potential functions of the intestinal microbiota were amino acid metabolism and purine metabolism. Additionally, the functions of metabolism and diseases in the intestinal microbiota of E. annandalei were greatly influenced by the season. Furthermore, the experimental results indicated that a lower ratio of Firmicutes to Bacteroidetes was associated with a larger body weight in shrimp. Overall, this study provides a theoretical reference for understanding the intestinal bacterial community of shrimp in estuaries and the healthy cultivation of E. annandalei and E. carinicauda ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Wang, Feng, Han, Zhang, Chen and Wu.)