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The study applied a tiered ecological risk assessment method to evaluate the long-term status and trend of the ecological risks of dissolved heavy metals from 2011 to 2019 in the Yangtze River Estuary and Zhejiang coastal waters, China. The results for spring, summer, and autumn of 2019 indicated that Pb, Cd, and Zn posed no adverse ecological risk, Cu posed a potential ecological risk, and As posed an ecological risk. The annual results from 2011 to 2019 suggested that Pb, Cd, and Zn posed no adverse ecological risks, and As and Cu posed an ecological risk. The trend analysis in the nine years showed that the ecological risk of Cu is gradually decreasing, while that of As is still a concern. The overall trend is attributed to the environmental protection policies that reduced these contaminants' terrestrial sources and atmospheric sources., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Xinxin Li reports financial support was provided by National Natural Science Foundation of China. Xinxin Li, Xiuqing Song reports financial support was provided by Shanghai Sheshan National Geophysical Observatory. Xinxin Li, Xiaohui Zhai reports financial support was provided by Shenzhen Marine Development Research Promotion Center. Wei Cai reports financial support was provided by Zhujiang Program. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Halogenated flame retardants (HFRs) have attracted global attention owing to their adverse effects on ecosystems and humans. The Shandong Peninsula is the largest manufacturing base for HFRs in East Asia, yet its impacts on marine ecosystems are unclear. Seventeen HFRs were analyzed in organisms captured from the Xiaoqing River estuary, Bohai Sea (BS), Yellow Sea and Northern East China Sea to investigate the distribution and bioaccumulation of HFRs on a broad scale. The results showed a downward trend in ΣHFR concentrations from the estuary (37.7 ng/g lw on average) to Laizhou Bay (192 ng/g lw) and to coastal seas (3.13 ng/g lw). The concentrations of ΣHFRs were significantly higher in demersal fish (0.71-198 ng/g lw) and benthic invertebrates (0.81-3340 ng/g lw) than in pelagic fish (0.30-27.6 ng/g lw), reflecting a habitat dependence. The concentrations of higher-brominated homologs were greater in benthic invertebrates, whereas a greater level of lower-brominated PBDE congeners was observed in fish, suggesting different profiles between species. Furthermore, the analogue composition of HFRs in fish was similar to that in the dissolved phase of seawater, whereas the HFR pattern in benthic invertebrates was consistent with the profile in sediment. The concentrations of HFRs in organisms vary widely depending on emissions from anthropogenic activities, whereas bioaccumulation patterns are strongly influenced by species and habitat., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

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 Δ 14 C-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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Anthropogenic input of excess nutrients stimulates massive nitrous oxide (N 2 O) production in estuaries with distinct seasonal variations. Here, nitrogen isotopic and isotopomeric signatures were utilized to investigate the seasonal dynamics of N 2 O production and nitrification at the middle reach of the eutrophic Pearl River Estuary in the south of China. Elevated N 2 O production primarily via ammonia oxidation (> 1 nM-N d -1 ) occurred from April to November, along with increased temperature and decreased dissolved oxygen concentration. This consistently oxygenated water column showed active denitrification, contributing 20-40 % to N 2 O production. The water column microbial N 2 O production generally constituted a minor fraction (10-15 %) of the estuarine water-air interface efflux, suggesting that upstream transport and tidal dilution regulated the dissolved N 2 O inventory in the middle reach of the estuary. Nitrification (up to 3000 nM-N d -1 ) played a critical role in bioavailable nitrogen conversion and N 2 O production, albeit with N 2 O yields below 0.05 %., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of interest regarding the publication of this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

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, PO 4 3- , and distance offshore (p < 0.05). Water depth, NH 4 + , and PO 4 3- 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 NO 3 - (or NO 2 - ) 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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Halogenated organic contaminants, such as chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs), are some of the most important emerging environmental pollutants. However, empirical data on Cl/Br-PAHs in estuarine and marine ecosystems are limited, rendering assessments of Cl/Br-PAH contamination in estuarine and offshore environments uncertain. Here the occurrence, sources, and ecological risks of 7 Cl-PAHs and 18 Br-PAHs were determined in surface sediments of the Yangtze River Estuary (YRE), a highly urbanized and industrialized area, and its adjacent marine area. The concentrations of Cl-PAHs ranged from 4.50 to 18.38 ng g -1 (average 7.19 ng g -1 ), while those of Br-PAHs ranged from 4.80 to 61.18 ng g -1 (average 14.11 ng g -1 ). The dominant Cl-PAH and Br-PAH in surface sediment were 9-chlorofluorene (17.79%) and 9-bromofluorene (58.49%), respectively. The distributions and compositions of Cl/Br-PAHs in the surface sediments varied considerably due to complex hydrodynamic and depositional conditions in the YRE and its adjacent marine area, as well as differences in physicochemical properties of different Cl/Br-PAHs. Positive matrix factorization revealed that the primary sources of Cl/Br-PAHs in the study area were e-waste dismantling (33.6%), waste incineration (23.2%), and metal smelting (11.0%). According to the risk quotient, the Cl/Br-PAHs in sediments posed no toxic risk to aquatic organisms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Carbon-fixing bacterial communities are essential drivers of carbon fixation in estuarine ecosystems that critically affect the global carbon cycle. This study compared the abundances of the Calvin cycle functional genes cbbL and cbbM and Reductive tricarboxylic acid cycle gene aclB, as well as compared carbon-fixing bacterial community features in the two estuaries, predicted potential ecological functions of carbon-fixation bacteria, and analyzed their symbiosis strategies in two estuaries having different geographical distributions. Gammaproteobacteria was the dominant carbon-fixing bacterial community in the two estuaries. However, a higher number of Alphaproteobacteria were noted in the Liaohe Estuary, and a higher number of Betaproteobacteria were found in the Yalujiang Estuary. The carbon-fixing functional gene levels exhibited the order of aclB > cbbL > cbbM, and significant effects of Cu, Pb, and petroleum were observed (p < 0.05). Nitrogen-associated nutrient levels are major environmental factors that affect carbon-fixing bacterial community distribution patterns. Spatial factors significantly affected cbbL carbon-fixing functional bacterial community structure more than environmental factors. With the increase in offshore distance, the microbial-led processes of methylotrophy and nitrogen fixation gradually weakened, but a gradual strengthening of methanotrophy and nitrification was observed. Symbiotic network analysis of the microorganisms mediating these ecological processes revealed that the carbon-fixing bacterial community in these two estuaries had a non-random symbiotic pattern, and microbial communities from the same module were strongly linked among the carbon, nitrogen, and sulfur cycle. These findings could advance the understanding of carbon fixation in estuarine ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Marine litter pollution poses a significant threat to offshore ecosystems, eliciting widespread concern. We investigated seafloor litter patterns in the Pearl River Estuary and adjacent coastal waters of China in 2023 via bottom trawl survey. Average number and weight densities were found to be 154.34 ± 30.95 n/km 2 and 2384.63 ± 923.98 g/km 2 , respectively. Plastic was the most abundant material by number density (79.07 %), and rubber the highest by weight density (22.93 %). Overall number density varied from 40.50 ± 22.50 to 221.13 ± 52.44 n/km 2 , with the highest in Daya Bay and the lowest in Guanghai Bay. Weight density varied from 189.93 ± 71.94 to 5386.70 ± 3050.30 g/km 2 , with the highest in Qiao Island and the lowest in Honghai Bay. The main source was plastic bags and wrappers. The Pearl River Delta and Daya Bay were identified as seafloor litter distribution hotspots. Controlling plastic waste input is crucial for reducing seafloor litter in the Pearl River Estuary., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The impact of heavy metal ions on the biodenitrification process remains unknown, which is the key to understand the nitrogen cycle in estuarine areas. Here, denitrification rate and the abundance of five denitrifying enzyme genes (narG, nirK, napA, norB and nosZ) in Liaohe Estuary sediments were examined, and the community structure of nirK denitrifying bacteria was also analyzed. The results demonstrate a significant positive correlation between heavy metal content (Cu 2+ , Zn 2+ , and Cr) and the denitrification rate, and the abundance of napA/norB (periplasmic nitrate reductase and nitric-oxide reductase) in sediments. The dominant narG denitrifiers were Pseudomonas, Hydrogenophaga, and Serratia known to be tolerant to heavy metal pollution. Sediment particle size, NO 3 - , NO 2 - , Zn 2+ , and Cd 2+ were the key factors influencing the denitrifying community structure. These findings suggest that heavy metals may enhance the aerobic denitrification process in sediments and mitigate the adverse effects of high dissolved oxygen levels., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The carbonate chemistry in river-dominated marginal seas is highly heterogeneous, and there is ongoing debate regarding the definition of atmospheric CO 2 source or sink. On this basis, we investigated the carbonate chemistry and air-sea CO 2 fluxes in a hotspot estuarine area: the Changjiang Estuary during winter and summer. The spatial characteristics of the carbonate system were influenced by water mixing of three end-members in winter, including the Changjiang freshwater with low total alkalinity (TA) concentration, the less saline Yellow Sea Surface Water with high TA, and the saline East China Sea (ECS) offshore water with moderate TA. While in summer with increased river discharge, the carbonate system was regulated by simplified two end-member mixing between the Changjiang freshwater and the ECS offshore water. By performing the end-member mixing model on DIC variations in the river plume region, significant biological addition of DIC was found in winter with an estimation of -120 ± 113 μmol kg -1 caused by wintertime organic matter remineralization from terrestrial source. While this biological addition of DIC shifted to DIC removal due to biological production in summer supported by the increased nutrient loading from Changjiang River. The pCO 2 dynamics in the river plume and the ECS offshore were both subjected to physical mixing of freshwater and seawater, whether in winter and summer. In the inner estuary without horizontal mixing, the pCO 2 dynamics were mainly influenced by biological uptake in winter and temperature in summer. The inner estuary, the river plume, and the ECS offshore were sources of atmospheric CO 2 , with their contributions varying seasonally. The Changjiang runoff enhanced the inner estuary's role as a CO 2 source in summer, while intensive biological uptake reduced the river plume's contribution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Nanhui Dongtan Wetland is an important part of Yangtze Estuary Wetland, and its species diversity has been affected by reclamation in recent years. To increase the diversity of species in reclamation areas, stock enhancement was implemented in the Nanhui Dongtan Wetland in May 2020 as a method of ecological restoration. We investigated macrobenthos before and after release, analysed changes in the macrobenthos and evaluated the ecological health of the sampled area. The diversity index showed species were more abundant and community structure were more diversified after release. Functional groups and redundancy analysis showed that the effects of stock enhancement on macrobenthos in Nanhui Dongtan wetland may be based on changes in secondary productivity. Stock enhancement may promote the resistance of macrobenthic communities to organic pollution without negatively affecting ecological health. As a method of ecological restoration, stock enhancement will play a positive role in the restoration of macrobenthic communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The Yellow River, renowned as the most sediment-laden river globally, grapples with sediment deposition issues compromising reservoir functionality and elevating downstream riverbeds, posing threats to human life and property safety. In response, the Water-Sediment Regulation Scheme (WSRS) has been innovatively implemented to address these challenges. While effectively mitigating sediment deposition, WSRS has concurrently disrupted the equilibrium of the estuarine ecosystem. This paper addresses the understudied but crucial topic of the interannual impact of WSRS on the estuarine ecosystem. Drawing upon physical, chemical, and biological data gathered through field surveys conducted before, during, and after WSRS from 2011 to 2022, the analysis delves into the interannual changes in the estuarine environment, fish eggs and larvae abundance, and species diversity under the influence of WSRS. The findings reveal an interannual decreasing trend in terrestrial material input due to WSRS, juxtaposed with an interannual increasing trend in fish eggs and larvae around the estuary, as well as the species diversity index. Notably, these trends became more pronounced post-2014. Compared to pre-2014, nutrient concentrations experienced a ~20 % decrease, chlorophyll-a concentration increased by 44 %, fish eggs proliferated approximately 1 time, and the species diversity index transitioned from a declining trend to an ascending trajectory. After 12 years of continuous WSRS implementation, the impact on the estuarine ecosystem has demonstrably diminished. This research aims to furnish reference experience and scientific basis for water and sediment regulation in major rivers around the world in terms of estuarine ecology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Information on long-term trends in total suspended solids (TSS) is critical for assessing aquatic ecosystems. However, the long-term patterns of TSS concentration (C TSS ) and its latent drivers have not been well investigated. In this study, we developed and validated three semi-analysis algorithms for deriving C TSS using Landsat images. Subsequently, the long-term trends in C TSS in the Pearl River Estuary (PRE) from 1987 to 2022 and the driving factors were clarified. The developed algorithms yielded excellent performance in estimating C TSS , with mean absolute percentage errors <25% and root mean square errors of <13 mg/L. Long-term Landsat observations showed an overall decreasing trend and significant spatiotemporal dynamics of the C TSS in the PRE from 1987 to 2022. The analysis of driving factors suggested that industrial sewage, cropland, forests and grasslands, and built-up land were the four potential driving forces that explained 87.81% of the long-term variation in C TSS . This study not only provides 36-year recorded datasets of C TSS in estuary water, but also offers new insights into the complex mechanisms that regulate C TSS spatiotemporal dynamics for water resource management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

This study examined the nutrient budgets and biogeochemical dynamics in the coastal regions of northern Beibu Gulf (CNBG). Nutrient concentrations varied spatially and seasonally among the different bays. High nutrient levels were found in the regions with high riverine inputs and intensive mariculture. Using a three end-member mixing model, nutrient biogeochemistry within the ecosystem was estimated separately from complex physical mixing effects. Nutrient consumption dominated in most bays in summer, whereas nutrient regeneration dominated in winter, likely due to phytoplankton decomposition, vertical mixing and desorption. Through the Land-Ocean Interaction Coastal Zone (LOICZ) model, the robust nutrient budgets were constructed, indicating that the CNBG behaved as a sink of dissolved inorganic nitrogen, phosphorus and silicon. River-borne nutrient inputs were the dominant nutrient source, while residual flows and water exchange flows transported nutrient off the estuaries. This study could help us better understand nutrient cycles and nutrient sources/sinks in the CNBG., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Historical reconstruction of heavy metals (HMs) contamination in sediments is a key for understanding the effects of anthropogenic stresses on water bodies and predicting the variation trends of environmental state. In this work, eighteen sediment cores from the Pearl River Estuary (PRE) were collected to determine concentrations and geochemical fractions of HMs. Then, their potential sources and the relative contributions during different time periods were quantitatively identified by integrating lead-210 ( 210 Pb) radioisotope dating technique into positive matrix factorisation (PMF) method. Pollution levels and potential ecological risks (PERs) caused by HMs were accurately assessed by enrichment factors (EF) based on establishment of their geochemical baselines (GCBs) and multiparameter evaluation index (MPE). HMs concentrations generally showed a particle size- and organic matter-dependent distribution pattern. During the period of 1958-1978, HMs concentrations remained at low levels with agricultural activities and natural processes being identified as the predominant sources and averagely contributing >60%. Since the reform and opening-up in 1978, industrial and traffic factors become the primary anthropogenic sources of HMs (such as Cu, Zn, Cd, Pb, Cr, and Ni), averagely increasing from 22.1% to 28.1% and from 11.6% to 23.4%, respectively. Conversely, the contributions of agricultural and natural factors decreased from 37.0% to 28.5% and from 29.3% to 20.0%, respectively. Subsequently, implementation of environmental preservation policies was mainly responsible for the declining trend of HMs after 2010. Little enrichment of sediment Cu, Zn, Pb, Cr and Ni with EFs (0.15-1.43) was found in the PRE, whereas EFs of Cd (1.16-2.70) demonstrated a slight to moderate enrichment. MPE indices of Cu (50.7-252), Pb (52.0-147), Zn (35.5-130), Ni (19.6-71.5), Cr (14.2-68.8) and Cd (0-9.90) highlighted their potential ecological hazards due to their non-residual fractions and anthropogenic sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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 (I geo ) 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., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Seasonal variations of environmental parameters usually lead to considerable changes in microbial communities. Nevertheless, the specific response patterns of these communities in coastal areas subjected to different levels of contamination remain unclear. Our results revealed notable fluctuations in the bacterioplankton community both seasonally and spatially, with seasonal variations being particularly significant. The diversity and composition of bacterioplankton communities in the estuaries varied significantly across seasons and between seas. Some bacterial phyla that were highly abundant in the dry season (e.g., Patescibacteria and Epsilonbacteraeota) were almost absent in the wet season. Furthermore, the network analysis revealed that the bacterioplankton networks were more complex during the wet season than in the dry season. In the wet season, the estuarine bacterioplankton network in the Yellow Sea region was more complex and stable, while the opposite was true in the dry season. According to the neutral community model, stochastic processes played a more significant role in the formation of bacterioplankton communities during the wet season than during the dry season. Estuarine bacterioplankton communities in the Yellow Sea region were more affected by stochastic processes compared to those in the Bohai Sea. In summary, in the estuaries of two differently contaminated coastal areas, the seasonal increase in nutrient levels enhanced the deterministic processes and network complexity of the bacterioplankton communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study investigated the sources of sedimentary organic matter (OM) in the Yangtze River estuary (YRE), using multiple biomarkers. The results of stable carbon isotope (δ 13 C) and total organic carbon to nitrogen ratio (TOC/TN) suggests the contribution of marine-derived OM significantly increased seawards, while fatty acid (FA) composition provides more specific information on OM sources. In total, 30 components of FAs were identified at the studied 17 sites, which mainly composed of phytoplankton FA, followed by ubiquitous FA and bacterial FA, while terrestrial FA contributed less to the total FAs. Under the strong impacts of the large physicochemical gradients in the YRE, TOC, TN and FA components showed higher concentrations in the estuary mixing zone (especially within the turbidity maximum zone), attributing to their strong binding with OM-enriched fine particles. The spatial heterogeneity of sedimentary OM sources was highly impacted by salinity and Chl-a, as well as bacteria-mediated OM degradation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Nutrients directly control the level of primary productivity and are crucial for the stability of marine ecosystems. Focusing on the survey results in August 2020 of the Yangtze River Estuary, this study elucidated the distribution characteristics and controlling factors of three nutrients: NO 3 -N, PO 4 -P, SiO 3 -Si. The results showed that the concentrations of NO 3 -N, PO 4 -P, SiO 3 -Si in the study area were generally higher near the shore than far shore, with average concentrations of 11.40, 0.70, and 23.73 μmol/L, respectively. The ocean currents drove the distribution of nutrients, and the transport of CDW and YSCC increased the nutrient levels. The resuspension of sediment caused by factors such as terrain and weather may lead to an abnormal increase in nutrients in the bottom waters. The main controlling factors of the three nutrients were different. NO 3 -N was significantly affected by human activities, PO 4 -P and SiO 3 -Si were mainly affected by natural factors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Phosphorus is the most limiting nutrient in coastal waters of China, particularly in the Pearl River (PR) estuary. Rivers have different P forms including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP), and particulate organic phosphorus (POP). Their input to coastal seas has been overlooked. We hypothesize that DIP is a small fraction of total phosphorus (TP). We investigated these P forms and estimated their fluxes in PR eight outlets during 2015-2019. DIP on average is only a 30.90 % fraction of TP with PIP, POP and DOP accounting for 22.43, 31.56 and 15.37 %, respectively. The average annual fluxes of TP, DIP, DOP, PIP and POP were 12.58×, 3.34×, 1.68×, 3.19× and 4.26 × 10 6  mol/month, respectively, which are regulated by runoff and suspended particulate matter (SPM). The finding reveals the importance of other P forms for phytoplankton in the Pearl River estuary and their bio-availability deserves further study., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This paper reports on an investigation of the spatial and temporal variation of main environmental indicators in the Pearl River estuary using a numerical water quality model. An integrated field survey was undertaken in 2006 and 2007, and the data obtained were used to set up and verify the model. The water quality model was driven by a hydrodynamic model in which the monthly average freshwater discharges from eight major entrances were taken into account and the seaward boundary elevations were specified based on eight major tidal constituents. Two environmental indicators - dissolved inorganic nitrogen and chemical oxygen demand - were chosen as nutrient and pollution indicators, respectively, according to the actual pollution conditions. Both land-based sources (carried by the discharges) and air-based sources (wet and dry atmospheric depositions) were included in the water quality model and the processes of advection, diffusion and degradation were also modelled. The model predictions generally agreed well with the sampling data, and existing field and model results. The present contributions of the main sources were investigated and prospective scenarios of pollution reductions were predicted. [ABSTRACT FROM AUTHOR]

We employed a validated method to assess the seasonal variation and distribution of caffeine in the Bohai and Yellow Seas, as well as in Yantai urban estuaries and offshore region in northern China. Caffeine concentrations were highest during the summer in the Yellow Sea (1436.4 ng/L) and lowest in the Yantai urban offshore region during the spring and autumn and in the Yantai urban estuarine area and Bohai Sea during the winter (0.1 ng/L). There was significant variation in maximum caffeine levels among seasons across all regions examined, reaching a difference of 5980.5 times at the same sampling site between summer and winter. The caffeine concentration in the Yantai offshore region was significantly higher than in the Bohai and Yellow Seas. This study is the first investigation of seasonal fluctuations in the pollution levels of neurotoxic substances in the northern seas of China., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

As the crucial confluences of rivers and lakes, the estuary areas with varied hydrodynamic exchanges intensively affect the bacterioplankton communities, whereas the ecological characteristics of the bacterioplankton in the areas have not been well understood. Here, the distribution patterns and assembly mechanisms of bacterioplankton communities in the estuary areas of the Taihu Lake were investigated using high-throughput sequencing and multivariate statistical analyses. Our results showed obvious seasonal variations in bacterioplankton diversity and community composition, which had significant correlations with water temperature. Neutral and null models together revealed that stochastic processes (especially dispersal limitation) were the major processes in shaping the communities across different seasons. By contrast, heterogeneous selection in deterministic processes exhibited increased impacts on community assembly during summer and autumn, which was significantly related to the comprehensive water quality index (WQI) rather than any single factor. In this study, rare communities displayed more pronounced seasonal dynamics compared to abundant communities, likely due to their sensitivity towards environmental factors. Accordingly, the heterogeneous selection of deterministic processes largely shaped the rare communities. These results enriched our understanding of the assembly mechanisms of bacterioplankton communities in estuary areas and emphasized the specific co-occurrence patterns of abundant and rare communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Two sediment cores from the Changjiang (Yangtze) River estuary and its adjacent East China Sea were collected and studied for eutrophication history using paleoecological records of environmental changes over the last century. A multiproxy approach by using biological and geochemical analyses revealed changes in diatom assemblages, total organic carbon (TOC), total nitrogen (TN) and biogenic silica (BSi) and give an indication of nutrient in status and trends in Changjiang River estuary and its adjacent East China Sea. The diatom assemblages in the two cores generally increased gradually from the 1970s, and accelerated from the 1990s until now, reflecting the increased eutrophication and causing large algae blooms/red tides. The TOC, TN and BSi showing the similar trends, supported the interpretation of the eutrophication process indicated by diatom analyses. The two cores were located in different sea areas of the East China Sea, and we discuss their relative changes based on their environment characteristics. We also discuss the potential effect of anthropogenic influences and ongoing projects on eutrophication in the Changjiang River and its adjacent East China Sea. [ABSTRACT FROM AUTHOR]

Seafood has long been considered a healthy food choice, but it is also an exposure source of contaminants that may bring potential health risks to humans. Here, 80 organohalogen contaminants (OHCs) and 36 fatty acids (FAs) were analyzed in 22 (n = 211) and 19 fishery species (n = 176) from the eastern- and western Pearl River Estuary (PRE), respectively, for risk-benefit analysis. The average concentrations of total FAs in seafood from the eastern- and western PRE were 26.0 ± 2.14 and 21.3 ± 1.66 mg g -1 wet weight, respectively. Seafood from the eastern PRE exhibited higher levels of OHCs than those from the western PRE, highlighting the spatial heterogeneity of OHC contamination within the PRE. Species occupying higher trophic levels (TLs) typically demonstrated higher levels of OHC accumulation, indicating the biomagnification potential of these contaminants in the PRE ecosystem. Significant negative correlations were observed between TLs and the proportions of monounsaturated fatty acids and polyunsaturated fatty acids, presumably attributed to the ability of fish to synthesize these FAs decreases with increasing TLs. Our benefit-risk quotient (BRQ) analyses revealed that, as far as OHCs are concerned, all seafood species had a BRQ ∑OHCs value <1, except for one-spot snapper and daggertooth pike conger, which had BRQ values of 1.03 and 1.14, respectively. The findings indicate that most marine species here analyzed may not pose significant health risks to consumers as a result of OHC exposure. However, considering that many other pollutants and nutrients are not analyzed here, the results of our risk assessments should be treated as preliminary, not final. Future data collection is essential to enhance the comprehensiveness of this type of analysis., Competing Interests: Declaration of competing interest The authors declare that there are no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Sediment is thought to be a vital reservoir to spread antibiotic resistance genes (ARGs) among various natural environments. However, the spatial distribution patterns of the sedimental antibiotic resistomes around the Bohai Bay region, a river-connected coastal water ecosystem, are still poorly understood. The present study conducted a comprehensive investigation of ARGs among urban rivers (UR), estuaries (ES) and Bohai Bay (BHB) by metagenomic sequencing. Overall, a total of 169 unique ARGs conferring resistance to 15 antimicrobial classes were detected across all sediment samples. The Kruskal-Wallis test showed that the diversity and abundance of ARGs in the UR were all significantly higher than those in the ES and BHB (p < 0.05 and p < 0.01), revealing the distance dilution of the sedimental resistomes from the river to the ocean. Multidrug resistance genes contained most of the ARG subtypes, whereas rifamycin resistance genes were the most abundant ARGs in this region. Our study demonstrated that most antimicrobial resistomes were highly accumulated in urban river sediments, whereas beta-lactamase resistance genes (mainly PNGM-1) dramatically increased away from the estuary to the open ocean. The relative abundance of mobile genetic elements (MGEs) also gradually decreased from rivers to the coastal ocean, whereas the difference in pathogenic bacteria was not significant in the three classifications. Among MGEs, plasmids were recognized as the most important carriers to support the horizontal gene transfer of ARGs within and between species. According to co-occurrence networks, pathogenic Proteobacteria, Actinobacteria, and Bacteroidetes were recognized as potential and important hosts of ARGs. Heavy metals, pH and moisture content were all recognized as the vital environmental factors influencing the distribution of ARGs in sediment samples. Overall, the present study may help to understand the distribution patterns of ARGs at a watershed scale, and help to make effective policies to control the emergence, spread and evolution of different ARG subtypes in different habitats., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

To address the complex biogeochemical processes and potential function of dissolved organic matter (DOM) in estuaries before it enters the sea, water samples were collected seasonally in a dozen Laizhou Bay estuaries and in the Yellow River estuary, North China. The results showed that chromophoric dissolved organic matter (CDOM) varied in abundance but had consistent spectral slopes at the same sampling time. Gradually, CDOM decreased while spectral slopes increased from freshwater to seawater. The spectral slope of CDOM varied temporally (higher in October and lower in August) more than it varied spatially. The fluorescent components and biological indices of CDOM indicated that in situ biological activities were the dominant sources in the waters examined in this study. The CDOM was generally more variable than the dissolved organic carbon (DOC) in most of the estuaries. However, marine CDOM may obviously increase in estuaries when indirectly stimulated by rapidly decomposing terrestrial DOM., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Estuarine ecosystems undergo pronounced and intricate changes due to the mixing of freshwater and saltwater. Additionally, urbanization and population growth in estuarine regions result in shifts in the planktonic bacterial community and the accumulation of antibiotic resistance genes (ARGs). The dynamic changes in bacterial communities, environmental factors, and carriage of ARGs from freshwater to seawater, as well as the complex interrelationships among these factors, have yet to be fully elucidated. Here, we conducted a comprehensive study based on metagenomic sequencing and full-length 16S rRNA sequencing, covering the entire Pearl River Estuary (PRE) in Guangdong, China. The abundance and distribution of the bacterial community, ARGs, mobile genetic elements (MGEs), and bacterial virulence factors (VFs) were analyzed on a site-by-site basis through sampling along the salinity gradient in PRE, from upstream to downstream. The structure of the planktonic bacterial community undergoes continuous changes in response to variations in estuarine salinity, with the phyla Proteobacteria and Cyanobacteria being dominant bacterial throughout the entire region. The diversity and abundance of ARGs and MGEs gradually decreased with the direction of water flow. A large number of ARGs were carried by potentially pathogenic bacteria, especially in Alpha-proteobacteria and Beta-proteobacteria. Multi-drug resistance genes have the highest abundance and subtypes in PRE. In addition, ARGs are more linked to some MGEs than to specific bacterial taxa and disseminate mainly by HGT and not by vertical transfer in the bacterial communities. Various environmental factors, such as salinity and nutrient concentrations, have a significantly impact on the community structure and distribution of bacteria. In conclusion, our results represent a valuable resource for further investigating the intricate interplay between environmental factors and anthropogenic disturbances on bacterial community dynamics. Moreover, they contribute to a better understanding of the relative impact of these factors on the dissemination of ARGs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

As vectors for microorganisms and genetic elements, vast amounts of solid wastes, including plastics and non-plastics, enter oceans through estuaries globally. The heterogeneity of microbiomes developed on different types of plastic and non-plastic matrices and their potential environmental risks in field estuarine regions have not been fully explored. Here, microbial communities, antibiotic resistance genes (ARGs), virulence factors (VFs), and mobile genetic elements (MGEs) on substrate debris (SD) covering non-biodegradable plastics, biodegradable plastics, and non-plastics were first comprehensively characterized based on metagenomic analyzes (substrate identity). These selected substrates were field-exposed at both ends of the Haihe Estuary, China (geographic location). For substrate identity: conspicuously diverse functional gene profiles on different substrates were obtained; the relative gene copies of ARGs, VFs, and MGEs on non-biodegradable plastics were highest at both locations; non-biodegradable plastic matrices recruited the most abundant unique ARGs from ambient waters; the relative abundance of potential bacterial hosts carrying multiple ARGs and VFs (BH-AV) was much higher on non-biodegradable plastic surfaces than on the other two substrates, especially in the coastal water environment. For geographic locations: more abundant specific ARGs, VFs, and MGEs were significantly enriched on SD from the upper estuary; the average relative abundance of identified BH-AV on SD from the upper estuary was 1.99-7.14 folds from the lower estuary. Finally, the results of the Projection Pursuit Regression model verified the higher comprehensive potential risks arising from non-biodegradable plastics (substrate identity) and SD from the upstream of the estuary (geographic location). Based on comparative analysis, our results alert us to pay particular attention to ecological risks triggered by conventional non-biodegradable plastics in rivers and coastal environments and highlight the microbiological risk from terrestrial solid waste to the downstream marine environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Estuaries are hotspots of plastic pollution due to accumulated waste from surrounding rivers and coasts. However, the molecular ecological resources that possess plastic-degrading traits and their biogeographic distributions in estuarine waters remain to be elucidated. In this study, we mapped the distribution profiles of plastic-degrading genes (PDGs) in 30 subtropical estuaries in China based on metagenomic sequencing. A total of 41 PDG subtypes were observed in these estuaries. The Pearl River Estuary had higher diversity and abundance of PDGs than the east and west region estuaries. Genes for degrading synthetic heterochain and natural plastics were the most diverse and abundant types, respectively. The abundance of synthetic PDGs was significantly higher in estuaries affected by intense anthropogenic activities. Further binning strategies revealed diverse microbes with plastic-degrading ability in these estuaries. Rhodobacteraceae, a dominant plastic-degrading bacterial family, primarily carried PDGs for degrading natural plastics. Pseudomonas veronii carrying diverse PDGs was identified, which may be of value for further technical improvement of plastic degradation. In addition, phylogenetic and structural analyses of 19 putative 3HV dehydrogenases, the most diverse and abundant DPGs, showed inconsistent evolution with their hosts, but different sequences were conserved with consistent key functional amino acids. A potential biodegradation pathway for polyhydroxybutyrate by Rhodobacteraceae was proposed. The result implied that plastic-degrading functions are widely distributed in estuarine waters and metagenomics could be used as a promising screening tool for large-scale profiling of plastic-degrading potential in the natural environment. Our findings have important implications and provide potential molecular ecological resources for developing plastic waste removal technologies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The microbial reduction of N 2 O serves as a "gatekeeper" for N 2 O emissions, determining the flux of N 2 O release into the atmosphere. Estuaries are active regions for N 2 O emissions, but the microbial functions of N 2 O-reducing bacteria in estuarine ecosystems are not well understood. In this study, the 15 N isotope tracer method, qPCR, and high-throughput sequencing were used to analyze N 2 O production, reduction, and emission processes in surface sediments of the Pearl River Estuary. The 15 N isotope tracer experiment showed that the N 2 O production rates declined and the N 2 O reduction potential (R r , the ratio of N 2 O reduction rates to N 2 O production rates) increased from upstream to downstream of the Pearl River Estuary, leading to a corresponding decrease of the N 2 O emission rates from upstream to downstream. The gene abundance ratio of nosZ/nir gradually increased from upstream to downstream and was negatively correlated with the water N 2 O saturation. The gene abundance of nosZ II was significantly higher than that of nosZ I in the estuary, and the nosZ II/nosZ I abundance ratio was positively correlated with N 2 O reduction potential. Furthermore, the community composition of NosZ-I- and NosZ-II-type N 2 O-reducing bacteria shifted from upstream to downstream. NosZ-II-type N 2 O-reducing bacteria, especially Myxococcales, Thiotrichales, and Gemmatimonadetes species, contributed to the high N 2 O reduction potential in the downstream. Our results suggest that NosZ-II-type N 2 O-reducing bacteria play a dominant role in determining the release potential of N 2 O from sediments in the Pearl River Estuary. This study provides a new insight into the function of microbial N 2 O reduction in estuarine ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The extensive conversion of carbon-rich coastal wetland to aquaculture ponds in the Asian Pacific region has caused significant changes to the sediment properties and carbon cycling. Using field sampling and incubation experiments, the sediment anaerobic CO 2 production and CO 2 emission flux were compared between a brackish marsh and the nearby constructed aquaculture ponds in the Min River Estuary in southeastern China over a three-year period. Marsh sediment had a higher total carbon and lower C:N ratio than aquaculture pond sediment, suggesting the importance of marsh vegetation in supplying labile organic carbon to the sediment. Conversion to aquaculture ponds significantly decreased sediment anaerobic CO 2 production rates by 69.2% compared to the brackish marsh, but increased CO 2 emission, turning the CO 2 sink (-490.8 ± 42.0 mg m -2 h -1 in brackish marsh) into a source (6.2 ± 3.9 mg m -2 h -1 in aquaculture pond). Clipping the marsh vegetation resulted in the highest CO 2 emission flux (382.6 ± 46.7 mg m -2 h -1 ), highlighting the critical role of marsh vegetation in capturing and sequestering carbon. Sediment anaerobic CO 2 production and CO 2 uptake (in brackish marsh) and emission (in aquaculture ponds) were highest in the summer, followed by autumn, spring and winter. Redundancy analysis and structural equation modeling showed that the changes of sediment temperature, salinity and total carbon content accounted for more than 50% of the variance in CO 2 production and emission. Overall, the results indicate that vegetation clearing was the main cause of change in CO 2 production and emission in the land conversion, and marsh replantation should be a primary strategy to mitigate the climate impact of the aquaculture sector., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

In this paper, water and sediments were sampled at eight monitoring stations in the coastal areas of the Yangtze River Estuary in summer and autumn 2021. Two sulfonamide resistance genes (sul1 and sul2), six tetracycline resistance genes (tetM, tetC, tetX, tetA, tetO, and tetQ), one integrase gene (intI1), 16 S rRNA genes, and microbial communities were examined and analyzed. Most resistance genes showed relatively higher abundance in summer and lower abundance in autumn. One-way analysis of variance (ANOVA) showed significant seasonal variation of some ARGs (7 ARGs in water and 6 ARGs in sediment). River runoff and WWTPs are proven to be the major sources of resistance genes along the Yangtze River Estuary. Significant and positive correlations between intI1 and other ARGs were found in water samples (P < 0.05), implying that intI1 may influence the spread and propagation of resistance genes in aquatic environments. Proteobacteria was the dominant phylum along the Yangtze River Estuary, with an average proportion of 41.7%. Redundancy analysis indicated that the ARGs were greatly affected by temperature, dissolved oxygen, and pH in estuarine environments. Network analysis showed that Proteobacteria and Cyanobacteria were the potential host phyla for ARGs in the coastal areas of the Yangtze River Estuary., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Zooplankton community is ecological important because of its high sensitivity to environmental changes especially in estuarine areas. The Yellow River estuary (YRE) in China is the fifth biggest estuary in the world with significant seasonal characteristics and anthropogenic influence of Water-Sediment Regulation (WSR). This study investigated the spatio-temporal patterns of zooplankton in the YRE to explore the response of zooplankton to seasonal variation and WSR. Results suggested that the temporal patterns of zooplankton were mainly characterized by seasonal shift of dominant species. Hierarchical cluster analysis and non-metric multidimensional scaling determined summer, summer-autumn and winter-spring three zooplankton assemblages. Zooplankton spatial distributions represented seasonal consistency, in which the abundance generally showed a decreasing gradient from the river mouth to sea. WSR caused a high species replacement rate in July-August (80.36%) and a dramatic abundance decline from 4224.60 ind./m 3 to 1541.10 ind./m 3 with persistency and hysteresis effect. The high zooplankton abundance moved seaward in spatial distribution after WSR. Summer spatial pattern was determined with two and three zooplankton station assemblages, which was more clear after WSR. Redundancy analysis identified SSS, SST and transparency as important factors structuring zooplankton spatio-temporal patterns, in which SSS was the key one. The results provide a necessary reference for understanding the response of zooplankton community in estuarine areas to spontaneous changes and anthropogenic factors, and can help the protection of estuarine ecosystems and the formulation of hydrological regulatory policies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Riverine microplastic (MP) discharge into the ocean contributes greatly to global MP contamination, yet our understanding of this process remains primitive. To deepen our interpretation of the dynamic MP variation throughout the estuarine water columns, we sampled at Xuliujing, the saltwater intrusion node of the Yangtze River Estuary, over the course of ebb and flood tides in four seasons (July and October 2017, January and May 2018 respectively). We observed that the collision of downstream and upstream currents contributed to the high MP concentration and that the mean MP abundance fluctuated with the tide. A model of microplastics residual net flux (MPRF-MODEL), taking the seasonal abundance and vertical distribution of MP along with current velocity into consideration, was developed to predict the net flux of MP throughout the full water columns. 2154 ± 359.7 t/year of MP was estimated to flow into the East China Sea via the River in 2017-2018. Our study suggests that riverine MP flux can be overestimated due to reciprocating current carried MP from the estuary. Using the tidal and seasonal variation in MP distribution, we calculated the tide impact factor index (TIFI) for the Yangtze River Estuary to be between 38.11% and 58.05%. In summary, this study provides a baseline of MP flux research in the Yangtze River for similar tidal-controlled rivers and a contextual understanding of how to appropriately sample and accurately estimate in a dynamic estuary system. The redistribution of microplastics may be impacted by complex tide processes. Although not observed in this study, it may merit investigation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The spread of antibiotic resistance genes (ARGs) is a growing concern over the world's various environments. Coastal environments may receive pollutants from land runoffs via estuaries. However, the impact of ARG contamination from estuarine regions to coastal areas is rarely reported. This study used high-throughput quantitative PCR to examine the diversity and abundance of ARGs in Pearl River Estuary (PRE) and adjacent coastal areas. We found that the distribution of ARGs in seawater exhibited the distance-decay phenomenon from the estuary to coastal areas, while the sediment samples did not exhibit an obvious distribution pattern. The estuarine water was found to be the hotspot of ARGs, with 74 ARG species detected and absolute abundance being 5.93 × 10 5 copies per mL, on average, while less species and lower abundance of ARGs were detected in coastal waters. Ordination analysis showed that estuarine ARG communities were significantly different from coastal ARG communities for water samples. SourceTracker analysis revealed that ARGs from the estuarine environment contributed only a minor fraction of ARG contamination to downstream coastal areas (1.5%-7.4% for water samples, and 0.7-1.8% for sediment samples), indicating the strong dilution effect of seawater. Mantel tests, redundancy analysis and random forest model analysis identified salinity, nutrients, microbial community structure and mobile genetic elements (MGEs) as important factors influencing ARG distribution. Partial least squares-path model revealed that, among all environmental factors, MGEs directly affected the distribution of ARGs, while other factors indirectly contributed by affecting the MGEs assemblage. Our study provides insight into the dissemination of ARGs from the PRE to adjacent coastal areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In this paper, a numerical method is employed to assess tidal current energy resources in the Pearl River Estuary, China. The numerical model for tidal current simulation in the estuary is developed based on the MIKE 21 model, which enables numerical simulations in estuaries, coastal areas, and oceans. The model has a grid resolution that varies from about 2500 m at the open boundary to 500–1000 m inside the estuary. Extensive model validation is performed by comparing the model predictions with field observations of tidal level and velocity at various stations in the Pearl River Estuary. The tidal characteristics are thoroughly analyzed. Energy fluxes and power densities are calculated along selected cross sections to evaluate the feasibility of tidal energy development in the Pearl River Estuary. The results indicate that the distribution of annual average tidal current power density in the Pearl River Estuary generally aligns with the spatial distribution of tidal currents. The annual average power density of tidal energy is typically below 0.10 kW/m2. The theoretical potential of tidal current energy resources in the Pearl River Estuary is assessed to be approximately 11,000 kW. [ABSTRACT FROM AUTHOR]

Spartina alterniflora, an invasive plant, was introduced to the Chinese coastal zone in the early 90s. As an eco-engineering species, S. alterniflora not only alters saltmarsh species distributions, previously described as habitat degradation, but it also plays a vital role in coastal protection, especially for the development of recently emerged intertidal shoals. To provide a reference for coastal management under global change, we quantified the impact of the invasion process on provided ecological and coastal protection functions, exemplified at the emerging Jiuduansha Shoals (JDS) in the Yangtze Estuary. Results obtained by high-precision satellite monitoring and numerical modelling showed that the establishment and growth of S. alterniflora can exert considerable changes on local environment. The invasion of S. alterniflora to JDS wetland can be divided into three distinct phases, (1) establishment 1998-2003, (2) expansion 2003-2009, and (3) dominant 2009-2018 stages according to the changes in saltmarsh composition. Spatially, S. alterniflora continuously replaced Scirpus mariqueter, forcing S. mariqueter and Phragmites australis slowly to the lower and higher intertidal habitats, respectively. Notably, S. alterniflora expansion was the main driver that contributed to over 70 % of recent JDS wetland expansion even under sediment deficit conditions. Established S. alterniflora marsh (directly) dampens more waves because of aboveground stems, but it also causes more accretion and indirectly leads to higher "morphological" wave dampening. Thus, it increases coastal defense provided by the saltmarsh in the context of sea-level rise and strengthening storms. In conclusion, the role of S. alterniflora invasion to the local environment under global changes is controversial. For sustainable coastal management, we need context-dependent S. alterniflora management to maximize the benefit of coastal protection and minimize the impact on local ecology, especially in sediment-starving estuaries with expected coastline retreat., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Estuaries are unique transition zones connecting terrestrial and coastal environments and are recognized as primary conveyors for land-derived plastics to open oceans. Riverine microplastics (MPs) have been commonly investigated using sequential sampling which might not effectively reflect the actual load. In this study, sampling at eight outlets was performed during a complete tidal cycle to estimate the MP flux to the Pearl River Estuarine (PRE) using a concurrent sampling strategy. The MP abundances ranged from 2.90 ± 0.57-5.9 ± 2.27 particles/L. A remarkable difference between tides in MP abundances suggests tidal effect should not be overlooked in assessment. The MP load through the eight outlets was estimated at 304 trillion particles or 1102 tons into the PRE annually. Additionally, similar potential ecological risk assessment among eight rivers implied that environmental threats posed by less urbanized and populated rural areas on the western side have been under-evaluating for decades., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Triazole is widely used in the synthesis of pharmaceuticals, pesticides, and fungicides. However, triazole organic compounds are often a source of toxicity in the water environment due to the presence of chlorobenzene. This study reported on the occurrence and distribution of 15 TrOCs in the surface waters of estuaries and the East China sea, and identified the influences of TrOCs originating from the estuarine environment on the ocean. The results showed that the total concentrations of ∑TrOCs in the surface water of estuaries along the coasts of Jiangsu (JS), Zhejiang (ZJ), and Shanghai (SH), China ranged from 0.020 to 104 ng L -1 (7.49 ± 18.2 ng L -1 ), whereas they ranged from 0.235 to 1.25 ng L -1 (mean 0.711 ± 0.235 ng L -1 ) in the East China sea. Difenoconazole and tebuconazole were the dominant TrOCs in the estuaries, whereas fenbuconazole and hexaconazole dominated in the ocean. TrOCs in surface water of estuaries showed a continuous spatial distribution and presented regional characteristics mainly related to agricultural activities. In contrast, TrOCs in the East China Sea showed a low spatial variation and dispersion, which may be related to complex disturbance by currents and dilution. The low levels of estuarine TrOCs measured in SH estuaries (<0.5 ng L -1 ) indicates that the Yangtze River may only pose a low-level TrOC contamination risk to the East China Sea. Moreover, estuary transport in the estuaries of ZJ may have influenced the occurrence of TrOCs in the offshore East China Sea area, although they may have also undergone a filter process in the estuary turbid zone; whereas it had little influence on the open sea. This study can act as a critical reference for the presence of TrOCs in surface water both estuaries and the ocean., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Purpose: To evaluate the effects of enhanced nitrogen (N) load on turnover of phosphorus (P) in Suaeda salsa marsh in the Yellow River estuary, the variation and allocation of P in the plant-soil system were investigated in the growing season. Methods: This study was explored by field N addition experiment which included four load levels: NNL (no N load treatment, 0 gN m−2 yr−1), LNL (low N load treatment, 3.0 gN m−2 yr−1), MNL (medium N load treatment, 6 gN m−2 yr−1), and HNL (high N load treatment, 12 gN m−2 yr−1). Results: In most sampling periods, the TP contents in soils in the LNL, MNL, and HNL treatments showed a decreasing trend compared to the NNL treatment. With increasing N load levels, the contents of non-available decomposed P in soils decreased by 3.08 ~ 5.22%, while those of easily available and moderately available P increased by 0.36 ~ 8.92% and 1.21 ~ 24.24%, respectively. The variations of NaOH-Po, Resin-Pi, and NaHCO3-Po contents primarily rested with the duration of N import, while those of NaOH-Pi, Residual-P, NaHCO3-Pi, and HCl-Pi contents mainly depended on the levels of N load. Dissimilar variations of TP contents in plant tissues in the growing season were observed among N load levels, which were dependent on the structure and function of organs and the nutrient function of P at distinct growth stages. The P absorption coefficients (PAC) of plants in N load treatments increased by 31.82 ~ 36.36%, while the P utilization coefficients (PUC) decreased by 4.96 ~ 13.33%. Conclusion: This paper found that the S. salsa was very likely to adjust its growth rhythm and P absorption/utilization capacity to adapt N load environment. Particularly, as N load reached medium level, the P supply relationships between aboveground and belowground tissues and the P transferences in the plant-soil system were greatly altered, indicating that the S. salsa might have a special response to the medium N enrichment. Thus, the potential impacts of medium N load level on S. salsa marsh should be emphasized in the future. [ABSTRACT FROM AUTHOR]

Rivers and estuaries are the main links between continents and oceans. The Paraíba do Sul River is among the most important rivers of the southeastern Brazilian region, carrying an average of 0.08 Tg of dissolved organic matter (DOM) to the ocean but has been facing significant changes in river discharge. In this study, we aimed to provide insights into the sources and transformations of chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) sources across a salinity gradient under changing river discharge scenarios. Three spatial surveys were performed covering the entire salinity gradient of the main estuarine channel and surrounding mangrove waters under contrasting river discharge (178 to 1240 m 3 s -1 ), and diel sampling was conducted in the mangrove tidal creek. The characterization of DOM through the parallel factor analysis (PARAFAC) model identified six components across the river-ocean gradient and mangrove creek: terrestrial origin (C1 - fulvic acid and C2 and C3 - humic-like), protein-like (C4), tryptophan-like (C5), and tyrosine-like (C6). Our results showed a shift in DOM composition and contribution along the salinity gradient, from terrestrial (C3) to autochthonous (C5 and C6) signatures. The October-17 dry campaign was characterized by a higher proportion of microbial protein-like component C4 and a lower contribution of humic-like components compared to February-17 and March-18 across the salinity gradient with an increase in the mixing zone. The DOM compositions of the February 17 dry and March 18 wet campaigns were similar. Additionally, the March-18 wet campaign, marked by the highest river discharge, showed higher inputs of terrestrial DOM (C1-C3 components) compared to February-17 in the estuary, which allowed DOM to be transported rather than transformed. The mangrove diel study showed that tidal fluctuations are also an important driver of carbon input to the mangrove creek with a possible impact on DOM composition in estuarine waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The Spartina alterniflora started to invade the Min River estuary (Southeast China) in 2002 and, thereafter, its invasion area showed an increasing trend. Since the siltation depths caused by S. alterniflora in the Min River estuary were much higher (4.8-7.2 cm yr -1 ) than the values reported in other coastal regions of China (3.5-6.5 cm yr -1 ), the impacts of siltation on nutrient cycle processes in this region might be more evident. In order to explore the potential effects of siltation by S. alterniflora on nutrient ((carbon (C), nitrogen (N), phosphorous (P) and sulfur (S)) variations in its decaying litters, three one-off siltation treatments (no siltation scenario (0 cm yr -1 , NSS), current siltation scenario (5 cm yr -1 , CSS) and strong siltation scenario (10 cm yr -1 , SSS)) were designed in coastal marsh of the Min River estuary and the in-situ decomposition experiment was conducted from February 2016 to February 2017 by litterbag technique. Results showed that the siltation caused by S. alterniflora showed significant impact on its decomposition rate, following the sequence of NSS (0.005638 d -1 ) > SSS (0.003005 d -1 ) > CSS (0.002478 d -1 ) (p < 0.05). The total carbon (TC) contents in decomposing litters in the three siltation treatments showed dissimilar fluctuations and significantly higher values were observed in the CSS and SSS treatments compared to the NSS treatment. The contents of total nitrogen (TN) and total sulfur (TS) in decomposing detritus in the three siltation treatments generally showed increasing trend during the whole decomposition, while those of total phosphorus (TP) showed increasing trend after decomposing for 30 days. The differences in nutrient variations among the three siltation treatments, to a great extent, rested with the alterations of substrate quality in detritus during the experiment. Although the stocks of C, N, P and S in detritus in the three siltation treatments evidenced the release from litters to the surroundings during decomposition, the release amounts of these nutrients in some periods were at a lower level. With increasing siltation depths, the release of C, N and P from detritus was generally restrained during the whole decomposition, while that of S from decaying litters was inhibited only at the late stage of decomposition. This paper found that the siltation caused by S. alterniflora reduced the nutrient return (particularly for C, N and P) from its detritus, which, in turn, might greatly alter the nutrient cycle in S. alterniflora marsh., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The pollution characteristics of the typical antibiotic resistance genes (ARGs) in the sediments of the sea area adjacent to the Yangtze Estuary, China were investigated with both seasonal and spatial insights. The positive rates of sulfonamides sul1, sul2, tetracycline tetW and quinolone gyrA resistance genes in the sediments of all sampling sites were 100%, indicating that the sea area adjacent to the Yangtze Estuary were extensively polluted by these ARGs. Occupying a dominance in most sampling sites, sul1 was found to be the dominant resistance gene in the sediments of the sea area adjacent to the Yangtze Estuary. In terms of seasonal variation characteristics, the absolute abundances of the ARGs in flood season were higher than those in dry season. In terms of spatial distribution characteristics, the absolute abundances of the ARGs in the southern sites were mostly higher than those in the northern sites, and the high abundance sites were mostly located near the coast. Different ARGs also showed different spatial distribution characteristics. The disclosure of the pollution characteristics of the typical ARGs in the sediments of the sea area adjacent to the Yangtze Estuary can provide valued information for protecting the environment of this area as well as the Yangtze River Basin., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

As one of the main interfaces of the Earth system, estuaries show the strongest land–sea interaction in the carbon cycle, which links terrestrial ecosystems to the marginal sea. Furthermore, estuaries are considered as one of the most active intermediate reservoirs for both terrestrial and marine matter due to complex hydrodynamic processes regulated by the river runoff, wave and tide. Processing of organic matter (OM) in tidal estuaries modifies its transfer and transformation from the river to the sea, so studies of on the source and distributions of estuarine OM can help us understand the behavior of production, exchange, transport and burial of diverse OM within this transition zone before entering the marginal sea. In this paper, we took the Minjiang River Estuary (MRE) as a typical system in which there is strong influence of the tide. The source, composition and spatial distribution of OM in surface sediments of MRE were deciphered based on multiple organic geochemical properties for source-specific biomarkers (n-alkanes, n-alkanols, sterols) and bulk OM. Results show that sedimentary organic components were negatively correlated with sediment grain size, which indicates fine particles such as silt and clay are the major carriers of the OM signals in tidal estuaries. Source-specific biomarker proxies indicate that in terms of source diversity the sedimentary OM in the MRE shows mixed signals of terrestrial and marine sources, and the proportion of terrestrial OM decreases with the increase in distance from the land. The fractional contributions of OM from the riverine (i.e., terrestrial), marine and deltaic sources were quantitatively estimated using a Monte Carlo (MC) three-end-member mixing model based on C/N and δ13C values, and the average contributions of the three sources are 40 ± 10%, 48 ± 10% and 12 ± 4%, respectively, with little contribution from deltaic sources. The dispersion of sedimentary OM from different sources in the MRE is primarily controlled by the depositional environment determined by dynamic conditions and tidal processes play a significant role in the redistribution of sedimentary OM dispersion patterns. Compared with other large estuaries in southeast China, the OM accumulation contribution in the tide dominated small and medium-sized estuaries such as the MRE which is largely dependent on riverine and marine deliveries. The MRE has a high potential for both terrestrial and marine organic carbon (OC) burial, with an accumulation rate of 3.39 ± 1.83 mg cm−2 yr−1 for terrestrial OC, and an accumulation rate of 3.18 ± 0.68 mg cm−2 yr−1 for marine OC in muddy sediment, making it an important contributor to the sedimentary carbon sink of the marginal sea. [ABSTRACT FROM AUTHOR]

Japanese eels (Anguilla japonica) are a typical migratory fish species with high commercial importance. The Pearl River estuary in southern China is an important natural growing ground for Japanese glass eels, but limited information on Japanese glass eel population characteristics is available, despite their ecological importance. In this paper, we examined the annual patterns of the occurrence of Japanese glass eels in the Pearl River estuary from 2011 to 2022. The most frequently occurring Japanese glass eel's total length is 5.3 cm. The collecting period extended from December to February, and the collection catch-per-unit-effort (CPUE) decreased significantly from 2011 to 2022. The generalized linear model (GLM) indicated that daily changes in Japanese glass eel collection were significantly affected by tidal range, water temperature, and lunar distance. The catch peak appeared when the tidal range rose to 1.7 m, and the water temperature dropped below 8 °C on the full moon days. Overall CPUE analysis showed no significant periodic and inter-annual variability in the period 2011–2022, with the ARIMA model suggesting that the CPUE is expected to remain stable but low in the coming years (2023–2026), although recruitment ultimately depends on the overall spawning stock. [ABSTRACT FROM AUTHOR]

East China Sea (ECS) is considered one of the largest dissolved oxygen (DO) depleted areas in the world's oceans. To assess the relative importance of water sources and biological processes to modulate low DO water over the ECS shelf, we conducted 7 cruises in the summers between 2004 and 2015. To cover a broad study area, observations were taken by both Chinese and Japanese research vessels in 2013, the consistent DO values were obtained in the intercalibration station from China and Japan. The subsurface/bottom water DO depletion was observed over both the inner and mid-outer shelves. In 2009 and 2013, the low DO (3-4.2 mg L -1 ) area covered ca. 4 × 10 4  km 2 on the mid-outer shelf, comparable with the reported area of summer hypoxia off the Changjiang estuary. On the basis of a seven endmember mixing model using heavy rare earth elements, temperature and salinity data collected in 2013 and 2015, we determined that on the southern shelf the low DO water mainly originated from Kuroshio Subsurface Water (28-72%). Both the DO level in the dominant source water and organic matter (OM) remineralization modulated the formation and expansion of low DO waters. Oxygen-depleted bottom waters featured with high nutrients were both transported from the water's source regions and produced by OM remineralization on the mid-outer shelf. The estimated regenerated nutrient fluxes derived from OM respiration in the bottom water of the mid-outer shelf were equivalent to 18-37% of the nitrate and nitrite, and 2 to 5-fold the phosphorus, delivered from the Changjiang River in summer. The large quantity of regenerated nutrients from oxygen-depleted bottom waters on the mid-outer shelf could be utilized and support primary production in the adjacent oceans. Our findings provide valuable observation for simulation models of nutrient cycles and budgets in the ECS and adjacent oceans., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

To explore the effects of exogenous nitrogen (N) import on decomposition of Suaeda salsa in coastal marsh of the Yellow River estuary, the decomposition rates and the variations of nutrient (C, N, P, and S) in decomposing litters were investigated from May 2014 to November 2015. The in situ experiment included four N addition treatments: N0 (no N import treatment, 0 g N·m−2·year−1), Nlow (low N import treatment, 3.0 g N·m−2·year−1), Nmedium (medium N import treatment, 6.0 g N·m−2·year−1), and Nhigh (high N import treatment, 12.0 g N·m−2·year−1). Results showed that N enrichment showed significant influence on the decomposition rate of S. salsa, in the order of Nmedium (0.00112 d−1) > Nhigh (0.00096 d−1) > Nlow(0.00092 d−1) > N0 (0.00075 d−1) (p < 0.05). Compared to the N0 treatment, the decomposition rates of S. salsa in the Nlow, Nmedium, and Nhigh treatments increased by 22.76%, 49.33%, and 28.00%, respectively. The contents of TC in decomposing litters in the four N import treatments generally showed a decreasing trend, while those of TN and TP showed an increasing trend. By comparison, dissimilar variations of TS contents in decomposing litters were observed among the four treatments. The differences in decomposition rate and nutrient variation among the four N addition treatments might be dependent on the alterations of substrate quality in decomposing litters. With a few exceptions, stocks of C and S in decomposing litters generally evidenced the export from litters to the environment, while those of N and P showed net accumulation. As N addition reached Nmedium level, although the C released from decomposing litters to the surroundings was stimulated, the S return was restrained. Moreover, N additions generally promoted the accumulation of N and P in decomposing litters. This paper found that, with increasing N addition, the decomposition rates and the nutrient variations in S. salsa would be altered greatly and the alteration was particularly evident in the Nmedium treatment. From the perspective of nutrient return, as N enrichment reached or exceeded Nmedium level in future, the deficient status of P and S in S. salsa marsh might be serious, which would affect the stability and health of ecosystems. [ABSTRACT FROM AUTHOR]

In this study, components, concentrations, distribution characteristics, sources of low-molecular-weight organic acids (LMWOAs) and relationships among the annual hypoxia, LMWOAs and seawater acidification were investigated in the Changjiang Estuary and its adjacent sea area in July 2015. Lactic, acetic and formic acids were detected in the seawater samples in the study area, and their total concentrations (ΣLMWOAs) varied from 0 to 262.6 μmol·L -1 , with an average value of 39.2 μmol·L -1 . In the surface seawater, high concentration areas of ΣLMWOAs occurred in the sea area near the Changjiang Estuary and the Hangzhou Bay, and north of study area. In the sampling stations along transect A6, high concentration areas of ΣLMWOAs appeared in the bottom seawater of nearshore stations and middle seawater of offshore stations. The terrigenous inputs, especially the Changjiang runoff, were the dominant sources for LMWOAs in the sampling period. The consistency of hypoxia areas, high concentration areas of ΣLMWOAs and low pH value areas in winter and summer suggested that annual hypoxia could cause the long-term seawater acidification by producing LMWOAs in the Changjiang Estuary and its adjacent sea area., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Purpose: The main objectives of this study were to investigate the distribution characteristics and evaluate the potential ecological hazard associated with rare earth elements (REEs) within the Pearl River Estuary (PRE) sediment. Furthermore, we still have not fully understood the contamination and potential ecological risks of REEs in aquatic sediments. Moreover, the factors influencing their distribution remain unidentified. Hence, we selected the PRE as the central focus for our case study in this paper. Materials and methods: Sediment samples in this study (0–20 cm) were collected from 156 locations. The total organic carbon (TOC) and grain size were measured. The concentrations of REEs were determined by inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, contamination models, including geoaccumulation index (Igeo), enrichment factor (EF), contamination factor ( C f i ), and pollution load index (PLI), along with ecological risk assessment models potential ecological risk factors ( E r i ) and ecological risk index (RI) have been employed to evaluate pollution levels and ecological risks. Results: The concentrations of sum REEs (ΣREEs) were in the range of 51.21 to 567.08 mg kg−1, with an average of 299.06 mg kg−1. We identified two accumulation centers for REEs, indicating that these elements primarily originated from these two centers. It can be seen from the values of EF of REEs that these elements showed minimal enrichment. Moreover, the pollution load index (PLI), which assesses the combined contamination of REEs, was computed to evaluate the collective contamination in the study area. The PLI results indicate a slight multi-element contamination in the research region. Furthermore, based on the E r i values, it is evident that all studied REEs pose a low ecological risk. Conclusions: The distributions of REEs were mainly controlled by TOC and median grain size. The RI was also calculated to assess the combined potential risks on the ecology. The study's findings indicate that the PRE's sediments produce low ecological risks. [ABSTRACT FROM AUTHOR]