Estuary Ecosystem Research Articles

Patterns in Anthropogenic Nitrogen and Water Quality Leading to Phytoplankton Blooms in Urban Estuaries

The San Francisco Estuary (SFE) ecosystem receives anthropogenic ammonium (NH4) from agricultural runoff and sewage treatment plants and has low chlorophyll levels. As observed in other aquatic systems, NH4 at concentrations < 4 µmol/L inhibits nitrate (NO3) uptake by phytoplankton and can reduce the frequency with which phytoplankton assimilate all available inorganic nitrogen (i.e., NO3 and NH4); paradoxically, elevated NH4 can reduce the chances of phytoplankton blooms in some high NH4 ecosystems. For blooms to occur, NH4 must first be reduced to non-repressive levels, then NO3 uptake can occur and is accompanied by more rapid carbon (C) uptake and chlorophyll accumulation. The consequence of this sequence is that when NO3 uptake, C uptake, or chlorophyll concentrations are plotted against ambient NH4, a rectangular hyperbola results. Here, these relationships are statistically described for a variety of SFE field data, and their management applications are discussed. These relationships enable ambient NH4 to be used to predict both the likelihood of blooms and to investigate historical changes in productivity when no rate measurements were made. We apply the statistical relationship to a 40-year time series from the SFE during which there was an ecosystem-scale change in the estuarine foodweb with a drastic decline in pelagic fishes (the pelagic organism decline) and suggest that this period aligned with the lowest annual primary production and highest NH4. The relationship may be generalizable to other high-nitrogen, low-growth systems and aid nutrient management decisions, assuming potential limitations are considered.

Harmful Microalgae Exhibit Broad Environmental Adaptability in High-Salinity Area Across the Dafengjiang River Estuary.

Harmful algal blooms (HABs) often occur in estuaries due to their unique environmental heterogeneity, posing significant environmental and human health risks. However, there is limited understanding of the community composition and community-level change points (thresholds) of harmful microalgae in subtropical estuaries. This study explored harmful microalgae community structure and thresholds in the Dafengjiang River estuary using a metabarcoding approach. The results revealed 63 harmful microalgae species, and major species included Guinardia flaccida, Prorocentrum cordatum, Thalassiosira punctigera, Pseudo-nitzschia galaxiae and T. gravida. Nonparametric change-point analysis and threshold indicator taxa analysis (TITAN) showed threshold responses of harmful microalgae community structure to ammonium (57.5-60 μg·L-1), total phosphorus (27.8-28.5 μg·L-1) and dissolved inorganic phosphorus (14.5-28 μg·L-1) along the salinity gradient. Wider environmental thresholds were also found in hypersaline areas. Additionally, Pyrodinium bahamense, Pfiesteria piscicida, Skeletonema tropicum and T. punctigera were sensitive to environmental changes and thus could be used as bioindicators. Overall, our study unveiled diverse abrupt transitions of harmful microalgal communities, providing a risk assessment for human health and ecological safety in subtropical estuary ecosystems.

Ecological networks reveal important taxa for ecosystem function in two subtropical South African estuaries

Biodiversity is essential for estuarine ecosystems' functioning, resilience, and persistence. While biodiversity assessments provide some insight into the ecosystem state, they cannot quantify every aspect of ecosystem-level function. We assessed aspects of estuarine ecosystem function and pinpointed taxa of interest that fulfil specific roles in estuarine ecosystems, using a series of novel food web model ensembles and Ecological Network Analysis. We investigated emergent network properties of two subtropical South African estuaries, the anthropogenically impacted large temporarily closed uMdloti Estuary and the ‘near natural’ predominantly open uMlalazi Estuary, during a drought period induced by the El Niño Southern Oscillation. In addition, important network components were identified to elucidate the importance of estuarine/marine taxa in maintaining ecosystem function. The key findings included (1) estuaries exhibit system-specific functional responses under drought conditions, and (2) estuarine/marine taxa are critical for overall ecosystem function. Both estuaries showed seasonal differences in ecosystem activity and reliance on trophic level I (microalgae and detritus) to fuel the food web, and persistently low cycling (<9.3 %). However, compared to uMdloti Estuary, uMlalazi Estuary showed less variation in mean seasonal activity (1597–2095 mgC m−2 d−1), and higher reliance on detritus to fuel the food web (D:H > 2.02), indicating greater ecosystem functional resilience to external perturbations. uMlalazi Estuary ecosystem function could be attributed to predominantly open mouth conditions maintaining a salinity gradient, and subsequent large contributions to overall ecosystem function from typically estuarine/marine invertebrate taxa. In contrast, the uMdloti Estuary, dominated by freshwater/brackish taxa under prolonged closed mouth conditions, showed greater seasonal variations in mean system activity (1084–2289 mgC m−2 d−1) and generally high reliance on microalgae (D:H < 1.26), indicative of decreased resilience to external perturbations. During this study, a single mouth breach acted as a ’biological reset’ of uMdloti Estuary, enabling recruitment of estuarine/marine taxa, and a temporary recovery in ecosystem function reflected in increased system cycling (FCI >14.05 %) and decreased reliance on microalgae (D:H > 1. 41). These findings suggest that future predicted drought impacts on estuarine ecosystem function may be partially system-specific due to differing estuarine types, anthropogenic impact, and invertebrate community composition. This study provides a scientific link between ecosystem-level indicators and the role of individual taxa within the system, which is a valuable complement to biodiversity assessments and ecosystem state evaluation.

Abundant small microplastics hidden in water columns of the Yellow Sea and East China Sea: Distribution, transportation and potential risk

Microplastics (MPs) pose significant concerns for marine ecological security due to their minuteness and ubiquity. However, comprehensive knowledge on their distribution and fate in seawater columns remains limited. This study investigated the abundances and characteristics of MPs across 3–6 water layers in the South Yellow Sea and East China Sea. Results indicate that high-abundance small MPs (< 100 µm) (average 6567 items/m3) were hidden beneath the sea-surface, predominantly fine-grained particles (< 20 µm) and high-density polymers (> 1.03 g/cm3). The total suspended MPs (5.0–834.2 µm) are estimated at 2.9–3.1 × 1017 particles, with most of them occurring in upper layers. In profiles, their distribution varied by physical properties with depth; fragment-shaped and high-density MPs increased in proportion at greater depths, contrasting with fibrous MPs. These MPs originated primarily from the Yangtze River and their winter transport was driven by the Yangtze River Dilution Water, East China Sea Coastal Current, and Yellow Sea Warm Current, resulting in their accumulation in coastal and estuarine regions. Consequently, the Yangtze River Estuary ecosystem faces substantial risks from MP pollution throughout the water column. This work unveils the prevalence of small MPs in coastal water columns and intricate interaction between their fate and hydrodynamic conditions.

Using macrobenthic community structure and biotic indices to assess the ecological status of Wulan Estuary, Demak, Indonesia

Abstract. Hartati R, Widianingsih W, Zainuri M, Wardianto Y. 2024. Using macrobenthic community structure and biotic indices to assess the ecological status of Wulan Estuary, Demak, Indonesia. Biodiversitas 25: 3073-3087. Estuaries provide critical habitats for species, and they are valued commercially, recreationally, and culturally. They also filter for sediments and pollutants from rivers before entering the ocean, providing cleaner waters for marine biota. This study presents a unique approach to assessing the ecological status of an estuary using microbenthic community structure and biotic indices with a case study of Wulan Estuary, Demak District, Central Java Province, Indonesia. AZTI’s Marine Biotic Index (AMBI) community structure and biotic indices were used to assess ecological quality at eleven stations and determine the marine macrobenthic fauna's sensitivity to disturbances in two periods, i.e. August 2021 and 2022. A distinct spatial and temporal variation was evident in the macrobenthic community structure, where higher species richness and density were observed in 2022, with some species being more dominant in 2022. The trophic structure analysis showed the dominance of deposit-feeding bivalves in the fine sediments during those sampling intervals. These trophic groups, however, were dispersed less uniformly in the sandy substratum. Compared to the previous year, the density of herbivorous grazers and suspension feeders was higher in 2022. It is also shown by AMBI values that Wulan Estuary belonged to the good (slightly disturbed) to the high (undisturbed) condition, along with other biotic indices, which showed an enhanced habitat quality for benthic organisms. This result revealed the comparative ecological quality of related estuary ecosystems in Indonesia.

Coupling Imports of Dissolved Inorganic Nitrogen and Particulate Organic Matter by Aquaculture Sewage to Zhangjiang Estuary, Southeastern China

Estuary ecosystems serve as crucial connectors between terrestrial and marine environments, thus playing vital roles in maintaining the ecological balance of coastal marine ecosystems. In recent years, the eutrophication in estuaries caused by aquaculture sewage has been revealed, highlighting the necessity to understand its influence on the nutrient conditions and carbon storage of estuaries. In this study, δ15N and δ18O were used to indicate the contribution of aquaculture-derived sewage to dissolved inorganic nitrogen in Zhangjiang Estuary, and δ13C and C:N ratio were used to reveal its effects on the particulate organic matter. The major results are as follows: (1) Aquaculture water contributed 62~86% and 60~100% of the total nitrate and ammonium in Zhangjiang Estuary, respectively, and the drainage periods of the cultured species has a great influence on the content and composition of dissolved inorganic nitrogen. (2) Aquaculture water was also the major source of particulate organic matter (24~33% of the total content) here, most of which may be derived from crab ponds. (3) The imports of nutrients by aquaculture water may potentially regulate particulate organic matter in Zhangjiang Estuary by promoting the growth of phytoplankton and zooplankton. Our study revealed the coupling effects of aquaculture activities on the nitrogen and carbon storage in an estuarine ecosystem. It also indicates that isotopes may be efficient in the monitoring of a coastal environment, which may further aid the management of inshore cultivation.

Spatial distribution, morphology, and risk assessment of microplastics in sediment from the Pearl River Estuary, China

Microplastics (MPs) (<5 mm) are a growing environmental problem and have garnered significant global interest from scientists and policy makers. Coastal ecosystems are vulnerable to MP pollution, and assessing their sources, fate, and transport in the environment is imperative for marine ecosystem health. Data for marine sediment are still limited, particularly in the Pearl River Estuary (PRE) ecosystem in China. Here, we assessed the abundance, characteristics, and risks of MPs in marine sediment from PRE. MPs abundance ranged from 2.05 × 103 items ·kg−1 to 7.75 × 103 items ·kg−1 (dry weight), and white and black MPs were the dominant colors. The majority (>64.12 %) of detected MPs were <0.85 mm and primarily consisted of pellets (36.84 %) and fragments (29.65 %). Three polymer types of MPs were identified by Fourier Transform Infrared Spectroscopy (FT-IR) including polyethylene (PE), polyethylene terephthalate (PET), and polypropylene (PP). Polyurethane (PU) sponge was reported for the first time in this study area. Observations of the surface morphology of typical MPs using Scanning Electron Microscopy (SEM) showed that all MPs exhibited varying degrees of erosion, characterized by cracks, folds, and bumpy structures. Based on type and quantity of MPs and the polymers identified, we assessed and classified the risk of MP contamination in PRE sediment as category III, indicating severe ecosystem contamination. Our results may serve as an effective model for other estuaries facing similar pollution regimes and provides valuable information for marine sediment risk assessment.

Community coalescence under variable hydrochemical conditions of the Chesapeake Bay shaped bacterial diversity and functional traits

Community coalescence related to bacterial mixing events regulates community characteristics and affects the health of estuary ecosystems. At present, bacterial coalescence and its driving factors are still unclear. The present study used a dataset from the Chesapeake Bay (2017) to address how bacterial community coalescence in response to variable hydrochemistry in estuarine ecosystems. We determined that variable hydrochemistry promoted the deterioration of water quality. Temperature, orthophosphate, dissolved oxygen, chlorophyll a, Secchi disk depth, and dissolved organic phosphorus were the key environmental factors driving community coalescence. Bacteria with high tolerance to environmental change were the primary taxa accumulated in community coalescence, and the significance of deterministic processes to communities was revealed. Community coalescence was significantly correlated with the pathways of metabolism and organismal systems, and promoted the co-occurrence of antibiotic resistance and virulence factor genes. Briefly, community coalescence under variable hydrochemical conditions shaped bacterial diversity and functional traits, to optimise strategies for energy acquisition and lay the foundation for alleviating environmental pressures. However, potential pathogenic bacteria in community coalescence may be harmful to human health and environmental safety. The present study provides a scientific reference for ecological management of estuaries.

Spatial and temporal distribution of juvenile Gulf Sturgeon in the Pearl River, Louisiana, and adjacent estuaries of the Gulf of Mexico

AbstractObjectiveAcoustic telemetry was used to examine the spatial‐temporal distribution and anadromous migration pattern of juvenile Gulf Sturgeon Acipenser desotoi within the Pearl River and associated coastal estuaries of Louisiana and Mississippi.MethodsAcoustic transmitters were surgically implanted in 52 juvenile Gulf Sturgeon (&lt;890 mm fork length) from the Pearl River between 2016 and 2019. Sturgeon were monitored on 247 acoustic receivers in the lower Pearl River and adjacent estuaries across numerous partnering arrays.ResultJuveniles were detected on receivers from Lake Pontchartrain, Louisiana, east to Bay St. Louis, and Biloxi Bay, Mississippi. The 3‐year study found that juvenile Gulf Sturgeon migration in the Pearl River occurred on cycles similar to those reported from other populations. Juveniles were rarely observed in the estuary and nearshore marine environments from May through mid‐October of each year, during which time most sturgeon inhabited the Pearl River. Conversely, most of the juveniles inhabited coastal estuaries from December through February of each year and were rarely observed in freshwater environments during this period. Migration from the river into the estuary occurred during late‐October through November, and migration from the estuary into the river occurred in March and April. Distribution patterns varied spatially within the river and estuary ecosystems during each phase of migration. Tagged juveniles occupied the lowest 40 km of the Pearl River while in freshwater, and they occupied the northeastern shoreline of Lake Pontchartrain and Bay St. Louis while in the estuary. Interestingly, juveniles seemed to target specific areas in the estuary during winter that were farther away from the mouth of natal rivers than has been previously reported.ConclusionThis study provides a new assessment of juvenile Gulf Sturgeon migration and seasonal distribution for the Pearl River and provides important information for designing and assessing the potential benefits and challenges of habitat restoration for Gulf Sturgeon.

Rare subcommunity maintains the stability of ecosystem multifunctionality by deterministic assembly processes in subtropical estuaries.

Microorganisms, especially rare microbial species, are crucial in estuarine ecosystems for driving biogeochemical processes and preserving biodiversity. However, the understanding of the links between ecosystem multifunctionality (EMF) and the diversity of rare bacterial taxa in estuary ecosystems remains limited. Employing high-throughput sequencing and a variety of statistical methods, we assessed the diversities and assembly process of abundant and rare bacterioplankton and their contributions to EMF in a subtropical estuary. Taxonomic analysis revealed Proteobacteria as the predominant phylum among both abundant and rare bacterial taxa. Notably, rare taxa demonstrated significantly higher taxonomic diversity and a larger species pool than abundant taxa. Additionally, our findings highlighted that deterministic assembly processes predominantly shape microbial communities, with heterogeneous selection exerting a stronger influence on rare taxa. Further analysis reveals that rare bacterial beta-diversity significantly impacts to EMF, whereas alpha diversity did not. The partial least squares path modeling (PLS-PM) analysis demonstrated that the beta diversity of abundant and rare taxa, as the main biotic factor, directly affected EMF, while temperature and total organic carbon (TOC) were additional key factors to determine the relationship between beta diversity and EMF. These findings advance our understanding of the distribution features and ecological knowledge of the abundant and rare taxa in EMF in subtropical estuaries, and provide a reference for exploring the multifunctionality of different biospheres in aquatic environments.

How the Water-Sediment Regulation Scheme in the Yellow River affected the estuary ecosystem in the last 10 years?

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.

Microplastic profile in the sediment of Jakarta Bay estuary, Indonesia: Characterization based on size fraction and the potential risk to the ecosystem

Jakarta Metropolitan is known as the most populated and busiest city in Indonesia and among the top urban areas in the world with a common problem of solid and liquid waste. The present study aimed to assess the occurrence of microplastic (MP) pollution in sediment from the downstream rivers and coastal water of Jakarta Bay and estimate the potential risk to the ecosystem. Two composite sediment samples (river and coastal) were collected from the Jakarta Bay estuary. Distribution of sediment size showed that the medium size (100–500 µm) was the most dominant in river and coastal samples. Our finding demonstrated the highest MP concentration reported from the estuary ecosystem, i.e., 1184–1337 particles/100 g of river sediment and 804–1055 particles/100 g of coastal sediment. Classification based on size category revealed that the medium size (100–500 µm) was the most dominant MP in river sediment, while the smaller one (50–100 µm) was the most dominant MP in the coastal sediment. The present study indicates that terrestrial origin contributes to the MP pollution of Jakarta Bay. Polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) were the most dominant polymers in the river and coastal sediments. The risk assessment of MP pollution in Jakarta Bay estuary potentially exhibits a very high risk to the ecosystem, primarily related to polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), and polyurethane (PU) polymers and the MP sizes.

Mangrove Biodiversity Conservation and Aquaculture Practices in Sri Lanka: An Overview

The tropical island of Sri Lanka is endowed with a diverse and resourceful coastal area of 1,700 km coastline and 152,000 ha of highly productive 82 lagoons and 93,075ha of 45 estuary ecosystems. Around 33% of the population in coastal areas is engaged in fishing as the main income source, which contributes to around 1.10% of the national GDP. The objective of the review was to provide an overview of the present status of Sri Lankan coastal aquaculture, mangrove coverage, and conservation status. Mangroves are ecologically and economically important ecosystems providing the best nursery grounds for both blackish and marine species, covering only 0.24% of Sri Lanka‘s total land area. In addition, as the most carbon-rich forests in the tropics, mangroves provide a wide range of ecosystem services and biodiversity conservation. Currently, Sri Lankan mangroves are estimated to cover 160 km2 and are distributed mainly in Jaffna, Kalpitiya, Batticaloa, Rekawa, and Trincomalee. Including endangered species such as Sonneratia apetala, Ceriops decandra, and Lumnitzera littorea, there are 21 true mangrove species, and 24 mangrove associate species can be found. However, mangrove ecosystems in Sri Lanka are progressively under threat due to coastal aquaculture practices, especially shrimp farming and development projects. Human settlements, overexploitation, and climatic variables such as coastal flooding, drought, rainfall, salinity changes, increased sea level, and sea surface temperature have significantly influenced coastal aquaculture and substantially damage the mangroves resulting in loss of mangrove biodiversity. Between 1980 and 2005, approximately 25% of mangrove habitats are estimated to have been destroyed. Recently, 1,000-1,200 hectares of mangroves have been established in 23 wetlands in Sri Lanka becoming leader of the mangrove conservation in Commonwealth countries. In conclusion, it is imperative to apply international standards for mangrove-based aquacultural practices, mangrove rehabilitation, and technical and management interventions. &#x0D; Keywords: Biodiversity, Coastal aquaculture, Coastal ecosystems, Mangroves

Identifying the external N and Hg inputs to the estuary ecosystem based on the triple isotopic information (δ15NNO3, Δ17ONO3 and δ18ONO3)

The supply and sources of N and Hg in the Geum estuary of the western coast of Korea were evaluated. Triple isotope proxies (δ15NNO3, Δ17ONO3 and δ18ONO3) of NO3− combined with conservative mixing between river and ocean waters were used to improve isotope finger-printing methods. The N pool in the Geum estuary was primarily influenced by the Yellow Sea water, followed by riverine discharge (821 × 106 mol yr−1) and atmospheric deposition (51 × 106 mol yr−1). The influence of the river was found to be greater for Hg than that of the atmosphere. The triple isotope proxies revealed that the riverine and atmospheric inputs of N have been affected by septic wastes and fossil fuel burning, respectively. From the inner estuary towards offshore region, the influence of the river diminishes, thus increasing the relative impact of the atmosphere. Moreover, the isotope proxies showed a significant influence of N assimilation in February and nitrification in May.

Application of Tesla Valve to Bidirectional Open-Channel Flows

Dams hinder water circulation and consequently disrupt the river continuum which adversely affects aquatic organisms and degrades water quality. An alternative new concept for a dam has been proposed with an optimal design that prevents seawater from flowing upstream while maintaining the continuity of the river–estuary ecosystem. A Tesla valve was used because its asymmetric geometry increases the flow resistance only in a single direction. The numerical model setup aimed to simulate wave-induced open-channel flows in OpenFOAM using the volume of fluid method and investigate the capability of the channel design to enhance the asymmetric flow resistance, and the model was validated by laboratory experiments. Various combinations, scales, shapes, and arrangements of the structures were considered for deployment. Subsequently, these designs were evaluated based on the difference in flow discharges in each flow direction. The optimal choice included a 30° angle between the sidewalls and the structures, and streamwise spacing between the structures at 5/3 times the channel width. Further, longer main structures with substructures and a slightly offset design can help increase the flow asymmetry in bidirectional open-channel flows. Although the present study has limitations in terms of methodology and complex structural factors, the proposed design suggests the basic design of a new concept for Tesla valve-like geometry.

Coastal wetland degradation and ecological problems in the Yellow River Delta during 2005�2021

The Yellow River Delta wetland is one of the rare estuarine wetland ecosystems in the world, and it is also the most complete wetland ecosystem in the warm temperate zone in China. To understand its ecological problems as a sensitive and fragile new wetland ecosystem, we investigated and analyzed its coastal erosion, changes in wetland types, encroachment of invasive species, changes in the areas of seagrass beds and oyster reefs, ecosystem health status, and low salinity area. The investigation of the coastal wetlands in the Yellow River Delta revealed that from 2005 to 2020, the maximum deposition distance of the Yellow River port beach was about 10 km, and the maximum erosion distance was about 5 km. The siltation rate gradually decreased. From 2016 to 2021, the total area of the coastal wetlands in the Yellow River Delta remained stable. The area change rates of Spartina alterniflora, Phragmites australis, and Tamarix chinensis were 587, 282, and 57 ha/year, respectively, and the annual rate of change in Suaeda salsa was �60 ha/year. From 2015 to 2021, S. alterniflora increased the most sharply in the southern part of the Yellow River Estuary, and this region became the largest area of S. alterniflora in the delta. In recent years, the area of the coastal seagrass beds in the Delta has decreased sharply, and the area of the degraded oyster reefs has decreased further. The high nitrogen and phosphorus content of seawater is the main factor leading to the continuous eutrophication of the delta sea area. From 2011 to 2021, the health status of the Yellow River Estuary ecosystem remained in a sub-healthy state. The monitoring results for the low salinity area revealed that the areas of the low salinity area in 2020 and May 2021 were about 1200 and 1650 km2, respectively. Based on the survey results, the ecological problems faced by the wetlands in the Yellow River Delta such as dynamic coastline changes, coastal wetland degradation, and invasion of S. alterniflora were investigated.

Coastal wetland degradation and ecological problems in the Yellow River Delta during 2005-2021

The Yellow River Delta wetland is one of the rare estuarine wetland ecosystems in the world, and it is also the most complete wetland ecosystem in the warm temperate zone in China. To understand its ecological problems as a sensitive and fragile new wetland ecosystem, we investigated and analyzed its coastal erosion, changes in wetland types, encroachment of invasive species, changes in the areas of seagrass beds and oyster reefs, ecosystem health status, and low salinity area. The investigation of the coastal wetlands in the Yellow River Delta revealed that from 2005 to 2020, the maximum deposition distance of the Yellow River port beach was about 10 km, and the maximum erosion distance was about 5 km. The siltation rate gradually decreased. From 2016 to 2021, the total area of the coastal wetlands in the Yellow River Delta remained stable. The area change rates of Spartina alterniflora, Phragmites australis, and Tamarix chinensis were 587, 282, and 57 ha/year, respectively, and the annual rate of change in Suaeda salsa was �60 ha/year. From 2015 to 2021, S. alterniflora increased the most sharply in the southern part of the Yellow River Estuary, and this region became the largest area of S. alterniflora in the delta. In recent years, the area of the coastal seagrass beds in the Delta has decreased sharply, and the area of the degraded oyster reefs has decreased further. The high nitrogen and phosphorus content of seawater is the main factor leading to the continuous eutrophication of the delta sea area. From 2011 to 2021, the health status of the Yellow River Estuary ecosystem remained in a sub-healthy state. The monitoring results for the low salinity area revealed that the areas of the low salinity area in 2020 and May 2021 were about 1200 and 1650 km2, respectively. Based on the survey results, the ecological problems faced by the wetlands in the Yellow River Delta such as dynamic coastline changes, coastal wetland degradation, and invasion of S. alterniflora were investigated.

Investigation of fish community structure and species diversity in two river estuary ecosystems, the Taehwa River and Changwon Stream, based on conventional survey and eDNA metabarcoding

Investigation of fish community structure and species diversity in two river estuary ecosystems, the Taehwa River and Changwon Stream, based on conventional survey and eDNA metabarcoding

ASSESSMENT OF THREE-DIMENSIONAL BAROCLINIC CIRCULATION MODEL FOR THE MUSI COASTAL AREA

The hydrodynamics of the Musi estuary ecosystem is influenced by the flow of water discharge from the river, tidal circulation within the estuary, and complex bathymetry. Numerical modeling is one of the best ways to explain the characteristics and processes occurring in the estuary. However, the obtained model requires validation to ensure its accuracy despite the complexity added by variability in tidal and bathymetric conditions, making the validation process more challenging. This difficulty can be overcome by using high-resolution data, which provides a refined understanding of the river-to-sea estuary flow and its variability. The validation process involves the use of conductivity-temperature-depth (CTD) instruments and mooring tidal stations. The validated model is considered capable of accurately simulating tidal propagation as it represents the temperature-salinity-density properties within the estuarine environment. The development of this model demonstrates the effective implementation of these parameters within the Musi estuary ecosystem domain. The 3D model simulation is used to consider the vertical discretization in the river-estuary-sea channel, which enhances the representation of temperature-salinity-density in the water column. The obtained results suggest that the 3D-MIKE modeling is well-suited for operational purposes, including the prediction of hydrodynamics and the management of estuarine areas, specifically in the Musi estuary ecosystem.

The path of microplastics through the rare biodiversity estuary region of the northern Bay of Bengal

Due to its harmful effects on ecosystems and human health, microplastic (MP) pollution has become a significant environmental problem on a global scale. Although MPs' pollution path and toxic effects on marine habitats have been examined worldwide, the studies are limited to the rare biodiversity estuary region of Hatiya Island from the northern Bay of Bengal. This study aimed to investigate the MP pollution path and its influencing factors in estuarine sediments and water in rare biodiversity Hatiya Island in the northern Bay of Bengal. Sixty water and sediment samples were collected from 10 sampling sites on the Island and analyzed for MPs. The abundance of MPs in sediment ranged from 67 to 143 pieces/kg, while the abundance in water ranged from 24.34 to 59 pieces/m3. The average concentrations of MPs in sediment and water were 110.90 ± 20.62 pieces/kg and 38.77 ± 10.09 pieces/m3, respectively. Most identified MPs from sediment samples were transparent (51%), while about 54.1% of the identified MPs from water samples were colored. The fragment was the most common form of MP in both compartments, with a value of 64.6% in sediment samples and 60.6% in water samples. In sediment and water samples, almost 74% and 80% of MP were <0.5 mm, respectively. Polypropylene (PP) was the most abundant polymer type, accounting for 51% of all identified polymers. The contamination factor, pollution load index, polymer risk score, and pollution risk score values indicated that the study area was moderately polluted with MPs. The spatial distribution patterns and hotspots of MPs echoed profound human pathways. Based on the results, sustainable management strategies and intervention measures were proposed to reduce the pollution level in the ecologically diverse area. This study provides important insights into evaluating estuary ecosystem susceptibility and mitigation policies against persistent MP issues.