Estuarine Ecosystems Research Articles

Ecotoxicological risk assessment of triclosan, an emerging pollutant in a riverine and estuarine ecosystems: A comparative study

Triclosan (TCS), an antibacterial biocide, pervades water and sediment matrices globally, posing a threat to aquatic life. In densely populated cities like Mumbai, rivers and coastal bodies demand baseline TCS data for ecotoxicological assessment due to the excessive use of personal care products comprising TCS. This pioneering study compares spatiotemporal TCS variations and risks in freshwater and marine ecosystems employing multivariate analysis of physicochemical parameters. Over five months (January to May 2022), Mithi River exhibited higher TCS concentrations (water: 1.68 μg/L, sediment: 3.19 μg/kg) than Versova Creek (water: 0.49 μg/L, sediment: 0.69 μg/kg). Principal component analysis revealed positive correlations between TCS and physicochemical parameters. High-risk quotients (>1) underscore TCS threats in both water bodies. This study furnishes crucial baseline data, emphasizing the need for effective treatment plans for TCS in effluent waters released into the adjacent aquatic systems.

Balancing aquaculture and estuarine ecosystems: machine learning-based water quality indices for effective management.

This study delves into the environmental impact of inland aquaculture on estuarine ecosystems by examining the water quality of four estuarine streams within the key inland aquaculture zone of South India. In this region, extensive and intensive aquaculture practices are common, posing potential challenges to estuarine health. The research explores the predictive capabilities of the Gaussian elimination method (GEM) and machine learning techniques, specifically multi-linear regression (MLR) and support vector regressor (SVR), in forecasting the water quality index of these streams. Through comprehensive evaluation using performance metrics such as coefficient of determination (R2) and average mean absolute percentage error (MAPE), MLR and SVR demonstrate higher prediction efficiency. Notably, employing key water parameters as inputs in machine learning models is also more effective. Biochemical oxygen demand (BOD) emerges as a critical water parameter, identified by both MLR and SVR, exhibiting high specificity in predicting water quality. This suggests that MLR and SVR, incorporating key water parameters, should be prioritized for future water quality monitoring in intensive aquaculture zones, facilitating timely warnings and interventions to safeguard water quality.

Nitrogen input modulates the effects of coastal acidification on nitrification and associated N2O emission

Acidification of coastal waters, synergistically driven by increasing atmospheric carbon dioxide (CO2) and intensive land-derived nutrient inputs, exerts significant stresses on the biogeochemical cycles of coastal ecosystem. However, the combined effects of anthropogenic nitrogen (N) inputs and aquatic acidification on nitrification, a critical process of N cycling, remains unclear in estuarine and coastal ecosystems. Here, we showed that increased loading of ammonium (NH4+) in estuarine and coastal waters alleviated the inhibitory effect of acidification on nitrification rates but intensified the production of the potent greenhouse gas nitrous oxide (N2O), thus accelerating global climate change. Metatranscriptomes and natural N2O isotopic signatures further suggested that the enhanced emission of N2O may mainly source from hydroxylamine (NH2OH) oxidation rather than from nitrite (NO2−) reduction pathway of nitrifying microbes. This study elucidates how anthropogenic N inputs regulate the effects of coastal acidification on nitrification and associated N2O emissions, thereby enhancing our ability to predict the feedbacks of estuarine and coastal ecosystems to climate change and human perturbations.

Characteristics of demersal fish community structure during summer hypoxia in the Pearl River Estuary, China.

In recent decades, hypoxic areas have rapidly expanded worldwide in estuaries and coastal zones. The Pearl River Estuary (PRE), one of China's largest estuaries, experiences frequent seasonal hypoxia due to intense human activities and eutrophication. However, the ecological effects of hypoxia in the PRE, particularly on fish communities, remain unclear. To explore these effects, we collected fish community and environmental data in July 2021 during the summer hypoxia development period. The results revealed that bottom-layer dissolved oxygen (DO) in the PRE ranged from 0.08 to 5.71 mg/L, with extensive hypoxic zones (DO ≤ 2 mg/L) observed. Hypoxia has varied effects on fish community composition, distribution, species, and functional diversity in the PRE. A total of 104 fish species were collected in this study, with approximately 30 species (28.6%) exclusively found in hypoxic areas. Species responses to hypoxia varied: species such as Sardinella zunasi, Coilia mystus, and Nuchequula nuchalis were sensitive, while Decapterus maruadsi, Siganus fuscescens, and Lagocephalus spadiceus showed higher tolerance. Within the hypoxia area, dissolved oxygen was the main limiting factor for fish community diversity. Functional diversity (FDiv) decreased with higher dissolved oxygen levels, indicating a potential shift in the functional traits and ecological roles of fish species in response to changing oxygen conditions. Further analysis demonstrated that dissolved oxygen had a significantly stronger effect on fish community structure at hypoxic sites than in the whole PRE. Moreover, other environmental variables also had significant effects on the fish community structure and interacted with dissolved oxygen in the hypoxia area. These findings suggest that maintaining sufficient dissolved oxygen levels is essential for sustaining fish communities and ecosystem health in the PRE. This study provides novel insights into the effects of hypoxia on fish communities in estuarine ecosystems and has significant implications for the ecological health and management of the PRE.

Habitat distinctness doesn't influence on the abundance and relative growth of the juveniles Atherinella brasiliensis (Quoy & Gaimard, 1824) in a subtropical estuarine ecosystem

Shallow coastal habitats with and without vegetation may perform nursery function from distinct way for many species, raising questions about the role of vegetation on structuring nursery ground. Unfortunately, degradation and inappropriate human use of these areas associated with the lack of ecological data about fish populations can limit appropriate strategies to protect both species and habitats. In this paper we examine the nursery value of different estuarine habitats by comparing the abundance and relative growth of juveniles Atherinella brasiliensis. Fish were sampled once a month from November 2018 to October 2019 in five habitats: no vegetation close to the ocean, no vegetation close to the river, no vegetation and distant from other sampling points (control), mangrove and saltmarsh. Juveniles are present and abundant in all habitats and specimens had similar relative growth in the salt marsh, mangrove habitats and non vegetated habitats. The results indicate that estuarine habitats offers suitable conditions to A. brasiliensis in early stages of life, indicating that these sites have nursery value for juveniles of this species. Conservation and/or preservation of estuarine shallows habitats along the coast is important for A. brasiliensis and probably for other species, and the identification of priority areas could help to provide subsidies to management policies on conservation of coastal marine environments.

Differential metal and metalloid contents in fresh and cooked Charu mussels (Mytella charruana) from a southeastern Brazilian estuary and associated human health risks

Sepetiba Bay, a key estuarine ecosystem in southeastern Brazil, faces significant metal inputs, with a differential pollution gradient from the bay's entrance to inner areas, raising environmental and public health concerns. This study assessed metal levels in fresh and cooked samples of highly consumed Charu mussels (Mytella charruana) from three bay areas, one near the bay entrance (P1), with higher water renewal rates, one in the northern bay area (P2) and one the eastern bay (P3), presenting lower water renewal rates. Variations in metal and metalloid concentrations across sites were observed, with P3 exhibiting higher levels in fresh mussels for most elements, except for As, which was higher at P2 (0.35 ± 0.45 mg kg−1). Cooked samples demonstrated similar trends for Cu (1.30 ± 0.39 mg kg−1), Ni (0.28 ± 0.20 mg kg−1), and V (0.75 ± 0.28 mg/kg−1), indicating that cooking in contaminanted estuary water does not significantly reduce contamination. Significant differences were detected for Ni, Cd (0.014 ± 0.008 mg kg−1), Zn (14.28 ± 2.50 mg kg−1), and V at P1, which were significantly higher than at P3. Significant Fe (246 ± 68 mg kg−1), Al (109 ± 33 mg kg−1), and Mn increases were observed from P1 to P3. Mussels sampled from P3, near an abandoned military area and urban center, exhibited high Fe and Al levels, attributed to both natural processes and industrial activities. Metal concentrations in Charu mussels often exceeded regulatory limits set by Brazilian, North American, and European agencies. Calculated Se molar ratios indicate that while Se can mitigate Hg toxicity, high Hg levels in Sepetiba Bay's Charu mussels still pose significant health risks. Similarly, high levels of Ag, Cd, and Pb suggest ineffective Se protection. However, Se appears effective against As toxicity. The Health Benefit Value of Selenium (HBVSe) indicate Se's overall protective benefits against Hg toxicity. Higher HBVSe values in cooked mussels at P1 and P2 suggest that cooking increases Se bioavailability. However, raw mussels at P3 had higher HBVSe values than cooked ones, highlighting the need for site-specific assessments. Calculated Hazard Indices indicate general high health risks from mussel consumption, and As levels in Charu mussels indicate high carcinogenic risks. These findings emphasize the need for comprehensive Charu mussel monitoring and environmental management efforts at Sepetiba Bay.

Distribution Status of Invasive Alien Species in the Estuarine Wetlands in East and South Coast, Korea

Based on the results of survey on estuarine ecosystem conducted from 2021 to 2023, this study analyzed the distribution pattern of invasive alien species. A total of six invasive alien species (<i>Micropterus salmoides</i> [<i>M. salmoides</i>], <i>Lepomis macrochirus</i> [<i>L. macrochirus</i>], <i>Lithobates catesbeianus</i> [<i>L. catesbeianus</i>], <i>Trachemys scripta</i> [<i>T. scripta</i>], <i>Pseudemys concinna</i> [<i>P. concinna</i>], and <i>Pseudemys nelsoni</i> [<i>P. nelsoni</i>]) were identified across 118 estuarine wetlands. The survey revealed 960 individuals of <i>M. salmoides</i>, 2,596 individuals of <i>L. macrochirus</i>, 1,088 individuals of <i>L. catesbeianus</i>, and 44 individuals of <i>T. scripta</i>, while 1 individual of <i>P. concinna</i> and <i>P. nelsoni</i> were found. These invasive species were found to be densely distributed in estuarine wetlands in the Haenam and Goheung regions of the southern coast. Furthermore, the distribution density varied depending on the characteristics and locations of the estuarine wetlands. It was observed that the distribution density was higher in closed type than in open type, in riverine than in lacustrine, and in the south coast than in the east coast. Once the basic survey of estuarine wetlands located on the west coast is completed, a clearer understanding of the nationwide distribution characteristics of invasive alien species in estuarine wetlands can be achieved. This information will be crucial for formulating appropriate management strategies tailored to the characteristics of wetlands or coastal areas in the future.

Metagenomic insights into microbial adaptation to the salinity gradient of a typical short residence-time estuary

BackgroundMicrobial adaptation to salinity has been a classic inquiry in the field of microbiology. It has been demonstrated that microorganisms can endure salinity stress via either the “salt-in” strategy, involving inorganic ion uptake, or the “salt-out” strategy, relying on compatible solutes. While these insights are mostly based on laboratory-cultured isolates, exploring the adaptive mechanisms of microorganisms within natural salinity gradient is crucial for gaining a deeper understanding of microbial adaptation in the estuarine ecosystem.ResultsHere, we conducted metagenomic analyses on filtered surface water samples collected from a typical subtropical short residence-time estuary and categorized them by salinity into low-, intermediate-, and high-salinity metagenomes. Our findings highlighted salinity-driven variations in microbial community composition and function, as revealed through taxonomic and Clusters of Orthologous Group (COG) functional annotations. Through metagenomic binning, 127 bacterial and archaeal metagenome-assembled genomes (MAGs) were reconstructed. These MAGs were categorized as stenohaline—specific to low-, intermediate-, or high-salinity—based on the average relative abundance in one salinity category significantly exceeding those in the other two categories by an order of magnitude. Those that did not meet this criterion were classified as euryhaline, indicating a broader range of salinity tolerance. Applying the Boruta algorithm, a machine learning-based feature selection method, we discerned important genomic features from the stenohaline bacterial MAGs. Of the total 12,162 COGs obtained, 40 were identified as important features, with the “inorganic ion transport and metabolism” COG category emerging as the most prominent. Furthermore, eight COGs were implicated in microbial osmoregulation, of which four were related to the “salt-in” strategy, three to the “salt-out” strategy, and one to the regulation of water channel activity. COG0168, annotated as the Trk-type K+ transporter related to the “salt-in” strategy, was ranked as the most important feature. The relative abundance of COG0168 was observed to increase with rising salinity across metagenomes, the stenohaline strains, and the dominant Actinobacteriota and Proteobacteria phyla.ConclusionsWe demonstrated that salinity exerts influences on both the taxonomic and functional profiles of the microbial communities inhabiting the estuarine ecosystem. Our findings shed light on diverse salinity adaptation strategies employed by the estuarine microbial communities, highlighting the crucial role of the “salt-in” strategy mediated by Trk-type K+ transporters for microorganisms thriving under osmotic stress in the short residence-time estuary.22YT9hkSS5Zn-gk-qyndrEVideo

Using shell shape analysis based on landmarks to trace the geographical origin of the common cockle (Cerastoderma edule)

Determining the geographical origin of seafood is crucial for regulators and fishing industries who seek to prevent commercial fraud, enforce food safety regulations, and encourage high standards in sustainable fisheries management. The cockle, Cerastoderma edule (Linnaeus 1768), is a key species in estuarine ecosystems and is harvested all over Europe. Therefore, traceability tools using quick and inexpensive techniques to identify the origin of this bivalve are of paramount importance to support law enforcement. In this work, we explore the potential of using Geometric Morphometric (GM) methods to identify the geographical origin of cockle specimens. This method is based on landmarks identified in the shell to trace the origin of specimens obtained in nearby aquatic systems (from <35 km to <250 km distance). Specimens were collected in five aquatic systems (Ria de Aveiro, the Tagus and Sado estuaries, and the Albufeira and Óbidos coastal lagoons) in Portugal. Shells were digitalized and 16 landmarks were identified in each right valve and analyzed using Generalized Procrustes Superimposition. The discriminating power for traceability of 12 statistical and machine learning methods was assessed based on the corresponding shape variables, using R and Python (Linear Discriminant Analysis (LDA), Canonical Variable Analysis (CVA), Principal Component Analysis (PCA), Between-Group PCA (bgPCA), Partial Least Squares Discriminant (PLSD), Classification Regression Tree (CRT), Logistic Regression (LR), Random Forest (RF), Gradient Boosting (GB), K Nearest Neighbors (KNN), Support Vector Machines (SVM), Extending Gradient Boosting (XGBoost) and Neural Networks (NNET). LDA, CVA, SVM, and NNET demonstrated greater accuracy and a F1-score >80%, even with a small and unbalanced sample size. The highest percentage of correctly assigned individuals was obtained in the Tagus estuary (mean 89%) and in the Albufeira lagoon (mean 93%), which were also the systems with more specimens measured (174 and 59 respectively), whereas the worst results were obtained in the Sado estuary (50%, 56 specimens). In the Albufeira coastal lagoon, the best classification methods reached 100% correct classifications. It further highlights the importance of establishing statistical standards, such as the ones developed in the current work, to evaluate different methods, as small changes in the procedure may cause substantial differences in the results and conclusions. The revision of previous works (presented as a table) showed often >90% of correct classification in both bivalves and gastropods, highlighting the potential of the techniques for other mollusks. Our results support the use of GM based on landmarks as a reliable tool for bivalve's traceability, since it is a quick, simple and inexpensive approach. Further research should extend these findings to other species and other shape analysis techniques.

Seasonal dynamics and habitat preferences of juvenile fish assemblages in the Wanquan Estuary, South China: Implications for conservation and management

Tropical estuaries encompass diverse habitats, which are crucial for supporting juvenile fish by providing nurseries, refuges, and migration routes. In the present study, we investigated the seasonal and spatial dynamics of juvenile fish assemblages in the Wanquan Estuary, Hainan Island, China, examining variations during the wet and dry seasons across four types of habitats. Our research aimed to test the hypotheses: (1) the wet season supports a greater abundance and species richness of juvenile fish compared to the dry season, and (2) juvenile fish showed varying habitat preferences across seasons. We recorded a total of 3617 individuals belonging to 33 families, 50 genera, and 78 taxa. Our findings revealed significant seasonal fluctuations in the assemblage structure, with peak abundance during the wet season in August, primarily consisting of diadromous species. A notable shift towards marine species was observed in March. Spatially, juvenile fish exhibited significant habitat preferences, with a strong preference for sand substrates for most species. Contrary to common expectations, mangrove fringe habitats were not identified as the primary nursery grounds for juvenile fish. Instead, our study highlights the importance of habitat diversity and connectivity in enhancing nursery functions. Water temperature and salinity were the key drivers influencing the seasonal and temporal patterns of juvenile fish assemblages in the Wanquan River estuary The pronounced temporal dynamics of these assemblages, driven by seasonal environmental alterations affecting water variations and habitat connectivity, were more significant than spatial differences. The findings emphasize the need for focused connectivity of various habitats to support the conservation of diverse fish communities in tropical estuarine ecosystems.

Food web attributes to assess spatial–temporal dynamics in estuarine benthic ecosystem

Threatened benthic ecosystems need urgent tools for effective bioassessment and relevant management. EU Marine Strategy Framework Directive (MSFD) obligates member states to achieve GES (Good Environmental Status) for 11 descriptors of environmental state (MSFD; 2008/56/EC). From all of the descriptors, D4 that focuses on Food Webs is the most functional-oriented indicator, but also the most challenging to implement due to our limited knowledge on benthic interactions. Particularly, it is still unclear how spatially and temporally regulated abiotic variables determine the entire benthic food webs, and which benthic food web attributes best respond to these spatially and temporally derived environmental variations. To fill this gap, we measured the natural isotopic ratios (δ13C and δ15N) of macrobenthic organisms and their food sources and build twelve food web topologies across three distinct sites (Navigator, Gambia, Tróia) in summer and winter during two consecutive years. To assess these food web topologies, we applied isotopic metrics, further integrated with univariate and multivariate analysis to find food web-based indicators that best respond to these spatial and temporal variability.We found clear spatial patterns associated to an increase in primary production and quantity and quality of organic matter (OM). Sites with higher organic load and less quality OM (Navigator and Gambia) had simpler food webs, likely associated to high abundance of opportunistic meiobenthic species. Site located inside protected area (Tróia) with high quality OM had the most complex food web characterized by high diversity of specialist consumers that used more efficiently available resources. Similarity metrics were valuable complementary tool that helped to further disentangle the causes of spatial variability, in this case distinguishing between two food webs (Navigator and Gambia) that had similar structures but different resource utilization.The temporal patterns were not so evident than the spatial patterns, although significant differences were reported between sampling occasions for the same metrics (maximum trophic position and the percentage of carnivores and omnivores, p < 0.05). The most complex Tróiás food web demonstrated greater responsiveness in capturing temporal differences in resource use, suggesting that more complex food webs are better equipped to reflect temporal variability. The integration of isotopic metrics complemented with multivariate and univariate analyses proved to be an important tool for the analysis of different aspects of the benthic food web complexity in a spatial–temporal context providing a promising approach to assess the functional integrity of the estuarine ecosystems, especially in the context of the descriptor 4 within MSFD.

Ray bioturbation rates suggest they shape estuary processes

AbstractBioturbation of sediments is a key ecosystem service in estuarine and marine ecosystems, and rays (superorder Batoidea: skates, stingrays, electric rays and shovelnose rays) are among the largest bioturbators, modifying their habitat through foraging and predation. Ray activities cycle nutrients, increase oxygen penetration and re‐stratify sediments. However, given rays are globally threatened, it is unclear to what extent the loss of rays, and the ecosystem services they provide, would affect ecosystem processes. This study assessed the likely amount of sediment displaced annually by rays during foraging activities at an estuary scale. To achieve this, an aerial drone was used to map daily ray bioturbation activity, as evident from the presence of feeding pits. High‐resolution, 2.6 cm px−1, Digital Elevation Models (DEM) were created and used to measure the volume of sediment displaced by feeding pits. We found rays within the Brisbane Water estuary in NSW, Australia excavated 1.20 (±0.68) tonnes of sediment per day within this 1443 m2 intertidal area, or a rate of 575.2 cm3 m−2 per day. This bioturbation rate is relatively high compared to bioturbation rates documented in other ray species. Spatial autocorrelation analysis indicated that the ray feeding pits were significantly clustered by location as well as size (P &lt; 0.01), suggesting size segregation of ray foraging. When bioturbation rates were conservatively extrapolated across measured feeding area in the estuary, we calculated rays displace 57.6 (±32.4) tonnes of sediment per day, or 21.0 (±11.4) kilotonnes per year. This underlines how ray bioturbation likely shape estuary processes, and how the loss of rays and their ecosystem services would likely have considerable impacts on estuarine sedimentary ecosystems. These findings emphasize the ecological importance of rays in an ecosystem and a need to better understand the consequences of anthropogenic pressures to these services.

Tidal effect on environmental DNA communities in Arctic estuarine and marine ecosystems

Tidal effect on environmental DNA communities in Arctic estuarine and marine ecosystems

Crab bioturbation reduces carbon storage in salt marshes under more robust mechanisms than plant invasiveness

IntroductionThe macrobenthos are crucial for the stability of estuarine ecosystems due to their burrowing behavior in the sediment and their uptake of nutrients from plants. These activities lead to significant alterations in both the morphological and biogeochemical processes within the region.MethodsHowever, there is limited investigation into carbon cycling processes specifically related to crab bioturbation. Additionally, few studies have examined enzymatic activities and carbon fractions in sediments from crab burrow walls at different crab growth stages. This study aims to explore the impact of both plant invasiveness and crab bioturbation on carbon storage.ResultsOur findings suggest that plant invasion leads to higher organic accumulation due to the reduction of recalcitrant organic carbon (ROC) (decreased by 11.6% in invasive and 62.6% in native site from April to December), faster photosynthetic rates (25.8 μmol/m2 s in invasive and 10.7 μmol/m2 s in native site), and an increased presence of arbuscular mycorrhizal fungi (AMF) in the soil over time. However, the increase of easy oxidized carbon (EOC) may lead to less carbon storage in soil (increase by 67.7% in invasive and 48.8% in native site from April to December). In addition to invasiveness, the bioturbation activities of macrobenthos also affect carbon storage. Sediments from crab burrows exhibit higher EOC content (33.6% more than the bulk soil) and higher levels of carbon cycling-related enzymes, including S-ACT, S-β-GC, and S-ACP activities (24.2%, 8.99%, and 135.6% higher than the bulk soil, respectively).DiscussionThese changes contribute to reduced carbon accumulation in the soil. Therefore, crab bioturbation is a more significant factor affecting carbon sink capacity than plant invasion.

Environmental DNA reveals ecologically relevant spatial and temporal variation in fish assemblages between estuaries and seasons

Estuarine ecosystems are threatened by numerous anthropogenic pressures. Fish assemblages are a dominant component of estuarine macrofauna and serve as indicators for the health of these transitional water ecosystems. Environmental DNA (eDNA) metabarcoding is increasingly used to assess the biodiversity of fishes in estuaries. However, there is a need to further establish how effective eDNA metabarcoding can be relative to conventional fish sampling methods across multiple estuaries and seasons. This study compared fish assemblages detected via eDNA metabarcoding of surface water samples to contemporary sampling with conventional fishing gears in three temperate estuaries (UK), during early summer and autumn. Most species caught by fishing were detected by eDNA. Species richness estimates from eDNA were two to ten times higher than estimates based on fishing, and included taxa of conservation importance and a non-native species. The eDNA assemblage composition was significantly different to the assemblage detected by seine nets. Importantly, eDNA methods could effectively discriminate between fish assemblages of different estuaries and seasons. Fish assemblages in estuaries are often not monitored due to resource constraints. The dynamic nature of estuaries may make fishing gear deployment difficult and inconsistent. The findings indicate that eDNA metabarcoding is suited to gathering large amounts of information on fish biodiversity, at a relatively low sampling effort, compared to established fishing methods. Therefore, eDNA shows promise as an assessment tool for fish assemblage structure and ecosystem health in estuarine environments, with application to statutory monitoring.

Integrated Assessment of Ecological Quality Combining Biological and Environmental Data in the Yellow River Estuary

The integrated assessment of ecological quality in estuarine ecosystems holds significant importance for environmental management. Previous monitoring programs predominantly focused on environmental data, lacking a comprehensive quality assessment approach. To address this gap, this study aimed to integrate environmental factors with macrofaunal community information to evaluate the ecological quality status of the Yellow River Estuary. A total of 13 stations were routinely monitored in August for four consecutive years to collect environmental and biological data. Candidate indicators were screened based on variation coefficients, distribution ranges, and redundancy analysis, identifying 16 indicators belonging to three categories (i.e., seawater, sediment, and biology). The model fit and the interrelationship of the components were determined using structural equation modelling (SEM). The main results were as follows. (1) A total of 144 macrofaunal taxa, belonging to eight animal phyla and 98 families, were identified, with a dominance of Annelida (37.8%) and Mollusca (33.3%). The environmental variables most strongly correlated with the macrofaunal community were TOC, DO, Cd, and Md. (2) NO2 and heavy metals represented the two most direct factors of environmental pollution, while the factor load of biodiversity indices (H’, J, and D) was large in the biology category. (3) The evaluation results indicated that 78.85% of the total samples were between the average and upper levels of ecological quality, but only 7.69% of samples were at the “high” level. The framework system for the evaluation of ecological quality constructed in this study provides a theoretical and practical basis for the evaluation of the effectiveness of conservation management of the Yellow River Estuary.

Linking microphytobenthos distribution and mudflat geomorphology under varying sedimentary regimes using unoccupied aerial vehicle (UAV)-acquired multispectral reflectance and photogrammetry

Microphytobenthic (MPB) biofilms play significant roles in the ecology of coastal mudflats, including provision of essential food resources to shorebird species. In these ecosystems, water-divergence structures like jetties and causeways can drastically alter sedimentation patterns and mudflat topography, yet their effects on MPB biofilm biomass and distribution are poorly understood. Here, we used a combination of unoccupied aerial vehicle (UAV) technologies, photogrammetric processing, and sediment field samples to compare biofilm and mudflat characteristics between areas of the Fraser River Estuary with varying sedimentary regimes and shorebird use. Our aims were to: (1) demonstrate the use of fine spatial resolution UAV-acquired multispectral imagery (cm2) with extensive spatial coverage (>km2) and a co-alignment photogrammetric processing techniques to survey MPB biofilm and mudflat topography at spatial scales and detail relevant to foraging shorebirds; and, (2) investigate the effects of water-divergence structures on mudflat elevation and microtopography, as well as MPB biofilm biomass, distribution, and spatial patterning. From a technical perspective, co-alignment allowed us to analyze aligned and continuous fine-resolution elevation models and orthomosaics for large areas of the estuary, while the normalized difference vegetation index was a good predictor of sediment chlorophyll-a (R2 = 0.9). Using these data products, we found that mudflats in close proximity to water-divergence structures have cross-shore profiles characteristic of low sediment supply as well as decreased microtopographic variability. At disturbed sites, elevation and microtopography had a weaker influence on biofilm biomass compared to intact estuarine ecosystem sites. Analysis of biofilm patch showed that sites either had a relatively small number of large, contiguous patches, or a large number of smaller, isolated patches; however, less disturbed sites did not necessarily have larger biofilm patches than more disturbed sites. We conclude that UAV-acquired multispectral imagery and co-alignment-based workflow are promising new tools for ecologists to map, monitor, and understand MPB biofilm dynamics in ecologically sensitive estuaries.

Extracellular Enzyme Activity and Stoichiometry Across Vegetated and Non-Vegetated Coastal Ecosystems

The conversion of organic matter by extracellular enzymes can reveal important insights into carbon and nutrient cycling. The activity and stoichiometry of hydrolytic extracellular enzymes were investigated to assess the effects of vegetation cover and sediment characteristics on microbial-enzyme-mediated decomposition in coastal ecosystems. Extracellular enzyme activity (EEA) was quantified across transects extending from mangrove to tidal flat habitats in two New Zealand coastal ecosystems that differ in mud content (sandy: Hobson Bay, muddy: Snells Beach). We determined the activity of five key hydrolyzing enzymes: β-glucosidase (hydrolyzes cellulose to glucose); β-N-acetylglucosaminidase (catalyzes the terminal reaction in chitin degradation); alkaline phosphatase (releases soluble inorganic phosphate groups from organophosphates); β-D-cellobiohydrolase (hydrolyzes cellulose to generate cellobiose); and β-xylosidase (catalyzes hemicellulose). All enzymes involved in C acquisition and in N and P cycling had higher activity at the muddy site. No habitat differences in EEA were observed at the sandy site, whereas EEA was lower in the non-vegetated habitats for some enzymes at the muddy site. Models of microbial metabolic limitations highlighted that most habitats at both muddy and sandy sites were predominately C and P limited. The EEA in these coastal wetlands was generally lower than has been reported for other terrestrial, freshwater, and estuarine ecosystems, with values often one to two orders of magnitude lower than other wetland studies. These results can be used to advance our understanding of the biogeochemical processes underpinning the response of coastal ecosystems to land-derived nutrient and sediment inputs.

Predicting ecotopes from hydrodynamic model data: Towards an ecological assessment of nature-based solutions

Estuaries worldwide are of substantial ecological value due to the presence of various gradients, such as salinity. Preserving the natural value of estuaries is vital for meeting the climate stabilization goals of the Paris Agreement. Recognizing nature as a stakeholder is imperative, given the surpassing value of ecosystem services over global gross domestic product. Quantifying the current ecological state and future ecological shifts faces challenges, including variable dependencies, spatial-temporal disparities, and the limitations in available information. This study introduces EMMA (Ecotope-Map Maker for Abiotics), a method for quantifying the effects of human interventions or climate change scenarios on estuarine ecosystems by linking abiotic characteristics derived from a hydrodynamic model to ecotopes. The Western Scheldt, an estuary connecting the Scheldt river to the North Sea in the Netherlands, serves as a case study. The method successfully reproduced an existing ecotope-map, which is dependent on real-time data such as aerial photographs. The developed method not only proves applicable in assessing the current ecological state and future ecological shifts for hypothetical scenarios but also demonstrates utility in predicting future situations, providing valuable insights for decision-makers in estuarine ecosystem management and contributing to climate and environmental preservation goals.

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.