Search Results (49)

This study presents the first comprehensive assessment of microalgal diversity in two Slovenian transitional waters (TWs): the shallow brackish lagoon of the Škocjanski Zatok Nature Reserve (SZNR) and the Rižana River estuary within the Port of Koper (PK) area. Between 2018 and 2021, water samples collected with a phytoplankton net were analyzed using light and scanning electron microscopy. In total, 240 species from 117 genera were identified in TW, dominated by diatoms and dinoflagellates, surpassing the diversity at a marine coastal station (91 species, 59 genera). Species richness was higher in PK (226) than in SZNR (154), mainly due to dinoflagellates and coccolithophores. Marine taxa predominated along the salinity gradient, with moderate contributions from brackish taxa and few freshwater forms, reflecting both natural and anthropogenic influences. Planktonic taxa dominated at all sites, while benthic forms were abundant in the lagoon, particularly in spring. Thirty-two taxa were recorded for the first time in Slovenian TW, mostly benthic or tychopelagic diatoms. The detection of Coolia monotis and five cyanobacterial genera with potentially harmful traits highlights the role of TW as an ecological interface. The taxonomic sufficiency analysis showed that the order level is sufficient to distinguish transitional from marine assemblages, beyond which ecological information is lost. Overall, this study highlights the importance of detailed taxonomic resolution for detecting microalgal diversity, including harmful and non-indigenous species to ensure robust ecological assessments under the WFD and MSFD directives. Full article

Flexible polyurethane foam (PUF) is a vital material across diverse applications, and its global market is projected to continue growing. Driven by regulatory and consumer demand for sustainable materials, the PUF industry is exploring alternatives to petroleum-derived raw materials, such as vegetable oil-derived bio-polyols. Although bio-based alternatives to fossil-derived foams have been developed, their environmental benefits remain to be fully assessed. Therefore, this study evaluates the environmental performance of flexible PUF production by comparing a conventional fossil-based formulation with a bio-based alternative using a cradle-to-gate Life Cycle Assessment (LCA). The bio-based PUF reduced global warming (6%), fossil resource scarcity (9%), and mineral resource scarcity (6%), but caused significant increases in freshwater eutrophication (91%) and marine eutrophication (19%), mainly due to agricultural processes associated with soybean cultivation. Regardless of the formulation, polyol and toluene diisocyanate production were identified as major environmental hotspots. These results highlight both the decarbonization potential and the trade-offs of bio-based raw materials, underlining the complexity of achieving sustainable PUF production. Overall, the findings provide quantitative insights to guide more sustainable design and sourcing strategies for flexible PUF in the transition from fossil to renewable feedstocks. Full article

Mixing zones in carbonate coastal aquifers are dynamic interfaces where freshwater and seawater converge, triggering complex biogeochemical processes. This study investigates diagenetic barite (BaSO₄) precipitation within such a mixing zone in the dolomitic aquifer of the Sierra de Gádor (SE Spain). Three sectors were analyzed: two active mixing zones—one associated with submarine discharge and the other affected by marine intrusion—and an uplifted, fossilized Pleistocene mixing zone. Mineralogical, petrographic, and geochemical analyses reveal extensive dissolution of the dolomitic bedrock, forming polygonal voids and fracture-controlled porosity, frequently covered by Fe and Mn oxides. Barite crystals were identified exclusively in the Fe oxide precipitates at depths where 80% of seawater is reached. The saturation index for barite in groundwater suggests near-equilibrium conditions across the fresh–brackish–saline transition; however, barite precipitation is localized where Fe oxides act as a geochemical barrier, concentrating Ba and enabling nucleation. SEM imaging shows well-formed euhedral barite crystals up to 100 µm in size. This form of crystallization would be similar to the marine diagenetic barite formation models involving organic matter degradation and Ba remobilization, translated to a coastal aquifer setting in this study. Trace metal analyses show significant enrichment of Pb (up to 20 wt%) and other elements (Zn, Ni, and Co), suggesting potential for ore-forming processes if redox conditions shift. This work proposes a conceptual model for diagenetic barite formation in coastal aquifers, emphasizing the role of Fe and Mn oxides as reactive substrates in metal cycling at the land–sea interface. Full article

The Mangalia–Limanu coastal lake system, located in southeastern Romania along the Black Sea, represents a transitional aquatic environment shaped by the interplay between freshwater and marine influences. This study provides an integrated assessment of its physicochemical water parameters, sedimentological and geochemical properties, and benthic macroinvertebrate communities, aiming to evaluate its current ecological status and environmental dynamics. Field measurements using a multiparameter sonde revealed a predominantly freshwater to oligohaline system with moderate spatial heterogeneity. DO levels frequently reached supersaturation (>180%), coupled with high pH (~9.1), indicating intense daytime photosynthetic activity. Conductivity, TDS, and salinity increased longitudinally toward the port water area, while nitrate concentrations showed stronger signals upstream. Sediments were dominated by organic matter (18–88%), with lower carbonate (3–53%) and siliciclastic (8–49%) contents. Organic-rich deposits prevailed in the western-central sector, where reduced hydrodynamics and submerged vegetation favor autochthonous organic accumulation, whereas the eastern sector, exposed to marine action, showed more siliciclastic-rich substrates. Geochemical analyses revealed localized exceedances of Cr, Ni, Cu, Zn, and Pb regulatory thresholds (Order 161/2006), suggesting potential contamination hotspots. Benthic communities included 26 taxa, dominated by polychaetas, gammarids, and gastropods, with moderate diversity (H′ < 2). The results highlight a system under moderate anthropogenic pressure but retaining transitional lagoon characteristics, emphasizing the need for continued ecological monitoring and integrated management measures. Full article

Coral reefs exposed to chronically turbid conditions challenge conventional assumptions about the optical environments required for reef persistence and productivity. This study investigates the utility of light absorption coefficients as indicators of optical water quality in Varadero Reef, an extreme coral ecosystem located in Cartagena Bay, Colombia. Field campaigns were conducted across three seasons (rainy, dry, and transitional) along a transect from fluvial to marine influence. Absorption coefficients at 440 nm were derived for particulate (a_p(440)) and chromophoric dissolved organic matter (a_CDOM(440)) to assess their contribution to underwater light attenuation. Average values across seasons show that a_p(440) reached 0.466 m⁻¹ in the rainy season (September 2021), 0.285 m⁻¹ in the dry season (February 2022), and 0.944 m⁻¹ in the transitional rainy season (June 2022). Meanwhile, mean a_CDOM(440) values were 0.368, 0.111, and 0.552 m⁻¹, respectively. These coefficients reflect the dominant influence of particulate absorption under turbid conditions and increasing a_CDOM(440) relevance during lower turbidity periods. Mean Secchi Disk Depth (ZSD) ranged from 0.6 m in the rainy season to 3.0 m in the dry season, aligning with variations in Kd PAR, which averaged 2.63 m⁻¹, 1.13 m⁻¹, and 1.08 m⁻¹ for the three campaigns. Chlorophyll-a concentrations at 1 m depth also varied significantly, with average values of 2.3, 2.7, and 6.2 μg L⁻¹, indicating phytoplankton biomass peaks associated with seasonal freshwater inputs. While particulate absorption limits light penetration, CDOM plays a potentially photoprotective role by attenuating UV radiation. The observed variability in these optical constituents reflects complex hydrodynamic and environmental gradients, providing insight into the mechanisms that sustain coral functionality under suboptimal light conditions. The absorption-based approach applied here, using standardized spectrophotometric methods, proved to be a reliable and reproducible tool for characterizing the spatial and temporal variability of IOPs. We propose integrating these indicators into monitoring frameworks as cost-effective, component-resolving tool for evaluating light regimes and ecological resilience in optically dynamic coastal systems. Full article

Plastic pollution is an increasing global concern, with estuaries being especially vulnerable as transition zones between freshwater and marine systems. These ecosystems often accumulate large amounts of waste, affecting wildlife and water quality. This study focuses on analysing the circulation patterns of the Ave Estuary, a small, shallow system on Portugal’s north-western coast, and their influence on litter transport and distribution. This site was selected for installing an aquatic litter removal technology under the EU-funded MAELSTROM project. A 2DH hydrodynamic model using Delft3D FM, coupled with the Wflow hydrological model, was implemented and validated. Various scenarios were simulated to assess estuarine dynamics and pinpoint zones prone to litter accumulation and flood risk. The results show that tidal action and river discharge mainly drive the estuary’s behaviour. Under low discharge, floating litter should be mostly transported toward the ocean, while high discharge conditions should result in litter movement at all depths due to stronger currents. High water levels and flooding occur mainly upstream and in specific low-lying areas near the mouth. Low-velocity zones, which can favour litter accumulation, were found around the main channel and on the western margin near the estuary’s mouth, even during high flows. These findings highlight persistent accumulation zones, even under extreme event conditions. Full article

Estuarine ecosystems, characterized by dynamic salinity gradients and complex physicochemical interactions, serve as critical transition zones between freshwater and marine environments. This study investigates the spatial evolution of sediment microbial communities across a freshwater–seawater continuum and their correlations with water quality parameters. Five sampling zones (upstream, midstream, downstream, transition zone, and ocean) were established in a typical estuary (Kuiyu Park, China). High-throughput 16S rRNA sequencing revealed significant shifts in microbial composition, with dominant phyla including Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Alpha diversity decreased from freshwater to the transition zone but rebounded in seawater, suggesting habitat filtering and niche differentiation. Redundancy analysis identified salinity, dissolved oxygen, nutrients, and heavy metals as key drivers of microbial community structure. Functional predictions highlighted metabolic adaptations such as methanogenesis, sulfur oxidation, and aerobic chemoheterotrophy across zones. This study explores how sediment microorganisms adapt to water quality variations during the freshwater–seawater transition, offering insights into estuarine resilience under global change. These findings elucidate microbial assembly rules in estuarine ecosystems and provide insights for ecological management under global environmental change. Full article

Cymothoidae (Crustacea: Isopoda) infest fish in marine, brackish, and freshwater environments. Cymothoa pulchrum Lanchester, 1902 is a cymothoid commonly found in the buccal cavity of mainly Tetraodontiformes fishes, distributed in the central and western Indo-Pacific region. This study describes the morphology of each life cycle stage of C. pulchrum: adult female, transitional, adult male, juvenile, and manca. In addition, we obtained DNA sequences linked to the morphological information of this species. We compared it with the sequences in the database using the neighbor-joining tree based on cytochrome c oxidase subunit I (COI) and 16S rRNA. Prior to this study, morphological data on the immature stages of Japanese Cymothoa was limited to juveniles of Cymothoa indica Schioedte and Meinert, 1884. The research identified 12 distinct morphological features that differentiate juvenile C. pulchrum from juvenile C. indica. Molecular analysis revealed that the COI sequences obtained in this study matched some of the C. pulchrum sequences in the database, whereas other sequences in the database formed a clade with Cymothoa eremita (Brünnich, 1783). In the phylogenetic tree based on 16S rRNA, C. pulchrum was also divided into two groups. In the COI phylogenetic tree, C. pulchrum and C. eremita form a total of five groups, and these two species might need to be re-examined taxonomically and molecularly. Full article

Marine–continental transitional shale is a focus of global energy exploration, offering significant but underexplored hydrocarbon potential. Unlike well-studied marine shales, these deposits pose challenges due to complex interactions between marine and continental influences. The lower Xujiahe Formation in the southeastern Sichuan Basin exemplifies this uncertainty, with its depositional environment debated as either continental or transitional. Resolving this issue is critical for refining facies models and improving exploration strategies. This study aims to determine the depositional environment of the lower Xujiahe Formation by integrating sedimentological, paleontological, and geochemical evidence. Field observations identify tidal rhythmites, reverse cross-stratification, and double mud drapes, indicative of tidal influence. Fossil assemblages, including Sulcusicystis sp. and marine-influenced sporopollen sequences, further support marine influence and align with records from the Tanba and Qilixia sections in northeastern Sichuan. Geochemical analysis reveals Sr concentrations (24.47–194.43 ppm), Sr/Ba ratios (0.11–0.65), m-values (4.37–33.08), and CaO/(Fe + CaO) ratios (0.03–0.80), suggesting freshwater to brackish conditions. V/Cr (0.92–2.22) and U/Th (0.18–0.48) ratios indicate a weakly oxidizing environment. Kerogen analysis classifies the organic matter as type II₂–III, suggesting periodic marine influence during deposition. These findings confirm that the lower Xujiahe Formation represents a marine–continental transitional facies, refining previous facies interpretations and providing a basis for more targeted shale gas exploration in the Sichuan Basin and comparable basins worldwide. Full article

The largescale blackfish, Girella punctata Gray, 1835, is important in the fishing industry and recreational fishing, and it is also cultured in East Asia. Cymothoidae (Crustacea: Isopoda) is a group of parasites that infest fish in marine, brackish, and freshwater environments. In this study, we report, for the first time, Ceratothoa arimae (Nunomura, 2001) (Cymothoidae) from the buccal cavity of G. punctata in the Seto Inland Sea, Japan. Ceratothoa arimae showed a prevalence of 29.4–66.7% in G. punctata. The morphology of the mancae of this species was also described in comparison with that of the adult female (ovigerous), transitional stage, and adult male. The manca of Ceratothoa arimae has more chromatophores than those of other Ceratothoa species from Japan, and is a candidate for a future taxonomic trait. This species may have a negative impact on cultured G. punctata, which would be important to determine in future studies. Currently, it is difficult to identify cymothoid mancae species based on their morphology, but the information provided in this study could be useful when combined with other methods developed in the future, such as molecular analysis. Full article

The introduction of renewable energy sources (RESs) in the electricity grid mix is essential for a greener world. Wind offshore energy, known for its high flexibility and social acceptance, plays a significant role in this transition. However, the disposal of non-recyclable epoxy–GFRP wind blades produced and installed in the 1990s and 2000s poses environmental challenges. This study explores the development of a novel wind blade using sustainable materials, aiming to enhance eco-friendliness. A comparative life cycle assessment (LCA) highlights the environmental benefits of replacing epoxy with a thermoplastic recyclable resin in GFRP blades. The findings demonstrate a substantial reduction in environmental footprint, with a 30% decrease in climate change impact, a 97% reduction in freshwater ecotoxicity and a 95% reduction in marine eutrophication. It is evident from the LCA that the replacement of epoxy with a thermoplastic recyclable resin in a GFRP blade substantially reduces its environmental footprint and significantly contributes to the circular economy of RESs. Full article

Estuarine wetlands are the transition zone between marine, freshwater, and terrestrial ecosystems and are more ecologically fragile. In recent years, the spread of exotic vegetation, specifically Spartina alterniflora, in the Yellow River estuary wetlands has significantly encroached upon the habitats of native species such as Phragmites australis, Suaeda glauca Bunge, and Tamarix chinensis Lour. With advances in land prediction modeling, predicting wetland vegetation distribution can aid management and decision-making for ecological restoration. We selected the core area as the study object and coupled the hydrological model MIKE 21 with the PLUS model to predict the potential future distribution of invasive and dominant species in the region. (1) Based on the fine classification results from satellite images of GF1/G2/G5, we gained an understanding of the changes in wetland vegetation types in the core area of the reserve in 2018 and 2020. (2) Using public data such as ERA5 and GEO as input for basic environmental data, using MIKE 21 to provide high-spatial-resolution hydrodynamic parameters for the PLUS model as an environmental driver, we modeled the spatial distribution of various wetland vegetation in the Yellow River estuary wetland in Dongying under different artificial restoration measures. (3) We predicted the 2022 distribution of typical vegetation in the region, used the classification results of GF6 as the actual distribution, compared the spatial distribution with the actual distribution, and obtained a kappa coefficient of 0.78; the predicted values of the model are highly consistent with the true values. This study combines the fine classification results of vegetation based on hyperspectral remote sensing, the construction of a coupled model, and the prediction effect of typical species, providing a reference for constructing and optimizing the vegetation prediction model of estuarine wetlands. It also allows scientific and effective decision-making for the management of ecological restoration of delta wetlands. Full article

This study focuses on the analysis of sediment core retrieved from the deepest part (25 m) of Pirovac Bay. A long sedimentary sequence (7.45 m) supplemented by a shorter sediment core (1.45 m) from a shallower part of the bay was analyzed for sedimentological, mineralogical, geochemical, and micropaleontological (ostracod) parameters. The sediment thickness above the underlying karst paleorelief (karstic bedrock) is up to 12 m. Sediments recorded a transition from a freshwater to a marine environment starting from post-Neapolitan Yellow Tuff tephra sedimentation. First, the floodplain developed in Pirovac Bay, with intermittent pools and ponds, followed by wetland environment. The formation of a shallow freshwater paleolake during the Middle Holocene at 10 cal kyr BP was enabled by the rising sea level and high freshwater input from the karstified underground from the adjacent Lake Vrana (Biograd na Moru). The onset of marine intrusions through the karstified underground is evident with formation of a brackish lake in the Pirovac Bay basin. Marine transgression and flooding of the bay occurred at 7.3 cal kyr BP, evidenced by the geochemical and ostracod parameters, providing crucial insights into the dynamics of coastal inundation under past climate change. Intriguingly, freshwater ostracod species were still present in the marine sediments, brought into the bay from Lake Vrana through surficial canal Prosika and groundwater discharge (numerous estavelles) along the northeastern shores of the bay, proving their mutual influence. This submerged Holocene freshwater paleolake, reported here for the first time, underlines the sensitivity of coastal karst systems to the rise in sea level and serves to stress how important understanding of these processes is for effective management in coastal zone and climate change adaptation strategies. The findings provided evidence supporting the existence of coastal marine basins as freshwater lakes prior to being flooded by seawater as a consequence of the Holocene post-glacial sea level rise. Full article

Freshwater slugs are scarce and belong exclusively to panpulmonate Acochlidimorpha. There is a radiation of eight species of large-sized slugs living benthically in rivers on tropical Indo-Pacific Islands. In the Western Atlantic, only one small interstitial slug, Tantulum elegans Rankin, 1979, is known from the Caribbean island of St. Vincent. We recently discovered a novel species of freshwater slugs in Cuba. Here, we describe Potamohedyle espinosai n. gen. n. sp., which is the first freshwater slug in the region of the Western Atlantic with a benthic lifestyle, in 3D-microanatomical and histological detail using light and scanning electron microscopy. It shows a mix of characters from different freshwater acochlidimorph genera, such as a medium body size, the presence of an osphradial ganglion, a distal gonoduct with a muscular sphincter, a penis with a solid thorn and cuticular comb, and a basal finger with a hollow stylet. Morphological adaptations to a life in freshwater include multiplicated renopericardioducts. The taxonomic character mix justifies the establishment of a novel genus within the herein diagnostically modified freshwater family Tantulidae. A molecular phylogenetic hypothesis of riverine slugs including the first Caribbean representatives suggests that the transition to freshwater occurred once along the stemline of limnic Acochlidiidae, secondarily marine Pseudunelidae and limnic Tantulidae. Full article

Water quality indicator algorithms often separate marine and freshwater systems, introducing artificial boundaries and artifacts in the freshwater to ocean continuum. Building upon the Ocean Colour- (OC) and Lakes Climate Change Initiative (CCI) projects, we propose an improved tool to assess the interactions across river–sea transition zones. Fuzzy clustering methods are used to generate optical water types (OWT) representing spectrally distinct water reflectance classes, occurring within a given region and period (here 2016–2021), which are then utilized to assign membership values to every OWT class for each pixel and seamlessly blend optimal in-water algorithms across the region. This allows a more flexible representation of water provinces across transition zones than classic hard clustering techniques. Improvements deal with expanded sensor spectral band-sets, such as Sentinel-3 OLCI, and increased spatial resolution with Sentinel-2 MSI high-resolution data. Regional clustering was found to be necessary to capture site-specific characteristics, and a method was developed to compare and merge regional cluster sets into a pan-regional representative OWT set. Fuzzy clustering OWT timeseries data allow unique insights into optical regime changes within a lagoon, estuary, or delta system, and can be used as a basis to improve WQ algorithm performance. Full article