Search Results (532)

Benthic chambers measure the sediment–seawater solute exchange. In cohesive sediments, this exchange may scale with the sediments’ diffusive boundary layer (DBL) thickness and thus the intensity of chamber water agitation. To investigate this, we deployed a customised Unisense A/S MiniChamber lander with an opaque, stirred benthic chamber on the subtidal seafloor of Queen Charlotte Sound, New Zealand. We deployed the chamber at 18 sites over six days, during the morning, midday, and the afternoon, using four stirrer speeds (10, 17, 26, 35 rpm). All but the highest stirrer speed allowed particles resuspended during chamber deployment to settle. Sediment total O₂ uptake (TOU) ranged from 614 to 1125 µmol m⁻² h⁻¹. Ammonium, phosphorus, and nitrate fluxes indicated consistent sediment release, except for two deployments that showed nitrate uptake. Statistical analyses revealed a negative effect of the initial chamber turbidity on TOU, but failed to detect effects of stirrer speed or time of day on any measured flux. Variation in TOU was minimal across stirrer speeds at midday but higher during the morning and afternoon. We discuss these observations in the context of sediment disturbance during deployment and diel variations in infaunal activity. Overall, our results align with those of previous studies using different chambers, indicating that chamber-derived sediment–seawater solute flux estimates may be unaffected by chamber water agitation intensity. Full article

This study evaluated the influence of Pseudocnus dubiosus density on the bioremediation of organically enriched marine sediments collected from El Ferrol Bay (Áncash, Peru). A laboratory experimental design was applied, comprising one control treatment without organisms and three treatments with increasing densities of P. dubiosus (27, 41 and 54 individuals per experimental unit), each with three replicates. The physicochemical parameters of the system, sediment organic matter reduction and the organoleptic changes associated with the process were assessed. The results showed that the presence of the organism significantly enhanced organic matter removal compared with the control, which achieved only a 0.97% cumulative reduction, whereas the treatments with organisms reached 34.42%, 40.97% and 43.36%, respectively. In the higher-density treatments, turbidity increased, while nitrate, phosphate and chemical oxygen demand (COD) decreased, suggesting intensified bioturbation, particle resuspension and transformation of organic compounds at the sediment–water interface. Although all evaluated densities produced a favourable functional response, the greatest numerical efficiency was recorded at the highest density. Overall, the findings support the potential of P. dubiosus as a benthic organism for application in bioremediation strategies aimed at coastal ecosystems degraded by organic matter accumulation. Full article

Upon entering aquatic ecosystems, coal fly ash (CFA) particles and their leachates distribute across all environmental compartments, from surface water to benthic sediments, rendering them accessible to aquatic organisms spanning multiple trophic levels. Although CFA is widely classified as non-hazardous waste, a growing body of toxicological evidence demonstrates its capacity to induce significant adverse biological effects. This discrepancy between laboratory-demonstrated toxicity and its current non-hazardous regulatory status highlights a critical knowledge gap in risk assessment frameworks and testing philosophies. Herein, we provide a comprehensive review of CFA characterization techniques, leaching methodologies and their environmental relevance, and the aquatic ecotoxicity of both particulates and leachates to primary, secondary, and tertiary consumers. Based on the findings from the review, we propose four paradigm shifts to more accurately characterize CFA ecotoxicological risks: from standardized leaching protocols to application-specific and maximum leachability tests, from single-species assays to multi-trophic-level bioassays, from single-metal analysis to comprehensive, whole-matrix testing that integrates particulate and dissolved fractions, and from standardizing the reporting of CFA provenance, coal types, and combustion conditions to meaningful meta-analyses and cross-study comparisons. It is believed that these suggestions will substantially advance the realistic ecotoxicological assessment of CFA and bridge the gap between laboratory toxicity data and regulatory classification. Full article

Microplastics (MPs) widely distribute in marine environments and generate severe hazards to marine biota, yet little is known regarding the toxic impacts of aged MPs on benthic invertebrates and their surrounding sediment microbiota. This work aimed to fill this research gap by exploring the comprehensive toxicity of aged polymethylmethacrylate microplastics (PMMA-MPs) toward Urechis unicinctus and its sediment habitat. A 21-day laboratory exposure trial was performed with two PMMA-MP treatments: environmentally realistic low concentration (10 μg/L) and extreme high concentration (1000 μg/L). Aged PMMA-MPs accumulated in the body wall and intestine of U. unicinctus, with markedly higher body wall MPs loads in the high-dose group (p < 0.05). High-concentration PMMA-MPs significantly raised intestinal total protein and triggered intense oxidative stress (p < 0.01), and the Integrated Biomarker Response value rose dose-dependently. Sediment microbial β-diversity was obviously reshaped (p < 0.05), with enriched pathogens including Klebsiella and Enterobacteriaceae under high MP exposure, while the worm’s intestinal α-diversity and core microbiome remained stable, showing host adaptability. This study reveals multi-level toxic outcomes of aged PMMA-MPs on benthic worms and their sediment microhabitat, offering fundamental data to evaluate the ecological risks of weathered MPs in marine benthic systems. Full article

This study presents a high-resolution geomorphological and habitat map of the Sinuessa coastal sector (Tyrrhenian Sea), revealing the presence of an extensive and exceptionally shallow coralligenous bank developed between 5 and 16 m water depth. Multibeam bathymetry, side-scan sonar backscatter, sediment analyses, and Remotely Operated Vehicle (ROV) observations were integrated within a Geographic Information System (GIS) framework to characterize seabed morphology, acoustic facies, and associated benthic habitats. ROV surveys document a diverse macro- and epimegabenthic community, including both sciaphilous and photophilous taxa, as well as several protected and structuring species. Water depth alone does not discriminate among the mapped substrate classes (Kruskal–Wallis, p = 0.578), whereas acoustic backscatter, slope, and terrain ruggedness all do (p < 0.01), indicating that depth-independent controls govern the distribution of the bioconstruction. We hypothesize that persistently elevated turbidity and terrigenous input from the Volturno and Garigliano river systems reduce light penetration and generate, at 5–16 m, optical conditions comparable to those normally found at greater depths. This hypothesis is consistent with the geomorphological, sedimentological, and biological evidence presented here and with published oceanographic observations in the Gulf of Gaeta, but it has not been verified by in situ optical measurement, which we identify as the priority for future work. Relative backscatter intensity correlates significantly with mean grain size (Spearman ρ = −0.710, p < 0.001) and with gravel and mud content, and the four mapped classes differ significantly in backscatter, slope, and terrain ruggedness. These findings provide new insights into the environmental controls on coralligenous development and highlight the ecological relevance of shallow, turbidity-driven coralligenous systems within highly impacted Mediterranean coastal areas, with direct implications for habitat conservation and spatial management. Full article

Understanding niche differentiation and interspecific coexistence patterns of macrobenthos provides critical references for ecological assessment of bivalve aquaculture. Seasonal field surveys (Autumn 2023–Summer 2024) across 12 sampling sites were conducted in an intensive Meretrix meretrix tidal flat farm in Rudong, Jiangsu. Synchronous water depth, sediment grain size and total organic carbon (TOC), and salinity were measured at each station to characterize habitat gradients; no unfarmed reference tidal flats were included, so all community patterns only reflect within-farm variation. The study area has sustained 10-year continuous bottom culture with baseline juvenile stocking density of 250 ind./m² and twice-yearly manual harvesting. A total of 58 macrobenthic taxa were identified, and 13 dominant species were screened with a dominance index threshold Y > 0.02. All abundance data were fourth-root-transformed before Bray–Curtis community analysis to reduce bias of hyper-abundant taxa. Standardized Shannon niche breadth (0–1 normalized, r = 48 site–season composite units) and permutation-tested (999 replicates) Pianka niche overlap/similarity coefficients were calculated to quantify resource utilization similarity. Niche breadth ranged from 0.018 to 0.971, with farmed M. meretrix showing the maximum value, indicating broader seasonal resource adaptation. High niche overlap (>0.50) was detected between M. meretrix and four wild dominant species (Nephtys californiensis, Moerella iridescens, Lingula anatina, Umbonium thomasi). Notably, niche metrics derived solely from spatial abundance data cannot directly confirm interspecific competition or trophic segregation; the stable coexistence observed in our assemblage is tentatively hypothesized to be driven by vertical sediment partitioning and divergent feeding guilds based on published functional studies, without direct in situ trophic or stratified sediment evidence from this work. Hierarchical UPGMA clustering (0.35 Bray–Curtis distance threshold) and corrected NMDS ordination (48 site–season units, dominant-species fitted vectors) illustrated distinct functional groups. Based on the observed niche convergence among filter-feeding bivalves under local farming conditions, the range of 230–280 ind./m² is presented as an observational reference. Controlled manipulative experiments with gradient stocking densities are needed to test whether this range can balance aquaculture yield and benthic biodiversity. Full article

Light limitation can constrain primary production and ecosystem recovery in shallow eutrophic lakes even when nutrients remain abundant. We evaluated the effects of reduced physical disturbance on underwater light availability in Utah Lake, Utah, USA, using large limnocorrals that reduced exposure to wave-driven disturbance and restricted access by benthivorous fishes. Water transparency was assessed using Secchi depth during 2022–2023 and vertical profiles of photosynthetically active radiation (PAR) during 2024; the two datasets were analyzed independently. The mean Secchi depth was approximately 81% greater inside than outside the limnocorrals (39.8 vs. 22.0 cm; p < 0.001). Similarly, PAR declined to a theoretical photosynthetic threshold of 0.01 µmol photons m⁻² s⁻¹ at an estimated depth of 101 cm inside the corrals compared with 81 cm outside the corrals, representing a 25% increase in potential photosynthetic depth. Phytoplankton biovolume was not a detectable predictor of Secchi depth after accounting for treatment and month (p = 0.996), although chlorophyll a and phycocyanin were associated with PAR at shallow depths and phytoplankton became more important during late-season bloom conditions. Total suspended solids (TSSs) were associated with PAR throughout the measured depth profile but differed only slightly between treatments (72.89 vs. 75.16 mg L⁻¹; p = 0.08). Thus, the large optical response cannot be explained by changes in bulk TSS concentration alone and may instead reflect changes in the optically active suspended-particle fraction, including preferential settling of fine, strongly scattering particles; particle-size distributions and optical properties were not directly measured. These results demonstrate that reducing physical disturbance can substantially improve underwater light conditions in a large, shallow, nutrient-rich lake. Management approaches that reduce sediment resuspension and restore benthic light availability may therefore provide a direct pathway toward ecosystem reorganization, particularly where large internal nutrient stores and atmospheric inputs limit the effectiveness of external nutrient reductions alone. Full article

River sediments act not only as important sinks for heavy metal pollution in watersheds, but also as potential secondary sources under changing environmental conditions. Heavy metals can enter river systems through industrial wastewater discharge, agricultural non-point runoff, urban stormwater and sewage inputs, mining and smelting activities, and atmospheric deposition. During adsorption onto suspended particles, sedimentation, and resuspension, metals such as Cd, Pb, Cr, Cu, Zn, Ni, As, and Hg progressively accumulate in sediments. Because heavy metals are persistent, non-degradable, and bioaccumulative, contaminated sediments can record historical watershed pollution while also releasing metals back into overlying water under hydrodynamic disturbance, pH and redox fluctuations, organic matter mineralization, benthic bioturbation, and dredging activities, thereby threatening aquatic ecosystem stability and human health. Using a global methodological framework with particular emphasis on Chinese river basins, this review systematically summarizes key issues in the study of heavy metal pollution in river sediments, including spatial–temporal distribution and operationally defined fractionation, pollution levels and ecological risk assessment, source apportionment, and remediation and management technologies. Current evidence indicates that heavy metal contamination in river sediments exhibits pronounced spatial heterogeneity and watershed-specific characteristics. Its distribution is jointly controlled by geological background, land use patterns, source input intensity, hydrodynamic conditions, sediment particle size composition, and organic matter content. Methodologically, the field has evolved from single total concentration monitoring and exceedance-based evaluation toward integrated assessment systems that combine total concentrations, operationally defined fractionation, bioavailability, ecological risk, health risk, and source contribution. The joint use of BCR sequential extraction, the geoaccumulation index (Igeo), the pollution load index (PLI), the potential ecological risk index (RI), the risk assessment code (RAC), sediment quality guidelines (SQGs), receptor models, isotope tracing, and machine learning has substantially improved pollution identification, risk zoning, and source apportionment. Overall, research on heavy metal pollution in river sediments has shifted from descriptive judgments of whether contamination exists toward mechanistic and management-oriented questions concerning pollution sources, risk evolution, and remediation strategies. However, important gaps remain in compound pollution transformation mechanisms, regional background values and evaluation benchmarks, uncertainty in model parameters, long-term dynamic monitoring, and engineering-scale verification of remediation technologies. Future studies should strengthen multi-media, multi-scale, and long-term monitoring and further integrate fractionation analysis, toxicological effects, source apportionment models, and remediation technologies to provide a scientific basis for watershed ecological security and precision management of contaminated sediments. Full article

Chemical weathering and biogenic silicate regeneration do not fully explain rapid benthic dissolved silicate (DSi) surges or the presence of polymeric species. This study investigates DSi distribution in freshwater lake pore water to identify alternative supply routes. Crucially, we distinguish this pathway from bio-silicification by demonstrating an abiotic, mineral-surface-induced polymerization pathway. DSi distribution strongly correlates with dissolved Fe and Mn. Under anoxia, the relative increase in dissolved metals contracts the practical gap with dissolved total silicate, supported by systematic shifts in standardized effect sizes (Fe: d = 0.35 to 0.21; Mn: d = 0.76 to 0.64). Furthermore, segmented regression analysis identified a statistically significant structural break at a distinct threshold of 665 µM (p < 0.01), beyond which the silicate accumulation rate sharply accelerates. By pooling datasets across divergent basins—robustly justified by size-independent standardized effect sizes (d = 0.220) and converged common language effect sizes (55–63%)—these findings provide compelling evidence for silicate polymerization mediated by iron oxides within lake sediments. We demonstrate that these internally synthesized polymers are released into the water column during benthic redox transitions, persisting as a stable fraction of the total DSi pool. Consequently, a substantial driver of DSi enrichment in anoxic benthos is the mobilization of silicates previously adsorbed onto metal oxides, a portion of which is sequestered in polymeric form. While these polymers diffuse into the hypolimnion alongside monomers, they remain biologically unavailable, representing a unique geochemical sink that constrains overall silicate bioavailability. Full article

Copper-based nanopesticides are increasingly explored as nano-enabled alternatives to conventional copper pesticides because they may improve deposition, antimicrobial efficacy, and material-use efficiency. Their environmental risk, however, cannot be inferred from total copper concentration or from the toxicity of pristine particles alone. After agricultural application, copper-based nanoforms may be transported to soils, drainage waters, wetlands, and sediments, where aggregation, dissolution, aging, sulfidation, organic complexation, and biological processing reshape their speciation and bioavailability. This review critically examines copper-based nanopesticides at the benthic interface, with emphasis on environmental transformation, synchrotron-resolved speciation, lower-trophic invertebrate exposure, trophic transfer, and food-web risk. We highlight that sediment-associated organisms are not only toxicity endpoints but also biological processors and vectors of transformed copper species. Evidence from stable-isotope tracing, dietary exposure studies, mesocosms, and micro-food-web experiments shows that copper-based nanoforms can enter aquatic, benthic, and terrestrial food chains. However, most studies demonstrate transfer or accumulation rather than consistent biomagnification across trophic levels. We further argue that future risk assessment should move beyond single-material and single-endpoint testing toward transformation-aware, route-specific, and food-web-relevant frameworks. Integrating total copper analysis with particle-specific measurements, synchrotron-based speciation where analytically feasible, realistic lower-trophic exposure models, and ecosystem-level endpoints will be essential for evaluating the long-term risks of copper-based nanopesticides. Full article

The Jobos Bay National Estuarine Research Reserve (JBNERR) includes the largest bay on the southern coast of Puerto Rico. The reserve includes diverse habitats ranging from mangrove forests, shallow lagoons, seagrass beds, cays and coral reefs, with a broad range of environmental gradients between the populated coastal plain and the oligotrophic Caribbean Sea. As the only research reserve in the region, resource managers seek cost-effective and reliable processes to restore and promote ecosystem health in the reserve. Benthic foraminiferal assemblages are widely applied bioindicators for assessing coastal environments, notably coral reefs and seagrass ecosystems. This study evaluated the applicability of three indices, the FoRAM Index (FI), the Epiphytic FoRAM Index (FI′), and the Long vs. Short Life-Span Index (I_LS), to assess bayside and reef habitats bordering three cays of Jobos Bay. Surficial sediment samples were collected in 2018 and 2019. Environmental data included sediment composition (e.g., texture, total organic content) and water quality (e.g., nutrients and pH). From a total of 57 samples, 4671 individuals were counted, representing 35 genera. Cluster analysis based on genus-level relative abundances revealed four main groups: Dominant (>10%), Common (5–10%), Occasional (1–4%), and Rare (<1%). Dominant genera included Quinqueloculina (24%) and Amphistegina (18%). Common taxa included smaller rotaliids such as Rotorbinella (6%) and miliolids such as Pyrgo (5%). Twelve genera were occasional, including Triloculina (4%) and Elphidium (3%). Tests of 16 genera occurred rarely (<1%), including agglutinated taxa such as Textularia and stress-tolerant forms like Bolivina. In total, FI values ranged from 1.3 to 9.6, FI′ from 1.9 to 9.7, and I_LS from 0.5 to 30.6. Bayside samples scored generally lower compared to reef samples. In summary, foraminiferal assemblages and associated bioindices indicated that environmental conditions supported Foraminifera that host algal symbionts in the reef environments and the prevalence of macroalgae and seagrass in the bayside benthos. Full article

Halimeda-dominated habitats are ecologically significant tropical benthic ecosystems whose structural complexity supports diverse marine organisms, particularly associated microbes. However, the characteristics and ecological roles of these bacterial communities and their connectivity within Halimeda-dominated habitats remain poorly understood. This study examined microbial diversity and composition across four microenvironments of a Halimeda meadow, namely, ambient seawater, sediment, Halimeda thalli, and Holothuria atra feces, using the V3–V4 region of the 16S rRNA gene. A total of 44 phyla, 733 genera, and 827 species were identified, with Proteobacteria, Cyanobacteria, Bacteroidota, Desulfobacterota, and Actinobacteriota dominating across all samples. Microbial diversity and composition differed significantly among microenvironments, with sediment showing the highest species diversity and seawater showing the lowest. Halimeda thalli were dominated by Alphaproteobacteria, particularly Phycisphaerae and Parcubacteria, associated with nutrient cycling on macroalgal surfaces. Sediment was enriched with Desulfobacteria, Actinobacteria, and Chloroflexi. Seawater was characterized by Synechococcus CC9902, a primary producer in tropical waters. H. atra feces were dominated by Bacteroidia and Bdellovibrionota, representing a distinct bacterial community shaped by both gut-associated taxa and microorganisms derived from ingested sediments. Only 6.95% of genera were shared across all microenvironments, and feces and sediment shared the highest overlap (47.28%), suggesting that H. atra acts as a biogeochemical bridge that repackages benthic organic matter without fundamentally altering its microbial identity. The low overlap between Halimeda and seawater, as well as between seawater and both sediment and sea cucumber feces, suggests strong habitat-specific bacterial community assembly, with algal-associated bacterial communities being distinct from pelagic communities and seawater communities differing from benthic and fecal communities. Full article

Seagrass and macroalgae are critical components of shallow coastal habitats undergoing fragmentation due to environmental and anthropogenic stressors. Mapping and monitoring their extent are essential for understanding and managing ecosystem changes. Hyperspectral imaging (HI) is an emerging tool for ocean mapping, providing spectral reflectance per image pixel for benthic habitat mapping. This study evaluated the use of multiscale hyperspectral mapping of shallow seagrass and macroalgae habitats using two platforms: an Uncrewed Aerial Vehicle (UAV-HI, 10 × 10 cm spatial resolution, 20,200 m² coverage) and an Uncrewed Surface Vehicle (USV-UHI, 1 × 1 cm resolution, 230 m² coverage). A spectral angle mapper (SAM) classification algorithm was applied with varying thresholds to assess classification performance. As much as 2316 m² (11.5% of total area) was estimated to be seagrass by spectral angle mapper algorithms; of this, 150 m² was mapped at the centimeter scale by the USV. The overall accuracies of the SAM classifications reached 89% and 86% for the UAV and USV, respectively, for a subsampled overlapping area. With the training data available, the UAV performs better in the accurate classification of seagrass and brown algae; however, this is collected at a coarser resolution (10 × 10 cm). The lower accuracy across both platforms is explained by a higher rate of false positives in the sediment class, which was supported by corresponding Intersect over Union (IoU) and recall metrics. The classification and accuracy assessment presented in this study support the proposed uses of both platforms. These results contribute to the development of a methodological approach to hyperspectral imaging applications for mapping seagrass and macroalgal habitats, with clear relevance for environmental monitoring and management. Full article

Shallow lakes are vulnerable to multiple anthropogenic stressors. However, the spatial responses of benthic ecosystems to these composite disturbances and the underlying mechanisms driving them remain poorly understood. Nansi Lake is a strategic water-regulating reservoir of the Eastern Route of the South-to-North Water Transfers. It has long been subjected to multiple human activities, and its aquatic ecological environment exhibits pronounced spatial heterogeneity. A systematic assessment is thus needed to evaluate the spatial distribution patterns of surface-sediment diatom communities and their trophic response characteristics. This study integrates the Trophic Diatom Index (TDI) with multivariate statistical approaches. It analyzes the spatial distribution and driving factors of surface-sediment diatom assemblages based on diatom and water quality data from 62 sampling sites. The results reveal three distinct community zones across the lake. The first is a high-disturbance zone dominated by hydraulic regulation and mining activities. In this zone, Stephanodiscus parvus Stoermer & Håkansson is the absolute dominant species, indicating a clear eutrophic status. The second is a hydrochemically stable zone dominated by Achnanthidium minutissimum (Kützing) Czarnecki, exhibiting relatively high community integrity. The third is a vast central open-water zone characterized by the dominance of Pseudostaurosira brevistriata (Grunow) Williams & Round, representing a mesotrophic transitional state. Partial redundancy analysis (pRDA) shows that multiple explanatory variables jointly explain 28.91% of the community variation. The independent explanatory powers of anthropogenic variables (9.12%) and environmental factors (7.94%) are both higher than that of pure spatial dispersal processes (0.35%). Redundancy Analysis (RDA) indicates that different types of human activities—such as reservoir regulation, coal mining, and estuarine inflows—may influence the spatial distribution patterns of surface-sediment diatoms. They do so by jointly driving variations in lake trophic status and the ionic environment, particularly Mg²⁺ and SO₄²⁻. This study provides a scientific basis for the water resource management of shallow lakes subject to anthropogenic impacts. Full article

Biodiversity loss in aquatic ecosystems is accelerating, yet whether the effects of different biodiversity facets on biogeochemical processes are consistent or environmentally contingent remains poorly understood. Benthic invertebrate bioturbators drive nutrient exchange at the sediment–water interface of shallow aquatic ecosystems, but how sediment trophic status modulates the effects of their richness, identity, and composition on benthic–pelagic nutrient cycling is unclear. We conducted a factorial microcosm experiment using three functionally and phylogenetically distinct species—Campsurus melanocephalus (Ephemeroptera), Heteromastus similis (Polychaeta), and Heleobia australis (Gastropoda)—assembled as monocultures, bicultures, and tricultures across a gradient of sediment organic matter concentration ([OM]) representative of natural variability in a neotropical coastal lagoon. Species richness produced a consistent, saturating enhancement of NH₃ fluxes that was independent of sediment trophic status, while species identity strongly differentiated monoculture effects in a pattern that was likewise stable across the [OM] gradient. In contrast, although biculture compositions did not differ from one another across the [OM] gradient, the overall magnitude of biculture-mediated NH₃ fluxes increased with sediment trophic status, suggesting that multispecies assemblage effects are more responsive to environmental context than those of single species. These findings reveal that biodiversity facets diverge not only in how strongly they affect ecosystem functioning, but also in how sensitive their effects are to environmental variation. We therefore conclude that predicting benthic–pelagic nutrient exchange in shallow coastal ecosystems requires considering both the biological structure of bioturbator assemblages and the organic matter context of the sediment. Full article