How sediment dredging alters phosphorus dynamics in a lowland rural river?

China's lowland rural rivers are facing severe eutrophication problems due to excessive phosphorus (P) from anthropogenic activities. However, quantifying P dynamics in a lowland rural river is challenging due to its complex interaction with surrounding areas. A P dynamic model (River-P) was specifically designed for lowland rural rivers to address this challenge. This model was coupled with the Environmental Fluid Dynamics Code (EFDC) and the Phosphorus Dynamic Model for lowland Polder systems (PDP) to characterize P dynamics under the impact of dredging in a lowland rural river. Based on a two-year (2020-2021) dataset from a representative lowland rural river in the Lake Taihu Basin, China, the coupled model was calibrated and achieved a model performance (R2>0.59, RMSE<0.04 mg/L) for total P (TP) concentrations. Our research in the study river revealed that (1) the time scale for the effectiveness of sediment dredging for P control was ∼300 days, with an increase in P retention capacity by 74.8 kg/year and a decrease in TP concentrations of 23% after dredging. (2) Dredging significantly reduced P release from sediment by 98%, while increased P resuspension and settling capacities by 16% and 46%, respectively. (3) The sediment-water interface (SWI) plays a critical role in P transfer within the river, as resuspension accounts for 16% of TP imports, and settling accounts for 47% of TP exports. Given the large P retention capacity of lowland rural rivers, drainage ditches and ponds with macrophytes are promising approaches to enhance P retention capacity. Our study provides valuable insights for local environmental departments, allowing a comprehensive understanding of P dynamics in lowland rural rivers. This enable the evaluation of the efficacy of sediment dredging in P control and the implementation of corresponding P control measures.

Impacts of rapidly urbanizing watershed comprehensive management on per- and polyfluoroalkyl substances pollution: Based on PFAS "diversity" assessment.

The impact of watershed comprehensive management (WCM) on per- and polyfluoroalkyl substances (PFAS) pollution in rapidly urbanizing areas remains unclear. In a typical rapidly urbanizing watershed of Shenzhen, China, we investigated temporal variations in contamination level, primary source and ecological risk of 50 emerging and legacy PFAS, as well as the replacement trends of emerging PFAS before and after WCM during a six-year sampling campaign. We found that large-scale dredging was a non-negligible factor in abnormally increased PFAS concentrations (6.43 %-456.16 %) during WCM through their release from river sediments. To better characterize the diverse and complex PFAS contamination, a novel pollution assessment method, PFAS "diversity", was adopted based on a modified Shannon-Weiner diversity index and Pielou evenness index, reflecting numbers of PFAS detected and how evenly each PFAS contributed to the total PFAS concentrations at specific sampling sites. Importantly, we found that the Pielou evenness index can indicate and quantify abnormal pollution sources (especially point sources) along the river. The results revealed that WCM did not effectively reduce total PFAS concentrations and diversity in the rapidly urbanizing watershed but obviously improved point source pollution. Furthermore, 6:2 polyfluorinated phosphate diesters and hexafluoropropylene oxide dimer acid (GenX) that posed high ecological risks emerged and the number of sampling sites with high risk increased from 16 to 20 after WCM. Finally, we summarize several important issues related to PFAS contamination during WCM and propose specific countermeasures, such as adopting environmental dredging and reducing the proportion of ecological water replenished by wastewater treatment plant effluent for better control of PFAS pollution. Our study highlighted the limited effectiveness of WCM in mitigating PFAS pollution and the importance of emerging contaminant regulation in rapidly urbanizing watersheds during WCM.

Assessment of the effects of dredging on metal levels in port waters using DGT passive samplers and spot sampling.

Aiming at assessing the effect of dredging activities on the levels of metals in Bilbao Port (northern Spain), dissolved and labile metal concentrations in the water were concurrently measured, before, during, and after dredging activities by spot sampling and Diffusive Gradients in Thin-films (DGTs) passive samplers, respectively. Most of the dissolved metal results were below the quantification limits (Cd, <0.06-0.26 µg/L; Co, <5 µg/L; Cu, <5-15 µg/L; Fe, <10-48 µg/L; Mn, <10-22 µg/L; Ni, <2.6-7 µg/L; Pb, <0.39-0.8 µg/L; Zn, <9-24 µg/L). In contrast, DGT results for all sampling times and stations were obtained (Cd, 0.02-0.12 µg/L; Co, 0.08-0.15 µg/L; Cu, 0.5-2.8 µg/L; Fe, 1.0-3.6 µg/L; Mn, 4.7-23.5 µg/L; Ni, 0.5-0.9 µg/L; Pb, 0.15-0.28 µg/L; Zn, 2.6-7.2 µg/L), enabling to determine those metals affected by dredging. Only labile-Pb concentration surpassed momentarily the DGT-Environmental Quality Standard, enabling to rule out biological effects on biota. DGTs are a promising technique for facilitating decision-making during dredging operations.

An assessment of maintenance works and their impact on macroinvertebrate communities and long-term recolonization to small lowland watercourses.

Due to their small size and high anthropogenic pressure, small watercourses are particularly prone to severe siltation and are densely overgrown with macrophytes. Many of these watercourses are subject to regular maintenance works (RMW), consisting of seasonal desilting and vegetation clearance, in order to ensure unobstructed water flow. The aim of the study was to assess the impact of three types of maintenance works: dredging and mud removal (DMR), river channel vegetation removal (RCVR) and river bank vegetation removal (RBVR) on taxa species richness, macroinvertebrate density and the Shannon-Wiener diversity index, as well as their changes and long-term benthic recolonization one and two years after completion of the works. The study was carried out in 21 habitats on eight rivers in the European Central Plains Ecoregion. A total of 107 zoobenthic taxa were found at all sites, and their species composition was characteristic of highly hydrophytic waters with low hydrological and hydrochemical quality parameters. A significant decrease in macroinvertebrate taxa richness was observed one year after the works, as the average number of taxa had dropped from thirteen to eight, with a further fall to seven taxa two years after the RMW. The same was true for density, which had decreased from an average of 2496 to 786 individuals per square meter one year after the RMW, while, a gradual recolonization was recorded two years after the RMW, with an average density of 1295 individuals per square meter. The Shannon-Wiener index, which had averaged 2.528 before the RMW, also decreased, falling to 1.982 and 1.832 one and two years after. BACI statistical analyses showed that of the three types of maintenance work, desilting and bottom sediment removal had the largest negative impact, significantly reducing taxonomic composition (by an average of 53%), density (by an average of 43%), and ecological index values (by an average of 40%). Over-frequent maintenance can prevent macroinvertebrate populations from recovering, thus depleting the environment of valuable taxa, including those that provide food for fish and other vertebrates.

Assessment of the renal function and fibrosis indexes of conventional western medicine with Chinese medicine for dredging collaterals on treating renal fibrosis: A systematic review and meta-analysis.

To investigate the renal function and fibrosis indexes of conventional western medicine with Chinese medicine for dredging collaterals in the treatment of renal fibrosis (RF). We searched articles from databases (PubMed, Embase, The Cochrane Library, CNKI, and Wanfang data) and references of included studies. The quality of literature was evaluated and data were extracted in regard to the inclusion and exclusion criteria. RevMan5.3 software was applied for all statistical analyses. Eleven eligible RCTs with a total of 898 patients were included in this meta-analysis. Compared with conventional western medicine alone, conventional western medicine with Chinese medicine for dredging collaterals in the treatment of RF has lower BUN levels and SCr levels (P < 0.05). As for fibrosis indexes, conventional western medicine with Chinese medicine for dredging collaterals has lower HA, laminin (LN), IV-Col, and PC-III levels (P < 0.05). Conventional western medicine with Chinese medicine for dredging collaterals with lower BUN, Scr, HA, LN, PC-III, and IV-Col levels, has an advantage in the treatment of RF. These lower serum levels may not be associated with the presence of RF. Ideally, kidney biopsies should be performed to confirm that these markers reduce RF. This is a major limitation of this study.

Scorpiones, Scolopendra and Gekko Inhibit Lung Cancer Growth and Metastasis by Ameliorating Hypoxic Tumor Microenvironment via PI3K/AKT/mTOR/HIF-1α Signaling Pathway.

OBJECTIVE: To investigate whether Buthus martensii karsch (Scorpiones), Scolopendra subspinipes mutilans L. Koch (Scolopendra) and Gekko gecko Linnaeus (Gekko) could ameliorate the hypoxic tumor microenvironment and inhibit lung cancer growth and metastasis by regulating phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin/hypoxia-inducible factor-1α (PI3K/AKT/mTOR/HIF-1α) signaling pathway. METHODS: Male C57BL/6J mice were inoculated with luciferase labeled LL/2-luc-M38 cell suspension to develop lung cancer models, with rapamycin and cyclophosphamide as positive controls. Carboxy methyl cellulose solutions of Scorpiones, Scolopendra and Gekko were administered intragastrically as 0.33, 0.33, and 0.83 g/kg, respectively once daily for 21 days. Fluorescent expression were detected every 7 days after inoculation, and tumor growth curves were plotted. Immunohistochemistry was performed to determine CD31 and HIF-1α expressions in tumor tissue and microvessel density (MVD) was analyzed. Western blot was performed to detect the expression of PI3K/AKT/mTOR/HIF-1α signaling pathway-related proteins. Enzyme-linked immunosorbent assay was performed to detect serum basic fibroblast growth factor (bFGF), transforming growth factor-ß1 (TGF-ß1) and vascular endothelial growth factor (VEGF) in mice. RESULTS: Scorpiones, Scolopendra and Gekko prolonged the survival time and inhibited lung cancer metastasis and expression of HIF-1α (all P<0.01). Moreover, Scorpiones, Scolopendra and Gekko inhibited the phosphorylation of AKT and ribosomal protein S6 kinase (p70S6K) (P<0.05 or P<0.01). In addition, they also decreased the expression of CD31, MVD, bFGF, TGF-ß1 and VEGF compared with the model group (P<0.05 or P<0.01). CONCLUSION: Scorpiones, Scolopendra and Gekko all showed beneficial effects on lung cancer by ameliorating the hypoxic tumor microenvironment via PI3K/AKT/mTOR/HIF-1α signaling pathway.

Naturally and Anthropogenically Induced Lingulodinium polyedra Dinoflagellate Red Tides in the Galician Rias (NW Iberian Peninsula).

Despite the fact that the first red tide reported on the coasts of the Iberian Peninsula was due to Lingulodinium polyedra, knowledge about their frequency and, particularly, about the environmental conditions contributing to bloom initiation is still scarce. For this reason, L. polyedra bloom episodes were observed and studied in three Galician rias during the summer season based on the 1993-2008 record database period; additionally, samples were collected in summer 2008. Proliferations of L. polyedra occurred in the rias of Ares and Barqueiro in June and August, respectively, while in the Ria of Coruña, they persisted from the end of June to early September. Red tides developed when the surface temperature reached 17 °C, with "seasonal thermal window" conditions, and when salinities were ≥30, i.e., an "optimal salinity window"; when these parameters were lower than these thresholds, cyst germination decreased. A cyst transport mechanism from sediments to the surface must also exist; this mechanism was found to be natural (tidal currents) in the ria of Barqueiro or anthropogenic (dredging) in the rias of Ares and Coruña. Surface temperatures during summer were usually favorable for cyst germination (85 to 100%) during the 1993-2008 period; however, water temperatures below 10 m depth only rarely reached the 17 °C threshold (2 to 18%). During this 16-year period, dredging activities could explain 71% (Coruña) and 44% (Ares) of the recorded bloom events. When a bloom episode developed in early summer, favorable conditions did not lead to a new red tide, probably due to the lag period required by cysts for germination. Moreover, blooms did not develop when high densities of diatoms (>1,000,000 cells·L-1) remained in the water column as a result of summer upwelling pulses occurring in specific years. The temperature-sediment disturbance pattern found in this study provides a useful tool for the prevention of eventual risks resulting from red tides of this dinoflagellate.

[A quantitative study of mechanics in the treatment of atlantoaxial joint disorder by tendon relaxation manipulation].

OBJECTIVE: To explore dose-effect relationship of biomechanical parameters in treating atlantoaxial joint disorder by slimming manipulation. METHODS: From October 2022 to May 2023, 18 patients with atlantoaxial joint disorders were treated, including 10 males and 8 females;aged from 24 to 27 years old with an average of (25.50±1.10) years old;CT of cervical vertebra showed 16 patients with right side distortion and 2 patients with left side distortion. The mechanical parameters of treatment of atlantoaxial joint disorder by tendon relaxation manipulation were measured by wearing massage manipulation gloves. The magnitude, frequency and mechanical curve of force during tendon relaxation and starting force, pulling force, pulling time and mechanical curve during rehabilitation were quantified, the differences between the affected and contralateral manipulations were compared. RESULTS: The maximum force and frequency of Fengchi(GB20) on the affected side were (19.82±2.02) N and (116.83±14.49) times/min, and opposite side were (13.87±2.19) N and (188.89±16.03) times/min, respectively. There were statistically difference in the maximum force and frequency of both sides (P<0.05). The maximum force and frequency of Quepen (ST12) on the affected side were (14.44±3.27) N and (139.06±28.47) times/min, and those on the opposite side were (9.41±1.38) N and (142.50±28.47) times/min. There was difference in maximum force on both sides (P<0.05). The starting force, turning force and turning time of the affected side were (14.16±5.98) N, (11.56±6.63) N, (0.14±0.03) S, and the contralateral side were (8.94±3.39) N, (8.30±4.64) N, (0.18±0.04) S, respectively. The difference of starting force, turning force and turning time on both sides were statistically significant (P<0.05). CONCLUSION: By applying a light relaxation force on the affected side, the mechanical balance between cervical vertebrae could be restored, and recovery trend of atlantoaxial joint disorder could be strengthened. On this basis, the atlantoaxial odontoid process could be reversed by applying a light rotation force, which reflects the characteristics of high safety of the manipulation.

Management of excavated soil and dredging spoil waste from construction and demolition within the EU: Practices, impacts and perspectives.

Excavated soil and rock (ESR) and dredging spoils (DDS) account for 23 % of the total EU waste generation in 2020. This study performs a life cycle assessment and life cycle costing to quantify the potential environmental and cost savings resulting from increasing the level of ESR and DDS prepared for reuse and recycled in comparison to the business-as-usual practice. Scenarios for the waste management pathways based on the status quo, technical feasibility or normative impositions are assessed, including the potential contribution to achieving the European Green Deal goals. Results show that promoting preparing for reuse and recycling could lead to non-negligible GHG reductions (up to 3.6 Mt. CO2 eq.) and economic savings (EUR 12.3 billion) annually. Depending upon the scenario, 0.2 % to 1 % of the net annual GHG emissions reductions sought by the European Green Deal could be facilitated by scaling up improved circular management of ESR and DDS at the EU level. Finally, the study highlights the main barriers to scaling up to more circular (i.e., preparing for reuse and recycling) and better performing management options in Europe. The results provide new insights for the European Green Deal and circular economy policymaking for CDW.

Geochemical characterization data of harbors dredged sediments in the Occitanie region (southern France).

Over the last 15 years, numerous analyses of sediment from the Mediterranean harbors of Occitanie (Southern France) has been made before dredging operations in order to assess geochemical quality of dredged sediment and define the extend of dredging project and the potential fate of dredged sediment (sea dumping vs management on land). However, these data are today scattered, printed and stored as archives, and not directly accessible. With time, those data are expected to be lost for the community whereas they constitute an irreplaceable and mobilizable knowledge base to address the challenges of the circular economy. Characterization data aid in developing regulations for better land-based management of dredged sediments. Existing data are also needed to define pollutant limits in sediments for different uses of marine resources. The collection of these data can thus offer a unique opportunity to assess the geochemical quality of dredged marine sediments and their determining factors. The dataset collected is composed of geochemical characteristics of 146 marine sediments wastes collected before dredging operations between 2010 and 2021. The sampling was designed to capture the large diversity of sediment distribution in harbors of southern France. The dataset contains a wide range of variability in the composition characteristics of dredged sediment (dry matter, organic matter, total nitrogen and phosphorus, sulphate, chloride, trace metals and organics elements). Because the dataset provides information about the characteristics defining the geochemical quality of dredged sediments, it can be used further for research, waste management or dredged sediment valorization, and represent a great interest to other researchers, harbors managers and stakeholders in search of references on the geochemical quality of dredged sediments for their reuse.

Risk assessment of e-waste - Liquid Crystal Monomers re-suspension caused by coastal dredging operations.

The Pearl River Estuary (PRE), one of the primary e-waste recycling centers in the world, has been suffering from the pollution of Liquid Crystal Monomers (LCMs), critical materials with persistent, bio-accumulative, and toxic substances used in electronic devices. It has been detected in seabed sediment with both high frequency and concentration near PRE - Hong Kong (HK) waters. In the same area, dredging operations with in-situ sediment have been frequently used in the last decades for coastal land reclamation projects. Dredging is known to cause a huge amount of sediment re-suspension into water columns, with potential damage to marine ecosystems and biodiversity. In this study, we proposed a new risk assessment strategy to estimate the secondary pollution due to the re-suspension sediment highly contaminated by LCMs. We formulate a robust and reliable probabilistic approach based on unsupervised machine learning and hydrodynamic and sediment transport numerical simulation. New risk indexes were also proposed to better quantify the impact of contaminated sediments. We applied the methodology to assess the potential impact of dredging operations in the PRE and Hong Kong waters on the local marine ecosystem. The results of the analysis showed how the potentially contaminated areas depended on the dredging locations.

Eco-friendly dredging methods of changing fluvial landforms for enhancing hydraulic habitat quality and river corridor continuum.

Hydraulic habitat connectivity, including the longitudinal continuum respect and lateral flood pulse, is critical for fish survival and organism dispersal. Inappropriate and excessive dredging for prevent flooding may harm river ecosystems. The main objective of this study is to evaluate whether eco-friendly dredging presented by changing local river landforms incorporating the concept of nature-based solutions could grow fish habitat quality for improving river continuity and achieving flood control effects. By combining various mathematical models and empirical formulas and verifying them with the data obtained through field surveys, we explore the interconnections of hydrology, river morphology, and the habitat dynamics of four endemic fishes in an alluvial river. The relationship between habitat structure, flood risk, and river topography, flow discharge was presented as the reference for developing the proper river dredging approaches. The results reveal that the primary habitat defects were lack of high-quality habitat, unsatisfied habitat diversity, deficiency in refugia, and disconnectivity. Longitudinal disconnectivity was induced due to shallow water depth, while lateral disconnectivity is primarily caused by fast flow velocity, suggesting different and specific dredging methods were instructed. We recommend that the corresponding eco-friendly dredging schemes for longitudinal and lateral suitable habitat linkages increase fish habitat quality and river corridor continuity. The win-win strategy for enhancing the connection between suitable habitats sustains a more beneficial aquatic corridor and simultaneously achieves alluvial flood disaster risk reduction.

Carcinogenic and non-carcinogenic health risks associated with the consumption of fishes contaminated with heavy metals from Manzala Lake, Egypt.

Manzala Lake was sampled to assess the concentrations and possible ecological risks of heavy metals. The mean heavy metal levels in the muscles of Nile tilapia, Flathead grey mullets and African catfish were 0.01, 0.15 and 0.29 mg/kg, respectively, for mercury; 3.16, 4.25 and 4.74 mg/kg for arsenic; 1.01, 0.87 and 0.95 mg/kg for lead; and 0.05, 0.12 and 0.06 mg/kg for cadmium. The levels of heavy metals exceeded their maximum permissible limits in most samples. The EDIs of some metals were higher than their PTDIs or BMDLs. The THQs and TTHQs from metal intake were >1 for Hg and Cd. In addition, the TCR values of As in all fish species were higher than 1.0 × 10-4 indicating a potential health risks from consumption of fish species which need strict hygienic procedures to prevent fish contamination with heavy metals and ensure that their levels did not exceed the maximum permissible limits.

Microplastic in Dredged Sediments: From Databases to Strategic Responses.

Microplastics (MPs) accumulate in sediments, yet guidelines for evaluating MP risks in dredged sediments are lacking. The objective of this study was to review existing literature on MPs in sediments to improve fundamental knowledge of MP exposures and develop a publicly available database of MPs in sediments. Twelve percent of the reviewed papers (nine studies) included sediment core samples with MP concentrations generally decreasing with depth, peaking in the top 15 cm. The remaining papers evaluated surficial grab samples (0 to 15 cm depth) from various water bodies with MPs detected in almost every sample. Median MP concentrations (items/kg dry sediment) increased in this order: lakes and reservoirs (184), estuarine (263), Great Lakes nearshore areas and tributaries (290), riverine (410), nearshore marine areas (487), dredge activities (817), and harbors (948). Dredging of recurrent shoaling sediments could be expected to contain MPs at various depths with concentrations influenced by the time elapsed since the last dredging event. These results offer key insights into the presence and variability of MPs in dredged sediments, informing environmental monitoring and risk assessment strategies.

Sediment Toxicity Tests: A Critical Review of Their use in Environmental Regulations.

Sediments are an integral component of aquatic systems, linking multiple water uses, functions, and services. Contamination of sediments by chemicals is a worldwide problem, with many jurisdictions trying to prevent future pollution (prospective) and manage existing contamination (retrospective). The present review assesses the implementation of sediment toxicity testing in environmental regulations globally. Currently, the incorporation of sediment toxicity testing in regulations is most common in the European Union (EU), North America, and Australasian regions, with some expansion in Asia and non-EU Europe. Employing sediment toxicity testing in prospective assessments (i.e., before chemicals are allowed on the market) is most advanced and harmonized with pesticides. In the retrospective assessment of environmental risks (i.e., chemicals already contaminating sediments), regulatory sediment toxicity testing practices are applied inconsistently on the global scale. International harmonization of sediment toxicity tests is considered an asset and has been successful through the widespread adoption and deployment of Organisation for Economic Co-operation and Development guidelines. On the other hand, retrospective sediment assessments benefit from incorporating regional species and protocols. Currently used toxicity testing species are diverse, with temperate species being applied most often, whereas test protocols are insufficiently flexible to appropriately address the range of environmental contaminants, including nanomaterials, highly hydrophobic contaminants, and ionized chemicals. The ever-increasing and -changing pressures placed on aquatic resources are a challenge for protection and management efforts, calling for continuous sediment toxicity test method improvement to insure effective use in regulatory frameworks. Future developments should focus on including more subtle and specific toxicity endpoints (e.g., incorporating bioavailability-based in vitro tests) and genomic techniques, extending sediment toxicity testing from single to multispecies approaches, and providing a better link with ecological protection goals. Environ Toxicol Chem 2024;43:1697-1716. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Kinematics Analysis and Gait Study of Bionic Turtle Crawling Mechanism.

Longer distance water delivery culverts pose obstacles such as deposited silt, stones, and dead trees. In this paper, a crawling robot is designed to mimic the joint structure of a turtle using bionic design principles. The mechanism and gait of the robot are analyzed. The kinematics model of the robot is established using the D-H method and analytical approach, while the dynamics model is established using Lagrange's method. Based on kinematics and dynamics analysis theory, compound cycloid and cubic polynomial motion trajectories for the robot foot are planned along with a crawling gait resembling that of a turtle's abdomen. Simulation experiments and scale prototype experiments confirm that when gait parameters are identical, the energy consumption of compound cycloid trajectory exceeds that of cubic polynomial foot trajectory. When planning these two types of foot trajectories, it was observed that energy consumption ratio decreases with increasing step length but increases with increasing step height.

Back on top: Resuspended by dredging and other environmental disturbances, organochlorine compounds may affect the health of a dolphin population in a tropical estuary, Sepetiba Bay.

Organochlorine compounds (OCs) are persistent organic pollutants linked to damaging the immune and endocrine systems, leading to a greater susceptibility to infectious diseases at high concentrations. Sepetiba Bay, in the Southeastern Brazilian coast, historically presents anthropogenic activities and environmental contamination that could negatively impact resident populations. In this context, this study aimed to investigate the temporal trends in the accumulation of organochlorine compounds over a 12-year database in the Guiana dolphins' (Sotalia guianensis) resident population from Sepetiba Bay, including individuals collected before, during, and after an unusual mortality event triggered by morbillivirus (n = 85). The influence of biological parameters was also evaluated. The OCs concentrations in the blubber ranged from 0.98 to 739 µg/g of ΣPCB; 0.08-130 µg/g of ΣDDT; <0.002-4.56 µg/g of mirex; <0.002-1.84 µg/g of ΣHCH and <0.001-0.16 µg/g of HCB in lipid weight. Increased temporal trends were found for OCs in Guiana dolphins coinciding with periods of large events of dredging in the region. In this way, our findings suggest that the constant high OCs concentrations throughout the years in this Guiana dolphin population are a result of the constant environmental disturbance in the area, such as dredging. These elevated OCs levels, e.g., ΣPCB concentrations found above the known thresholds, may impair the response of the immune system during outbreak periods, which could lead the population to a progressive decline.

Changes in maerl-associated macroalgal community dynamics as evidence of anthropogenic pressure.

BACKGROUND AND AIMS: Maerl-associated communities have received considerable attention due to their uniqueness, biodiversity and functional importance. Although the impacts of human activities are well documented for maerl-associated macrofauna, the spatio-temporal variations of macroalgae have comparatively been neglected, and the drivers that influence their dynamics are poorly known. We investigate the links between maerl-associated macroalgal communities, anthropogenic pressures and environmental conditions, and hypothesize that sites under human pressure would exhibit different dynamics when compared to reference sites. METHODS: To better understand community variation through space and time, four subtidal maerl beds under different pressures were consistently monitored over one year in the bay of Brest, Brittany, France. Both macroalgae community monitoring and environmental data were acquired through field sampling and available models. KEY RESULTS: Higher macroalgal biomass was observed within eutrophic sites, especially in summer (more than ten times higher than in the Unimpacted site), caused by free-living forms of opportunistic red macroalgae. The Dredged site also exhibited distinct macroalgal communities during summer from the Unimpacted site. Nutrient concentrations and seasonality proved to be key factors affecting the macroalgal community composition, although dredging and its effects on granulometry also had a strong influence. Over the long term, fewer than half of the species identified during historical surveys were found, indicating major temporal changes. CONCLUSIONS: Human pressures have strong impacts on maerl-associated macroalgal communities. Nutrient concentrations and dredging pressure appear as the main anthropogenic factors shaping maerl-associated macroalgal communities. Additionally, our results suggest historical changes in maerl-associated macroalgal communities over 25 years in response to changes in local human pressure management. This study suggests that maerl-associated macroalgal communities could be used as indicators of anthropogenically driven changes in this habitat.

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment.

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

Geochemical fractionation of trace metals and ecological risk assessment of surface sediments in Sepetiba Bay, Brazil.

The Sepetiba Bay (Southeast Brazil) is a known Cd- and Zn-contaminated site that received spills of a large slag pile leachate from a Zn smelter. With important harbors, Sepetiba Bay demands periodic dredging operations which affect the mobility of the metals. The main goal of this work was to assess metal mobility in sediments and its associated toxicity in a fictive dredging area, to evaluate the risks of the operation. To achieve this goal, 18 superficial sediment samples were collected and characterized for pH and Eh. Sediments were analyzed for grain size, organic carbon, and total nitrogen, and metal mobility was evaluated with a sequential extraction procedure, proposed by the European Community Bureau of Reference (BCR). The results demonstrate that Cd and Zn are mainly associated with the exchangeable fraction (mean concentrations 1.4 mg kg-1 and 149.4 mg kg-1, respectively) and reducible fractions (mean concentrations 0.3 mg kg-1 and 65.5 mg kg-1, respectively), while Fe, Cr, Cu, Ni, and Al were associated with the residual fraction. Metals in the residual fraction are probably associated with the mineral lattice of the sediment and should not represent an environmental risk for the biota. The application of the enrichment factor and three risk assessment indexes (Risk Assessment Code, Risky Pollution Index, and Bioavailability Risk Assessment Index) show that the sediments are considerably enriched in metals that constitute a relevant risk for the sediment biota. In the case of dredging operations, Cd and Zn should be released to the overlying waters and be available to organisms, threatening the whole ecosystem. The proposed approach was shown to be much more precise than what is frequently presented in the Environmental Impact Assessments that only consider the threshold limits of the legislation.