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In response to the long-term non-degradation and environmental pollution caused by the use of horizontal plastic drainage boards, a new approach is proposed in this study, which involves employing horizontal straw drainage system under vacuum preloading treatment for dredging sludge. Through laboratory model tests, the results show that horizontal straw drainage system exhibited excellent performance in treating dredged sludge, with an optimal spacing design of 40–60 cm. During the vacuum preloading test, the straw drainage system continuously degraded, and the degradation by-products of straw, in turn, enriched elements like nitrogen, phosphorus, potassium, etc., in the soil. The two processes of the degradation of straw drainage system and the eco-reinforcement of dredged sludge interacted actively with each other. Finally, a new reinforcement method for on-site dredging sludge was proposed by installing layered straw drainage boards. Therefore, straw drainage system was highly recommended for field application, due to their cost-effective and environmentally friendly characteristics. [ABSTRACT FROM AUTHOR]

Sparse borehole data and unreasonable sampling strategies pose challenges in accurately constructing geological profiles, resulting in inaccurate soil distribution information and impacting the design of implementation plans for dredging engineering. Therefore, an automatic construction and uncertainty analysis approach to the geological profile of dredging engineering is proposed using multiple-point geostatistics. The approach uses a training image instead of the variogram function, considering the spatial variability of the soil and adapting to learn high-order spatial information. This enables the characterization of spatial relationships and distribution patterns between multiple points. Subsequently, statistical uncertainty analysis is conducted based on the results obtained from stochastic simulations. The effects of neighboring cell numbers, threshold, and borehole spacings on the performance of our approach are systematically investigated and the optimal simulation parameters are determined. Additionally, the simulated geological profiles are categorized into three areas (high, medium, and low) based on the level of uncertainty, quantifying the uncertainty of the proposed approach. The equidistant method is then used for comparison and verification. When applied to a dredging engineering case in the Lianyungang Channel, the approach achieved a prediction accuracy of over 93.7% and successfully quantified boundary areas with high uncertainty in soil layers. This shows the enhanced capacity of the approach to capture characteristics of soil distribution. The approach reduces the area of high uncertainty by 11.4%, demonstrating advancements in selecting drilling locations. The study will provide decision support for geological surveys in dredging engineering and provide reliable soil information for subsequent construction. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of an underwater retrogressive slope failure caused by the concurrent construction of a wharf access causeway and dredging near the end of the causeway for the wharf structure cofferdams. A cross section was developed along the causeway and analyzed to simulate the retrogressive slope failure using limit equilibrium analyses. The compound failure surface for the inverse stability analysis of each of the five retrogressive failure masses agrees with observations before, during, and after the failure. Soil stratigraphy is discussed and the mobilized undrained strength of the seabed clay underlying the causeway fill was estimated using an inverse analysis of each of the five failure masses. The inverse analysis shows that the concurrent dredging and causeway construction reduced the factor of safety (FoS) of the causeway underwater slope, which eventually initiated the retrogressive failure. The stability analyses show that the causeway construction contributed to the reduction of the FoS but dredging triggered the first slope failure, which started the retrogressive failure. Nevertheless, had dredging not occurred, a slope failure would still have occurred if the causeway construction had extended another 5 m from where the first slope failure occurred. Practical Applications: There are several practical lessons from the slope failure discussed in this paper. First, in any slope modification, the existing soils in the area of construction should be sampled and tested. Engineers and owners should be cautious of construction methods that make implicit assumptions about soil strength and/or other engineering characteristics. Even though gathering underwater geotechnical data is difficult, it is recommended to perform field tests to evaluate the shear strength of soil layers to perform slope stability analyses. Further, planned modifications to a slope that could destabilize it should be thoroughly analyzed, and such analyses should not be restricted to a circular failure surface. If possible, the construction sequence should be modified to reduce the extent to which the slope is destabilized. In this case, that would mean constructing the wharf before the causeway. Finally, construction should be monitored to verify that the proposed methods are working as intended. In this case, it was assumed that the rockfill would displace the marine clay when constructing the causeway. This should have been verified as filling progressed. Photographs of the dredged marine indicated a medium to medium stiff clay, which indicated that the clay was not as soft as anticipated. [ABSTRACT FROM AUTHOR]

Sediment dredging and aeration are used as important technical measures to remediate internal loading of sediment in polluted rivers. However, previous studies have overlooked the impact of dredging and aeration on Greenhouse gases (GHGs) emission. We established three aeration rate(six different aeration intervals), one dredging treatment to investigate the effect of aeration and dredging on pollutant removals and CO2, CH4 and N2O emissions. The results indicated the pollutants and GHGs at 2.4, 3.4, 4.4 L min−1 aeration rates reached collaborative emission reduction after more than 3 h or within 1.5 h. Meanwhile, the GHGs fluxes after aeration decreased with the increasing aeration rate, with the mean CO2, CH4 and N2O fluxes of 69.74, 0.16, 7.53 mg m−2 h−1 and 33.64, 0.09, 4.17 mg m−2 h−1 before and after aeration, respectively. With respect to dredging, the pollutants and N2O reached synergic effects between reduction of pollution and carbon emissions after 1 h dredging. Specifically, the CO2 and CH4 emissions after dredging was lower than those of before dredging, but the N2O emissions was higher than those of before dredging. In addition, our analysis revealed that the dissolved oxygen (DO), oxidation-reduction potential (ORP), available potassium (AK) and ammoniacal nitrogen (NH4+-N) in the sediment influenced GHGs fluxes at the water-air interface in the aeration. Our study indicated moderate aeration and dredging can achieve the synergistic effect in reducing pollution and carbon emissions. [ABSTRACT FROM AUTHOR]

The disposal and reutilization of the enormous amounts of slurry-like mud (MS) dredged from navigation channel construction, ecological dredging, and other construction activities have been receiving increasing attention. In this paper, a flocculation–solidification–high-pressure filtration combined method (FSHCM) is used to treat MS, and the consolidation characteristics of The SHCM-treated MS are studied by conducting a series of one-dimensional consolidation compression tests. Various parameters, including the dosage of the curing agent, initial water content, and dry weight of the MS, are systematically analyzed to evaluate their influence on the consolidation behavior. The experimental results demonstrate that higher curing agent and initial water contents enhance the structural yield stress and compressive resistance, while increased dry weight decreases the structural yield stress but increases the compressive strain and void ratio. As the curing age increases, the ability of the FSHCM-treated MS to resist compressive deformation is further enhanced. In addition, the compressibility of the mud cake samples changes significantly at the yield point. This study has practical guiding significance for the optimal design and long-term application of FSHCM-treated MS. [ABSTRACT FROM AUTHOR]

Navigation channels provide a vital link in the supply chain of inland transport. Excavation of sediment from the river bed and fluvial islands is necessary to make the large braided river navigable for transportation. Present research work investigates the feasibility of dredging operations in the mid-sand bars of the Brahmaputra River (Assam, India) for navigation purposes. Pernicious metal (Cu, Zn, Fe, Mn, Ni, Co, Cr, Pb, Cd) concentrations were assessed at 42 sampling locations, covering a reach length of approx. 600 km (reaches 1 and 2). Vertical samples were obtained from 0 cm, 50 cm, and 100 cm of the mid-sand bar. Various indices were evaluated to quantify the contamination level in the mid-sand bars. Based on the enrichment factor (EF), reach 2 was highly enriched with toxic metal-limiting dredging operation. Conversely, reach 1 was found suitable for dredging operations, owing to the low EF value. Various anthropogenic activities are likely to be the causative factor for the heavy metal enrichment in reach 2, including effluents from pharmaceutical industries, oil refineries, and industrial and domestic runoff. Statistical analysis also endorsed those heavy metals possess similar anthropogenic origins. Overall, the dredging can be feasible for reach 1 and at localized zones for reach 2 across the Brahmaputra River. Further, the study tries to present a suitable mitigation measure to carry out dredging operations and manage contaminated dredged sediment for reach 2. [ABSTRACT FROM AUTHOR]

Coastal areas are at the centre of human–nature relationship, shaped by recreation, tourism and aesthetic values. However, socioeconomic drivers of biodiversity change in coastal areas have received less attention.Soft sediment seafloors support diverse species communities and contribute to ecosystem functionality. One of the main threats is dredging, which sweeps resident organisms. Dredgings are commonly done to deepen waterways, but also for the purposes of private housing. The ecological impacts of these small‐sized dredgings are not well known over broad environmental and geographical gradients.We developed a simple approach for spatial integration of ecological and socioeconomic system, to describe how recreational land use change contributes to the loss of marine biodiversity. It shows how human behaviour, such as preference for a location of second home, can be derived from spatial data and coupled with ecological change.We characterize typical locations of second homes based on accessibility, aesthetics and environment, and with the information identified suitable areas for new second homes. We also quantified typical areas of dredging, based on the depth and substrate of the sea floor, and the extent of the reed beds, influencing the access to properties. We then simulate an annual increase of new second homes and expected land‐use change, namely dredging of shores. Finally, we quantified the realized and projected loss of marine biodiversity from dredged sites, based on species distribution models, relying on extensive ecological data collected from over 170,000 underwater sites.We found that small‐sized dredging can be detrimental to coastal biodiversity, as dredging targets shallow, photic bays and lagoons, with diverse algal and aquatic plant communities, with limited recovery potential. Dredgings also had broad impacts on benthic faunal habitats, which maintain ecosystem processes and functions. Our results reveal a significant ecological change driven by recreational land use.Reversing the trend of biodiversity loss requires a holistic understanding of socioecological systems. Our results highlight the need for integrating land–sea interactions into conservation policies and reforming current land‐use regulation for the benefit of marine biodiversity. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Due to observed impacts of sea level rise, many sediment management strategies in coastal settings are seeking ways to beneficially use locally dredged sediment in restoration, nourishment, and construction projects. The placement of sediment in shallow, near-marsh areas is a promising application of dredged material to both increase accretion and provide protection to marshes and intertidal flats in back bay areas. However, dredged material in these areas often include fine-grained (<63 mm) sediments (FGS), that frequently raise questions concerning dispersion, stability, and environmental impact of the placement project. In 2020, approximately 30,500 m³ of FGS from the New Jersey Intracoastal Waterway (NJIWW) was placed along the southern edge of Gull Island, New Jersey to evaluate the feasibility of using FGS for beneficial use projects in near marsh environments. Gull Island was experiencing extensive marsh edge erosion through margin collapse. The placement was unconfined and resulted in the formation of two intertidal muddy berm-like features up to 0.7 m thick along more than 500 m of marsh. Bathymetric surveys showed that approximately 60-70% of the berm volume remained 36 months after placement, however maximum berm thickness reduced to ~0.5 m. Field monitoring performed during construction found that turbidity plumes were localized to within 100 m of the placement site and sediment cores collected in June 2022 did not show systemic winnowing from the berm surface. Laboratory and field observations indicated that the berm material was cohesive in nature and produced large aggregates upon erosion, limiting the dispersal of FGS. Observations of current velocities and waves in the area indicate a low energy system such that the cohesive berm was largely resistant to erosion and that reduction in berm volume was largely due to consolidation and compaction. This suggests that shallow water features can be constructed with FGS in similar low energy environments with limited dispersal during and following construction, while being robust enough to help stabilize the marsh edge and improve marsh survivability against sea level rise. [ABSTRACT FROM AUTHOR]

The dredging ship's cutter tools operates underwater at different temperatures, water conditions (pollution, waves, salinity etc.), different dredging soil, the velocity of rotating, and time1. However, it is necessary to develop new methods of processing and repair which will increase the wear resistance, corrosion resistance and increase the operating life of the working surfaces. The main objective of this report is to present a test stand for experimental research of the hydro-abrasive wear of hard coatings applied on the surface of the dredging cutter tool after reconditioning. Experimental research is possible by changing different factors -- velocity, time, type of water, welding layer, and the abrasive tool2,3. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the growth rates and general body condition of two common game fishes (largemouth bass Micropterus nigricans and bluegill Lepomis macrochirus) in a productive midwestern USA lake, Lake Winona, 20+ years after one of its two separate basins was partially dredged. We also used historical lake survey data spanning 19 years before and 15 years after dredging to assess the pre- and post-dredging growth of these species. Dredging was expected to improve the growth rates and conditions (relative weights) of both species due to post-dredging changes to lake habitats (more open water and reduced macrophyte beds) and the fish community structure in the dredged basin. Both species displayed significantly faster growth in the dredged basin, with the bluegill by age 3 and the bass by age 6. The mean relative weights of both species were significantly higher in the non-dredged basin (bass were in good condition: 106% versus 100%; bluegill were in fair condition: 84% versus 80%), although both bluegill and largemouth bass exhibited significant declines in relative weight with increasing lengths in the non-dredged basin. The growth rates for largemouth bass have declined from historical levels, especially in the non-dredged basin, whereas bluegill growth rates have remained stable or improved, especially in the dredged basin. Overall, largemouth bass and bluegill growth rates and relative weights are responding to differences in habitat and fish communities between dredged and non-dredged basins, indicating that the two lake basins are isolated enough from one another to allow for separate biological responses to occur in each. [ABSTRACT FROM AUTHOR]

Submarine pipeline route detection is of great significance for waterway dredging construction, while the traditionaldetection techniques have many problems, such as single technical means, low efficiency, unable to determine the buriedsection information and so on. In order to improve the accuracy of submarine pipeline detection results and operationalefficiency, relying on Ningbo -Zhoushan port Tiaozhoumen waterway expansion project, comprehensively uses the side -scansonar, sub-bottom profiler and marine magnetic detection technology to detect the submarine pipeline in the engineering area.The side-scan sonar results are used as the base data support of the submarine pipeline in the exposed section, and the subbottom profiler buried depth results and the magnetic detection inversion buried depth results confirm each other, which jointlyimproves the accuracy of submarine pipeline discrimination. The engineering application results show that the joint applicationof the three detection techniques in submarine pipeline detection is reliable, with significantly improved detection accuracy andoperational efficiency, and good applicability. It has a good reference and promotion role in similar projects. [ABSTRACT FROM AUTHOR]

As the shafts in Xiaoqinling Gold District gradually close, it has become imperative to conduct geological hazard investigations and implement remediation measures. Based on the geological environment of the mining area, this study analyzes the types of geological hazards in the region and implements targeted remediation measures, such as waste residue cleaning and transportation, construction of protective dikes, debris retention dams, debris retention walls, trench rehabilitation, road repairs, and vegetation restoration. In Xiaoqinling Gold District, 28 800 m³ of debris retention walls were constructed, stabilizing 20.02 million t of ore residue, cleaning and transporting 5.84 million t of residue, leveling 1.435 million m² of residue slopes, constructing 21.2 km of drainage channels along residue slopes, clearing and dredging 15.5 km of river channels, planting 807 000 saplings, and sowing 14. 6 t of grass seeds. The environmental benefits have been significant, providing valuable insights and references for similar geological hazard remediation efforts. [ABSTRACT FROM AUTHOR]

Sediment management is a significant part of the decision-making process that hydraulic engineers need to undertake as it has a direct bearing on the environment. Sediment dredging from around intake structures and reservoirs impose a high operating cost. Jets can efficiently remove large quantities of sediment at low operational costs. This study assesses the scouring pattern development by changing nozzle parameters to achieve maximum scouring conditions. Toward this end, scour holes induced by jets generated using the nozzles with four inner angles (30°, 45°, 60°, and 90°) are tested on a cohesionless sediment bed. The experimental results show that the inner nozzle angle, α, and the densimetric Froude number, F0, affect the scour pattern. This work illustrates that the scour hole dimensions grow with increasing α and F0. Based on the velocity measurements, for the range of jet discharges considered herein, the relative velocity Um/U0 is increased by 20%–25% for the nozzle with α = 90° compared to the nozzle with α = 30°. [ABSTRACT FROM AUTHOR]

The USACE boasts a navigation portfolio of over 19,312 km (12,000 mi) of shallow draft [from 2.74 m (9 ft) to 4.27 m (14 ft)] inland and intracoastal waterways, 20,921 km (13,000 mi) of deep draft [4.27 m (14 ft) and greater] channels, and 400 ports, harbors, and turning basins. To ensure that these channels remain navigable and at congressionally authorized dimensions, channel maintenance practices are performed annually by dredging. Most of these dredging operations are performed by private companies under contract to the USACE districts. With an abundance of navigation channel maintenance needs and a limited dredging fleet, accurate scheduling and the timely arrival of the dredging fleet is required. Project delays due to production issues, weather delays, contracting issues, or both will generally impact future scheduled projects, navigation, and commerce. Nonawardable bids happen when the contractor(s) proposal(s) are too high compared with the Independent Government Estimate (IGE). These nonawardable bids lead to significant time delays, because the USACE district must then engage in bid verification calls, negotiations, the potential cancellation of the contract solicitation, or both and the subsequent resolicitation for work. Therefore, it is extremely important that USACE cost estimates adequately reflect the level of effort the project requires when capturing all project-associated costs. This paper aims to summarize the USACE conceptual approach to dredge cost estimating by highlighting the complex variables that are associated with this type of estimate. [ABSTRACT FROM AUTHOR]

Reservoir sediment severely impacts water supply in water-scarce regions, making reservoir dredging an urgent global issue. The investment required for deep-water dredging far exceeds that for dry land dredging. Therefore, against the backdrop of the national water network construction, this study focuses on a typical inter-basin water transfer project in Northern China. To increase the proportion of dry land dredging volume and save costs, this study uses compensation reservoirs to replace the emptied reservoir in undertaking water supply tasks as a constraint. Single-objective optimization models for single reservoirs and multi-objective optimization models for reservoir groups are established, using game theory comprehensive subjective and objective weighting methods to select the optimal solution. The following conclusions are drawn from comparing the water supply effects under various emptying sequences: the optimal sequence for emptying reservoirs should be determined through precise quantitative analysis; as the dredging is completed, the water supply tends to stabilize; the satisfaction with the water supply and the variance of the water shortage rate are primarily related to reservoirs with a large inflow and storage capacity; dredging occurs according to the descending order of the storage capacity of reservoirs; and the startup proportion of pump stations shows an increasing trend. [ABSTRACT FROM AUTHOR]

Purpose:In order to solve the problem of endogenous pollution mainly caused by sediment,engineering measures such as dredging and dredging have been widely applied in water environment management projects such as rivers, lakes, and reservoirs. At present, the amount of sediment generated by dredging and dredging in China is as high as 70 million tons,and it is still growing at a rate of 4%to 6%annually. At the same time,the dual attributes of "pollution" and "resources" of sediment also bring opportunities and challenges for its resource utilization. Method: Therefore, this article systematically reviews the principles, advantages and disadvantages, costs, and future development directions of current sediment resource utilization technology. Result and Conclusion: It is found that sediment resource utilization has involved multiple fields such as ecological restoration, construction, building material manufacturing, energy recovery, and environmental protection materials. In the future, the resource utilization of sediment should be achieved by establishing a sediment database in different zones to improve the accuracy of dredging engineering. Based on this, sediment should be utilized in different zones, layers, and classifications,and resource utilization technologies should be selected according to local conditions; At the same time,it is necessary to optimize the pre-treatment technology of sediment, improve the quality grade of sediment related products,and focus on toxic and harmful substances and new pollutants in sediment to achieve their safe utilization;Finally, we will improve the standard system for the entire process of sediment resource utilization and gradually standardize the market for sediment resource utilization. [ABSTRACT FROM AUTHOR]

Sedimentation is the natural process of sediment transportation and deposition in quiescent water conditions. Sedimentation can affect the functionality of ports, harbours and navigation channels by reducing water depth, making navigation difficult, if not impossible. Different solutions are available to guarantee infrastructure functionality against sedimentation, with maintenance dredging being the most widely adopted. Alternative technologies for dredging have been developed and tested to reduce the environmental concerns related to dredging operations. Among other solutions, applying a sediment by-pass system based on a jet pump emerged as one of the most promising. While the existing literature covers the techno-economic aspects of sediment by-pass systems, the environmental impacts must be better evaluated and assessed. This paper aims to resolve this gap by evaluating, through the ReCiPe2016 life cycle assessment (LCA) methodology, the environmental impact of an innovative sediment by-pass system called an "ejectors plant". The LCA results are based on the demonstrator established in Cervia Harbour in Italy, which was extensively monitored for 15 months during its operation. This paper shows how energy consumption during the operation phase highly affects the considered midpoint and endpoint categories. For example, the GWP100 of the ejectors plant, considering the Italian electricity mix, equals 1.75 million tons of equivalent CO2 over 20 years, while under a low-carbon scenario, it is reduced to 0.17. In that case, material consumption in the construction phase becomes dominant, thus highlighting the importance of eco-innovation of ejectors plants to minimise oxidant formation. Finally, this paper compares the ejectors plant and traditional dredging through environmental LCA. The ejectors plant had a lower impact in all categories except for GWP-related categories. The sensitivity analysis showed how such a conclusion may be mitigated by considering different electricity mixes and maintenance dredging working cycles. [ABSTRACT FROM AUTHOR]

Abstract Sediment dredging and aeration are used as important technical measures to remediate internal loading of sediment in polluted rivers. However, previous studies have overlooked the impact of dredging and aeration on Greenhouse gases (GHGs) emission. We established three aeration rate(six different aeration intervals), one dredging treatment to investigate the effect of aeration and dredging on pollutant removals and CO2, CH4 and N2O emissions. The results indicated the pollutants and GHGs at 2.4, 3.4, 4.4 L min−1 aeration rates reached collaborative emission reduction after more than 3 h or within 1.5 h. Meanwhile, the GHGs fluxes after aeration decreased with the increasing aeration rate, with the mean CO2, CH4 and N2O fluxes of 69.74, 0.16, 7.53 mg m−2 h−1 and 33.64, 0.09, 4.17 mg m−2 h−1 before and after aeration, respectively. With respect to dredging, the pollutants and N2O reached synergic effects between reduction of pollution and carbon emissions after 1 h dredging. Specifically, the CO2 and CH4 emissions after dredging was lower than those of before dredging, but the N2O emissions was higher than those of before dredging. In addition, our analysis revealed that the dissolved oxygen (DO), oxidation-reduction potential (ORP), available potassium (AK) and ammoniacal nitrogen (NH4 +-N) in the sediment influenced GHGs fluxes at the water-air interface in the aeration. Our study indicated moderate aeration and dredging can achieve the synergistic effect in reducing pollution and carbon emissions.

Abstract Coastal areas are at the centre of human–nature relationship, shaped by recreation, tourism and aesthetic values. However, socioeconomic drivers of biodiversity change in coastal areas have received less attention. Soft sediment seafloors support diverse species communities and contribute to ecosystem functionality. One of the main threats is dredging, which sweeps resident organisms. Dredgings are commonly done to deepen waterways, but also for the purposes of private housing. The ecological impacts of these small‐sized dredgings are not well known over broad environmental and geographical gradients. We developed a simple approach for spatial integration of ecological and socioeconomic system, to describe how recreational land use change contributes to the loss of marine biodiversity. It shows how human behaviour, such as preference for a location of second home, can be derived from spatial data and coupled with ecological change. We characterize typical locations of second homes based on accessibility, aesthetics and environment, and with the information identified suitable areas for new second homes. We also quantified typical areas of dredging, based on the depth and substrate of the sea floor, and the extent of the reed beds, influencing the access to properties. We then simulate an annual increase of new second homes and expected land‐use change, namely dredging of shores. Finally, we quantified the realized and projected loss of marine biodiversity from dredged sites, based on species distribution models, relying on extensive ecological data collected from over 170,000 underwater sites. We found that small‐sized dredging can be detrimental to coastal biodiversity, as dredging targets shallow, photic bays and lagoons, with diverse algal and aquatic plant communities, with limited recovery potential. Dredgings also had broad impacts on benthic faunal habitats, which maintain ecosystem processes and functions. Our results reveal a significant ecological change driven by recreational land use. Reversing the trend of biodiversity loss requires a holistic understanding of socioecological systems. Our results highlight the need for integrating land–sea interactions into conservation policies and reforming current land‐use regulation for the benefit of marine biodiversity. Read the free Plain Language Summary for this article on the Journal blog.

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 (R 2>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. [Display omitted] [ABSTRACT FROM AUTHOR]

The direct effects of converting coastal wetlands to open water by dredging them can be magnified by indirect effects. For example, dredged canals allow for recovery of mineral fluids 1000 s of m belowground which may induce geological subsidence or faulting; the dredged material deposited at the surface creates levees that redirect overland water flows. These indirect factors may stress wetland plants enough so that additional wetland habitat is converted to open water as a result of longer intervals of wetland soil waterlogging and drying, sulfide toxicity, less organic matter and sediment accumulation, and greater erosion. We quantified the indirect effects by demonstrating a robust dose–response relationship between coastal land loss and canal density in the Mississippi and Niger river deltas over 5 decades. Importantly, the ratio of land loss to canal area increases with time—a legacy effect. Surface impediments to water movements rather than belowground subsidence are the dominant causal factor. We also found that flood protection levees on the main river channel did not significantly magnify the effect of dredging on wetland loss. The cumulative effect of these direct and indirect consequences in coastal Louisiana is enormous and continuing, equaling many tens of billions dollars annually. Understanding these effects supports the rejection of a hypothesis that regional river channel flood protection levees or fluid withdrawal is of greater importance than the local changes in wetland hydrology. Wetland restoration/mitigation of dredging impacts on these two coasts can be implemented at a relatively low cost and quickly if this paradigm of the causes of coastal wetland losses is adopted. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the growth rates and general body condition of two common game fishes (largemouth bass Micropterus nigricans and bluegill Lepomis macrochirus) in a productive midwestern USA lake, Lake Winona, 20+ years after one of its two separate basins was partially dredged. We also used historical lake survey data spanning 19 years before and 15 years after dredging to assess the pre- and post-dredging growth of these species. Dredging was expected to improve the growth rates and conditions (relative weights) of both species due to post-dredging changes to lake habitats (more open water and reduced macrophyte beds) and the fish community structure in the dredged basin. Both species displayed significantly faster growth in the dredged basin, with the bluegill by age 3 and the bass by age 6. The mean relative weights of both species were significantly higher in the non-dredged basin (bass were in good condition: 106% versus 100%; bluegill were in fair condition: 84% versus 80%), although both bluegill and largemouth bass exhibited significant declines in relative weight with increasing lengths in the non-dredged basin. The growth rates for largemouth bass have declined from historical levels, especially in the non-dredged basin, whereas bluegill growth rates have remained stable or improved, especially in the dredged basin. Overall, largemouth bass and bluegill growth rates and relative weights are responding to differences in habitat and fish communities between dredged and non-dredged basins, indicating that the two lake basins are isolated enough from one another to allow for separate biological responses to occur in each.

In this work, the Fenton preoxidation and composite coagulant method was used to carry out the rapid dewatering experiment of Chaohu Lake (China) dredging slurry. The changes in extracellular polymeric substances (EPS), particle size distribution, zeta potential, specific resistance to filtration (SRF), and capillary suction time (CST) of the dredging slurry were characterized. The results showed that the molar ratio of H2O2 and Fe2+ had the greatest effect on the dewatering of dredging slurry by Fenton preoxidation. The coagulant selected through the coagulation test was polyaluminum ferric chloride. The model simulated by the response surface method exhibited significant adaptability and high accuracy (p < 0.01, R2 = 0.9461, accuracy is 12.115). Fenton preoxidation resulted in the transformation of tightly bound EPS to soluble EPS. After preoxidation-coagulation treatment, the dewatering performance of the slurry improved significantly. The EPS quantity rose by 20.3%, while the SRF (3.65 × 109 s2/g), CST (71.25 s), and zeta potential (− 28.0 mV) shifted to 0.33 × 109 s2/g, 27.60 s, and − 14.9 mV, respectively. The disintegration of EPS by Fenton peroxidation and the subsequent adsorption bridging and charge neutralization through coagulation were the key mechanism for improving the dewatering performance of the dredging slurry. [ABSTRACT FROM AUTHOR]

With the continuous development of dredging engineering and dredging business, the requirements for monitoring the dredging construction process are also increasing. Aiming at the problems of poor display effect and low accuracy in 3D visualization monitoring during the dredging process of existing dredgers, a universal 3D visualization system for dredger construction operations was designed and developed based on the Unity3D engine. The system realizes the 3D visualization display of key dredging equipment driving, underwater terrain generation and rendering, and real-time terrain reconstruction. Through actual dredger application verification, the system can effectively improve construction efficiency and quality, enhance construction accuracy, reduce the occurrence of missed excavation and over excavation, and has important engineering application value. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Silt removal is crucial for maintaining navigable waterways in harbors. Jet pumps, without moving parts, are highly suitable for underwater operations such as channel dredging in port environments. Despite their structural advantages in slurry handling, the prolonged transport of solid–liquid two-phase flows can lead to wear on the wall materials, resulting in decreased efficiency and potential pump failure. The wear characteristics of the jet pump walls due to sand particles of varying grain sizes were experimentally investigated. The characteristic of the sands having a higher distribution above the axis as they enter the jet pump was captured by a high-speed camera. The experiment recorded the variations in mass loss at different sections of the jet pump over a period of 120 h, identifying that backflow within the throat region is a significant contributor to wall wear. Scanning electron microscopy was employed to examine the microstructure of the abraded pump surfaces. It was found that there are noticeable differences in the surface wear microstructure across various pump areas, and that particles of different grain sizes result in distinct wear patterns on the pump surfaces. The underlying causes of this phenomenon were discussed from the perspective of particle motion. [ABSTRACT FROM AUTHOR]

Copyright of Sociologia Italiana is the property of EGEA S.p.A and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the dredging of the Yellow River, a common practice involves extracting alluvial fill from the river and depositing it on the rear side of the embankment, serving the dual purpose of river dredging and reinforcing the embankment. Nevertheless, there are few studies on the consolidation of alluvial fill extracted from the Yellow River. In this paper, laboratory experiments were conducted to examine the change in hydraulic conductivity during the consolidation process of the alluvial fill. Besides, a numerical model was established to investigate the dissipation law of excess pore water pressure and the settlement law of layered consolidation of alluvial fill. According to the research, the main conclusions can be drawn as follows: (1) During the consolidation process of the alluvial fill, the hydraulic conductivity exhibited a linear decline as the consolidation pressure increased. (2) The consolidation speed under the variable hydraulic conductivity case is lower than that on the condition when the hydraulic conductivity is constant. (3) In layered construction, the consolidation rate of alluvial fill decelerates with the augmentation of layers. Additionally, the dissipation rate of pore water pressure at the top of the alluvial fill surpasses that at the bottom. (4) Setting a geotextile mat can accelerate the consolidation speed and shorten the consolidation time of alluvial fill by 8.3%–30%. [ABSTRACT FROM AUTHOR]

Freshwater species face numerous threats across the globe, including urbanization. Within cities in regions with drier climates, dewatering and channelization of rivers commonly occur and reduce or eliminate freshwater biodiversity. The discharge of effluent (treated wastewater) has been used to restore flow in some of these rivers, but our knowledge is negligible about how ecological communities develop and change in these unique but increasingly common ecosystems. In this study, we quantified aquatic macroinvertebrate community development in the Santa Cruz River (Arizona, U.S.A.), where effluent‐restored flow more than 100 years after the river dried up. We tracked community development over a 2‐year period in reaches where flow had been restored and compared those findings with data from a reference reach. Our study period also encompassed a massive disturbance where effluent releases temporarily ceased and sediment was dredged from the channel, allowing us to quantify the impacts of urban channel maintenance activities on recovering communities. Macroinvertebrate colonization was rapid following the initial flow restoration and channel dredging, with density and species richness values reaching or exceeding those of the reference reach within a few months, but community composition remained quite distinct after 2 years. Flow duration and the number of dry days in the month prior to sampling were the most influential factors in macroinvertebrate metrics. Simply adding effluent to dewatered urban rivers has the potential to restore diverse aquatic fauna, but targeted reintroductions may be needed for sensitive or dispersal‐limited taxa. [ABSTRACT FROM AUTHOR]

This study is based on a natural experiment carried out in the Biebrza National Park, Poland. The study site was a channel inhabited by Anodonta anatina, A. cygnea, Unio pictorum and U. tumidus. The deepening of the channel to restore ecosystem connectivity provided an opportunity to conduct this study. Mussels were collected before dredging, held in captivity for 48 h, measured, individually tagged and released post-dredging to the same 5-m channel sections they originated from. They were subsequently monitored for three consecutive years. Mussel survival remained high throughout the study, and no increased mortality in the year following reintroduction was observed. There was no growth retardation. Mussel mobility was low, with most individuals remaining in the same channel section in which they were released. Recolonisation patterns were consistent with the composition of mussel communities in adjacent unaffected habitats. Although dredging drastically changes mussel habitat, some characteristics: microclimate, water chemistry, nutrient availability and host fish can remain adequate. Our study shows that reintroducing mussels to the same site can serve as an effective mitigation conservation measure and can be preferable to translocation, particularly when carried out under time pressure with limited possibilities of assigning appropriate destination sites. [ABSTRACT FROM AUTHOR]

The significant importance of the Nile River emerges not only from the fact that it represents the main water source for Egypt but also from its being an important water path for sailing to transport goods or for Nile tourism cruises. Because of climate change and the construction of the Ethiopian Renaissance Dam, Egypt may have to reduce the discharges from the High Aswan Dam (HAD), which may cause a reduction in water depth below a safe level for navigation. Consequently, this study aims to present a quasi-real-time approach to detect the locations of bottlenecks that threat navigation path via mobile Google Maps. Accordingly, the topographic, hydraulic data, the alignment and geometry of the navigational channel, were collected from the Ministry of Water Resources and Irrigation of Egypt. AutoCAD Civil 3d is adopted in this study to determine navigational bottleneck locations of the Nile River's first reach. Two surface models were created: The Riverbed surface and the navigational path surface using a Triangular Irregular Network (TIN). As a result of the created TIN-Surface modelling via the current study; the amount of sediment, that should be dredged, was estimated (at about 2.1 million.m³). In addition, the navigation path bottlenecks map for the studied reach was created based on minimum water levels at Aswan High Dam's winter closure and the navigational path's geometry. In conclusion, this study provides a simple solution for avoiding bottlenecks by presenting a user-friendly web Google Maps of these locations to represent the Nile River's current navigation condition in quasi-real-time and support the decision-maker on river navigation conditions. [ABSTRACT FROM AUTHOR]

Copyright of Stratum Plus Journal is the property of P.P. Stratum plus and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Hybrid System of Fluidization-sediment flushing is a dredging technique that combines the functions of fluidization and suction in the same fluidization pipe using a perforation pipe. The purpose of this study was to address an easier dredging method using fluidization pipes. 2-dimensional (2D) experimental physical modeling research and multiple linear regression analysis were used to process the test result. The results found that for optimal sediment flushing after the sediment layer was agitated by fluidization, the influence parameter was analyzed must follow the limitations of the experimental result, such as the hole diameter (Df) is not more than 5 mm (Df < 5 mm), the hole distance (ɑ) is less than 5 cm (ɑ/db < 5 cm), the pump head (HP) is small, and the fluidization pipe depth/sediment thickness (db) can be larger. The research findings are presented in the correlation equation which indicates the relationship of dimensionless parameters was Vs/Vw = 1/Df ((ɑ/db), (HP/db), (t.(g×0.5)/(db0.5)), (v/(g.db(S – 1)0.5)) which can be applied to 3-dimensional experiments and field experiments. One of the advantages of the hybrid system of fluidization-flushing sediment is its ease of use and lack of impact on the aquatic environment as a dredging technique. [ABSTRACT FROM AUTHOR]

Sedimentation at docks represents a critical concern in coastal and inland water environments, where the dynamic interplay of natural processes and human activities can lead to the gradual accumulation of sediments. The presence of sediment near ports can lead to difficulties in navigation, reduced water depths, and higher costs for upkeep. By comprehensively consolidating and evaluating the current understanding of sedimentation at ports, extensive analysis will offer vital insights that will inspire academics to further their research and make significant advancements in tackling the difficulties related to sedimentation in port environments. This study utilizes quantitative methodologies, using VOS Viewer and Publish and Perish, specifically descriptive and correlational designs, to elucidate characteristics, trends, and relationships related to the research topic. The connectivity is demonstrated through the Network Visualization Diagram and Density Visualization Diagram, which show a significant interconnectedness among the keywords. The primary utilization of data mainly consists of books and journals. The trend showed a fluctuation in 2004, with the highest peak occurring in 2016. This bibliometric analysis suggests that the ongoing discussion about sedimentation in dock environments remains relevant. [ABSTRACT FROM AUTHOR]

The port of Tanger Med stands as the first port in Africa and the Mediterranean, with a throughput capacity of up to 9 million TEUs annually, accommodating the globe's largest vessels, such as ULCVs and MGX-24 classes, which boast capacities nearing 24,000 TEUs. To advance the safety and efficiency of handling deep-drafted vessels, the Tanger Med Port Authority, in cooperation with other terminals partners, try to deploy a sophisticated IoT-based system. This system integrates a high-precision non-linear 3D sea-keeping engine with detailed metocean forecasts, encompassing data on waves, winds, and other hydrodynamic factors. This IoT solution has been instrumental as a decision-support tool, facilitating the Harbormaster and Pilot teams in safely managing vessel transits. It has enabled an increase in the maximum allowable draft to 17.4 meters without requiring dredging. This paper delves into a model validation study assessing the effectiveness of the IoT solution in enhancing dynamic under-keel clearance management at Port Tanger Med, underlining its crucial role in improving operational efficiencies and ensuring navigational safety. [ABSTRACT FROM AUTHOR]

In the current implementation process for dredging projects, due to the lack of an accurate understanding of underwater soil characteristics, construction teams often find it difficult to accurately understand the soil condition. Not only does this lead to a reduced dredger operation efficiency, but it may also cause delays to the project's progress, as well as increasing its cost. Therefore, there is an urgent need to closely integrate soil analysis technology with dredging construction to ensure that projects can be completed efficiently and to a high standard. Therefore, this paper proposes a soil modeling and prediction method based on a three-dimensional point cloud model. The research objective is to propose a new method of soil mass identification with a strong generalization ability and function, which can not only be applied to dredging engineering but can also identify and analyze statistics of land soil and its mass. The accuracy of this method, based on a convergent grid, can reach 95%. [ABSTRACT FROM AUTHOR]

Ecological restoration in dredging areas has attracted increasing attention. The reconstruction of a submerged plant ecosystem is an important method for aquatic ecosystem restoration. This study has systematically investigated the effect of biochar-improved sediment on the plant growth and decontamination efficiency of a constructed ecosystem. Microbial community composition and structure in the sediment were detected. The results showed that a supplement of 20 mg/g of biochar significantly increased the biomass of the submerged plants compared with other doses (0, 10, and 40 mg/g). The biomass and chlorophyll content were significantly inhibited by supplementing 40 mg/g of biochar. In the Ceratophyllum demersum L. system, TP and NH4+-N concentrations were significantly lower after treatment with 20 mg/g of biochar compared to other doses. In Vallisneria spiralis L. and Hydrilla verticillata (L. f.) Royle systems, NH4+-N, TP, and DO concentrations were significantly different among different biochar treatments. In general, 20 mg/g of biochar improved water quality in different submerged plant systems, while 40 mg/g of biochar had adverse effects on water quality, such as higher NH4+-N and TP concentrations. The dominant microbial community included Proteobacteria, Acidobacteria, Chloroflexi, Actinobacteriota, and Bacteroidota. The structure and function of microbial communities were different among submerged plants and biochar treatments. Our results proposed a construction strategy of submerged plants in the dredging area. [ABSTRACT FROM AUTHOR]

Introduction: Agricultural drainage ditches are essential for maintaining flow efficiency and are often managed by brushing (i.e., vegetation clearing along ditch banks) and dredging. These maintenance practices not only impact flow but also the ditches' capacity to process and assimilate agricultural chemicals. However, the influence of ditch management on microbial activities, essential in processing and transforming these contaminants, remains underexplored. Methods: We conducted a four-year surface water sampling campaign in two long-established (over 40 years) agricultural drainage ditches situated in eastern Ontario, Canada. One drainage ditch underwent intensive bank brushing and channel dredging, while the other remained unmanaged. We assessed the impact of these contrasting ditch management practices on the diversity and compositional structure of surface water microbiome communities, with a particular focus on the distribution of genes associated with nitrogen (N) cycling, using shotgun metagenomics sequencing and an assembly-based metagenome approach. Results and discussion: From 117 surface water samples, we reconstructed 157 metagenome-assembled genomes (MAGs), predominantly from the Patescibacteria superphylum. Brushing alone, conducted about 10 months prior to dredging, had an insignificant impact on the aquatic microbial community. However, dredging led to a significant reduction in community diversity and abundance of genes affiliated with denitrification, dissimilatory nitrate reduction to ammonia, and complete nitrification through comammox. Ditch management resulted in noticeable shifts in the microbial community, evidenced by the enrichment of taxa in Polaromonas, Emticicia, Flectobacillus, and Patescibacteria in the water of the managed ditch sites. The metagenomes of these taxa harbor genes involved in various nitrogen biotransformation pathways. Interestingly, following dredging, the levels of ammonia and ammonium, nitrite, and total Kjeldahl N in the managed ditch did not increase, but significantly decreased; likely due to ditch substrate removal and potentially increased flow efficiency and dilution. Being one of the few studies conducted to date, this study provided unique insights into the consequences of drainage ditch management on freshwater microbiomes involved in N cycling. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Santos is the most important Brazilian port, handling about 162 million of tons in 2022. In 2010, there was a great capital dredging to deepen the Access Channel to 15 m deep (Chart Datum - CD). This depth was not achieved, due to inefficiency on dredging procedures. Previous studies have indicated that, in order to maintain the bathymetric condition presented by the survey carried out in March 2016, an annual dredging of approximately 4,325,000 m³ would be necessary. This value increases for different project depths, increasing by 15%, 55%, and 80%, considering drafts of 15, 16, and 17 meters, respectively. Considering this situation, this study evaluated the possibility of implementing jetties in the region of the Port of Santos, using a calibrated hydrodynamic and morphological computational model for the area of interest. From the simulation of two different scenarios to represent local hydrodynamic conditions, reductions of approximately 45%, 40%, 35%, and 30% were estimated for the condition presented by the 2016 bathymetry and for draft depths of 15, 16, and 17 meters, respectively. [ABSTRACT FROM AUTHOR]

The Paraguay River Waterway is a crucial axis for integration in South America, with a course of 3.442 km from Cáceres (Brazil) to Nueva Palmira (Uruguay). To provide the navigation, improve the safety, the reliability and efficiency of the waterway transport, for a minimum period corresponding to 90% of the year, interventions with amelioration works are necessary. Among them, dredging in critical stretches stand out, which currently present some form of obstacle to navigation, either by natural factors (widths, radius of curvature and depths) or by structures, such as bridges, and sand shoals. This paper proposes a reassessment of the current nautical dimensions based on new guidelines, assessing critical sections for depth, width, and radius of curvature. The aim is to increase safety and study the feasibility of expanding the waterway by accommodating larger convoys. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Waluyo G, Laksono FXAT, Zaenurrohman JA, Mishra M, Piranti AS, Kovács J. 2024. Sediment dredging assessment of the Mrica Banjarnegara hydroelectric reservoir based on technical and economic aspects. Lake Reserv Manage. 40:145–158. The Mrica Dam, built in Banjarnegara Regency, Indonesia, in 1988, was designed to have a usable life of 50 yr. However, the current life span is estimated to be less than 50 yr due to a decrease in the dam's capacity. This dam is facing a significant challenge in the form of intensive sedimentation, resulting in siltation issues. Active measures such as dredging efforts and catchment area management have been initiated to address this problem and prolong the dam's durability. Consequently, a comprehensive technical and economic analysis is imperative to gauge the efficacy of the dredging program. The engineering aspect of the study focused on sedimentation dispersal patterns and the identification of suitable dredging methods to combat the sedimentation problem effectively. Meanwhile, the economic review factored in both the cost of dredging operations and the profits derived from the sale of sedimentation materials. The findings from our assessment reveal the existence of 17 lucrative spoil banks, yielding an average annual gain of USD 118,575. However, it is crucial to note that dredging the foreset slope costs USD 1.65 million per year. Optimally, the most effective and efficient dredging initiatives should commence at the foreset slope and extend upstream of the dam. A strategically positioned disposal area has been designated south of the dredging location to facilitate the mobilization of dredged products. In conclusion, our analysis indicates that the cost incurred by the company for dredging the dam exceeds the profit generated from the sale of sedimentation materials. [ABSTRACT FROM AUTHOR]

The marine environment in Tanzania faces significant pollution originating mainly from land-based sources such as industrial, agricultural, and municipal waste, as well as coastal construction, oil discharges, and dredging activities. Siltation, a significant problem in the Dar es Salaam harbor, has led to a decrease in the depth of the entrance channel, requiring more frequent dredging.