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Seagrass meadows are highly productive ecosystems which provide many ecological services to organisms. Seagrass canopies create a hydrodynamically low-energy environment which can increase sediment deposition and reduce resuspension, thus enhancing habitat stability. Direct measurements of sediment deposition usually employ cylindrical traps, but results from this method have been debated. Flat sediment plates are an alternative method that minimise the problems of cylindrical traps but do not measure the exact same processes. Plate traps were used in conjunction with cylindrical traps to measure sediment deposition in a seagrass bed and nearby barren site in Estero Bay, Florida, U.S.A. Sediment plates and cylindrical plates were deployed every 2–3 months in a Thalassia testudinum dominant seagrass bed and nearby barren site to examine seasonal differences in sediment deposition and differences between the vegetated site and the barren site. The data from the plate traps corroborate the reduction of resuspension in the seagrass bed compared to the barren site found in other studies. This result was supported by measurements of reduced near-bed velocity and shear stress in the seagrass meadow. Plate traps had more consistent results than cylindrical traps. Differences between the barren and vegetated sites from the cylindrical traps were variable. [ABSTRACT FROM AUTHOR]

Halifax Harbour, a crucial Atlantic Canadian port, has extensive commercial, environmental, and strategic value to Canadians. Despite thorough hydrographic research, knowledge about the influence of the bottom current on the resuspension of sediments within the Harbour is lacking. To address this knowledge gap, we utilized a high-resolution, three-dimensional, barotropic finite volume community ocean model (FVCOM) to simulate the tidal-driven maximum bottom current in the Harbour. We used the critical Shields parameter, a threshold for sediment movement, to quantify the areas susceptible to sediment resuspension. Our results indicate that regions in the Narrows and west of McNabs Island are susceptible to sediment resuspension due to the interaction of maximum bottom current and sediment grain sizes. These findings are important for detecting sediment changes in the Harbour and potentially improving existing monitoring and management practices. [ABSTRACT FROM AUTHOR]

Seagrass meadows are highly productive ecosystems which provide many ecological services to organisms. Seagrass canopies create a hydrodynamically low-energy environment which can increase sediment deposition and reduce resuspension, thus enhancing habitat stability. Direct measurements of sediment deposition usually employ cylindrical traps, but results from this method have been debated. Flat sediment plates are an alternative method that minimise the problems of cylindrical traps but do not measure the exact same processes. Plate traps were used in conjunction with cylindrical traps to measure sediment deposition in a seagrass bed and nearby barren site in Estero Bay, Florida, U.S.A. Sediment plates and cylindrical plates were deployed every 2–3 months in a Thalassia testudinum dominant seagrass bed and nearby barren site to examine seasonal differences in sediment deposition and differences between the vegetated site and the barren site. The data from the plate traps corroborate the reduction of resuspension in the seagrass bed compared to the barren site found in other studies. This result was supported by measurements of reduced near-bed velocity and shear stress in the seagrass meadow. Plate traps had more consistent results than cylindrical traps. Differences between the barren and vegetated sites from the cylindrical traps were variable.

Major hurricanes can greatly affect sediment biogeochemical processes in coastal bays and estuaries through strong storm surges and resuspension, yet the impacts on sediment geochemistry have rarely been evaluated. Here, the sediment geochemistry of the Mission Aransas Estuary, Texas, was systematically evaluated prior to and after Hurricane Harvey, a Category 4 storm. The median grain size of the surface sediments in the estuary significantly increased, but the bulk sediment total organic carbon content (TOC%) remained relatively constant. The concentration and composition of several organic chemical classes in the sediment were altered in distinctly different patterns. Accessory pigments showed that cyanobacterial materials in surface sediments increased immediately after Harvey, but returned to pre-Harvey levels 5 months post-hurricane. Pheophorbide decreased significantly after Harvey, but also recovered within 7 months, suggesting resilience of the benthic community. In contrast, polycyclic aromatic hydrocarbons (PAHs) and n-alkanes decreased (5–10 folds) 5 months after Hurricane Harvey and remained low 1 year later. The loss of PAHs and n-alkanes from the sediment might be related to increased solubility due to decreased salinity and strong resuspension during the storm surge. Overall, the strong storm surge and resuspension of sediment by Hurricane Harvey presented a major disturbance to the geochemistry of surface sediment in the MAE, but the impact on individual organic chemical classes depended on their sources, chemical properties, and/or association with fine clay minerals. [ABSTRACT FROM AUTHOR]

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The Bohai Sea, known for being the lowest latitude seasonally frozen sea area in the world, experienced severe ice conditions with a 30-year recurrence period during the winter of 2009-2010. Water-sediment flux is a crucial parameter for water quality management in marine environment. Using a highly accurate three-dimensional hydrodynamic and sediment transport numerical model, the significant wave height (Hs), current velocity, suspended sediment concentration (SSC) and water-sediment flux in the Bohai Sea during ice-covered and ice-free conditions are compared. Our findings indicate that the current velocity and sediment resuspension decrease under the ice coverage, but increase at the edge of the ice. The net outflow tidal flux (TF) in winter under ice-free conditions accounts for 24.5% of the whole year. The net outflow TF increases by 32.7% during ice-covered conditions, primarily due to the pressure difference between high air pressure superimposing heavy sea ice in the northwest Bohai Sea and the low air pressure in Bohai Strait, resulting in increased ebb velocity and decreased flood velocity. The net outflow suspended sediment flux (SSF) during ice-free conditions in the winter is 2.32×109 kg, while SSF increases by 1.24 times during ice-covered conditions, leading to worse water quality in the outer sea. The decrease of TF in the southern part of the Bohai Strait and the reduction of suspended sediment concentration by nearly 15 mg/l lead to the significant decrease in SSF. This study has significance guiding value for understanding the source-sink sedimentation system and water quality research in East China Sea. [ABSTRACT FROM AUTHOR]

Storm-induced episodic sediment redistribution in coastal systems can reshape geomorphic bodies, disrupt ecosystems, and cause economic damage. However, cold-wave-storm-induced hydrodynamic changes and residual sediment transport in large, exposed subaqueous deltas, such as the Yangtze Delta, are poorly understood because it is typically expensive and difficult to obtain systematic field data in open coast settings during storm events. We conducted a successful field survey of waves, currents, changes in water depth, and turbidity at a station (time-averaged water depth of 20 m) in the offshore subaqueous Yangtze Delta over 10 days during winter, covering two storms and two fair-weather periods. During the storm events, strong northerly winds drove southward longshore currents (~0.2 m/s) and resulted in increased wave height and sediment resuspension, thereby leading to massive southward sediment transport. In contrast, both southward and northward transports were limited during the fair-weather periods. A better understanding of the storm-induced sediment transport can be obtained by using an approximately half-day lag in sediment transport behind wind force, given the time needed to form waves and longshore drift, the inertia of water motion, and the slow settling velocity of finegrained sediment. Our results directly support previous findings of southward sediment transport from the Yangtze Delta during winter, which is deposited in the Zhejiang-Fujian mud belt in the inner shelf of the East China Sea. In addition, the southward sediment transport from the Yangtze Delta occurs mainly during episodic storm events, rather than during the winter monsoon, and winter storms dominate over typhoons in driving southward sediment transport from the delta. This study highlights the importance of storms, especially during winter storms, in coastal sediment redistribution, which is of particular significance when considering the projected increase in storm intensity with global warming. [ABSTRACT FROM AUTHOR]

The Salton Sea is the largest lake in California and is a shallow, hypersaline lake. The endorheic lake has been significantly maintained by agricultural return flows from Imperial Valley farming and two rivers- the New River and Alamo River- which originate in Mexicali, Mexico. The current salinity is at 74 ppt and is expected to increase due to the Quantification Settlement Agreement signed in 2003, stipulating the transfer of nearly 0.616 km³ per year of Colorado River water to urban areas for up to 75 years. This has resulted in inflows reduction, and the dust storms created by the dried-up playa have become a prominent risk to public health in the region. Massive fish and bird kills began in the 1980s and continued to occur periodically. In this study, the Delft3D numerical modeling suite- FLOW, WAVE, and WAQ- was utilized to investigate the transport and cycling of nutrients under the influence of wind-induced sediment resuspension activity. The three-dimensional hydrodynamic and water quality combined model was applied to simulate mitigation scenarios to assess long-term effects on salinity and water quality of (1) emerged islands as a nature-based solution, (2) seawater import/export, and (3) seawater import/export in addition to treating tributary rivers to remove nutrients. Overall, this study supported the findings fromprevious studies and showed that sediment resuspension is the driving force for nutrients cycling in the water column and that emerged islands have long-term potential to enhance burial activity for pollutants removal in the Salton Sea. Furthermore, the seawater import/export scenario showed promising results of reducing salinity level from 46 ppt to 38-39 ppt in 2 years. The 3D numerical hydrodynamic/water quality model developed in this work is the first and latest integrated modeling approach tailored to the Salton Sea's system and has the capacity to improve understanding of the complicated water quality dynamics changes in various restoration concepts. This study demonstrated that being able to explore the full potentials of restoration designs using a comprehensive 3D water quality modeling framework is critical in achieving wholesome planning that will create environmental, social, and economic benefits in the long term for the Salton Sea. [ABSTRACT FROM AUTHOR]

Purpose: The increase in maritime traffic in the Bay of Koper (Gulf of Trieste, northern Adriatic Sea) has been made possible given the increase in the local port capacity and logistics, which, in turn, means an increase in the number of arrivals of larger vessels (which were the original motive for port expansion); this poses a potential risk for coastal environments due to the impact of the resuspension of bottom sediment which affects the physical and chemical characteristics of the water column. The aim of this work was to assess the magnitude of these perturbative events. Materials and methods: Turbidity (NTU) measurements were made using a CTD multiprobe during a vessel manoeuvre in the port navigational canal and in the entire Bay of Koper. In the highest turbidity zone, samples were collected from the surface water layer (0.5 m), at a depth of 6.0 m and 12.0 m. Total suspended solids (TSS) and suspended organic matter (SOM) were measured gravimetrically. TSS grain-size distribution was determined using a laser granulometer. Results and discussion: The effect of the vessel manoeuvre was evident on turbidity with a maximum value of 137 NTU (TSS = ~ 139 mg l−1) and a sampled concentration of TSS of 37 mg l−1 (bottom layer) in the water column immediately after the ship manoeuvre. Grain-size analysis shows a spectrum of particles with a mode size between 22 and 88 μm (medium silt and very fine sand, respectively). The estimated resuspension mass of total suspended solids (TSS) was ~ 109 t in the restricted manoeuvre area extending about ~ 736 × 493 m and with an average depth of 15 m. Conclusions: The results demonstrated the significant impact of vessel manoeuvres on the measured parameters, the impact of which cannot be underestimated in terms of marine environmental protection and maritime traffic safety. Moreover, this impact is expected to increase in the near future. [ABSTRACT FROM AUTHOR]

Seagrass ecosystems are ecologically important but are declining worldwide, prompting restoration efforts. However, restoration success is partially reliant on ensuring that donor material and planting methods are suitable under the environmental conditions expected within restoration sites. This may require planting at critical densities needed to initiate favorable environmental feedbacks, ensuring plants are pre‐adapted to local conditions, and setting realistic restoration goals. An understanding of the relationship between local environmental conditions (e.g. the local light environment and seagrass structural complexity) can be particularly important in guiding restoration decision‐making. Here, we investigate how sediment‐light conditions interact with seagrass structural complexity (density and above‐ground morphology) to guide restoration planting approaches for the intertidal seagrass Zostera muelleri. Using generalized additive models and empirical data, we identified significant relationships between the local sediment‐light environment and the structural complexity of Z. muelleri meadows present in Western Port, Victoria, southeast Australia. We found a decrease in shoot density and leaf length with decreasing light availability, potentially reflective of an adaptive change in the species morphology in response to low‐light environments. We also found a decrease in sediment sorting and increased fine particles with increasing meadow structural complexity, suggesting that seagrass structural complexity increases sediment stability, and accretion, and may contribute to local water clarity via ecological feedbacks. These findings suggest that understanding both environmental drivers and the potential for ecological feedbacks to occur is needed before large‐scale planting begins and that restoration targets should reflect the meadow form most likely to occur under the environmental conditions present. [ABSTRACT FROM AUTHOR]

Sediment resuspension caused by the movement of propellers during manoeuvring is a major problem in daily port operations. Negative impacts include: Marine flora and fauna, sediment erosion that weakens berth structures, sediment deposits that require dredging. Later, this leads to delays in port operations. Several authors have proposed different methods to cope with this problem. This paper presents methods and tools to determine the critical propeller jet velocities, which are the most important parameter to determine the size of the bank stabilisation system. The tool is a bridge simulator that can be used to simulate the intrusive departure manoeuvre of a ship. The ship motion data are analysed to determine the critical shear stress of the sediment particles. The critical velocity induced by the propeller jet is determined using the German method. [ABSTRACT FROM AUTHOR]

With the consumption of terrestrial metal resources, deep-sea polymetallic nodule minerals have been widely exploited around the world. Therefore, the environmental impact of deep-sea polymetallic nodule mining cannot be ignored. In this study, for the first time, a field disturbance and observation device, integrated with multiple sensors, is used to simulate the disturbance process of mining on seabed sediments in the polymetallic nodule area of the western Pacific Ocean at a depth of 5700 m. The impact of the process of stroking and lifting on the bottom sediment in the polymetallic nodule area is 30 times higher than that caused by the waves or the current. The time for turbidity to return to normal after the increase is about 30 min, and the influence distance of a disturbance to the bottom bed on turbidity is about 126 m. The time it takes for density to return to normal is about four hours, and the influence is about 1000 m. At the same time, the resuspension of the bottom sediment leads to an increase in density anomaly and salinity. Moreover, suspended sediments rich in metal ions may react with dissolved oxygen in water, resulting in a decrease in the dissolved oxygen content and an increase in ORP. During the observation period, the phenomenon of a deep-sea reciprocating current is found, which may cause the suspended sediment generated by the continuous operation of the mining vehicle to produce suspended sediment clouds in the water near the bottom of the mining area. This could lead to the continuous increase in nutrients in the water near the bottom of the mining area and the continuous reduction in dissolved oxygen, which will have a significant impact on the local ecological environment. Therefore, the way mining vehicles dig and wash in water bodies could have a marked impact on the marine environment. We suggest adopting the technology of suction and ore separation on mining ships, as well as bringing the separated sediment back to the land for comprehensive utilization. [ABSTRACT FROM AUTHOR]

Trace metals (TM) delivered by atmospheric dust play a key role in oceanic biogeochemical cycles. However, the impact of short‐term environmental perturbations such as dust storms and sediment resuspension events on the oceanic water column is poorly constrained due to the low temporal sampling resolution and episodic nature of these events. The Gulf of Aqaba (GoA), Red Sea, is a highly accessible deep oligotrophic water body featuring exceptionally high atmospheric deposition fluxes that provide the main source of TMs to the GoA surface water. Here, we present a 2‐year time series of dissolved manganese, cobalt, nickel, copper, zinc, cadmium, and phosphate concentration profiles sampled in the GoA. The study focuses on daily time scale dust storms and episodes of sediment resuspension to quantify the immediate impact of these events on dissolved TM cycling. Counter‐intuitively, upper mixed layer TM inventories decrease with increasing aerosol loads, with the effects of aerosol‐induced TM scavenging and dissolution peaking 5–6 days after aerosol deposition. Dust storms promote intense TM scavenging, with TM inventories decreasing by up to 44%, but seldom lead to TM enrichment. Similarly, sediment resuspension and flash flood events triggered significant TM scavenging. These findings highlight the potential dual role of atmospheric deposition in the oceans as a long‐term source of dissolved TMs and a short‐term sink. The in situ observations presented here may be used to understand and quantify the global impact of abrupt environmental events on oceanic chemical compositions. Plain Language Summary: Trace metals (TM) in the oceans are essential nutrients for marine life and serve as the base for various oceanic processes. The main source of these metals in the upper part of the ocean is dust that settles from the atmosphere. This dust is largely delivered during short‐term dust storms. However, little is known about their impact since sampling in open ocean environments is rarely conducted in association with such storms. This study focuses on the Gulf of Aqaba in the Red Sea, which is one of the dustiest regions on Earth. We measured TM in seawater on a daily basis before and after dust storms to record their effects on TM levels in seawater. The results show that surprisingly, increases in dust loads during dust storms are associated with lower levels of TM in seawater. This reflects a process of metal adsorption onto dust particles sinking in seawater. These unique findings allow us to quantify the impacts of dust on seawater trace metal contents, and demonstrate that on the long term, dust is a source of metals to the oceans, but on shorter time scales, dust is also capable of removing metals from seawater. Key Points: Dissolved trace metals were measured at a daily resolution in the Gulf of Aqaba, Red Sea, across dust storms and other perturbative eventsUpper water column trace metal inventories decrease with increasing dust loads. Aerosol‐induced shifts peak ∼5–6 days after dust depositionDust storms and sediment resuspension events drive a decrease in trace metal (Mn, Co, Ni, Cu, and Cd) concentrations due to particle scavenging [ABSTRACT FROM AUTHOR]

Ocean dynamic processes in the bottom boundary layer (BBL) are crucial for sedimentation, such as deposition and resuspension of marine sediments. In this study, we conducted in-situ tripod observations of the sediment ridge of a contourite drift in the northern South China Sea to understand the main dynamic processes affecting sedimentation on the contourite drifts. It was found that the diurnal tidal current was the strongest current at the study site, thus acting as the main dynamic affecting sedimentation processes. Periodic events of elevated suspended sediment concentration (SSC) were observed, some of which occurred only within 15 m above the seafloor and were termed near-bottom high SSC events, while others covered the entire range of the observed water column and were termed full-depth high SSC events. In-situ sediment resuspension at the sediment ridge is not an important factor affecting the formation of high SSC events. Rather, these high SSC events were mainly caused by lateral transport of sediments from the main body of the contourite drift by the northwestward diurnal tidal currents. The seafloor sediments at the main drift body are resuspened owing to the near-critical reflection of diurnal tidal currents on the slope topography of the drift. During periods when diurnal tidal currents were weak, locally generated internal waves could also induce burst-like full-depth high SSC events. This study highlights the diurnal tidal current as the main dynamic regulating the sedimentary processes of the contourite drifts in regions where the near-critical reflection prone to occur, implying the complexity of sediment dynamics of contourite drifts.

The environmental effects of ship propellers were not even close to fully examined before the current massive ships were introduced to sea trade. Larger ships, result in greater length, beam, draft and propulsion power. Of concern here is the under-keel clearance (UKC) and applied power, the most important parameters causing sea bottom sediment resuspension and, consequently, the transport and deposition of washed sediments. The problems are multifarious: shorelines could be contaminated with heavy metals, petroleum hydrocarbons and other organic chemicals, which are sometimes buried deep in the sediment bed. The effects of resuspension on marine life have been well documented by marine biologists. Further, a ship passing through a flow field may have a significant hydrodynamic effect on the shipping channel: waves generated by moving vessels can accelerate shoreline erosion; erosion around quay piles have a negative impact on sea flora. Waves can also affect other manoeuvring vessels or ships at berth. Available empirical models are applicable for a steady state condition, addressing velocity and, consequently, shears at the sea bottom for defined UKC and states of applied power. The idea here is to calculate material resuspension dynamically in the water column based on realistic manoeuvring conditions, which can be a matter of some complexity. During a manoeuvre, the pilot must bring the ship into or out of the harbour in the safest possible way, operating the telegraph, rudder, thrusters and possibly tugs, and also co-ordinating the work of the linesmen. The jet speed powering the vessel is not only a function of the speed of the propeller, but also of the present speed of the ship, which has an effect on the propeller's constantly changing torque. Additionally, the bathymetry is constantly changing, and the streamlines hit not only the seabed, but also the bank and other structures of the harbour basin. The resuspended material remains in the column long after the ship has finished manoeuvring, moving slowly through the entire water column and being transported not only by the remaining streamlines of the ship but also by general currents. Realistic manoeuvring parameters can be obtained from real-time simulations with a real crew using state-of-the-art Full Mission Bridge Simulators (FMBS); eddies and the like contribute to the distribution and material resuspension and can be calculated by applying numerical modelling. In this paper, a container ship departure manoeuvre is simulated dynamically using Wartsila FMBS obtained data, which are postprocessed and coupled with the MIKE 3 FM hydrodynamic modelling application to which we add the precise port of Koper bathymetry to gain ship propeller spatial jet velocity distribution in specific time domains. Obtained jet velocity distribution is further coupled with the MIKE 3 MT particle tracking application to visualize total resuspended sediment transport patterns, etc. Container ships were selected to amplify the urgency of this phenomenon; they are the most intrusive in terms of resuspending and scouring the seabed given their powerful engines and larger propellers. Passenger ships could have been used, car carriers, or even tankers; but the fear among scientists is that the issue will not be taken seriously enough by certain stakeholders. [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) are nonlinear fluctuations in nature that could cause significant interactions between seawater and the seabed. ISWs have been proven to be an adequate cause of sediment resuspension in shallow and deep-sea environments. In the South China Sea, ISWs have the largest amplitude globally and directly interact with the seabed near the Dongsha slope in the northern South China Sea. We analyzed the water profile and high-resolution multibeam bathymetric data near the Dongsha slope and revealed that submarine trenches have a significant impact on the sediment resuspension by ISWs. Moreover, ISWs in the zone of the wave-wave interaction enhanced sediment mixing and resuspension. The concentration of the suspended particulate matter inside submarine trenches was significantly higher than that outside them. The concentration of the suspended particulate matter near the bottoms of trenches could be double that outside them and formed a vast bottom nepheloid layer. Trenches could increase the concentration of the suspended particulate matter in the entire water column, and a water column with a high concentration of the suspended particulate matter was formed above the trench. ISWs in the wave-wave interaction zone near Dongsha could induce twice the concentration of the bottom nepheloid layer than those in other areas. The sediment resuspension caused by ISWs is a widespread occurrence all around the world. The findings of this study can offer new insights into the influence of submarine trench and wave-wave interaction on sediment resuspension and help in geohazard assessment. [ABSTRACT FROM AUTHOR]

In this study, we sampled the original sediment columns from three points located in the eastern, central, and western areas of Chaohu Lake, and then investigated sediment resuspension under hydraulic disturbances in the laboratory. The results showed that when the hydraulic disturbance is weak and sediment surface shear stress is small (

Abstract The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks. Graphical abstract

Parameterizations for bottom shear stress are required to predict sediment resuspension from field observations and within numerical models that do not resolve flow within the viscous sublayer. This study assessed three observation‐based bottom shear stress (τb) parameterizations, including (a) the sum of surface wave stress and mean current (quadratic) stress (τb=τw+τc ${\tau }_{b}={{\tau }_{w}+\tau }_{c}$); (b) the log‐law (τb = τL); and (c) the turbulent kinetic energy (τb = τTKE); using 2 years of observations from a large shallow lake. For this system, the parameterization τb = τw + τc was sufficient to qualitatively predict resuspension, since bottom currents and surface wave orbitals were the two major processes found to resuspend bottom sediments. However, the τL and τTKE parameterizations also captured the development of a nepheloid layer within the hypolimnion associated with high‐frequency internal waves. Reynolds‐averaged Navier‐Stokes (RANS) equation models parameterize τb as the summation of modeled current‐induced bottom stress (τc,m) and modeled surface wave‐induced bottom stress (τw,m). The performance of different parameterizations for τw,m and τc,m in RANS models was assessed against the observations. The optimal parameterizations yielded root‐mean‐square errors of 0.031 and 0.025 Pa, respectively, when τw,m, and τc,m were set using a constant canonical drag coefficient. A RANS‐based τL parameterization was developed; however, the grid‐averaged modeled dissipation did not always match local observations, leading to O(10) errors in prediction of bottom stress. Turbulence‐based parameterizations should be further developed for application to flows with mean shear‐free boundary turbulence. Plain Language Summary: Bottom shear stress is the link between hydrodynamic motions and sediment resuspension, further relating to water quality in the lake. However, it is impractical to directly measure the bottom shear stress in the field. We assessed three observation‐based bottom shear stress parameterizations, using 2 years of observations from a large shallow lake, and found that the parameterization consisting of surface wave‐induced stress and bottom current‐induced stress is sufficient to capture major sediment resuspension events. In the numerical models, which averaged the turbulence dissipation, the parameterization based on modeled surface wave‐induced stress and bottom current‐induced stress was also assessed and compared against the values from observation‐based parameterizations. The usage of a constant, observed or literature‐based parameter in the model parameterization is recommended, and it should be calibrated to account for inaccuracies in modeled hydrodynamic variables (i.e., surface waves and bottom currents). Key Points: Three observation‐based bottom shear stress parameterizations were assessed in a large shallow lakeThe parameterizations of bottom shear stress in Reynolds‐averaged Navier‐Stokes equation models was assessed against the observations [ABSTRACT FROM AUTHOR]

Resuspension and redistribution of sediments induced by propeller wash may significantly influence aquatic ecosystems at contaminated sediment sites. This study describes a numerical modeling method developed to predict the sediment resuspension and subsequent transport processes resulting from ship traffic, with a fully coupled simulation of hydrodynamics, sediment transport, and propeller wash. By including propeller momentum effects in the flow field computation, the advection and dispersion of resuspended sediments are better represented than in previously available methods. To achieve this improvement, a computational algorithm was first developed to calculate the propeller wash effects from one or more ships (e.g., erosion rate and momentum flux); these results were then dynamically linked to a hydrodynamic and sediment transport computation using Environmental Fluid Dynamics Code Plus (EFDC+). This modeling framework was evaluated using a field experiment conducted by the US Navy. The model was calibrated with flow velocities and sediment erosion depths, and then validated with resuspended sediment concentrations in the water column. The model results reproduced the horizontal and vertical distributions of resuspended sediments better when the propeller-induced momentum was incorporated into the flow field computation. The sensitivity test indicated that the increased flow energy from propeller momentum resulted in significant dispersion of resuspended sediments in both longitudinal and lateral directions. The maximum scour was dependent on the propeller revolution speed, the ship engine power, and the distance between the propellers and the sediment bed. [ABSTRACT FROM AUTHOR]

The resuspension of marine sediments plays a key role in the biogeochemical cycle and marine ecology system. Internal solitary waves are considered to be important driving forces of the resuspension of bottom sediments. In this paper, the movement of turbidity currents, the generation and the effects on the bottom bed of internal solitary waves and excitation waves are studied by flume tests and numerical simulations, and the sediment resuspension are analyzed. The results show that the excitation wave can lead to the resuspension of the bottom sediments under all the conditions, while the internal solitary wave can lead to the resuspension of the sediment only under some special conditions, such as high amplitude or large underwater slope. Under the experimental conditions, the change in the near-bottom velocity caused by the excitation wave is close to three times that of the internal solitary wave. [ABSTRACT FROM AUTHOR]

Summertime oxygen depletion has been more and more frequently observed in the bottom water of the Bohai Sea in the last decade. Based on comprehensive hydrography and microstructure measurements in summer in the Bohai Sea, the physical structure and bottom dissolved oxygen (DO) dynamics were investigated. The study area is characterized by strong tidal currents and obvious horizontal temperature and DO gradients in the bottom boundary layer. The strong tidal forcing induces large near-bottom turbulent kinetic energy dissipation rates (ϵ ~ 5 × 10-5 W kg-1) which can be well parameterized by the law of the wall. Tidal horizontal advection effects dominate the short-term variations of bottom hydrography. Although the residual current is in a near-perpendicular direction with the horizontal DO gradient (~94°), the horizontal residual DO transport was calculated to be 67.4 mg m-2 d-1 which is ~ 33% of the magnitude of sediment oxygen demand. During the observation period, we observed an intense high-turbidity event leading to a severe drawdown of near-bottom DO concentration (0.16 mg L-1) in 1.5 hours. The DO consumption rate due to this event was then estimated to be ~ 33.3 g m-2 d-1 (1.39 g m-2 h-1) which is two orders of magnitude larger than the sediment oxygen demand. Rapid DO consumption can be induced by the great increase in bioavailable surface area in bottom water and seabed when benthic organic matter is resuspended. This process should be incorporated into the coupled physical-biogeochemical model to improve accuracy in simulating DO depletion.

Abstract Parameterizations for bottom shear stress are required to predict sediment resuspension from field observations and within numerical models that do not resolve flow within the viscous sublayer. This study assessed three observation‐based bottom shear stress (τb) parameterizations, including (a) the sum of surface wave stress and mean current (quadratic) stress (τb=τw+τc ${ au }_{b}={{ au }_{w}+ au }_{c}$); (b) the log‐law (τb = τL); and (c) the turbulent kinetic energy (τb = τTKE); using 2 years of observations from a large shallow lake. For this system, the parameterization τb = τw + τc was sufficient to qualitatively predict resuspension, since bottom currents and surface wave orbitals were the two major processes found to resuspend bottom sediments. However, the τL and τTKE parameterizations also captured the development of a nepheloid layer within the hypolimnion associated with high‐frequency internal waves. Reynolds‐averaged Navier‐Stokes (RANS) equation models parameterize τb as the summation of modeled current‐induced bottom stress (τc,m) and modeled surface wave‐induced bottom stress (τw,m). The performance of different parameterizations for τw,m and τc,m in RANS models was assessed against the observations. The optimal parameterizations yielded root‐mean‐square errors of 0.031 and 0.025 Pa, respectively, when τw,m, and τc,m were set using a constant canonical drag coefficient. A RANS‐based τL parameterization was developed; however, the grid‐averaged modeled dissipation did not always match local observations, leading to O(10) errors in prediction of bottom stress. Turbulence‐based parameterizations should be further developed for application to flows with mean shear‐free boundary turbulence.

Transport processes in coastal oceans are important for understanding mass transport between land and ocean. Investigations of mixing processes are essential to reveal the transport processes. This paper presents mixing processes due to internal tides and the associated mass transport, on the basis of field observations and numerical simulations conducted by the author who is a recipient of Okada Prize from the Oceanographic Society of Japan, 2022. The Yoing Ocean Data Acquisition (YODA) Profiler, has been developed to observe small scale dynamics and mixing processes in coastal oceans. Results from the profiler revealed mixing in river plumes and breaking of nonlinear internal tides on a shallow slope. Breaking of internal tides results in strong turbulent mixing, sediment resuspension and generation of intermediate nepheloid layers in Otsuchi Bay, Japan. It was found that vertical mixing was enhanced by a collision of a receding internal tide and a subsequent run-up nonlinear internal bore on a gentle slope. In addition, numerical models were developed to investigate internal tides breaking. Large scale oceanic numerical models showed enhanced diurnal internal tides caused by a resonance of Kelvin waves around islands over the Izu-Ogasawara Ridge and strongly enhanced the internal tide energy flux toward the upstream of the Kuroshio owing to an interaction of the Kuroshio and tides. This study also applies methods established in oceanic studies to analysis of mixing processes in a lake. [ABSTRACT FROM AUTHOR]

Sediment incipient motion is the first step in sediment resuspension. Previous studies ignored the effect of seepage flow on the mobility of sediment particles and simplified the seabed surface as a rigid boundary. A flume experiment was designed to innovatively divide the seabed into two parts to control the dynamic response of the seabed and control the seepage conditions. In the experiment, the seabed sediments and the amplitude of internal solitary waves (ISWs) were changed to compare and analyze the impact of seepage flow on the sediment resuspension by shoaling ISWs. Moreover, parametric research and verification were carried out. Results indicate that seepage flow can greatly influence fine sand, promote sediment resuspension, and increase the amount of suspension by two times on average. However, seepage flow had a little effect on the suspension of clayey silt and sandy silt. Besides, seepage force was added to the traditional gravity, drag force, and uplift force, and the parameterization of threshold starting shear stress of coarse-grained sediments was developed. The results of this parameterization were verified, and seepage force was critical to parameterization. The threshold starting shear stress was reduced by 54.6% after increasing the seepage force. The physical mechanism of this process corresponded to the vertical reciprocating transient seepage in and out the seabed interface caused by the wave-induced transient excess pore water pressure. This quantitative study on seepage flow for shear stress of coarse-grained sediments induced by ISWs is critical to geohazard assessment. [ABSTRACT FROM AUTHOR]

The effects of sediment elutriate, prepared from a sediment resuspension simulation process, on the growth of bacterioplankton and of different sized phytoplankton as well as on their grazing by protozooplankton were investigated in Mediterranean coastal ecosystems during spring phytoplankton bloom. In parallel, the response of bacterioplankton, phytoplankton and protozooplankton to sediment elutriate enrichment was assessed in microcosm experiments. Elutriate addition provoked a high enrichment in nutriments of the overlying water, particularly in ammonium, dissolved organic matter but also in trace metal elements and herbicides. Overall, elutriate addition significantly increased the biomass of bacterioplankton and of total phytoplankton, but the phytoplankton size fractions responded differently to elutriate enrichment. The picophytoplankton showed a significant strong enhancement in both growth and production rates, relatively to control, while these rates significantly decreased for nano- and microphytoplankton. Accordingly, the phytoplankton size structure shifted in elutriate microcosm toward a dominance of the picophytoplankton concomitant with a significant reduction in larger size fractions. The elutriate addition caused also a clear shift in the taxonomic composition of protozooplankton, associated with a significant modification of its functional diversity, with the dominance of pico-sized cell consumers (such as aloricate ciliates, heterotrophic nanoflagellates and mixotrophic dinoflagellates) in the detriment of grazers of nano- and microphytoplankton (such as heterotrophic dinoflagellate). The protozooplankton grazing on small prey (bacterioplankton and picophytoplankton) increased, while feeding on nano- and micro-sized phytoplankton decreased after elutriate addition. These results have implication for the carbon transfer pathway, which could change from an herbivorous food web to a microbial food web, influencing so the exportation of biogenic carbon through the other trophic compartments. [ABSTRACT FROM AUTHOR]

Shallow water has low depth, and hydrodynamic conditions may change with the effect of wind and waves, resulting in sediment suspension and pollutant release. To investigate the influence of sediment incipient motion on ammonia nitrogen (NH3-N) release in shallow lakes under hydrodynamic disturbance, we monitored ammonia nitrogen concentration in the overlying water of sediments in Chaohu Lake under static, weak, and strong disturbance conditions and analyzed the ammonia nitrogen release rate based on the these concentrations. In static condition, the sediment particles on the surface moved individually (individual movement), and the ammonia nitrogen release rate was 9.59 mg/m2/day. When the disturbance was weak and a small proportion of sediment particles started to move (small movement), the ammonia nitrogen release rate increased to 34.21 mg/m2/day. When the disturbance was further strengthened, and most of the sediment particles moved (general movement), the ammonia nitrogen release rate was 77.04 mg/m2/day. Distribution showed that the release rate varied the most in the western area followed by the eastern area, and the central area had the lowest release rate. The daily release of ammonia nitrogen in Chaohu Lake ranged from 8742.3 kg to 61,008.59 kg. In this experiment, we combined sediment movement and pollutant release, which provides a new reference for the study of pollutant release in shallow lakes and for ammonia nitrogen management in other shallow lakes. [ABSTRACT FROM AUTHOR]

Excess nitrogen (N) loading in summer often boosts phytoplankton growth and increase algal turbidity. In eutrophic shallow lakes, the increased algal production may also augment the abundance of deposit-feeding tubificid worms and thereby sediment resuspension and non-algal turbidity. However, few studies have explored the effects of high N loading on this benthic process in eutrophic shallow lakes. Here, we conducted an outdoor mesocosm experiment in a summer-winter season (177 days) on the shore of subtropical Lake Taihu, China. Each mesocosm contained a 10 cm layer of lake sediment and 450 L of lake water. Nitrate was added weekly to three of the mesocosms, while another three functioned as controls. Our results showed that N addition significantly increased algal particles as water chlorophyll a (Chl-a) increased significantly following N addition. Moreover, significantly higher levels of inorganic suspended solids (ISS) were observed in the mesocosms with added N, indicating elevation of non-algal turbidity as well by the N addition. We attribute the latter to increased sediment resuspension as the abundance of tubificid worms was significantly higher in the N addition mesocosms. Accordingly, our study indicates that high N loading in subtropical shallow lakes may boost both algal and non-algal turbidity in part via benthic-pelagic coupling processes. Our results suggest that alleviation of eutrophication in shallow eutrophic lakes may require a strategic approach to adequately control both N and phosphorus. [ABSTRACT FROM AUTHOR]

The estuary delta is an area where human economic activities are active and natural ecological environment is fragile. With global change and the intensification of human activities, coastal and seabed erosion around the world is becoming more and more serious. In this paper, we used the Delft 3D numerical simulation to compare the hydrodynamic effects of sediment transport paths in the Yellow River delta (river-controlled type), Yangtze River delta (tidal type) and Mekong River delta (tidal wave type) in the East Asian monsoon area, and analyzed the causes of accumulation erosion landform distribution in three different types of subaqueous deltas. This study finds the Yellow River Delta has experienced varying degrees of erosion at the estuary, but its subaqueous delta is still dominated by deposition; the Yangtze River Delta has ensured the stability of its shoreline under the influence of artificial shoreline reinforcement, but the subaqueous delta (water depth: 0–15 m) is in a state of erosion all year round; and in the Mekong River Delta the erosion occurs in both its shoreline and subaqueous delta. Additionally, only by analyzing the erosion and deposition within the transport range of resuspended sediment, the changes in the properties of the entire subaqueous delta could be recognized. The research results can not only be helpful to analyze whether the change of river sediment will lead to the change of delta type under human influence, but also provide more powerful scientific support for the protection of delta ecological environment, geological environment safety and geological disaster prevention. [ABSTRACT FROM AUTHOR]

• Sediment resuspension (SR) controls algae by light reduction and TDP removal. • SR improves sediment quality by increasing ORP and inhibiting phosphorus releases. • SR technology is green and economical, can be applied in drinking water reservoirs. Mitigating harmful cyanobacterial blooms is a global challenge, particularly crucial for safeguarding source water. Given the limitations of current technologies for application in drinking water reservoirs, we propose an innovative strategy based on in-situ sediment resuspension (SR). This method's effectiveness in cyanobacterial control and its potential impacts on water quality were assessed through laboratory culture experiments and further validated via field applications in five drinking water reservoirs. The results revealed that SR could significantly mitigate cyanobacterial growth, evidenced by the treated sets (removal rate: 3.82×106 cells L −1 d −1) compared to the control set (growth rate: 2.22×107 cells L −1 d −1) according to the laboratory experiments. The underlying mechanisms identified included underwater light reduction (2.38× increase in extinction coefficient) and flocculation and entrainment of cells by resuspended particles (30 % reduction per operation). Additional contributions were noted in the reduction of bioavailable phosphate and remediation of anaerobic sediment characterized by increased redox potential. This facilitated the oxidation of iron, which in turn promoted the co-precipitation of phosphate (removal rate: 46 μg L −1 d −1) and inhibited its release from the sediment. The SR operation, devoid of importing extra substances, represents a safe and economical technology for controlling harmful cyanobacteria in drinking water reservoirs. [Display omitted] [ABSTRACT FROM AUTHOR]

Subaqueous sand waves have been observed where nonlinear internal waves (NLIWs) shoal on continental margins. To investigate their generation mechanisms, we propagated periodic NLIWs of depression to shoal upon a sloping bed in a laboratory flume. Following fission of the incident waves, ripple-type bedforms were observed between the point of incipient suspension and interaction point (where the quiescent pycnocline intersects the sediment bed). The largest ripples were centered on the bolus birth point, where the NLIWs of elevation, generated by fission, transform into boluses and maximum near-bed velocities occurred. The ripple height and wavelength were consistent with fluvial scaling. In two experiments, where bedload transport was not predicted, the observations showed resuspension to influence ripple generation. Net upslope sediment movement was observed beyond the turning point. • Ripple bedforms were generated beneath shoaling nonlinear waves of depression in the laboratory • Ripples formed between the point of incipient suspension and the pycnocline-bed intersection • The largest ripples were at the bolus birth point, where waves of elevation transformed to boluses • The ripple height and wavelength were consistent with fluvial scaling [ABSTRACT FROM AUTHOR]

• High resolution observations of sediment remobilization over subaqueous sand waves. • Internal solitary waves are the primary force driving sediment remobilization. • Internal wave induced sediment resuspension and ejection with different dynamics. • Daily high turbidity in bottom water due to critical reflection of internal tides. High-resolution tripod observations were conducted in a subaqueous sand-wave field in the northern South China Sea. The objective was to gain insight into the dynamic mechanism by which sandy sediments are remobilized by oceanic dynamic processes, in particular internal solitary waves and internal tides. Daily-recurring high suspended sediment concentrations were observed, likely due to lateral transport of sediments resuspended by critical reflection of diurnal internal tides at the shelf break. The passage of extreme internal solitary waves results in resuspension of sediments from the seabed and ejection of these sediments out of the boundary layer. The resuspension of sediments from the seabed is controlled by current-induced strong bed shear stress, while the ejection of sediments out of the bottom boundary layer is driven by the compression and subsequent expansion of the mixing layer, together with the developments of the separation bubbles behind the internal solitary waves. These findings provide new insights into understanding the dynamic mechanism of sediment remobilization by internal solitary waves. Moreover, they contribute to our understanding of the migration of subaqueous sand waves. [ABSTRACT FROM AUTHOR]

Intertidal coastal sediments are important centers for nutrient transformation, regeneration, and storage. Sediment resuspension, due to wave action or tidal currents, can induce nutrient release to the water column and fuel primary production. Storms and extreme weather events are expected to increase due to climate change in coastal areas, but little is known about their effect on nutrient release from coastal sediments. We have conducted in-situ sediment resuspension experiments, in which erosion was simulated by a stepwise increase in current velocities, while measuring nutrient uptake or release in field flumes positioned on intertidal areas of a tidal bay (Eastern Scheldt) and an estuary (Western Scheldt). In both systems, the water column concentration of ammonium (NH4+) and nitrite (NO2−) increased predictably with greater erosion as estimated from pore water dilution and erosion depth. In contrast, the phosphate (PO43−) dynamics were different between systems, and those of nitrate (NO3−) were small and variable. Notably, sediment resuspension caused a decrease in the overlying water PO43− concentration in the tidal bay, while an increase was observed in the estuarine sediments. Our observations showed that the concentration of PO43− in the water column was more intensely affected by resuspension than that of NH4+ and NO2−. The present study highlights the differential effect of sediment resuspension on nutrient exchange in two contrasting tidal coastal environments.

An estuarine turbidity maximum (ETM) functions as a filter and plays a key role in transporting suspended sediment. The features of ETM and their formation mechanisms vary with different types of estuaries. Their responses to morphological factors require further study. In this study, the Modaomen Estuary of the Pearl River was selected to examine the formation mechanisms of the ETM and roles of the mouth bar. Hydrodynamics, suspended sediment concentration, and sediment size distribution were measured via cruise shipboard in the mouth bar zone during the dry season of 2020, which indicated that the ETM occurred in the central and western bars. Furthermore, numerical modeling of an idealized estuary based on Delft3D was performed to explore the effects of the existence of a mouth bar on the dynamic structures causing the ETM, including saltwater intrusion, residual longitudinal circulation, and bed sediment resuspension. The results indicated that the existence of a mouth bar contributed to the occurrence of double residual circulations and enhanced bed shear stress on the mouth bar, which favor the ETM formation. In general, two different dynamic regimes were responsible for the ETM formation, that is, sediment trapping by saltwater intrusion and sediment resuspension induced by tidal currents. The mouth bar played a key role in these two mechanisms, including altering the estuarine circulation and bed shear stress. The results contribute to a better elucidation of the ETM formation in estuaries and provide scientific guidelines for estuarine management and engineering. Plain Language Summary: In estuaries, sediment can accumulate forming a sediment‐rich zone with high suspended sediment concentration. The occurrence and distribution of sediment‐rich zones affect water quality and ecological systems in estuary, as well as dredging and shipping needs, which has attracted significant interests of scientists and engineers. We have conducted a field survey to investigate the locations of the sediment‐rich zone and their causes. And we find that high sediment concentration mainly occurs on a shallow depth zone in estuary, which is caused by saltwater intrusion and sediment resuspension. Furthermore, we use a computer model to explore the roles of shallow topography on the accumulation of massive sediment. The results indicate that the shallow topography enhances the impacts of saltwater intrusion and sediment resuspension on sediment accumulation, favoring the occurrence of sediment‐rich zones. These findings have important scientific implications for estuarine management and engineering efforts. Key Points: Formation of turbidity maximum in different mouth bar zones was caused by estuarine circulation and sediment resuspension varying with timeSill topography favored the formation of double estuarine circulation and subsequently trapped sediment on the mouth barExistence of mouth bar enlarged the bed shear stress and then strengthened sediment resuspension caused by tidal current scouring [ABSTRACT FROM AUTHOR]

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks. [ABSTRACT FROM AUTHOR]

Dissolved aluminium (Al) is a primary tracer of atmospheric deposition to the open ocean. However, the impact of short-term environmental perturbations such as dust storms, sediment resuspension and rainfall events on the oceanic water column is poorly constrained due to the typically low temporal resolution sampling in open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a highly accessible deep oligotrophic water body featuring exceptionally high atmospheric deposition fluxes delivered by dust storms, which constitutes as the main terrigenous input to the GoA surface water. Here, we present a time series of dissolved Al and silicate (Si) concentration profiles sampled during 2017 and 2018, with a particular focus on daily time scale dust storms, episodes of sediment resuspension and rain events. We evaluate the results in conjunction with high temporal resolution measurements of airborne aerosols and sediment trap -based water column sinking particulate fluxes. Dissolved Al and Si concentrations ranged between 22 and 91 nmol kg−1 and 0.6 and 3.2 µmol kg−1, respectively. These two elements correlated at depth but decoupled in the upper water column. Counter intuitively, mixed layer Al (Al ML) inventories decrease with increasing aerosol loads, with dust storms promoting intense Al scavenging, causing scavenging rates to surpass dissolution rates and abruptly driving down Al ML by up to 14 %. Concurrently, post dust storm Al ML change rates increase linearly with increasing theoretical dissolution rates and thus net dissolution is predicted for higher dust loads than observed in this study. However, low seawater particle loads during low magnitude dust storms and deep mixing depths will result in conditions that favor scavenging. Similarly, a sediment resuspension event triggered a decrease of 34 % in the Al water column inventory. By contrast, wet deposition may enhance the soluble Al flux from mineral dust by a factor of 11. Atmospheric deposition flux estimates (29.8 ± 4.4 g m−2 year−1) calculated using long-term average Al ML and mixed layer depths agree with independent flux estimations. Conversely, fluxes calculated using discrete profiles yielded a wide range of values (8–93 g m−2 year−1). The combined results demonstrate that atmospheric deposition in the oceans acts as a long-term source for Al while concomitantly serving as a short-term sink through scavenging. The in-situ rates and insights presented here may be used to understand and quantify the true impact of abrupt environmental events on water column chemical compositions. [ABSTRACT FROM AUTHOR]

An estuary delta is an area with active human economic activities and a fragile natural ecological environment. With the intensification of global changes and human activities, coastal and seabed erosion around the world is becoming more and more serious. This study compared the hydrodynamic effect and sediment diffusion path at the Yellow River subaqueous delta (river control type) and the Yangtze River subaqueous delta (tide-river type) in the East Asian monsoon area using a Delft 3D numerical simulation to analyse the causes of the distribution of accumulation and erosion landform in the different types of subaqueous deltas. This study found that the river deltas were dominated by the river when the accumulation landforms concentrated in the direction of the Coriolis forces, which was due to hydrodynamic erosion driven by wind, and the sediment diffusion range was mainly concentrated in shallow water areas (water depth < 6 m), resulting the Yellow River subaqueous delta presenting the pattern of "northern erosion and south accumulation". The Yangtze River subaqueous delta was controlled by tidal effects, making the southern part of the estuary more susceptible to erosion. The research results can not only further deepen the understanding of the physical process and mechanism of erosion and deposition in the subaqueous delta but also provide stronger scientific support for the deltas' ecological environment protection, geological environment safety, and disaster geology prevention. [ABSTRACT FROM AUTHOR]

This study proposes new insights for the interpretation of GEOVIDE particle measurements. Potential resuspension sites due to internal tides (ITs) have been identified along the western Iberian shelf slope using a tidal regional model. Iberian shelf is mainly a source of lithogenic material whereas Galicia Bank is a source of biogenic matter. The potential pathways for particles from the resuspension sites toward the GEOVIDE stations are identified using IBIRYS reanalysis to infer their transport by the ocean circulation. It appears that each station is influenced by a specific pathway and mixed particles from several resuspension sites. This methodology reveals that the criticality of the bathymetry slope, commonly used to track resuspension sites from internal waves, is not sufficient to investigate ITs. An explicit resolution of ITs using a numerical tidal model is required for an exhaustive identification of the resuspension sites. Plain Language Summary: Internal tides (ITs) are waves with a tidal period generated when tides cross a steep slope of the sea floor. ITs then propagate in every stratified layer of the open ocean over hundreds to thousands of kilometers. The encounter of ITs with underwater relief, either at the generation site or after propagation, results in high bottom friction that enhances sediment resuspension. Evidence of lithogenic particles was found at various depths during the GEOVIDE cruise, from the Iberian continental slope to thousands of kilometers away. The present study identifies the sites where ITs are responsible for sediment resuspension. Additionally, the oceanic circulation is investigated to establish the trajectories of the resuspended sediment that could explain the GEOVIDE measurements. Key Points: Sites of high bottom tidal velocity along the Iberian continental slope were identified using a semi‐realistic internal tides modelSediment resuspension was confirmed on five sites based on earlier sediment surveys and Shields criterion thresholdParticle trajectories were proposed based on circulation modeling to improve the interpretation of geochemical tracers measurements [ABSTRACT FROM AUTHOR]

We present a numerical model for the simulation of 3D sediment transport in a Newtonian flow with free surfaces. The Navier–Stokes equations are coupled with the transport, deposition, and resuspension of the particle concentrations, and a volume‐of‐fluid approach to track the free surface between water and air. The numerical method relies on operator splitting to decouple advection and diffusion phenomena, and a two‐grid method. An appropriate combination of characteristics, finite volumes, and finite elements methods is advocated. The numerical model is validated through comparisons with numerical experiments, sediment flushing, shear flow erosion, and the formation of dunes. [ABSTRACT FROM AUTHOR]

Laboratory resuspension experiments were performed using three sediments and seawater, contrasted in terms of metals concentration/contents, metals partitioning in sediments as well as physical-chemical characteristics of both sediment and seawater. The aim of the study was to examine if the variability in metals content and metals distribution onto carrier phases are influencing the dynamics of metal transfers from and to sediment. Since Cu and Pb are classical contaminants found in coastal areas, their dissolved concentrations were monitored (up to 360 h) to assess their release or removal by particles, with a particle concentration of 2.5 g L -1 (wet weight). The dynamics of Cu and Pb transfers were similar between experiments while the amplitude of transfers was specific to each sediment. The results of the study clearly demonstrated that while Cu first undergoes an adsorption onto particles (after few minutes of mixing), Pb first undergoes a desorption from particles (after few hours of mixing). Then Cu was desorbed from particles (from 48 to 360 h), while Pb remained adsorbed onto particles (from few 24 to 360 h). The impact of the quantity of resuspended particles was evaluated after 24 h (Pb) and 360 h (Cu) of mixing with different sediment:water ratio. The increase of resuspended particles leads to a non-linear release of dissolved Cu with Cu concentration overpassing the trigger values to protect 80 % (La Spezia), 90 % (Toulon) and 95 % (Olbia) marine species as defined by the ANZECC (Australian and New Zealand Environment and Conservation Council). On the contrary, the increase of resuspended particles leads to a bell-shaped curve for dissolved Pb pointing out Pb affinity for particles., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The number of Vibrio -related infections in humans, e.g., by Vibrio vulnificus , has increased along the coasts of the Baltic Sea. Due to climate change, vibriosis risk is expected to increase. It is, therefore, pertinent to design a strategy for mitigation of the vibriosis threat in the Baltic Sea area, but a prerequisite is to identify the environmental conditions promoting the occurrence of pathogenic Vibrio spp., like V. vulnificus . To address this, we sampled three coastal Baltic sites in Finland, Germany, and Denmark with salinities between 6 and 21 from May to October 2022. The absolute and relative abundances of Vibrio spp. and V. vulnificus in water were compared to environmental conditions, including the presence of the eelgrass Zostera marina , which has been suggested to reduce pathogenic Vibrio species abundance. In the water column, V. vulnificus only occurred at the German station between July and August at salinity 8.1-11.2. Temperature and phosphate (PO 4 3- ) were identified as the most influencing factors for Vibrio spp. and V. vulnificus spp. in the sediment and the co-occurrence with sediment bacteria in the water column indicate that sediment resuspension contributed to Vibrio spp. in the sediment and the co-occurrence with sediment bacteria in the water column indicate that sediment resuspension contributed to V. vulnificus abundance. Interestingly, V. vulnificus co-occurred with specific cyanobacteria taxa, as well as specific bacteria associated with cyanobacteria. Although we found no reduction in Vibrio associated with eelgrass beds, our study underscores the importance of extended heatwaves and sediment resuspension, which may elevate the availability of PO V. vulnificus associated with eelgrass beds, our study underscores the importance of extended heatwaves and sediment resuspension, which may elevate the availability of PO 4 3- , for Vibrio species levels at intermediate salinities in the Baltic Sea., Importance: Elevated sea surface temperatures are increasing the prevalence of pathogenic Vibrio at higher latitudes. The recent increase in Vibrio -related wound infections and deaths along the Baltic coasts is, therefore, of serious health concern. We used culture-independent data generated from three Baltic coastal sites in Denmark, Germany, and Finland from May to October (2022), with a special focus on Vibrio vulnificus , and combined it with environmental data. Our temporal model shows that temperature, combined with sediment resuspension, drives the prevalence of V. vulnificus at intermediate salinities in the coastal Baltic Sea., Competing Interests: The authors declare no conflict of interest.

With the consumption of terrestrial metal resources, deep-sea polymetallic nodule minerals have been widely exploited around the world. Therefore, the environmental impact of deep-sea polymetallic nodule mining cannot be ignored. In this study, for the first time, a field disturbance and observation device, integrated with multiple sensors, is used to simulate the disturbance process of mining on seabed sediments in the polymetallic nodule area of the western Pacific Ocean at a depth of 5700 m. The impact of the process of stroking and lifting on the bottom sediment in the polymetallic nodule area is 30 times higher than that caused by the waves or the current. The time for turbidity to return to normal after the increase is about 30 min, and the influence distance of a disturbance to the bottom bed on turbidity is about 126 m. The time it takes for density to return to normal is about four hours, and the influence is about 1000 m. At the same time, the resuspension of the bottom sediment leads to an increase in density anomaly and salinity. Moreover, suspended sediments rich in metal ions may react with dissolved oxygen in water, resulting in a decrease in the dissolved oxygen content and an increase in ORP. During the observation period, the phenomenon of a deep-sea reciprocating current is found, which may cause the suspended sediment generated by the continuous operation of the mining vehicle to produce suspended sediment clouds in the water near the bottom of the mining area. This could lead to the continuous increase in nutrients in the water near the bottom of the mining area and the continuous reduction in dissolved oxygen, which will have a significant impact on the local ecological environment. Therefore, the way mining vehicles dig and wash in water bodies could have a marked impact on the marine environment. We suggest adopting the technology of suction and ore separation on mining ships, as well as bringing the separated sediment back to the land for comprehensive utilization.

The environmental effects of ship propellers were not even close to fully examined before the current massive ships were introduced to sea trade. Larger ships, result in greater length, beam, draft and propulsion power. Of concern here is the under-keel clearance (UKC) and applied power, the most important parameters causing sea bottom sediment resuspension and, consequently, the transport and deposition of washed sediments. The problems are multifarious: shorelines could be contaminated with heavy metals, petroleum hydrocarbons and other organic chemicals, which are sometimes buried deep in the sediment bed. The effects of resuspension on marine life have been well documented by marine biologists. Further, a ship passing through a flow field may have a significant hydrodynamic effect on the shipping channel: waves generated by moving vessels can accelerate shoreline erosion; erosion around quay piles have a negative impact on sea flora. Waves can also affect other manoeuvring vessels or ships at berth. Available empirical models are applicable for a steady state condition, addressing velocity and, consequently, shears at the sea bottom for defined UKC and states of applied power. The idea here is to calculate material resuspension dynamically in the water column based on realistic manoeuvring conditions, which can be a matter of some complexity. During a manoeuvre, the pilot must bring the ship into or out of the harbour in the safest possible way, operating the telegraph, rudder, thrusters and possibly tugs, and also co-ordinating the work of the linesmen. The jet speed powering the vessel is not only a function of the speed of the propeller, but also of the present speed of the ship, which has an effect on the propeller’s constantly changing torque. Additionally, the bathymetry is constantly changing, and the streamlines hit not only the seabed, but also the bank and other structures of the harbour basin. The resuspended material remains in the column long after the ship has finished manoeuvring, moving slowly through the entire water column and being transported not only by the remaining streamlines of the ship but also by general currents. Realistic manoeuvring parameters can be obtained from real-time simulations with a real crew using state-of-the-art Full Mission Bridge Simulators (FMBS); eddies and the like contribute to the distribution and material resuspension and can be calculated by applying numerical modelling. In this paper, a container ship departure manoeuvre is simulated dynamically using Wartsila FMBS obtained data, which are postprocessed and coupled with the MIKE 3 FM hydrodynamic modelling application to which we add the precise port of Koper bathymetry to gain ship propeller spatial jet velocity distribution in specific time domains. Obtained jet velocity distribution is further coupled with the MIKE 3 MT particle tracking application to visualize total resuspended sediment transport patterns, etc. Container ships were selected to amplify the urgency of this phenomenon; they are the most intrusive in terms of resuspending and scouring the seabed given their powerful engines and larger propellers. Passenger ships could have been used, car carriers, or even tankers; but the fear among scientists is that the issue will not be taken seriously enough by certain stakeholders.

Quantifying the effect of hydraulic disturbances on sediment phosphate release is a key issue in the water quality assessment of lakes, especially for the shallow lakes which are susceptible to winds and waves. Here, we sampled the original sediment columns from 12 positions in the eastern, central, and western areas of the Chaohu Lake, a representative shallow lake in China, and observed phosphate release under three levels of hydraulic disturbances in the laboratory. When the disturbance was weak and sediment on the surface of bottom mud moved individually (the Individual Motion Mode), sediment phosphate release rate was insignificant (0.24 mg/m2/day). When the disturbance was medium and only a small percentage (< 16%) of surface sediment started to move (the Small Motion Mode), the phosphate release rate sharply increased to 4.81 mg/m2/day. When the disturbance was further strengthened and most (≥ 16%) of the surface sediment moved (the General Motion Mode), the phosphate release rate was more than doubled (10.23 mg/m2/day). With the increase in hydraulic disturbance intensity, the variation range of phosphate release also became wider. Spatial distribution showed that the release rate varies the most in the western area, followed by the eastern and the central areas. By extrapolating the experimental results to the real scale, it was found that the phosphate release fluxes would probably fall within a wide range between 203.43 to 7311.01 kg/day under different levels of hydrodynamic disturbances which considerably affects phosphate release from shallow lakes. This study also has implications for the pollutant management in other shallow lakes. [ABSTRACT FROM AUTHOR]

Concentrations and isotopic compositions of mercury in surface water and surface sediment of the Jiulong River Estuary (JRE) were measured. Differences in total mercury (THg) concentrations in surface water between dry and wet seasons were insignificant, which was also the case with surface sediment THg levels. Large variations in Hg isotopic compositions were observed both in surface water (δ202Hg: − 1.53 to 0.61‰; Δ199Hg: − 0.22 to 0.20‰) and surface sediment (δ202Hg: − 2.64 to − 0.96‰; Δ199Hg: − 0.27 to 0.25‰). Concentration correlations between mercury and dissolved inorganic nitrogen (DIN) implied that mercury in surface sediment may undergo resuspension and be re-emitted to the water surface. The negative Δ199Hg in most of the surface sediments and the correlation between mercury and DIN in the wet season indicate that soil erosion is the major source of mercury. The main sources of mercury in surface water are precipitation and natural soil. The correlation between mercury and dissolved inorganic carbon, perfluoroalkyl substances, polycyclic aromatic hydrocarbons, and dissolved Cd indicates that the contribution of underground water and industrial and urban waste cannot be ignored, which is supported by the positive signature of Δ199Hg. The results of the isotopic analysis also indicate that atmospheric dry deposition is another source of mercury in surface water. The study suggests that the mercury distribution in the estuary is related to some other pollutants. Both using mercury isotope signatures and the distribution links between mercury and other pollutants can be used to better understand the processes and sources of mercury in the estuary. [ABSTRACT FROM AUTHOR]

Resuspended sediment is an important carrier of underwater material circulation, and bed shear stress is usually considered to be closely related to sediment resuspension. To analyze the resuspension dynamics in severely eutrophic Lake Chaohu, China, three fixed stations were set up to collect wave, current, and suspended sediment concentrate (SSC) data under windy weather, and two significant sediment resuspension events were recorded. Based on the Gaussian-shaped spectrum characteristics of waves in Lake Chaohu, the wave orbital velocity was estimated by using the wave parameter method. The selection of the general wave spectrum is important for the accurate estimation of wave orbital velocity. The results of the simple linear wave method were very similar to those of the wave parameter method with a Gaussian-shaped spectrum in Lake Chaohu. The total bed shear stress combining waves and currents during the observation period was calculated, and most of it was contributed by wind-driven waves. The bed material of Lake Chaohu has silt-enriched and weak cohesive features, and an examination of critical shear stress showed that the modified Shields curve method was still applicable to Lake Chaohu. When a sediment resuspension event occurred, the vertical gradient of SSC increased significantly, and the peak SSC value depended on the peak value of bed shear stress. As a predictor, bed shear stress only showed a good linear relationship during sediment resuspension events. At other times, the prediction of SSC using bed shear stress may be biased, especially at the time after a significant sediment resuspension event. [ABSTRACT FROM AUTHOR]

Top‐down surface mixers are increasingly used in drinking water reservoirs to prevent the development of stratification, control cyanobacteria, and limit sediment release of soluble manganese. A targeted field investigation enabled the discrimination of artificial mixing by surface mixers from wind and convection in a shallow (6.6 m), eutrophic drinking water reservoir. Top‐down surface mixers were effective at reducing vertical temperature and dissolved oxygen gradients over a 20 m radius, within which turbulent kinetic energy (TKE) input from the mixers exceeded the maximum TKE contribution from wind and convection. Meteorological conditions appeared to have a stronger influence beyond a 60 m radius from the mixers. Near‐bed velocities measured using an Acoustic Doppler Velocimeter (ADV) ∼ 30 m north of the mixers were significantly lower when the mixers were not operating; when operating, ADV signal amplitude showed localized sediment resuspension. Cyanobacteria cell counts were high throughout the reservoir but counts of low‐light adapted Planktothrix sp. were highest near the mixers, indicating mixer operation may improve growing conditions for Planktothrix. While the destratification goal of mixers was accomplished locally, the limited range of influence left >90% of the reservoir subject to diurnal stratification, anoxia, and potential internal loading of inorganic nutrients and soluble metals, restricting mixer effectiveness as an in‐reservoir management technique to improve raw water quality in shallow systems. Plain Language Summary: Increasingly, top‐down surface mixers are used in drinking water reservoirs to provide additional mixing so water temperatures and concentrations of dissolved oxygen (DO) are uniform throughout. This uniformity minimizes (a) the likelihood of harmful algal blooms and (b) the release of nutrients and soluble manganese from the sediments. The current lack of understanding regarding surface mixers prevents effective evidence‐based management by users. Here, top‐down surface mixers were turned off and on in a shallow, nutrient‐rich drinking water reservoir to distinguish the effects of the mixers from natural mixing. The surface mixers were found to effectively reduce temperature and DO differences over a 20 m radius and a depth of 6.6 m. The effects of the mixers were not seen at 60 m from the mixers. Within the region of influence, the mixers added more energy to the water column than natural mixing. Sediment resuspension was observed 30 m away when mixers were on, and there was a higher prevalence of algae adapted to lower light conditions in the water column closer to the mixers. Overall, it was determined that the limited range of mixing from surface mixers in shallow reservoirs restricts their effectiveness as a tool for water quality management. Key Points: Top‐down surface mixers reduced vertical temperature and dissolved oxygen gradients over a localized area (20–60 m radius)Within this area, input of turbulent kinetic energy from one mixer was higher than inputs from both the wind and natural convectionThe localized energy input resuspends bottom sediments and benefits low‐light adapted cyanobacteria leading to poor water quality outcomes [ABSTRACT FROM AUTHOR]

Sediment resuspension is critical to ecosystem function in shallow lakes. Turbidity is one of the most commonly used indicators of sediment resuspension and has proven to be strongly related with wind. However, it is still difficult to predict sediment resuspension due to its complicated mechanisms. In this study, a support vector regression (SVR) model considering the cumulative effect of wind speed was trained to predict sediment resuspension based on intensified field observations at two sites in Lake Taihu. The accuracy of the SVR model was evaluated, and the initial turbidity was introduced to the model to illustrate its contribution to sediment resuspension. The critical wind speed was also evaluated based on this model. The results indicate that the SVR model considering the cumulative effect of wind speed can increase the accuracy of prediction in comparison with traditional fitting methods. The root-mean-square error (RMSE) of the predicted turbidity dropped to 11.36 NTU at one site and 16.78 NTU at the other, and the maximal information coefficient (cimax) for the relationship between wind speed and turbidity increased to 0.56 for both observation sites. The introduction of initial turbidity significantly improved the performance of the SVR model, with an RMSE value lower than 8.00 NTU and a cimax value higher than 0.95. Analysis of the critical wind speed using the SVR model shows that the critical wind speed generally increased with the rise of initial turbidity. The critical wind speeds at initial turbidities of 30, 40, 50, and 60 NTU were 5, 6, 7, and 7 m/s, respectively.

Weather conditions and lake basin morphometry are of key importance in the study of sediment accumulation rate in lakes. This study aims to determine how these factors affect spatial and seasonal variations in sedimentation rate in the epilimnion and hypolimnion of Lake Gościąż. To determine sedimentation rates, six sedimentation traps were set up at different locations and depths in the lake. Weather data were obtained from a meteorological station near the lake. Furthermore, temperature in the lake water column was measured continuously, and during field work oxygenation and transparency were also measured. Seasonal changes in sediment composition were analyzed on smear slides under microscope. The study showed that sedimentation rate increased as bottom steepness increased, and that there was more sediment in the hypolimnion than the epilimnion, especially in spring and autumn. There was a clear seasonal variation in early-spring and autumn peaks in sedimentation. The obtained results were significantly dependent on bottom relief, wind and air temperature through these factors’ influence on water temperature. The results show that the sediment accumulation rate in Lake Gościąż depends on the hydrodynamic conditions, which are determined by wind speed, wind direction, water temperature, and the shape and steepness of the lake basin. The relief features of the lake bottom and its orientation relative to the prevailing wind are significant factors in the spatial differentiation in sediment accumulation rate and composition of sedimenting material. It has been shown that the lake’s shallow-water zone (littoral and sublittoral) is an important source of the material accumulated in the profundal zone. The patterns and mechanisms of the course of contemporary sedimentation in Lake Gościąż, as determined based on the conducted investigations, can be applied in the study of other lakes and in assessing the representativeness of sampling sites for laminated bottom sediments to be used in palaeo-environmental studies.