Initial Sediment Research Articles

Long-Term Effects of 90Sr and 239+240Pu Contaminated on the Seafloor Sediment on the Transfer through Marine Food Web: Sensitivity to the Physical Property- and Sediment-Related Parameters

This study, as a follow-up to the <sup>137</sup>Cs study of Kim et al. (2023), performs a set of sensitivity experiments on ocean physical properties and sediment-related parameters based on initial bottom contamination of <sup>90</sup>Sr and <sup>239+240</sup>Pu in the upper sediment layer. Both studies utilizes the Extended BURN model proposed by Bezhenar et al. (2016). The initial contamination levels were set to 3 and 0.4 Bq/kg, respectively, based on observations off the coast of Fukushima. The sensitivity experiments were divided into EXP-WOHAD, which examined the effects of the vertical diffusion coefficient and vertical sediment flux, and EXP-WHAD, which investigated the effects of ocean currents. The results of the EXP-WOHAD experiments showed that both radionuclides are more sensitive to sediment fluxes than to vertical diffusion coefficients. For both <sup>90</sup>Sr and <sup>239+240</sup>Pu, transport was dominated by transport to the intermediate sediment layer rather than to seawater. Specifically, for <sup>239+240</sup>Pu, transport to seawater was insignificant due to its strong sorption properties in sediments. In terms of bioaccumulation, <sup>90</sup>Sr accumulated most in fish and invertebrates, while <sup>239+240</sup>Pu accumulated most in invertebrates, followed by zooplankton. Notably, <sup>239+240</sup>Pu showed high bioaccumulation despite its low initial sediment contamination. The changes in radioactivity concentrations in the EXP-WHAD experiments were similar to those in the EXP-WOHAD experiments, and the bioaccumulation trends in biota were also comparable. This study confirms that the accumulation of radionuclides in seawater, intermediate sediments, and biota is sensitive to the marine physical environment and varies by nuclide. When the sediment flux increased by a factor of 100, the remaining radioactivity levels of <sup>90</sup>Sr and <sup>239+240</sup>Pu in biota after 100 years showed a significant reduction, decreasing by more than 900 and 30,000 times, respectively; it highlighting the importance of parameterization according to the physical environment of the area of interest.

Provenance, paleoweathering, sediment maturity, and depositional environment of intertrappean sediments in Angot–Gazo volcanic plateau, northeastern Ethiopia: Evidence from field mapping, petrography and geochemistry

Numerous intertrappean beds have been reported in different sections of the Ethiopian highlands; however, their detailed paleo-sedimentological characteristics have not been fully examined. This study investigates the source rock composition, tectonic setting, degree of past weathering, paleoclimatic conditions, sediment maturity, and depositional environments of the Angot–Gazo terrestrial sediments through geological mapping, mineralogical analysis, and geochemical approaches. Two terrestrial beds, consisting of mudrock and sandstone, were identified. The sandstone is characterized by massive, medium to coarse, and poorly sorted grains that range from sub-rounded to angular shapes. Minerallogically, the sandstone comprises quartz, feldspar, and lithic fragments grains with a proportional amounts of ash material. Both mineralogical (Q–F–R) and geochemical classification plots categorize the sandstone as arkosic to lithic greywacke. Felsic volcanic rocks are the main source material for the investigated sediments, as evidenced by multiple discrimination plots (DF1 vs. DF2, V–Ni–Th∗10, La–Th–Sc, Cr/Th–Th/Sc, La/Co–Th/Co, La/Sc–Th/Co and Y/Ni–Cr/V), LREE/HREE patterns, elemental ratios, and the appearance of abundant felsic-derived lithic fragments within the sandstone. A new bivariate discriminant function plot from DF1 vs. DF2 analysis, coupled with ternary diagrams of Zr/10–Th–Sc for the studied intertrappean sediments, revealed a continental rift setting, particularly a passive continental margin. Ternary diagram of A–CN–K, binary plots of Al₂O₃/Na₂O vs. average values of weathering indices (CIA, CIW, PIA, & MIA), and SiO2 vs. Al2O3+K2O + Na2O plot demonstrate slight to moderate degree of weathering for the sandstone, and deep weathering for the mudrock under semi-arid paleoclimatic conditions. The binary schemes of SiO2/Al2O3 and Ni–TiO2 ratio, along with the significant abundance of angular to sub-angular framework grains, reflect both immaturity and initial sediment recycling. Finally, the examined sediments were deposited in freshwater under oxic conditions, as evidenced by binary plots of Sr/Ba, Th/U, U/Th, and Ni/Co.

The Impact of Foreshore Slope on Cross-Shore Sediment Transport and Sandbar Formation in Beach Berm Nourishment

Foreshore slope is crucial in designing beach berm nourishment schemes and understanding coastal responses to wave forces. Beach berm nourishment often suffers from a high loss rate, necessitating theoretical research and design parameter comparison to mitigate these losses early on. This study uses Bagnold’s energy conservation method and the small-angle approximation method to establish a relationship between cross-shore sediment transport and foreshore slope. The feedback mechanism between these factors shows that when the foreshore slope is fewer than 10 degrees, a smaller initial slope results in a reduced rate of sediment transport. Over time, the foreshore slope decreases and eventually reaches equilibrium, promoting the formation of an offshore sandbar, which helps reduce sediment loss. Using data from Guanhu Beach in Dapeng Bay, this study constructs a realistic numerical beach model to simulate the dynamic behavior of beach profiles with varying foreshore slopes under the influence of monsoon waves and storm surges. The simulation results support the feedback mechanism findings, demonstrating that profiles with minimal foreshore slopes experience the least initial sediment loss, thus facilitating sandbar formation more effectively. These insights can inform beach berm nourishment strategies, emphasizing early-stage efforts to expand beach areas and reduce sediment loss.

Submerged macrophyte root oxygen release reduces sediment oxygen demand: A positive feedback loop in shallow lakes

Shallow lakes have two stable ecological states, macrophyte dominated or algal dominated. The macrophyte dominated state is the more desired state as it generally has clearer water that is safe for contact recreation. Whereas the algal dominated state is considered degraded, resulting from high anthropogenic nutrient inputs, with turbid water that is often unsafe for contact recreation. These ecological states are somewhat resilient due to in-lake feedback loops that maintain or enhance conditions for the dominate primary producer. For the macrophyte dominated state, many of these feedback loops are theoretically plant density dependent, but rarely has the plant density required to initiate these feedback loops been identified. Here we illustrate the plant density dependence of a previously unstudied feedback loop present in the macrophyte dominated state. Increased densities of Isoëtes kirkii were able to reduce sediment oxygen demand through their root oxygen releases. This reduction in sediment oxygen demand occurred at 32 plants m−2 in a garden soil and 63 plants m−2 in the sediment of a hypo-eutrophic lake, a disparity likely due to the higher initial sediment oxygen demand present in the lake sediments. In a shallow lake, plants present in the hypolimnion will reduce sediment oxygen demand, increasing the amount of time required before anoxic conditions are created and the resulting release of dissolved reactive phosphorus. This will likely decrease the potential for subsequent algal blooms and the associated shading of submerged macrophytes, thus maintaining in-lake conditions that favour macrophytes.

Application of ultrasonic waves to evaluate the rheological properties of non-Newtonian slurries: a preliminary study

An ultrasonic-wave system was developed to measure the rheological properties of non-Newtonian materials based on their responses to shear and pressure waves. This system was composed of a commercial shear wave transducer and various homemade devices, including a signal generator, a signal conditioner, and a transmission/receiving switch. The shear wave reflections at the interface between the delay line and the unknown test materials can be interpreted by the signals measured with calibration materials (e.g. air, water, olive oil and honey) that have well-known rheological properties. If the Voigt viscoelastic model is used to describe the dynamic behaviour of these test materials, the interpreted data can be used to determine the acoustic impedances, and thus solve for their shear moduli (G), kinematic viscosities (ν) and bulk densities (ρ). After the calibration procedures, the proposed system was used to test a consolidating kaolinite slurry with zero salinity and an initial suspended sediment concentration of 420 g l–1. The measurements showed that the shear modulus G is developed until consolidation for approximately 100 h. Afterward, the G gradually approached a value on the order of 500 N m–2 after approximately 200 h. This corresponded to an initial viscosity of approximately 7 × 10−5 m2 s–1, which decreased slowly over time to approximately 4 × 10−6 m2 s–1 after 300 h. With minor modification to capture pressure waves from the shear wave transducer, the bulk density can also be measured. The integrated system offers a non-invasive and efficient method for characterizing non-Newtonian fluids, providing valuable insights into their rheological properties, which are crucial for a wide range of industrial and scientific applications.

Evaluating Effective Particle Size Distributions of Cohesive Sediment under Varying Shear Stress and Bed Configurations in a Rotating Annular Flume

Despite the environmental significance and ecological importance of cohesive sediment (<63 μm), improved knowledge of how effective particle size distributions (EPSDs) change due to flocculation under different conditions of shear stress and bed configuration is required to better understand in situ transport and storage properties and refine existing sediment transport models. Here, a rotating annular flume was used to (i) evaluate EPSDs under different shear stress and bed types (plane-impermeable and -porous gravel bed) for deposition and erosion experiments; (ii) assess flocculation processes with EPSDs; and (iii) compare flume and field EPSDs observations with respect to measured shear stress. While deposition experiments over the impermeable bed led to an EPSD equilibrium in all shear conditions (constant EPSD percentiles), the ingress experiment over the gravel bed resulted in varying EPSDs, and no equilibrium was observed. During the erosion experiment, deposited flocs became coarser due to bed consolidation, and no particle breakage was observed once particles were resuspended. The ingress experiment showed high efficiency in entrapping suspended particles (~95% of initial suspended sediment), and no exfiltration or resuspension was recorded. Flocculation ratios calculated using EPSDs showed negative correlations with shear stress, indicating that increasing flow energy promoted flocculation for flume and field observations. Our results showed that both suspended and bed sediments can flocculate into coarser flocs that, in turn, are preferentially ingressed and stored in the substrate when in suspension. These findings have important implications regarding legacy impacts, as substrate-stored particles can potentially extend the effects of upstream landscape disturbances.

Diagenetic effect on reservoir quality of siliciclastic and volcaniclastic sandstones from a Paleogene volcanic rifted margin, East Greenland

ABSTRACT Siliciclastic and volcaniclastic sediments in a volcanic rifted-margin succession may experience a complex diagenetic history during burial that can have a large impact on sandstone reservoir properties. To understand such changes, variations in initial sediment composition and succeeding diagenetic changes have been studied for a Paleogene outcrop analogue in the Kangerlussuaq area, East Greenland. The nature of the mafic volcanics-bearing succession, which consists of intra-volcanic sandstones, accommodated over quartz-rich pre-volcanic fluvial sandstones, are comparable to the settings of recently discovered hydrocarbon-producing sandstones in the Faroe–Shetland Basin on the conjugate Atlantic margin. Our petrographic and provenance investigations of the pre- and intra-volcanic sandstones are supported by geochemical and X-ray diffraction analyses. The intra-volcanic sandstones were deposited in shallow marine environments with mixed siliciclastic and volcaniclastic input, the latter rich in felsic to mafic volcanic rock fragments and feldspar grains. Similar zircon age distributions of pre- and intra-volcanic sandstones support a continued supply from the same siliciclastic sediment source after the onset of volcanism. Variations in initial detrital grain and pore-fluid (fresh to marine) compositions resulted in different diagenetic changes in the pre- and intra-volcanic sandstones. However, where siliciclastic sandstones were overlain by volcaniclastic rocks rather than massive lava flows, the diagenetic changes resemble those of the intra-volcanic sandstones. The cementing phases are typically quartz, illite (probably illitized kaolinite), and rare anatase in the pre-volcanic sandstones. Chlorite, calcite, zeolite/feldspar, opal/quartz, and titanite are characteristic authigenic phases in the intra-volcanic sandstones. Precipitation of different minerals in the pre- and intra-volcanic sandstones show that the detrital composition (and to a lesser extent depositional environment) played a major role during early and late diagenesis after deep burial (up to 6–8 km). Inter-eruptive siliciclastic units may prove to form highly valuable reservoirs when they are composed of mixed siliciclastic and volcaniclastic material. In the stratigraphically youngest intra-volcanic sandstones and pre-volcanic sandstones overlain by hyaloclastite or tuff, there is a high potential for preservation of interparticle porosity during burial (< 5 km) due to early chlorite rims and the generation of secondary porosity after the dissolution of early zeolite cement.

Screening of Pharmaceutical Pollutants Along with Emerging Contaminants in the Sediments of the Periyar River, Located in Kerala (India) by Using High-Resolution Mass Spectrometry (UPLC-Q-ToF-MS).

In this study, ultra-performance liquid chromatography coupled with a quadruple time-of-flight mass spectrometry (UPLC-Q-ToF-MS) was employed to screen and identify pharmaceutical pollutants and emerging contaminants (ECs) in the Periyar River near Aster Medicity hospital, the dumping yard of Amrutha hospital, and the Vaduthala bridge regions in Kerala, India. The analysis was conducted in both positive and negative ionization modes using electrospray ionization (ESI). The QuEChERS method was employed for initial sediment sample preparation. Among the twenty-five identified ECs, four compounds were identified as pharmaceutical pollutants. This study have great significance as it represents the first comprehensive investigation of pharmaceutical pollutants in these hospital regions, highlighting the urgent need for further analysis and understanding of the situation. The presence of ECs poses an urgent need for attention due to the irreversible harm caused to the riverine ecosystem by the degradation of water quality resulting from industrial and domestic discharge.

Flocculating oil sands tailings with dual anionic/cationic polymers: Dose and charge density effects

AbstractA two‐step process, with anionic hydrolyzed polyacrylamide (HPAM) and cationic poly(vinylbenzyl trimethylammonium chloride) (PVBTMAC), was used to flocculate oil sands mature fine tailings (MFT). The charge density of HPAM and the dosages of HPAM and PVBTMAC were varied to maximize the dewatering of MFT and minimize the turbidity of the supernatant. The dual flocculant system performed better at lower doses than when used alone. The best HPAM charge density for fast initial settling rate and high sediment solids content was 32%, but it increased to 38% for best sediment dewatering, as measured by capillary suction time. The clearest supernatants were found when the zeta potential approached 0 mV because the cationic PVBTMAC neutralized the surface charges of the particles suspended in the MFT. More importantly, undiluted MFT was flocculated with the HPAM/PVBTMAC system and then filtered at low‐pressure (69 kPag), resulting in a filter cake with a high solids content of 61 wt.%. This study shows that treating MFT with a combination of anionic and cationic polymer is a flexible way to optimize flocculation performance.

Numerical study of effects of flushing gate height and sediment bed properties on cleaning efficiency in a simplified self-cleaning device.

Sediment accumulation in combined sewers can induce blockage and odor problems. Among various cleaning methods, using self-cleaning device-generated flushing waves has been thought to be an effective solution. In this study, a series of numerical tests were conducted using CFD software to investigate the cleaning efficiency of deposited sediment particles based on a simplified self-cleaning device. The CFD model was validated by the experimental and numerical results in the literature. The effects of several parameters including the flushing gate height, sediment bed thickness, sediment bed length, and sediment bed position on cleaning efficiency were discussed. A relative accumulative transport rate was defined to analyze the cleaning efficiency. Results showed that the lowest height of the flushing gate had the best effects on sediment removal. The flushing waves generated from the sudden opening of the flushing gate were capable of cleaning sediment deposits in the given initial sediment bed thickness, length, and position. The required time duration for cleaning the sediment deposit completely increased about 6, 3, and 3 times when the sediment bed thickness, sediment bed length, and distance between the flushing gate and sediment bed increased 10, 4, and 7 times, respectively.

Refining fine sediment source identification through integration of spatial modelling, concentration monitoring and source tracing: A case study in the Great Barrier Reef catchments

Excess fine sediment delivery is a major contributor to the declining health of the Great Barrier Reef and identifying the dominant source areas of fine sediment has been critical to prioritising erosion remediation programs. The Bowen River catchment within the Burdekin Basin has been recognised as a major contributor and hence received considerable research investment over the last two decades. This study adopts a novel approach to integrate three independently derived sediment budgets produced from a catchment scale sediment budget model (Dynamic SedNet), targeted tributary water quality monitoring and geochemical sediment source tracing to refine and map the sediment source zones within the Bowen catchment. A four year study of water quality monitoring combined with modelled discharge estimates and geochemical source tracing both identified that the Little Bowen River and Rosella Creek were the largest sources of sediment in the Bowen River catchment. Both data sets contradicted initial synoptic sediment budget model predictions due to inadequate representation of hillslope and gully erosion. Recent improvements in model inputs have resulted in predictions that are consistent with the field data and are of finer resolution within the identified source areas. Priorities for further investigation of erosion processes are also revealed. Examining the benefits and limitations of each method indicates that these are complimentary methods which can effectively be used as multiple lines of evidence. An integrated dataset such as this provides a higher level of certainty in the prediction of fine sediment sources than a single line of evidence dataset or model. The use of high quality, integrated datasets to inform catchment management prioritisation will provide greater confidence for decision makers when investing in catchment management.

Metal Preservation and Mobilization in Sediments at the TAG Hydrothermal Field, Mid‐Atlantic Ridge

AbstractAt the Trans‐Atlantic Geotraverse hydrothermal field, metalliferous sediments cover extinct hydrothermal mounds and the surrounding seafloor. Here, we report the morphological, mineralogical and geochemical processes that deposit these sediments, remobilize their metals, and affect their preservation. We found that the initial sediment metal tenor is controlled by physical transport of hydrothermal material from its source, followed by diagenetic redistribution and potentially diffuse fluid flow after high‐temperature hydrothermal activity has ceased. We distinguished three different environments: (a) proximal metalliferous sediments on top of extinct mounds are mainly derived from oxidative weathering of primary sulfide structures and are predominantly composed of Fe oxyhydroxides with low contents of Cu, Co, and Zn; metal enrichments in specific layers are likely related to upward flow of low‐temperature hydrothermal fluids; (b) medial distant metalliferous sediments found at the base of the mounds, deposited by mass transport, contain cm‐thick layers of unsorted sulfide sands with high base metal contents (e.g., up to 28% Cu); these buried sulfides continue to undergo dissolution, resulting in metal release into porewaters; (c) distal metalliferous sediments, found in depositional basins a few hundreds of meters from the extinct mounds, include fining‐upwards sequences of thin sulfide sand layers with Fe oxyhydroxides and were deposited by recurrent turbiditic flows. Dissolved metals (e.g., Cu2+ and Mn2+) diffuse upwards under reducing conditions and precipitate within the sediment. Hence, when using hydrothermal sediments to construct reliable geochronological records of hydrothermal activity, distance from source, local seafloor morphology, mass‐transport and depositional, and diagenetic modification should all be considered.

Specific power or droplet shear stress: Which is the primary cause of soil erosion under low-pressure sprinklers?

Specific power and droplet shear stress are generally considered to be the most critical indicators of soil erosion in sprinkler irrigation, but there is controversy about which indicator has a greater impact. This creates uncertainty in the optimization design of low-pressure sprinkler irrigation systems. In this study, a commonly used low-pressure sprinkler, i.e., Nelson D3000, was used to carry out in soil box experiments, to study the effects of specific power and average droplet shear stress at the end of a spray jet on soil erosion during sprinkler irrigation under three nozzle diameters (3.97, 5.95, and 7.94 mm), two operating pressures (103 and 138 kPa), and two soil textures (loamy sand and silty loam). Overall, the larger specific power or average droplet shear stress resulted in higher initial and steady runoff rates and a shorter time until runoff occurs and stabilizes. Enlarging the specific power or average droplet shear stress could significantly increase the initial infiltration rate, sediment yield, and surface soil bulk density, but the infiltration depth prior to runoff and surface soil porosity decreased. Furthermore, the specific power was observed to have greater correlations than average droplet shear stress with the surface runoff rate, initial infiltration rate, and increase in the soil bulk density and decrease in the soil porosity after irrigation. However, it was weakly related to the infiltration depth prior to runoff and sediment yield, indicating that the specific power could more accurately reflect the soil erosion with respect to the shear stress. To minimize the risk of soil erosion, a small operating pressure (103 kPa) is recommended in the design of center pivot irrigation systems, especially for the overhang of the system with large nozzle diameters. This research can provide the technical support for soil erosion prevention under low-pressure sprinkler irrigation.

Modeling uncertainties of reservoir flushing simulations

Every dam or barrage construction affects the watercourse and the retention of sediment that previously was carried by the river, which can lead to siltation of the reservoir and obstruction of water intakes over time, reducing their capacities. However, the information available regarding the effect of sediment and drawdown parameters, sediment management at reservoirs, as well as different equational approaches, is scarce. The current research aims to evaluate the effect of parameters associated with numerical modeling of sediment management in reservoirs considering scenarios with different drawdowns, transport equations, sediment size distributions, and thickness of the initial sediment layer. The case study of the Aimorés Hydropower Plant (HPP) is used, applying the Delft3D-FLOW model for two-dimensional modeling. All parameters influenced the volume of mobilized sediment, among which the initial layer thickness was the parameter that resulted in the greatest changes in simulated results. In general, the results show that the uncertainties in the input parameters outweigh the uncertainties between the techniques, which found large variations in results when evaluating the use of different transport equations. These results indicate the importance of proper estimation of model parameters for predicting effects with accuracy and the need for such studies before planning and management operations are evaluated to avoid environmental harm and energy waste.

Uncertainties in Models Predicting Critical Bed Shear Stress of Cohesionless Particles

Our data show large scatter in the critical Shields stress values for initial sediment motion. The main sources of dispersion are related to the methodological procedures defining the inception of movement (i.e., visual observations or extrapolation of sediment transport rate) and to the estimation of the bed shear stress. The threshold for sediment motion varies with many factors related not only to grain size but also to bed composition (e.g., presence of fine sediments in a coarse matrix), arrangement (e.g., bed roughness, grain orientation, and characteristic lengths of bed structures) and slope. New models to estimate the critical Shields number are proposed using grain size or bed slope or a combination of both. Model parameters and uncertainty are estimated through Bayesian inference using prior knowledge of these parameters and measured data. Apart from the uncertainty in observations, two types of uncertainty can be evaluated: one related to the parameter estimation (i.e., parametric) and one related to the choice of the model (i.e., structural). Finally, a four-parameter model based on the grain size and bed slope yields the best results and demonstrates potential interaction between these two parameters. Model uncertainty, however, remains large, which indicates that other input parameters may be needed to improve the proposed model.

The response of high density turbidity currents and their deposits to an abrupt channel termination at a slope break: Implications for channel–lobe transition zones

ABSTRACTThe transition between the slope and basin floor is typically marked by a slope break, in some cases causing channels to terminate and turbidity currents to undergo a loss of confinement. It is thus essential to understand how these slope breaks and losses of confinement influence the hydrodynamic evolution of turbidity currents and impact their depositional variability within natural scale channel mouth settings. Flume experiments, utilizing Shields scaling, are conducted to study how channel slope angle (3°, 6° and 9°) and initial suspended sediment concentrations (12 to 18% by volume) impact the hydrodynamics and deposit geometries of high density turbidity currents, subject to a simultaneous break of slope and loss of confinement. Measured velocity and concentration profiles indicate that turbidity currents are supercritical, with mean velocities between 0.80 m s−1 and 1.04 m s−1 and depth‐averaged basal concentrations between 9.2% and 23.9%, yielding bed shear velocities between 0.050 m s−1 and 0.064 m s−1. Upon encountering the slope break and loss of confinement, turbidity currents exhibit increases to their densimetric Froude numbers and shear velocities. This is due primarily to two factors: firstly, turbidity currents continue to accelerate during an initial period of velocity lag as their residual momentum gradually dissipates; and, secondly, expansion via flow relaxation collapses their structure towards the bed. The corresponding depositional geometries of these processes reveal that turbidity currents produce elongate channel–lobe transition zones that disconnect channel and basin deposits. The length to width ratios of channel–lobe transition zones decrease as the initial sediment concentrations of turbidity currents increase, while a reduction in the channel slope break angle reduces their length to width ratios. Corresponding, lobe elements are observed to increase in length, width and thickness with increasing initial sediment concentrations, while a reduction in channel slope break angle reduces their dimensions due to enhanced slope deposition.

Establishment of a projection-pursuit-regression-based prediction model for the filtration performance of a micro-pressure filtration and cleaning tank for micro-irrigation

Filtration is a key process of a micro-irrigation system. To achieve water conservation, improve the energy efficiency, and meet the low-carbon environmental requirements, this study investigates a new type of pre-pump filtration measure—the micro-pressure filtration and cleaning tank, and the sediment removal (SR), mass of intercepted sediment (Ma), and filtration time (t) are used as evaluation indicators. A uniform orthogonal test was designed to evaluate the influences of the initial sediment concentration, flow rate, and filter area. We carried out simulations using the projection pursuit regression (PPR) method based on physical measurement data, and then NSGA-II (fast elitist non-dominated sorting genetic algorithm) algorithm was used to find the optimal parameter values. The results showed that the order of the factors influencing the SR and Ma of the micro-pressure filtration and cleaning tank was the filter area > initial sediment concentration > flow rate. The order of the factors influencing the filtration time was flow rate > initial sediment concentration > filter area. A PPR prediction model was built based on the filter area, initial sediment concentration, flow rate, and assessment indicators, and the optimal operating conditions were determined (initial sediment concentration: 0.36 kg/m3, flow rate: 7 m3/h, and filter area: 2000 cm2). The research results demonstrated the filtration performance of the micro-pressure filtration and cleaning tank and provide a theoretical basis for the popularization and application of such tanks as well as a reference for sustainable new irrigation technologies.

Impact of Floods on Sediment Trap Efficiency of a Small Shallow Reservoir—A Case Study

Silting is the main factor limiting the ability to perform the tasks that small reservoirs are intended for. Therefore, the change in sediment trap efficiency was studied for a small shallow reservoir, Krempna, which, due to high silting intensity, was desilted twice (2005, 2018). Siltation measurements were performed in two periods (1987–2005, 2006–2018) after the reservoir was desludged. It was found that the sediments were composed of fine-fraction sediment; therefore, a series of measurements of suspended sediment transport were performed. These data allowed us to calculate the daily sediment transport flowing into and out of the reservoir and water-level measurements. Then, the sediment trap efficiency was calculated. The aim of this study was: (1) to determine the impact of flood flows on the sediment trap efficiency (STE) of a small shallow reservoir, (2) to determine changes in the value of the sediment trap efficiency of a small shallow reservoir in two different periods of its operation, and (3) to demonstrate whether it is possible to determine the value of the initial sediment trap efficiency and changes in the STE values during operation using empirical formulas. Finally, during flood flows, the amount of sediment retained in the studied reservoir was several times lower than during freshets with a much smaller flow. It is these small freshets that reduce the capacity of the reservoir. A correlation relationship was developed for 18 data—flood flows (Q) and sediment trap efficiency (STE).

On how defining and measuring a channel bed elevation impacts key quantities in sediment overloading with supercritical flow

The manuscript presents the results of an aggradation experiment performed in a laboratory channel with supercritical flow. The channel was fed with a stationary sediment load exceeding the transport capacity of the flow in the initial condition, thus inducing sediment aggradation and an increase of the bed slope. The experiment is part of a laboratory campaign mimicking sediment overloading in mountain rivers, a process that can determine increased hydraulic risk levels at key spots. A crucial issue in measuring sediment aggradation is the definition and determination of the bed elevation, this issue being quite relevant in experiments with a relatively large transport capacity, where a thick bed-load layer exists and hinders the possibility to determine with confidence a reference bed elevation. The determination of the bed elevation, in turn, impacts the quantification of a number of properties, including the initial sediment transport capacity of the flow, temporal scales of the aggradation process, water depth and Froude number. The manuscript presents a sensitivity analysis of the results to two extreme definitions for the bed elevation: the first one locates the bed at the upper edge of the bed-load layer, while the second one at the lower edge of the bed-load layer where the particles do not move. The presentation of the two alternatives is focused on the experimental methods they use, consistently with the intent of the special issue. Furthermore, it is demonstrated that the definition of the bed elevation also has a major impact on numerical models of the process. The experimental results have been reproduced numerically, demonstrating that the calibration parameters returning a best fit are also impacted significantly by how the bed is defined. The preferred definition for analyzing an experimental campaign is locating the bed below the bed-load layer.

Effects of physical disturbance of sediment on the cycling of mercury in coastal regions

Mercury (Hg) is a global pollutant of health concern due to formation and bioaccumulation of methylmercury (MeHg) during its biogeochemical cycle. Coastal areas are important regions in the biogeochemical cycling of Hg (Liu et al., 2017), where often-occurring natural and anthropogenic perturbations affect Hg transport and transformation and the associated health risk from Hg. The rapidly growing mariculture associated with the rising global demand for food may have a profound effect on coastal Hg cycling, due to the environmental alterations (e.g., resuspension and sedimentation) caused by maricultural activities (e.g., bottom sowing and harvesting). Through simulating the effect of water scouring, a common harvesting method, this study investigated Hg migration and distribution in particulate and dissolved phases in Laizhou Bay of Bohai Sea, China, where mariculture exists extensively. Particulate total and methyl Hg (PTHg and PMeHg) in water (expressed as ng/L) increased sharply due to the resuspension of sediment, but decreased rapidly after a one-off scouring event. When normalized by particle mass, PTHg and PMeHg (ng/g) in suspended sediment particles were significantly higher than that in the initial sediment, suggesting a higher distribution coefficient and higher affinity to bind Hg in the suspended particles. This may be due to the smaller particle sizes, and higher contents of organic matter and Fe/Mn of suspended sediments compared to the initial sediment. While the concentrations of dissolved THg (DTHg) in water column showed minimum changes or decreased, dissolved MeHg (DMeHg) concentrations increased sharply after the perturbation, due to the possible release of MeHg from porewater and potential Hg methylation during the event. These results provide fundamental information needed for ecological and health risk assessment of Hg in mariculture, and highlights the increased mobility and bioaccumulation of MeHg during anthropogenic perturbations in these areas.