Sediment Flux Research Articles

Characteristics of Cd Fluxe in Topsoil Around Typical Mining Area in Hezhou, Guangxi

Guangxi is a typical geological high background area in southwest China, where carbonates, black rock series, basic-ultrabasic rock mass, and metal deposits (mineralized bodies) exhibit strong weathering into loam, resulting in higher cadmium (Cd) content in the soil than that in other areas of China. In order to investigate the degree of influence of mining activities on topsoil environmental quality in the area with high geological background, we chose a mining area and control area in Hezhou for this research and systematically carried out a comparative study on Cd transport routes and transport flux density in topsoil. The results showed that the average atmospheric dry and wet deposition flux densities of Cd in the soil of the mining area and control area were 1.87 g·(hm2·a)-1 and 1.52 g·(hm2·a)-1, accounting for 61.5% and 60.3% of the total input flux density, respectively. The flux density of Cd in the soil by fertilization and irrigation was lower. Surface water infiltration was the main avenue of soil Cd output in both the mining area and control area, accounting for 75.4% and 86.6% of the total output flux density, respectively. The harvest output flux density in the mining area was higher than that in the control area, and the Cd content of rice planted in the mining area was higher than the standard, whereas that of maize was safe. On the whole, the net transport flux densities of soil Cd in the mining area and control area were -3.05 g·(hm2·a)-1 and -4.05 g·(hm2·a)-1, both of which showed Cd leaching in the soil. However, the points of high atmospheric deposition flux density and exceeding Cd content in rice were mainly distributed around the mining area, which may have posed a potential threat to the health of local residents. Therefore, it is suggested to control the soil Cd pollution through monitoring and planting structure adjustment.

Check dam impact on sediment loads: example of the Guerbe River in the Swiss Alps – a catchment scale experiment

Abstract. The construction of check dams is a common practice around the world where the aim is to reduce the damage by flooding events through mountain streams. However, quantifying the effectiveness of such engineering structures has remained very challenging and requires well-selected case studies, since the outcome of such an evaluation depends on site-specific geometric, geologic and climatic conditions. Conventionally, the check dams' effectiveness has been estimated using information about how the bedload sediment flux in the stream changes after the check dams are constructed. A permanent lowering of the bedload flux not only points to a success in reducing the probability of sediment transport occurrence but also implies that the sediment input through the system is likely to decrease. Here, we applied a method for data acquisition and two different equations (Meyer-Peter–Müller and Recking approach) to estimate and compare the sediment transport in a mountain stream in Switzerland under engineered and non-engineered conditions. Whereas the first equation is derived from a classical approach that is based on flume experiment data with a slope of less than 0.02 m m−1, the second equation (Recking) has been derived based on a bedload field dataset comprising active mountain streams under steeper conditions. We selected the Guerbe (Gürbe) River situated in the Swiss Alps as a case study, which has been engineered since the end of the 19th century. This has resulted in more than 110 check dams along a ca. 5 km reach where sediment has continuously been supplied from adjacent hillslopes, primarily by landsliding. We measured the riverbed grain size, topographic gradients and river widths within selected segments along this reach. Additionally, a gauging station downstream of the reach engineered with check dams yielded information to calibrate the hydroclimatic situation for the study reach, thus offering ideal conditions for our catchment-scale experiment. Using the acquired data and the dataset about historical runoff covering the time interval between 2009 and 2021 and considering the current engineered conditions, we estimated a mean annual volume of transported bedload which ranges from 900 to 6000 m3 yr−1. We then envisaged possible channel geometries before the check dams were constructed. We inferred (1) higher energy gradients which we averaged over the length of several check dams and which we considered a proxy for the steeper river slope under natural conditions; (2) channel widths that are smaller than those measured today, thereby anticipating that the channel was more confined in the past; and (3) larger grain size percentiles, which we consider to be similar to the values measured from preserved landslides in the region. Using such potential non-engineered scenarios as constraints, the two equations both point towards a larger sediment flux compared to the engineered state, although the results of these equations differed significantly in magnitude. Whereas the Recking approach returned estimates where the bedload sediment flux is ca. 10 times larger in comparison with the current situation, the use of the Meyer-Peter–Müller equation predicts an increase of ca. 100 times in bedload fluxes for a state without check dams. These results suggest that the check dams in the Guerbe River are highly efficient not only in regulating sediment transport by decreasing the probability of high sediment flux occurrence during torrential conditions but also in stabilizing the channel bed by avoiding incision. The most likely consequence is a stabilization of the terrain around such structures by reducing the activation of landslides.

Weathering Intensity, Paleoclimatic, and Progressive Expansion of Bottom-Water Anoxia in the Middle Jurassic Khatatba Formation, Southern Tethys: Geochemical Perspectives

The Jurassic Period was a significant phase of variable organic matter accumulation in paleo-shelf areas of the southern Tethys (Egypt). Reconstructing the paleoredox conditions, paleoclimate, and weathering intensity, along with the role of terrigenous sediment flux and mineralogical maturity, is important for understanding basin infill history and prevalent paleoenvironmental conditions. Here, inorganic geochemical data are presented from the Middle Jurassic Khatatba Formation and two samples from the underlying Ras Qattara and the overlying Masajid formations in the Jana-1x well, Shushan Basin, Western Desert. Twenty-four (24) whole-rock samples were analyzed for their major and trace element composition and carbonate content. The Khatatba Formation represents one of the major hydrocarbon source rocks in the North Western Desert, Egypt. Redox conditions were assessed based on enrichment factors of redox-sensitive elements Mo, V, U, and Co. Results revealed that the Khatatba Formation was deposited under predominant anoxic bottom and pore water conditions, in contrast to the oxic settings that were prevalent during the deposition of the Ras Qattara and Masajid formations. Continental weathering intensity and paleoclimate were reconstructed based on several proxies, such as the chemical index of alteration (CIA), K2O/Rb, Rb/Sr, Ln(Al2O3/Na2O), and Al/K ratios, indicating that the studied succession was deposited during alternating phases between weak and moderate weathering intensity under arid and warm-humid climates, respectively. Periods of enhanced continental weathering were associated with high values of clastic ratios such as Si/Al, Ti/Al, and Zr/Al, suggesting increased terrigenous sediment supply during intensified hydrological cycling. These ratios further provided inferences about the changes in sediment grain size, such as a change from shale to coarse silt- and sand-size fractions.

A DFT-based kinetic Monte Carlo simulation of multiphase oxide-metal thin film growth

Functional thin films of nanoscale metal pillars in oxide or nitride matrices known as vertically aligned nanocomposite (VAN) have gained much interest owing to their unique strain-coupled and highly anisotropic properties. So far, the deposition of these films has been explored mostly experimentally. In this work, a density functional theory (DFT)-based kinetic Monte Carlo simulation model using Bortz–Kalos–Lebowitz algorithm was developed to understand the growth of VAN films deposited by pulsed laser technique on mismatching substrates. The model has been parameterized and applied to understand the kinetics of growth thin films consisting of Au pillars in CeO2 matrix deposited on SrTiO3 substrates. The effects of pulsed laser deposition (PLD) conditions including the pulse frequency, deposition flux, and substrate temperature were explored. The simulations indicate that the Au pillar size and shape exhibit significant dependence on the PLD conditions. Namely, increasing the temperature increases the average pillar size and lowers the pillar density, and vice versa. In addition, the simulations revealed that increasing the deposition rate results in lowering the average pillar size and increasing the density. Particularly, the DFT results suggest that Au pillar size can be tuned during the initial growth of the first monolayer due to the significantly low activation barrier. Our analysis showed that the relationship between the average pillar size and pillar density is influenced by the kinetics. Furthermore, autocorrelation analysis showed that pillars self-organize in quasi-ordered patterns at certain windows of the deposition conditions, which is attributed to the complex nature of the chemical interactions in the system, the kinetics, and the deposition parameters.

Fluid-evolving landform interaction by a surface-tracking method

This paper introduces a continuous finite element model to simulate fluid flow-bedform interaction problems. The approach utilizes a non-oscillatory finite element algorithm to compute the fluid dynamics by solving the complete Navier–Stokes equations. Additionally, it addresses the evolution of the fluid–bedform interface as a consequence of spatially non-balanced sediment fluxes through the solution of a conservation equation for the erodible layer thickness. A sign preservation algorithm is particularly relevant for landform tracking because a positive definite thickness of the erodible sediment layer is essential to model the interaction between evolving cohesionless sediment layers and rigid beds. The fluid/terrain interface is explicitly captured through a surface tracking methodology. First, new nodes fitting the interface are incorporated into the finite element mesh; then, elements beneath this interface are deactivated, while intersected elements are restructured to get a mesh composed exclusively of tetrahedral elements. Numerical experiments demonstrate capabilities of the method by exploring relevant problems related with civil engineering, such as the evolution of trenches and the scour of a submerged pile.

Quantification of sediment fluxes and intermittencies from Oligo–Miocene megafan deposits in the Swiss Molasse basin

AbstractThe conglomerates preserved in alluvial fans in the Swiss Molasse basin provide crucial insights into the sedimentary dynamics of these routing systems. In particular, the architectural trends and grain sizes of such deposits reveal information on the sediment fluxes and record variations in the intermittency — a proxy for the fan's activity — that indicate on the relative importance of tectonic or climatic controls on sediment production and transport. Here, we calculated intermittencies from sediment transport dynamics using the ratio between the long‐term average and the short‐term instantaneous unit sediment fluxes during bankfull discharge conditions. For this, we collected grain size data from three palaeo‐fan systems that were active through Oligo–Miocene times and that reveal preserved proximal–distal relationships. The three fan systems, which we term the western, central and eastern fans, show significant differences in their long‐term sediment budget but equivalent magnitudes of the sediment transport dynamics expressed through the intermittency factor. The eastern fan records a low long‐term sediment flux (5.7 km2 Myr−1), which needed the fan to be active during ca. 8 h yr−1 (intermittency factor of 0.89 × 10−3). The western fan reveals a higher long‐term sediment flux (16.2 km2 Myr−1), which could have accumulated during ca. 16 h yr−1 (intermittency factor of 1.83 × 10−3), thereby reflecting a more active system. The central fan records the largest long‐term sediment flux (40.3 km2 Myr−1), where ca. 57 h yr−1 of sediment transport would be required to deposit the supplied material (intermittency factor of 6.53 × 10−3), thus representing the most active system. By relating these characteristics to the regional exhumation history, we consider that the central fan mainly recorded the transient response of the Alpine surface to the break‐off of the European mantle lithosphere slab. Contrarily, the western and eastern fans were formed during the Alpine evolution when steady‐state conditions between uplift and erosion were reached and when sediment fluxes to the basin were lower. Despite differences in the tecto‐geomorphic and climatic boundary conditions, our data suggest that these Oligo–Miocene megafans could accomplish their mean annual sediment transport work within a few hours or days per year.

Transverse variability of residual currents, sediment fluxes, and bed level changes in estuaries with an estuarine dam: Role of estuarine type, dam location, and discharge interval

Estuarine dams are constructed in estuaries for reasons such as freshwater, flood control, and navigation. By changing tidal and river properties, estuarine dams can change the circulation and sediment transport in estuaries. Previous studies have investigated the along-channel changes in flow and sediment transport, however across-channel changes due to an estuarine dam are not well understood. To increase our understanding, this study analyzed an idealized estuary using the COAWST numerical modeling system. Models of strongly stratified, partially mixed, periodically stratified, and well-mixed estuaries were run for one year. Then, the models were subject to the construction of an estuarine dam and run for another year. For each estuarine type, scenarios with an estuarine dam at x = 20, 55, and 90 km from the mouth and freshwater discharge intervals of Δt = 0.5, 3, and 7 days were investigated, and the scenarios were compared. The results indicated that the river-dominated and tide-dominated estuaries behaved differently. In river-dominated estuaries, the residual circulation tended to be inflow in the channel and outflow over the shoals due to the estuarine exchange flow, and the secondary circulation was bottom divergent due to differential advection. The exchange flow and secondary circulation were found to weaken with longer discharge interval. The sediment fluxes in the channel were dominant, and, despite the weaker exchange flow, were found to be greater and directed seaward due to strong dam discharge for long discharge intervals. In tide-dominated estuaries, the residual circulation tended to be inflow over the shoals and outflow in the channel due to the tide-induced circulation, and the secondary flow was bottom convergent due to differential advection resulting from Stokes return flow. As the estuarine dam was located nearer to the mouth, the tide-induced circulation was replaced with exchange flow, and the secondary flow became bottom divergent. The sediment fluxes in the channel were dominant in this case as well, and were determined by tidal asymmetry from the interaction of the tides with the residual current, becoming directed landward as the seaward tide-induced circulation decreased with the estuarine dam near the mouth. With respect to bed level change, gradients in along-channel sediment fluxes were found to contribute most to bed level change near the mouth and estuarine dam, whereas gradients in across-channel sediment fluxes contributed most to deposition on the estuarine shoals. This study demonstrates that estuarine dam location and discharge interval can alter estuarine transverse variability and improves our understanding compared to previous analyses based solely on along-channel processes.

Modelled sources of airborne microplastics collected at a remote Southern Hemisphere site

Airborne microplastics have emerged in recent years as ubiquitous atmospheric pollutants. However, data from the Southern Hemisphere, and remote regions in particular, are sparse. Here, we report airborne microplastic deposition fluxes measured during a five-week sampling campaign at a remote site in the foothills of the Southern Alps of New Zealand. Samples were collected over 24-hour periods for the first week and for 7-day periods thereafter. On average, atmospheric microplastic (MP) deposition fluxes were six times larger during the 24-hour sampling periods (150 MP m−2 day−1) than during the 7-day sampling periods (26 MP m−2 day−1), highlighting the importance of sampling frequency and deposition collector design to limit particle resuspension. Previous studies, many of which used weekly sampling frequencies or longer, may have substantially underestimated atmospheric microplastic deposition fluxes, depending on the study design. To identify likely sources of deposited microplastics, we performed simulations with a global dispersion model coupled with an emissions inventory of airborne microplastics. Modelled deposition fluxes are in good agreement with observations, highlighting the potential for this method in tracing sources of deposited microplastics globally. Modelling indicates that sea-spray was the dominant source when microplastics underwent long-range atmospheric transport, with a small contribution from road dust.

Improving Simulation of Gas‐Particle Partitioning of Atmospheric Mercury Using CMAQ‐newHg‐Br v2

AbstractMercury (Hg) is a global pollutant whose atmospheric deposition is a major input to the terrestrial and oceanic ecosystems. Gas‐particle partitioning (GPP) of gaseous oxidized mercury (GOM) redistributes speciated Hg between gas and particulate phase and can subsequently alter Hg deposition flux. Most 3‐dimensional chemical transport models either neglected the Hg GPP process or parameterized it with measurement data limited in time and space. In this study, CMAQ‐newHg‐Br (Ye et al., 2018, https://doi.org/10.1002/2017ms001161) was updated to CMAQ‐newHg‐Br v2 by implementing a new GPP scheme and the most up‐to‐date Hg redox chemistry and was run for the northeastern United States over January‐November 2010. CMAQ‐newHg‐Br v2 reproduced the measured spatiotemporal distributions of gaseous elemental mercury (GEM) and particulate bound mercury (PBM) concentrations and Hg wet deposition flux within reasonable ranges and simulated dry deposition flux in agreement with previous studies. The GPP scheme improved the simulation of PBM via increasing winter‐, spring‐ and fall‐time PBM concentrations by threefold. It also improved simulated Hg wet deposition flux with an increase of 2.1 ± 0.7 μgm2 in the 11‐month accumulated amount, offsetting half of the decreasing effect of the updated chemistry (−4.2 ± 1.8 μgm2). Further, the GPP scheme captured the observed Kp‐T relationship as reported in previous studies without using measurement data and showed advantages at night and in rural/remote areas where existing empirical parameterizations failed. Our study demonstrated CMAQ‐newHg‐Br v2 a promising assessment tool to quantify impacts of climate change and emission reduction policy on Hg cycling.

Impact of temporal beach grain size variability on aeolian sediment transport and topographic evolution in a microtidal environment

While the impact of the spatio/temporal variability of grain size on morphological beach state is reasonably well understood, relatively little is known on its impact at a scale of days/months on aeolian sediment transport. This study focuses on five short intensive wind events during which aeolian sediment transport measurements, beach surface sampling and elevation change surveys were carried out for 1 to 3 days, over a 16-month period on a microtidal beach dominated by offshore winds. Monthly observations show a high temporal variability in beach grain size in relation to the decoupling between hydrodynamic and aeolian processes, from medium sand after a marine storm and inundation of the beach, to very coarse sand after several weeks of storm-force winds. During each wind event, topographic change on the beach ranged from zero, to 0.55 m. The time scale of coarsening depended on the initial beach grain size and could be very fast when the beach was composed of medium sand (e.g. 388 μm sand changed to coarse sand of 547 μm in 40 h). In contrast, it took one month to transition from a coarse median beach grain size of 883 μm to a very coarse one of 1323 μm. This variability in grain size results in dramatically different rates of sediment flux. For example, during average wind speeds of 10 to 14 m/s the sediment flux when the beach was composed of medium sized sand ranged between 21 and 154 kg/m/h compared to 0.4 to 50 kg/m/h when the beach was composed of coarse and very coarse sized grains. Overall, this study highlights the importance of beach grain size variability on aeolian sediment transport and shows that for similar incident wind and climatic conditions aeolian sediment transport rates vary dramatically. The study demonstrates the importance of taking care when using a constant median grain size in the calculation of long-term aeolian sand transport on beaches with heterogeneous spatial and temporal beach grain size variability.

Modified stochastic diffusion particle tracking model driven by skew Brownian motion: Analysis of sediment particle motion in turbulent flow under the effects of ejection and sweep.

Turbulent bursting events have been classified into outward interactions (Q1), ejections (Q2), inward interactions (Q3), and sweeps (Q4) in various studies. Ejections (Q2) and sweeps (Q4) have been identified as significant contributors to time consumption, momentum flux, and sediment flux. Additionally, research has shown that the distribution of these events varies nonuniformly at different bed elevations. Despite extensive investigations into the nonuniform distribution of turbulent bursting events, their impact on sediment transport has been rarely explored. In this work, we developed a modified stochastic diffusion particle tracking model (SD-PTM) driven by skew Brownian motion (SBM) using the stochastic Lagrangian approach to scrutinize sediment particle movement in turbulent flows. The model incorporates turbulent characteristics derived from a direct numerical simulation dataset, allowing for a comprehensive analysis of sediment particle dynamics. Moreover, the proposed model accounts for the nonuniform spatial distribution of ejection and sweep events, as well as the particle movement direction during these events. Numerical simulations of the model were conducted to trace sediment particle trajectories in the streamwise and vertical directions. The analysis of sediment transport involved calculating the variance of particle trajectories to examine anomalous diffusion. The model's performance was evaluated by comparing it with flow velocity and sediment concentration profiles obtained from measurements in previous studies. In conclusion, our study suggests that the motion of sediment particles in turbulent flow can be thoroughly investigated under extreme flow conditions using the modified SD-PTM driven by SBM.

Architecture and evolution of shelf‐margin clinoforms developed in a back‐arc tectonic setting: Insights from quantitative analysis on the south‐west shelf margin of the Ulleung Basin

AbstractGeophysical and geological research in the Ulleung Basin has been ongoing since the 1970s, involving continuous seismic acquisition and multiple well‐drilling projects. This study utilized an integrated quantitative approach with conventional seismic interpretation based on recent trends to understand the history of the shelf‐margin development and individual controls that may have influenced each period in the Ulleung Basin. Quantitative analysis was conducted by measuring the progradation (Pse), aggradation (Ase) and sediment influx (Fc) of individual shelf margins in seven dip‐oriented seismic profiles, and calculating the shelf‐edge gradient (αse) and the P/A ratio. Based on these data and the ratio of accommodation to sediment supply (A/S ratio), which was interpreted from the stratal stacking pattern, five shelf‐edge trajectory types were defined and assigned to each shelf margin. By considering individual controls (eustatic fluctuations, sediment supply and tectonic events), we defined the three evolution intervals of the Ulleung Basin during the Middle Miocene to Late Miocene (15 to 6.5 Ma): (1) the upper Middle Miocene (15 to 11.63 Ma) characterized by a moderate sediment supply and high aggradation margin induced by rapid subsidence, (2) the lower Upper Miocene (10.8 to 10 Ma) as a high sediment supply and low aggradation margin associated with reworked sediments from the uplifted Dolgorae Thrust and (3) the uppermost Miocene (9.2 to 6.5 Ma) characterized by a low sediment supply and low aggradation margin experiencing sediment starvation. A comparison with worldwide continental margins indicated that the Ulleung Basin formed under a relatively low rate of progradation (low sediment supply; 4.79 km/Myr) and a high rate of aggradation (high shelf accommodation; 361.04 m/Myr) condition. The SW margin of the Ulleung Basin provides a unique example of understanding stratigraphic architecture variations under changing stress regimes of back‐arc setting (extensional to compressional) and understanding of individual controls that influence margin development.

Geochemical and mineralogical characteristics of shales from the early to middle Permian Dohol Formation in Peninsular Malaysia: Implications for organic matter enrichment, provenance, tectonic setting, palaeoweathering and paleoclimate

The early to middle Permian Dohol Formation is characterized by a significant presence of shale deposits. While these shales exhibit a low potential to generate hydrocarbons, there is a need to ascertain the possible reasons for the low hydrocarbon generation potential. Also, there are several unidentified properties and attributes associated with these shales in terms of their inorganic geochemical characteristics and their mineralogy. This study is focused on using XRF, ICPMS, and SEM with EDX to determine the mineralogical and geochemical characteristics of these shales and use these data to discuss their provenance history and tectonic setting and interpret the paleoclimatic and paleoweathering conditions. The inorganic geochemical analysis shows that the shales from the Dohol Formation are from a felsic igneous source. The shales were also identified to be from a passive margin based on the bivariate plot of SiO2 vs log (K2O/Na2O) and several multidimensional diagram plots. The CIA and CIW data, as well as the A–CN–K plot, all point to a significant degree of chemical weathering, ranging from mild to intense. The Sr/Cu ratio and C-value, combined with various other geochemical proxies, indicate that the shales were formed in warm-humid climatic conditions. The SEM analysis shows that the samples are mainly composed of kaolinite and illite, and this result was supported by the EDX elemental composition. The high terrigenous influx of sediments, the oxic to sub-oxic conditions in which the sediments were deposited, and finally low marine productivity were found to be the reasons for the low TOC in the shales from the Dohol Formation.

Large‐Scale Channel Response to Erosion‐Control Measures

AbstractErosion‐control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large‐scale channel response in the form of migrating bed level and sediment sorting waves. Our objective is to investigate the large‐scale channel response to such measures. We consider the lower Rhine River from Bonn (Germany) to Gorinchem (the Netherlands), where numerous erosion‐control measures have been implemented since the 1980s. We analyze measured bed level data (1999–2020) around four erosion‐control measures, comprising scour filling, bendway weirs, and two fixed beds. To get further insight on the physics behind the observed behavior, we set up an idealized one‐dimensional numerical model. Finally, we study how the geometry and spacing of the measures affect channel response. We show that erosion‐control measures reduce the sediment flux due to (a) lack of erosion over the measure and (b) sediment trapping upstream of the measure, resulting in downstream‐migrating incision waves that travel tens of kilometers at decadal timescales. When the measures are in close proximity, their downstream effects may be amplified. We conclude that, despite fulfilling erosion‐control goals at the local scale, erosion‐control measures may worsen large‐scale channel‐bed incision.

Transitional circulation patterns from full ice cover to ice-off in a seasonally ice-covered lake

There is consensus that under-ice circulation presents multiple phases through the winter, and that different mechanisms dominate each period. In this work, measurements of temperature, water velocity, conductivity, and dissolved oxygen from Lake Massawippi, Quebec, Canada, obtained during the ice-covered season in 2019, were used to characterize the time scales of different winter regimes and transitions among dominating circulation mechanisms. Lake circulation during this period began with a single-cell convection induced by sediment flux pulses in early winter. The single-cell convection decayed into a brief quiescent period. Radiatively driven convection then formed a convectively mixed layer in late winter. The defined mixed layer and temperature structure provided the necessary conditions for the formation of a potential rotational feature, which briefly formed immediately prior to ice break-up. Ice break-up led to complex hydrodynamics that persisted for nearly 28 days following full ice-off. Dissolved oxygen was directly correlated with the varying circulation features throughout the field campaign. This work provides a quantitative measure to delineate the transitions between under-ice regimes and provides novel insights into the subsequent circulation during and after ice break-up.

Determining sediment deposition dynamics influenced by check dams in a semi‐arid mountainous watershed

AbstractSemi‐arid environments are characterized by infrequent large magnitude rainfalls that produce flash flood events with high sediment concentration. Control structures such as check dams are widely used in this environment for mitigation. However, their impact on the overall sediment balance of watersheds, particularly those severely affected by anthropogenic activity, is sparsely documented. This study used topographic measurements, sediment analysis, and fallout isotope techniques to assess the effectiveness and service life of 18 rock and masonry check dams that were constructed in the 1930s for controlling sediment fluxes in an 11 ha mountainous watershed in southern Arizona. All of the dams are currently filled with sediment resulting in reduction of local channel gradients by 35 to 71% to between 0.04 and 0.28 depending on location within the reach. Sedimentation occurred over multiple decades at a relatively slow average rate of 0.59 t ha−1 y−1 indicating low instantaneous retention efficiency. The smaller headwater dams were filled soon after construction; however, their share of the overall storage capacity was minor. Although evaluation of 137Cs was an effective method for dating sediment, the 210Pb dating method was not satisfactory because of sediment sorting effects and complex deposition patterns. The abundance of similar control structures in the region points to the opportunity to better understand the process impacts of check dams over multiple decades to inform planning and design of their use in future mitigation projects.

Analysing the performance of the NARX model for forecasting the water level in the Chikugo River estuary, Japan

Estuaries are dynamic environments which are driven by various natural processes like river discharge, tides, waves, influx of saline water and sediments, etc. These ecosystems are the most sensitive to sea level rise and fluctuations in river discharge associated with climate change. A direct response of sea level rise and river discharge can be observed in the water level of estuaries. However, existing models have not considered these parameters for forecasting water level. This paper focuses on developing a water level forecast model for the Chikugo River estuary in Japan using Nonlinear Autoregressive with Exogenous inputs (NARX Model). NARX neural network was used to do the one-step-ahead prediction of water level considering the various parameters that can very well be influenced by climate change: previous water level, river discharge, and salinity. Accordingly, three models were developed: (i) Model I considering previous water level; (ii) Model II additionally considering river discharge; and (iii) Model III additionally considering salinity. All the models showed appreciable performance in forecasting the water level. Model III had the best correlation with the water level with a cross-correlation value of 0.6030, while the river discharge had only a cross-correlation of 0.1113 indicating that the Chikugo River estuary is tide-dominated. The model was trained using different combinations of available data - previous water level, river discharge, and salinity. Cross-correlation results showed a better correlation between water level and salinity than various other combinations trained. Therefore, tidal intrusion influences the water level in the estuary, thereby depicting that sea level rise can affect the water level, and its influence can be well predicted by the developed model. The water level significantly affects the flora and fauna and the predictability of future estuarine floods can help in taking necessary mitigation strategies.

Modelling mass accumulation rates and 210Pb rain rates in the Skagerrak: lateral sediment transport dominates the sediment input

Sediment fluxes to the seafloor govern the fate of elements and compounds in the ocean and serve as a prerequisite for research on elemental cycling, benthic processes and sediment management strategies. To quantify these fluxes over seafloor areas, it is necessary to scale up sediment mass accumulation rates (MAR) obtained from multiple sample stations. Conventional methods for spatial upscaling involve averaging of data or spatial interpolation. However, these approaches may not be sufficiently precise to account for spatial variations of MAR, leading to poorly constrained regional sediment budgets. Here, we utilize a machine learning approach to scale up porosity and 210Pb data from 145 and 65 stations, respectively, in the Skagerrak. The models predict the spatial distributions by considering several predictor variables that are assumed to control porosity and 210Pb rain rates. The spatial distribution of MAR is based on the predicted porosity and existing sedimentation rate data. Our findings reveal highest MAR and 210Pb rain rates to occur in two parallel belt structures that align with the general circulation pattern in the Skagerrak. While high 210Pb rain rates occur in intermediate water depths, the belt of high MAR is situated closer to the coastlines due to lower porosities at shallow water depths. Based on the spatial distributions, we calculate a total MAR of 34.7 Mt yr-1 and a 210Pb rain rate of 4.7 · 1014 dpm yr-1. By comparing atmospheric to total 210Pb rain rates, we further estimate that 24% of the 210Pb originates from the local atmospheric input, with the remaining 76% being transported laterally into the Skagerrak. The updated MAR in the Skagerrak is combined with literature data on other major sediment sources and sinks to present a tentative sediment budget for the North Sea, which reveals an imbalance with sediment outputs exceeding the inputs. Substantial uncertainties in the revised Skagerrak MAR and the literature data might close this imbalance. However, we further hypothesize that previous estimates of suspended sediment inputs into the North Sea might have been underestimated, considering recently revised and elevated estimates on coastal erosion rates in the surrounding region of the North Sea.

Influences of sources and weather dynamics on atmospheric deposition of Se species and other trace elements

Abstract. Atmospheric deposition is an important source of the micronutrient selenium for terrestrial ecosystems and food chains. However, the factors determining the total concentrations and chemical forms (speciation) of selenium in atmospheric deposition remain poorly understood. Here, aerosol samples were collected weekly over 5 years at Pic du Midi Observatory (French Pyrenees), alongside highly temporally resolved samples of aerosols, precipitation, and cloud water taken during a 2-month campaign. Firstly, measurements of selenium, other elements, and water isotopes were combined with sophisticated modelling approaches (aerosol–chemistry–climate SOCOL-AERv2 model and air parcel backward trajectories and Lagrangian moisture source analyses). Aerosol selenium measurements agreed well with SOCOL-AERv2-predicted values, and interestingly, higher fluxes of selenium and other elements were associated with deep convective activity during thunderstorms, highlighting the importance of local cloud dynamics in high deposition fluxes. Our results further indicate the coupling of element and water cycles from source to cloud formation, with decoupling during precipitation due to below-cloud scavenging. Secondly, selenium speciation was investigated in relation to sulfur speciation, organic composition, and moisture sources. While in the 5-year aerosol series, selenite (SeIV) was linked to anthropogenic source factors, in wet deposition it was related to pH and Atlantic moisture sources. We also report an organic selenium fraction, tracing it back to a marine biogenic source in both aerosols and wet deposition. With a comprehensive set of observations and model diagnostics, our study underscores the role of weather system dynamics alongside source contributions in explaining the atmospheric supply of trace elements to surface environments.

Quantifying denudation rates and sediment recycling of low-relief, high-elevation landscapes using in-situ and meteoric cosmogenic nuclides

Quantifying Earth’s surface denudation rates is crucial for estimating sediment flux and its role in regulating global climate change. The inability of in-situ cosmogenic 10Bein to quantify denudation rates in quartz–free environment has prompted the need for a new proxy–the ratio of meteoric 10Bemet to mineral-weathered 9Be in reactive phase (precipitated in or adsorbed onto secondary minerals). This study utilized 10Bein–26Alin, 10Bemet/9Be, and major element analyses of reactive and mineral phases of bedload sediments to infer basin-wide denudation rates and sediment recycling (reworking of deeply buried sediments) in the Three River Source Region (TRSR) of the central Tibetan Plateau. Results from 10Bein-26Alin analysis of bedload sediments and bedrock samples (quartz grain, 250–500 μm) suggest that the sediments underwent burial events since at least 0.54 ± 0.16 million years ago. Combining paleoclimate records in the central Tibetan Plateau, we interpret the “Great Burial” as most likely the result of climate-controlled deglaciation and denudation at the termination of Naynayxungla glaciation during the MIS 13–15 period. This event marks the first widespread deglaciation on the Tibetan Plateau. The 10Bein-26Alin derived paleo–denudation rates range from 4.2-0.8+0.9 to 151-32+37 mm/kyr, consistent with previous 10Bein–derived modern denudation rates of 10–117 mm/kyr in TRSR. These rates show a moderate positive correlation with regional topography, particularly channel steepness, indicating a decrease in both relief and denudation rates from lower to upper streams. This spatial discrepancy is likely due to enhanced river headward incision and active neotectonic activities in the southeast. Denudation rates derived from the 10Bemet/9Be proxy range from 13 to 248 mm/kyr, alongside a chemical weathering intensity ranging from 43 % to 67 %. These denudation rates are strongly correlated with, but about 1.5 times higher than, the 10Bein–26Alin derived paleo–denudation rates from the same watershed. This suggests that the 10Bemet/9Be extracted from fine grains (<64 μm) may reflect a different sediment recycling pattern compared to 10Bein–26Alin in quartz sediments. Alternatively, the 10Bemet/9Be ratio could indicate a mixture of carbonate rock with a high denudation rate and silicate rock with a lower denudation rate, whereas 10Bein–26Alin reflects a single silicate denudation signal.