Sediment Sources Research Articles

Eocene to Miocene sediment provenance features and evolution history of the western slope area in the Xihu Sag of the East China Sea Continental Shelf Basin

Rift basins are commonly characterised by multiple sediment sources (e.g. transverse and longitudinal) that change over time during different rifting evolution stages. Therefore, tracing sediment provenance to decipher the sedimentary source-to-sink analyses processes in rift basins is important to predict sandy reservoirs. The Xihu Sag in the East China Sea Shelf Basin, particularly its western slope, features large-scale sand bodies of unclear origin. We used petrography, heavy minerals and geochemistry to study sediment provenance in the Eocene Baoshi to Miocene Longjing formations. Our work suggests there are three distinct areas (namely zones A, B and C) affected by different source areas. Zone A, influenced by the Hupijiao uplift, primarily contains metamorphic rock minerals; Zone B, affected by the Haijiao and Hupijiao uplifts, contains igneous and metamorphic rock minerals; and Zone C, dominated by the Haijiao uplift, features igneous with some metamorphic sources, which increase over time, indicating stronger sediment input from the northern Hupijiao uplift. Rare earth element analysis suggests a continental margin and island arc setting, primarily with intermediate–acid felsic rock sources. However, a Eu negative anomaly in Eocene upper Pinghu Formation to the Miocene Longjing Formation indicates some basic source contributions, possibly from a volcanic belt east of the South Yellow Sea. This intermediate–basic volcanic rock belt is located to the northwest of the Hupijiao uplift and may provide clasts for zones A and B through axial channels. These findings indicate that varied sediment sources in the different zones and basin evolution stages with a growing extra-basinal contribution from the Eocene to Miocene, which align with the tectonic shift from the rifting to post-rift period, are essential for understanding the sedimentary filling in this area.

Shaping the future of conservation: a model for restoring oxbows in Iowa and beyond

Oxbows, once an abundant and natural feature of the landscape, have been nearly eliminated due to the effects of the Anthropocene, consequently impacting water quality, flood storage capacity, and the wildlife that depend on this habitat. These depressional basins within floodplains naturally accumulate sediment over time, but the sedimentation rate of oxbows over the last 100 years has greatly increased. The primary sources of sediment are from human activity, including erosion from agricultural fields and urban developments, drainage alterations, precipitation changes associated with climate change, and disconnection from their rivers and natural river hydraulics. Outlined in this manuscript is a step-by-step guide for restoring oxbows, based on 20 years of experience and lessons learned implementing oxbow restorations in Iowa on first-, second-, and third-order streams. Our goal is to provide conservation services providers and others interested in restoring degraded oxbows with the tools and expertise to confidently restore oxbows to achieve conservation goals.

Developing an Approach for Integrating Chemical Analysis and Transcriptional Changes to Assess Contaminants in Water, Sediment, and Fish.

Pharmaceuticals in aquatic environments pose threats to aquatic organisms because of their continuous release and potential accumulation. Monitoring methods for these contaminants are inadequate, with targeted analyses falling short in assessing water quality's impact on biota. The present study advocates for integrated strategies combining suspect and targeted chemical analyses with molecular biomarker approaches to better understand the risks posed by complex chemical mixtures to nontarget organisms. The research aimed to integrate chemical analysis and transcriptome changes in fathead minnows to prioritize contaminants, assess their effects, and apply this strategy in Wascana Creek, Canada. Analysis revealed higher pharmaceutical concentrations downstream of a wastewater-treatment plant, with clozapine being the most abundant in fathead minnows, showing notable bioavailability from water and sediment sources. Considering the importance of bioaccumulation factor and biota-sediment accumulation factor in risk assessment, these coefficients were calculated based on field data collected during spring, summer, and fall seasons in 2021. Bioaccumulation was classified as very bioaccumulative with values >5000 L kg-1, suggesting the ability of pharmaceuticals to accumulate in aquatic organisms. The study highlighted the intricate relationship between nutrient availability, water quality, and key pathways affected by pharmaceuticals, personal care products, and rubber components. Prioritization of these chemicals was done through suspect analysis, supported by identifying perturbed pathways (specifically signaling and cellular processes) using transcriptomic analysis in exposed fish. This strategy not only aids in environmental risk assessment but also serves as a practical model for other watersheds, streamlining risk-assessment processes to identify environmental hazards and work toward reducing risks from contaminants of emerging concern. Environ Toxicol Chem 2024;43:2252-2273. © 2024 SETAC.

Rates of sedimentary organic carbon preservation in the Bering Sea and Chukchi Sea, and their response to climate change over the past 75 years

The Arctic Ocean is rapidly warming. In this paper, we document changes in the source, distribution, and accumulation rate of organic matter (OM) for three sediment cores in the Bering and Chukchi seas to investigate changes to the oceanic carbon cycle over the past ∼75 years. Analyses were undertaken using bulk properties, such as total organic carbon (OC), total nitrogen (TN), stable carbon isotope (δ13C), OC to TN molar ratio (C/N), and biomarkers (lignin phenols). The OC, TN, and lignin (Σ8, in mg (g sediment)−1) contents were found to be significantly related to the fraction of sand (Sand%) as a result of sediment sorting and/or different sediment sources. Using an end-member mixing model, we estimated marine OM accounted for ∼67% of all organic matter in all cores, being the dominant source. Moreover, terrestrial OM mainly originated from angiosperm non-woody tissue, while moss contribution was negligible. In the Bering Sea shelf, OC% has not changed over time, but there have been some extreme peaks around the 1960s–1970s and in 2005, which correspond to increased terrestrial input from North American rivers. In the southern core from the Chukchi Sea, the OC% showed an apparent decrease after 2000, accompanied by an increase in sand content, likely due to enhanced delivery of volcanic rocks by the Pacific Inflow from the Bering Sea. In contrast, in the northern core from the Chukchi Sea, the OC% showed a significant increasing trend, with some peaks occurring at the same time as in the Bering Sea core. The mean increase rate was compared to the increase in Siberian riverine discharge, which both could be caused by long-term climate changes. The results highlight the regional differences in the response of OC preservation to climate change and other controlling factors. Further studies with higher spatial resolution are required to better understand the preservation of OC in response to climate change.

Provenance of the late Jurassic to Cenomanian sedimentary succession of the Araripe Basin (NE Brazil) and implication for the geodynamic evolution of Western Gondwana

The separation of Gondwana was controlled by preexisting Proterozoic structures and by the development of rift aborted basins, of which the Araripe Basin (NE Brazil) is one of the best examples. Previous studies have focused on the presence and provenance of Aptian–Albian shallow-marine incursions in the Araripe Basin but to date, little attention has been given to its paleodrainage evolution during sedimentation stages. Understanding the paleodrainage evolution is crucial for determining sediment sources and how topographic changes relate to the geodynamic development of the northern part of South America during the fragmentation of Gondwana, and this study investigates the provenance of Mesozoic rift and post-rift sedimentary rocks in the Araripe Basin using a multi-proxy dataset comprising major and trace element concentrations, Sm–Nd isotopic composition, and detrital zircon U–Pb ages. The low Eu/Eu* ratios (0.3–0.9) and high Th/Sc ratios (>0.64) in the most of analyzed samples suggest a felsic and silicic source. The εNd(0) values (−12.3 to −23.7) and TDM ages (1.68 to 2.55 Ga) of analyzed samples suggest overall ancient crustal sources. The presence of oval and elongated zircon grains suggests a major contribution of first-cycle transport sediments. The presence of 2.3–1.8 Ga and 0.63–0.58 Ga U–Pb zircon ages further indicates the dominant contribution of the Borborema Province influenced by the Brasiliano cycle (650–520 Ma). The low contribution of Tonian (∼940 Ma) zircons to the U–Pb zircon age distribution of the rift-beginning stage sample associated with published paleocurrent direction suggests sources located in the northern and northwestern terranes of the Borborema Province. The increase of Tonian (0.9–1.0 Ga) zircon grains during the rift stage suggests a provenance change with a dominant source in the eastern terranes during the rift stage. During the post-rift I stage, the decrease of 1.2–0.72 Ga zircon ages suggests a change in the source areas, with the paleodrainage coming from northern Borborema Province, similar to that of the rift-beginning stage. The samples of the post-rift II stage exhibit dominant contributions of Paleoproterozoic and Neoproterozoic U–Pb ages related to the Albian to Cenomanian uplift of the Borborema plateau during the opening of Equatorial Atlantic Ocean. Together with previous published studies, these findings highlight the significant role played by the post-rift continental uplift to the paleodrainage of the northern part of South America.

Quaternary tectonic and climatic forcing on the spatio-temporal evolution of the Meuse fluvial terrace staircase

The Quaternary is characterized by pronounced alterations between cold and warm climatic states, with the Mid-Pleistocene Transition marking a strong increase in the intensity of cold-climate conditions. River systems are sensitive to environmental perturbation (e.g., climate, tectonics, base level) and are expected to respond to such profound changes. This study uses a combination of terrace mapping and analysis of a dense borehole database to investigate the Meuse terrace staircase (and its deposits), and gain insight on how it reflects climatic and tectonic perturbations during the Quaternary. The lower reaches of the Meuse river, which has both its main water and sediment source in the Ardennes displays a well-developed terrace staircase that was sculpted mainly throughout the Quaternary. The staircase is located near the cities of Maastricht (southern Netherlands) and Liège (northwestern Belgium). About 30 terrace levels reflect signals of environmental perturbations in the lithological composition, gradients, thicknesses, and spatial distribution. The terraces are organized in groups, based on their morphological position, from old to young; these are the East Meuse terrace group and West Meuse High-, Middle- and Low terrace groups. Our findings show a consistent increase in the gravel content from older to younger terraces. The sandier composition of the deposits of the oldest terraces (Early Pleistocene) is closely related to the supply of the Miocene-Pliocene weathered material from the Ardennes. Younger terraces (Middle and Late Pleistocene) are much richer in gravel, evidencing sediment input from fresh or partially weathered bedrock. These changes point to a downstream migration of the gravel front throughout the Quaternary. The mean thickness of the terrace groups shows a slight increase, even though the same trend is not clear when each terrace is analyzed on an individual basis. The anomalous thickness of the Caberg 1 terrace suggests increased sediment input during the cold climatic conditions of the Elsterian (MIS 12), the first Quaternary glacial during which an ice sheet extended into the northern Netherlands. Reconstruction of terrace gradients reveals that older East Meuse terraces show a (reversed) gradient opposite to reconstructed palaeo flow directions, which is attributed to a combination of low gradients during terrace formation and footwall back-tilting of the Feldbiss Fault Zone. In our analysis we do not see clear evidence for the imprint of the Mid-Pleistocene Transition, which suggests that due to its gradual nature, its signal is either buffered or assimilated by the overall climatic signal of the Quaternary. This study offers a first complete temporal analysis of the Meuse terrace staircase, providing an important basis for better understanding the effects of Quaternary climatic change and tectonics, and their resulting effects in other river systems worldwide.

Characterization and Modernization of the Depositional System in Modern Ebinur Lake Basin, Northwest China

The Ebinur Lake Basin is a typical terrestrial sedimentary Basin in Northwest China that has developed a piedmont distributive fluvial system (DFS) sedimentary environment, lake sedimentary environment, and desert sedimentary environment. The Ebinur Lake receives the sediments carried by the rivers in the basin and is the regional sedimentary center. In this study, a division scheme of modern sedimentary system tracts in the Ebinur Lake Basin was proposed. According to the landform, sedimentary environment, structure, and sedimentary system types, the Ebinur Lake Basin was divided into five system tracts. The area with high altitude and steep gradients mainly develops the rapid sedimentary system DFS, and the area with the lowest altitude in the region develops the lake sedimentary system. The main action area of climate drought and wind field is the dune sedimentary area. The wind field under the influence of hydrological climate and geomorphology has an important influence on the distribution of the sedimentary system tract. The structure determines the development of different types of sedimentary systems by controlling the topographic fluctuation and sedimentary space. Hydroclimate and geomorphology affect the development of sedimentary systems by controlling the sediment source rate in the sedimentary area. Based on the analysis of the characteristics and distribution of the modern sedimentary system in the Ebinur Lake Basin, a method for determining the level of the sedimentary system of the Ebinur Lake was established together with a plane model of the sedimentary system of the Ebinur Lake, which provides a reference for the study of the sedimentary system of continental basins.

Genetic types and provenance indication of clastic amphibole in the South Yellow Sea

The main focus of studying sediment sources in marine areas is to determine the properties of clastic minerals originating from different rivers. Variations in the characteristics of clastic minerals occur due to differences in the types of source rocks within the watershed. Determining the source rock of clastic minerals in the marine area can improve the accuracy of provenance analysis. Electron probe microanalysis of 258 amphibole grains from six surface stations in the South Yellow Sea (SYS) was conducted to calculate the numerical and characteristic values of cations in the crystal structure. The results showed that amphibole in the SYS is mainly magnesiohornblende (52.2% ~ 81.4%) in the calcic amphibole subgroup, followed by tschermakite. The source rock types of amphibole are mainly different types of magmatic (ultrabasic, basic, and intermediate acidic) and metamorphic rocks. Amphibole derived from intermediate-acid intrusive rocks accounts for a large proportion (>40%). The genetic analysis of clastic amphibole in the SYS showed that most of the medium-acid invading amphibole belong to crust-mantle type, followed by mantle type. Most of the amphibole from metamorphic origins are of medium-low pressure type (± 80%). Combined with electron probe analysis of amphibole from the Huanghe River (the Yellow River, HH) and Changjiang River (the Yangtze River, CJ), the amphibole in the SYS exhibits characteristics inherited from these two rivers. The northern sea area has a strong resemblance to the sediments from the HH, while the southern area is more influenced by sediments supply from the CJ. The central area represents a mixed zone with a higher sediment supply from the HH. The clastic amphibole deduces the type of source rock in different watersheds, serving as a crucial link between the source rock, watershed, and marine area, providing a basis for provenance analysis.

Architecture and history of uranium-bearing Palaeocene–Eocene strata deposited on the eastern margin of the Peri-Tethys (Chu-Sarysu Basin, south Kazakhstan)

Deciphering the facies and architecture of alluvial successions provides invaluable insights into the interplay of tectonics, climate, eustasy, and autogenic processes affecting terrestrial sedimentary systems. The stratigraphic response of fluvial systems to variations in discharge and sediment-supply regimes is now well-understood and is tied to changes in climate, precipitation patterns, or sediment sources. The uraniferous Chu-Sarysu Basin in south Kazakhstan occupies the tectonically stable Turan Platform on the eastern margin of the Peri-Tethys, and the study of its Palaeocene–Eocene sedimentary fill offers an opportunity to unravel eustatic and climatic controls that drove the architecture of reservoirs hosting economically important deposits. The stratigraphic succession comprises two multistorey, laterally extensive, sheet-like sandstone bodies floored by prominent erosion surfaces and interpreted as the deposits of channel belts. These packages are interstratified with floodplain, coastal-wetland, and marine-embayment complexes reflecting major extra-channel belt avulsions and marginal-marine incursions on the low-gradient alluvial plain. The stratal architecture was controlled by changes in accommodation likely induced by well-documented sea-level changes in the Peri-Tethys during the Palaeogene, which permitted the development of a chronostratigraphic framework. Eustatic variations culminated in the widespread flooding of the Turan Platform in the middle Eocene, reflected by transgressive lags above a wave ravinement surface capping terrestrial and marginal-marine deposits. Marked changes in fluvial facies, floodplain styles, and inferred channel planforms between Palaeocene and Eocene strata suggest a climatic overprint on river discharge and sedimentation. Upper Palaeocene meandering channel deposits encased in well-drained floodplain strata are indicative of perennial discharge under a semi-arid climate, whereas lower Eocene low-sinuosity channel fills, displaying evidence for transcritical flows and abundant in-situ vegetation, point to intermittent runoff patterns consistent with a humid and seasonal climate. An evolution in atmospheric moisture at the Palaeocene–Eocene boundary from arid to humid conditions has been reported across the Tethys region, and linked to global climatic perturbations of the Palaeocene–Eocene Thermal Maximum.

The impact of glacier retreat on Andean high wetlands: Assessing the geochemical transfer and sediment provenance in the proglacial area of Huayna-Potosí (Bolivia)

The accelerated decline of tropical Andean glaciers is affecting the water cycle of mountains in the region. In the Cordillera Real (Bolivia) on the Huayna-Potosí peak (6088 m a.s.l.), the rapid retreat of the Oeste Glacier is exposing new rock outcrops and glacial materials. Changes in the hydrological regime by glacier retreat are likely to modify the supply of sediments and subsequently affect the geochemical transfer of particle-bound elements within proglacial and downstream ecosystems. To address this issue, a sampling campaign in the proglacial area of Huayna-Potosí aimed to identify and collect sediments from the primary active landforms. To characterise elemental transfer and identify sediment provenance using fingerprinting techniques, streambed sediments were collected along the main stream from the glacier tongue at 5002 m a.s.l. to a wetland shallow lake at 4700 m a.s.l.. Geomorphological features control the production of fine particles and the distribution of particle-bound geochemical elements. Complex processes of solubilization, mobilisation, and retention govern the elemental transfer. Significant increases in 238U, as well as some major elements, were observed in the surface lake sediments, while Pb, Cr, and Cu decreased, and 137Cs was not detected. The spatial distribution patterns of geochemical elements and the assessment of the sediment provenance indicate that deglaciation fosters geochemical processes and the elemental transfer dynamics in the wetlands. Moraines and colluvium were found to be the primary contributors to sediment yield (93 %) while the rich organic soils in swamps contributed the least (7 %). The enhanced supply of sediments to the shallow lake in parallel to glacier decline may affect water quality and bring about further changes in the wetlands. Identifying primary sediment sources is essential for water management. Our findings enhance understanding of the compositional characteristics of mobilised sediment and their variations, aiding in more effective resource management to preserve these high-altitude wetlands.

Estimation of vertical transport timescales of sediment in the Changjiang Estuary and its adjacent regions

The concept of resuspension age was employed to assess the timescales of vertical sediment transport in the Changjiang Estuary (CJE) and its adjoining areas. Resuspension age refers to the duration elapsed since particles last made contact with the seabed. Energetic tidal current in the study area results in a significant amount of sediment being eroded into the water during spring tides, causing the resuspension age to consistently remain lower during spring tides compared to neap tides. Spatially, consistently low resuspension ages occur in the North Branch and turbidity maximum because suspended sediment in these areas primarily originates from local erosion. While advective sediment dominates in the HZB, leading to highest resuspension age there. During the wet season, the South Branch experiences an average resuspension age surpassing 10 days, primarily due to particles predominantly transported from the river. Sediments deposited on the seabed during the wet season become the primary source of suspended sediment after being eroded into the water column during the dry season, leading to a reduction in resuspension age. Likewise, the decrease in resuspension age in the Subei Coast during the dry season is closely associated with the appearance of sediment mass advected by the northern branch plume. When stratification occurs, the upward diffusion of sediment is impeded, constraining newly eroded sediment close to the bed. As a result, these sediments exhibit lower ages than those in the upper water column, where sediment transport is primarily dominated by horizontal advection.

Sedimentary records of giant landslide-dam breach events in western Sichuan, China

Introduction: Landslide-dammed lake outburst floods (LLOFs) are common natural disasters in high-mountain regions, posing serious safety threats to residents’ livelihoods and properties and causing major damage to engineering facilities. Giant landslides and river damming events commonly occur in the Eastern Tibetan Plateau in southwestern China. Dam failure generate LLOFs that form outburst deposits (ODs). This phenomenon is particularly common in some giant ancient landslide-dammed lakes.Methods: This study conducted a detailed investigation of the sedimentary characteristics of large-scale landslide-dammed lake outburst deposits in the Diexi Reach of the Upper Minjiang River and Tangjiashan Reach of the Tongkou River Basin, West Sichuan Plateau, China. Meanwhile, typical evidence of high-energy ODs was recorded.Results and Discussion: The longitudinal distribution of these ODs is similar to an elongated fan-shaped terrace along the river channel, presenting a distinctive sedimentary disordered–sub-ordered–ordered sequence from upstream to downstream. Several typical units of “sedimentary facies” are developed in the OD profiles, such as boulder units deposited by high-energy outburst flood (OF) events and the gravel and sand units representing pulsating-flow sedimentary environments during the recession stage. The grain size frequency curves are bimodal, and the granularity accumulated curves are upward convex, which reflect that the detrital characteristics of the sediment source area are mainly composed of coarse gravel and boulders. This indicates that the coarse gravel sediment gradually become decreased from upstream to downstream. Moreover, the OD hydrodynamic intensity displays a gradual weakening, and sediment sorting is improved. From upstream to the downstream, the mean particle-size and sorting of the ODs gradually decrease. The skewness become larger, and the kurtosis of the ODs is distributed in all the types. In addition, the different combinations of quartz sand surface microtextures indicate the transformation from high-to low-energy impacts over a short distance, which is controlled by flood hydrodynamics and regime.Significance: These sedimentary characteristics of ODs explain the hydrodynamic changes during the propagation of OFs, and are also important records for distinguishing between ODs, and “normal” floods.

Reconstruction of a Long-Term, Reach-Scale Sediment Budget Using Lateral Channel Movement Data as a Proxy: A Case Study on the Lowland Section of the Tisza River, Hungary

Humans have influenced the sediment transport of rivers on a centurial scale. Our goal was to use the rate of lateral channel processes as a proxy to reconstruct sediment budget (SB) changes of a lowland river (Middle Tisza, Hungary) on a historical scale (1838–2017). The gross sediment budget (GSB) refers to the total area of eroded and accumulated surfaces, and the net sediment budget (NSB) indicates the sediment sink or source characteristics. At the beginning (1838–1890), the artificial cut-offs increased the slope and channel erosion, but the eroded sediment deposited in the oxbows, so the reach acted as a sediment sink (NSB: +0.1–0.8 m2/m/y). Then (1890–1929), a quasi-equilibrium state developed (NSB: −0.2 m2/m/y to +0.4 m2/m/y). Later (1929–1976), the bank protections impeded lateral erosion, so the system became a sediment sink again (NSB: +0.1–0.7 m2/m/y). Finally (1976–2017), the erosional processes accelerated due to dam construction and revetment collapses, and now the river is a sediment source (NSB: −0.03 to −0.08 m2/m/y). This study proved that (1) the actual SB could not be projected in the long term, as it was heavily modified, and (2) lateral channel changes could be used as a proxy to estimate long-term SB.

Evaluating opportunities for broad-scale remote sensing of total suspended solids on small rivers

Although broad-scale remote sensing applications are increasingly being integrated into water quality assessments, the feasibility of such applications on smaller rivers (<150 m. width) is not well understood, even though smaller rivers comprise most of the river network and can constitute significant sources of sediment and nutrients. We evaluated the application of a widely used Total Suspended Solid (TSS) algorithm within ten small (16–117 m wide) tributaries of the Lake Champlain Basin in the Northeastern US. Sentinel-2 images captured within 5 h of depth-integrated TSS samples were identified and corrected for atmospheric conditions to generate TSS estimates. Linkages between sample attributes and errors in the relationship between measured and predicted TSS values were explored to identify potential limits on the application of existing TSS algorithms to small rivers. From a dataset of 64 unique measured-predicted values on rivers whose channel width was greater than one pixel (i.e., 10 m), we found that there are settings along smaller rivers, and discrete flow and seasonal conditions, under which broad-scale remote sensing applications may be applicable. The remote sensing algorithm had the greatest success predicting TSS for rivers with high background levels of sediment (i.e., large concentrations during smaller discharges). Errors in estimated TSS were three times greater on rivers with low background levels (average error of 174%) of sediment than high levels (average error of 57%), likely due to differences in the proportion of fine-grained particle-sizes in transport. We also found that estimated TSS error was less outside the growing season, when biological activity was limited and plants were dormant, and when higher flows occurred such that backscatter from the channel bed is less likely to interfere with the reflective signal. This effect was most pronounced on rivers with low background sediment loads; errors in estimated TSS were more than six times greater during the growing season on rivers with low background loads (average error of 216%) than when plants were dormant (average error of 48%). We hypothesized that algorithm performance on smaller rivers, as measured by channel width, would be prone to larger errors due to the greater influence of contrasting reflectance signals from soils and vegetation along riverbanks. The degree of limitation from this adjacency effect was not evident in our dataset perhaps because of a correlation between river size and sediment characteristics unique to our study area. An alternative parameterization of a single-band empirical TSS model for small rivers in the region, based on inclusion of readily identifiable geologic and temporal characteristics, suggests improved predictive power for small rivers. Results highlight the feasibility of extending remote sensing applications throughout the river network in temperate regions of the Northeastern U.S. Certain geologic settings, specifically those that transport finer-grained loads, are more likely to have accurate predictions, especially during the colder months, when in situ monitoring is particularly challenging, yet highly important because a significant portion of runoff events in the Northeastern U.S. occur in this time.

Combining hillslope erosion and river connectivity models to assess large scale fine sediment transfers: Application over the Rhône River (France)

AbstractSediment connectivity at the catchment scale includes the processes linking sediment sources, sinks and the river outlet. Soil erosion models usually estimate yields without considering riverine processes or human infrastructure that may affect sediment connectivity. Quantifying these processes at a large scale is a determinant of understanding sediment transfers from continental lands to marine ecosystems. This study tries to fill this gap by coupling the soil erosion model WaTEM/SEDEM (WS) with the riverine connectivity tool CASCADE to quantify sediment fluxes in the Rhône watershed. The coupling returned a good fit, with deviations of −51.7%. WS alone predicts the exported fluxes better with a deviation of −34.9%. Nevertheless, this paper shows the importance of considering connectivity and transport capacity to develop a more realistic representation of fine sediment dynamics at a large scale. However, connectivity tools depend on the quality of the models (soil erosion and hydrology) and the geomorphological data on which they depend, which is a limiting factor in large‐scale studies.

Evolution of riverbed morphology in a main‐stem river due to management of sediment source areas

AbstractThe evolution of riverbeds is greatly impacted by changes in the water–sediment relationship resulting from the movement of debris flows. However, little is known about the influence of management in chronic sediment source areas on the evolution of main‐stem riverbed morphology. In this study, we used multi‐source remote sensing images covering the past 50 years along with water–sediment and topographic data from a river basin, and sediment transport data from debris flows, to analyze the evolutionary processes of the middle and lower reaches of the Daying River (DYR) at the China‐Myanmar border. Our results showed that (1) management of the sediment source area shifted the riverbed morphology from aggradation to erosion, transforming the river surface from wide and shallow to narrow and deep, and the channel from multi‐threaded to single‐threaded; (2) the active alluvial area, marginal bar area, and average river width exhibited an inverted V‐shaped trend, increasing by at least 23% and then decreasing by more than 59%; and (3) the evolution of riverbed morphology contributed to the stability of downstream riverbeds, improved flood control, and enhanced utilization of the floodplains.

Heavy metals in afforested mangrove sediment from the world's largest delta: Distributional mapping, contamination status, risk assessment and source tracing

This study aims to assess seasonal and spatial variations, contamination status, ecological risks, and metal sources (Ni, Pb, Cr, Cu, Mn, and Zn) in human-afforested mangrove sediments in a deltaic region. Five sampling locations were sampled during dry and wet seasons. Heavy metal concentrations followed the order: Mn > Zn > Ni > Cr > Cu > Pb. Metal loads, except Cu and Pb, were higher during the dry season, aligning with national and international recommendations. Sediment quality guidelines, contamination factor, geoaccumulation index, enrichment factors, and pollution load index indicated uncontaminated sediment in both seasons. Potential ecological risk assessment showed low risk conditions in all sites. However, modified hazard quotient indicated moderate pollution risk from all metals except Pb. Analysis suggests anthropogenic sources, particularly evident near shipbreaking yards in Sitakunda. While initially uncontaminated, ongoing metal influx poses a potential risk to mangrove ecosystems.

Spatial variation characteristics and influencing factors of sediment connectivity in the black soil region of northeast China

Connectivity has become an important indicator of the sediment transfer potential through sediment sources to catchment sinks. Connectivity plays a vital role in investigating the rate of soil erosion caused by runoff and sediment output across the watershed landscape. However, there have been few quantitative studies on the spatial variations in sediment connectivity in the black soil region of Northeast China. Seven classic watersheds in the northeast black soil region were selected to discover spatial variations in sediment connectivity and their influencing factors. The connectivity index (IC) was used to study the spatial variation of sediment connectivity, and the weight of IC was calculated using the vegetation cover management factor (C), which reflected the influence of human activities on the soil erosion process caused by cultivated land expansion and encroachment of forest grassland. The redundancy analysis method (RDA) was used to determine the main factors affecting the spatial variation of IC. The results showed that IC decreased from north (0.45) to south (0.12). The spatial variations of watersheds in sediment connectivity showed significant spatial heterogeneity. IC was correlated with topographic, climatic, and artificial management characteristics at 0.01 or 0.05 levels except soil structural index; RDA results showed that topography and human activities were the main factors affecting sediment connectivity. Topographic and climatic factors explained more sediment connectivity changes in the southern watersheds than in the northern watersheds, while the human activities factor explanation was the opposite of topographic factors. Human activities refer to changes in vegetation cover and soil structure and properties resulting from human logging and farming that affect sediment connectivity.

Sediment source areas and the role of floods in sediment mixing on the Letaba River, South Africa

ABSTRACT The morphodynamics of rivers in semiarid environments tend to be controlled by episodic flood events, but the precise nature of sedimentary processes and sediment source areas within catchments affected by episodic floods remains not well understood. This study presents geomorphological, sedimentary and mineralogical data from different river reaches along the semiarid Letaba River within Kruger National Park, northeast South Africa. Geomorphological and sedimentary data were used to evaluate river morphodynamic behaviour and identify the major controls on landform development. Mineralogical data (heavy minerals and trace elements) were examined from surface sediment samples from different river reaches to determine the potential source areas for sediment reworking within the catchment (channel bank, channel bed, tributaries) for flood-transported sediments. Results of this analysis on downstream reaches show catchment-averaged sediment contributions from the channel bed of 42.5%, tributaries of 35%, and channel bank of 22.5%. These sediment contributions likely arise as a result of the different flow conditions experienced in different locations of the river system during floods. However, there is significant variability between samples from individual reaches, likely related to valley width and bedrock vs sediment availability. The contributions of river sediments from different sources are conceptually developed through a model of sediment source variability at different hydrodynamic stages. This highlights the role of floods in reactivating non-perennial tributaries and adding new sediment into the main channel. Measurements of perennial channel storage, therefore, do not give the whole picture of total sediment availability or activation during floods.

Paleozoic to Mesozoic paleotectonic reconstructions of Gondwana assembly: Insights from petrography, heavy mineral chemistry and detrital U–Th–total Pb monazite geochronology of sandstones in the Pranhita-Godavari Basin (SE India)

The provenance study of Paleo-Mesozoic sediments of the Pranhita-Godavari (P-G) Basin, located in the southeastern India is crucial for the reconstruction of the eastern Gondwanaland, including the India-Antarctica connection. This study examines petrography, heavy mineral chemistry and detrital monazite geochronology of the Permo-Carboniferous to Cretaceous, predominantly fluviatile sandstones in the P-G Basin to track the possible sediment sources in East Antarctica and Eastern India. The sandstones show a gradual shift in composition from feldspatho-quartzose to quartzose arenite from older to younger succession, accompanied by a change in source terranes in a changing setting from transitional continental to the cratonic interior. The heavy minerals of the sandstones are dominated by garnet, rutile, ilmenite, monazite and zircon in order of decreasing abundance. The mineral chemistry of garnet and rutile indicates the predominance of sources from amphibolite to granulite facies rocks with minor inputs from metapelitic sources. The increase in textural and mineralogical maturity of sandstones accompanied by a gradual increase in ilmenite alteration from the bottom to the top of the succession indicates the attainment of tectonic stability with time. U–Th–total Pb dating of detrital monazites yielded three distinct major clusters at (1) 2556–2125 Ma, (2) 969–715 Ma, and (3) 581–418 Ma. Based on the correlation of source composition and monazite geochronology and paleocurrent data, the source of sediments is traced to the orogens of the Eastern Ghats mobile belt, East Antarctica (including Rayner and Napier complex), Karimnagar granulite belt, Khammam schist belt, and Bhopalpatnam granulite belt, situated to the west, south, and southeast of the present outcrops of the P-G Gondwana succession. The younger age populations possibly represent the sediment input from Kuunga Orogen, which represents the youngest orogenic event (635–488 Ma) in the Gondwana assembly. The rocks of Kuunga orogeny, occurring to the south of the basin, was a minor contributor to the P-G Gondwana sediments of this basin. The new data supports that the Eastern Ghats Mobile Belt of India and East Antarctica were conjugate to each other till the Late Triassic Period, both of which contributed major sediments to the P-G Gondwana Basin.