River Bed Sediments Research Articles

Numerical modeling of graded sediment transport with limited bed material supply – A case study in the Middle Yangtze River

Suspended sediment concentration in the Middle Yangtze River (MYR) has reduced sharply below the Three Gorges Dam since 2003, and led to significant channel degradation and riverbed coarsening. However, the complex interaction between riverbed coarsening and sediment transport is essential for channel evolution processes but is poorly understood. This paper presents a one-dimensional model for simulating graded sediment transport when the bed material supply is limited. The model takes account of the effect of bed material composition (BMC) and threshold probability on graded sediment transport, and thus improve the accuracy of recovery coefficient. The modeling results of graded sediment concentrations was calibrated and then satisfactorily verified using field observations in the JingJiang Reach from 2015 to 2016. The results showed bed material composition affect the simulated fine, medium, and coarse sediment concentrations, and the improvements of normalized errors are 17.6%, 45.9%, and 330.7%, respectively. With the BMC effect considered, the recovery factor of fine and medium were far less than coarse sediment in the MYR. In addition, the recovery ratios of medium and coarse sediment concentrations along the MYR were improved by 88.6%-265.4% and 75.1%-105.9% respectively, owing to the bed material supply after the TGD operation; however, there was no significant effect on fine sediment, with a low recovery ratio of 8.3%-8.6%. Therefore, the effect of bed material composition on graded sediment transport and channel evolution needs to be considered for higher simulation accuracy in the MYR.

Sediment properties control riverine methane emissions: A case study of the Liao River in northern China

River and stream sediments act as biogeochemical reactors for greenhouse gases, particularly methane. However, understanding how riverbed sediment properties influence river carbon emissions remains relatively unclear. The Liao River in northern China is a typical watershed with heterogeneous water and sediment sources, characterized by varying sediment properties. In this study, we surveyed CH4 and CO2 emissions from its mainstem and tributaries during flood and dry seasons. We found consistent seasonal patterns in CH4 and CO2 emissions, with peaks occurring during the flood season. The average CH4 and CO2 fluxes were 1.64 ± 1.80 mmol·m−2·d−1 and 59.66 ± 44.60 mmol·m−2·d−1, respectively. Notably, the percentage of sediment silt was significantly correlated with CH4 concentration and flux (R2 = 0.12−0.30, p < 0.05). Fine particles dominated the availability of sediment organic matter and redox conditions, which were related to riverine CH4 production and emissions. Structural equation modeling revealed that both grain size and the percentage of TOC (total organic carbon) directly influenced riverine CH4 and CO2 emissions. The organic content and redox conditions of the riverbed sediment collectively explained 65% of riverine CH4 emissions, while grain size composition indirectly controlled CH4 emissions by altering sediment substrate quality and redox conditions. In contrast, river CO2 emissions were only weakly dependent on anaerobic metabolism in riverbed sediments. These findings enhance our understanding of the sources and metabolic mechanisms of riverine CH4 and CO2 emissions and offer potential improvements for estimating carbon fluxes in regional or global riverine networks by considering riverbed sediment properties.

The first spatio-temporal study of the microplastics and meso–macroplastics transport in the Romanian Danube

BackgroundTransport, accumulation, and degradation of microplastics (MiPs) in the aquatic environment represent a significant concern to the researchers and policy-makers, due to the detrimental impact on biota and human health through food ingestion. Although consistent investigations and research data are available worldwide, comparing the results is still challenging due to the need for more regulations regarding the sampling methods, analysis, and results reporting. The European regulatory efforts include studies on the MiPs transport in the western basin of the Danube River developed with active nets-based multipoint sampling methods from suspended sediments and proposed for standardization. In this context, the present study aimed to address for the first time the transport of MiPs in the Romanian sector of the Danube, starting after entering the country (Moldova Veche) and before the formation of the Danube Delta (Isaccea).ResultsThe multipoint nets sampling procedure facilitated the collection of suspended sediments in the water columns as deep as 0.0–0.6 and 3.0–3.6 m depths and near riverbed sediments (autumn 2022 sampling) during an extensive spatio-temporal study from spring 2022 until spring 2023. The estimate of the maximum annual transport of 46–51 and 93–100 t·y−1 for MiPs and total (micro–meso–macroplastics) MPs at Moldova Veche was based on 135 collected and processed samples using 2021 water flow data. Polyethylene (58–69%) and polypropylene (21–33%) were the main polymer components in the separated fragments, foils, microfibers, and different colors spheroids of MiPs ( < 5 mm), and the foils and fibers of meso–macroplastics (5–100 mm). Advanced investigations highlighted various microstructural degradations of the plastic fragments at the micro- and nanoscale and attached minerals (clays) and heavy metals.ConclusionThis paper presents the first comprehensive data set for microplastic annual transport in the "Low Danube", filling the need for a complete transport assessment in one of the most significant European rivers. 4–5 times lower values were measured before the entrance to the Danube Delta than those from Moldova Veche. The investigations should continue, including flooding events, and the sampling points should be expanded to deeper water column layers during all the campaigns for further validation.Graphical

Concentrations and Health Risk Valuation of Possibly Toxic Metals in Soil and Sediment in Parts of Ona River, Ibadan, Nigeria

The accumulation of contaminants in the soils and sediments may negatively affects people within the vicinity of Ona River and increase potential of human health risk. This study appraised the concentration status, probable origins and human health risks of some possibly toxic elements (Fe, Cu, Zn, Mn, Pb and Cd) in the riverbank soils (RBK) and riverbed sediments (RBS) of Ona River section bordering residential community in Ibadan, Southwest Nigeria. Therefore, six composite samples of RBK and RBD were analyzed for heavy metals using atomic absorption spectrophotometry (AAS). Enrichment factor (EF) and quantification of contamination (QoC) are used to examine potential origins of tested metals. Furthermore, hazard index (HI) and total cancer risk (TCR) have been utilized to evaluate the extent of non-carcinogenic and cancer risks of studied metals to inhabitants of the study site. The results of metal contamination assessment revealed low concentration &lt;1.0 mg/kg for each analyzed metal in both RBK and RBD while EF and QoC advocate lithogenic origins of assessed metals with little or none anthropogenic inputs in both studied soils and sediments. The computed HI values were lower than 1.0 and thus no adversative health effects on adults and children via ingestion, skin contact and inhalation routes. The CR computation exposed that adults and children are at growing risk of developing cancer over a lifetime when exposed to RBK and RBD via ingestion and dermal pathways. Cadmium contributed largely to TCRs among the assessed metals. The study indicates the inevitability of initiating actions that reduce exposure of residents to nearby soil and sediment and safeguard their health, particularly the children.

River network‐scale drying impacts the spatiotemporal dynamics of greenhouse gas fluxes

AbstractRivers significantly contribute to global biogeochemical cycles; however, we have a limited understanding of how drying may influence these cycles. Drying fragments river networks, thereby influencing important ecosystem functions such as the processing of carbon and nitrogen, and associated fluxes of greenhouse gases (GHGs) both locally, and at the river network scale. Our objective was to assess, using a network‐scale approach, the lateral, longitudinal, and temporal dynamics of GHG fluxes in a river network naturally fragmented by drying. We used a closed‐loop chamber with automated analyzers to measure carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from dry sediments, flowing waters, isolated pools, and riparian soils, along with a suite of environmental variables, over 9 months at 20 sites across a non‐perennial river network in France. Network‐scale drying had a spatial and temporal legacy effect on GHG fluxes. On average, CO2 fluxes were up to 29 times higher from perennial than non‐perennial sites under flowing conditions. At non‐perennial sites, CO2 and N2O fluxes positively covaried with time since rewetting. In addition, CO2 and N2O fluxes at perennial sites positively covaried with the percent of non‐perennial reaches upstream, indicating a spatial effect of drying. GHG fluxes from riparian soil and dry riverbed sediments had markedly different magnitudes and covariates. This research demonstrates that drying not only has a local‐scale impact but also influences GHG fluxes at the network scale, contributing valuable insights for upscaling global riverine GHG estimates.

NATURALLY OCCURRING RADIONUCLIDES AND THEIR RADIOLOGICAL RISK ASSESSMENT IN RIVER SEDIMENTS FROM THE DITRAU ALKALINE MASSIF

Naturally occurring 238U, 232Th and 40K radionuclides within river bed sediments of Jolotca and Ditrău rivers from Ditrău Alkaline Massif (DAM) and their environmental risk and spatial distribution have been analyzed. The DAM metamorphic formations have been the subject of multiple studies due to their structure and high variety of mineral species. This led to the execution of many mining operations. River bed sediment samples have been collected from two of the main drainage basins of DAM, Ditrău and Jolotca rivers. The samples were analyzed using gamma-ray spectrometry in order to determine the concentration of the naturally occurring radionuclides and the risk parameters such as RLI (Representative level index), AGDE (Annual gonadal dose equivalent), Hex (External hazard index), Hin (Internal hazard index) and DR (absorbed gamma dose rates in air). 238U, 232Th and 40K show values higher than the Upper Continental Crust (UCC) and other studies from around the world. DR, AGDE and RLI are higher than the global average and the safe limits. These values are a consequence of the geological context which determined the presence of heavy minerals and Th and U bearing minerals.

Oxide Analysis of River Bed Sediments from Lower Reaches of River Forcados along Patani and Environ

Oxide Analysis of River Bed Sediments from Lower Reaches of River Forcados along Patani and Environ

From pollution to solutions: Insights into the sources, transport and management of plastic debris in pristine and urban rivers

River systems are important recipients of environmental plastic pollution and have become key pathways for the transfer of mismanaged waste from the land to the ocean. Understanding the sources and fate of plastic debris, including plastic litter (>5 mm) and microplastics (MPs) (<5 mm), entering different riverine systems is essential to mitigate the ongoing environmental plastic pollution crisis. We comprehensively investigated the plastic pollution in the catchments of two rivers in the Yangtze River basin: an urban river, the Suzhou section of the Beijing-Hangzhou Grand Canal (SZ); and a pristine rural river, the Jingmen section of the Hanjiang River (JM). The abundance of plastic pollutants in SZ was significantly higher than in JM: 0.430 ± 0.450 items/m3 and 0.003 ± 0.003 items/m3 of plastic litter in the water; 23.47 ± 25.53 n/m3 and 2.78 ± 1.55 n/m3 MPs in the water; and 218.82 ± 77.40 items/kg and 5.30 ± 1.99 items/kg of MPs in the sediment, respectively. Plastic litter and MPs were closely correlated in abundance and polymer composition. Overall, the polymer type, shape and color of MPs were dominant by polypropylene (42.5%), fragment (60.4%) and transparent (40.0%), respectively. Source tracing analysis revealed that packaging, shipping, and wastewater were the primary sources of plastic pollutants. The mantel analysis indicated that socio-economic and geospatial factors play crucial roles in driving the hotspot formation of plastic pollution in river networks. The composition of the MP communities differed significantly between the sediments and the overlying water. The urban riverbed sediments had a more pronounced pollutant ‘sink’ effect compared with the pristine rivers. These findings suggested that the modification of natural streams during urbanization may influence the transport and fate of plastic pollutants in them. Our results offer pivotal insights into effective preventive measures.

A methodology for evaluating the relative pollution level of metal pollution in surface sediments of rivers based on the statistical results of relevant literatures covering world-wide rivers

Due to the intervention of human activities, the background values of riverbed sediment exhibit spatiotemporal variability, which can affect the accuracy of risk assessment results. Using risk assessment that do not rely on background values is an executable alternative to avoid such problems. In this study, a relative pollution level assessment (RPLA) method which was based on the statistical results of relevant literatures was proposed. This method includes a four-step data processing procedure to extract the evaluation indexes of relative pollution degree of pollutants in environment and a series of relative pollution status assessment methods to evaluate the overall relative pollution level and regional difference of world-wide rivers. To demonstrate how to use RPLA method, 310 relevant literatures covering world-wide rivers were selected. And the ambient background value (x̅), the world-wide threshold values (WWTV) and the relative pollution grades (LEVEL I ∼ IV) of 9 target metals (Cr, Ni, Cu, Zn, As, Cd, Pb, Sb and Tl) in riverbed surface sediments of world-wide rivers were extracted and used for evaluation. Moreover, the stability and applicability of RPLA method were evaluated. Results show that the evaluation results of RPLA method are robust and comparable with traditional evaluation method.

Multi-isotopic constraints on the impacts of landslide on weathering and erosion in an active mountain range

In active mountains, landslides are the primary agent of erosion that readily generates materials with high weatherability. Understanding the linkage between landslide activity, erosion, and chemical weathering is critical for assessing how tectonic uplift affects the carbon cycle and Earth's climate. However, quantifying the contribution to chemical weathering and erosion fluxes from landslides remains challenging because of the lack of effective tracers related to landslide activities. Recent studies suggest that a suite of isotopic tracers, including the U, Sr and Be isotopes, have the potential to trace solutes and materials associated with landslide activities. Here we use three isotope ratios (234U/238U, 10Be/9Be, 87Sr/86Sr) to quantify the contribution to solid and solute fluxes from landslides in the tectonic-active eastern Tibetan mountains. We focus on 22 small catchments (drainage area < 50 km2) draining the epicentral region of the 2008 Wenchuan earthquake using samples collected in 2018 and 2019. Landslide seepage water and landslide sediment samples are used to constrain the landslide-weathering end-member. Tree branch and regolith topsoil samples are used to characterize the weathering end-member of regolith. We show that the U-Be-Sr isotopes can trace the solutes and solids sourced from landslide debris and quantify that landslides contribute 33.1 ± 16.2% (1SE) to the riverine solutes and 43.4 ± 20.8% (1SE) to the riverbed silt-sized sediment. These proportions are lower than the landslide-derived proportions in high-order catchments immediately (1 to 4 years) after the Wenchuan earthquake, which may relate to changes in landslide-material inputs across drainage networks and/or weathering processes over time. We also find that across 87 catchments with variable basin areas (from <1 km2 to ∼20,000 km2) draining the broad eastern Tibetan mountains, the 234U/238U activity ratio of river water and silt-sized riverbed sediment shows distinct characteristics for the catchments grouped by mean slope angles (mean slope angles shallower versus steeper than a common threshold angle of 32°). These findings suggest that U isotopes are a promising tracer of landslide-sourced solutes and materials. Overall, our work provides a case study showing that a multi-isotope approach can be used to quantify the impacts of landslides on erosion and weathering, providing new insights into how tectonic activities could affect the carbon cycle.

Long-term mercury loading and trapping dynamics in a Western North America reservoir

Study RegionThe Carson River including Lahontan Reservoir in Northwestern Nevada, USA Study FocusThe discovery, mining, and processing of silver and gold from the Comstock Lode in northwestern Nevada heavily contaminated the Carson River system with mercury (Hg). The river now contains some of the highest recorded water column and bed sediment Hg concentrations reported in peer-reviewed literature. Acute Hg contamination in river and reservoir bed sediment has led to elevated methylmercury (MeHg) concentrations across all trophic levels of Lahontan Reservoir, culminating in significant health risks to humans. Lahontan Reservoir, located downstream from the mills that processed Comstock ore, has served as a Hg trap since the completion of the dam in 1915. Starting in 1997 and extending through 2021, the U.S. Geological Survey has collected and analyzed hundreds of discrete water samples entering and exiting Lahontan Reservoir for unfiltered total Hg (uf.THg), thereby providing a first-of-its-kind opportunity for studying long-term Hg trapping efficiencies within a western North American reservoir. Continuous time series of uf.THg concentration and flux above and below the reservoir were estimated using the weighted regressions on time, discharge, and season with the Kalman filtering (WRTDS-K) method employed with newly developed methods to account for non-natural (i.e., managed) hydrographs below a reservoir. New hydrological insights for the regionAn estimated 31,650 kg (34.89 US tons) of uf.THg entered Lahontan Reservoir during the 25 year period of analysis, accounting for approximately 0.5% of the total uf.THg estimated to have been released to the Carson River system [6.8 million kg (7500 US tons)] over a multi-decade mining boom. Moreover, approximately 92% of the estimated uf.THg entering Lahontan Reservoir was trapped. On an annual basis, however, trapping efficiencies range between 34% and 98%, and are closely related to the total annual discharge. Results also indicate that flow-normalized uf.THg concentrations and loads above and below the reservoir are trending down.

Prediction of dissolved organic nitrogen via spectroscopic fingerprint in the shallow riverbed sediments of effluent-dominated rivers: A case study in Xi’an, northwest China

An evaluation on the impacts of effluent discharge to receiving rivers is in demand. Discharged dissolved organic nitrogen (DON) with high eutrophication potentials tends to accumulate in the shallow riverbed sediments especially for effluent-dominated rivers. Since DON characterization requires for advanced analytical tools, there is thereby a need but it is still a challenge to evaluate their distribution and transformation in the riverbed sediments. Considering the fact that DON is an important part of dissolved organic matter (DOM), which has plentiful spectral information, the authors hypothesize if it is feasible to predict DON variations in riverbed sediments via the DOM properties in surface water or sediment porewater? Here, the spatiotemporal spectral characteristics of DOM in river water and sediment porewater of two effluent-dominated rivers were investigated. Compared to surface water, more abundant relationships among fluorephores and spectra-derived parameters in porewater were observed. The relatively high DON contents in both surface water (0.16–0.47 mg-N/L) and sediment porewater (0.35–5.02 mg-N/L) compared to those reported in other natural waters highlighted the importance in predicting DON in effluent-dominated rivers. The DON in the oxic zone from winter samples carried more humus-like signals, while the fractions in summer samples recognized protein-like and humus-like signals. Two machine learning methods, i.e., random forest (RF) and extreme gradient boosting (XGBoost) were employed to provide evidence-based information on how DON contents and properties differed at variable depths. RF (R2: 0.920, 0.475) outperformed XGBoost (R2: 0.488, 0.316) in predicting DON in winter-oxic zone and winter-suboxic zone. While XGboot (R2: 0.515, 0.787) is superior than RF (R2: 0.317, 0.567) in summer-oxic zone and summer-suboxic zone. Fluorophore of C1 served as the most important variable for predicting DON in winter samples in both models. SUVA260 and SUVA280 were verified most impressive predictor for samples from suboxic zone in summer in both models. HIX represented the most important variable predicting DON in summer samples in XGBoost model. These findings are critical for understanding the transformation processes of DON in the shallow riverbed sediments in receiving rivers, and could provide important implications to improve wastewater discharge management and river health.

Redox gradients drive microbial community assembly patterns and molecular ecological networks in the hyporheic zone of effluent-dominated rivers

The impacts of effluent discharge on receiving waterbodies have been a research hotspot. Nonetheless, limited information is available on the microbial community assembly patterns in the hyporheic zones (HZ) responding to the changes in the microenvironments, e.g., solute transport and redox gradient variations. Using two representative effluent-dominated rivers as model systems, the spatio-temporal bacterial community dynamics and assembly patterns in oxic and suboxic zones in the shallow riverbed sediments were disentangled via null model- and neutral model-based approaches. Bacterial dynamics in community composition were observed driven by environmental filtering, i.e., impacts of environmental variables, more than geographic distances, i.e., the depths of sediments. The communities in samples collected in summer were largely shaped by stochasticity, in which homogeneous selection occupied a higher proportion in oxic (∼39%) than in suboxic zone (∼23%). Deterministic processes contributed to a more complex community structure for samples from oxic zones, whereas weakened the interspecies interactions in suboxic zones. The richness and abundances of non-neutral community were confirmed governing the deterministic assembly in oxic zones. Key species ascribed to ‘connectors’ and ‘network hubs’ dominated the community assembly variations in samples collected in winter, and in oxic zones, respectively. Significant positive relationships between β-nearest taxon index and dissolved organic nitrogen (DON) and nitrate highlighted their vital roles in community assembly via deterministic selective pressures in oxic zones. The significance thresholds of nitrogen species for community transition in winter (ΔDON: 2.81 mg-N/L, ΔNO3−: 1.09 mg-N/L) were lower than in summer, probably implying that stricter effluent quality standards should be established in colder seasons. Combined, our work poses first insights on the roles of redox zonation in driving microbial community assembly in HZ, which is of significance in guiding ecological remediation processes in effluent-dominated rivers.

Assessing the threats of small lowland reservoirs under climate change on the example of Supraśl Water System (NE Poland)

The Supraśl River is a stable water ecosystem in North-Eastern Poland. This is indicated by the flow rate over many years, as well as the water quality monitored for years. Despite this, there are periods of oxygen deficiency in the water, causing massive fish kills. Our research shows that climate change resulting in an increase in the frequency of hydro-meteorological extremes may contribute to negative processes taking place in aquatic ecosystems. On the example of Supraśl Water System (SWS), we present an analysis of the phenomenon of suspension caused by the underground inflow, supplying the surface waters with a significant load of organic matter. The accelerated decomposition of peat formations in the Supraśl River catchment after heavy rains makes it easier for organic matter to penetrate into the aquatic ecosystem. Intensive flushing of valley and river bed sediments during summer floods has a particularly negative impact on the ecosystem of inland waters. If there are organic sediments on the bottom, their re-suspension is very dangerous. Then there is the immediate demand for oxygen, which can lead to deoxygenation of the water. Although this is a natural process, alarm and monitoring procedures should be established and countermeasures sought to respond in time and prevent mass fish kills.

Impact of shale gas wastewater discharge on the trace elements of the receiving river in the Sichuan Basin, China.

The potential contamination of shale gas wastewater generated from hydraulic fracturing to water resources is of growing concern, yet minimum attention has been paid to the impact of shale gas wastewater on the trace elements of the receiving waters. In this study, we analyzed the levels of 50 trace elements of a river that receives effluent from a shale gas wastewater treatment facility in the Sichuan Basin, China. Sixteen trace elements were detected in the surface water sample from the effluent discharge site, all of which were of higher concentrations than the upstream background level. Among the 16 shale gas wastewater-related elements, Sr, Ba, and Li were of elevated levels in the downstream water samples (24.9-44.2%, 5.0-8.0 times, and 17.8-22.8 times higher than the upstream background level, respectively). Shale gas wastewater effluent may be related to the accumulation of Sr, Ba, Li, and Cs in riverbed sediments near and/or downstream of the effluent discharge site and may lead to elevated pollution level of Sr and Li in downstream sediments. The ecological risk of the riverbed sediments was of medium to high level, with Cd contributing to the most risk, while shale gas wastewater-related elements are of low potential risk throughout the river. Our results suggested that shale gas wastewater effluent discharge had limited impacts on the trace elements of the receiving river within two years.

Traces of life in Río Tinto (Spain): Decoupling of morphological and geochemical biosignatures

The Río Tinto system located in southern Spain is a 100-km long acidic (pH ≈ 2.3) river rich in dissolved iron, sulfate and heavy metals. The red-tinted river, formed as a product of natural acid rock drainage that has been exacerbated over the years by anthropogenic mining activities, hosts a variety of extremophilic microorganisms that are potential analogues to those found on early Earth and ancient Mars. Here we detailed the investigation of potential biosignatures in the forms of microbialites and sediments deposited along the river. The 20-50 cm thick microbialites (estimated age at most 100 years) are composed of layered structures of Fe(III) minerals with alternating porosities. High resolution imaging and elemental mapping coupled to mineralogical analysis suggest the transformation of K-jarosite (KFe3(SO4)2(OH)6; Vm = 153 cm3/mol) to goethite ( α -FeOOH; Vm = 21 cm3/mol), generating porosities in the process due to a reduction in the molar volume Vm. Meanwhile, riverbed sediments are composed of mixtures of schwertmannite (Fe 8 O8(OH)6(SO4) · nH2O), jarosite, goethite and other minor minerals (ferrihydrite, lepidocrocite, hematite). Culture experiments indicate that crystalline jarosite is formed via transformation from poorly-crystalline schwertmannite (Fe 8 O8(OH)6(SO4) · nH2O), but that the presence of Acidithiobacillus thiooxidans actually inhibits this transformation, possibly due to organic matter stabilization of schwertmannite. Fe isotopic analyses show no clear variations between layers in the microbialites (δ56Fe = -0.85 ± 0.10 ‰), while the riverbed sediments indicate progressively more negative values downstream over a 5-km distance (δ56Fe = +0.4 to -0.8‰). The spatial isotopic pattern of the riverbed sediments is consistent with rapid microbial oxidation of Fe2+ and inconsistent with the much slower abiotic Fe2+ oxidation rate. Taken together, our results show that while the microbialites’ structure is suggestive of microbially-induced precipitation, its geochemical features are not. Meanwhile, the inconspicuous-looking riverbed sediments provide clear evidence of biogenicity from their isotopic compositions. This highlights the challenge in detecting life especially when decoupling of morphological and geochemical biosignatures is to be expected.

Investigations on microplastic infiltration within natural riverbed sediments

Several studies focused on the role of rivers as vectors of microplastics (MPs) towards the sea. It is well known that during their path through the fluvial environment, MPs interact with riverbed sediments; however, the main factors impacting the mobility of MPs within the upper part of the hyporheic zone are not clear yet. The present work investigates the role of different sediment size layers in affecting the mobility of the most common MP (Polyethylene terephthalate - PET - spheres, PET 3D-ellipsoids, polystyrene - PS - fragments and polyamide - PA - fibers) within sediment porous media under different hydraulic loads (HL) and time scales (t) conditions. Results indicated the relationship between the characteristic MP diameter and that of the grains as the main parameter for the MP infiltration into the sediment layer. The maximum infiltration depth was found to not depend on HL and t. However, HL was able to influence the percentage of MPs penetrating the superficial layer and their distribution within the first 10–15 cm of the sediment layer. None of the MPs were found at depths >20–25 cm, where only PET spheres were detected. Starting from the suffusion theory, a model able to predict the MP maximum infiltration depth in the range of parameter values was provided.The outcome indicates the importance of considering geometrical and hydrodynamic aspects of the riverbed sediment layer to better characterize the spatial and temporal scales of MP transport in freshwater environments.

From Desiccation to Re‐Integration of the Yellow River Since the Last Glaciation

AbstractThe desiccation (extreme drying) of rivers has important implications for the broader Earth System. However, the desiccation history and its linkage to climate are rarely known for numerous major river systems, primarily due to difficulties in recognizing desiccation events from available stratigraphic records. Here, using a combination of geochemical techniques (major and rare‐earth element geochemistry, detrital zircon geochronology, and optically stimulated luminescence dating), we demonstrate that the Yellow River, which maintains the highest sediment load on Earth, became desiccated during the Last Glacial Maximum at approximately 20 thousand years ago. This finding implies that transportation of sediments and dissolved constituents to the oceans via the Yellow River may have decreased substantially or ceased during glacials, which would have ramifications for ocean chemistry and biology. Furthermore, our work highlights the importance of desiccated riverbed sediments as potential dust sources during glacial periods, a finding that is different from what is observed today.

Parameters of the gross composition of propolis from Brazilian Meliponini

Propolis is a resinous and complex bee product containing resin derived from plants, beeswax, pollen and other minor constituents. The present study aimed to determine the parameters of the gross composition of propolis collected by nine stingless bee species from eight different Brazilian localities. The moisture content varied depending on the bee species and localities. Wax content enables us to distinguish between samples of Melipona and Scaptotrigona, samples of the former containing considerably less wax than samples of the latter genus. The ash content has an inverse trend, with samples of Melipona and Scaptotrigona having high and low ash content, respectively. The results indicated that Melipona species produce geopropolis (propolis containing aggregated soil material), while Scaptotrigona produces propolis devoid of soil, with the exception of S. tubiba. Most Melipona species collected sediments with high clay content. The size and color of ash crystals varied, mostly according to the locality of the meliponaries, although differences were observed between samples of the same species, growing in the same meliponary. Mineralogical analysis was relevant to determine that M. flavolineata from North Brazil aggregates river-bed soil sediments to the geopropolis.

Response of redox zoning and microbial community structure in riverbed sediments to the riverbed scouring during bank filtration

Riverbed sediments are an important zone and interface for the interaction of surface water and groundwater; hence, biochemical processes in the riverbed sediments are critical to maintain the ecology of the system and water quality. Riverbed sediment scouring can substantially alter the hydrodynamic conditions of river water infiltration and redox conditions at the surface–groundwater interface, which in turn affects the biochemical processes. Currently, in-depth understanding of the distribution characteristics of the microbial community structure in riverbed sediments, especially their response to riverbed scouring, is lacking. This study revealed the temporal and spatial changes in redox indicators in the Liaohe riverbed sediment and discussed the response of the microbial community to the influence of riverbed scouring. The results showed that during the investigation period (September to November 2020), the riverbed sediments in the river reach were generally in a state of scouring in the low water stage, and the scour depth was 4–9 cm. The redox zone in the nearshore area moved up by 5.5–23 cm, and moved down by 0.1–10 cm in the intermediate transition area and the center of riverbed, and the maximum overlapping depth of the redox zone could reach 50 cm. The relative abundance of dominant bacteria species had a good correlation with the intensity of geochemical reactions, decreasing in low-water levels close to the center of the riverbed, which further indicated the weakening of the reduction rate. Influenced by riverbed scouring, the species of denitrifying bacteria in the surface layer increased, multiple dominant bacteria of iron, manganese and sulfate often coexist in deep riverbed sediments, and were slightly different in the low water level. The results provide a better understanding of the chemical composition of the pore water in the riverbed sediments, which are of great significance for maintaining the ecological safety of river water.