Riverine Sediments Research Articles

Behaviour of barium in the tropical estuaries: Implications to its marine budgets and paleo-oceanographic applications

Marine Barium (Ba) is extensively used as a tracer for biogeochemical processes and paleo-oceanographic proxy for past river discharge, salinity, and long-term hydrological changes. However, poor constrain on the riverine Ba flux to oceans due to its modification in the estuary hinder such applications. The prerequisite for an accurate Ba flux estimate is to have a detailed understanding of Ba behaviour, extent of modifications in the estuary, and net input to the ocean. A comprehensive study of Ba was conducted in four Indian estuaries draining through diverse geological/tectonic settings under different climatic regimes, such as the Narmada, Tapi, and the Mandovi falling into the Arabian Sea and the Hooghly (a distributary of the Ganga) into the Bay of Bengal. Dissolved Ba distributions in the surface waters of these estuaries exhibit nonconservative behaviour along the salinity gradient, exhibiting a systematic gain of Ba at low (∼2.5–7) salinity in the Hooghly and mid-salinity (∼8–18) in the estuaries linked to the Arabian Sea. The Ba gain is attributed to its release from the particulates and contributions via submarine groundwater discharge (SGD). The Ba gain in the Narmada and the Hooghly estuary was higher during nonmonsoon despite lower riverine sediment supply and SGD compared to monsoon, suggesting that tidally induced resuspension of estuary sediments and solute-particulate interactions that release Ba through the ion exchange process are the primary driver in determining surface water Ba distributions in these estuaries. The estimate of excess Ba supply in these estuaries is much higher than its riverine supply, ∼4 times higher in the Hooghly to ∼30 times in the Narmada estuary. The estimate of excess Ba supply from the global estuaries ∼4.5 Gmol yr−1 is comparable to global riverine supply∼5.5 G mol yr−1, highlighting its significant role in global marine budgets. Mass balance calculation of Ba suggests that SGD and particulate release contribute an average of ∼17% and ∼ 32% of the total dissolved Ba in the Hooghly estuary, whereas ∼10% and ∼ 76% in the Narmada estuary respectively. The Ba/Ca ratio shows inverse relation with salinity and is compatible with the exponential fits. Extrapolation of the Ba/Ca-salinity relation to open ocean Ba/Ca ratio yields salinity of ∼35 in the Hooghly, close to the average open ocean salinity within ∼10% uncertainty, whereas it yields salinity ∼41 in the Narmada (pre-monsoon), which translates to large uncertainty (∼20%) due to huge release of particulate Ba. This uncertainty could further amplify in longer time scales (e.g. glacial-interglacials) due to sea level and climate changes and its impact on estuarine process. Therefore, regional calibrations in conjunction with other constraining proxies are the way forward to employ Ba/Ca ratio as a paleo-oceanographic proxy in coastal oceans.

Subfossil oaks from riverine sediments of the Seda River in Latvia: The first results of dendrochronological and radiocarbon analysis

The article presents a dendrochronological investigation of subfossil oaks from the riverine sediments of the Seda River in the Lake Burtnieki Undulating Plain, northern Latvia. Thirty-nine oak trunks were investigated for our study. Cross-dating of samples resulted in six floating chronologies spanning 141–636 years. The longest chronology was absolutely dated to AD 652–1287 against regional oak chronologies from Lithuania, Latvia, Belarus and central European Russia. 14C dating revealed that oaks grew on the site from the last century of the third millennium cal BC to the first half of the second millennium cal AD. We assessed the depositional anomalies from two best-replicated chronologies. The germination of oaks occurred during climate warming, and dying-off phases were triggered by climate cooling and increased precipitation throughout Europe. Our results give new insights into the forest history in northern Latvia and provide a potential to construct absolute-dated millennial oak chronologies in the Baltic countries.

Effects of human-induced riverine sediment transfer on deposition–erosion in the South Passage of the Changjiang (Yangtze) delta

Deltaic channels, as the essential part in system of river deltas where river and ocean connect, are influenced profoundly on its deposition and erosion processes, by changes of riverine sediment due to human activities from catchment to mouth of large rivers and sea-level rise worldwide. Here, based on a series of hydrological, sedimentary and morphological records in the main outer channel South Passage (SP) of the river-tide dominant Changjiang (Yangtze) Delta (CJD) for more than half a century, regional deposition–erosion process and the implication mechanism were examined. The results showed that fluvial sediment supply declined by over 70% stepwise during the past decades and local suspended sediment concentration in the SP reduced by half within recent years. Correspondingly, three distinct stages of morphodynamic process came out one after another, which were phases of rapid deposition (1959–1979), moderate deposition (1979–1997) and dramatic erosion (1997–2021), respectively. Channel and shoal had asynchronous performance during this deposition–erosion transition, especially after 1979, when channel entered a rapid erosion period earlier after a stable volume period, while shoal suffered slow erosion after high-speed deposition. Moreover, the current erosion phase was furtherly explained as two main modes by the Empirical Orthogonal Function analysis, accounting for 61% and 14%, respectively. The dominant mode describes the continuous scouring in channel contributed by transfer in riverine sediment regime, consisting of the reducing upstream sediment, local increasing flow diversion, dredging activities and sea-level rise. The second mode suggests decadal shift from deposition to slight erosion of shoal zones, which was also adjusted to episodic events and local engineering projects like shoal embankment and reclamation. It’s predictable that the SP would constantly suffer long-term erosion under riverine sediment reduction, sea-level rise and artificial waterway regulation, together with aggradation of the fringing shoals by reclamation. This highlights channels in the river deltas are faced with the erosion risk caused by anthropogenic activities, which calls for compelling attention.

Call for joint international actions to improve scientific understanding and address soil erosion and riverine sediment issues in mountainous regions

During the International Workshop on Soil Erosion and Riverine Sediment in Mountainous Regions held in November 2022, scientists from many countries shared their state-of-the-art knowledge and brainstormed to improve scientific understanding for coping with climate change and anthropogenic impacts. Information summarized in this discussion includes proposed key scientific questions and suggested joint actions to reduce soil erosion and riverine sediment problems in mountainous regions.

Surrogate Method for Suspended Sediment Concentration Monitoring on the Alluvial Reach of the River Danube (Baja, Hungary)

Sediment balance is essential for understanding changes in river morphology and ecosystems and related services depending on them. However, the currently used methods to quantify riverine sediment processes are not adequate enough. We have examined the sediment regime of the Danube River, particularly the suspended sediment yield. This parameter can be calculated based on stage or discharge using a suspended sediment yield rating curve; however, the uncertainty of this method can reach even 150%. The suspended sediment yield of a section does not only depend on processes that take place in the riverbed; thus, it cannot be described by only one easily measurable parameter. An integrated surrogate method based on turbidity registration is tested in order to determine suspended sediment yield on the lower Hungarian (sand-bed alluvial) reach of the Danube River. The near-bank turbidity is converted into suspended sediment concentration and then into suspended sediment yield. The turbidity is measured with a built-in turbidity probe, while the suspended sediment yield is determined with traditional methods (discharge measurement, suspended sediment sampling, laboratory processing, and calculation). The traditional and integrated surrogate methods are compared based on the results of the measurements, and different aspect correlations are established between flow parameters, turbidity, and suspended load. The results achieved with the integrated method are promising, but more measurements are required in order to refine the relationships in a broader interval.

Morphological change and its response to human activities in the estuary of Minjiang River, China, since last early century

AbstractThe evolution of subaqueous deltas in mountain rivers is highly sensitive to variations in sediment load and hydrodynamic conditions, and human activities can rapidly alter these parameters. To better understand the evolution of the subaqueous Minjiang River Delta (MRD) under human activities, we investigated the effects of construction of reservoirs, channel training walls, land reclamation activities, and sand mining from 1910 to 2010. Analysis of bathymetric and fluvial discharge data revealed that the MRD shoals generally experienced slight development during the study period, but with alternating stages of erosion and deposition that were related closely to sediment discharge and the role of human activities. The northern MRD was more strongly affected by decreasing sediment load, while the southern MRD was more influenced by land reclamation. Human activities in the MRD can be divided into five stages: Weak (before 1935), blockage (1935–1950), slight strong (1950–1970), strong (1970–2000), and stable (since 2000). Correspondingly, the geomorphic evolution of the MRD can also be divided into five stages: Natural evolution, channel blockage, southern channel erosion, divergence, and degradation. Furthermore, the morphodynamic response time of MRD to a decrease in riverine sediment was found to be less than 10 years, which is much faster than the morphodynamic changes observed in large‐scale estuaries and deltas. These results provide further insight into interpreting morphodynamic changes in typical small/medium‐sized estuaries and deltas under various human activities.

Sediment Heavy Metal Pollution Assessment in Changwang and Wuyuan Rivers in Hainan Island, China

Heavy metal pollution may pose a significant threat to aquatic ecosystems. To assess heavy metal pollution, sediment samples were collected from Changwang and Wuyuan Rivers between June and December 2019. An inductively coupled plasma mass spectrometer was used to analyze the concentrations of As, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn. The results revealed that Changwang River had significantly high concentrations of Cr (240.70 mg kg−1), Co (36.02 mg kg−1), Ni (108.70 mg kg−1), and Cu (36.61 mg kg−1), whereas As (7.55 mg kg−1) was elevated in Wuyuan River. In addition, Cd, As, Pb and Zn concentrations were below China’s sediment quality standard limits (GB 3838-2002), but the Cr level exceeded the limit. However, Cr and Ni exceeded the probable effect concentrations (PEC) and thus may cause toxic effects. The contamination factor, geo-accumulation index, and modified degree of contamination revealed that Changwang experienced considerable to very high heavy metal pollution, while Wuyuan had low to moderate pollution. The pollution load index demonstrated that the rivers were polluted during all seasons. Additionally, the risk index showed considerable and moderate risks in Changwang and Wuyuan, respectively. The metal ecological risk was ranked as Cd > Ni > As > Co > Cu > Cr > Mn > Pb > Zn. Multivariate analyses categorized heavy metals into two groups based on their potential sources: group one included Cr, Co, Ni, Cu, Mn, and Zn, while group two contained As, Cd, and Pb. The study provides valuable data on heavy metal pollution, which needs improvement for the studied rivers. The data can be used to assess pollution risks and manage riverine sediment quality.

Depositional history of the subaqueous delta off the southeastern coast of Korea during the post-glacial period

The distal mud deposit (DMD) of the Korea Strait Shelf, located along the southeastern coast of Korea and detached from the main sediment source, the mouth of the Nakdong River, is considered a subaqueous delta system. The complex spatiotemporal changes in the stratigraphic architecture of the DMD were reconstructed, based on combined seismic and sediment core data, according to the three stages of post-glacial sea-level rise. During the early transgressive stage (from ca. 19 to 10.9 ka), transgression occurred at a relatively deeper northern outer shelf of the DMD, where Unit A began to be deposited in an aggradational stratal stacking pattern. During the late transgressive stage (ca. 10.9 to 8 ka), further sea-level rise provided sufficient accommodation for DMD, but an insufficient sediment supply from the Nakdong River might have prevented sedimentation. At the highstand stage (ca. 8 ka to the present), the increased supply of suspended sediments from the Nakdong River coupled with the entrance of the Tsushima Warm Current through the Korea Strait may have enabled the along-shore lobate progradation of Unit B on the flat and wide southern shelf. After appoximately 2 ka, as Unit B proceeded into the narrow, steep northern shelf, it started to prograde in a shore-normal direction, controlled by a rapid downslope decrease in near-bed shear stress. Over the last 700 years, sediments have been actively deposited at the depocenter of the DMD by frequent storm surges during the summer season. The reconstructed depositional history of the DMD demonstrates the importance of the pre-existing shelf morphology, along-shore currents, and storm surges in offshore sediment transport for a subaqueous delta in a microtidal shelf with a relatively small riverine sediment load.

Three gorges dam shifts estuarine heavy metal risk through suspended sediment gradation

Damming alters downstream sediment supply relationships and erosion in the estuarine delta. Given that sediment grainsize serves as a key parameter for the ability to adsorb heavy metals from water, the assessment of estuarine heavy metal risk needs to get connected initially. Hence, fine suspended sediment (<63 μm) in the Yangtze River estuary (YRE) was divided into four grainsize fractions to simulate the surface suspended sediment concentration (SSC) and grainsize composition before and after the completion of the Three Gorges Dam (TGD). Representative months were selected for flood peak reduction (October) and runoff compensation in the dry season (March) to maximize the scheduling impact of the TGD on runoff and riverine sediment input to the YRE. An improved Water Quality Index (WQI) approach was proposed to assess the combined risk alteration of five heavy metals in six estuarine sensitive targets due to TGD-induced sediment characteristics. The results demonstrated that TGD significantly but tardily reduced the SSC and the proportion of fine sediment in the YRE, decreasing the risk of heavy metals resuspension. Seasonally, the total SSC became higher in the flood season than in the dry season during post-TGD period. However, the fine SSC in the flood season was averaged only 59.7% of that in the dry season due to the pronounced grainsize coarsening effect. As the significant reduction in fine SSC overcomes the increase in heavy metal content per unit of SS, the integrated resuspension risk declined significantly, particularly for Pb and Cr. Spatially, the risk reduction for sensitive targets near the turbidity maximum zone (TMZ) is 8.4 times greater than for inner river channel. However, undiminished anthropogenic metal inputs to the YRE signified greater pressures on the depositional environment.

Spatial distribution, eco-environmental risks, and source characterization of heavy metals using compositional data analysis in riverine sediments of a Himalayan river, Northern Pakistan

Spatial distribution, eco-environmental risks, and source characterization of heavy metals using compositional data analysis in riverine sediments of a Himalayan river, Northern Pakistan

Downdrift Port Siltation Adjacent to a River Mouth: Effects of Mesotidal Conditions and Typhoon

The Zhuoshui River has one of the highest sediment yields in the world. The riverine sediment may have been transported away from the river mouth by strong tidal currents and deposited in a navigational channel and a harbor basin south of the Zhuoshui River. This study describes the dispersal of riverine sediments in mesotidal conditions, including transport processes of sediments via river plumes, initial deposition, resuspension, and long-term net accumulation. Our results revealed that the distribution of suspended sediment concentration (SSC) and the transport process of the river plume was markedly modulated by tidal currents in a north–south direction. Under high-discharge conditions, energetic winds and ocean currents interrupted the offshore propagation of the sediment-laden river plume with a high SSC to the ocean. The plume, induced by typhoon floods, was either propagated northward due to the Coriolis effect or was deposited near the river mouth. The sediments deposited within the inner shelf were resuspended by intensive tidal currents and transported through southward residual circulations to the navigation channel south of the river mouth.

Sediment-water partitioning and risk assessment of organochlorine pesticides along the urban, peri-urban and rural transects of Krishna River Basin, Peninsular India

Organochlorine pesticides (OCPs) were widely used in the past for pest control in agricultural lands and vector control programs in India. Due to their persistence and toxic impacts, we have quantified twenty OCPs in surface water, groundwater, and surface sediment samples along the Krishna River Basin (KRB), flowing through Peninsular India. Samples were collected along the urban, peri-urban, and rural transects of the KRB to understand the relation between the occurrence of pesticidal organochlorine pollutants based on the land use and land cover (LULC) and asses potential risk. Diagnostic ratios revealed ongoing Lindane usage in rural and peri-urban transects. On the contrary, the urban transect of the Musi River (MR) showed fresh inputs of technical HCH. The ratios of (p,p'-DDE+ p,p'-DDD)/ΣDDT >0.5 and α/β-Endosulfan < 2.33 for most of the sites across the three transects for surface water, groundwater, and sediment indicate past DDT and Endosulfan usage across KRB. Excluding p,p'-DDE, and heptachlor in most of the sites, the logKOC' was higher than logKOC for other OCPs in the urban transect. However, for all the OCPs, the logKOC' was lower than logKOC in the peri-urban and rural transects of KRB thereby indicating that riverine sediment is acting as a sink for OCPs. The Krishna River annually transport about 0.24 tons HCH, 0.11 tons of DDT and 0.1 tons of Endosulfan. Despite having low water discharge, the compound-specific fluxes of the Wyra river are higher than the other two tributaries. Ecotoxicological risk assessment based on the Hazard Quotient suggested DDT pose higher risks to scud (zooplankton) and dinoflagellate and diatom (phytoplankton) whereas Endosulfan poses a threat to Bluegill (fish).

Tracing the dominant sources of sediment flowing towards Lake Victoria using geochemical tracers and a Bayesian mixing model

PurposeLake Victoria has been increasingly silting over the past decades, impacting water quality and loss of biodiversity. Sediment control strategies require information on the relative and absolute contributions of sediment from different sources. However, to date, there is no continuous monitoring of sediment flux or water quality in any of the tributaries, prohibiting an assessment of the scale of the problem. The aim of this study was to trace the dominant sources of riverine sediment using geochemical fingerprinting, thereby generating a knowledge base for improving land management and reducing sediment yields in Simiyu River catchment, one of the main contributing rivers to Lake Victoria.Materials and methodsGeochemical tracer concentrations were analyzed in transported sediment from the main river and two tributaries (riverbed sediments) and from soils in five dominant land use types (agricultural land, bush land, forest land, channel banks, and main river banks). Dominant sources to the Simiyu main river sediment were attributed using the Bayesian MixSIAR model.Results and discussionThe mixing model outputs showed that the Simiyu tributary was the dominant source of sediment to the Simiyu main river with 63.2%, while the Duma tributary accounted for 36.8%. Cultivated land was shown to be the main land use source of riverine sediment, accounting for 80.0% and 86.4% in Simiyu and Duma sub-tributaries, respectively, followed by channel banks with 9.0% in both sub-tributaries. Direct unmixing of the Simiyu main river sediment to the land use sources yielded 64.7% contribution of cultivated land and 26.5% of channel banks.ConclusionThe demonstrated application of sediment source tracing provides an important pathway for quantifying the dominant sources of sediment in the rivers flowing towards Lake Victoria. Eroded soil from agricultural areas is the biggest contributor to transported sediment in the Simiyu River. This information is vital for the design of catchment wide management plans that should focus on reducing soil erosion and sediment delivery from farming areas to the river networks, ultimately supporting both food security and water quality in the Lake Victoria Basin.

Experimental Analysis of 3D Flow Structures around a Floating Dike

Floating dikes have several advantages over spur dikes including less influence on riverine sediment transport, bed topography, and ecosystems, and a good adaptability to fluvial conditions. Despite these advantages, floating dikes have not been used in many river regulation schemes due to the limited understanding of the 3D flow structures around floating dikes. In this study, a series of experiments were conducted to investigate the 3D flow structures around floating dikes. Results show that, after installing a floating dike on one side of a flume, the surface water flow is deflected to the opposite side of the flume, and a backflow develops around the outer and downstream side of the dike, where both the vertical turbulent intensity and the absolute magnitude of the Reynolds stress are relatively large. Due to the blocking effect of the dike, the cross-sectional area decreases, causing an increase in velocities below and alongside the dike, as well as a decrease in velocities upstream of the dike. Increasing the submerged depth or length of the dike results in an increase in flow velocity adjacent to the dike, as well as an increase in the vertical or lateral scale of the backflow. On the contrary, increasing the dike thickness leads to a weakening or disappearance of the backflow, along with a decrease in the acceleration rate of flow adjacent to the dike.

Post-glacial RSL changes and the demise of a local remnant Laurentide Ice-Sheet ice cap: A view from Anticosti island beach-ridges (Gulf of St Lawrence, Canada)

Widely spread worldwide, beach-ridge systems are established along prograding coastlines, either fostered by a falling Relative Sea-Level (RSL), by substantial sediment stocks being provided to the coastline, or by the combination of both agents. As such, they can form valuable archives of either large scale RSL and isostatic dynamics and/or of more local coastal processes, e.g. related to variations in riverine sediment supply. In this study, we analyze three raised beach-ridge complexes located on the island of Anticosti (Gulf of St.-Lawrence, Québec, Canada). Using both field and LiDAR DEM data, we produce new RSL histories for the north-eastern and north-western sectors of Anticosti Island region over the ca. 14.400 to 8.300 yrs cal. B.P. period. These new sea-level data allow to considerably refine the postglacial RSL history of the region, hence carrying large implications for the comprehension of the isostatic dynamics of the St-Lawrence region. Considerable misfits between our observations and outputs of the GIA models notably allow to propose refinements on the LIS architecture and melting history as well as on the rheological characteristics of the St-Lawrence valley. Locally, chronologies of progradation of the beach-ridges were mostly forced by RSL changes, yet also apparently recorded the demise of the local Anticosti remnant ice-cap throughout the changes in sediment supply the melting of the latter produced locally. Finally, some results of paleo-oceanographic significance could also be derived from the study of the beach-ridges, pertaining for instance to changes in sea-ice cover.

Modulation of sediment load recovery downstream of Three Gorges Dam in the Yangtze River

The sediment load in the Yangtze River downstream of the Three Gorges Dam (TGD) has substantially declined in recent decades. The decrease is more profound below the TGD, e.g., a 97% decrease at Yichang, compared with that at the delta apex, 1200 km downstream, e.g., a 75% decrease, implying along-river sediment recovery. Two large river-connected lakes, i.e., Dongting and Poyang Lakes, may play a role in the re-establishment of the river’s morphodynamic equilibrium, but a quantitative data-based understanding of this interaction is not yet available. In this work, we collected a series of field data to quantify the sediment gain and loss in the river-lake system in the middle-lower Yangtze River, and evaluate the lake’s response to the reduction in riverine sediment supply. We find that Dongting Lake and Poyang Lake shifted from net sedimentation to erosion in 2006 and 2000, and back to a sedimentation regime again after 2017 and 2018, respectively. Natural morphodynamic adaptation and sand mining play an important role in the regime changes in the Dongting Lake whereas sand mining dominates the abrupt changes in the Poyang Lake. The Dongting and Poyang Lake contributed maximum by 38% (2015) and 17% (2006) (respectively) to the sediment recovery in the erosion regime, whereas the riverbed erosion dominates the main sediment source. These changes in the relative contribution of sediment sources also indicates a response time of ~ 20 years in the lakes towards a new equilibrium state. It is noteworthy that the lakes’ buffer effects may be overestimated as the supplied sediment from the lakes is rather small compared to the significant dam trapping in the upstream basin and sediment source from downstream degradation. The results imply that river management and restoration should take into account of the river-lake interactions and feedback impact at decadal time scales.

A morphological guide of neotropical freshwater sponge spicules for paleolimnological studies

Freshwater sponges (Porifera: Spongillida) are sessile invertebrates with skeletons composed of siliceous elements termed spicules. Sponge spicules (megascleres, microscleres, and gemmuloscleres) are characterized by widely varying sizes and shapes. These spicules are well-preserved in lacustrine, wetland, and riverine sediments and hold significant ecological and limnological information that can be applied as diagnostic tools in reconstructions of Quaternary environments. However, problems with taxonomy and the absence of systematic guidelines and standards of identification represent major challenges to utilizing freshwater sponges as a paleo-proxy. Here, we present a well-illustrated extraction protocol and morphological guide to the Neotropical freshwater sponge fauna. This guide is intended to introduce researchers and students to the study of freshwater sponges and their use as a diagnostic tool in paleoecology and paleolimnology.

On the occurrence of low concentration hyperpycnal river plumes in a small mountainous river-canyon system

This study aimed to understand the mechanisms controlling the formation of hyperpycnal river plumes in small mountainous rivers. The suspended sediment concentration (SSC) and grain size distribution in the Gaoping River were obtained by field observations and used as the basis for numerical simulations. The SSC of the Gaoping River during Typhoon Soudelor was lower than 20 g/L according to the real-time SSC estimated using the calibration curve between turbidity and SSC. The calculated median grain size of the suspended sediments was 15.15 μm, which indicated that the silt accounted for a large proportion of the flow. The observed grain-size distribution and SSC were incorporated into a numerical model to examine the conditions under which hyperpycnal river plumes occur. The model results revealed a three-dimensional process near the river mouth: cross-canyon currents converge near the head of the canyon, and the topography of the submarine canyon further confines the path and width of the hyperpycnal river plume. The descending plume continues to move through the steep slope of the submarine canyon. In addition, the simulation results showed that the SSC of the hyperpycnal river plumes increases as the grain size of riverine sediment decreases. However, if the sediment grain size is smaller than 8 μm, most of the suspended sediment remains on the sea surface in a surface plume.

Source-oriented risks apportionment of toxic metals in river sediments of Bangladesh: a national wide application of PMF model and pollution indices.

Intense human activities, particularly industrial and agricultural output, has enriched metal(loid)s in riverine sediment and endangered aquatic ecosystems and human health. Promoting proper river management requires an assessment of the possible ecological hazards and pollution posed by metal(loid)s in sediments. However, there are limited large-scale risk assessments of metal(loid)s contamination in riverine sediment in heavily populated nations like Bangladesh. This study compiled data on sediment metal(loid)s, for example, Cd, As, Cu, Ni, Cr, Pb, Mn, and Zn, from 24 major rivers located across Bangladesh between 2011 and 2022 and applied positive matrix factorization (PMF) to identify the critical metal(loid)s sources and PMF model-based ecological risks. Based on studied metal(loid)s, 12-78% of rivers posed higher contents than the upper continental crust and 8% of the river sediments for Cr and Ni, whereas 4% for Cd and As exceeded probable effect concentration. Cr and Ni in the sum of toxic units (STU), whereas Mn, As and Cd in potential ecological risk (PER) posed the highest contribution to contaminate sediments. In the studied rivers, sediment contaminant Mn derived from natural sources; Zn and Ni originated from mixed sources; Cr and Cu were released from the tannery and industrial emissions and Cd originated from agricultural practices. Source-based PER and NIRI indicated that mixed source (4% rivers) and tannery and industrial emission (4% rivers) posed very high risks in sediments. For the creation of macroscale policies and the restoration of contaminated rivers, our national-scale comprehensive study offers helpful references.

Impact of microplastics on lead-contaminated riverine sediments: Based on the enzyme activities, DOM fractions, and bacterial community structure

Microplastics (MPs) are able to interact with diverse contaminants in sediments. However, the impacts of MPs on sediment properties and bacterial community structure in heavy metal-contaminated sediments remain unclear. In this study, we investigated the adsorption of Pb(II) by sediment-MPs mixtures and the effects of different concentration MPs on sediment enzyme activities, DOM fractions, and Pb bioavailability in riverine sediments, and further explored the response of sediment microbial community to Pb in the presence of MPs. The results indicated that the addition of MPs significantly decreased the adsorption amount of Pb(II) by sediments, especially decreased by 12.6% at 10% MPs treatment. Besides, the changes in enzyme activities, DOM fractions exhibited dose-dependent effects of MPs. The higher level of MPs (5% and 10%) tends to transform Pb into more bioavailable fractions in sediments. Also, MPs amendment was observed to alter sediment bacterial community structures, and community differences were evident in the uncontaminated and lead-contaminated sediments. Therein, significant increase of Bacteroidota, Proteobacteria and decrease of Firmicutes abundance in Pb-contaminated sediment at the phylum level were observed. These findings are expected to provide comprehensive information for assessing the combined ecological risks of heavy metals and MPs in riverine sediments.