Sediment Dynamics Research Articles

Mercury cycling in contaminated coastal environments: modeling the benthic-pelagic coupling and microbial resistance in the Venice Lagoon

Anthropogenic activities have been releasing mercury for centuries, and despite global efforts to control emissions, concentrations in environmental media remain high. Coastal sediments can be a long-term repository for mercury, but also a secondary source, and competing processes in marine ecosystems can lead to the conversion of mercury into the toxic and bioaccumulative species methylmercury, which threatens ecosystem and human health. We investigate the fate and transport of three mercury species in a coastal lagoon affected by historical pollution using a novel high-resolution finite element model that integrates mercury biogeochemistry, sediment dynamics and hydrodynamics. The model resolves mercury dynamics in the seawater and the seabed taking into account partitioning, transport driven by water and sediment, and photochemical and microbial transformations. We simulated three years (early 2000s, 2019, and 2020) to assess the spatio-temporal distribution of mercury species concentrations and performed a sensitivity analysis to account for uncertainties. The modeled mercury species concentrations show high temporal and spatial variability, with water concentrations in some areas of the lagoon exceeding those of the open Mediterranean Sea by two orders of magnitude, consistent with available observations from the early 2000s. The results support conclusions about the importance of different processes in shaping the environmental gradients of mercury species. Due to the past accumulation of mercury in the lagoon sediments, inorganic mercury in the water is closely related to the resuspension of contaminated sediments, which is significantly reduced by the presence of benthic vegetation. The gradients of methylmercury depend on the combination of several factors, of which sediment resuspension and mercury methylation are the most relevant. The results add insights into mercury dynamics at coastal sites characterized by a combination of past pollution (i.e. sediment enrichment) and erosive processes, and suggest possible nature-based mitigation strategies such as the preservation of the integrity of benthic vegetation and morphology.

Multi-method geochronological approach to reconstruct post-1800 floodplain sedimentation in the upper Rhine plain, France

The precise dating of sedimentary archives covering the last 200 years in floodplains massively impacted by human activities is a major challenge. A combination of geochronological approaches is necessary to accurately date post-1800 sedimentary deposits. Here, we use a combination of a wide range of methods to unravel floodplain sedimentary dynamics, through the example of the Upper Rhine which is a highly regulated river. This comprises short--lived radionuclides (137Cs, 210Pbxs) and Infrared Stimulated Luminescence (IRSL) single-grain dating. Luminescence profiling methods (IRSL screening, portable luminescence reader) were also used to further characterise sedimentation dynamics. These were combined with a hydrogeomorphological approach based on historical planimetric and hydrological data, the knowledge of engineering works as well as the morpho-sedimentary adjustments they induced. Our study demonstrates the value of historic maps as well as historical hydrological data, which provide precise time markers for dating the sedimentary archive under study. We illustrate different assumptions, validity domains and limitations inherent to each method, especially the complexity of 137Cs to date floodplain sediments and the potential of luminescence methods for dating and estimating sedimentation continuity. We finally show the advantage of combining geochronological approaches in the construction of robust age models for young floodplain sedimentary archives in highly anthropized fluvial environments.

Functional connectivity related to road linear erosion at rainfall event scale in an agricultural watershed on the Loess Plateau

Intersections of road and channel networks assist in better understanding of runoff and sediment transportation process feedback using the hydrological connectivity concept. However, quantifying functional connectivity and exploring the complex relationship between hydrological connectivity and the processes of runoff and sediment associated with road networks have largely been unexamined by field work. Therefore, our team conducted a 3-year monitoring of hydrological connectivity and road erosion from selected road segments in an agricultural watershed on the Loess Plateau. Rainfall events occurring during 2020–2022 were categorized into three types using K-means clustering analysis: small amounts of low-intensity rainfall (SL-R), large amounts of low-intensity rainfall (LL-R), and large amounts of high-intensity rainfall (LH-R). The monitored roads primarily consist of paved roads and unpaved roads (agricultural roads, abandoned roads, and petroleum roads). In our study, the intersections extracted by the road and channel networks were defined as hydrological connections, and sticks wrapped with clean gauze at the hydrological connections were monitored under variable rainfall conditions for functional connectivity assessment. The runoff heights and sediment traces attached to the sticks are alternative hydrological connectivity indicators. The results revealed an obvious increasing trend in the activation frequency and degree of hydrological connectivity as rainfall types transitioned from SL-R to LL-R and LH-R. Agricultural roads had a more intense response to hydrological connectivity between upslope drainage areas and road surfaces, and petroleum roads performed well in response to hydrological connectivity between road surfaces and down hillslopes. Random forest models indicate that PI30 is the most dominant influencing factor of road erosion and hydrological connectivity between road upslope drainage areas and road surfaces. Road surface erosion rates are the primary determinants of hydrological connectivity between road surfaces and down hillslopes. These findings suggest a close interaction between road erosion and hydrological connectivity driven by these off-site effects. They offer additional evidence concerning runoff and sediment patterns and dynamics in relation to road networks and identify hydrological connectivity and road erosion hotspots. Coordinating measures for hydrological connectivity regulation and road erosion mitigation are essential for minimizing hydrological connectivity and road erosion off-site effects within watersheds.

Integrated methodology for gas content assessment and prediction in shallow muddy lake sediments: acoustic mapping and correlation analysis

This paper provides a step-by-step description of integrated methodology for quantification and prediction of gas (methane, CH4) content dynamics in shallow aquatic sediments under changing spatial and temporal conditions. Presence of gas bubbles even in small concentrations significantly affects sediment compressibility, which in turn decreases sound speed in sediment. Our integrated methodology consists of two basic steps. In the first step, free gas content is evaluated by acoustic applications based on the sound speed inferred from the reflection coefficient from gassy bottom. The experimental bottom reflections are registered and compared to the simulated ones, using a geoacoustic inversion technique. The best match between the model and the experiment provides sediment sound speed estimate, which is converted into free gas content using a basic relation. In the second step, a multivariate linear regression is fitted for gas content and closed form expression of gas content dependence on the following predictors, which change spatially and temporally over the aquatic ecosystem, is obtained: 1) water depth, 2) short-leaving CH4 production rate peaks fueled by punctuated organic matter deposition; and 3) CH4 bubble dissolution rates.•Gas content and sound speed in the sediment are estimated via the geoacoustic inversion technique by matching the experimentally recorded and simulated bottom reflections•Only single source and receiver are required for the acoustic methodology•A multivariate linear regression is fitted for gas content to indicate its dependence on various predictors that change spatially and temporally over the lake

Deciphering quaternary sediment dynamics: a synthesis of X-ray CT imaging and grain size endmember modeling

Deciphering quaternary sediment dynamics: a synthesis of X-ray CT imaging and grain size endmember modeling

Estimating stream sediment loads to assess management options for a Southern Appalachian mountain lake

Enka Lake is a 25-ha reservoir in the Southern Appalachian mountains surrounded by the Biltmore Lake residential neighborhood. The aesthetic and recreational value of Enka Lake can be negatively affected by turbid water and sediment buildup, resulting from stormwater originating upstream in its 15.38 km2 watershed. In this study, we monitored streamflow and sediment loads for nearly 2 years to better understand sedimentation dynamics and evaluate management options. We collected nearly 500 water samples throughout the watershed, focusing on two tributaries that provide the majority of streamflow into Enka Lake. During baseflow conditions, those tributaries are very clear (turbidity ranging from 1 to 20 NTU), but sediment-laden stormflow (turbidity > 1000 NTU) from dirt roads, gravel driveways, and poorly vegetated yards is common and, during extreme storm events, causes lake discoloration. Discharge-sediment data pairs were used to construct sediment rating curves and estimate sediment fluxes through these tributaries. The predicted sediment fluxes were tested with high-frequency sampling during and after three storms in different seasons; predicted values underestimated the peak sediment fluxes (0–400%) but generally matched total measured sediment loads. Estimates of annual sediment load from the two tributaries (540–900 tonnes/year) suggest that a dredging effort commissioned by the neighborhood association in 2016 may have removed only about 1–3 years’ worth of sediment. Installing sediment forebays or other retention structures is likely the preferred sediment management strategy moving forward (over a regular dredging schedule) since they can be maintained more easily without affecting lake levels. Designing these retention structures will benefit from the estimates of stormflow and sediment fluxes, and the study design presented here—including the help of community-based volunteer samplers—provides a model that could be used at other sites in the Southern Appalachians and elsewhere.

Unraveling marine phosphogenesis along the Miocene coast of Peru: Origin and sedimentological significance of the Pisco Formation phosphorites

Phosphorite deposits form through phosphogenesis, a mechanism of diffusion and concentration of interstitial phosphate in sediments leading to Ca-phosphate mineral precipitation in a favorable sedimentary regime at the seafloor. Stretching along the Peruvian coast, the East Pisco Basin is known to host phosphorite beds of Miocene age. In this study, we investigate the petrographic, mineralogical and chemical composition of the Miocene phosphorite layers of the East Pisco Basin, and discuss the phosphogenetic mechanism(s) and sedimentary dynamics that led to the genesis and accumulation of P-rich deposits. Phosphorite samples were collected from layers overlaying stratigraphic unconformities within the Pisco Formation and subsequently analyzed through multiple methods: optical microscopy, XRD, XRF, SEM-EDS, EPMA, ICP-MS and LA-ICP-MS. Our results indicate that these layers consist of phosphatic clasts and nodules along with dolomite clasts, basement boulders, shark teeth, mollusk molds and vertebrate bone fragments. The P-rich clasts are mainly composed of phosphatic intraclasts and small phosphatic nodules. They occur associated with minor amounts of dolomite clasts coated by Fe-oxyhydroxides and laminites. Clasts and nodules are cemented by both early and late diagenetic cements, such as dolomite, calcite, silica, gypsum/anhydrite and baryte. Our observations suggest that the Pisco phosphorite deposits are transgressive lags laying on ravinement surfaces. They formed just below the sediment-water boundary during the early transgression phases, when the porewaters were enriched in phosphorus due to the abundance of organic-rich sediments and the microbial activity, as typical of upwelling settings. These deposits formed in shallow marine conditions, characterized by high biological productivity and low net sedimentation rates, with suboxic conditions at and beneath the sediment-water interface. The concentration of phosphate-coated clasts was then favored by a sedimentary condensation mechanism of dynamic bypassing. Overall, this study provides new insights into the genesis of phosphorite layers in the East Pisco Basin and highlights the importance of understanding the complex interplay between authigenic and sedimentological processes in the formation of these economically and geologically relevant sedimentary rocks.

Factors Controlling the Formation and Evolution of a Beach Zone in Front of a Coastal Cliff: The Case of the East Coast of Evia Island in the Aegean Sea, Eastern Mediterranean

The present study examines the recent evolution of a cliff coast along the Aegean Sea, considering its geotectonic context, oceanographic factors, sediment dynamics, and human impact. Initially, the formation of this coastal stretch was influenced by neotectonic faults, oriented both semi-parallel and diagonally relative to the present coastline orientation (NE–SW). Subsequently, the delivery of terrestrial sediment from ephemeral rivers and cliff erosion, along with nearshore wave-induced hydrodynamics have played a secondary role in shaping its current configuration, which includes a beach zone along the base of the cliff. This secondary phase of coastal evolution occurred over the past 4–5 thousand years, coinciding with a period of slow sea level rise (approximately 1 mm/year). Evidence such as uplifted notches and beachrock formations extending to around 5 m water depth suggests intervals of relative sea level stability, interrupted by episodic tectonic events. Anthropogenic interventions, related to both changes in coastal sediment budget and coastal engineering projects, have caused beach erosion, particularly in its central and northern sectors.

Spatiotemporal variations in the grain size distribution in the water column and sediments from the Yellow River Delta to distal areas under coastal currents

The differentiation of sediment grain size from large river deltas to distal areas in a coastal flow system and its evolution are vital because they greatly contribute to matter transport, pollution accumulation, and carbon cycling on the inner shelf. Here, the Yellow River sedimentary system in the adjacent seas is studied, including the proximal delta of the Yellow River and the distal mud patch. The grain size distributions of the suspended particulate matter (SPM), surface sediments, and core sediments in the Shandong Peninsula Coastal Current (SPCC) system were integrated and analyzed. The results show that apparent variations in the grain size distribution exist in the SPM and sediments in the SPCC system. The grain size distribution of the SPM near the proximal delta of the Yellow River is multimodal and variable with water depth, whereas that in the distal mud area is typically unimodal. The coarse-grained endmember of suspended sediments is restricted in the proximal area by ocean fronts under fair weather conditions in both summer and winter and is only transported to the distal mud area under strengthened coastal currents in winter. In contrast, fine-grained endmembers can be transported far away under tidal currents and coastal currents year-round. The temporal grain size variation near the proximal delta is also significantly affected by historical shifts in the Yellow River mouth, while the strength of coastal currents associated with the East Asian Winter Monsoon (EAWM) controls the grain size distribution in the distal mud area. The roles of river behaviors, ocean fronts, tides, and winds are all highlighted in the control of grain size differentiation. These results potentially have significance for understanding sediment dynamics and mass transport processes in similar coastal current systems involving large rivers worldwide.

Sediment dynamic on the tidal flat sheltered by artificial engineering: A case study on eddies

Tidal flats are important ecological and terrestrial resources. With the increasing development of coastal engineering projects, it is important to understand the dynamic response of tidal flats to human activities. Hence, the time series of wave, current, and suspended sediment during the spring tide from April 30, 2013 to May 1, 2013 were recorded by three tripod observation systems placed on the upper, middle, and lower parts of the tidal flats south of a constructed harbor in Wanggang, Jiangsu, China. The results showed that eddies formed south of the reclamations during flood tides. The directions of local tidal currents changed from their original southwest to the present northwest, and the ebb tides also changed but continued to flow northeast. The sediment transport process was basically consistent with the currents. The total net sediment fluxes during the tidal cycle (mean values of two tides) on the mudflat were two orders of magnitude larger than those on the salt marsh. Most of the sediments on both the mudflat and the salt marsh were transported northward alongshore, and a small portion of the sediments was transported seaward on the mudflat but shoreward on the salt marsh. The portion of the tidal flat with an elevation >1 m was wide in the north but narrow in the south, as determined by analysis of LiDAR elevation data, which coincided with the local sediment dynamics. The sediments were transported northward from southern deep waters during flood tides, which assisted in the expansion of the tidal flats in the north. This phenomenon reflected unique local sediment dynamics that were highly constrained by reclamations and Dafeng Harbor in the north as well as seawalls in the west. The tidal flat influenced by eddies can extend up to approximately 10 km south of the Dafeng Harbor. This case study has significant implications for the protection of tidal flats and the construction of coastal artificial engineering projects.

Evolution of a late Quaternary succession by interpretation of high‐resolution seismic and bathymetric data, Adriatic Sea

AbstractThis paper presents the results of the interpretation of a set of high‐resolution seismic lines integrated with multibeam echosounder data acquired in a coastal area in the Northern Adriatic Sea. The aim of the study was to reconstruct the stratigraphic evolution of a late Quaternary sedimentary succession offshore the town of Bibione, North‐Eastern Italy, by recognising the key unconformities, identifying the main depositional units, dating them and reconstructing the depositional environments in relation to relative sea‐level variations. Specifically, four sedimentary units, separated by erosional unconformities associated with the development of deep channels, were identified and dated based on literature information. By interpreting the seismic data, sedimentary dynamics were reconstructed and palaeoenvironments identified. The lower unit corresponds to a paludal environment, showing abundant gas seeps and accumulations (bright spots); the two intermediate units correspond to fluvial deposits, filling the deep incisions that characterise the bounding surfaces. Finally, the shallowest unit, bounded by a wave‐ravinement surface incised by tidal currents, corresponds to the Holocenic progradation of the coastal wedge. In addition, several vertical gas chimneys were identified, ranging in width from a few metres to 20–30 m. These were present in all units, often reaching the sea floor. Finally, elongated mounds, about 300 m wide, at the sea floor were recognised. The bathymetric and seismic characteristics of these elongated bodies and their relationship to adjacent sedimentary bodies suggest that they are probably methane‐derived carbonate formations known as ‘Trezze’ or ‘Tegnùe’. These names recall the fact that the trawls of the local fishermen were often hindered (‘tegnù’ in the Venetian language) or even cut off by these formations.

HOTSED: A new integrated model for assessing potential hotspots of sediment sources and related sediment dynamics at watershed scale

In this paper we introduce HOTSED, a novel, innovative GIS-based model designed for assessing potential hotspots of sediment dynamics at watershed scale. HOTSED integrates geomorphic spatial information with both structural and functional properties of connectivity. HOTSED provides a single and intuitive output that depicts the location of sediment source hotspots. Moreover, it enables the identification of “relative hazard” classes for sediment production and related effects. The general methodological framework is based on the initial elaboration of an Inventory Map (IM) of sediment-related landforms and processes, along with the implementation of a corresponding database. Subsequently, we used data stored in the IM to estimate the geomorphic Potential of Sediment Sources (PSS) through a relative scoring system. Furthermore, we computed Structural Sediment Connectivity (STC) and the Potential for Sediment Transport (PST) by combining terrain and hydrological parameters, vegetation roughness, and rainfall erosivity. Afterwards, PSS, STC, and PST components are integrated through a raster-based calculation method yielding the HOTSED model. We tested the HOTSED procedure in the upper Val d’Arda-Mignano watershed, which is a representative geomorphologically highly active Mediterranean area of the Northern Apennines (Italy). Through photointerpretation, terrain analysis, and fieldwork, we mapped sediment-related geomorphic features for a total of 4640 ha including: badlands and gullies (0.26%), rill-interrill erosion (15.03%), fluvial erosion (0.03%), landslides (70.06%), litho-structural erosional systems (0.87%), slope deposits (12.56%), and alluvial deposits (1.19%). HOTSED revealed hotspots with a very high hazard potential located near main channels or upstream of the reservoir. These areas are often linked with active landslides highly connected to the drainage system and frequently associated with other processes like bank erosion or surficial soil erosion. The model also highlighted linear hotspots corresponding to drainages flowing alongside or intersecting complex geomorphic systems such as landslides. Furthermore, HOTSED identified areas where sediments are stored in depositional landforms, exhibiting a low hazard potential, considering both low geomorphic potential and sediment connectivity. Our conceptual model is generally applicable but proves to be particularly effective in areas characterized by complex and polygenetic geomorphic systems, such as the Northern Apennines. HOTSED offers a valuable tool for watershed authorities to support sustainable watershed and reservoir management.

Microbial mat-induced microfacies in clastic deposits – An overview

Abstract This contribution reviews microbial microfacies recognisable in vertical sections through modern or fossil mat-overgrown sediment. Microfacies are products of endobenthic or epibenthic microbial mats interacting with sediment dynamics. Laminae of such mats form during sediment dynamic quiescence by organisation of filaments to an interwoven mat fabrics (binding), and biomass enrichment (growth) by cell replication and the production of extracellular polymeric substances (EPS). Vertical sections through mat-covered sediment may show buried stacks of subrecent mat laminae (biolaminites) that rose from alternating periods of mat development and sediment deposition. Mat laminae that drape ripple marks are visible as sinoidal structures in sediment core or sections. If the sediment-stabilising properties of a microbial mat is overcome by currents or waves of high strengths, cm-size mat fragments (mat chips and roll-ups) are ripped off and redeposited. Intrasedimenary gases, trapped beneath mat layers, may cause a high secondary porosity (sponge pore sand) in the sandy substrates. The internal build-up (microfabrics) of mat laminae is investigated under high magnification. Endobenthic microbial mat fabrics include filamentous and coccoid cells forming a network, EPS, and sedimentary grains. The grains derived from interaction of the endobenthic mats with bed load. Epibenthic microbial mat fabrics may include also silt-size particles syndepositionally enriched by baffling and trapping of suspension load. The fabrics of these mats commonly also include oriented sedimentary grains. These grains (now aligned bedding parallel) were dragged upward from the substrate during the development and growth of the mat. Overall, microbial microfacies provide insight into the sedimentation pattern of the (paleo-)environment and into the types of the substrate-colonising microbial mats.

Reservoir Mud Releasing May Suboptimize Fluvial Sand Supply to Coastal Sediment Budget: Modeling the Impact of Shihmen Reservoir Case on Tamsui River Estuary

AbstractRegular release of sediment from reservoir has been increasingly adopted as a strategy for sustainable management. Here, we use a process‐based morphodynamic model to simulate the estuarine sediment dynamics impacted by turbidity current venting implemented by the Shihmen Reservoir during three typhoon events in 2008. Upon validation with the post‐event bathymetries, the model hindcasts reveal that mud releasing can be effective in mitigating reservoir siltation, yet may be a suboptimal strategy for alleviating coastal sediment deficit. A vast majority of the released muds were delivered through the estuary and exported to offshore by flood advection, wave dispersion, and tidal flushing. The flood‐driven sands, sourced mainly from downstream tributaries, were instead the major contributor to coastal sediment budget. However, mud mantling (covering and immobilizing sand deposits by the reservoir‐released muds) reduced sand availability and thus sand delivery to the coast. For the present case, 25% of the released muds were deposited along the way, presence of these mud covers reduced sand delivery by 15%, compared to a hypothetical scenario of clear‐water flood releases. The relative sand transport deficit is found to increase linearly with the degree of bed mud saturation, 1–D/R, with D/R the ratio of single‐event mud deposit to release. Given broad relevance to global reservoirs encountering the problems of siltation and coastal sediment deficit, our findings highlight that sustainable management needs to look beyond just a bulk amount of sediment, but it is critical to consider how different sediment fractions are interacting and impacted by human activities.

Sediment dynamics and geomorphology in coastal areas affect long-term abundance of waders

Millions of migrating and wintering waders depend on coastal areas and estuaries for feeding and to replenish body reserves. These habitats are dynamic, with changing intertidal flats and sediments due to natural and climate-driven processes. The aims of this study were to examine whether physical conditions of intertidal flats such as geomorphology and sediment compositions could explain abundance of wader species, and furthermore whether changes in these conditions over time influenced changes in abundance of waders. In addition to physical structures such as datum (level), slope and sediment composition of intertidal flats, dynamic variables connected to tidal cycles such as distance of the waterline from the coast and duration of water cover were included. Penetration of the sea floor was measured as a proxy for sediment composition. The study was conducted in the Danish section of the Wadden Sea during 1981–1986 and 2008–2009 with additional data from 2020. The focus was on 12 widespread wader species. PCA analysis revealed that wader species were distributed in relation to tidal cycles such as duration of water cover and the position of waterline and to the physical structures, datum, slope and penetration, in decreasing order. With regard to the physical structures, pairwise comparisons of distribution of waders species showed that mean datum (level) was significantly different for 51 pairs of species out of 66 comparisons, mean penetration values differed for 34 pairs, and mean slope differed for 26 pairs of wader species. Long-term changes of physical structures of transects revealed that changes of densities of 10 wader species were significantly correlated with changes per year in one or more of the physical structures: seven wader species were significantly correlated with changes per year of mean datum (level) of transects (Lapwing was positively correlated while Avocet, Golden Plover, Grey Plover, Dunlin, Bar-tailed Godwit and Redshank were negatively correlated), five species with mean slope (Oystercatcher, Ringed Plover and Knut were positively correlated and Grey Plover and Redshank were negatively correlated), and three species with mean penetration values (sediment composition) of transects (Avocet and Bar-tailed Godwit were positively correlated and Lapwing was negatively correlated). The study shows that long-term changes of physical structures of intertidal flats affected abundance of wader species. The results are important for interpretation effects of erosion and accretion of coastal areas as consequences of natural and climate driven processes such as sea level rise and coastal squeeze.

Mixed response of trace element concentrations in fluvial sediments to a flash flood in a former mining area

BackgroundFloods, especially flash floods, are the major transporting agent for fluvial sediments, whose pollution is a global concern. As floods result in the dispersion of and exposure to these sediments, a profound understanding of sedimentary dynamics during flood events and the related pollutant dispersion is of relevance. However, the characteristics of extreme flood events concerning pollutant dynamics are insufficiently known so far.ResultsIn a Central European catchment impacted by intense industrial activities and former mining, over the course of five years, we surveyed six high-discharge events, five of them approx. bankfull discharge and one major flash flood event, supplemented by sampling of bank sediments. Fluvial sediments were analyzed for elemental composition by X-Ray fluorescence and for grain size distribution of the fine faction by laser diffraction. By applying a local enrichment factor, trace metal(loid) signatures in these sample sets were compared. Furthermore, Positive Matrix Factorization was used to investigate the trace metal(loid)s’ sources.The sediments deposited by minor flooding had continual trace metal(loid) signatures. However, for the extreme event, significant divergencies arose and persisted for the following years: The enrichment of anthropogenically influenced elements increased, with a slowly decreasing trend in the subsequent two years. Naturally dominated metal(oid)s decrease in enrichment without indicating a return to original levels. In contrast, other elements were insensitive to the extreme event. Positive Matrix Factorization identified anthropogenic influences in elements originating from copper and lead processing and mining activities. Furthermore, bed sediments and a natural background factor were found to dominate the non-anthropogenically influenced metal(loid)s.ConclusionsIn between extreme events, winnowing processes slowly alter the elemental composition of bed sediments. The depletion of such sediments due to the flash flood proves catchment-wide flushing, which induces a natural resetting of the geochemical signals. This ability to renew is an integral part of resilience in fluvial systems. This mechanism is disturbed by industrial activities in floodplains. The exceptional flooding reaches infrastructure that is assumed to be safe and, therefore, unprotected. These additional sources can shift flood sediments’ trace metal(loid) signature, which has a long-lasting impact on the catchment sediments. However, the modifications depend on the flooding extent, possible emitters, and protection measures.

Sedimentation dynamics of passive particles in dilute bacterial suspensions: emergence of bioconvection

Microorganisms are ubiquitous in nature and technology. They inhabit diverse environments, ranging from small river tributaries and lakes, to oceans, as well as wastewater treatment plants and food manufacturing. In many of these environments, microorganisms coexist with settling particles. Here, we investigate the effects of microbial activity (swimming E. coli) on the settling dynamics of passive colloidal particles using particle tracking methods. Our results reveal the existence of two distinct regimes in the correlation length scale ( $L_u$ ) and the effective diffusivity of the colloidal particles ( $D_{eff}$ ), with increasing bacterial concentration ( $\phi _b$ ). At low $\phi _b$ , the parameters $L_u$ and $D_{eff}$ increase monotonically with increasing $\phi _b$ . Beyond critical $\phi _b$ , a second regime is found where both $D_{eff}$ and $L_u$ are independent of $\phi _b$ . We demonstrate that the transition between these regimes is characterized by the emergence of bioconvection. We use experimentally measured particle-scale quantities $L_u$ and $D_{eff}$ to predict the critical bacterial concentration for the diffusion–bioconvection transition.

Shift away from Nile incision at Luxor ~4,000 years ago impacted ancient Egyptian landscapes

Although the Nile is one of the largest rivers in the world and played a central role in ancient Egyptian life, little is known about its response to climatic change during the Holocene. Here we present a framework for the evolution of the Egyptian Nile, demonstrating how climatic and environmental changes have shaped the landscape of the Egyptian Nile Valley over the past 11,500 years, including the civilization of ancient Egypt (~5,000 to 2,000 years ago). Using data from over 80 sediment cores drilled in a transect spanning the Nile Valley near Luxor, pinned in time by 48 optically stimulated luminescence ages, we reconstruct the dynamics of the Nile River during the Holocene in the vicinity of UNESCO World Heritage sites such as Karnak and Luxor temples. According to our reconstruction, valley incision occurred from the start of the record until approximately 4,000 years ago and then rapidly shifted to massive floodplain aggradation. We argue that this relatively abrupt change in the riverine landscape near Luxor from the Middle to Late Holocene was linked to a shift towards a drier regional hydroclimate around this time. Such a dramatic change in river sediment dynamics could have had local agro-economic consequences.

High-resolution seismic record of the Quaternary palaeoenvironments along a Dalmatian-type coast (Lošinj Channel, Adriatic Sea)

Coastal systems have changed considerably in response to Quaternary glacial–interglacial variability. Here, we offer the first detailed assessment of geomorphic features and late Quaternary sedimentation dynamics in the Lošinj Channel in the Adriatic Sea. The present study attempts to resolve the complex evolution of the environments by applying high-resolution seismic records that build upon sediment core data. Within this coastal karst basin, a significant amount of sediment accumulated during the Quaternary. Notably, the existence of several prominent erosional and depositional environments was revealed. We distinguished recurrent episodes of fluvio-lacustrine and marine sedimentation that probably occurred since Marine Isotope Stage (MIS) 6. The preserved record consists of erosional features and subparallel and oblique reflectors attributed to glacial periods (Seismic Units SU-II, SU-IV, and SU-V). Interglacial units are acoustically semitransparent and generally reflection-free (Seismic Units SU-I and SU-III). The mutual influence of sea level and climate change, sill depth, and karst hydrology enabled environmental changes in the Lošinj Channel. The area proves to be important for Quaternary studies because it contains a long sediment succession spanning at least the middle and late Pleistocene and Holocene. Our study has implications for the assessment of the long-term palaeoenvironmental evolution of similar coastal settings and reconstruction of the regional palaeogeography which is in turn crucial for understanding prehistoric human occupation and/or dispersal. This is one of the few well-preserved records in the Adriatic Sea that provides insight into submerged landscapes and sea levels since the penultimate glacial.

Effects of chironomid larvae density and mosquito biocide on methane and carbon dioxide dynamics in freshwater sediments.

Small lentic water bodies are important emitters of methane (CH4) and carbon dioxide (CO2), but the processes regulating their dynamics and susceptibility to human-induced stressors are not fully understood. Bioturbation by chironomid larvae has been proposed as a potentially important factor controlling the dynamics of both gases in aquatic sediments. Chironomid abundance can be affected by the application of biocides for mosquito control, such as Bti (Bacillus thuringiensis var. israelensis). Previous research has attributed increases in CH4 and CO2 emissions after Bti application to reduced bioturbation by chironomids. In this study, we separately tested the effect of chironomid bioturbation and Bti addition on CH4 production and emission from natural sediments. In a set of 15 microcosms, we compared CH4 and CO2 emission and production rates with high and low densities of chironomid larvae at the bioturbating stage, and standard and five times (5x) standard Bti dose, with control sediments that contained neither chironomid larvae nor Bti. Regardless of larvae density, chironomid larvae did not affect CH4 nor CO2 emission and production of the sediment, although both rates were more variable in the treatments with organisms. 5xBti dosage, however, led to a more than three-fold increase in CH4 and CO2 production rates, likely stimulated by bioavailable dissolved carbon in the Bti excipient and priming effects. Our results suggest weak effects of bioturbating chironomid larvae on the CH4 and CO2 dynamics in aquatic ecosystems. Furthermore, our results point out towards potential functional implications of Bti for carbon cycling beyond those mediated by changes in the macroinvertebrate community.