Sediment Accumulation Patterns Research Articles

Geology aspects and formation of the erosional structure of Upper Miocene deposits of the Western Cicaucasus

The results of regional studies of the Early Miocene deposits of the Western Ciscaucasia, carried out on the basis of seismic stratigraphic analysis, are presented. The spatial pattern of sediment accumulation is analyzed and the paleogeographic conditions during the regressive stages of the Late Miocene in the Western Ciscaucasia are clarified. Erosion incisions of several levels were identified, which developed during the fall of the erosion base level during major regressions in the studied time interval. By spatial correlation of paleochannels based on a selected series of intersecting seismic profiles, the buried river valleys of the Paleo-Don and Paleo-Donts were reconstructed and constructed at the Sarmatian‒Meotis boundaries and within the Late Meotis‒Late Pontian interval.

Addressing Configuration Uncertainty in Well Conditioning for a Rule-Based Model

Rule-based reservoir models incorporate rules that mimic actual sediment deposition processes for accurate representation of geological patterns of sediment accumulation. Bayesian methods combine rule-based reservoir modelling and well data, with geometry and placement rules as part of the prior and well data accounted for by the likelihood. The focus here is on a shallow marine shoreface geometry of ordered sedimentary packages called bedsets. Shoreline advance and sediment build-up are described through progradation and aggradation parameters linked to individual bedset objects. Conditioning on data from non-vertical wells is studied. The emphasis is on the role of ‘configurations’—the order and arrangement of bedsets as observed within well intersections in establishing the coupling between well observations and modelled objects. A conditioning algorithm is presented that explicitly integrates uncertainty about configurations for observed intersections between the well and the bedset surfaces. As data volumes increase and model complexity grows, the proposed conditioning method eventually becomes computationally infeasible. It has significant potential, however, to support the development of more complex models and conditioning methods by serving as a reference for consistency in conditioning.

Foredune initiation and early development through biophysical interactions

Coastal dunes result from complex interactions between sand transport, topography and vegetation. However, uncertainty still persists due to limited quantitative analyses, integrating plant distribution and morphologic changes. This study aims to assess the initiation and maintenance of feedback processes by analysing the early development stages of incipient foredunes, combining data on the evolution of the plant cover and communities and dune morphology. Over three years, the monitoring of a newly formed dune (1 ha plot) reveals the progressive plant colonisation and the episodic accumulation of sand around vegetated areas controlled by sediment availability. Distinct colonisation rates were observed, influenced by inherited marine conditions, namely topography and presence of beach wrack. Berm-ridges provided elevations above the critical threshold for plant colonisation and surface roughness, aiding sediment accumulation. Beach wrack above this threshold led to rapid expansion and higher plant concentration. In the initial stages, vegetation cover significantly influenced sediment accumulation patterns, with higher accumulation around areas with high plant cover and low slopes or around areas with sparse vegetation but milder slopes. As the dune system matured and complexity grew, the link between vegetation cover and accumulation became nonlinear. Mid to low coverages (5–30 %) retained most of the observed accumulation, especially when coupled with steep slopes, resulting from positive feedbacks between vegetation, topography and sand transport. As foredune developed, vegetation cover and diversity increased while inherited morphologies grew vertically, explaining the emergence of dune ridge morphological types. Flat surfaces lacking wrack materials experienced a three-year delay in colonisation and sand accumulation, leading to the formation of terrace-type incipient foredunes. These observations underline feedback processes during the early stages of dune formation, with physical feedbacks primarily driving initiation and biophysical feedbacks prevailing in subsequent colonisation stages.

Seasonal variations in the coastal beach profiles at Calabonita Beach in AL Hoceima Bay, Morocco

Sandy beaches are among the Earth's most dynamic natural environments, with wave action and swells critically influencing the energetics of erosion and sediment transport. This energy's temporal and spatial distribution significantly affects coastal morphological evolution. This study investigates the seasonal morphodynamic variability and short-term alterations at Calabonita Beach, located within Al Hoceima Bay, by analyzing topographic profiles collected from June 2022 to May 2023. Findings indicate that Calabonita Beach is relatively narrow, averaging a width of 27.53 meters with a slope of 6.82%. The annual vertical movement balance was found to be negative, showcasing a distinct pattern of sediment accumulation during autumn and increased erosion during winter. These results highlight the beach's dynamic nature, governed by natural processes and human activities, underscoring the intricate interplay between accumulation and erosion patterns.

Controls on bioturbation and sediment distribution in carbonate shoreface deposits: insights from heterogeneity in Pleistocene and Recent strata

ABSTRACT Burrowing organisms alter sedimentary textures, influence cement distribution, and affect petrophysical characteristics of carbonate strata. Although many descriptions of carbonate successions reference bioturbation, quantitative data on spatial variability of trace fossils is rare, and fewer studies address trace-fossil influence on postdepositional modification of sedimentary deposits, which can affect petrophysical properties. To address these unknowns and determine the controls on ichnology in carbonate shoreface successions, this study evaluates the along- and across-strike distribution of sediment and bioturbation in recent, Holocene, and Pleistocene shoreface deposits on the leeward margin of Crooked–Acklins Platform (CAP), southern Bahamas. To the north, the extant margin shelf is characterized by poorly to moderately sorted, very fine–fine, skeletal–peloid–ooid sand with an average of 16% mud (< 62.5 µm) that is moderately to intensely bioturbated (ii3–6). Trace assemblages are diverse, and include horizontal tracks and trails, abundant horizontal deposit-feeding and locomotion traces, as well as dwelling and resting burrows attributable to the proximal Cruziana Ichnofacies. In marked contrast, shelf margin deposits to the south are well-sorted, medium ooid–peloid sand with < 1% mud, and display a range of bioturbation, from nonbioturbated to moderately intense bioturbation (ii1–4). Trace-fossil assemblages exhibit low ichnodiversity, dominated by vertical dwelling burrows with reinforced wall lining attributable to the Skolithos Ichnofacies. Holocene and Pleistocene strata show similar proximal-to-distal and along-strike variations in sediment attributes, ichnodiversity, and bioturbation. These trends reflect a progressive, north-to-south increase in energy reflecting the change in margin orientation relative to the direction of dominant wave energy, analogous to the recent system. This study provides data for an integrated sedimentologic–ichnologic conceptual model for processes and patterns of sediment accumulation on carbonate shorefaces, and are distinct from siliciclastic analogs.

Growing Salix spp. on heavy metal contaminated sediment (Oskarshamn, Sweden) as a joint phytoremediation and circular economy approach

The sediments of rivers or harbours have always been considered sinks for numerous heavy metals, pesticides, chemicals and contaminants of anthropogenic origin. The eco-friendly management of contaminated sediment have received attention due to their large-scale presence in harbour areas. Application of bioenergy crop species, such as Salix spp., have shown a strong potential for reducing heavy metals from the contaminated sediment. The aim of this study was to investigate the application of Salix spp. on contaminated dredged sediment and heavy metal accumulation and translocation patterns in different parts of plants. Two Salix cultivars (Wilhelm and Ester; commercially available in Sweden) were cultivated in contaminated sediment for 5 weeks in a field setting. Heavy metals (Cd, Cu, Pb, Ni and Zn) content in different plant parts (root, cutting, shoot and leaves) were analysed by using atomic absorption spectrophotometer (AAS). The result indicated that the root biomass production was negatively affected for both cultivars due to the contaminated sediment medium, even though no morphological symptoms were present. Both Cd and Cu net accumulation were found to be significantly higher in Ester cultivars. The low translocation of heavy metals in Salix spp. hints that accumulated heavy metals are stored in the root parts. Low translocation of heavy metals from contaminated sediments gives a strong potential for using a growth medium to utilize phosphorus (P) in the sediment from a circular economy and bioeconomy perspective.

Bio-physical determinants of sediment accumulation on an offshore coral reef: A snapshot study

Sediments are found on all coral reefs around the globe. However, the amount of sediment in different reservoirs, and the rates at which sediments move between reservoirs, can shape the biological functioning of coral reefs. Unfortunately, relatively few studies have examined reef sediment dynamics, and associated bio-physical drivers, simultaneously over matching spatial and temporal scales. This has led to a partial understanding of how sediments and living reef systems are connected, especially on clear-water offshore reefs. To address this problem, four sediment reservoirs/sedimentary processes and three bio-physical drivers were quantified across seven different reef habitats/depths at Lizard Island, an exposed mid-shelf reef on the Great Barrier Reef. Even in this clear-water reef location a substantial load of suspended sediment passed over the reef; a load theoretically capable of replacing the entire standing stock of on-reef turf sediments in just 8 h. However, quantification of actual sediment deposition suggested that just 2 % of this passing sediment settled on the reef. The data also revealed marked spatial incongruence in sediment deposition (sediment trap data) and accumulation (TurfPod data) across the reef profile, with the flat and back reef emerging as key areas of both deposition and accumulation. By contrast, the shallow windward reef crest was an area of deposition but had a limited capacity for sediment accumulation. These cross-reef patterns related to wave energy and reef geomorphology, with low sediment accumulation on the ecologically important reef crest aligning with substantial wave energy. These findings reveal a disconnect between patterns of sediment deposition and accumulation on the benthos, with the ‘post-settlement’ fate of sediments dependent on local hydrodynamic conditions. From an ecological perspective, the data suggests key contextual constraints (wave energy and reef geomorphology) may predispose some reefs or reef areas to high-load turf sediment regimes.

Impacts of Tectonic Subsidence on Basin Depth and Delta Lobe Building

AbstractChannel avulsions on river deltas are the primary means to distribute sediment and build land at the coastline. Many studies have detailed how avulsions generate delta lobes, whereby multiple lobes amalgamate to form a fan‐shaped deposit. These studies often assume a steady subsidence and uniform basin depth. In nature, however, lobe building is disrupted by variable subsidence, and progradation of lobes into basins with variable depth: conditions that are prevalent for tectonically active areas. Herein, we explore sediment dispersal and deposition patterns across scales using measurements of delta and basin morphology compiled from field surveys and remote sensing, collected over 150 years, from the Selenga Delta (Baikal Rift Zone), Russia. Tectonic subsidence events, associated with earthquakes on normal faults crossing the delta, displace portions of the topset several meters below mean lake level. This allogenic process increases regional river gradient and triggers lobe‐switching avulsions. The timescale for these episodes is shorter than the predicted autogenic lobe avulsion timescale. During quiescent periods between subsidence events, channel‐scale avulsions occur relatively frequently because of in‐channel sediment aggradation, dispersing sediment to regional lows of the delta. Avulsion settings for the Selenga Delta preserve discrete stratal packages that could contain predominately deep channels. Exploring the interplay between tectonic subsidence and sediment accumulation patterns will improve interpretations of stratigraphy from active margins and basin models.

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Examining sediment accumulation pattern and storage capacity loss of Lake Ziway, Ethiopia

Sediment Infill of Tropical Floodplain Lakes: Rates, Controls, and Implications for Ecosystem Services

Shallow lakes in tropical floodplains provide significant ecosystem services that can be altered by natural and anthropogenic forces. Despite their importance, little is known about the infill patterns and timescales and the magnitude of these changes in tropical floodplain lakes. Here, we present a global meta-analysis of sediment core-derived accumulation rate data for shallow floodplain lakes in tropical lowlands to quantify the timescales of basin infill. Environmental variables (e.g., sediment accumulation rates, bathymetry, surface area) were compiled from the literature or derived from remote sensing imagery, resulting in a database (n = 76 lakes) that includes various lake morphologies. Our results show an exponential increase in sediment accumulation rates in many of these lakes over the past 50 years, which we interpret as a response to growing human populations and deforestation, particularly in topographically steep watersheds with pronounced seasonal rainfall. Over centennial periods, tropical floodplain lakes accumulate sediment faster than many other extratropical lakes. The dataset suggests that complete infill of some tropical floodplain lakes will occur in as little as a few centuries. Our findings also reveal the critical environmental and human factors that influence sediment accumulation patterns and affect ecosystem services in shallow tropical floodplain lakes. These findings have important implications for water and sediment management in low latitude watersheds, many of which are located in densely populated and/or developing nations.

Accumulation of windblown sand in impact craters on Mars

Abstract Loose sand, blown away from source regions by winds, is transported across Mars's surface into sand sheets and dunes and accumulates within topographic sinks. In the absence of plate tectonics, impact craters constitute a dominant sink for windblown sediments on Mars today. We analyzed the volume of all mapped eolian sands in martian craters >1 km in diameter to reveal spatiotemporal patterns of sediment accumulation on the planet's surface. We combined our results with global climate simulations, maps of depth to the ice table and dust cover, as well as lithologic and age information of the underlying geologic units, to better understand the controls on intracrater sand accumulation rates. We find that crater age, latitude, and lithology influence the accumulation rate of windblown sand and, notably, that it is enhanced in mechanically weaker substrates, high-latitude craters (suggesting that modern cryogenic processes may enhance sand production), and in Late Noachian and Early Hesperian craters (possibly hinting at increased erosion rates at that time).

Non‐Monotonic Floodplain Responses to Changes in Flooding Intensity

AbstractOverbank flooding is common along most rivers, and it influences the dispersal of sediment to floodplains. While variable discharge is a critical aspect of fluvial landscape evolution, it is typically modeled by simplifying the hydrograph to an equivalent steady discharge: the channel‐forming discharge. However, for all formulations used to simplify hydrographs, many different inputs can produce the same channel‐forming discharge. Here, we investigate how hydrographs with different flood intensities affect channel mobility, sediment accumulation patterns, and alluvial morphology using a suite of physical experiments where a fan delta grew by dispersing a cohesive sediment mixture into a basin. The experiments spanned three levels: no flooding, low‐intensity flooding, and high‐intensity flooding, while the time‐averaged water and sediment discharge was equivalent between all flooding regimes. Across this gradient, channel mobility, alluvial morphology and sediment dispersal scaled non‐monotonically with flooding intensity, and the data suggest that levee‐building feedbacks are the cause. We found that flood intensity modulates the relative balance between sediment delivery to channel margins, which nourishes levee growth, and the intensity of overbank flow, which inhibits levee growth. When flooding was absent, levees experienced consistent overbank flow and sediment delivery, leading to moderate levee aggradation and sporadic levee breaches. In contrast, when low‐intensity flooding was imposed, levees experienced enhanced sediment delivery by low‐amplitude floods, but only intermittent scouring. A further increase in flood intensity generated intense overbank flows that inhibited levee growth altogether. These results imply the existence of an optimum levee‐building condition, where flooding conditions stabilize channels through levee‐building feedbacks.

Sequence stratigraphy of the Niobrara Formation: Implications for age-constraining tectonic events and stratigraphic complexities in the Denver-Julesburg Basin, United States

The Upper Cretaceous Niobrara Formation in the Denver-Julesburg (D-J) Basin, United States, records late Turonian–early Campanian transgressive–regressive cycles that governed the rhythmic character of pelagic and detrital sedimentation along the former carbonate ramp of the Western Interior seaway (WIS). The general stratigraphic and architectural complexity of the full Niobrara section has long been recognized; however, fine-scale subdivision of the formation from a sequence stratigraphic aspect has been lacking and is critical for basin-scale analysis. The timing and controls of significant changes in architectural and sediment-accumulation patterns have important implications for the Niobrara petroleum system. As part of this study, we present a sequence stratigraphic framework appropriate for the distal carbonate ramp of the WIS. We project published biozone mapping and radiometric ages into basin-wide well control to establish the timing of chronostratigraphic surfaces. Age-constrained isochore maps reveal a chronology of dynamic paleoseafloor morphology that is critical to understanding the stratigraphic and architectural evolution of the Niobrara. At a regional scale, thickness patterns suggest that the north-south–oriented flexural forebulge in the Sevier foreland basin had migrated eastward to the position of the future Rocky Mountains, a location coincident with the western edge of dominantly pelagic carbonate deposition in the backbulge of the WIS basin. At the D-J Basin scale, chronostratigraphic isochore maps of four third-order sequences, and their finer-scale subintervals, record two broadly distinct periods of depositional influence in the Niobrara. Between ca. 90.0 and ca. 85.7 Ma (upper Turonian–lower Santonian), relatively even deposition was dominated by a pattern of differential sediment accumulation. Systematic reversals of thicks and thins through time are indicative of compensational infilling patterns with no influence of tectonic uplifts along the seafloor. In contrast, from ca. 85.7 to ca. 81.7 Ma (lower Santonian–lower Campanian), a reorganization of earlier architecture was driven by the influence of sublinear uplifts along the trend of the emergent Transcontinental arch. As a result, sediment accumulation was dominated by patterns of draping over the long-lived paleohighs. Absolute timing of the architectural changes of the Niobrara suggests a link among Sevier thrusting events, a migrating flexural forebulge, and uplifts at reactivated basement shear zones in the distal foreland. Thus, both active tectonics and the inherited Proterozoic basement fabric of the WIS influenced the evolution of the Niobrara Formation. This example from the Cretaceous WIS shows that age-constraining sequence stratigraphy for regional isochore mapping can reveal relationships among the structural response to far-field tectonic events, oceanographic variations, and stratigraphic architecture.

Characterisation of aeolian sediment accumulation and preservation across complex topography

Topography fundamentally influences the distribution and morphology of aeolian landforms via the modification of surface wind flow and the creation of space for sediment deposition. This has been observed at both landform (individual topographic dune forms) and macro-landscape (sand sea) scales. Although previous studies have considered several aspects of the impact of topography on aeolian landforms, the patterns of landscape-scale aeolian sediment accumulation that emerge at the meso-scale, within topographically complex environments have received less consideration.To address this, we present an approach that combines information on the presence of surficial sand (via remote sensing) with the morphometric feature classification method, LandSerf. Using the Cady Mountains in the Mojave Desert as a case study, we explore the relationships between sand cover and topographic indices over length scales of 102–103 m. Field observations are then used to refine our understanding of these patterns.Aeolian deposits across the Cady Mountains are strongly controlled by the topography. Although sand cover is often continuous and highly variable in depth, four archetypal “accommodation space types” are identified from the morphometric analysis: Slopes, Plains, Valley-Fills, and Slope-Valley composite. Specific aeolian landforms within these accommodation spaces may manifest as sand ramps and climbing - falling dunes, particularly on mountain front Slopes, and as sand sheets on downwind Plains within the mountain block. In areas of high sediment supply these may also coalescence, as exemplified by the extensive and compositionally complex Slope-Valley composites in the northern Cady Mountains.In conjunction with field observations, we argue that topography, moderated by proximity to sediment supply, strongly influences the character of the aeolian sedimentary record. However, even within the relatively complex landscape studied here, 90% of the mapped sand accumulation is associated with the four identified accommodation space types. The implication is that areas of such complex topography are amenable to analysis within the scheme outlined and that this can potentially be used to support interpretations of accompanying dune chronologies.

Stratigraphy, age, and provenance of the Eocene Chumstick basin, Washington Cascades; implications for paleogeography, regional tectonics, and development of strike-slip basins

Strike-slip faults form in a wide variety of tectonic settings and are a first-order control on the geometry and sediment accumulation patterns in adjacent sedimentary basins. Although the structural and depositional architecture of strike-slip basins is well documented, few studies of strike-slip basins have integrated depositional age, lithofacies, and provenance control within this context. The Chumstick basin formed in central Washington during a regional phase of dextral, strike-slip faulting and episodic magmatism associated with Paleogene ridge-trench interaction along the North America margin. The basin is bounded and subdivided by major strike-slip faults that were active during deposition of the intra-basinal, non-marine Chumstick Formation. We build on the existing stratigraphy and present new, detailed lithofacies mapping, conglomerate clast counts (N = 16; n = 1429), and sandstone detrital zircon analyses (N = 16; n = 1360) from the Chumstick Formation to document changes in sediment provenance, routing, and deposition. These data allow us to reconstruct regional Eocene paleo-drainage systems of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed to a forearc or marginal basin on the newly accreted Siletzia terrane. More generally, excellent age control from five interbedded tuffs and high sediment accumulation rates allow us to track the evolving sedimentary system over the Formation’s ca. 4−5 m.y. depositional history. This is the first time lithofacies and provenance variations can be constrained at high temporal resolution (0.5−1.5 m.y. scale) for an ancient strike-slip basin and permits a detailed reconstruction of sediment routing pathways and depositional environments. As a result, we can assess how varying sediment supply and accommodation space affects the depositional architecture during strike-slip basin evolution.

Spatial variability in nearshore sediment pollution in Lake Tanganyika (East Africa) and implications for fisheries conservation

Climate warming coupled with local disturbances within lakes is an accelerating global problem. This issue is acute at Lake Tanganyika (eastern Africa), where warming and overfishing have resulted in declining rates of pelagic fish catches and structural damage to diverse littoral cichlid communities. This deterioration has fueled demand for alternative livelihoods, and thus conversion of shoreline-adjacent forests to agricultural fields and oil palm orchards, which in turn heightens the threat of siltation on nearshore benthic habitats. The spatial variability of sediment pollution is unknown, however, posing a barrier to effective conservation. This paper assesses the spatial patterns of nearshore sediment accumulation within the Tuungane Project co-managed area of Lake Tanganyika in Tanzania. Analysis of lead-210 data show that the mean nearshore mass-based sediment accumulation rate is 0.06 g * cm−2 * year-1 (g cm-2 yr-1) across six sites adjacent to deforested watersheds, double the mean rate (0.03 g cm-2 yr-1) at a comparable but undisturbed control site. Spatial variance among rates is best explained by distance to deltaic point sources and bathymetric gradients. Data documenting carbon flux demonstrate that organic matter burial is higher in surface sediments offshore from deforested watersheds, consistent with onshore land use changes that promote erosion. Knowledge of sediment pollution patterns, coupled with maps of rocky benthic habitats, provide the necessary framework for effective conservation planning of fisheries in the present era of accelerated human interactions with the lake and its watershed. Findings provide a model for improved integrated management practices in large tropical artisanal fisheries in other parts of Africa.

Evolution of the Western Interior Seaway in west-central Alberta (late Campanian, Canada): Implications for hydrocarbon exploration

This study presents the first integrated, high-resolution stratigraphic analysis of a large area of the Cretaceous Western Interior Basin in Alberta (western Canada), providing new tools to discriminate sedimentary processes and stratigraphic patterns of transgressive-regressive (T-R) cycles in correlative marine and non-marine domains. We integrate gamma ray well-log analysis, measured sections, and paleontological data to determine sediment accumulation and distribution during the second-order T-R cycle of the late Campanian Western Interior Seaway over a previously unstudied area encompassing approximately 97,000 km2 of the Alberta foreland basin. The Bearpaw Formation, historically regarded as the product of a single transgression, is shown to include two T-R cycles, whose timing is constrained by new chronostratigraphic data that provides an unprecedented resolution (~200 kyr) for the Cretaceous of western North America. Seven reference stratigraphic markers were mapped across the study area from the marine deposits into the fluvial domains. 3D-modelled stratigraphic surfaces and stratigraphic intervals resulted in isopach maps for consecutive systems tracts, allowing detailed interpretations of their architecture and patterns of sediment accumulation. Our analysis provides paleogeographic maps for the Western Interior Seaway, focusing primarily on the evidence of the paleo-coastlines during the documented cycles. The distribution of fine-grained, primarily marine, sediments resulted in an effective seal for hydrocarbon accumulation in the Belly River Group. Further oil migration upsection, within the Edmonton group, was prevented by the occurrence of these sealing units. Data support the interpretation that eustasy provided the main control on the evolution of the Western Interior Seaway during the late Campanian.

Reduction of ballast tank sediment: Evaluating the effect of minor structural changes and developing a pneumatic cleaning system

Ballast tank sediments host organisms that pose invasion risk even if the ships are installed with ballast treatment systems. The bottom sediments also contribute to corrosion and cause cumulative deadweight loss over the years.This study presents the outcomes of the project “Conceptual Ballast Tank Design for Reducing Sediment Accumulation” (TUBITAK, Grant No: 115Y740). In the published first phase of the project, sediment accumulation pattern was determined and the center girder was found to be critical.In this study, the findings of the second and third phases are presented. In the second phase, the tank model design was revised aiming to reduce total sediment accumulation. The contribution of this revision was found to be is numerically insignificant. However, this revision drove more sediment towards the center girder. Thus, in the third phase, a pneumatic cleaning system targeting the center girder was designed to mobilize water to suspend sediment and facilitate discharge from the tank. The pneumatic cleaning system reduced the total sediment deposition in the ballast tank up to 45%. Operating the pneumatic system before de-ballasting operations on a regular basis would decrease the amount of sediment to be managed; reduce the invasion risk, tank corrosion, and cumulative deadweight loss.

Accumulation pattern and possible adverse effects of organic pollutants in sediments downstream of combined sewer overflows

The present study was conducted to investigate sediment accumulation patterns of PAHs, PCBs, flame retardants and pesticides along 100 m transects downstream from three different combined sewer overflows (CSOs). Additionally, the concentrations of PAHs and PCBs were quantified to allow a characterization of the sediment quality.The suspect screening revealed that usually more substances, especially pesticides and flame retardants, were detected in sediments located in the vicinity of CSOs. Except for PAHs at Location 1 and 3, all substances followed the same accumulation pattern, showing higher contaminations in sediments sampled downstream from the CSOs compared to an upstream located reference site. With increasing distance to the respective input, sediment concentrations decreased. Different accumulation patterns of PAHs at Locations 1 and 3 were related to high background concentrations of the receiving creek.Although the general contamination patterns were similar, the level of contamination was different at each location. PAH concentrations are indicative for the occurrence of sediment toxicity at Location 3. However, higher background concentrations in the receiving creek compared to concentrations present in the retention zone indicate a higher probability for sediment toxicity due to inherited waste or contamination from upper reaches. PCBs introduced by the sewer outfall at Location 1 significantly increased the toxic potential of sediments located in the vicinity of the CSO. The retention zones at Locations 2 and 3 appeared to be a good measure to trap particles and their associated pollutants before they accumulate in the creek sediments where they became potentially harmful for the aquatic biota.Based on this study recommendations for sampling strategies were concluded to harmonize sampling designs in studies analyzing the impact of point sources on the sediment quality and to minimize misinterpretation of results.