Sediment Distribution Research Articles

Effects of Trophic State on the Composition and Distribution of Bacteria in the Surface Sediments of Lake Taihu

ABSTRACT1. The trophic state of water significantly affects the structure of bacterial communities in sediments. The direct and indirect impacts of trophic state, along with trophic‐induced changes in the properties of organic matter, on the composition and distribution of bacteria in sediments, remain largely unknown.2. We collected surface sediments from 21 sites across five areas of Lake Taihu, the third largest freshwater lake in China. These sites represented a range of trophic states from mesotrophic to moderately eutrophic. We investigated how trophic state influences bacterial composition and distribution in the surface sediments of Lake Taihu.3. Proteobacteria, Firmicutes and Bacteroidetes were the most abundant phyla identified in the DNA sequences of surface sediments from the sampling sites in Lake Taihu, regardless of the water trophic state. The relative abundance of Proteobacteria and Firmicutes in the surface sediments increased with trophic level index (TLI) of the water column. In contrast, the relative abundance of Bacteroidetes, Acidobacteria and Fibrinobacteria decreased with increasing TLI. The α‐biodiversity of the sediment bacterial community in Lake Taihu did not vary significantly among different water trophic states. However, surface sediments from sites with varied trophic states exhibited different groups of bacteria that were either specifically present or in higher relative abundance.4. Several factors influenced the sediment bacterial communities in Lake Taihu, including sediment total nitrogen, sediment total phosphorus, sediment organic carbon, δ13C and trophic state. However, the primary influencing factors varied between sites and trophic states. For mesotrophic states, sediment organic carbon was the most important factor, while for moderately eutrophic states, trophic state was the most significant factor.5. Our findings provide evidence for both the direct and indirect influences of water trophic state on the composition and distribution of bacteria in sediments.

Sediment transport characteristics at the flood-event scale in the Minjiang River Basin, China

ABSTRACT In recent years, the significant change in the runoff–sediment distribution in the upper Yangtze River has led to an increased sediment contribution from the Minjiang River Basin (MRB) to the Three Gorges Reservoir. However, previous studies on sediment load changes in the MRB have focused mainly on annual-scale characteristics, thereby neglecting features driven by floods. Therefore, this study focused on examining the changes in flood-event sediment loads in the MRB based on mathematical statistics and comprehensive measurement data. The results indicated that human activities, climate change, and seismic events have caused an increasing trend in the flood-scale sediment load in the upper MRB and a decreasing trend in the lower MRB. The changes in the flood-scale sediment modulus at low runoff erosion power levels were greater than those at high runoff erosion power levels at different abrupt-change stages. During extreme flood events, the actual sediment concentration in the MRB remained below the sediment-carrying capacity. This study provides novel insights into water resource management during the flood season in the MRB and similar basins.

Distribution and bi-directional transport of surface sediments driven by monsoons on the northwest continental shelf of the South China Sea

Distribution and bi-directional transport of surface sediments driven by monsoons on the northwest continental shelf of the South China Sea

The Characteristics of Methylsiloxane Distribution in the Marine Surface Sediment, Masan Bay, Korea, in August 2018 and Suggesting Directions for Further Studies

The present study determined the distribution of fifteen methylsiloxane compounds (total methylsiloxanes, TMSs), including four cyclic (CMSs) and eleven linear (LMSs), in the marine surface sediment of Masan Bay, Korea, in 2018. The levels ranged from 76.6 to 2320 (median 264 ± 680), 5.00 to 3570 (median 359 ± 1310), and 81.6 to 5890 (median 607 ± 1940) ng/g-dw., in ΣCMSs, ΣLMSs, and ΣTMSs, respectively. The CMSs: LMSs ratio was 34:66, and the most dominant compound was D5 (27%), followed by L11 (22%) and L12 (20%). Principal component and cluster analyses categorized the ten sampling points into four groups based on the point sources: Group A (MS1) representing the industrial wastewater from the Changwon National Industrial complex; Group B (MS2) representing the ship movements; and Groups C (MS3, MS5, MS6, and MS7) and D (MS4, MS8, MS9, and MS10) representing the organic carbons. The present study hypothesized that the missing link between the methylsiloxane levels in 2013 and 2021 was due to the considerable industry recession in the bay. This was verified by positive correlations between the median ΣCMSs and the monthly production, the median ΣLMSs and ΣTMSs and the monthly employment in the complex. However, the hypothesis should be supplemented with the following perspectives: (1) selecting the sampling areas representing only the industrial wastewater, (2) considering the seasonal fluctuations, (3) estimating half-lives, and (4) investigating time series. This study is the first to link methylsiloxane levels and social issues in the bay, providing insights into illuminating the distribution characteristics of various pollutants.

Three-Dimensional Hydrodynamic Modelling to Estimate Sediment Rate in Lamong Bay

Abstract Lamong Bay Terminal, part of Tanjung Perak Port in Surabaya, functions as a container terminal. The port in the Surabaya area causes high ship traffic activity in the waters of Lamong Bay and sediment may be carried away from rivers heading towards the sea. The sedimentation process in waters can cause problems because it can cause shallowing of the waters, so it is necessary to maintain and monitor the depth of shipping lanes to maintain the safety of sea traffic. Therefore, understanding the hydrodynamics of seawater and sediment movement in the water region is necessary for successful dredging operations and assessing the impact of silt on port areas. In this research, the approach used to determine current patterns and sediment distribution was through the application of a numerical model with three– dimensional baroclinic hydrodynamic equations. The numerical modeling study in this research uses tidal data, sediment samples, salinity, and temperature to determine current patterns and the rate of sediment distribution. This process is carried out periodically and continuously as part of the evaluation of Lamong Bay Terminal. The results can serve as a reference for dredging planning to maintain the depth of the waters at the Lamong Bay Terminal. In this study, the highest current velocity was obtained at the time of spring tide reaching 0.9 ms−1 and at the neap tide of 0.4 ms−1. The sediment distribution pattern in the waters of Lamong Bay affected the existence of the pier and the morphological conditions of the seabed. The largest siltation or sedimentation that has occurred at Lamong Bay Port is 0.055 m/month near the jetty, thus depth monitoring is needed in this area, regularly. This study supports SDG 9 by advancing resilient infrastructure solutions to manage the sedimentation process in waters.

Diversity, composition, and assembly processes of bacterial communities within per- and polyfluoroalkyl substances (PFAS)-contained urban lake sediments

Per- and polyfluoroalkyl substances (PFAS) are widespread, highly persistent, and bio-accumulative compounds that are increasingly found in the sediments of aquatic systems. Given this accumulation and concerns regarding the environmental impacts of PFAS, their influence on sedimentary bacterial communities remains inadequately studied. Here, we investigated the concentrations of 17 PFAS in sediments from six urban lakes in Nanjing, China, and assessed their effects on the diversity, composition, potential interactions, and assembly mechanisms of sedimentary bacterial communities. Sediment concentrations of PFAS ranged from 4.70 to 5.28 ng·g−1 dry weight. The high concentrations of the short-chain perfluorobutanesulfonic acid (PFBS) suggested its substitution for the long-chain perfluorooctanesulfonic acid (PFOS). As alternatives to long-chain PFAS, short-chain PFAS had similar effects on bacterial communities. The short-chain perfluoropentanoic acid (PFPeA) and the long-chain perfluorotridecanoic acid (PFTrDA) were the most important PFAS related to the ecological patterns of the co-occurrence network and may alter the composition of the sedimentary bacterial communities in the urban lakes. The Anaerolineaceae family represented as keystone bacteria within the PFAS-affected bacterial co-occurrence network. Deterministic processes (65.9 %), particularly homogeneous selection (63.2 %), were the dominant process driving bacterial community assembly. PFAS promoted the phylogenetic clustering and influenced the community dispersal capabilities to shape bacterial community assembly. This study provides a comprehensive analysis of PFAS distribution in sediments across six urban lakes in Nanjing and provides novel insights into the effects of PFAS on sedimentary bacterial communities. Further research is required to elucidate the mechanisms underlying the impacts of PFAS on microbial communities and to evaluate their broader ecological consequences.

Physicochemical Parameters, Grain Size Distribution and Mineralogical Composition of Recent Bottom Sediments and water of Qaroun Lake, Fayoum, Egypt.

Physicochemical Parameters, Grain Size Distribution and Mineralogical Composition of Recent Bottom Sediments and water of Qaroun Lake, Fayoum, Egypt.

Reservoir Regulation Changed Terrestrial Particulate Organic Carbon Transport and Burial Processes off the Yellow River Mouth

AbstractThe dynamic behavior of particulate organic carbon (POC) is crucial for understanding biogeochemical carbon cycling in coastal and oceanic environments. However, intense watershed human activities have significantly altered the POC transport and burial in the estuary‐coast continuum. Here, we developed a novel parameterization scheme that incorporates grain‐size constraints to investigate the dispersal and accumulation processes of POC off the Yellow River mouth during the water‐sediment regulation scheme (WSRS) using a three‐dimensional hydrodynamic model (FVCOM). The result shows that the model successfully captures the offshore transport and hydrodynamic sorting of POC, which leads to a progressive increase in POC content with offshore dispersion and significant variations in POC and sediment deposition across different isobaths. Rapid fluctuations in river discharge and sediment composition during WSRS stages result in noticeable differences in sedimentation patterns for sediment and POC. At the Water‐regulation stage, distinct differences are observed in the distribution of riverine POC and sediment across various isobaths. In contrast, during the Sediment‐regulation stage, these differences are significantly reduced due to the finer riverine sediment. Compared to the sediment‐regulation, the Water‐regulation plays a crucial role in enhancing the effective burial of POC. Coarse‐grained sediment can form an armored layer that protects OC from disturbance. Additionally, increased runoff during this stage promotes the offshore transport of POC to a less energetic environment (>10 m in depth). This study provides valuable insights into POC dynamics in high‐turbidity estuarine and coastal environments. It underscores the importance of employing comprehensive modeling approaches to elucidate these complex processes.

Particle size and settling velocity of bed and suspended sediments for mud-sand beds

The particle size and the settling velocity of sediments are key parameters in sediment transport studies. However, it remains surprisingly difficult to determine particle size and settling velocity distribution of fine-grained sediments (mud-sand). A large range of methodologies exist to measure either the particle size distribution or to measure the settling velocity. An important influential parameter is the shape of fine-grained sediments, with clay minerals being shaped as plates rather than as spheres. Furthermore, the settling velocity of fine particles is influenced by turbulent shear and flocculation processes. Sometimes, the sediment samples are pre-treated (destroying inter-particle bonds) to measure the primary particle sizes involved while in other cases samples are not pre-treated in order to represent the effect of flocs. As a result, a large uncertainty exists in the way particle size and settling velocity should be measured. A range of methodologies (sedimentation, video camera, and laser-diffraction) to measure the settling velocity and particle size distribution in the field and in the laboratory is used and compared. The labour-intensive sedimentation methods measure a particle size distribution which can be used for sedimentation studies. The particle size distribution measured by the most commonly applied laser diffraction method is representative of the plate diameter of the clay particles, but the corresponding settling velocity is not correct. This difference can be explained by the shape of the clay particles through a derivation of the settling velocity of non-spherical particles resulting in a simple relationship to convert the particle size measured by laser diffraction to a representative particle size to be used in sedimentation studies. A comparison of the settling velocity measured by an in situ settling method and by a video camera method shows good agreement for high concentrations (> 2000 mg/L) but deviating results for low concentrations (< 500 mg/L).

Comprehend Analysis of Surface and Subsurface Sediment Distribution Using Underwater Acoustic Instruments

Abstract Ports play an important role in shipping and transporting while its fundamental challenge is sedimentation that occurs continuously at a location. A management system is required to respond to this siltation problem by dredging the underwater sediments parallel with Sustainable Development Goal 11 about sustainable cities and communities. Therefore, analyzing the area’s sediment types and distribution is necessary, especially using acoustic instruments. In this research, the dredging plan shows the relative depth distribution is around 4 to 18 meters with deep sloping topography on the north side. Furthermore, the overall result of the backscatter value of the multibeam echosounder ranges from −45.86 dB to −55.73 dB. According to the Angular Response Analysis, the sediment type of the seabed surface is clay with depths ranging up to 5.40 meters. The result of the sub-bottom profiler processing discovers step or bowl-like features where the curvature seems to have an unequal height. It considers the difference in sediment height around the area while the intensity is relatively low. Through acoustic processing analysis, it informs that the total area of 643872 m2 needs to be dredged with an estimated dredging volume of around 2181105 m3 both in surface and subsurface areas. The qualitative analysis of Multibeam Echosounder, and Sub Bottom Profiler data shows that the acoustic instrument’s products are accurate with validation data in the field.

Bering Strait gateway currents and their implications for sediment distribution, shelf conceptual models and economic potential

This paper addresses a gap in our knowledge about strong geostrophic current control of epicontinental shelf deposits. The northward current that accelerates towards the Bering Strait gateway affects sediment distribution in the northern Bering Sea leading to the Strait, in the Strait and in the Chukchi Sea where currents slack. Leeside sand bodies develop when the northward geostrophic current shears and accelerates against topographic projections into the current. When currents slack downstream, leeside sand bodies deposit. Yearly 1 m and decadal catastrophic up to 5 m storm surges resuspend the Yukon sediment. Most of this sediment is then entrained by strong northward currents and transported up to 1000 km north, bypassing Chirikov Basin and the Bering Strait gateway, to deposit in the Chukchi Sea. Northern Bering Sea depositional patterns reinforce evidence that epicontinental shelf sedimentary sequences are different from more regular proximal to distal offshore sequences on marginal shelves. Compared with marginal shelves, strong currents, Coriolis force and topographic constrictions result in sediment bodies detached from the shoreline and large areas of sediment bypass on epicontinental shelves. The Bering Sea currents prevent Holocene sediment from covering both relict gravel with the world's largest offshore gold deposits and large areas of surficial sediment with heavy-mineral concentrations &gt;16% that contain scarce rare earth metals.

Reactivity and potential mobility of metals in human-impacted harbor sediments (port of Rotterdam, the Netherlands)

Abstract Purpose Vast amounts of harbor sediments are being dredged every year globally. These sediments are often enriched in potentially toxic elements (PTEs), the abundance and potential mobility of which are important for sustainable harbor management practices. In this study, we investigate metal (especially PTE) distribution, abundance, and reactivity in sediments along a salinity gradient in the waterways of Europe’s largest harbor, the Port of Rotterdam. Materials and methods Bulk surface sediments were analyzed for general physicochemical properties (e.g. grain size, total metal concentration). From selected locations covering the local salinity gradient, sediments were subjected to three independent chemical extractions to determine chemically reactive metal pools. Additionally, metal retention in two contrasting sediments (high versus low salinity) was further explored using pH-dependent leaching experiments in combination with a geochemical model. Results and discussion The majority of the investigated sediments consisted predominantly of silt and were rich in organic matter. Concentrations of Cd, Pb, Zn, Cu decreased with increasing salinity. Concentrations of Al, Fe, V correlated negatively with grain size, because these geogenic metals are enriched in fine-grained silicates. Results from the chemical metal extractions showed clear differences in the reactivity and mobility potential of metals, that could be grouped into four clusters. The combined chemical and modeling results indicate that sorption onto metal (oxyhydr)oxides and organic matter as well as precipitation of metal sulfides and carbonates control metal retention. High reactivity and mobility potential were observed for Pb, Cd, Zn, particularly at low pH. Limited spatial variability in metal chemistry along the salinity gradient indicates that the highly variable depositional conditions have little impact on metal behaviors. Conclusions Chemical extractions and pH-dependent leaching experiments revealed distinguishing metal reactivities from four clusters. Our results provide insight into metal distribution in the dynamic estuarine environment of the Port of Rotterdam and highlight the importance of understanding chemical speciation in addition to abundance for harbor sediment management.

Spatial distribution and transport characteristics of debris flow sediment using high resolution UAV images in the Ohya debris flow fan

Debris flows are significant geomorphic processes that can pose hazards to human settlements and infrastructure, making the understanding of their sediment transfer characteristics and impacts on the surrounding landscape crucial for effective land management and hazard mitigation strategies. This study investigates the distribution patterns of sandstone, vegetation, and shale classes within the Ohya debris flow fan, aiming to gain insights into the sediment characteristics, grain size variations, and vegetation cover trends along the flow path. Using a combination of field surveys and image processing we analyzed sediment characteristics and grain size variations a three study zones: upstream, transfer, and downstream. Statistical parameters such as mean, mode, skewness, and kurtosis were employed to quantify the grain size distribution and identify variations across the study zones. Results reveal distinct spatial variations in the distribution of sandstone, vegetation, and shale classes along the flow path. We observed a decrease in sandstone and vegetation cover from the upstream to the downstream sections, while the area covered by the shale class exhibited an increasing trend in the downstream direction. These findings suggest that debris flows selectively remove smaller particles downstream. The distribution of particle sizes within the sandstone class also exhibited variations, with a higher proportion of smaller pebbles downstream due to more effective removal of finer particles in the upstream zone. This study highlights the complex interplay between debris flow dynamics, sediment transport, and vegetation colonization. The findings contribute to the scientific knowledge of debris flow processes and can be used to inform land management decisions and mitigate the hazards associated with debris flows in similar environments.

Combined effect of a pretreatment and optical settings on the laser diffraction particle size distribution of soils and sediments

Combined effect of a pretreatment and optical settings on the laser diffraction particle size distribution of soils and sediments

Model Sensitivity Analysis for Coastal Morphodynamics: Investigating Sediment Parameters and Bed Composition in Delft3D

Numerical simulation of sediment transport and subsequent morphological evolution rely on accurate parameterizations of sediment characteristics. However, these data are often not available or are spatially and/or temporally limited. This study approaches the problem of limited sediment grain-size data with a series of simulations assessing model sensitivity to sediment parameters and initial bed composition configurations in Delft3D, leading to improved modeling practices. A previously validated Delft3D sediment transport and morphology model for Dauphin Island, Alabama, USA, is used as the benchmark case. A method for the generation of representative sediment grain sizes and their spatially varying distributions is presented via end-member analysis of in situ surficial sediment samples. Derived sediment classes and their spatial distributions are applied to two sensitivity case simulations with increasing bed composition complexity. First, multiple sediment classes are applied in a single fully mixed layer, regardless of sediment type. Second, multiple sediment classes are applied in a thin, fully mixed transport layer with underlayers containing only the non-cohesive sediment classes below. Simulations were carried out in a probabilistic, Delft3D MorMerge configuration to capture long-term morphology change for 10 years. We found there is sensitivity to the inclusion of additional sediment classes and sediment distribution made evident in bed level and morphology change. Inclusion of highly mobile fine sediments altered model results in each sensitivity case. The model was also found to be sensitive to initial bed composition in terms of bed level and morphology change, with notable differences between sensitivity cases on decadal timescales, indicating an armoring effect in the second sensitivity case, which used the transport and underlayer bed configuration. The results of this study offer guidance for numerical modelers concerned with sediment behavior in coastal and estuarine environments.

Grain-size distribution in suspension through open channel turbulent flow using space-fractional ADE

The main aim of the present study is to develop a mathematical formulation that can describe the grain-size distribution (GSD) of non-uniform sediments in suspension over erodible sediment beds in a wide open channel under non-equilibrium conditions. The two important characteristics of sediment particles, such as non-local mixing and the hiding-hindering effect during settling, has been considered in the current study. The traditional advection–diffusion equation (ADE) is taken in the modified form as fractional ADE which is capable of capturing non-local movement of particles unlike the traditional diffusion theory where particles jump within a restricted distance along the vertical direction over a small time interval. The equation is further modified for any kth class of non-uniform sediment and the effect of non-local movement is included in the expression of depth averaged sediment diffusivity also. The settling velocity of a particle is taken in a form that contains the effect of hiding and hindering due to the presence of non-uniform particles in the flow. The space-fractional derivative is taken in the Caputo sense where the order α of the fractional derivative varies from 1<α≤2. The non-local effect is considered in the bottom and top boundary conditions also and the governing equation with boundary and initial condition have been solved by Chebyshev collocation method along with Euler’s backward method. The temporal variation of concentration profiles for different size particles is studied by varying α and it is observed that the magnitude of concentration decreases for each size as α increases. Non-local effect on bottom concentration for different size particle is also studied and it is seen that overshooting of bottom concentration gradually decreases as α increases for a particular size. Sensitivity analysis of α on GSD at different heights also has been done. The model has been validated for GSD under equilibrium conditions with available experimental data and it is found that the model aligns well when the non-local mixing effect is taken into account. At the end, an error analysis has been conducted to confirm the accuracy of the presented model.

Applicability of reconstruction of temporal changes in 137Cs concentrations in pond water based on the vertical distribution of bottom sediments: a case in three ponds in the Fukushima evacuation zone.

Long-term changes in particulate and dissolved 137Cs concentrations in rivers and dam reservoirs have been reconstructed using 137Cs depth distributions in bottom sediments near Chornobyl and Fukushima. However, few studies have applied this method to pond water. This study tested the applicability of this reconstruction method in ponds within the Fukushima evacuation zone. Bottom sediments in ponds were collected in November 2019. Our reconstruction of a shallow closed pond disagreed with our observations. Even in ponds where the reconstruction agreed well with observations, underestimations may have occurred because the time constant for the decrease in 137Cs concentration was lower than those previously reported. We conclude that the present reconstruction method may be applied to deeper Fukushima ponds with inflow and outflow, but underestimations of initial 137Cs concentrations in water may lead to uncertainties. For realistic reconstruction, attention should be paid to pond characteristics, catchment conditions, and sediment core selection.

Correlation of Seismic Data and Sediment Cores From the Seabed in the Medieval Harbour at Avaldsnes, Norway

ABSTRACTThis interdisciplinary study demonstrates the successful integration of non‐destructive geophysical methods and sediment core analyses for mapping the seabed in the historical harbour at Avaldsnes in south‐west Norway. In the Medieval Period, this was a royal manor, with the harbour as a central hub for the Hanseatic League in the 14th to 15th centuries. The use of an Autonomous Surface Vehicle (ASV) mounted with two distinct sub‐bottom profiler (SBP) systems facilitated the acquisition of high‐resolution seismic data, providing efficient imaging of the seafloor and subsurface layers. Sequence of fifteen sediment cores allowed for the description and dating of stratigraphy and the depositional environment. In combination, these methods provided a multidimensional understanding of the distribution of subsea sediments in the harbour, while preserving most of the archaeological context. The analysis revealed organic‐rich sediments, primarily consisting of fine detritus gyttja, accumulated over the last 1700 years, trapping certain archaeological features. Deposition of the soft sediments likely commenced due to a lower relative sea level, possibly accompanied by intensified land‐use and harbour activity. The study identified several minor anomalies in the seismic data, potentially representing artefacts of archaeological importance. An anomaly of significant size might correspond to a buried shipwreck or harbour structure. By providing a comprehensive understanding of sediment dynamics and human‐environment interactions in the harbour, the research contributes to the preservation and management of an important cultural heritage site.

Relationship between stratigraphic overlap and sedimentary facies evolution of the Junggar Basin, Northwest China

The interaction between the topography of the slope zone on the edge of the basin and the distribution of sediments is crucial for accurately predicting sediment distribution, but few studies emphasize the impact of stratigraphic overlap on the spatial evolution of sedimentary facies. The tectonic movement and sedimentary environment of Hala’alat Mountain in the northwest margin of the Junggar Basin are complex, and the sedimentary model of the whole Cretaceous system is still unclear. This article uses lithology, logging, and seismic data to explain the evolution process and sedimentary model of the Cretaceous system. The significant overlap of Cretaceous strata in the research area has a significant impact on the distribution of sedimentary facies zones and the development of sedimentary systems. Furthermore, this article explores the genesis mechanism of the Cretaceous stratigraphic overlap phenomenon, clearly defines the boundary range of stratigraphic overlap, and deeply analyzes how sedimentary facies zones are distributed and their subsequent evolution trends after the formation of overlap. The results demonstrate that there are apparent stratigraphic overlap phenomena in the second member (K1q2) and the third member (K1q3) of the Cretaceous Qingshuihe Formation in this area. The lithology at the bottom of the formation is grey sand conglomerate with finer grain size in the upper part, and the sedimentary facies are transitioned from fan delta facies to shore shallow lake beach bar facies. In member 1 (K1h1), member 2 (K1h2) and member 3 (K1h3) of the Hutubi Formation, due to the gradual slope and relatively stable sedimentary environment, the distance of stratigraphic overlap becomes shorter, the stratigraphic overlap phenomenon is no longer apparent and the sedimentary facies zone does not change. The study not only reveals the intrinsic relationship between stratigraphic overlap and the distribution of sedimentary facies zones, but also deepens the understanding of the dynamic evolution laws of sedimentary systems. The study on the overlap sedimentary mechanism of the Hala’alat Mountain in the northwest margin of Junggar Basin has reference significance.

Distribution and sources of polycyclic aromatic hydrocarbons in cascade reservoir sediments: influence of anthropogenic activities and reservoir hydrology.

The construction of dams has caused disruptions to river connectivity, leading to alterations in the deposition of hydrophobic organic contaminants in reservoir sediments. Further investigation is warranted to explore the impact of cascade reservoirs with differing hydrological characteristics on polycyclic aromatic hydrocarbons (PAHs) distribution in sediment. This study examines the presence of 30PAHs in the sediments collected from six cascade reservoirs situated in the Wujiang River basin during January and July 2017. The results showed that Σ30PAHs ranged from 455-3000ng/g dw (mean 1030ng/g dw). Anthropogenic activities and reservoir hydrology determined the distribution trend of PAHs in sediments, with an overall increase from upstream to midstream and then a decrease downstream. The PAH levels were highly linked to the secondary industry (P < 0.05). This was further supported by the relationship between the PAH emissions from coal combustion and traffic sources analyzed by the positive matrix factorization model and economic parameters in the wet season (P < 0.01). At the same time, reservoir age (RA) showed a positive correlation with PAH concentrations (P < 0.05), while hydraulic retention time (HRT) exhibited a negative correlation with PAH levels (P = 0.03). The relationship between total organic carbon (TOC) and PAHs in stream sediments worldwide was nonlinear (P < 0.01), with PAH concentrations initially rising and then falling as TOC levels increased. Concerns regarding carcinogenic risk were raised due to contributions from coal and vehicular sources, with the risk increasing with RA.