Sediment Core Samples Research Articles

Distribution and Preservation of Total Organic Carbon and Total Inorganic Carbon in Pipahai Lake over the Past Century

Carbon burial patterns in lakes and their dynamic changes significantly impact terrestrial carbon sink fluxes and global carbon budgets. In this study, multi-indicator analysis of sediment core samples (P1, P2, and P3) from Pipahai Lake was conducted. Integrating the chronological sequences of 210Pb and 137Cs, we identified the historical changes and spatial characteristics of total organic carbon (TOC) and inorganic carbon (TIC) burial in Pipahai Lake since 1884. The results show that the TOC content was higher than that of the TIC. They exhibited an increasing trend with decreasing depth. Linear regression results indicated that the variation of TOC is less directly affected by precipitation (R = 0.39) and temperature (R = 0.58), while temperature may have a greater impact on TOC. From 1884 to 1995, nutrients were not the primary factor influencing changes in TOC. The synchronous variation in TIC and TOC contents reflects a higher contribution of external inputs to carbon burial in the Pipahai Lake basin. After 1996, nutrients may have begun to affect variations in TOC. The TOC primarily originates from distal aeolian transport or autochthonous sources, though human activity has played a role in its evolution. The TIC content is controlled by the TOC content and autochthonous sources. This study will contribute to the understanding of the carbon cycling dynamics and their influencing mechanisms in a high-altitude lake ecosystem.

Untangling the coupling effect of water quality and quantity on lake algal blooms in Lake Hulun from a dual perspective of remote sensing and sediment cores

Algal blooms and sediment diatoms are crucial indicators of lake water ecology, influenced by water quantity and quality. However, the coupled effects of water quality and quantity changes on algal blooms are still unclear, especially for lakes in cold and arid regions. This study assessed the long-term variations in algal blooms in Hulun Lake using a novel approach combining remote sensing and sediment core samples for diatom analysis. Two mutation points from the structural change test were identified in approximately 2000 and 2010 for algal bloom area (MBE) and sediment diatom richness, indicating asynchronous algal blooms. A structural equation model (SEM) demonstrated that water level (WL) changes were the dominant influencing factor, co-driving the variations in algal blooms and sediment diatoms in conjunction with total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD). The results revealed nonlinear relationships between the lake WL, TN, Chla, and COD. The water level of 543 m emerged as a critical threshold affecting the relationship between water quality and quantity. Distinct differences in this relationship were observed when water levels were above or below this threshold. These variations became particularly pronounced during periods of high and low water levels. The results provide novel insights into the dynamics of algal blooms and can further support lake ecosystem conservation and management.

Microbial communities and metagenomes in methane-rich deep coastal sediments

Coastal sediments are rich in embedded recalcitrant organic carbons that are biotransformed into methane. In this study, gas composition (carbon dioxide, methane and nitrogen) and chemical indicators (total nitrogen, total carbon, and total sulfate) were examined in five deep sediment cores (up to 130 m in length) obtained from the Hangzhou Bay. The V3-V4 region of the 16S rRNA gene amplicons was amplified and sequenced for the prokaryotic community analysis. The species composition, along with the physicochemical factors of the sediments, revealed a strong correlation with methane content in one of the sediment cores. We then obtained metagenomes of the two sediment samples selected for their high methane content and enrichment of methanogenic Bathyarchaeota with phylogenetic evidence. A total of 27 draft genomes were retrieved through metagenomic binning methodologies and were classified into Bathyarchaeota, Asgard archaea, Planctomycetes, and other microbial groups. The data provided are valuable for understanding the relationship between methane generation and microbial community composition in deep sediment core samples from coastal to marine environments.

A sedimentary DNA perspective about the influence of environmental and food‐web changes on the microbial eukaryotic community of Lake Biwa

Abstract The impacts of environmental change on Lake Biwa have been explored for decades, with water monitoring and palaeolimnological studies revealing how environmental forcing, including climate warming, eutrophication, water level manipulation and human manipulation of fish populations, has influenced the food web of Lake Biwa. However, these studies have rarely accounted for microbial food‐web components. This knowledge gap is mostly due to the lack of time series spanning more than a couple of decades, coupled with the high taxonomical expertise required to identify organisms belonging to very diverse groups. The use of a sedimentary DNA approach allows for the reconstruction of past changes in the diversity, composition and structure of the microbial eukaryotic community of aquatic systems. The application of 18S metabarcoding has been proven successful to describe the response of unicellular eukaryotes (protists) and aquatic fungi in lake ecosystems, encompassing a large taxonomic and functional diversity such as phototrophs, heterotrophs and mixotrophs. We applied 18S metabarcoding to 31 sediment core samples from Lake Biwa, spanning the past 100 years and explored the response of microbial eukaryotic communities to changes in multiple environmental stressors, including nutrient levels, lake water level, climate, as well as fish and zooplankton biomass for the period 1973–2010. We found that the manipulation of the water level and changes in fish community composition were the primary factors impacting (indirectly) the structure of the lake microbial eukaryotic community with minor, but significant, effects of climate warming and phosphorus levels. Co‐occurrence network analysis highlighted the potential food web impacts on the microbial eukaryotic community, suggesting that organisms from this compartment were impacted by both bottom‐up and top‐down processes.

Sediment microbial diversity, functional potentials, and antibiotic resistance pattern: a case study of Cochin Estuary core sediment.

Marine sediments are an important part of the marine environment and the world's greatest organic carbon source. Sediment microorganisms are important regulators of major geochemical and eco-environmental processes in marine environments, especially nutrient dynamics and biogeochemical cycles. Despite their importance, core marine microorganisms are virtually unknown due to a lack of consensus on how to identify them. Most core microbiotas have been characterized thus far based on species abundance and occurrence. The combined effects of habitat and depth on benthic bacterial communities and ecological functions were studied using "Next-Generation sequencing (NGS) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) predictive functional profiling" at the surface (0.2cm) and bottom depth (250cm) in a sediment core sample from Cochin Estuary, Kerala, India. The results showed that bacterial diversity and richness were significantly higher in the surface sediment sample with the most abundant phyla being Proteobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes. The major metabolic functions were metabolism, followed by environmental information processing and genetic information processing. Antibiotic resistance genes between the surface and bottom samples help to understand the resistance pattern among multidrug resistance is the most prominent one. Among viruses, Siphoviridae is the dominant family, followed by Myoviridae. In the case of Archea, Crenarchaeota is dominant, whereas among eukaryotes phyla Streptophyta and Chordata were dominant in the surface and the bottom samples respectively.

Current state, sources, and potential risk of heavy metals in sediments of typical inner lakes in the Dongting Lake Area

The region has been increasingly experiencing environmental issues related to heavy metals (HMs) due to human activities. However, the contamination levels of HMs (Cr, Ni, Cu, Zn, As, Cd, and Pb) in various inner lakes in the Dongting Lake area remain unclear. In this study, surface sediment samples from 9 inner lakes and sediment core samples from 3 typical inner lakes were collected to evaluate the spatial distribution, contamination status, environmental and ecological risks, and possible sources of these HMs. The results showed that all HMs, except Zn, exceeded background values, with particularly high levels observed in aquaculture lakes compared to other lakes. Vertical profiles of HMs from 3 lakes show that the various types of lakes in the study area have different pollution histories. Additionally, results from Sediment quality guidelines (SQGs), Contamination factor (CF), Geo-accumulation index method (Igeo), and Hakanson potential ecological risk index (PERI) indicated that As, Cd, and Pb are the primary pollutants. The multivariate analysis concluded that Ni, Cu, Zn, As, Cd, and Pb had anthropogenic sources, primarily from agricultural, fisheries, industrial, and transportation activities, while Cr was influenced by natural factors. The results of this study enhance our understanding of sedimentary metal content in inner lakes and emphasize the importance of controlling HMs content in these lakes. This information is crucial for developing effective lake management and pollution control strategies.

Accumulation Patterns of Polychlorinated Dibenzo-p-Dioxins, Dibenzofurans and Dioxin-like Polychlorinated Biphenyls in Sediments of the South-Eastern Baltic Sea

The current research paper presents the results of the first regional assessment of sediment contamination by dioxins (polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs)) in the south-eastern part of the Baltic Sea (Lithuanian and Polish marine areas) during the periods of 2014 and 2019–2020. In total, 143 surface and core sediment samples were taken of existing offshore dredged-soil-disposal sites in the area of the former shipyard in the Port of Gdynia (Poland), as well as in a profile from the nearshore to the deeps of the Gdansk basin, following the natural pattern of sediment migration in the region. The obtained results indicated wide variation in both the total content of the investigated compounds as well as the profiles of congeners, indicating the likely sources of their origin. Based on the obtained concentration characteristic profiles of the congeners, we determined the amount of dioxins and the likely sources of their origin in the Gdansk Basin. The profiles showed elevated contents of octa- and hepta-chlorodibenzodioxins (OCDD and HpCDD) in the sediments, while the fractions of most other toxic congeners were considerably lower. The domination of OCDF in the spectrum of the studied PCDFs suggests the possible contribution of industrial processes. The obtained results have filled the gaps in our knowledge while providing a perfect background for more detailed discussions concerning the accumulation of dioxins in surface sediments from the south-eastern part of the Baltic Sea.

Continuous deposition of pre-aged organic carbon in the southern Mariana Trench since the last deglaciation

One of the key challenges in understanding the role of hadal trenches in the marine organic carbon (OC) cycle is the need to distinguish OC sources, assess accumulation rates, and identify controlling processes. To address this, sediment core samples from the southern Mariana Trench were analyzed for their contents and carbon isotopes (13C and 14C) of both total OC (TOC) and saturated long-chain fatty acid (n-LCFA). Our findings indicate that sedimentary OC in the southern Mariana Trench is primarily derived from marine sources, as indicated by TOC-δ13C values ranging from −19.9‰ to −17.0‰ and the ratios of TOC to total nitrogen (TOC/TN) of 5.5–8.4. The 14C ages of TOC and n-LCFA ranged from 7159 to 22,662 yr and 8713 to 22,819 yr, respectively, with both showing gradual down-core increasing trends. This allows for a conservative estimation of sedimentation rate of 17.5–18.7 cm kyr−1 in the southern Mariana Trench, leading to a sedimentary OC accumulation rate of 529–942 g C m−2 kyr−1, which is 1–2 orders of magnitude higher than that observed in the abyssal plain. We propose that the continuous lateral downslope transport played a significant role in focusing pre-aged OC into the southern Mariana Trench. Therefore, hadal trenches are likely to accumulate substantial amounts of sedimentary OC in the deep ocean.

A Microplastic Pollution Hotspot: Elevated Levels in Sediments from the San Francisco Bay Area

San Francisco Bay’s sediment is currently monitored for a variety of contaminants; however, data regarding the microplastics (MPs) in the area are still scarce. MPs’ occurrence in sediment samples has gained recognition as a reservoir for MP accumulation. Moreover, Bay sediment is also an important matrix for monitoring because sediment tends to accumulate certain contaminants and act as a source of contaminants in the Bay food web. This study analyzed MPs ranging from 25 µm to 5 mm in surface sediment grab samples (n = 8) and two sediment core samples (n = 2 cores analyzed with 11 samples from different depths). Our findings provide an evaluation of MP levels in different regions of the bay. The MP levels detected in Bay surface grab samples ranged from 2.1 to 11.9 MPs/g dry weight (n = 8), with a mean value of 6.2 MPs/g. The most abundant morphology was fibers, followed by fragments and films.

Spatiotemporal and multi-isotope assessment of metal sedimentation in the Great Lakes

This study investigates spatiotemporal dynamics in metal sedimentation in the North American Great Lakes and their underlying biogeochemical controls. Bulk geochemical and isotope analyses of n = 72 surface and core sediment samples show that metal (Cu, Zn, Pb) concentrations and their isotopic compositions vary spatially across oligotrophic to mesotrophic settings, with intra-lake heterogeneity being similar or higher than inter-lake (basin-scale) variability. Concentrations of Cu, Zn, and Pb in sediments from Lake Huron and Lake Erie vary from 5 to 73 mg/kg, 18–580 mg/kg, and 5–168 mg/kg, respectively, but metal enrichment factors were small (<2) across the surface- and core sediments. The isotopic signatures of surface sediment Cu (δ65Cu between −1.19‰ and +0.96‰), Zn (δ66Zn between −0.09‰ and +0.41‰) and Pb (206/207Pb from 1.200 to 1.263) indicate predominantly lithogenic metal sourcing. In addition, temporal trends in sediment cores from Lake Huron and Lake Erie show uniform metal concentrations, minor enrichment, and Zn and Pb isotopic signatures suggestive of negligible in-lake biogeochemical fractionation. In contrast, Cu isotopic signatures and correlation to chlorophyll and macronutrient levels suggest more differentiation from source variability and/or redox-dependent fractionation, likely related to biological scavenging. Our results are used to derive baseline metal sedimentation fluxes and will help optimize water quality management and strategies for reducing metal loads and enrichment in the Great Lakes and beyond.

Geochemistry of Arsenic and Salinity-Contaminated Groundwater and Mineralogy of Sediments in the Coastal Aquifers of Southwest Bangladesh

This study aimed to develop a geochemical database by thoroughly analyzing groundwater and sediments from coastal aquifers of southwest Bangladesh. Moreover, we investigated the source of sediment deposition and the mechanisms behind the presence of arsenic and salinity in groundwater. The seasonal distribution patterns of arsenic among the shallow and deep coastal aquifers were found to be 45.12 µg/l and 20.65 µg/l during dry and wet seasons, respectively. Moreover, the groundwater salinity distribution ranged from 3262.88 mg/l to 1930.88 mg/l during the dry and wet seasons. Cored sediment samples showed fine to medium sands of 92%, with silt and clay particles. The petrographic study of authigenic and heavy minerals revealed that the mineral grains were subangular to angular, indicating their textural immaturity of coastal sediments. The reactivity of goethite (FeOOH) and siderite (FeCO3) minerals suggests that the aquifers were subjected to slightly oxidized to moderately reducing conditions, with ORP values ranging from +50.40 mv to −149.5 mv. Such redox conditions could potentially result in the enrichment and mobility of arsenic in the groundwater. Although arsenic concentrations in deep aquifers are relatively low, higher salinity values are found in both shallow and intermediate coastal aquifers.

Pockmarks Offshore Big Sur, California Provide Evidence for Recurrent, Regional, and Unconfined Sediment Gravity Flows

AbstractRecent surface ship multibeam surveys of the Sur Pockmark Field, offshore Central California, reveal &gt;5,000 pockmarks in an area that is slated to host a wind farm, between 500‐ and 1,500‐m water depth. Extensive fieldwork was conducted to characterize the seafloor environment and its recent geologic history, including visual observations with remotely operated vehicles, sediment core sampling, and high‐resolution, near‐bottom Chirp and multibeam surveys collected with autonomous underwater vehicles to capture the morphology and stratigraphy of the pockmarks. No evidence of high methane concentrations in sediments, chemosynthetic biological communities, or methane‐derived diagenetic byproducts was found. Chirp data and sediment cores showed alternating layers of slowly accumulating hemipelagic drapes interrupted by more reflective turbidite horizons that extend throughout the pockmark field and beyond. Chirp data showed multiple episodes of lateral migration over time in some of the pockmarks in association with erosion and infilling events. Laterally continuous turbidite horizons that overlay erosional surfaces indicated that pockmark migration occurred synchronously in multiple pockmarks separated by tens of kilometers. These shifts are presumed to be the result of asymmetrical erosion of the pockmark flanks caused by passing sediment gravity flows. While some pockmarks occur in chains, most are not clustered or randomly spaced but are regularly dispersed within the pockmark field. We hypothesize that intermittent, unconfined sediment gravity flows occurring over at least the last 280,000 years are the source of the regionally continuous turbidite deposits and the mechanism that maintained the regularly dispersed pockmarks.

Microplastic in Dredged Sediments: From Databases to Strategic Responses.

Microplastics (MPs) accumulate in sediments, yet guidelines for evaluating MP risks in dredged sediments are lacking. The objective of this study was to review existing literature on MPs in sediments to improve fundamental knowledge of MP exposures and develop a publicly available database of MPs in sediments. Twelve percent of the reviewed papers (nine studies) included sediment core samples with MP concentrations generally decreasing with depth, peaking in the top 15cm. The remaining papers evaluated surficial grab samples (0 to 15cm depth) from various water bodies with MPs detected in almost every sample. Median MP concentrations (items/kg dry sediment) increased in this order: lakes and reservoirs (184), estuarine (263), Great Lakes nearshore areas and tributaries (290), riverine (410), nearshore marine areas (487), dredge activities (817), and harbors (948). Dredging of recurrent shoaling sediments could be expected to contain MPs at various depths with concentrations influenced by the time elapsed since the last dredging event. These results offer key insights into the presence and variability of MPs in dredged sediments, informing environmental monitoring and risk assessment strategies.

Dynamic Climate Influence on Magnesium Isotope Variation in Saline Lacustrine Dolomite: A Case Study of the Qianjiang Formation, Jianghan Basin

The investigation of magnesium (Mg) isotopes in dolomite has mainly focused on marine dolomite environments, leaving a significant gap in the understanding of their dynamics within lacustrine settings, especially in saline lake basins. In this study, a total of 16 sediment core samples from Well BX-7 in the Qianjiang Depression were sequentially selected for scanning electron microscope observation, whole-rock analysis for major and minor elements, and isotopic measurements including δ18Ocarb, δ13Ccarb, δ26Mgdol, and δ26MgSi. In addition, two intact cores were subjected to detailed analysis on the centimeter scale. Sedimentation models were established to elucidate dolomite formation under contrasting climatic conditions, specifically humid climates with a significant riverine Mg input versus relatively dry conditions with a lower Mg input. Furthermore, a quantitative model was developed to assess the magnesium flux and isotopic mass balance within lacustrine systems, simulating the magnesium isotope variations in lake water under different climatic scenarios. The dolomite sample data at a smaller scale (sampling interval ≈ 3~5 mm) demonstrate a consistent trend with the established model, providing additional confirmation of its reliability. Dolomite precipitated under humid climatic conditions exhibits a lower and relatively stable δ26Mgdol, lower δ18O, and higher CIA, indicating higher river inputs and relatively stable Mg isotope values of lake water controlled by river input. Nevertheless, dolomite formed under relatively dry climatic conditions shows a relatively high δ26Mgdol, higher δ18O, and lower CIA, suggesting reduced river inputs and weathering intensity, as well as relatively high magnesium isotope values of the lake water controlled by dolomite precipitation. This study contributes to the understanding of magnesium isotopes in lacustrine dolomite systems.

The Distribution Characteristics and Risk Assessments of Organochlorine Pesticides in the Sediments of Sanshan Lake, China

ABSTRACT Situated in the middle reaches of the Yangtze River, Sanshan Lake represents a typical rural-urban junction lake. In May 2019, sediment core samples were gathered from five distinct sites within the lake to assess contamination levels and potential health hazards stemming from organochlorine pesticides (OCPs). The OCPs scrutinized included p,p’-DDE, α-HCH, γ-HCH, β-HCH, and δ-HCH, with concentrations of ∑DDTs and ∑HCHs ranging from 0.03 to 1.49 mg/kg and from 0.03 to 1.42 mg/kg, respectively. Average DDT and HCH residues stood at 0.04 ± 0.03 and 0.51 ± 0.41 mg/kg, respectively. This study unveiled substantial OCP contamination in Sanshan Lake, notably with remarkably elevated HCH residue levels compared to other analyzed compounds. The predominant OCP detected was β-HCH, prevalent across all samples. Moreover, the average HCH residue concentrations were an order of magnitude higher than those found in soils of the United States and Italy. At some sampling points, DDT residue levels surpassed both the ecological screening benchmark for soil DDT established by the U.S. Environmental Protection Agency (0.0025 mg/kg) and China’s primary standard as per soil environmental quality regulations (GB15618–2008, 0.05 mg/kg). Source analysis indicated that historical agricultural practices primarily contributed to DDT contamination, while technical blends accounted for HCH pollution. Carcinogenic risk assessments conducted on HCH exposure through ingestion, inhalation, and dermal contact revealed higher non-carcinogenic risks for children, with α-HCH posing the most significant carcinogenic risk among the various homologues studied. Conversely, the associated carcinogenic and non-carcinogenic risks linked with DDT residue exposure were minimal or negligible.

Source apportionment of polychlorinated biphenyls in the sediment of the Newtown Creek superfund site

Polychlorinated biphenyls (PCBs) are a primary contaminant of potential concern at the Newtown Creek superfund site. Measurements of PCBs in hundreds of samples of sediment (surface and cores) within Newtown Creek and at nearby reference locations were obtained from the Remedial Investigation (RI) databases. This data set was analyzed using Positive Matrix Factorization (PMF). A weight-of-evidence approach was used to attribute the PMF-generated fingerprints to sources. The PMF analysis generated eight factors (fingerprints or sources) that represent primary sources, such as Aroclors, as well as secondary sources, including the East River and Combined Sewer Outfalls (CSOs). In addition to the high-production volume Aroclors (1016/1242, 1248, 1254, and 1260), some less-widely used Aroclors (1232 and 1268) were found in Newtown Creek sediment. Aroclor 1268 is disproportionately abundant in the deepest sediments, while PCBs likely from CSOs are relatively more abundant in surface sediment.

Baltic Sea shipwrecks as a source of hazardous pollution

Background Shipwrecks on the Baltic Sea seabed pose a serious threat to the marine environment. Fuel, ammunition and chemicals in their holds can enter the ecosystem at any time, causing an ecological disaster. It is known that oil spills from ship accidents can affect life and health of different species of animals, both immediately after catastrophe and for many years thereafter. This article discusses the negative impact of shipwrecks on the ecological status of the Baltic Sea and presents the contamination status of bottom sediment core samples taken in the vicinity of shipwrecks located in the South Baltic, i.e., S/s Stuttgart, t/s Franken, S/T Burgmeister Petersen and m/s Sleipner. It is based on the results of research carried out by the Maritime Institute between 2011 and 2016. Methods Core samples were taken by a VKG-2 vibrating probe and analysed towards content of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), total petroleum hydrocarbons (TPHs) and total organic carbon (TOC). Seven PAHs and Seven PCBs were determined using solid phase extraction (SPE) technique followed by gas chromatography-mass spectrometry (GC-MS) detection. In order to determine the concentration of TPH, the SPE technique was applied followed by gas chromatography with flame ionisation detector (GC-FID) analysis. TOC content was established by TOC analyser using infrared detection. Results Samples taken in the vicinity of the S/s Stuttgart shipwreck have shown the highest concentrations of all analysed parameters compared to the examined wrecks and significantly differed from the results typical for these areas. This studies have shown that the S/s Stuttgart shipwreck poses a serious threat to the marine environment of Baltic Sea and it is necessary to continue studies in this area and to perform a wider range of analysis.

Fibre optic sensing technology for field assessment of thermal conductivity of aquatic sediments

PurposeThis study explores the in situ variability of sediment thermal conductivity (K) in a pond, integrating field-deployed fibre optic sensing with laboratory analyses of sediment properties to enhance our understanding and management of aquatic systems.Materials and methodsA 20-m cable setup, consisting of a fibre optic cable (FOC) and a heating tape, was buried at two depths within a channel-shaped section of a pond. Induced temperatures along the FOC were recorded during several heating and cooling periods using distributed temperature sensing (DTS). Thermal conductivity (K) was estimated at five locations along the FOC during the heating periods using the heat conduction theory for an infinite line source. Sediment core samples collected from these locations were analyzed to determine dry bulk density (DBD), organic matter content (OM), and particle size distribution (PSD), exploring their effects on K variability.ResultsAnalysis of core samples identified three distinct layers, each with varying PSD, OM, and DBD. The study revealed substantial spatial differences in the thermal conductivity of sediments, even over very short distances along the FOC, attributed to variations in sediment properties. Through a combination of field and laboratory results, we developed quadratic regression models (R2 > 0.9) to characterize the influence of DBD and OM on K. These models enabled detailed vertical and horizontal characterization of K within specific sediment contexts.ConclusionThe study demonstrates the effectiveness of active DTS in detecting in-situ variations in K, emphasizing the impact of OM and DBD on temperature propagation. This study highlights the necessity of considering sediment property variability in modelling heat transfer for accurate water resource management and environmental assessments.

Temporal evolution of plastic additive contents over the last decades in two major European rivers (Rhone and Rhine) from sediment cores analyses

Although global plastic distribution is at the heart of 21st century environmental concerns, little information is available concerning how organic plastic additives contaminate freshwater sediments, which are often subject to strong anthropogenic pressure. Here, sediment core samples were collected in the Rhone and the Rhine watersheds (France), dated using 137Cs and 210Pbxs methods and analysed for nine phthalates (PAEs) and seven organophosphate esters (OPEs). The distribution of these organic contaminants was used to establish a chronological archive of plastic additive pollution from 1860 (Rhine) and 1930 (Rhone) until today. Sediment grain size and parameters related to organic matter (OM) were also measured as potential factors that may affect the temporal distribution of OPEs and PAEs in sediments. Our results show that OPE and PAE levels increased continuously in Rhone and Rhine sediments since the first records. In both rivers, ∑PAEs levels (from 9.1 ± 1.7 to 487.3 ± 27.0 ng g−1 dry weight (dw) ± standard deviation and from 4.6 ± 1.3 to 65.2 ± 11.2 ng g−1 dw, for the Rhine and the Rhone rivers, respectively) were higher than ∑OPEs levels (from 0.1 ± 0.1 to 79.1 ± 13.7 ng g−1 dw and from 0.6 ± 0.1 to 17.8 ± 2.3 ng g−1 dw, for Rhine and Rhone rivers, respectively). In both rivers, di(2-ethylhexyl) phthalate (DEHP) was the most abundant PAE, followed by diisobutyl phthalate (DiBP), while tris (2-chloroisopropyl) phosphate (TCPP) was the most abundant OPE. No relationship was found between granulometry and additives concentrations, while organic matter helps explain the vertical distribution of PAEs and OPEs in the sediment cores. This study thus establishes a temporal trajectory of PAEs and OPEs contents over the last decades, leading to a better understanding of historical pollution in these two Western European rivers.

The first deep-sea ctenostome bryozoan from the Indian Ocean: Aethozoon flavum sp. nov.

Aethozoid ctenostome bryozoans are an unusual, small group of solitary ctenostome bryozoans, occurring almost exclusively in deep-sea habitats. Currently, there are only five species belonging to four, still insufficiently known genera, which have been reported from the Atlantic and Pacific Oceans. Recent examination of sediment core samples from an active volcanic area near Mayotte revealed a high abundance of aethozoids, recorded for the first time in the Indian Ocean. A comparative approach identified the specimens as belonging to a new species, Aethozoon flavum sp. nov. There are particular characters diagnostic of this new species, such as basally oriented duplicature bands, a highly denticulate proximal vestibular wall, and a highly elongated anal tube terminating in an almost vestibular anus. This species is the first ctenostome observed at depths of over 3.000 m in the Indian Ocean. Morphological characters are compared among all aethozoids, but still require more detailed analyses in most species. Aethozoids appear to be globally distributed and often occur in high numbers, which indicates that additional efforts will increase their distribution and species range. Ultimately, additional studies will be able to show the ecological importance of these bryozoans and molecular studies should reveal more about their diversity and phylogenetic affinities.