Sediment Reference Research Articles

Distribution and in situ bioaccumulation test of radioecologically relevant metals in boreal freshwater sediments

Sediments act as important sinks for metals and their radionuclides in aquatic environments and play a crucial role in their transfer and uptake to aquatic organisms. Traditional radioecological models use radionuclide concentrations in water to predict concentrations in aquatic organisms. In this study, we investigated the distribution of radioecologically important metals (Ba, Co, Ni, Sr, U) among sediment, porewater and hypolimnion over seasons. We also studied the uptake of these metals to benthic organisms and importance of sediment as an uptake source by conducting a 28-day in situ bioaccumulation experiment with oligochaete worms (Lumbriculus variegatus). The studied metals were chosen based on common occurrence of their radioactive isotopes in nuclear fuel cycle. Measurements of total elemental concentration were used as proxies to study the behavior of specific radionuclides. Sediment and water samples were collected from two small lakes connected to a former uranium mine in Eastern Finland, and from a nearby reference lake connected to a different drainage area. Environmental characteristics and concentrations measured from sediment, porewater and overlying water indicated only minor changes between seasons. Measured metals were highly associated with sediment particles, rather than porewater or hypolimnion. Both the distribution of metals and in situ experiment indicated the importance of sediment as the main source of bioaccumulation. Significant differences in Ba, Ni and U concentrations between treatments containing contaminated sediment and reference sediment were noted, regardless of water concentrations. Additionally, as U contaminated lakes lacked seasonal overturn during our monitoring period, metal distribution and environmental conditions remained unchanged in deeper parts of those lakes. Lastly, the results of this in situ bioaccumulation experiment are in line with the findings of our previous laboratory study using sediments from these same lakes.

Biotransformations of arsenic in marine sediments across marginal slope to hadal zone

Arsenic compounds are accumulating in deep ocean, but their ecological impacts on deep-sea ecosystem remain elusive. We studied 32 sediment cores (101 layers for metagenomes, along with 41 global reference sediment metagenomes) collected from the South China Sea and the Mariana Trench (MT), characterized with high arsenic accumulation in MT. In these metagenomes we revealed a significantly positive correlation between relative abundance of arsenite methyltransferase gene (arsM) and sampling depth, which suggests that arsenic methylation is the most prevalent arsenic biotransformation process in the deep sea. Lower relative abundance of arsenic efflux gene, compared with arsM, indicates that microbes in deep-sea sediments were prone to methylate arsenite and retain it rather than efflux it. Phylogenetic analysis identified seven clades of ArsM proteins, including two new clades derived primarily from deep-sea microorganisms. Five metagenome-assembled genomes containing aioA for arsenite oxidation also harbor carbon fixation genes in the deep-sea sediment layers, suggesting previously unnoticed contribution of arsenite-oxidizing autotrophic bacteria to the carbon cycle. Therefore, deep-sea microorganisms adopt different detoxification and transformation strategies in response to arsenic compounds, which renews our understanding of arsenic in their ecological impacts and potential contribution in deep ocean.

Long-term effects of an early-life exposure of fathead minnows to sediments containing bitumen. Part II: Behaviour, reproduction, and gonad histopathology

The oil sands area of northern Alberta has river sediments that contain natural bitumen. Eggs and fish in these rivers may be exposed to bitumen-related chemicals early in life. This paper assesses a short embryo-larval fish exposure to oil sands sediment and follows the fish behaviour as they mature in clean water and examines their breeding success as adults (5 months afterwards). The three different oil sands river sediments tested were: a sediment collected outside of the bitumen deposit (tested at 3 g/L, Reference sediment from upstream Steepbank River site), and two sediments collected within the deposit (each tested at low (1 g/L) and high (3 g/L) concentrations). The sediments within the bitumen deposit were from the Ells and Steepbank (Stp) Rivers, and both contained significant total PAHs (>170 ng/g wet weight sediment) and alkylated PAHs (>4480 ng/g). Fish were exposed to these sediments for 21 days (as eggs and larval fish), and then transferred permanently to clean water to mature and breed. There was a significant decrease in the number of egg clutches produced by fish exposed early in life to Stp downstream high sediment (compared to Reference sediment). There was also a decrease in overall cumulative egg production, with fish from Stp downstream high sediment producing just over 1000 eggs in total while fish exposed to Ref sediment produced nearly 6900 eggs. The fish with reduced egg production were also less social than expected as they matured, and they had a lower % of early vitellogenic eggs in their ovaries. Overall, the exposure shows that a single, brief exposure during early life stages to natural bitumen can affect fish in adulthood. Naturally occurring bitumen-derived PAHs can reduce fish reproductive output by complex mechanisms, measurable as lower ovary maturity and changes in social behaviour.

Reaching environmental levels of 244Pu by accelerator mass spectrometry at the Centro Nacional de Aceleradores

244Pu (T1/2 = 81 My) is the longest-lived, most minor, and the most understudied Pu isotope. The anthropogenic production of 244Pu is linked to nuclear detonations. Reported 244Pu/239Pu atom ratios in environmental samples range from below 10−6 to above 10−3. This work discusses the performance of the 1 MV Accelerator Mass Spectrometry system at the Centro Nacional de Aceleradores (CNA, Seville, Spain) to analyse 244Pu at environmental levels. The presence of 232Th traces in the Pu sample limits the sensitivity of the technique through the formation of the diatomic trication (232Th12C)3+, of mass 244 u, which must be suppressed by adjusting the stripper gas pressure. A244Pu background of 0.0075 fg (2 × 104 at) is demonstrated for samples that have undergone a chemical treatment. The reliability of the technique is proved through the analysis of three reference sediments provided by the International Atomic Energy Agency (IAEA-412, IAEA-465, IAEA-385). 244Pu results are complemented with 239Pu, 240Pu, 241Pu and 236U and their relative isotopic abundances are discussed.

Teasing out the Effects of Natural Stressors at Chemically Contaminated Sites.

Aquatic ecosystems are often impacted by a multitude of stressors, many of which are introduced by a combination of anthropogenic activities such as agricultural development, urbanization, damming, and industrial discharge. Determining the primary stressors responsible for ecological impairments at a site can be complex and challenging; however, it is crucial for making informed management decisions. Improper diagnosis of an impaired system can lead to misguided attempts at remediation, which can be both time consuming and costly. We focused on the development, implementation, and evaluation of methodologies that, in combination, allowed us to identify the primary stressors. These included a four-phase, weight-of-evidence (WOE) assessment including in situ Toxicity Identification and Evaluation (iTIE) testing, physicochemical and macrobenthos characterization, reciprocal sediment transplants, and laboratory and in situ toxicity testing. The contaminants of concern (COCs) at the site were elevated levels of ammonia, chloride, pH, and total dissolved solids in groundwater upwellings into a high-quality waterway. Reciprocal transplants of site sediments and nearby reference sediments and traditional benthic sampling showed impaired benthic indices and multiple stations around a contaminated industrial settling basin. Impaired stations had elevated COCs in groundwaters but exhibited a steep vertical concentration gradient, with concentrations decreasing near the sediment-surface water interface. We describe Phase 4 of the study, which focused on teasing out the role of dissolved oxygen sags in benthic macroinvertebrate responses. Extensive submerged and emergent macrophytes, algae, and cyanobacteria co-occurred at the impaired sites and increased throughout the summer. Laboratory testing suggested that ammonia and pH were possibly toxic at the sites, based on groundwater concentrations. The in situ toxicity testing, however, showed toxicity occurring even at stations with low levels of COCs concurrently with large diurnal fluxes in dissolved oxygen (DO). A final phase using a type of iTIE approach utilized limnocorrals with and without aeration and with in situ toxicity measures using Hyalella azteca. The Phase 4 assessment revealed that low DO levels were primarily responsible for impaired benthic communities, and COC upwellings were diluted at the sediment-water interface to nontoxic levels. These findings will allow for improved management decisions for more efficient and effective restoration activities. Environ Toxicol Chem 2024;43:1524-1536. © 2024 SETAC.

Recent increase in sediment dry matter, carbon, and phosphorus accumulation in small boreal lakes with clayey catchments

This study estimated the mass accumulation rates of sediment (MAR), carbon (CMAR), and phosphorus (PMAR) in small Finnish lakes with agricultural clayey catchments over a 25-year period (1986–2011) and compared these with the conditions before major agricultural land use. Twenty-two lakes were cored for recent and reference (pre-disturbance) sediments. The recent sediment section was selected based on the 1986 137Cs fallout peak (TOP), whereas the pre-disturbance section (REF) was selected immediately below the first signs of human-induced erosion. The 50-cm reference section was dated with 14C at both ends. The mass accumulation rates were estimated based on dating, weighing, and chemical analysis for both sediment sections. Furthermore, sediment-penetrating echo soundings were used to estimate the amount of sediment in the whole lake basins. These data were used to examine area-specific loading from clay-rich catchments. The average whole-basin pre-disturbance MAR, PMAR, and CMAR were 62 g m−2 a−1, 0.06 g m−2 a−1, and 4.7 g m−2 a−1, respectively. The corresponding recent rates were 11, 13, and 8-fold (693 g m−2 a−1, 0.79 g m−2 a−1, and 37 g m−2 a−1). In the recent conditions, sediments were generally more minerogenic and MAR, PMAR, and CMAR were higher in lakes with more arable fields in their catchments. Average area-specific suspended sediment load from the catchment for the region (∼39% clayey soils) was approximately 69–137 kg ha−1 a−1 in the undisturbed state and 767–1534 kg ha−1 a−1 in recent conditions based on 100–50% retention. The results demonstrate that the increases in sediment, nutrient, and organic matter accumulation due to agriculture can be several fold over undisturbed state.

Geoacoustic and geophysical data‐driven seafloor sediment classification through machine learning algorithms with property‐centered oversampling techniques

AbstractThis study aims to classify seafloor sediments using physics‐inspired and data‐driven soil models combined with machine learning algorithms and oversampling techniques. The field data used for the input variables include porosity, S‐ and P‐wave velocities and depth. The soil information reported in the original literature and the “six reference sediments” and effective stress‐versus‐depth models proposed by the previous study confirm the sediment type across all of the input variables. We use three machine learning algorithms and four oversampling methods to enhance the performance accuracy and overcome data imbalance in the minority class. The results show that the averaged accuracy of sediment classification with original data corresponds to 0.88 for porosity, 0.61 for S‐wave velocity, and 0.97 for P‐wave velocity. In particular, the enhanced accuracy with oversampled input variables becomes more pronounced when the depth data are considered in a dataset. The class‐oriented grouping method newly proposed in this study appears to be a robust approach to enhancing performance. Surprisingly, model‐based input variables lead to the best performance in all cases. The proposed analyses conducted using machine learning algorithms and oversampling techniques within the physics‐inspired models could be extended to obtain a first‐order assessment of marine sediment properties.

Organochlorine contaminants in sediments and factors influencing their distribution in the natural marine protected area in the gulf of Mexico

The aim of this study was to determine the concentration of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in marine sediments of a natural marine protected area (NMPA), Veracruz Reef System (VRS), in the Gulf of Mexico (GoM). This NMPA represents one of the first coastal sites with port activity in Mexico, which causes a range of human activities that require adequate planning so as not to impact and destroy this marine protected area; In this sense, this work represents the first effort aimed at diagnosing the presence of organochlorine contaminants in reef sediments from the mainland, both from the adjacent port area and from more distant regions with dominant agricultural activities that ultimately affect this NMPA. Content of organic matter (OM), carbonates and grain-size composition were determined to investigate their influence on compounds distribution in the sediment through multivariate analysis. The potential risk represented by organochlorines concentrations was evaluated taking as reference Sediment Quality Guidelines (SQGs). Levels of ∑PCBs, ∑DDTs, ∑HCHs and ∑Cyclodienes ranged from 11.59 to 29.79, < 0.01 to 34.11, 22.10 to 102.80, and 17.21–104.45 ng g−1 dry weight (DW), respectively. The statistical analysis revealed that the content of mud and organic matter were the parameters that might influence PCBs distribution in the sediment while OCPs could be influenced by sand and carbonate. The theoretical risk assessment estimated with the results obtained showed that concentrations of lindane, endrin, dieldrin and p,p’-DDT could have an adverse effect on the reef benthic community and continued monitoring is required. The data obtained on the organochlorine contaminants (OCs) considered in this work will contribute to support the strategies proposed by the Mexican federal government entity to continue with the conservation and surveillance of this NMPA and thereby guarantee the least impact derived mainly from port and related agricultural activities.

Semi-analytical modeling of sediment-laden open-channel flows with the effects of stratification, hindered settling, and eddy viscosities.

This study proposes semi-analytical models for simultaneous distribution of fluid velocity and suspended sediment concentration in an open-channel turbulent flow using three kinds of eddy viscosities. Apart from the classical parabolic eddy viscosity which is based on a log-law velocity profile, we consider two recently proposed eddy viscosities based on the concept of velocity and length scales. To deal with the flows with high sediment concentration, several turbulent features such as the hindered settling mechanism and the stratification effect are incorporated in the model. The governing system of highly nonlinear differential equations is solved using the homotopy analysis method (HAM), which produces solutions in the form of convergent series. Numerical and theoretical convergence analyses are provided for all three types of eddy viscosities. The effects of parameters on the derived models are discussed physically. Experimental data on both dilute and non-dilute flows are considered to verify the HAM-based solutions. The effects of the stratification correction factor (β) and the turbulent Schmidt number (α) reveal that they should be determined optimally for applicability of the proposed models in terms of accurate prediction with data. This optimal procedure required further investigation of these parameters, and, thus, an analysis of β and α is carried out, which linked them with the particle diameter through particle settling velocity, reference fluid velocity, and reference sediment concentration by proposing regression equations. Furthermore, using the optimal values of the parameters, the proposed models corresponding to the eddy viscosities based on the exponentially decreasing turbulent kinetic energy function and von Karman's similarity hypothesis are seen to be superior to the model corresponding to a parabolic eddy viscosity. Finally, a comment on the HAM is made where it is observed that the method can remove the numerical singularity of the governing equations at the water surface, which arises because of the consideration of vanishing eddy viscosity thereat.

Impact of the Controlled Dump of Fez City (Morocco): Evaluation of Metallic Trace Elements Contamination in the Sediments

In order to qualify and quantify the impact of sediment contamination in hydric settings by metallic trace elements (MTE) emanating from the controlled dump of Fez city (northern Morocco), leachate and sediment sample analyses were carried out. The leachates collected from the 24 sites are characterised by a pH between 6.91 and 8, a COD varying between 430.7 and 7962 mg/L, an NTK content up to 1955 mg/L, with an average of 1514 mg/L, and a nitrate concentration reaching 46 mg/L in some samples, which exceeds the standards for discharges into the natural environment. The chromium content emanating mainly from household waste varies between 1.69 and 4.90 mg/L. The MTE content (As, Cd, Co, Cr, Cu, Ni, Pb, Zn and Fe) of the different leachates varies from one basin to another. The sediments downstream of the dump along the sampling profile show pH values between 7.34 and 8.21 (compared to 7.96–8.82 for the reference samples), and electrical conductivity values fluctuate between 1.21 ms/cm and 5.37 ms/cm for the contaminated sediments (compared to 0.8 ms/cm for the reference sediment). The analysis of metallic trace elements in the sediments by ICP-AES shows that their content varies slightly from one sampling point to another. Furthermore, they do not vary considerably from the surface (0 cm) to the depth (20 cm). The average values of metallic element concentrations are 45.83 ± 2.14 mg/Kg for Cu, 4.40 ± 0.07 mg/Kg for Cd, 43.76 ± 3.40 mg/Kg for Cr, 72.99 ± 1.85 mg/Kg for Ni, 21.71 ± 6.55 mg/Kg for Pb and 102.02 ± 7.28 mg/kg for Zn. In effect, the negative environmental impact of Fez controlled dumping site is ostensibly underlined both by (i) the pollution load index values, which indicate a strong and progressive deterioration along the thalweg, and (ii) the statistical analysis (PCA), which reveals a common origin of the deduced pollutants through the strong correlation between the majority of the analysed elements.

Molecular evidence for the production of labile, sulfur-bearing dissolved organic matter in the seep sediments of the South China Sea

Cold seeps with methane-rich fluids leaking out of the seafloor usually support massive biomass of chemosynthetic organisms and associated fauna. A substantial amount of methane is converted to dissolved inorganic carbon by microbial metabolism, and this process also releases dissolved organic matter (DOM) into pore water. Here, pore water samples from “Haima cold seeps” sediments and the non-seep reference sediments in the northern South China Sea were analyzed for optical properties and molecular compositions of pore water DOM. Our results showed that the relative abundance of protein-like DOM, H/Cwa and molecular lability boundary percentage (MLBL%) in the seep sediments were significantly higher than those in the reference sediments, indicating that more labile DOM related to unsaturated aliphatic compounds is produced in the seep sediments. Spearman's correlation of the fluoresce and molecular data suggested that the humic-like components (C1 and C2) mainly constituted the refractory compounds (CRAM, highly unsaturated and aromatics compounds). In contrast, the protein-like component (C3) had high H/C ratios featuring high degree of DOM lability. The amount of S-containing formulas (CHOS and CHONS) was greatly elevated in the seep sediments, likely caused by abiotic and biotic sulfurization of DOM in the sulfidic environment. Although the abiotic sulfurization was proposed to have a stabilizing effect on organic matter, our results implied that the biotic sulfurization in the cold seep sediments would increase DOM lability. Overall, the labile DOM accumulated in the seep sediments is closely linked to methane oxidation, which not only support heterotrophic communities and but also likely have an impact on carbon and sulfur cycling in the sediments and the ocean.

Horizontal to Vertical Spectral Ratio (HVSR) Analysis of the Passive Seismic Data on Alluvial Lithology: An Example from Bandung Basin Rim

Bandung basin is surrounded by active volcanoes at the center of Western Java region. Soil type of this area consists mostly of volcanic alluvial, formed by the past volcanic activities. At this location, we performed passive seismic surveys to reveal the sedimentary characteristics using a triaxial seismometer, to study the properties which have potential implications on environmental aspects, such as natural disaster mitigation and the city planning. In this work we reported the analysis of three component vibration signals by means of the Horizontal to Vertical Spectral Ratio (HVSR) calculation to identify the sediment thickness through the dominant frequency of the earth vibration. The method signal processing successfully revealed the amplification factor of the area, which is very important to determine the potential ground motion induced disasters. The data was collected using a laboratory developed seismic logging device with sensitivity of 0.28 ± 5% V⋅s/cm. The signal preconditioning was carried out to shape the acquired signals with high noise level, prior to the HVSR calculation. From the measurements and computation, we obtained the thickness variation at the chosen survey area of around 32 to 64 meters, corresponding to the measured dominant frequency of around 2.5 to 5.0 Hz. The results agree very well with the reference sediment thickness measured by the microtremor surveys. The vibration frequencies are also consistent with the range suggested by the literature

Phosphorus reference conditions in lowland streams: Survey in old forests and anaerobic sediment release

The reference (pristine) concentrations of total dissolved phosphorus (TDP) in surface waters are difficult to define in lowland regions because of their high population density. Here, we estimated reference conditions of TDP from headwaters and their riverbed sediments (n = 140) in old forests. Surface waters and sediments were collected in the lowland region of Belgium as transects starting in 20 different old forests (before 1775; pristine) to up to 1.5 km outside the forest edge (disturbed). Sediment P concentrations in disturbed samples readily increased with increasing distance from the borders of old forests. The P mobilized from the sediments to the overlying water was also measured in laboratory incubations to mimic P release during seasonal redox cycles. The sediment respiration was larger in disturbed than in the reference sediments. Disturbed sediments released more P during anaerobic than aerobic incubations, while reference sediments did not show such a difference. The mean TDP in the reference surface water samples is 57 μg TDP L−1 [95 % confidence interval 41; 72], very close to the pre-industrial background previously estimated for the Scheldt river. The 90th percentile of the reference water is 137 [110; 180] μg TDP L−1. That P90 is just under the prevailing TP limit of 140 μg P L−1, illustrating that this limit is very close to the upper baseline of reference conditions. The P75, often proposed as the threshold for high ecological status, was 84 [55; 122] μg P L−1. This study showed that soil or sediments in old forests might serve to identify reference conditions. The well-established summer peaks of TDP in lowland rivers are unlikely to occur in pristine areas.

Platinum Nanoparticle Extraction, Quantification, and Characterization in Sediments by Single-Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Particulate emissions from vehicle exhaust catalysts are the primary contributors to platinum group elements (PGEs) being released into roadside environments, especially platinum (Pt) particles. With increasing traffic density, it is essential to quantify the emission, accumulation, and potential health effects of traffic-emitted Pt particles. In this study, three procedures were investigated to extract Pt nanoparticles (NPs) from sediments and characterize them by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOF-MS). For this purpose, a reference sediment sample was spiked with manufactured Pt NPs. Pt NPs’ extraction recoveries reached from 50% up to 102%, depending on the extraction procedure and whether the particle mass or number was used as the metric. Between 17% and 35% of the Pt NPs were found as unassociated Pt NPs and between 31% and 78% as Pt NPs hetero-aggregated with other sediment particles. Multi-elemental analysis of Pt-containing NPs in the pristine sediment revealed frequently co-occurring elements such as Au, Bi, and Ir, which can be used to determine a natural background baseline. Our results demonstrated that spICP-TOF-MS elemental characterization allows for distinguishing anthropogenic Pt NPs from the natural background. In the future, this could enable the sensitive monitoring of PGE release from anthropogenic sources such as vehicle exhausts.

The assessment of particle selection and blank correction to enhance the analysis of microplastics with Raman microspectroscopy

Although microplastics research has received enormous attention in the last decade, both the research practices and the quality of produced data should still be improved. In this study, the identification process of microplastics with Raman imaging microscope was improved by decreasing the time needed for the analysis. To do that, new features, including terrain mosaic and automatic particle selection, were utilized and various ways of handling the produced microplastics data were implemented and discussed. Furthermore, blank correction of microplastic concentrations was demonstrated and its effects on the recovery of spiked microplastics was assessed with aqueous and solid samples.Six types of microplastics, including fragments and fibers, were spiked in triplicates of ultra-pure water and reference sediment samples. The spiked samples were pretreated by a modified method of the universal enzymatic purification protocol. Microplastics were analyzed with Raman imaging microscope, using terrain mosaic combined with automatic particle selection. The microplastics data were subjected to different identification steps to estimate the potential overestimation and underestimation of microplastics counts.With the complete correction of Raman-based data, the average recovery rates of fragments (77–80%) were higher than fibers (20–33%). The decrease in recovery rates of spiked microplastics (49–57%) were observed when blank correction was applied (28–47%). The impact of the blank correction depended on the polymer, causing exclusion of PE, PET, and PP from sediment samples. For the completely corrected Raman-based data, the average recovery rates of microplastics were higher for water than sediment samples both with and without blank correction.The results demonstrated the impact of blank correction on the microplastics recovery rates. To our knowledge, this is the first study to explore the use of automatic particle selection of Raman imaging microscope for microplastics analysis. Hence, potential drawbacks and advantages of the new features of Raman imaging microscope were explicitly discussed.

Sediment-yield prediction using map correlation method

Sediment yield is of utmost importance in estimating soil erosion, reservoir sedimentation, aquatic life protection, change in river cross-section, and many more. Daily sediment time series can be readily obtained from sediment gauging stations; the problem lies at ungauged sites where information on daily sediment data is unavailable. At ungauged catchments, the most common methods to estimate sediment time series involve the use of a reference sediment gage, which shifts the properties of the sediment flow time series at a reference station to the ungauged catchment. The appropriate selection of reference stations is challenging in the estimation of daily sediment flows at ungauged watersheds. At most times in conventional methods, the parameters at the ungauged sites are determined by assuming the nearest gage station as a reference station. In the present paper, it is established that the near neighbour catchment may not always be the most correlated one. One of the techniques termed as map correlation method is undertaken to identify the most correlated sediment gage station as a reference to an ungauged station. To assess the efficacy of the present method daily sediment data for two years at forty sediment gauging stations of the USA watershed are utilized. Sample and model variograms were used to model the spatial structure of Pearson's r correlation coefficient. Observed and estimated correlations resulting from the cross-validation of the variograms are in line with each other for most of the stations. This method selects the most related reference station for an ungauged sediment site.

Characterizing the habitat function of bivalve aquaculture using underwater video

Bivalve aquaculture is an expanding coastal industry with the potential to modify the habitat of fish and crab species, affecting their refuge, movement, and feeding. The habitat function of shellfish aquaculture is not yet well understood, in part due to difficulties in data collection using traditional methods. Underwater video was used to observe fish and crab species’ affiliations with cultured Pacific oyster Crassostrea gigas and Manila clam Venerupis philippinarum aquaculture sites in comparison to uncultured reference sediment and eelgrass habitats. Sites were monitored in 9 locations across 3 regions of Puget Sound, Washington, USA, in the summers of 2017 and 2018. Of the 3038 fish and crabs observed, 98% were represented by Embiotocidae (surfperch), crabs, three-spined stickleback Gasterosteus aculeatus, Cottidae (sculpins), and Pleuronectiformes (flatfish). Overall, the affiliations of fish and crabs with bivalve aquaculture varied by species groups, culture type, and regional environmental and habitat conditions. These interactions varied on a scale of approximately 150 km, highlighting variation of aquaculture-ecological interactions at a scale not previously recorded in Puget Sound. Species composition varied between aquaculture and non-aquaculture habitats in 2 of the 3 regions studied. Species diversity and richness in aquaculture habitats varied regionally, relative to reference habitats. Pelagic species were more abundant in aquaculture and reference sites that had vertical structure, but abundances of demersal and benthic species on aquaculture habitat relative to reference sites varied regionally. The availability of habitats within intertidal regions, including varying types of aquaculture, could determine community structure for marine organisms such as fish and crab.

A simple, selective and eco-friendly method for quantification of polychlorinated biphenyls in sediment samples at ultra-trace levels by headspace solid-phase microextraction-gas chromatography-ion trap tandem mass spectrometry

ABSTRACT An analytical method based on headspace solid-phase microextraction gas chromatography- ion trap tandem mass spectrometry (HS-SPME-GC-ITMS/MS) was optimised and developed for estimating 20 predominant polychlorinated biphenyl (PCB) concentrations in sediment samples. The effect of experimental parameters involving fibre materials, amount of water added, temperature effect, sorption time, stirring effect, and the addition of solvents were examined with gas chromatography-electron capture detector (GC-ECD). The analytical performance of association of HS-SPME-GC-ITMS/MS proposed methodology was examined by spiked sediment with the selected PCB congeners. The repeatability and reproducibility of measurements (n = 6), expressed with relative standard deviation (RSD), was below 13% and 16%, respectively. Good linearity was observed within the concentration range studied and the LODs were between 0.02 and 0.82 ng g−1. Accuracy was assessed by analysing a reference sediment sample with certified concentrations of several PCBs. Standard addition calibrations were done and concentrations of PCBs with the proposed method were in good agreement with the certified PCB concentrations. The method was also efficiently applied to real sample sediment from Bizerte Harbour, revealing the existence of several congeners at level less than 1.1 ng g−1. These obtained results were also on concordance with analysis of this real sample using a conventional soxhlet extraction method. The developed procedure is highly effective and selective, free of organic solvents, relatively simple and fast, and become a suitable alternative for routine monitoring of residues of PCB from sediments at ultra-trace levels.

Statistical comparisons of sediment particle size distributions

Particle size distributions of marine sediments are key factors affecting biodiversity. It is, therefore, often important to make statistical comparisons between groups of distributions to assess whether natural or anthropogenic impacts have changed sediment composition over time or spatial area. We derive two new metrics to measure particle size distributions. One, Difference in Means, is a general index that can be used to compare groups of reference and test samples. The second, the Unusual Index, was specifically developed to compare a single test distribution with a set of reference distributions, although its use can be extended for when there are multiple test distributions. These two indices, along with more established measures, are embedded in a randomisation procedure to assess statistical significance of differences between test and reference distributions.A statistical power study to assess the ability of the new and established metrics to detect change shows that simple summary statistics such as the mean, standard deviation and 10th percentile can have high power under some change scenarios but can fail badly in others. The Difference in Means approach, along with the established ANOSIM method, has consistently high power under all scenarios. The Unusual Index does not have such high power as these two approaches. However, the index is shown to provide a clear way to communicate differences between a site and surrounding reference sediment distributions, as illustrated in a case study of Norfolk, U.K., sediments. Overall, our findings and R software provide a methodological framework, and extend the ‘statistical toolkit’ for comparing particle size distributions.

Geochemical and molecular characteristics of ferromanganese deposits and surrounding sediments in the Mariana Trench: An Implication for the geochemical Mn cycle in sedimentary environments of the trench zone

Trench systems are some of the most important geodynamic settings on Earth and have a substantial influence on the global metal cycle. Trench environments are affected not only by episodic deposition of volcanic ash, but also exhibit a continuous water–rock chemical exchange. Ferromanganese nodules, which are archives for the marine Mn cycle, were first discovered in the southern Mariana Trench during China’s major 10,000-meter hadal trench scientific expedition in 2016. Nevertheless, their geochemical characteristics and formation mechanism in sedimentary environments of the trench zone remain enigmatic. In this study, these ferromanganese nodules and surrounding sediments were examined by geochemical and microbial methods. Bulk geochemistry indicated that trench nodules are characterized by high Mn/Fe ratios and nodule textures indicate a rapid growth rate, with Mn mainly from two sources: volcanic ash alteration and fluids discharge from the trench seabed. High-resolution in situ geochemical analysis categorized microlayers of an individual nodule into three types. Type I is the interior part that has a high Mn/Fe ratio (>20) and high growth rate (52.19–3571.73 mm/Myr), and formed by the influence of fluid discharge activities around this region. Type II is laminae from the exterior part that have a hydrogenetic origin with lower Mn/Fe ratio (0.01–2.50) and lower growth rate (4.54–9.86 mm/Myr). Type III is laminae from the exterior part that have a diagenetic origin with moderately high Mn/Fe ratio (2.5–15.0) and moderately high growth rate (12.40–18.93 mm/Myr). 16S rRNA gene sequence analysis revealed that the bacterial community structures in the nodule-bearing sediment samples, dominated by Shewanella and Colwellia, were substantially different from those of reference sediment samples. For the first time, we propose a conceptual model for a geochemical Mn cycle and nodule formation in trench sedimentary environments using both geochemical and microbial data.