Role Of Sediments Research Articles

Каменные индустрии ранних этапов среднего палеолита стоянки Дарвагчай-Залив-4 (исследования 2021 года)

The territory of Primorsky Dagestan is one of the places on the Eurasian continent, where a constant and massive presence of Neanderthal populations in antiquity was noted. In particular, this is evidenced by a large number of Middle Paleolithic sites in a relatively small territory of the Darvagchay geoarchaeological region (Southeastern Dagestan), discovered and studied in the last decade. This article is devoted to the results of the latest studies of the Middle Paleolithic complexes of the Darvagchay-Zaliv-4 site, the materials of which belong to the early stages of the Middle Paleolithic and significantly supplement the evidence material of this cultural-chronological period in the territory of the North-Eastern Caucasus. In the field season of 2021, two sets of artifacts related to different stages of the Middle Paleolithic were discovered at the site. The age of the geological horizons, where they were discovered, was previously based on the results of absolute dating by OSL. The stone industry of the first complex is characterized by the Levallois technique and a typical Middle Paleolithic toolkit; artifacts were located in horizon 1c. Chronologically, the time of its existence is determined by the period of the Riess-Wurm (Eem, Mikulino) interglacial, in the range of 120-110 ka BP (MIS 5e). Artifacts of another complex, discovered at the site for the first time, were found in the middle part of Layer 2 (light loam, loess). Aeolian-deluvial processes played a leading role in sedimentation here. The technical and typological characteristics of a small collection of stone products make it possible to attribute it to the earliest stages of the Middle Paleolithic. The age of the culture-bearing horizon was based on a series of the OSL dates in the range of 200-180 ka BP (MIS 8).

Some Aspects on the Role of Sediments in the Development of Karst Surface Morphology (Island of Krk, Croatia)

Some Aspects on the Role of Sediments in the Development of Karst Surface Morphology (Island of Krk, Croatia)

New insights into the role of lake sediments in understanding watershed non-point source phosphorus pollution

A deep understanding of the relationship between watershed non-point source (NPS) pollution and lake total phosphorus (TP) accumulation is the basis of watershed–lake environmental management and ecological reconstruction, in which the acquisition of long-term NPS P and lake TP data over corresponding temporal and spatial scales seems to be the key issue. In this study, three typical sub-basins within Hongze Lake were selected as study sites. The sediment TP concentrations were designated as the lake indicator to relate with the NPS P loads, and the role of sediment in representing watershed NPS pollution was quantitatively analyzed. The results showed that, first, a notable fluctuation tendency in NPS P loads, which was largely influenced by policy, was found for all three sub-basins. Second, the deposition rate for three sediment cores was approximately 0.40 cm per year, with 13 cm cores reflecting the period since 1990. Third, the sediment is a faithful recorder of watershed NPS P pollution and lake nutrient enrichment. The correlation coefficient (r) between watershed NPS P loads and lake sediment TP concentrations showed notable differences when each watershed was considered separately. In particular, an ideal relationship was found in Basins 1 and 2, especially in the bottom 7 and 8 cm of the sediment cores, in which r exceeded 0.8. This showed that sediment can be an effective indicator of NPS P pollution during certain periods, such as 1990 – 2002, and diverse roles can be attributed to land-use/cover change and lake resuspension conditions. In addition, the weakest relationship existed in the No. 3 watershed, largely due to higher rainfall amounts compared with other two watersheds. For all the watersheds, lake sediment is a suitable indicator of watershed NPS P pollution over certain temporal and spatial scales.

Impact of ambient conditions on the Si isotope fractionation in marine pore fluids during early diagenesis

Abstract. Benthic fluxes of dissolved silicon (Si) from sediments into the water column are driven by the dissolution of biogenic silica (bSiO2) and terrigenous Si minerals and modulated by the precipitation of authigenic Si phases. Each of these processes has a specific effect on the isotopic composition of silicon dissolved in sediment pore fluids, such that the determination of pore fluid δ30Si values can help to decipher the complex Si cycle in surface sediments. In this study, the δ30Si signatures of pore fluids and bSiO2 in the Guaymas Basin (Gulf of California) were analyzed, which is characterized by high bSiO2 accumulation and hydrothermal activity. The δ30Si signatures were investigated in the deep basin, in the vicinity of a hydrothermal vent field, and at an anoxic site located within the pronounced oxygen minimum zone (OMZ). The pore fluid δ30Sipf signatures differ significantly depending on the ambient conditions. Within the basin, δ30Sipf is essentially uniform, averaging +1.2±0.1 ‰ (1 SD). Pore fluid δ30Sipf values from within the OMZ are significantly lower (0.0±0.5 ‰, 1 SD), while pore fluids close to the hydrothermal vent field are higher (+2.0±0.2 ‰, 1SD). Reactive transport modeling results show that the δ30Sipf is mainly controlled by silica dissolution (bSiO2 and terrigenous phases) and Si precipitation (authigenic aluminosilicates). Precipitation processes cause a shift to high pore fluid δ30Sipf signatures, most pronounced at the hydrothermal site. Within the OMZ, however, additional dissolution of isotopically depleted Si minerals (e.g., clays) facilitated by high mass accumulation rates of terrigenous material (MARterr) is required to promote the low δ30Sipf signatures, while precipitation of authigenic aluminosilicates seems to be hampered by high water ∕ rock ratios. Guaymas OMZ δ30Sipf values are markedly different from those of the Peruvian OMZ, the only other marine OMZ setting where Si isotopes have been investigated to constrain early diagenetic processes. These differences highlight the fact that δ30Sipf signals in OMZs worldwide are not alike and each setting can result in a range of δ30Sipf values as a function of the environmental conditions. We conclude that the benthic silicon cycle is more complex than previously thought and that additional Si isotope studies are needed to decipher the controls on Si turnover in marine sediment and the role of sediments in the marine silicon cycle.

Iron redox cycling, sediment resuspension and the role of sediments in low oxygen environments as sources of iron to the water column

Continental margin sediments represent a potentially large, but poorly constrained, source of iron to surface waters to support primary productivity. To investigate this problem, we examined iron redox cycling in the sediments of Santa Monica Basin (SMB), CA as it relates to benthic sources of iron to the water column. Our results show that iron redox cycling in SMB sediments results in the formation of a thin layer at the sediment surface (<2 cm thick) that is highly enriched in amorphous, reactive iron oxides. Such oxides, when resuspended into the water column, may be a source of bioaccessible iron to primary producers. Calculations show that the resuspension flux of reactive amorphous iron oxides from SMB sediments may be up to two orders of magnitude greater than benthic fluxes of soluble dissolved iron from most continental margin sediments. The factors which favor the formation of this surface sediment layer enriched in reactive amorphous iron oxides appear to be related to the dissolved O2 level in SMB bottom waters, and its impact on iron redox cycling and the occurrence of sediment bioturbation. These factors are not necessarily unique to SMB, and other sediment sites on the open continental margin that lie within the O2 minimum zone may also have similar properties. Furthermore, expansion of O2 minimum zones due to global warming could possibly increase the areal extent of such environments, and potentially act as a negative feedback on rising atmospheric CO2 by providing additional iron to stimulate primary production. Further work examining iron biogeochemistry in low O2 continental margin settings will be needed to more critically examine these possibilities, along with studies that better define the role sediment resuspension fluxes may play as an iron source to surface waters. Such efforts will ultimately lead to an improved understanding of the role that ocean deoxygenation may play in enhancing this sediment iron source to support surface ocean primary production.

Fate simulation and risk assessment of TBT and TPhT considering water level fluctuations in the TGR before and after AFS Convention implementation in China

BackgroundThe Three Gorges Reservoir (TGR) is the largest freshwater reservoir in China. Previous studies showed that organotin pollution is present in the TGR. In June 2011, the AFS Convention went into effect in China. In order to explore the pollution evolution processes of tributyltin (TBT) and triphenyltin (TPhT) before and after implementation of the AFS Convention and their variations with water level fluctuations in the TGR, the characteristic parameters of the TGR and the physicochemical parameters of TBT and TPhT were used to develop a level IV multimedia fugacity model considering water level fluctuations to simulate the fate, transfer, and transport of TBT and TPhT in the TGR. Based on the simulation results, exposure concentrations of TBT and TPhT were then used to assess the ecological and health risks in the TGR region (TGRR).ResultsThe simulation results showed that the average concentrations of both TBT and TPhT decreased in all compartments except the sediment, whereas the total content of the system continued to increase after the AFS Convention was implemented. The concentration of TBT in the sediment was higher than that in fish, while the concentration of TPhT in fish was much greater than that in the sediment. The total contents of both TBT and TPhT were highest in the sediment phase. In addition, variations in water level of the TGR significantly affected the distribution and transport of TBT and TPhT in the TGR.ConclusionsSediment is an important source and sink of TBT and TPhT, and the water level regulation of the TGR strengthened the two roles of sediment. Both TBT and TPhT in surface water, but especially TBT, carried significant chronic exposure risks to the aquatic community of the TGR. Intake of TPhT, mainly through eating fish, posed a potential health risk to the population in the TGRR.

Soil erosion-related transport of neonicotinoids in new citrus orchards

The widespread use of neonicotinoids has increased the risk of non-point source pollution. Previous studies mainly focused on neonicotinoid transport by runoff on gentle slopes and ignored the role of sediment. Neonicotinoid migration due to erosion could be underestimated because a considerable amount of sediment migration is caused by erosion on steep slopes. Here, we focused on the transport of two typical neonicotinoids, imidacloprid (IMI) and clothianidin (CLO), via runoff and sediment in new citrus orchards on steep slopes. The total runoff from the bare land (BL), biological crust (BC) and Kummerowia striata (Thunb.) Schindl. (KS) plots was 77.73, 66.22 and 46.94 mm, respectively, and the corresponding total sediment was 162.47, 54.00 and 3.51 kg ha-1, respectively. The on-site pollution was mainly due to IMI and CLO retention in topsoil (0-2 cm). A linear relation between the loss of IMI and CLO and the loss of runoff and sediment (p < 0.05) indicated that the migration of IMI and CLO with runoff and sediment was the main cause of off-site pollution. Compared with the BL plot, the risks of on-site and off-site pollution were reduced significantly in the BC and KS plots: BC reduced on-site IMI and CLO by 33.50% and 19.28% and off-site IMI and CLO by 57.47% and 52.78%, respectively; KS reduced on-site IMI and CLO by 44.97% and 46.42% and off-site IMI and CLO by 75.32% and 57.42%, respectively. This finding reveals that the ability of vegetation to decrease IMI and CLO transport was mainly associated with a reduction of runoff and sediment loss. Therefore, the introduction of biological crust and fast-growing plants is recommended in new citrus orchards because it is a cost-effective method of mitigating soil erosion and non-point source pollution.

The Recent Sediment Record as an Indicator of Past Soil-Erosion Dynamics. Study in Dehesa Areas in the Province of Cáceres (Spain)

The work presented is a study of the recent sediment deposits in a pilot basin in dehesa areas in the province of Cáceres (Spain) through analysis of the sediment record, radiocarbon dating and correlation with historic data to assess the factors that conditioned the deposit in these areas over time. It is a qualitative study based on the important role of sediments as recorders of history, given that sediment facies and their architecture provide one of the best records of past processes and environmental factors. For the study, sediment profile surveys were used to determine the configuration and characteristics of the infill and its chronology. The sediment model of the facies studied is associated with a context of slope water erosion that led to the infill of the watercourse areas, mainly sand and fine gravel, where alterations in the normal rate were detected due to the insertion of a thicker level of materials (soil stoniness) that was able to be dated. The sediment and chronological results obtained can be used to determine the historical events in the area that could have affected the erosion and deposit processes in the basin for the estimated period, from the late 18th to the early 19th century. During this period, pastureland that maintained the ecological balance of the dehesa, with a balanced, stable displacement of soil particles, was converted to cropland, in most cases resulting in soil with a limited profile, overuse and the consequent loss of structure and texture, making it more vulnerable to erosion. Greater remobilisation would have carried thicker material to the watercourses than the material deposited as a result of limited ploughing. This study provides data for the dehesa areas studied with regard to their hydrogeomorphological dynamics, from which past environmental impacts due to tillage can be inferred.

Spatial-Temporal Variation of Bacterial Communities in Sediments in Lake Chaohu, a Large, Shallow Eutrophic Lake in China.

Sediment bacterial communities are critical for the circulation of nutrients in lake ecosystems. However, the bacterial community function and co-occurrence models of lakes have not been studied in depth. In this study, we observed significant seasonal changes and non-significant spatial changes in the beta diversity and community structure of sediment bacteria in Lake Chaohu. Through linear discriminant analysis effect size (LEfSe), we observed that certain taxa (from phylum to genus) have consistent enrichment between seasons. The sudden appearance of a Firmicutes population in spring samples from the Zhaohe River, an estuary of Lake Chaohu, and the dominance of Firmicutes populations in other regions suggested that exogenous pollution and environmental induction strongly impacted the assembly of bacterial communities in the sediments. Several taxa that serve as intermediate centers in Co-occurrence network analysis (i.e., Pedosphaeraceae, Phycisphaeraceae, Anaerolineaceae, and Geobacteraceae) may play an important role in sediments. Furthermore, compared with previous studies of plants and animals, the results of our study suggest that various organisms, including microorganisms, are resistant to environmental changes and/or exogenous invasions, allowing them to maintain their community structure.

The responses of bacterial community and N2O emission to nitrogen input in lake sediment: Estrogen as a co-pollutant

Excessive nitrogen (N) input is one of the most important causative factors of lake eutrophication, which has aroused increasing public attention in past decades. Estrogen contamination is also an increasing environmental problem in aquatic systems around the world. Although both substances usually co-exist in aquatic ecosystems, many researches have only investigated the influences of either N or estrogen individually on sediment bacterial community and nitrous oxide (N2O) emission. Knowledge regarding the combined effects of N and estrogen is still very limited. In this study, a 30-day laboratory incubation experiment was performed to examine the impacts of different N sources (ammonium and nitrate) combined with 17β-estradiol (E2) on sediment bacterial community. High-throughput 16S rRNA gene sequencing technique was used and N2O emission was measured. The results revealed that the relative abundances of Proteobacteria and Bacteroidetes were higher in nitrate treatment than ammonium treatment. Compared to N treatments, N and E2 combined treatments showed higher relative abundances of Proteobacteria, Bacteroidetes, and Firmicutes, but lower relative abundances of Chloroflexi, Acidobacteria, and Actinobacteria over entire incubation period. At the genus level, the relative abundances of genera Flavobacterium, Pseudomonas, Arenimonas, Novosphingobium, Massilia, Aquabacterium, and Bacillus were enhanced by N treatments and especially N and E2 combined treatments, compared to sediment without addition of N and E2. However, the relative abundances of Sporacetigenium, Gaiella, Desulfatiglans, Nitrospira, and Haliangium were decreased in N treatments. Apart from the changes in bacterial community structure, N2O emission was also influenced by different treatments. Nitrate exerted a more significant positive effect on N2O emission than ammonium, and the cumulative emission of N2O was highest in nitrate and E2 combined treatment. Very low abundances of ammonia monooxygenase (amoA) gene and hydroxylamine oxidase (hao) gene were observed in sediments compared to other genes involved in N cycles (such as nitrate reductase (narG and napA) genes, nitrite reductase (nirB, nirK, and nrfA) genes, and nitric oxide reductase (norB) gene), implying that denitrification rather than nitrification played an important role in sediments. The abundances of napA, nirK, and norB were higher in N and E2 combined treatments, indicating that E2 might provide a carbon source for denitrifiers. Moreover, decrease in the abundance of nitrous oxide reductase (nosZ) gene during the denitrifying process in N and E2 combined treatment might be an important reason for increases of N2O emission. These results indicated that alterations of the bacterial community structure due to the co-existence of N and E2 could also change the abundances of genes involved in N cycle.

The role of sedimentation in the structuring of microbial communities in biofloc-dominated aquaculture tanks

In no water exchange aquaculture operations, sedimentation has been employed to control the level of microbial flocs to decrease oxygen consumption and to prevent clogging of gills in cultured organisms. Nevertheless, the impact of this practice on the culture microbial community was not documented. The current study evaluated the impact of adding different concentrations of sedimentation from an intensive shrimp culture tank on the microbial communities in an experimental tank system operated with no water exchange. The trial evaluated three concentrations (mg L−1) of total suspended solids levels: <200, 680, and 1030. The analysis showed that settleable microbial community has a different set of species compared with the unsettled biomass, which was also less diverse. We argue that the difference in species composition is probably related to the biological flocculation, i.e., the ability exhibited by microorganisms to spontaneously form large, dense and quick settling aggregates. The results suggest that settling tanks act as a selective force by reducing the abundance of microorganisms strongly associated with the settled flocs, whilst favoring planktonic lifestyle bacteria or microorganisms associated with small and open flocs. These effects, especially loss of diversity, need to be considered in aquaculture management practices since it can increase the risk for invasion of opportunistic pathogenic species.

Tips for the childhood immunisation OSCE

The effectiveness of check dams on channel morphology of managed torrents is rarely assessed. Therefore, there is a need for studies that focus on the impacts of existing engineering check dams on the planoaltimetric characteristics of the torrent, particularly in Mediterranean areas, where the hydrological regime of ephemeral channels is dynamically unsteady. The quantitative evaluation of the effects of the check dams on channel morphology after many years (i.e., at least four or five decades) helps introduce innovations to the usual analysis of check dam efficacy which have often been limited to qualitative observations for only a few years after installation. As a contribution to make up these shortcomings, this paper investigates the geomorphologic asset of a torrent in southern Italy containing 10 check dams (installed in the 1950s to 1960s) and analyzes the dynamics of the scouring and sedimentation processes upstream and downstream of selected check dams after 8 rainfall events; moreover, the capability of the model by Castillo (2007) to predict scouring/sedimentation in proximity to these check dams is assessed. Sediment stored upstream of each check dam (where lower channel gradients and wider channel sections formed very long and wide sedimentary wedges) is more than one order of magnitude higher compared to scouring downstream. The morphological analysis revealed that the check dams installed in the headwater reach play a function of bed stabilization (due to the longitudinal slope reduction) and flood lamination (because of the wider channel section) rather than a role of sediment collectors as their sediment storage capacity has already been completed. Scouring/sedimentation dynamics depend mainly on the channel slope and width in proximity to the check dams rather than on structure height. Finally, Castillo9s model showed an acceptable performance in predicting scouring/sedimentation in the channel bed close to check dams after the monitored rainfall events, the model efficiency being satisfactory and the differences between the mean observed and simulated values low. This investigation improves the understanding about morphological effects of check dams in Mediterranean torrents based on field observations and quantitative analysis.

The role of sediments in the carbon and pollutant cycles in aquatic ecosystems

Abstract Aim Anthropogenic modifications in the landscape are accelerating biogeochemical cycles and causing unbalances in terrestrial and aquatic ecosystems with still unknow impacts on biotic and abiotic processes. Therefore, there has been increasing scientific interest in the links between human activities and ecosystems functions. Methods Here we review the role of aquatic sediments in the carbon and pollutant cycle. Results We briefly explore the historical context, origin, and composition of the sediments, as well as the factors that influence the processes of carbon and contaminants cycling and the role of sediments in the greenhouse gases emissions in aquatic ecosystems. Conclusions Aquatic sediments can help to understand the terrestrial and aquatic ecosystem changes, once they are good sentinels, reflecting key biogeochemical processes over time.

When hydrosociality encounters sediments: Transformed lives and livelihoods in the lower basin of the Ganges River

The hydrosocial cycle is a central analytical framework in political ecological approaches to water. It helps foreground multiple and subtle interactions between water and society, culture and politics. However, to date it has dealt little with matters other than water flows. In river contexts, biotic and abiotic components play critical roles in the way people engage with and make a living out of rivers, beyond water. This article aims to advance the hydrosocial framework with a deeper consideration of the materiality of rivers. To initiate this approach, the focus is here on sediments. Lives and livelihoods connected to river sediments remain both officially and academically under-explored. This certainly applies to the context of the Lower Ganges basin whose active channels transport huge loads of sediments mainly originating from the Himalayan slopes. Building upon an environmental history perspective and drawing on three spatially nested cases in West Bengal, India, the paper analyses instances of water-sediment-society interactions. The general case study presents colonial state interventions in the Lower Ganges basin waterscapes. The second case study zooms the focus on the 2 km long Farakka Barrage. These explorations reveal how an ‘imported’ conceptual land-water divide infused those interventions, leading to unforeseen effects on riverine lives and livelihoods. Focusing on Hamidpur char, situated few kilometres upstream of the barrage, the third case study recounts the contemporary efforts of local communities to obtain revision of administrative decisions unable to deal with ‘muddyscapes’. Finally, the paper engages with recent debates on the concept of hybridity in land-water nexus to reflect on the specific meaning and role of sediments.

The properties and spatial distributions of flocs adjacent to the Yangtze Estuary

Flocculation plays an important role in sedimentation of estuaries and continental shelves. The process of flocculation in estuary or shelf is extremely complicated. In this paper, the flocs observed at five sections that include 36 stations within the Yangtze Estuary of the East China Sea were studied systematically using scanning electron microscopy and energy dispersive X-ray spectrometry. The characteristics and spatial distributions of the flocs were obtained, and the factors about the spatial distributions of the flocs were discussed. The flocs were divided into 6 types according to their components: mineral flocs, bio-detritus flocs, mineral-biological flocs, organic-mineral flocs, organic-biological flocs and complex flocs. The percent of the mineral flocs is the highest. The mean particle size of the flocs ranges from 4.00 to 5.00 Ф. The sizes of the mineral flocs are the finest, while the sizes of the complex flocs are the coarsest. The percent of mineral flocs is high near the coastal areas and decreases toward the open sea; this trend is similar to those of organic-mineral flocs and complex flocs. High percentage of bio-detritus flocs and organic-biological flocs is observed to the east of the Taiwan Warm Current. The types and spatial distributions of the flocs are restricted by the properties of the water masses, and they are affected by the interactions of electrolytes, organic matter, biological processes and estuarine authigenesis process. The formation of flocs increases the settling velocity of suspended particles and has an important effect on the formation of mud areas on the continental shelf of the East China Sea.

The role of sedimentation and natural compaction in a prograding delta: insights from the mega Mekong delta, Vietnam

The Vietnamese Mekong Delta was formed by rapid transgression during the second half of the Holocene by deposition of mainly unconsolidated, fine-grained (clayey) sediments undergoing high compaction rates. The natural subsidence can seriously impact the already vulnerable delta plain as its low elevation exposes the delta to global sea level rise, flooding, salinization. Human activities such as groundwater pumping, infrastructural loading, sand mining and dam construction have exacerbated the effects of natural consolidation. Here we present a novel modeling study that has allowed to reproduce the formation and evolution of the Mekong delta over the past 4000 years. Using an adaptive finite-element mesh, the model properly simulates accretion and natural consolidation characterizing the delta evolution. Large soil grain motion and the delayed dissipation of pore-water overpressure are accounted for. We find that natural compaction of Holocene deposits following delta evolution exceeds predicted values of absolute sea level rise. The unprecedented high rates (up to ~20 mm/yr) threaten the lower delta plain with permanent inundation and inevitably reduce the designed service life of flood defense structures along the coast. Total subsidence and sediment delivery to the delta plain will determine its future elevation and vulnerability to relative sea level rise.

Role of Sediments in Insecticide Runoff from Urban Surfaces: Analysis and Modeling.

Insecticides, such as pyrethroids, have frequently been detected in runoff from urban areas, and their offsite transport can cause aquatic toxicity in urban streams and estuaries. To better understand the wash-off process of pesticide residues in urban runoff, the association of pyrethroids with sediment in runoff from residential surfaces was investigated in two watersheds located in Northern California (Sacramento County). Rainfall, flow rate, and event mean concentrations/loads of sediments and pyrethroids, collected during seasonal monitoring campaigns from 2007 to 2014, were analyzed to identify relationships among stormwater quality and rainfall characteristics, primarily using Principal Component Analysis (PCA). Pyrethroid wash-off was strongly related to sediment wash-off whenever sediment loads exceeded 10 mg; this value was conveniently selected as a threshold between dissolved and particle-bound control of off-site pyrethroid transport. A new mechanistic model for predicting pyrethroid wash-off profiles from residential surfaces at basin-scale was implemented in the Storm Water Management Model (SWMM). The accuracy of the model predictions was estimated by evaluating the root mean square error (RMSE), Nash–Sutcliff efficiency (NSE), and Kling–Gupta efficiency (KGE) for each pyrethroid detected (RMSEtot = 0.13; NSEtot = 0.28; KGEtot = 0.56). The importance of particle-bound transport revealed in this work confirms previous field investigations at a smaller scale, and it should be a key consideration when developing policies to mitigate pesticide runoff from urban areas.

PERSISTENCE OF EXTERNAL ANATOMY OF SMALL CRUSTACEANS IN A LONG TERM TAPHONOMIC EXPERIMENT

Abstract: Although studied for more than a century, the preservation mechanisms of soft-bodied organisms in Lagerstatten remain disputable. One aspect of this phenomenon, the role of sediments in the decay and preservation of soft tissues, is understudied. We present the results of an 18-month decay experiment that shows the difference between the preservation of the crustacean Artemia salina buried in marine water and inside clay sediment. We found that the decay of the external tissues of A. salina is slower in the sediment than in marine water, while the internal anatomy decays rapidly in both settings. This results in the formation of exuviae-like structures, accounted for not by the recalcitrance of external tissues, but by the burying conditions in the thick marine sediment. The experiment indicates the importance of organic-mineral interactions in the understanding of the taphonomic retarding of soft-tissue decay and the persistence of fine external anatomical features.

Synthetic and non-synthetic anthropogenic fibers in a river under the impact of Paris Megacity: Sampling methodological aspects and flux estimations

Processed fibers are highly present in our daily life and can be either natural, artificial (regenerated cellulose) and synthetic (made with petrochemicals). Their widespread use lead inevitably to a high contamination of environment. Previous studies focus on plastic particles regardless of their type or shape as long as they are comprised between 330μm and 5mm. On the contrary, this study focuses exclusively on fibers using a smaller mesh size net (80μm) to sample freshwater. Moreover, all processed organic fibers are considered, irrespective to their nature. First, the short term temporal variability of the fibers in the environment was assessed. While exposing the sampling net during 1min a coefficient of variation of approx. 45% (with n=6) was determined. It was of only 26% (n=6) when the exposure was of 3min. The assessment of the distribution through the section showed a possible difference in concentrations between the middle of the water surface and the river banks which could be attributed to the intense river traffic within the Paris Megacity. The vertical variability seems negligible as turbulence and current conditions homogenize the distribution of the fibers. A monthly monitoring showed concentrations of 100.6±99.9fibers·m−3 in the Marne River and of: 48.5±98.5, 27.9±26.3, 27.9±40.3 and 22.1±25.3fibers·m−3 from the upstream to downstream points in the Seine River. Once these concentrations are converted into fluxes, it seems that the impact generated by the Paris Megacity cannot be distinguished. Investigations on the role of sedimentation and deposition on the banks are required. This study helped fill some major knowledge gaps regarding the fibers in rivers, their sampling, occurrence, spatial-temporal distribution and fluxes. It is encouraged that future studies include both synthetic and none synthetic fibers.

Nearshore circulation on a sea breeze dominated beach during intense wind events

A field experiment was conducted on the northern Yucatan coast from April 1 to April 12, 2014 to investigate the role of intense wind events on coastal circulation from the inner shelf to the swash zone. The study area is characterized by a micro-tidal environment, low-energy wave conditions, and a wide and shallow continental shelf. Furthermore, easterly trade winds, local breezes, and synoptic-scale events, associated with the passage of cold-fronts known as Nortes, are ubiquitous in this region. Currents were measured concurrently at different cross-shore locations during both local and synoptic-scale intense wind events to investigate the influence of different forcing mechanisms (i.e., large-scale currents, winds, tides, and waves) on the nearshore circulation. Field observations revealed that nearshore circulation across the shelf is predominantly alongshore-directed (westward) during intense winds. However, the mechanisms responsible for driving instantaneous spatial and temporal current variability depend on the weather conditions and the across-shelf location. During local strong sea breeze events (W > 10ms-1 from the NE) occurring during spring tide, westward circulation is controlled by the tides, wind, and waves at the inner-shelf, shallow waters, and inside the surf/swash zone, respectively. The nearshore circulation is relaxed during intense land breeze events (W ≈ 9ms-1 from the SE) associated with the low atmospheric pressure system that preceded a Norte event. During the Norte event (Wmax≈ 15ms-1 from the NNW), westward circulation dominated outside the surf zone and was correlated to the Yucatan Current, whereas wave breaking forces eastward currents inside the surf/swash zone. The latter finding implies the existence of large alongshore velocity shear at the offshore edge of the surf zone during the Norte event, which enhances mixing between the surf zone and the inner shelf. These findings suggest that both sea breezes and Nortes play an important role in sediment and pollutant transport along/across the nearshore of the Yucatan shelf.