Sediment Traps Research Articles

Statistical analysis of the association between El Niño and the biological carbon pump in the East Sea (Japan Sea)

Understanding the impacts of climate change on oceanic carbon cycling is important from a carbon sequestration perspective. A sediment trap study focused on the biological carbon pump system in the Ulleung Basin (UB) in the southwestern part of the East Sea (Japan Sea) was conducted from 2011 to 2017. Particulate organic carbon (POC) flux significantly increased by 37, 56, and 43% from 2014 to 2016 during the El Niño phase. We examined data related to water current variability, such as sea surface height, current velocity, and eddy frequency to understand their roles in particle transport. In addition, a Martin curve was employed to analyze the rate of vertical attenuation of POC flux in the UB. Current variability could be the most important factor influencing the increase in sinking-particle flux during the El Niño phase.

Dam Siltation in the Mediterranean Region Under Climate Change: A Case Study of Ahmed El Hansali Dam, Morocco

Dams are vital for irrigation, power generation, and domestic water needs, but siltation poses a significant challenge, especially in areas prone to water erosion, potentially shortening a dam’s lifespan. The Ahmed El Hansali Dam in Morocco faces heightened siltation due to its upstream region being susceptible to erosion-prone rocks and high runoff. This study estimates the siltation at the dam from its construction up to 2014 using bathymetric data and the Brown model, which is a widely-used empirical model that calculates reservoir trap efficiency. Additionally, the study evaluates the impact of Land Use and Land Cover (LULC) changes and projected future rainfall until around 2076 based on siltation rates. The results indicate that changes in LULC, particularly temporal variations in precipitation, have a significant impact on the siltation of the Ahmed El Hansali dam. Notably, rainfall is strongly correlated with the siltation rate, with an R2 of 0.92. The efficiency of sediment trapping (TE) is 97.64%, meaning that 97.64% of the sediment in the catchment area is trapped or deposited at the bottom of the dam. The estimated annual specific sediment yield is about 32,345.79 tons/km2/yr, and the sediment accumulation rate is approximately 4.75 Mm3/yr. The dam’s half-life is estimated to be around 2076, but future precipitation projections may extend this timeframe due to the strong correlation between siltation and precipitation. Additionally, soil erosion driven by land management practices plays a crucial role in future siltation dynamics. Hence, this study offers a comprehensive assessment of the siltation dynamics at the Ahmed El Hansali dam, providing essential information on the long-term effects of erosion, land use changes, and climate projections. These findings may assist decision makers in managing dam reservoir sedimentation more effectively, ensuring the durability of the dam and extending the reservoir life.

Estimation of the soil erosion and sediment trapping using Gerlach troughs in different Land Uses in Luangprabang Province

This study aims to study sediment loss in different areas by collecting data from the Reservoir and Gerlach troughs in the Luangprabang Province, Laos The implementation of this experiment was a selection of study areas to install soil sediment retention tools (Gerlach trough) according to 6 treatments such as T1: No teak+Ruzi grass; T2: No teak + Fallow; T3: Teak with low understory density + Natural regrowth; T4: Teak with low understory density + Ruzi grass; T5: Teak with high understory density+ Natural regrowth; T6: Teak with high understory density+ mixed fodder cover (Ruzi and Napier grass). In 3 replicates/treatments by RCBD design, a total of 18 instruments will be installed by installing them in a row on both sides of the soil, to trap the soil sediment that flows with the water, then there will be a collection of samples that can be collected, and then filter the soil sediment and dry it at a temperature of 105 degrees, for a period of 48 hours and calculate the amount of soil sediment loss in the area. Results found that the highest soil loss (sediment) was in the area planted teak with low understory density + Natural regrowth (T3) followed by the area planted teak with low understory density + Ruzi grass, (T4), and the lowest soil loss was in the area no teak+Ruzi grass (T1) and the area no teak + fallow (T2). While the highest surface water runoff was in the area planted teak with low understory density + Natural regrowth (T3) and the area planted teak with low understory density + Ruzi grass, (T4). On the other hand, factors that are related to surface water runoff and soil sediment loss such as percentage of land cover density, slope of the land, and residue or humus on the land were found that the area no teak with planted Ruzi grass and the area no teak with fallow (natural growth) had lowest rate of surface water runoff and lowest soil sediment loss compared to other areas. It can be concluded that the land cover factor has an important role in helping to reduce surface water runoff and help prevent soil sediments from being lost to runoff in agricultural land and upland cultivation.

Gradual Replacement of Soybean Meal with Brewer’s Yeast in Fingerling Nile Tilapia (Oreochromis niloticus) Diet, Resulting in a Polynomial Growth Pattern, Independent of Whether Reared in a Biofloc or Clear-Water System

A 60-day feeding experiment was conducted to examine whether (i) soybean meal (SBM) protein in the diet of Nile tilapia (Oreochromis niloticus) can be replaced with protein from spent brewer’s yeast (SBY); (ii) co-rearing with biofloc alters fish growth, feed conversion and protein efficiency compared with rearing in clear water; and (iii) accumulated protein quantity and quality in biofloc acts as a possible feed source for the fish in periods of low feed intake. The fish were reared in either a bio-recirculating aquaculture system (Bio-RAS) or a clear-water RAS (Cw-RAS). In Bio-RAS, the mechanical and biological filters used in Cw-RAS were replaced with an open bioreactor that delivered heterotrophic-based biofloc to the rearing tanks and also acted as a sedimentation trap for effluent water before recirculating it back into the rearing unit. The fish were fed four iso-nitrogenous and iso-energetic diets (~28% crude protein, ~19 MJ kg−1 gross energy) in which SBM protein was replaced with increasing levels of SBY, with triplicate tanks per inclusion level. The results revealed that average fish growth was greater in a biofloc environment compared with clear water and also greater at higher inclusion levels of SBY. However, in both rearing environments, fish growth displayed a second-degree polynomial distribution with increasing SBY inclusion level, with a peak between 30% and 60% inclusion. Fish in the biofloc environment showed better feed conversion ratio and protein retention, likely through ingesting both given feed and biofloc. Biofloc contained a significant amount of accumulated protein with a high biological profile, thereby constituting a possible feed reserve for the fish. A conclusion underlined by the apparent improved feed conversion of Bio-RAS reared fish, where that ingestion of biofloc will reduce the need for external feed per unit growth.

Inflation-induced motility for long-distance vertical migration.

The vertical migrations of pelagic organisms play a crucial role in shaping marine ecosystems and influencing global biogeochemical cycles. They also form the foundation of what might be the largest daily biomass movement on Earth. Surprisingly, among this diverse group of organisms, some single-cell protists can transit depths exceeding 50m without employing flagella or cilia. How these non-motile cells perform large migrations remains unknown. It has been previously proposed that this capability might rely on the cell's ability to regulate its internal density relative to seawater. Here, using the dinoflagellate algae Pyrocystis noctiluca as a model system, we discover a rapid cell inflation event post cell division, during which a single plankton cell expands its volume 6-fold in less than 10min. We demonstrate this rapid cellular inflation is the primary mechanism of density control. This self-regulated cellular inflation selectively imports fluid less dense than surrounding seawater and can thus effectively sling-shot a cell and reverse sedimentation within minutes. To accommodate its dramatic cellular expansion, Pyrocystis noctiluca possesses a unique reticulated cytoplasmic architecture that enables a rapid increase in overall cell volume without diluting its cytoplasmic content. We further present a generalized mathematical framework that unifies cell-cycle-driven density regulation, stratified ecology, and associated cell behavior in the open ocean. Our study unveils an ingenious strategy employed by a non-motile plankton to evade the gravitational sedimentation trap, highlighting how precise control of cell size and cell density can enable long-distance migration in the open ocean.

Utility of Certain AI Models in Climate-Induced Disasters

To address the current challenge of climate change at the local and global levels, this article discusses a few important water resources engineering topics, such as estimating the energy dissipation of flowing waters over hilly areas through the provision of regulated stepped channels, predicting the removal of silt deposition in the irrigation canal, and predicting groundwater level. Artificial intelligence (AI) in water resource engineering is now one of the most active study topics. As a result, multiple AI tools such as Random Forest (RF), Random Tree (RT), M5P (M5 model trees), M5Rules, Feed-Forward Neural Networks (FFNNs), Gradient Boosting Machine (GBM), Adaptive Boosting (AdaBoost), and Support Vector Machines kernel-based model (SVM-Pearson VII Universal Kernel, Radial Basis Function) are tested in the present study using various combinations of datasets. However, in various circumstances, including predicting energy dissipation of stepped channels and silt deposition in rivers, AI techniques outperformed the traditional approach in the literature. Out of all the models, the GBM model performed better than other AI tools in both the field of energy dissipation of stepped channels with a coefficient of determination (R2) of 0.998, root mean square error (RMSE) of 0.00182, and mean absolute error (MAE) of 0.0016 and sediment trapping efficiency of vortex tube ejector with an R2 of 0.997, RMSE of 0.769, and MAE of 0.531 during testing. On the other hand, the AI technique could not adequately understand the diversity in groundwater level datasets using field data from various stations. According to the current study, the AI tool works well in some fields of water resource engineering, but it has difficulty in other domains in capturing the diversity of datasets.

Wave‐Influenced Delta Morphodynamics, Long‐Term Sediment Bypass and Trapping Controlled by Relative Magnitudes of Riverine and Wave‐Driven Sediment Transport

AbstractRiver sediment supply (Qs) and longshore sediment transport (LST) are recognized as two paramount controls on river delta morphodynamics and stratigraphy. We employed the Delft3D model to simulate the evolution of deltas from fluvial to wave‐dominated conditions, revealing the interplay between river‐ and wave‐driven sediment quantities. Wave‐influenced deltas may show alternating accumulation and retreat patterns driven by avulsions and wave‐induced sediment diffusion, posing coastal management challenges. Deltas with higher wave energy evolve under a fine balance between river supply and intense wave‐mediated sediment redistribution and are highly vulnerable under conditions of sediment reduction. Reducing Qs by ∼40%–70%, common in modern dammed rivers, can rapidly shift bypass from ∼0 to 1 (no bypass to complete bypass). This leads to accelerated diffusion and potential sediment loss in modern deltas. The study highlights the importance of accurately computing sediment quantities in real‐world deltas for improved management, especially under increasing anthropogenic and climatic pressures.

Stratification controls the magnitude of in-lake phosphorus cycling: insights from a morphologically complex eutrophic lake

AbstractUsing a combination of sediment trap experiments, sedimentary biogeochemical analyses and mass balance calculations, we conducted a comprehensive quantitative evaluation of the in-lake phosphorus (P) cycles including in both the water and sediment phases for Lake Hiidenvesi, a dimictic eutrophic lake in southern Finland. We explicitly demonstrated the heterogeneity of the in-lake P cycles between basins with distinct morphological features. Enhanced interactions between waters and sediments occur in shallow and non-stratified areas, as evidenced by the magnitudes of gross sedimentation and total internal P loading. In such shallow areas, sediment resuspension contributes over 60% of the total internal P loading throughout the entire open water season. In contrast, sedimentary P cycling is less intensive in deep and stratified areas, where diffusive fluxes account for an average of 70% of total internal P loading. We show that sedimentary P burial plays a key role in controlling the in-lake P cycle. Permanent burial of P showing higher rates and efficiencies tends to occur in deeper areas. Overall, sediments in Lake Hiidenvesi act as a net P sink under modern biogeochemical settings; the lake is in the process of long-term recovery from eutrophication due to the larger annual P output than external loading.

Estimating Sediment Trap Efficiency of Flood Events During Flood Season in the Three Gorges Reservoir

AbstractSediment trapping significantly influences the comprehensive benefits of reservoirs and hinders the connection between sediment and nutrients in the upstream and downstream of rivers. Quantifying the role of sediment trapping by dams is important because this operation controls fluvial geomorphology, aquatic ecology, and water quality, particularly for flood processes with highly variable inflows. This study developed a new model to calculate the sediment trap efficiency (TE) of flood events during the flood season in the Three Gorges Reservoir (TGR) using a generalized theoretical approach. The TE of 55 flood events that occurred since the impoundment of the TGR were calculated and ranged from 16.0% to 99.8%, with a mean of 77.8%. Contrary to the previous understanding that large reservoirs have consistently large TE values based on long‐term data, our results show that large reservoirs can have a wide range of TE values during short‐term flood events. The proposed model estimates TE using three variables: inflow discharge, outflow discharge, and reservoir water level. Furthermore, the additional sedimentation risk to the TGR by optimized scheduling during the flood season is discussed. The results provide a reference for sedimentation management and optimal operation in the TGR.

A Global Ocean Opal Ballasting–Silicate Relationship

AbstractOpal and calcium carbonate are thought to regulate the biological pump's transfer of organic carbon to the deep ocean. A global sediment trap database exhibits large regional variations in the organic carbon flux associated with opal flux. These variations are well‐explained by upper ocean silicate concentrations, with high opal ‘ballasting’ in the silicate‐deplete tropical Atlantic Ocean, and low ballasting in the silicate‐rich Southern Ocean. A plausible, testable hypothesis is that opal ballasting varies because diatoms grow thicker frustules where silicate concentrations are higher, carrying less organic carbon per unit opal. The observed pattern does not fully emerge in an advanced ocean biogeochemical model when diatom silicification is represented using a single global parameterization as a function of silicate and iron. Our results suggest a need for improving understanding of currently modeled processes and/or considering additional parameterizations to capture the links between elemental cycles and future biological pump changes.

Vortex Trapping of Suspended Sand Grains Over Ripples

AbstractCoastal hydrodynamics and morphodynamics integrate the effects of small‐scale fluid‐sediment interactions; yet, these small‐scale processes are not well understood. To investigate sediment trapping by turbulent coherent structures or vortices, the transport of coarse sand over ripples was analyzed in a small‐oscillatory flow tunnel with phase‐separated Particle Image and Tracking Velocimetry. Results from one of the first direct measurements of vortex‐trapped sand grains under oscillatory flows are presented. The vortices mobilized sand grains along the ripple slopes just prior to flow reversal and transported the suspended sediment grains. During several flow cycles, some sand grains were temporarily trapped in the vortex, prescribing semi‐circular trajectories off‐center from the vortex core in quadrants of the vortex that were closest to the ripple slope, as illustrated by Nielsen (1992, https://doi.org/10.1142/1269). Comparisons of the horizontal sediment grain velocity with the horizontal fluid velocity yielded a linear relationship with a slope of 0.87. The vertical grain velocities also varied linearly with the vertical fluid velocity with a slope of approximately 1 and an offset of −0.08 m . The offset is close to the still water settling velocity for coarse sand grains, as hypothesized during vortex trapping. Additionally, estimates of the off‐center distance, between the centers of the semi‐circular sediment paths and vortex cores, compared well with the ratio of the settling velocity to the radian frequency of the vortex yielding a linear regression slope of 0.99. Improved understanding of vortex trapping effects on sediment dynamics may decrease uncertainty in model predictions of large‐scale coastal hydrodynamics and sediment transport.

Proximity to inlet channel drives spatial variation in sediment carbon across a lagoonal seagrass meadow

Seagrass meadows can be sinks for organic carbon, but estimates of global organic carbon stocks are complicated by substantial spatial variability in organic carbon burial observed within meadows. To improve estimates of organic carbon burial in seagrass meadows, it is necessary to understand the causes of the spatial heterogeneity. This study investigated relationships between spatial patterns in sediment organic carbon storage and accretion rates, hydrodynamics, and proximity to sources of organic carbon in a current-dominated Zostera marina Linnaeus meadow in Menemsha Pond, Massachusetts, USA. Sediment and velocity measurements were conducted at six stations along a 150-m transect across the meadow oriented perpendicular to the pond's unvegetated inlet channel. The meadow's edge near the channel had higher organic carbon than the channel as well as the highest organic carbon within the meadow. With increasing distance from the meadow's edge, all of the following decreased: sediment organic and total carbon, sediment accretion rates, peak tidal velocity, sediment trap mass deposition rate, and the relative contribution of non-seagrass sources to sediment organic carbon. Lower tidal velocities farther from the inlet channel reduced sediment resuspension, consistent with lower sediment trap mass deposition, which should enhance organic carbon content and organic carbon accretion rates. However, the opposite trend of decreasing organic carbon content (>50 % across the transect) and decreasing accretion rates with distance from channel was observed. This suggested that the local hydrodynamic intensity was not controlling organic carbon accretion, which was instead constrained by supply limitation and controlled by the lagoon-scale flow circulation.

Vertical growth rate of planted vegetation controls dune growth on a sandy beach

The integration of coastal dunes planted with vegetation and dikes combines traditional infrastructure with dynamic aeolian sediment and ecological processes to enhance coastal resilience. The functioning of such dune-dike hybrid Nature-based Solution strongly depends on aeolian sediment transport and the vertical growth rate of vegetation. We used the AeoLiS numerical model to investigate the relative importance of aeolian and vegetation dynamics in the evolution of a 120 m long and 20 m wide marram grass-planted dune field on a Belgian sandy beach backed by a seawall, constructed in 2021. AeoLiS proved to be a promising tool for predicting these systems, effectively capturing aeolian sediment deposition, vegetation growth, and profile development three years post-construction. Seasonal variations in vegetation trapping efficiency, driven by sediment burial, and seasonal plant growth emerged as important factors controlling dune growth. Profile development discrepancies were attributed to unaccounted biotic and abiotic factors, highlighting the complexity of coastal eco-geomorphological processes. Dunes planted with vegetation wider than 20 m were identified to enhance sediment trapping without an increase in dune height. These findings offer actionable insights for coastal management, promoting strategic dune design and planting approaches to reinforce shoreline resilience. Additionally, the findings underscore the necessity for advancing eco-morphodynamic models and deepening our knowledge of coastal dune dynamics.

Predicting particle catchment areas of deep-ocean sediment traps using machine learning

Abstract. The ocean's biological carbon pump plays a major role in climate and biogeochemical cycles. Photosynthesis at the surface produces particles that are exported to the deep ocean by gravity. Sediment traps, which measure deep-carbon fluxes, help to quantify the carbon stored by this process. However, it is challenging to precisely identify the surface origin of particles trapped thousands of meters deep due to the influence of ocean circulation on the sinking path of carbon. In this study, we conducted a series of numerical Lagrangian experiments in the Porcupine Abyssal Plain region of the North Atlantic and developed a machine learning approach to predict the surface origin of particles trapped in a deep-ocean sediment trap. Our numerical experiments support the predictive performance of the machine learning approach, and surface conditions appear to provide valuable information for accurately predicting the source area, suggesting a potential application with satellite data. We also identify factors that potentially affect prediction efficiency, and we show that the best predictions are associated with low kinetic energy and the presence of mesoscale eddies above the trap. This new tool could provide a better link between satellite-derived sea surface observations and deep-ocean sediment trap measurements, ultimately improving our understanding of the biological-carbon-pump mechanism.

Seasonal and annual variations of sediment trapping and particulate organic carbon burial in Yellow River reservoirs

The Yellow River is distinguished by the highest sediment load in mainland China and significant siltation in artificial reservoirs along its main channel, reducing water availability, sediment trapping, and carbon burial in the hydrological project. Since 2002, the Water Sediment Regulation Scheme (WSRS) has been progressively implemented as a hydraulic management strategy to mitigate reservoir sedimentation in the middle-lower basin reservoirs. However, this substantial release of sediment and water has also affected river morphology, carbon burial, and sediment trapping.This research assesses the evolution of particulate organic carbon burial and sediment trapping in eight Yellow River reservoirs from 2002 to 2018, covering the upper and middle-lower basins and two reservoirs in the Yiluo River sub-basin. We calculated the annual and seasonal variations using hydrological data from 11 stations along the Yellow River. A hydrological framework was developed to calculate sediment trapping, and a Monte Carlo analysis was performed to estimate particulate organic carbon burial across all the evaluated reservoirs.We found that sediment trapping and carbon burial in upper basin reservoirs are most influenced by shifts in the precipitation regime, particularly by natural events such as severe droughts or heavy rainfall. A strong correlation was observed between annual precipitation variations and sediment load. In middle-lower basin reservoirs, the major artificial sediment regulation is strongly linked to a significant reduction in sediment trapping and particulate organic carbon burial. This impact is especially notable in the Yiluo River Sub-basin reservoirs, which have experienced a >90 % reduction compared to levels before the WSRS implementation.Finally, we highlight the consequences of climate change and artificial water management strategies in reservoirs, demonstrating how both affect their capacity for sediment trapping and impact their role as significant carbon sinks.

A New Method for the Detection of Siliceous Microfossils on Sediment Microscope Slides Using Convolutional Neural Networks

AbstractDiatom communities preserved in sediment samples are valuable indicators for understanding the past and present dynamics of phytoplankton communities, and their response to environmental changes. These studies are traditionally achieved by counting methods using optical microscopy, a time‐consuming process that requires taxonomic expertise. With the advent of automated image acquisition workflows, large image data sets can now be acquired, but require efficient preprocessing methods. Detecting diatom frustules on microscope images is a challenge due to their low relief, diverse shapes, and tendency to aggregate, which prevent the use of traditional thresholding techniques. Deep learning algorithms have the potential to resolve these challenges, more particularly for the task of object detection. Here we explore the use of a Faster Region‐based Convolutional Neural Network model to detect siliceous biominerals, including diatoms, in microscope images of a sediment trap series from the Mediterranean Sea. Our workflow demonstrates promising results, achieving a precision score of 0.72 and a recall score of 0.74 when applied to a test set of Mediterranean diatom images. Our model performance decreases when used to detect fragments of these microfossils; it also decreases when particles are aggregated or when images are out of focus. Microfossil detection remains high when the model is used on a microscope image set of sediments from a different oceanic basin, demonstrating its potential for application in a wide range of contemporary and paleoenvironmental studies. This automated method provides a valuable tool for analyzing complex samples, particularly for rare species under‐represented in training data sets.

Vertical Flux of Microplastics in the Deep Subtropical Pacific Ocean: Moored Sediment-Trap Observations within the Kuroshio Extension Recirculation Gyre.

The Kuroshio Extension recirculation gyre in the western North Pacific is an accumulation site of plastic litter transported by the Kuroshio Current. A sediment trap was moored at a depth of 4900 m at Station KEO within the Kuroshio Extension recirculation gyre, and the vertical flux of microplastics in sinking particles of size <1 mm was observed. Forty-one sediment-trap samples collected from July 1, 2014, to October 2, 2016, were analyzed with a micro-Fourier transform infrared spectrometer and microplastics were detected in all samples. Seventeen polymer types were identified, and 90% of the microplastics were less than 100 μm in size. Microplastic sinking was driven by the action of the biological pump, which was in turn driven by seasonal variations in solar radiation and increased surface primary production typical of the spring season. Microplastic mass flux varied from 4.5 × 10-3 to 0.38 mg m-2 day-1 during the sampling period, with a mean and standard deviation of 0.054 ± 0.075 mg m-2 day-1. Extrapolating the annual microplastic mass flux at Station KEO to the entire Kuroshio Extension recirculation gyre, it is estimated that 0.028 million metric tons of microplastics are transported annually to 4900 m depth in this area.

Soil redistribution rates along the forested and cultivated steep hillslope in the mid‐Himalayas using fallout—137Cs and RUSLE model

AbstractSoil erosion emerged as a significant land degradation concern, causing serious threat to soil ecosystem services in the Himalayan region. The complex topography of the region poses limitations to the measurement of soil redistribution (erosion, transport, and deposition) rate, necessitated for the effective soil conservation planning. The study investigated soil redistribution processes over a typical complex hillslope of the mid‐Himalayan region using the fallout radionuclide (FRN)—137Cs method and Revised Universal Soil Loss Equation (RUSLE) model. It involved a comparison of 137Cs measured soil redistribution and the RUSLE model estimates, aiming to assess its correspondence over the complex hillslope. Analysis of 137Cs measurements revealed the highest net erosion (−13.2 t ha−1 year−1) at the upper hillslope with a convex shape, while sediment deposition occurred at the lower (36.9 t ha−1 year−1) and valley (32.5 t ha−1 year−1) hillslope positions with a concave shape. The RUSLE model also estimated the highest erosion on the upper hillslope (−12.3 t ha−1 year−1) but the lowest erosion at the lower (−0.88 t ha−1 year−1) and valley (−0.32 t ha−1 year−1) hillslopes, that differed with the 137Cs method. The 137Cs method provided soil redistribution rate (either net erosion or deposition), whereas RUSLE model only showed the gross erosion rate. Thus, the estimate from RUSLE corresponds only to hillslope positions with a convex and straight shapes. The distribution of 137Cs measurements has clearly revealed the influence of slope shape and steepness in governing erosion and deposition processes at the hillslope positions with convex and concave slope shapes, respectively. In addition, terraces effectively trap sediments from upslope areas. Investigation of soil erosion using 137Cs measurement along with the RUSLE model helped to validate erosion and deposition processes over the hillslope positions. The study will help to suggest suitable conservation measures for the various hillslope positions in the mid‐Himalayan region.

What to monitor? Microplastics in a freshwater lake – From seasonal surface water to bottom sediments

Marine microplastics have received considerable attention, and efforts are underway to develop standardised methods for sampling, sample treatment, and analysis, while the observation of freshwater ecosystems remains relatively overlooked. To address this understudied environment, we present a comprehensive case study on microplastics in an urban lake from Baltic region of Northern Europe covering the seasonal dynamics of microplastics in surface water, deposition rate throughout one year in sediment traps and distribution of microplastics in dated sediment archive to determine the most representative environmental compartment for microplastic pollution monitoring. The following well-established microplastic research methods have been used: Manta trawling for surface water, trapping for assessing microplastics sedimentation rate and coring for sediments. Attenuated total reflection and micro-Fourier transform infrared spectroscopy methods were used to investigate the synthetic nature of identified particles. The sediment core chronology was based on 210Pb and Bayesian Plum model revealing sediment layers to represent even the time before the beginning of plastic mass production (approximately 1950). The surface water microplastic concentrations were higher in summer (5.71 particles/m3) and gradually decreased towards winter (0.75 particles/m3); they were almost 25 times higher in more recent (2018) sediments than in the deeper layers referring to years prior to 1890. Surprisingly, microplastic particles were found in sediments before the year 1950. The microplastic deposition rate was 9.47 particles/cm2/year or 4.31 µg/cm2/year. The most abundant polymers were polyethylene, polystyrene and polypropylene, and the prominent particle shapes were fibres in surface water and fragments in sediments. Our results provide a baseline for evaluating future contamination level changes in highly urbanized area. We recommend the combination of surface water filtering with net and sediment trapping methods for monitoring microplastics in lakes since this method requires little time and financial resources for sampling and processing and produces information on temporal microplastic occurrence and deposition.

Mesoproterozoic siliciclastic stromatolites of Chapada Diamantina (Brazil): Morphological types, genesis and environmental context

Laminations of organosedimentary structures can be formed by three distinct processes: (i) bio-induced mineral precipitation, (ii) trapping and binding, and (iii) abiotic mineral precipitation and each of these processes predominates in a certain geological time interval. Agglutinated stromatolites are rare and seem to form in specific environmental conditions. Siliciclastic stromatolites are an even rarer class of agglutinated stromatolites, which are formed in response to the process of trapping and binding of siliciclastic grains by upright filaments or by extracellular polymeric substances (EPS). This study describes and interprets one of the oldest siliciclastic stromatolites of the geological record and discusses the microbial evidence and mechanisms that controlled their accumulation and preservation. Two compound sections were analyzed and ten thin sections were prepared to characterize the siliciclastic stromatolites from the Mesoproterozoic Caboclo Formation (Brazil). Stromatolites are present in two different lithofacies associations: (i) shoreface and (ii) offshore transition. The shoreface stromatolites are characterized by silty to sandy texture and poor lamination, and the distal ones by clay, silt grains, less sand, and distinct lamination. The volume of siliciclastic grains composing the stromatolite fabric is >85% in the shoreface and >30% in offshore transition. These stromatolites were deposited in a favorable environment for trapping and binding of siliciclastic sediments: a wave-dominated siliciclastic ramp with the availability of siliciclastic grains and frequent water column agitation. The marine environment is favorable for forming EPS with good adhesive properties. Besides, the Caboclo Formation age (1.3–1.0 Ga) coincides with an abrupt fall in the amount of atmospheric CO2 reflected in CaCO3 saturation in the oceans. This change in ocean chemistry may have led to a change in stromatolite fabric, from the sparry crust and fine-grained precipitated to agglutinated.