Sediment Layers Research Articles

Assessing the changes in marine microalgae diversity in the Nanji Islands Nature Reserve over the past decades using sediment eDNA

The Nanji Islands, designated as one of China’s national nature reserves, are renowned for their abundant microalgal resources. Changes in microalgae can serve as indicators of marine environmental shifts. Despite this significance, the absence of comprehensive historical records on microalgal diversity has limited the evaluation of marine environmental protection efforts. This study addresses this gap by analyzing surface sediments and sediment cores from the Nanji Islands, utilizing 210Pb dating and employing environmental DNA (eDNA) technology to trace historical shifts in the molecular diversity of microalgae. Chloroplast gene fragments were amplified using rbcL primers, and 210Pb dating determined the deepest sediment layer (78-80 cm) to date back to 1994. From the 70-72 cm layer to the 60-62 cm layer, the number of microalgal reads increased rapidly from 27,716 to 65,143, signifying enhanced abundance over the 10 years following the establishment of the nature reserve. This was followed by a deceleration in microalgal abundance growth over the subsequent 20 years, potentially reflecting variations in primary production of microalgae. Concurrently, the rise in operational taxonomic units (OTUs) and the Margalef index suggest a boost in microalgal diversity, which may be attributed to improvements in the marine environment. The microalgal community composition has shifted from a dominance of Dinoflagellata and Streptophyta to a predominance of Bacillariophyta, the change in phosphate would be one of the impact factors worth noting. This study provides foundational data on the historical changes in microalgae in the Nanji Islands and serves as a reference for exploring the relationship between environmental conditions and microalgal dynamics.

Investigating Arctic Permafrost Dynamics Using Electrical Resistivity Imaging and Borehole Measurement in Svalbard

This study utilized electrical resistivity imaging (ERI) to investigate subsurface characteristics near Nicolaus Copernicus University Polar Station on the western Spitsbergen-Kaffiøyra Plain island in the Svalbard archipelago. Surveys along two lines, LN (148 m) collected in 2022 and 2023, and ST (40 m) collected in 2023, were conducted to assess resistivity and its correlation with ground temperatures. The LN line revealed a 1- to 2-m-thick resistive unsaturated outwash sediment layer, potentially indicative of permafrost. Comparing the LN resistivity result between 2022 and 2023, a 600 Ohm.m decrease in the unsaturated active layer in 2023 was observed, attributed to a 5.8 °C temperature increase, suggesting a link to global warming. ERI along the ST line depicted resistivity, reaching its minimum at approximately 1.6 m, rising to over 200 Ohm.m at 4 m, and slightly decreasing to around 150 Ohm.m at 7 m. Temperature measurements from the ST line’s monitoring strongly confirmed that the active layer extends to around 1.6 m, with permafrost located at greater depths. Additionally, water content distribution in the ST line was estimated after temperature correction, revealing a groundwater depth of approximately 1.06 m, consistent with measurements from the S4 borehole on the ST line. This study provides valuable insights into Arctic subsurface dynamics, emphasizing the sensitivity of resistivity patterns to climate change and offering a comprehensive understanding of permafrost behavior in the region.

Proximal Sensing for Characterising Seaweed Aquaculture Crop Conditions: Optical Detection of Ice-Ice Disease

Crop monitoring is a fundamental practice in seaweed aquaculture. Seaweeds are vulnerable to several threats such as ice-ice disease (IID) causing a whitening of the thallus due to depigmentation. Crop condition assessment is important for minimizing yield losses and improving the biosecurity of seaweed farms. The recent influence of modern technology has resulted in the development of precision aquaculture. The present study focuses on the exploitation of spectral reflectance in the visible and near-infrared regions for characterizing the crop condition of two of the most cultivated Eucheumatoids species: Kappaphycus alvareezi and Eucheuma denticulatum. In particular, the influence of spectral resolution is examined towards discriminating: (a) species and morphotypes, (b) different levels of seaweed health (i.e., from healthy to completely depigmented) and (c) depigmented from silted specimens (thallus covered by a thin layer of sediment). Two spectral libraries were built at different spectral resolutions (5 and 45 spectral bands) using in situ data. In addition, proximal multispectral imagery using a drone-based sensor was utilised. At each experimental scenario, the spectral data were classified using a Random Forest algorithm for crop condition identification. The results showed good discrimination (83–99% overall accuracy) for crop conditions and morphotypes regardless of spectral resolution. According to the importance scores of the hyperspectral data, useful wavelengths were identified for discriminating healthy seaweeds from seaweeds with varying symptoms of IID (i.e., thalli whitening). These wavelengths assisted in selecting a set of vegetation indices for testing their ability to improve crop condition characterisation. Specifically, five vegetation indices (the RBNDVI, GLI, Hue, Green–Red ratio and NGRDI) were found to improve classification accuracy, making them recommended for seaweed health monitoring. Image-based classification demonstrated that multispectral library data can be extended to photomosaics to assess seaweed conditions on a broad scale. The results of this study suggest that proximal sensing is a first step towards effective seaweed crop monitoring, enhancing yield and contributing to aquaculture biosecurity.

Dynamic landscape response to Younger Dryas and earliest Holocene cooling events in the European Eastern Alps (Austria)

In classic loess areas research into dust deposition and concomitant environmental changes has a long history and numerous well-investigated loess-palaeosol sequences provide insights into Late Quaternary landscape responses to climatic change on orbital to centennial time scales. This contrasts with mountain regions, where an understanding of dust deposition under rapidly changing climatic and environmental conditions is much less developed. Here we describe two sediment records from the Austrian Alps that provide rare evidence for intramontane loess accumulation. Dust deposition has been numerically constrained to the Younger Dryas (YD) to earliest Holocene interval, making these sites the first proof of significant intramontane aeolian activity during this time interval in the Eastern Alps.At study site 1, located in the Northern Calcareous Alps, a loess layer 10–20 cm in thickness and laterally exposed over more than 300 m is sandwiched into an alluvial-fan succession. Two optically-stimulated luminescence ages of quartz and four radiocarbon ages of charcoals indicate loess accumulation during the Younger Dryas to earliest Holocene. This laterally extensive loess drape suggests much drier climatic conditions compared to today, which is corroborated by palynological investigations. Macro- and micro-charcoal particles within the loess indicate regional wildfires that might have exaggerated climatically induced sedimentary processes. The second site is a Mesolithic site located ∼30 km southeast of site 1. At site two, redeposited till and pebbly scree are sharply overlain by a few centimetre thick light-grey loess layer, which is capped by the archaeological living floor hosting 14C dated fireplaces suggesting human presence as early as 10.9 ± 0.2 cal ka BP. These radiocarbon ages in combination with single-grain IRSL dating of feldspar at site two suggests concomitant aeolian deposition at site 1 and 2.Recently, a widespread drape of loess deposited immediately subsequent to the LGM was described for the same sector of the Eastern Alps (Gild et al., 2018). The present study expands on these findings and provides evidence for the recurrence of loess deposition also during the YD to earliest Holocene, and suggests a highly sensitive response of the geomorphic system in mountain ranges to abrupt post-LGM climate fluctuations. We conclude that, in addition to moraine records of Alpine glaciers and speleothems that accurately chronicle Late Glacial temperature fluctuations, the spatio-temporal pattern of inner-Alpine loess deposits records the mode and sensitivity of landscape responses to such cooling events. Because such aeolian sediment layers can be redeposited or pedologically overprinted, they are often overlooked, and are thus still severely under-researched.

Qualitative variability of dissolved organic matter in the Baltic Sea sediments apparent from fluxes and optical properties

IntroductionThe release of dissolved organic matter (DOM) from sediments serves as an important part of the carbon cycle.MethodsHere, we address pore water DOM quality and its release from shallow sediments (0–10 cm) of the central and southern Baltic Sea - Gdansk, Bornholm, and Eastern Gotland Basins - using excitation–emission matrix spectroscopy and size-exclusion chromatography.ResultsDOM release from sediments displayed spatial variability, with diffusive DOC fluxes ranging from 0.02 to 1.06 mmol m−2 d−1, and basin-averaged fluxes increased in the order Gotland < Bornholm < Gdansk. DOM qualitative characteristics also varied among investigated basins. In the oxygen-limited study sites from the Gdansk Basin, we observed elevated abundances of low apparent molecular weight DOM fraction and proteinaceous-like fluorescent DOM, while in the Bornholm Basin, pore water DOM was generally more humic-like and of higher apparent molecular weight. Pore waters from the deepest study sites in the Gotland Basin were qualitatively very similar to those of the pore waters from the upper sediment layers (0–4 cm) from all other investigated sites, suggesting little organic matter reworking at depth at those stations.DiscussionOur results suggest that the spatial variability in the magnitude of DOM release may be linked to the qualitative differences of DOM in sediments.

Distribution features of <sup>238</sup>U, <sup>232</sup>Th and <sup>226</sup>Ra in bottom sediments of the shelf and continental slope of Svalbard

The features of the distribution of concentrations of238U,232Th and226Ra in the surface layer of bottom sediments in the bottom sediments of the shelf and continental slope of Svalbard are considered. The content of226Ra,232Th, and238U varied in the range 22–134.3, 22.4–50.9, and 10.9–37.7 Bq/kg, respectively. The amount of226Ra nonequilibrium with238U (226Raex) ranged from 23 to 73% of the total226Ra content in sediments. The maximum concentrations of226Ra,238U,232Th and226Raex(134.3, 37.7, 50.9, and 98.2 Bq/kg, respectively) were obtained in the area of increased bioproductivity (Eagle Trough). In this zone, the relationship between the concentrations of226Ra and226Raexwith the content of organic matter in sediment is well expressed, the correlation coefficients areR= 0.94 and 0.92, respectively, which indicates a significant contribution of the biological community to the accumulation of226Ra in bottom sediments. The226Ra concentration and the226Ra excess value are negatively related to the redox potential of the sediment (R= –0.88). This pattern is also true in other areas of the Svalbard waters. In general, for the entire array of observations, the concentrations of238U and232Th increase with increasing content of organic carbon in the sediment (R= 0.72 and 0.7, respectively). The concentrations of238U and232Th decrease with increasing Ccarbcontent in the sediment (R= –0.79 and –0.81, respectively). The data obtained indicate the need to take into account the226Ra excess when assessing the total natural radioactivity of marine sediments, the value of which may exceed the radioactivity of238U and232Th.

Specialists regulate microbial network and community assembly in subtropical seagrass sediments under differing land use conditions

Microorganisms in the sediment play a pivotal role in the functioning and stability of seagrass ecosystems and their dynamics are influenced by the nutrient acquisition strategies of host plants. While the distinct impacts of microbial generalists and specialists on community dynamics are recognized, their distribution patterns and ecological roles within seagrass ecosystems remain largely unexplored. To address this issue, we conducted an analysis of community assembly processes and co-occurrence relationships of both microbial generalists and specialists within sediment profiles (0–100 cm) from seagrass habitats subjected to differing land use conditions. The results revealed that seagrasses in Yifeng Estuary experienced the large proportion of cultivated land and exhibited higher organic carbon content in the 0–20 cm surface sediment layer. Nitrogen-cycling bacteria were predominantly associated with seagrasses from Yifeng Estuary, whereas Vibrio spp. was more prevalent in seagrasses from Liusha Bay. Notably, seagrass Halophia beccarii (YHB) in Yifeng Estuary harbored higher niche breadths for both microbial generalist and specialist compared to Halodule uninervis (LHU) and Halophia ovalis (LHO) from Liusha Bay. Stochastic processes were pivotal in shaping seagrass sediment microbial communities, with a higher immigration rate observed in YHB, suggesting greater microbial turnover in this area. Additionally, YHB sediment presented lower drift and higher dispersal limitation among generalists compared to LHU and LHO, whereas the pattern was reversed among specialists. Specialists were found to play a crucial role in shaping microbial interactions within YHB sediment, with genera Halioglobus identified as keystone species in the network. The specialists were further found to significantly influence microbial β-diversity in seagrass sediment directly. Overall, our findings illustrated how microbial generalists and specialists were distributed in seagrass sediments in response to land use changes and provided new insights into the potential roles of microbial regulation in degraded seagrass ecosystems.

Diving into the Depths: Uncovering Microplastics in Norwegian Coastal Sediment Cores.

High concentrations of microplastics (MPs) have been documented in the deep-sea surface sediments of the Arctic Ocean. However, studies investigating their high-resolution vertical distribution in sediments from the European waters to the Arctic remain limited. This study examines MPs in five sediment cores from the Norwegian Coastal Current (NCC), encompassing the water-sediment interface and sediment layers up to 19 cm depth. Advanced analytical methods for MP identification down to 11 μm in size were combined with radiometric dating and lithology observations. MPs were present across all sediment cores, including layers predating the introduction of plastics, with concentrations exhibiting significant variation (54-12,491 MP kg-1). The smallest size class (11 μm) predominated in most sediment layers (34-100%). A total of 18 different polymer types were identified across all sediment layers, with polymer diversity and depth correlations varying widely between stations. Our findings suggest that differences in seafloor topography and the impact of anthropogenic activities (e.g., fishing) lead to varying environmental conditions at the sampling sites, influencing the vertical distribution of MPs. This challenges the reliability of using environmental parameters to predict MP accumulation zones and questions the use of MPs in sediment cores as indicators of the Anthropocene.

A Detailed Sedimentological Analysis of Colour Lake, Axel Heiberg Island, Nunavut

This research project examines sediments in Colour Lake, a non-glacial lake on Axel Heiberg Island in the Canadian High Arctic. Analyzing the mineralogical composition, structural morphology and deposition patterns of the accumulated lake sediments provides information about the depositional environment and can serve as proxies for past environmental conditions. Work focused primarily on a 53 cm long sediment core collected in 2019. The objectives were: (1) to document distinct sediment units and interpret their depositional history by high resolution image analysis and microscopic observations in thin sections; (2) to identify schwertmannite, an iron oxyhydroxy-sulfate mineral within the sediments using scanning electron microscopy and x-ray fluorescence (XRF); (3) to determine this mineral’s relationship with siliciclastic deposits; and (4) to establish sediment chronology by 210Pb and 137Cs dating. Data was organized into pollen charts, incorporating images, scans, sediment stratigraphy, and grain size distributions to better understand sediment layers and their positions within the core. Thirteen lithozones were identified based on observed variations in the core, differing in terms of mud and clay lens distribution, the presence of schwertmannite, lamination patterns (graded or non-graded detrital laminations), the occurrence of biological components, and detrital mineral grain sizes. A recurring lithozone featuring non-graded, amorphous clay with schwertmannite, typically overlying either graded or reverse-graded mud, was observed throughout the core. While the mechanisms responsible for sediment deposition have not been fully explored, they are suspected to be related to hyperpycnal flows and slumping events. An Intervaled Sediment Extruder (ISE) was developed for precise sediment extrusion from a core collected in July for 210Pb and 137Cs dating, which will constrain sedimentation rates and correlate depositional events with past environmental conditions. Future work will focus on linking sediment structures to climatic events, identifying annually laminated layers (varves), and completing dating analyses to better understand past climate variations.

Revisiting past savanna environments: Pollen analysis of the Colbyn wetland on the southern African central plateau

A high-resolution, radiocarbon dated, pollen sequence of the ecotone between the Grassland and Savanna Biomes, was extracted from a 2.5 m peat core at the Colbyn wetland in South Africa. The lithology indicates transitions between organic sediment, clay, and well-preserved peat layers. The pollen and micro-charcoal records suggest interactions between the seasonal climate, burning and possible human and other disturbance. The vegetation development over the last 4000 cal yr BP is compared with chronologically parallel pollen sequences from the nearby Moreleta River and Rietvlei Dam sequences. The study, that can be correlated with wider regional isotopic records of the region, shows drier conditions c. 3800 to 3400 cal yr BP, and around 800 cal yr BP, and a wetter phase at Colbyn c. 3000–1500 cal yr BP.

REWARE: a seismic processing algorithm to retrieve geological information from the water column

SUMMARY When interpreting marine very high-resolution (VHR) single-channel seismic reflection data, the signal in the water column is generally considered as noise and is often eliminated by a water-mute application to focus on geological information under the seafloor. Alternatively, the signal in the water column can be used to study ocean currents or gas/fluid emissions. To provide images of the sedimentary formations and tectonic structures beneath the seafloor in shallow water regions, such as continental shelves and lakes, marine seismic reflection profiles are often acquired using a single-channel streamer and sparker-type source, providing VHR data, with limited penetration depth. To exploit the full potential of these single-channel data, we propose a simple algorithm, called REWARE (Recovery of Water-column Acoustic Reflectors). This algorithm allows to extract further geological information from the water-column data using open-source codes (Seismic Un*x), adding the coherent signal from the previous shots, recorded in the water column, to the previous traces. The record length becomes longer while maintaining a very high trace-to-trace consistency. To demonstrate its efficiency, we present two examples of the REWARE processing in two different geological contexts: the East Sardinia shelf (Italy) and the North Evia Gulf (Greece). This method provides deeper images than with original data for seismic data acquired across steep slopes, such as canyons or continental shelf breaks. Thus, depending on the seafloor geometry and subseafloor structures, it is possible to image or map sediment layers and tectonic structures at depth, keeping a very high structural resolution.

Fine Shallow Structures of Binchuan Basin Inverted From Receiver Functions and Implications for Basin Evolution

AbstractThe understanding of the velocity structure and basement morphology within the basin is crucial for seismic hazard mitigation and the study of basin evolution. To explore the intricate structure of the Binchuan Basin in western Yunnan, China, we deployed a linear dense array in the northern region of the Binchuan Basin, with inter‐station distance ranging from 50 to 100 m. We propose a novel receiver function processing workflow. Initially, we extracted coherent receiver functions based on the dense array, followed by a inversion of basement morphology, S‐wave velocities, and sedimentary layer's average Vp/Vs ratio jointly with frequency‐dependent teleseismic apparent shear velocity and receiver function waveforms. The results show that S‐wave velocity anomalies correspond to the unconsolidated sediments. The thickness of the sedimentary layer ranges from ∼0.5 to ∼0.75 km. The basement morphology suggests the basin is controlled by normal faults. Additionally, intra‐basin faults displayed higher fault displacement to length ratios (∼0.27) than most isolated normal faults (10−3–10−1), which may result from accumulated fault displacement due to interactions between fault segments. These results emphasize the significant role of N–S trending intra‐basin faults in basin evolution, suggesting that micro‐block rotations and transitional movements within the Northwestern Yunnan Rift Zone are primary mechanisms shaping the Binchuan Basin. We further proposed a multi‐stage model for the evolution of the Binchuan Basin. The robustness testing validates that the proposed processing flow is an effective approach to comprehensively image the basin velocity structure and the basement morphology.

Plane-wave and cylindrical-wave acoustic reflection from a marine sediment with layering representative of the New England Mud Patch.

An analysis is presented of reflection from a marine sediment consisting of a homogeneous mud layer overlying a sand-mud basement, the latter with an upward-refracting, inverse-square sound speed profile. Such layering is representative of the sediment at the New England Mud Patch (NEMP). By applying appropriate integral transforms and their inverses to the Helmholtz equations for the ocean and the two sediment layers, along with the boundary conditions, a Sommerfeld-Weyl type of wavenumber integral is obtained for the cylindrical-wave reflection coefficient of the sediment, R. A stationary phase evaluation of this integral yields a closed-form expression for the plane-wave reflection coefficient, R0. In the absence of attenuation, the plane-wave solution exhibits total reflection up to a critical grazing angle, ac, but when attenuation in the sediment is introduced, the region of total reflection in |R0| is replaced by a sequence of contiguous peaks. With realistic levels of sediment attenuation, the cylindrical-wave solution, |R|, exhibits a quasi-critical grazing angle, less than ac, which is strongly dependent on the source-plus-receiver height above the seabed, which is mildly dependent on the depth of the mud layer but is essentially independent of frequency. Such behavior is consistent with independent experimental observations at the NEMP.

Small grazing angle reflection and the sound siphon effect over a low velocity layer of sediments.

The low-order normal modes with small grazing angles (SGA) often control long-range sound field characteristics in shallow water. The SGA reflection loss from a half-space low-velocity bottom (LVB) is independent of the sound attenuation, except around the angle of complete transmission; the SGA bottom reflection loss (BRL) from a seafloor with a top low-velocity layer is very insensitive to the LVB attenuation also, except around a few selected frequencies. Thus, the "seafloor velocity-attenuation coupling" problem will be more fatal for LVB geo-acoustic inversions. The dispersion equation of the normal modes in the LVB layer is coincidentally the same as the singularity expression of the SGA reflection coefficient in the water column, resulting in a sound siphon effect that causes the abnormally high SGA BRL and transmission loss in the water at the siphon frequencies. The siphon effect is very sensitive to seafloor acoustic parameters, might offer a physical base for geo-acoustic inversion, and show a dim light in a "gray area" for inverting the LVB sound attenuation at low to mid frequencies. As an example, the acoustic siphon effect and related seafloor geophysical parameters forming it in the Yellow Sea are reported in this paper.

Датирование современной осадочной толщи краевых бассейнов Восточного Мурмана (Кольский полуостров) на примере губ Ярнышная и Зеленецкая

The authors have studied sediment genesis in the Kola Peninsula bays, the most popular and developed part of the coastal shelf by the population. The main tool used is the method of radioisotope chronology of sedimentary layers based on changes in the specific activity of the natural isotope 210Pb and technogenic 137Cs. It has been revealed that the marginal basins of Murman are characterized by monotonous sedimentation in recent centuries. The average sedimentation rate is 0.15—0.17 cm/year. The sedimentary sequence is composed of silty-pelite-sized material. It has been established that the role of ice rafting in the formation of bottom sediment in coastal bays has decreased over the past centuries.

A new perspective of sediment layering scour and migration under the coupled effects of particle distribution and bio-viscosity–cavitation erosion

The scouring and migration of sediments in sewer systems are the key contributors to overflow pollution. Both physical and biological factors affect the erosion and migration of layered sediments. However, the functional characteristics of these factors and their quantification process still need to be further explored. In this study, the physical form and biological metabolism of the sediment are coupled, and the suspension mechanism under the dual action is proposed systematically and deeply. The influence coefficient of scour initiation was redefined as A^/prime, where the physical factors were particle size and mass, and the biological factors were bio-viscosity and internal cavitation. The bio-viscosity of layered sediment particles is provided by Extracellular Polymeric Substances (EPS). The slope value of |ΔD/−Δf| (ΔD: Dissipation; Δf: frequency) of surface EPS decreased from 0.489 to 0.315 when Quartz Crystal Microbalance with Dissipation (QCM-D) was used to analyse EPS viscosity, indicating that biological activities formed a dense biofilm on the sediment surface and enhanced the bond between particles. Meanwhile, by monitoring the accumulation density of sediments at different depths, it was found that the packing density of the bottom layer decreased from 1.50 to 1.45 g/cm3, which was mainly due to the internal cavitation caused by microorganism consuming organic matrix and releasing H2S and CH4. The delamination difference of EPS results in the uneven change of adhesion between different layers. This, combined with the internal erosion characteristics triggered by microbial stratified metabolism, collectively constitutes the biological effects on the sediment structure. Finally, the coupling mechanism of particle distribution and bio-viscous-cavitation erosion was formed, and the correctness of the formula was verified by repeated experiments, which proved the agreement between the theory and the practice and provided a scientific method for systematically analysing the erosion and migration law of sediment in the sewer system.

Subsurface Sediment Layer Analysis at the Dendam Tak Sudah Lake Flyover Construction Site in Bengkulu City Using the HV-Inv Method

Bengkulu City is situated within a subduction zone where the Indo-Australian and Eurasian tectonic plates converge, rendering the area highly susceptible to seismic activity. This study employs the microseismic method to assess seismic vulnerability and the subsurface rock structure at the Dendam Tak Sudah Lake Flyover Construction Site in Bengkulu City, which encompasses a swampy region. The microseismic method used was an inversion of the horizontal to vertical (H/V) spectral ratio (HV-Inv) for determining the dominant frequency (f0), amplification factor (A0), seismic sensitivity index (Kg), and shear wave velocity (Vs). The findings reveal that f0 in the study area range from 2.16 to 7.53 Hz, A0 vary from 0.40 to 3.79, and Kg values span from 0.03 to 6.04. The sedimentary layers exhibit an average thickness of 5-10 meters, with some locations showing significantly thicker sedimentary deposits. Notably, the highest seismic susceptibility is recorded at point T8. The Vs values range from 185.19 to 539.49 m/s, which are inversely proportional to the Kg values and indicate soil classifications varying from soft to medium. The overall seismic risk in the study area is moderate. These results offer key insights into geophysical and geological conditions in Bengkulu City, crucial for earthquake mitigation.

Nature‐based shoreline protection in newly formed tidal marshes is controlled by tidal inundation and sedimentation rate

AbstractMany tidal marshes have been lost by past land use changes, but are nowadays increasingly restored and created to provide valuable ecosystem services such as nature‐based flood and erosion protection along estuarine shorelines. To be functional for flood and shoreline erosion protection, restored and created tidal marshes should develop erosion resistant sediment beds. Here, we investigated which factors drive the spatial variations in sediment strength and erosion resistance in a developing tidal marsh restoration site. Our results show that decreasing tidal inundation frequency, decreasing sedimentation rate, and better drainage led to stronger consolidation in deeper sediment layers. This consolidation resulted in greater sediment strength, quantified here by shear strength and penetration resistance. Generally, sediment strength was greater when sediment had higher bulk density, while a higher water and fine fraction (= clay and silt) content decreased sediment strength. Overall, all measurement locations were relatively erosion resistant, likely caused by the dense root network and cohesive sediment. To restore or create resilient tidal marshes for nature‐based flood and shoreline erosion protection, we should thus aim for sites with relatively low tidal inundation frequency, moderate sedimentation rates, and cohesive sediment mixtures of clay, silt, and sand, which are well drained and have potential for vegetation establishment. These conditions have a high likelihood of resulting in restored or created tidal marshes that contribute to nature‐based flood and shoreline erosion protection.

The Saint-Leonard Urban Glaciotectonic Cave Harbors Rich and Diverse Planktonic and Sedimentary Microbial Communities.

The terrestrial subsurface harbors unique microbial communities that play important biogeochemical roles and allow for studying a yet unknown fraction of the Earth's biodiversity. The Saint-Leonard cave in Montreal City (Canada) is of glaciotectonic origin. Its speleogenesis traces back to the withdrawal of the Laurentide Ice Sheet 13,000 years ago, during which the moving glacier dislocated the sedimentary rock layers. Our study is the first to investigate the microbial communities of the Saint-Leonard cave. By using amplicon sequencing, we analyzed the taxonomic diversity and composition of bacterial, archaeal and eukaryote communities living in the groundwater (0.1 µm- and 0.2 µm-filtered water), in the sediments and in surface soils. We identified a microbial biodiversity typical of cave ecosystems. Communities were mainly shaped by habitat type and harbored taxa associated with a wide variety of lifestyles and metabolic capacities. Although we found evidence of a geochemical connection between the above soils and the cave's galleries, our results suggest that the community assembly dynamics are driven by habitat selection rather than dispersal. Furthermore, we found that the cave's groundwater, in addition to being generally richer in microbial taxa than sediments, contained a considerable diversity of ultra-small bacteria and archaea.

Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study

This research provides a comprehensive examination of flood risk mitigation in Saudi Arabia, with a focus on Wadi Al-Laith. It highlights the critical importance of addressing flood risks in arid regions, given their profound impact on communities, infrastructure, and the economy. Analysis of morphometric parameters ((drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If)) reveals a complex hydrological landscape, indicating elevated flood risk. due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. Effective mitigation strategies are imperative to protect both communities and infrastructure in Wadi Al-Laith. Geophysical investigations, using specialized software, improve the quality of the dataset by addressing irregularities in field data. A multi-layer geoelectric model, derived from vertical electrical sounding (VES) and time domain electromagnetic (TDEM) surveys, provides precise information about the geoelectric strata parameters such as electrical resistivity, layer thicknesses, and depths in the study area. This identifies a well-saturated sedimentary layer and a cracked rocky layer containing water content. The second region, proposed for a new dam, scores significantly higher at 56% in suitability compared to the first region’s 44%. The study advocates for the construction of a supporting dam in the second region with a height between 230 and 280 m and 800 m in length. This new dam can play a crucial role in mitigating flash flood risks, considering various design parameters. This research contributes to flood risk management in Saudi Arabia by offering innovative dam site selection approaches. It provides insights for policymakers, researchers, and practitioners involved in flood risk reduction, water resource management, and sustainable development in arid regions globally.