Thin Sediment Layer Research Articles

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.

Integrating near-surface geophysical methods and remote sensing techniques for reconstructing fault-bounded valleys (Mellieha valley, Malta)

The island of Malta (central Mediterranean) is dissected by several WSW-trending fault-line valleys related to Miocene-Pliocene extensional tectonics. Some valleys host remnants of alluvial deposits that could provide information on possible Quaternary faulting, but the thickness of these deposits and their subsurface extent is poorly constrained. Our study aimed to investigate the structural configuration of the southern sector of the Mellieha valley, which is located in the north-west part of the island and is limited by the ENE-WSW general trending Mellieha and Ghadira faults, and their relation with a thin layer of infill sediments. We employed different near-surface geophysical techniques (electrical resistivity tomography, active and passive seismic methods, ground-penetrating radar), as well as remote sensing techniques (unmanned aerial vehicle digital photogrammetry and ground-based Light Detection and Ranging) to complement classic structural surveys. The valley structure has an asymmetric graben configuration, being bounded by a normal fault to the southeast (Mellieha Fault) and other to the north-west (Ghadira Fault). Our study provides insights of possible Quaternary fault displacements and revealed the presence of an additional fault splay, the previously unmapped NNW-dipping Mellieha Fault 2 at the south-eastern edge of the valley. Additionally, by integrating results from geophysical surveys, we estimated the thickness of the valley's recent deposits, being thicker towards the Mellieha Bay sector, with maximum values of 8–10 m. Our study aligns with the general model of horst and graben structuring with associated regional tilting since the late Miocene, and supports the hypothesis that some segments of NW-trending normal faults within the North Malta Graben exhibit Quaternary activity, although with minimal throw rates (<< 0.1 mm/yr).

Analysis of Microtremor Data for Identification of Sediment Layer Thickness Based on Ground Profile Vs in Solok City, West Sumatera

&lt;p class="Abstract"&gt;&lt;span lang="EN-US"&gt;Research has been carried out to analyze the thickness of the sediment layer based on the value of the ground profile Vs (S-wave velocity) from microtremor measurement data sources in Solok City. The thickness of the sediment layer is one of the parameters that affect the amplification or amplification of incoming waves when an earthquake occurs. This study aimed to determine the sediment thickness level in Solok City based on the Vs value in the ground profile model from microtremor data sources. So that the analysis of sediment layers can be used as a form of disaster mitigation caused by tectonic activities such as earthquakes. Single station and array microtremor data were collected, then processed using a combination of HVSR and SPAC methods. The data processing results indicate that the value of S-wave velocity (Vs) derived from microtremor data analysis can be used to determine the thickness of the sediment layer (h), and vs values in Solok City ranged from 126.15-193.35 m/s with depths between 7.23-19.06 m. For areas with unseparated volcanic rock (QTau) lithology, the Vs value is 182.41 m/s. Meanwhile, for areas with geological conditions like alluvium (Qal), the Vs value is 161.66 m/s. The area with a thick layer of sediment, which is 62.74 m, is in the center of the northeastern part of Solok City, covering most of Vi Suku, Nan Balimo, and Javanese Village with alluvium (Qal) lithology and low topography through which rivers flow. Meanwhile, the thin layer of sediment, which is 23.12 m, is located in the western part of Solok City, precisely in Tanah Garam, with undivided volcanic rock lithology (QTau) and high topography in hilly areas.&lt;/span&gt;&lt;/p&gt;

Manifestations of the weak shear rigidity of marine sediments in amplitudes and travel times of acoustic normal modes and lateral waves

Compressional-to-shear wave conversion at interfaces within unconsolidated marine sediments and interference of shear waves within thin sediment layers have been found to make significant contributions to sound attenuation [O. A. Godin, J. Acoust. Soc. Am. 149, 3586–3598 (2021)] and produce unexpectedly strong perturbations in the normal mode group speed even when the shear speed is small compared to the compressional wave speed. This paper extends the previous analysis to the lateral waves and their applications to characterize the compressional wave speed and attenuation in the seabed. Shear wave-induced contributions to horizontal refraction of normal modes over horizontally inhomogeneous seabed are modeled to characterize the bearing and travel time errors that arise in the fluid-bottom approximation. The acoustic travel time and amplitude effects of the shear waves are found to accumulate at different rates with the propagation range depending on the stability of the shear wave interference within the seabed. The ways to distinguish between the manifestations in acoustic observables of the weak shear rigidity in the seabed and the other environmental uncertainties are discussed for range-independent, range-dependent, and horizontally inhomogeneous shallow-water waveguides. [Work supported by ONR.]

Paleoenvironmental characteristics and organic matter enrichment mechanisms of the upper Ordovician-lower Silurian organic-rich black shales in the Yangtze foreland basin, South China

The Wufeng Formation-Longmaxi Formation (O3w-S1l1) black shales within the Yangtze foreland basin (South China) hold significant potential as unconventional oil and gas resources. However, several challenges, including sluggish sedimentation rates, thin sedimentary layers, and notable homogeneity, hinder a comprehensive grasp of the organic matter enrichment (OME) mechanism within these shales. These challenges impede the exploration of unconventional oil and gas resources. This study aims to identify the O3w-S1l1 black shales in the Weiyuan area through a combined approach of organic and inorganic geochemical analyses. By doing so, it delves into the controlling mechanism behind OME in the black shales of the Yangtze foreland basin. The findings of this research reveal that the O3w-S1l1 black shales primarily consist of sapropelic kerogen and exhibit signs of over-maturation, with TOC content ranging from 0.43% to 8.21%. These shales are classified as organic-rich, mainly composed mixed and siliceous lithofacies. The presence of silica in the shales originates mainly from biogenic sources, and the highest TOC content coincides with a Sixs contribution of around 30% to the total silica content. During the late Katian, a global sea level drop led to an oxic paleoenvironment, transitioning into a euxinic paleoenvironment as sea levels rose in the early Rhuddanian. Notably, TOC content exhibited a significant correlation with paleoceanographic conditions (e.g., V/Cr, Ni/Co) and paleoproductivity levels (e.g., P/Al, Babio), while displaying a negative correlation with paleoclimate conditions (e.g., CIA, C-value), terrigenous detrital input intensity (e.g., Sixs, Ti/Al), and sedimentation rate ((La/Yb)N). Specifically, favourable conditions for OME encompass robust reducing seawater conditions, high paleoproductivity, a humid climate, reduced influx of terrigenous debris, and relatively elevated sedimentation rates. Regional tectonic movements (Guangxi movement) and fluctuations in relative sea levels exert influence over the deposition of O3w-S1l1 black shales. This study provides a valuable case study for exploring and developing shale gas resources within the Yangtze foreland basin.

Modal structure of the sound field in a shallow-water waveguide with a gassy sediment layer: Experiment and theory

Motivated by a series of experiments in the Lake Kinneret (Israel), the paper investigates low-frequency sound propagation in the three-layer model of the shallow water waveguide, where a thin layer of gas-saturated sediment is situated between a homogeneous fluid sub-bottom and a continuously stratified water column. Typical values of the thickness and sound speed in the gassy layer are 1 m and 250 m/s. The layer is thin compared to typical water depth of about 40 m. Normal mode structure of the acoustic field is analyzed. It is shown that with increasing frequency each normal mode transforms into a mode trapped in the gassy layer. These modes have unusually small phase and group speeds that are significantly less than the sound speed in water. Theoretically predicted normal mode dispersion curves are compared to the dispersion curves retrieved from observations of shipping noise. Phase speeds of normal modes are measured by cross-correlatingthe noise recorded on two sparse vertical arrays. A technique is proposed for solving the inverse problem of determining the parameters of a gas-saturated layer by matching the measured and modeled frequency dependencies of the normal mode phase speed.

Seismic Time‐Lapse Monitoring of Near‐Surface Microbubble Water Injection by Full Waveform Inversion

AbstractMonitoring time‐lapse changes in subsurface physical properties of the near‐surface critical zone is increasingly important with respect to climate change, environmental conservation/remediation, geohazard mitigation, and geotechnical engineering activities. Innovative controlled‐source cross‐well seismic monitoring surveys combined with full waveform inversion analysis enable us to map small and highly localized changes by repeatedly scanning the subsurface between borehole sensors at depth. In the Kanto Basin, Japan, we successfully monitor the dynamic transient fluid‐flow effects of the subsurface injection of microbubble water, which is of interest for soil contamination remediation and preventing earthquake liquefaction. The fluid migration is detected by observing P‐wave velocity changes (∼1%) within a very thin (∼1 m) sediment layer at a depth of ∼25 m. The injected microbubble water of the differential physical properties (temperature) is observed to follow geological and hydrologic preferential fluid‐flow paths rather than diffusing equally in all directions away from the injection well.

Factors controlling the net ecosystem production of cryoconite on Western Himalayan glaciers

In situ experiments were conducted to determine the net ecosystem production (NEP) in cryoconite holes from the surface of two glaciers (Patsio glacier and Chhota Shigri glacier) in the Western Himalaya during the melt season from August to September 2019. The study aimed to gain an insight into the factors controlling microbial activity on glacier surfaces in this region. A wide range of parameters, including sediment thickness, TOC %, TN %, chlorophyll-a concentration, altitudinal position, and grain size of the cryoconite mineral particles were considered as potential controlling factors. From redundancy analysis, the rate of Respiration observed in cryoconite at Chhota Shigri glacier was predominantly explained by sediment thickness in cryoconite holes (37.1% of the total variance, p < 0.05) with Photosynthesis largely explained by the chlorophyll-a content of the sediment (39.6%, p < 0.05). NEP was explained primarily by the TOC content and sediment thickness in cryoconite holes (35.8% and 22.1% respectively, p < 0.05). The altitudinal position of the cryoconite is strongly correlated with biological activity, suggesting that the stability of cryoconite holes was an important factor driving primary productivity and respiration rate on the surface of Chhota Shigri glacier. We calculated that the number of melt seasons required to accumulate organic carbon in thin sediment layers (< 0.3 cm), based on our measured NEP rates, ranged from 11 to 70 years, indicating that the organic carbon in cryoconite holes largely derives from allochthonous inputs, such as elsewhere on the glacier surface. Phototrophic biomass in the same thin sediment layer of cryoconite was estimated to take atleast 4 months to be produced in situ (with mean estimated time upto 1.7 ± 1.5 years). Organic matter accumulated inside the cryoconite holes both through allochthonous deposition and via biological activity on the glacier surface in these areas may have the potential to export dissolved organic matter and associated nutrients to downstream ecosystems. Given the importance of Himalayan glaciers as a vital water source for millions of people downstream, this study highlights the need for further investigation in aspects of the quantification of in situ produced organic matter and its impact on supraglacial melting in the Himalaya.

New and interesting records of marine fishes (Actinopterygii) from the Maltese Islands (central Mediterranean)

The occurrence of three bony ray-finned fishes, Thorogobius ephippiatus (Lowe, 1839), Chlopsis bicolor Rafinesque, 1810, and Grammonus ater (Risso, 1810) is reported for the first time in the scientific literature from Maltese coastal waters. The leopard-spotted goby, T. ephippiatus, was mostly recorded within the 8–32 m depth range on soft sediment and rocky bottoms within caves, but one individual was recorded on a rocky bottom with a thin layer of silt at a depth of 117 m where no cave was present. The bicolour eel, C. bicolor, was recorded within the 318–518 m depth range on rocky bottoms covered with a thin layer of muddy-detritic sediment; and the cusk-eel G. ater was recorded at a depth of 10 m within a cave. Notes on these three species as well as on another bony fish, the Azores rockling, Gaidropsarus granti (Regan, 1903), including new information on their bathymetric range and habitat association, are presented.

Differentiation of diamictons (glacigenic – non-glacigenic) using microstructure abundancies and types

As mobile diamicton sediments move across already deposited sediments whether on land or into oceans generated by either glaciers/ice sheets or landslides, a series of soft-sediment deformation processes occur. These sediments carry signatures of processes at both macro- and micro scales. The processes occur across thin layers of sediment, it is at the microsedimentological scale that deformation structures are detected and is the subject of this paper. Examination of numerous diamicton thin sections of both known glacigenic and non-glacigenic sediments illustrate a myriad of microstructures. Microstructures can be subdivided into brittle, ductile, porewater induced and plasmic fabrics. These fabrics are part of a spectrum of development from grain stacks, to microshear to rotations and, in addition, domains are likely to occur due to scavenging and are all part of a repeating cycle of deformation as sediment is added, eroded, re-transported into the accumulating sediment pile. Diamictons can be subdivided into several levels of abundance of microstructure types from very common to rare to being absent. In general, other than ‘tile’ structures, all diamictons have all types of microstructures. A table is presented illustrating the differentiation of various type of diamictons in terms of microstructure type abundancies in relation to individual environments in which diamictons occur around the past margins of glaciated continents. A distinction can be successfully drawn that allows diamictons to be distinguished and differentiated.

Thermal Lithospheric Thickness of the Sichuan Basin and its Geological Implications

AbstractThermal lithospheric thickness is an important parameter in studying the tectonic‐thermal evolution of basins and plate dynamics. Based on the measured geothermal data and thermophysical properties of the rocks, the thermal lithospheric thickness of the Sichuan Basin was calculated according to the principles of heat conduction in the crust and lithospheric mantle. The calculation results revealed that the thickness of the thermal lithosphere in the Sichuan Basin is 140–190 km and is unevenly distributed. The thickness of the thermal lithosphere in central Sichuan and southwestern Sichuan is less than 160 km, while that in the western Sichuan depression and eastern Sichuan is larger (∼180 km). The distribution of the thermal lithospheric thickness in the basin has a good correlation with the geological units and the thickness of the sedimentary layers. The thickness of the thermal lithosphere in the depression area, which has thick sedimentary layers and the fault‐fold zone with shallow crustal deformation and thickening, are larger than that in the basement uplifted area, which has thin sedimentary layers. The calculated thermal lithospheric thickness is in good agreement with the geophysical data and reflects the stable conduction temperature field in the Sichuan Basin. The present thermal regime and thermal lithospheric thickness of the Sichuan Basin indicate that flexural thickening of the lithosphere occurred in the eastern Sichuan fault‐fold belt and the Longmen Mountain–Western Sichuan depression foreland basin system, while asthenospheric uplift occurred in the central Sichuan region, which were the result of the expansion of the Xuefeng orogeny from the east and the compression of the Tibetan Plateau from the west.

Comparison between conventional and high-resolution measurements for unlocking the thin laminated potential reservoir, a case study

In Low resistivity low contrast (LRLC), also known as low resistivity pay (LRP), one of the factors is, the existence of alternating thin sedimentary layers of various rock types in hydrocarbon reservoirs, commonly consist of sandstone, siltstone and claystone and have been widely reported today. This phenomenon causes the potential intervals to be misinterpreted as non-hydrocarbon bearing zone due to its ability to reduce the measured apparent resistivity which result in overestimated water saturation calculation and due to its low contrast, in comparison with water bearing interval, this phenomenon always make well analyst to by passed this interval. As a result, from falsified measured resistivity, the final reserves volume tends to be underestimated. A huge number of studies have proven this kind of interval able to produce oil with very low water-cut therefore this paper would like to present the case study of solving this complex lithology by using sophisticated petrophysical modeling with a combination of Thomas-Stieber plot. Measured vertical (Rv) and horizontal (Rh) resistivity is available for this study and will be used as comparison. In general, this paper will present two case studies for final saturation computation, a) The sand resistivity will be estimated through inversion using measured resistivity anisotropy (Rv - Rh), b) The sand resistivity is reconstruct based on identified volume fraction of clay, whereas the shale resistivity estimated from conventional resistivity (RDEEP). Both of the cases will be calibrated using measured saturation from core by using Dean-Stark technique. Selected interval in this study (X1 zone) is a proven oil interval with a standard volume production rate 698 bbl/day. The final comparison of saturation computed using measured resistivity anisotropy yield a high correlation in contrast, the inversion using conventional resistivity yields less correlation with saturation from core. Nonetheless, by comparing with conventional computed saturation i.e. Waxman Smith, the final saturation of these two cases is significantly increased and unmasked the hydrocarbon-bearing interval. Therefore, case b indicates the best approach to be used whenever the advance measured resistivity anisotropy is unavailable.

Coarsening Dynamics of 2D Subaqueous Dunes

AbstractFluid flow over an initially flat granular bed leads to the formation of a surface‐wave instability. The sediment bed profile coarsens and increases in amplitude and wavelength as disturbances develop from ripples into dunes. We perform experiments and numerical simulations to quantify both the temporal evolution of bed properties and the relationship between the initial growth rate and the friction velocity u∗. Experimentally, we study underwater bedforms originating from a thin horizontal particle layer in a narrow and counter‐rotating annular flume. We investigate the role of flow speed, flow depth and initial bed thickness on dune evolution. Bedforms evolve from small, irregular disturbances on the bed surface to rapidly growing connected terraces (2D equivalent of transverse dunes) before splitting into discrete dunes. Throughout much of this process, growth is controlled by dune collisions which are observed to result in either coalescence or ejection (mass exchange). We quantify the coarsening process by tracking the temporal evolution of the bed amplitude and wavelength. Additionally, we perform Large Eddy Simulations (LES) of the fluid flow inside the flume to relate the experimental conditions to u∗. By combining the experimental observations with the LES results, we find that the initial dune growth rate scales approximately as . These results can motivate models of finite‐amplitude dune growth from thin sediment layers that are important in both natural and industrial settings.

Tidal marsh restoration at Blackwater National Wildlife Refuge, Maryland: A case study in thin-layer placement

Tidal marsh loss at Blackwater National Wildlife Refuge (NWR) has been a major concern of refuge managers in recent decades. The approximately 2,035 hectares (5,028 acres) of tidal marsh that have converted to open water in Blackwater NWR since 1938 (Scott et al. 2009) represent one of the most significant areas of marsh conversion within the Chesapeake Bay. In 2013, a suite of climate adaptation strategies focused on sea level rise was developed for Blackwater NWR and surrounding areas of Dorchester County by the Blackwater Climate Adaptation Project (BCAP). The BCAP is a collaboration of The Conservation Fund, Audubon Maryland-DC, and the U.S. Fish and Wildlife Service, assisted by the Maryland Department of Natural Resources (MD DNR), U.S. Geological Survey, and others. In 2016, the BCAP implemented a thin-layer placement (TLP) project at Shorter’s Wharf in Blackwater NWR on 16 hectares (40 acres) of subsiding and fragmenting tidal marsh dominated by Schoenoplectus americanus, Spartina alterniflora, and Spartina patens. The purpose of the project was to increase the 16 hectares’ (40 acres’) resiliency to climate-driven sea level rise and storm impacts. The project built up the marsh elevation by applying thin layers of sediment dredged from the adjacent Blackwater River. The sediment enhancement was designed to extend the longevity of the marsh and increase its resiliency by raising its surface elevation in relation to the tidal regime and to return the habitat to its prior high-marsh condition with S. patens dominating. The colonization of this site by saltmarsh sparrow would be an indicator of success in reaching this goal. Dredging operations in November and December 2016 placed approximately 19,900 cubic meters (26,000 cubic yards) of sediment on the project site. Post-restoration elevations obtained one year after material placement indicated that, although the target elevations were achieved in 78% of the surveyed placement area, the material was not distributed uniformly. Coarser material tended to stack up at the discharge location while the grain size declined and the slopes flattened toward the periphery of the discharge area. In 2017, natural vegetation had regenerated through the placed sediment with vigorous regrowth of S. americanus and S. alterniflora . This regrowth was supplemented with hand-planting of more than 200,000 plugs of S. patens. Vegetation monitoring is ongoing to determine the plant composition evolution within the placement site. Pre-dredge and post-dredge bathymetric surveys reveal 70% accretion nearly two years after dredging within the borrow area footprint.

Thin layer placement for marsh enhancement: Planning, design, construction, and monitoring considerations

Thin layer placement (TLP) is the purposeful placement of thin layers of sediment in an environmentally acceptable manner to achieve a target elevation or thickness. TLP is used for a variety of purposes, such as sediment management, beneficial use of dredged material (DM), and ecological enhancement. The term “thin” is used to distinguish TLP from other methods of sediment placement in which sediments are applied in layers on the order of several meters thick. In this paper, DM disposal refers to the deposition of sediment in a location and manner where no beneficial use is attained; with DM placement the sediment is used to benefit society and the environment. The application of thin layers of sediment has advantages over more traditional, thicker sediment applications in environments where these thicker layers pose potential challenges to natural resources, infrastructure, navigation, or other assets. Although TLP projects are most often conducted in wetlands, there are open-water applications as well. But because TLP is relatively early in its development, there is a dearth of design and construction information and guidance available to practitioners. This paper provides a high-level summary of pending national TLP guidance being developed by the authors on behalf of the U.S. Army Corps of Engineers’ Engineer Research and Development Center (USACE ERDC).

Preliminary Results of Receiver Function Forward Velocity Modelling at Merapi Volcano

The tectonic setting of Java island, located at southwestern edge of the Eurasia continent, is dominated by the subduction of Indo-Australia plate. One of the characteristics of active subduction is active seismicity, the generation of arc magmatism and volcanic activity. Mt. Merapi is one example of active volcano related with the subduction process. It is one of the most active volcanoes with location close to high population area. To better understand this area, we employed the Receiver Function technique, a method to image sub surface structure by removing the vertical component from horizontal component. First, we collected high magnitude events and processed RF with water level deconvolution method. Then, we constructed synthetic model with initial velocity input from previous tomography model. Note that we used reflectivity method in generating synthetic model with input parameters matched with parameters from real data processing. Next, we adjusted velocity inputs mainly on tops sediments (1-3 km) to include sediment layers and volcanic rocks, mid-depth low velocity zone that may be related with magma chamber and depth of crust-mantle boundary. Current forward velocity models show a relatively good agreement from 3 stations (ME25, ME32 and ME36). We estimate a thin layer of sediments followed a zone of velocity layer at a depth of 10-15 km and crust-mantle boundary ranging from 26-29 km. In this study, simulated that the signal of sediments layer and low velocity layers interfere main crust mantle boundary that supposed to be highest signal after the P wave in the typical receiver function study.

Biotransformation of Chemicals at the Water-Sediment Interface-Toward a Robust Simulation Study Setup.

Studying aquatic biotransformation of chemicals in laboratory experiments, i.e., OECD 308 and OECD 309 studies, is required by international regulatory frameworks to prevent the release of persistent chemicals into natural water bodies. Here, we aimed to address several previously described shortcomings of OECD 308/309 studies regarding their variable outcomes and questionable environmental relevance by broadly testing and characterizing a modified biotransformation test system in which an aerated water column covers a thin sediment layer. Compared to standard OECD 308/309 studies, the modified system showed little inter-replicate variability, improved observability of biotransformation, and consistency with first-order biotransformation kinetics for the majority of 43 test compounds, including pharmaceuticals, pesticides, and artificial sweeteners. To elucidate the factors underlying the decreased inter-replicate variability compared to OECD 309 outcomes, we used multidimensional flow cytometry data and a machine learning-based cell type assignment pipeline to study cell densities and cell type diversities in the sediment and water compartments. Our here presented data on cell type composition in both water and sediment allows, for the first time, to study the behavior of microbial test communities throughout different biotransformation simulation studies. We found that sediment-associated microbial communities were generally more stable throughout the experiments and exhibited higher cell type diversity than the water column-associated communities. Consistently, our data indicate that aquatic biotransformation of chemicals can be most robustly studied in test systems providing a sufficient amount of sediment-borne biomass. While these findings favor OECD 308-type systems over OECD 309-type systems to study biotransformation at the water-sediment interface, our results suggest that the former should be modified toward lower sediment-water ratios to improve observability and interpretability of biotransformation.

Identification of and Favorable Conditions for a New Long-Offset Seismic Phase from Offshore–Onshore Seismic Surveys

Abstract Offshore–onshore seismic survey is one of the main methods to study crustal structures in offshore–onshore transitional zones. At present, the seismic waves commonly used in imaging are the crustal refraction (Pg), the crustal reflection from the Moho (PmP), and the upper-mantle refraction (Pn) waves. The propagation distances of Pg and PmP are commonly less than 210 km, and Pn propagates with an apparent velocity of ∼8 km/s. In 2015, two offshore–onshore wide-angle seismic lines with a length of ∼350 km were acquired in the Pearl River Estuary. In addition to Pg, PmP, and Pn, a new seismic phase was observed, which has a long propagation distance (offset of ∼170–290 km), low apparent velocity (∼5.85 km/s), and low frequency (∼4–7 Hz). Similar seismic phases have been widely reported in previous offshore–onshore and reservoir seismic surveys, but the understanding of these phases is still limited. Herein, we used both raytracing and waveform modeling methods to identify the new seismic phase as the secondary Pg phase, which reflects from the surface (named Pg2Pg). We also discuss favorable conditions for Pg2Pg, including (1) a thin sedimentary layer with low velocity at the surface in which the reflection of Pg occurs, which can reduce the incidence angles and hence increase the energy of the reflected waves; (2) a sedimentary basement dipping toward the sea at the positions of the air gun shots, which focuses seismic waves; (3) relatively smooth interfaces of the medium, which can reduce the scattering of Pg2Pg; and (4) air guns that can excite low-frequency signals, which can reduce the attenuation of seismic waves. Checkerboard tests and practical applications show that Pg2Pg can significantly improve upper-crustal resolution, especially for onshore areas. Our research promotes the data mining of offshore–onshore seismic surveys, which is important for obtaining more detailed crustal structures.

Vegetation succession and soil cover transformation after extreme flood: A case study from the Sázava river floodplain

The goal of this study was to assess impact of flood on soil and vegetation cover in the Sazava river floodplain after an extreme spring flood in 2006. The impact on soil cover resulted mainly in vast erosion and sedimentation leading to differentiation of three fluvisol subtypes according to sediment coarseness. The impact on vegetation resulted in regeneration of herbaceous alluvial vegetation buried under a thin layer of sediments, succession of vegetation on eroded sites and succession of vegetation on new sediments. The regeneration of alluvial vegetation, expressed by vegetation cover, reached the same level as vegetation on undisturbed sites after 8 months. The succession of vegetation on new sites, studied within 25 m2 sampling plots and tested by using multivariate statistical methods, was primarily dependent on diaspores left on sites by the flood and on site type as well. The vegetation cover reached 100 percent at the end of the first vegetation season in both cases. There was a significant difference in species’ composition between eroded sites and sites on thick layers of sediments each year as hypothesized. There was also significant difference in vegetation succession between site types. <b>Sukcese vegetace a přeměna pokryvnosti půdy po extrémních záplavách. Případová studie v nivě Sázavy</b> Vliv extrémních záplav na vegetaci a půdní kryt byl studován v nivě Sázavy po jarní povodni v roce 2006. V prostoru nivy mezi Čerčany a Poříčím nad Sázavou došlo k rozsáhlé erozi a sedimentaci. Sledována byla jednak obnova aluviální vegetace pohřbené pod málo mocné vrstvy sedimentu, jednak sukcese vegetace na erozních plochách a mocných sedimentech. Regenerace aluviální vegetace byla rychlá. Pokryvnost vegetace disturbovaných ploch dosáhla po 8 měsících stejné pokryvnosti jako na plochách nedisturbovaných. Oproti předpokladu nebyla prokázána rozdílná rychlost zarůstání studovaných ploch (regenerující vegetace aluviálních luk, sukcese na erozních plochách a sukcese na sedimentech). Druhové složení vegetace na sukcesních plochách však bylo průkazně závislé na typu plochy. Druhové složení také průkazně závisí na typu plochy a sukcesním stáří.

Changes in selected physico-chemical properties of floodplain soils in three different land-use types after flooding

This article provides information on selected physico-chemical properties, including soil colour, texture, electrical conductivity, pH&lt;sub&gt;H&lt;/sub&gt;2O, pH&lt;sub&gt;CaCl&lt;/sub&gt;2, content of total carbon and Q&lt;sub&gt;4/6&lt;/sub&gt; quotient, of the topsoil and subsoil of former flood sediments at three diverse vegetation plots in a floodplain and in two reference plots unaffected by floods, and changes of some soil properties caused by a new subsequent flood. Aggradation of flood sediments in the area was controlled both by local terrain morphology and vegetation type cover. Differences in the properties of sediments in the individual plot types were caused by the different production of litter, root biomass and carbon cycling before the new flood. Vertical distributions and inventories of &lt;sup&gt;137&lt;/sup&gt;Cs in soils revealed the position and proportion of modern sediments in soil profiles, man-made filling of former erosion grooves and ploughing depths. The new flood of a lower hydrological power aggraded a thin layer of organo-clay sediment on the soil surface but showed minor effects on the investigated soil properties. The lowest dry bulk density and highest total porosity values were found in the topsoil of woody and grassy plots after the flood implying no substantial break down of soil aggregates by the flood. The highest dry bulk density values in the subsoil of fields indicated soil compaction from agricultural machinery. No increased soil salinity was found after the flood. The flood did not significantly affect the pH&lt;sub&gt;H&lt;/sub&gt;2O of the topsoil and subsoil; however, a significant increase in pH&lt;sub&gt;CaCl&lt;/sub&gt;2 was found for the topsoil of grassy plots and for all topsoil samples from the park. No significant increases in total carbon (C&lt;sub&gt;tot&lt;/sub&gt;) contents were found in topsoils of any plot types after the flood in spite of an accumulation of thin organo-clay material on the soil surface after the flood. However, significant increases in C&lt;sub&gt;tot&lt;/sub&gt; in subsoils of all plot types indicate the vertical migration of colloidal and dissolved organic carbon in soils during the flood. C&lt;sub&gt;tot&lt;/sub&gt; contents positively correlated with electrical conductivity values and negative correlated with pH values. The relatively minor changes in soil physico-chemical properties found after the flood can be explained by the short duration and small dynamic power of the flood, and the timing of sampling when the flood had receded and soil aeration was already being restored.