Bottom Conditions Research Articles

Forecast of Fine Particles in Chengdu under Autumn-Winter Synoptic Conditions.

We conducted an evaluation of the impact of meteorological factor forecasts on the prediction of fine particles in Chengdu, China, during autumn and winter, utilizing the European Cooperation in Science and Technology (COST)733 objective weather classification software and the Community Multiscale Air Quality model. This analysis was performed under four prevailing weather patterns. Fine particle pollution tended to occur under high-pressure rear, homogeneous-pressure, and low-pressure conditions; by contrast, fine particle concentrations were lower under high-pressure bottom conditions. The forecasts of fine particle concentrations were more accurate under high-pressure bottom conditions than under high-pressure rear and homogeneous-pressure conditions. Moreover, under all conditions, the 24 h forecast of fine particle concentrations were more accurate than the 48 and 72 h forecasts. Regarding meteorological factors, forecasts of 2 m relative humidity and 10 m wind speed were more accurate under high-pressure bottom conditions than high-pressure rear and homogeneous-pressure conditions. Moreover, 2 m relative humidity and 10 m wind speed were important factors for forecasting fine particles, whereas 2 m air temperature was not. Finally, the 24 h forecasts of meteorological factors were more accurate than the 48 and 72 h forecasts, consistent with the forecasting of fine particles.

Monitoring sediment transport pathways from an artificial nearshore berm, South Padre Island, Texas, USA, August 2018 to November 2019—Implications for coastal management

During August 2018 – November 2019, the transport pathways of dredge material from a specially constructed nearshore feeder berm were investigated as part of a collaborative study by the City of South Padre Island, U.S. Army Corps of Engineers–Galveston District, U.S. Geological Survey, Partrac GeoMarine Inc., and Texas A&M University, into the efficacy of beneficial use dredge material (BUDM) as a method of replenishing the beach profile and shoreface at South Padre Island, Texas with sediment. Dual-signature (fluorescent and ferrimagnetic) tracer particles, designed to be hydraulically equivalent to the dredge material, were placed on the berm, and a sampling program was initiated to monitor the spatiotemporal movement of tracer particles under the influence of the prevailing hydrodynamic regime. Wave and current data were collected and were used together with available metocean data to identify the forcing mechanisms of sediment transport; improved understanding garnered from the consideration of multiple datasets can be used to inform future coastal management decisions.Tracer analysis results indicated low magnitude, shoreward transport of dredge material from the berm and along shore transport in both northerly and southerly directions. Small amounts of tracer detected in beach face samples demonstrated connectivity between the constructed feeder berm and the shoreface. However, the generally low tracer concentration within beach face samples indicated low rates of sediment transport for berm sediments, and a low magnitude sediment transport pathway from the berm directly to the beach face, with possible storage of sediment in the nearshore bar system.Given that the berm was at or beyond the closure depth and considering the relatively weak prevailing near bottom hydrodynamic conditions, the potential for sediment to be mobilized and transported during the study period was generally low. Periods of higher energy waves, driven by north-northwest winds, were identified as a key driver of sediment transport but due to the infrequent nature of these events the sediment transport regime across the area of interest was temporally limited. Longshore movement of sediment was both north and south, mainly dependent on prevailing wind directions and resulting longshore currents.We discuss implications for coastal zone management and the use of feeder berms as an artificial beach nourishment mechanism to replenish sediments lost by coastal erosional processes. The insight into nearshore emplacement of material can be used by local governments and coastal managers to optimize the efficacy of berm emplacement and implement such schemes as a cost-effective nourishment option, or when onshore placement of material is not feasible.

Holocene millennial-scale variability of coastal environments on the southern coast of Korea and its controlling factors

AbstractCoastal evolution is influenced by past sea-level changes and resultant shifts from fluvial- to marine-dominant environments and the accompanying significant geochemical and isotopic changes in the water mass and sediments. We investigated the elemental and isotopic features of coastal sedimentary cores (27 m in length) from a small paleo-bay located on the southern coast of Korea to determine such geochemical variability and specify past changes in the bay environment and anoxic conditions and possible links to past climate changes. We analyzed total organic carbon (TOC), total sulfur (TS), their isotopes (δ13CTOC and δ34STS), and pyrite. The δ13CTOC values ranging from −25 to −19‰ (a proxy for terrestrial influence) were lower than average (−22.5‰) before 8300 cal yr BP and since 500 cal yr BP, while the intervening Early to Late Holocene showed higher δ13CTOC values, indicating a shallow coastal environment. The δ34STS values fluctuating between −35 and +5‰ resembled sedimentation rate change. Based on the changes in the ratios of TOC to TS (C/S ratios), sedimentation rate, and δ34STS, we found five possible periods with higher salinity and intensified anoxic conditions at millennial timescales: 8900–8200, 7950–6500, 5200–4300, 3500–2600, and 2000–1100 cal yr BP. These intensified anoxic conditions seem to have been influenced by increased air temperature and sea-surface temperature conditions, which could have intensified the intensity of thermal stratification (less ventilation and mixing) between surface and bottom waters and resultant anoxic conditions.

S2SHORES: A PYTHON LIBRARY FOR ESTIMATING COASTAL BATHYMETRY

Understanding coastal zone dynamics covering large spatial and dense temporal scales is paramount to understand and mitigate emerging coastal issues relating to climatological changes. However, the uncertainties on the coastal zone risks are still too large to predict effectively impacts on an overall increasing coastal population. Prediction, by deploying numerical models for waves, tide, and currents in the coastal zone, requires accurate and up-to-date bottom boundary conditions (bathymetry) to simulate coastal hydrodynamics accurately, let alone predict morphological change. There are three main approaches for estimating coastal bathymetry using satellite sensors: 1) linking water depth to a spectral response (colour), 2) underwater photogrammetry and 3) linking wave kinematics to a water depth. Here, we present S2Shores (Satellite to Shores), a python library that detects and extracts local wave parameters (geometry and kinematics) to derive coastal bathymetry.

Superior crack propagation inhibitory effectiveness of MWCNT reinforced SBS toward improving oil/gas well cement integrity

The brittleness and low cracking resistance of oil- and gas-well cement threaten its integrity, specially under the high stress concentrations at bottom-hole conditions. Fortunately, the excellent mechanical properties of carbon nanotubes and elastomers motivate researchers to utilize them as versatile candidates that can positively modify the breakage behaviors of cement-based materials. Herein, we investigated the hybridization effects of multi-walled carbon nanotubes (MWCNTs) and styrene–butadiene–styrene (SBS) on the mechanical properties and breakage behaviors of oil- and gas-well cements. MWCNTs and SBS were synthesized and then, characterized with a wide range of techniques, signifying successful syntheses of these two materials. Afterward, SBS was dry mixed with cement powder and then added to the aqueous suspension of MWCNT prepared via sonication method. The mechanical testing (e.g., uniaxial, triaxial, and Brazilian tests), numerical simulation, and imaging analysis showed that incorporation of the SBS into the cement matrix promoted the ductility and macro-scale cracking resistance. The introduction of MWCNTs improved the cohesion, micro-scale cracking resistance, and strength properties of the cement matrix. Thereupon, the hybridization of 0.075 wt% of MWCNT and 9 wt% of SBS endowed great mechanical behavior and cracking resistance to the conventional oil-well cement in both micro and macro structures. These specifications can maintain cement’s durability under the critical thermal and mechanical stress concentrations at various bottom hole conditions. This improvement contains the increasing of strain energy, tensile strength, cohesion, and Poisson’s ratio by 219.27%, 141.17%, 750% and 100%, respectively and reducing the elastic modulus by 41.67%. Fourier Transform Infrared Spectroscopy (FTIR) analysis exhibited that these enhancements can be attributed to favorable interactions between MWCNT and SBS in the cement matrix.

The macro and micro analysis on EOR mechanisms during steam and solvent thermal recovery in heavy oil reservoirs

Using only pure steam as a driving medium in heavy oil reservoirs may result in a low oil recovery factor. Solvent is a good oil displacement medium that can be dissolved in heavy oil, which can greatly reduce the viscosity and improve the mobility of heavy oil. Therefore, the method of solvent assisted displacement and drainage has the unique advantage during steam flooding. In this paper, a quantitative method is proposed to choose appropriate solvents. Then a series of experiments are carried out, including oil displacement experiment to measure oil displacement efficiency, 2D visualization experiment to analyze the sweep efficiency and remaining oil distribution, and 3D scaling physical simulation setting with bottom water condition, which are used to analyze production performance, the expanding characteristics of steam chamber and study reservoir fluid distribution. The results show that steam moving upwards to heat and drive heavy oil to production well under the action of displacement and drainage. In a heavy oil reservoir with thin bottom water, if only steam is injected into reservoir, then there is no obvious stage of stable oil production and the oil recovery factor is only 32.7%. However, when solvent and steam are co-injected into reservoir, the stage of stable oil production maintaining about 0.6 PV and the oil recovery factor is 43.2%. During steam and solvent flooding, solvent can greatly reduce the oil viscosity to improve its mobility; meanwhile solvent can promote the expansion of steam chamber. The co-injection of steam and solvent can obviously expand steam chamber and increase oil recovery factor in heavy oil reservoirs (even connecting with bottom water layer). The method of steam and solvent flooding further enriches EOR technologies of thermal recovery in heavy oil reservoirs.

Exploration of the candidate beneficial bacteria for P. vannamei culture by core microbiome analysis using amplicon sequencing.

Globally, P. vannamei is the vital species in aquaculture production. Beneficial bacterial exploration of gut, sediment and water were investigated in P. vannamei culture using Illumina Miseq sequencing of 16S RNA V3-V4 hypervariable regions. Predominant phyla identified were Proteobacteria, Tenericutes, Bacteroidetes in gut; Proteobacteria, Bacteroidetes, Planctomycetes in sediment and Cyanobacteria, Proteobacteria and Planctomycetes in water. In total, 46 phyla, 509 families and 902 genera; 70 phyla, 735 families and 1255 genera; 55 phyla, 580 families and 996 genera were observed in gut, sediment and water, respectively. Diversity of microbial communities in respect of observed Operational Taxonomic Units, diversity indices (Shannon and Simpson), richness index (Chao1) were significantly high P(<0.05) in 60 DoC in gut and 30 DoC in sediment. Beta diversity indicated separate clusters for bacterial communities in gut, sediment and water samples and formation of distinct community profiles. Core microbiome in P. vannamei rearing ponds over a time consisted of 9, 21 and 20 OTUs in gut, rearing water and sediment, respectively. This study helps to intervene with suitable beneficial microbes to establish aquaculture system thereby contributes to enhance the productivity, improve water quality and pond bottom condition and control the pathogenic agents at each stage of the culture.

Dry-out characteristics of debris bed under different water injection conditions

A porous debris bed may form through the interaction between melting corium and coolant during a pressurized water reactor severe accident, which continues to emit large amounts of decay heat. The cooling of debris bed is a critical phenomenon and serves as a potential mitigation measure to halt the accident. In this paper, an experimental facility DBC was constructed to study the cooling properties and dry-out heat flux under different water injection conditions and system pressures. The debris bed consisted of stone particles ranging in diameter from 1～10 mm, with a porosity of 0.37. In the debris bed, a total of thirty-three electrical heating elements, twelve optical fibers equipped with 204 temperature sensors, and thirty-three thermocouples were embedded. Additionally, a computer program MIDEC was developed to investigate the vapor-liquid flow characteristics and dry-out mechanism. The experimental results indicated that the cooling of debris bed can be significantly improved by increasing system pressure. Furthermore, it was observed that the dry-out heat flux under bottom water injection conditions was considerably higher compared to that of top water reflooding. Under top reflooding conditions, the counter-current flow of vapor-liquid impeded the downward flow of coolant, resulting in insufficient coolant supply and leading to a dry-out phenomenon at the bottom region. However, under bottom injection conditions, both vapor and liquid flowed in an upward direction. As a result, the void fraction reached its maximum value at the top region of the debris bed. The distinct vapor-liquid flow characteristics under top and bottom injection conditions resulted in notable discrepancies in dry-out heat flux and dry-out positions. Based on the comparison between the calculated dry-out heat flux (DHF) and experimental results, it was observed that the Reed model accurately predicted the cooling of debris bed under top-flooding conditions when compared with measured data obtained from DBC experiments. However, for very small particle sizes, the Lipinski model would be more suitable and provided better predictions.

Oxidative conditions along the continental shelf of the Southeast Pacific during the last two millennia: a multiproxy interpretation of the oxygen minimum zone variability from sedimentary records

The oxygen minimum zone (OMZ) is an essential feature along the Pacific margin, extensively studied for its influence on benthic fauna, acquiring relevance in coastal zones due to its impact on aquaculture species, marine-managed areas, and marine-protected areas. The most evident temporal variability beyond seasonal timescales observed for the OMZ was related to inter-annual variability associated with El Niño, when warmer and more oxygenated waters arrive at shallower zones and the OMZ becomes deeper. However, the impact of oxygen-deficient water that appears sporadically over the shelf is not yet understood. This study provides an integrated view of the oceanographic and climatic conditions behind bottom oxygen conditions along the Chilean continental margin, considering the temporal variability in the South East (SE) Pacific during the last ~2000 years. We organized the information on redox-sensitive metals and δ15N from sedimentary cores obtained from shelf zones from 23°S to 36°S at water depths lower than 100 m. The results demonstrate the variability in the upper part of the OMZ over the shelf, which seems to respond to climatic oscillations. The element distribution indicated in particular a more intense OMZ was developed over the shelf before 1400 AD, followed by more oxygenated bottom conditions afterward, except between 1925 and 1970 off 36°S when the OMZ was intensified, a condition that was not observed at the northern sites. This period mostly coincided with a low Pacific Decadal Oscillation amplitude and reduced El Niño Southern Oscillation (ENSO) activity. In the last 50 years, the proxy data suggests less intense suboxic environment along the Chilean margin. This weakening of the upper boundary of the OMZ in the last decades is interpreted as resulting from the accumulative effect of ventilation processes at different time scales.

An unstable mode of the stratified atmosphere under the non-traditional Coriolis acceleration

The traditional approximation neglects the cosine components of the Coriolis acceleration, and this approximation has been widely used in the study of geophysical phenomena. However, the justification of the traditional approximation is questionable under a few circumstances. In particular, dynamics with substantial vertical velocities or geophysical phenomena in the tropics have non-negligible cosine Coriolis terms. Such cases warrant investigations with the non-traditional setting, i.e. the full Coriolis acceleration. In this manuscript, we study the effect of the non-traditional setting on an isothermal, hydrostatic and compressible atmosphere assuming a meridionally homogeneous flow. Employing linear stability analysis, we show that, given appropriate boundary conditions, i.e. a bottom boundary condition that allows for a vertical energy flux and non-reflecting boundary at the top, the atmosphere at rest becomes prone to a novel unstable mode. The validity of assuming a meridionally homogeneous flow is investigated via scale analysis. Numerical experiments were conducted, and Rayleigh damping was used as a numerical approximation for the non-reflecting top boundary. Our three main results are as follows: (i) experiments involving the full Coriolis terms exhibit an exponentially growing instability, yet experiments subjected to the traditional approximation remain stable; (ii) the experimental instability growth rate is close to the theoretical value; (iii) a perturbed version of the unstable mode arises even under sub-optimal bottom boundary conditions. Finally, we conclude our study by discussing the limitations, implications and remaining open questions. Specifically, the influence on numerical deep-atmosphere models and possible physical interpretations of the unstable mode are discussed.

Trace elements in sedimentary pyrite track redox and nutrient fluctuations in the Ediacaran/Cambrian Bambuí Group, Brazil

We apply trace element analysis of syn-sedimentary pyrite to track the redox and nutrient variations in the Ediacaran-Cambrian Bambuí Group of eastern Brazil. Sedimentary pyrite from black shales interleaved within the basal cap carbonate of the 635–600 Ma Pedro Leopoldo Member, deposited in an open marine setting connected to the global sea, preserve high Mo up to >200 ppm, erratic enrichment of micronutrients such as Cu, Ni, Ba, Zn and uniform enrichment of Se. This indicates the importance of oxidative continental weathering and development of an enhanced Redox Sensitive Elements (RSE) dissolved reservoir on the aftermath of the Marinoan glaciation, with atmospheric O2 levels, calculated from Se/Co ratios of pyrites, around 2.5–3.5 wt%. A shallow oxic layer over deep euxinic realms made possible by high concentrations of dissolved sulfate was probably maintained up to the late Ediacaran, during deposition of the Cloudina-bearing Lagoa Santa Member (585–540 Ma). Upsection, however, radical shifts to muted Mo concentrations and overall low micronutrient concentrations are recorded in the Serra de Santa Helena Formation, with O2 levels plunging below 1 wt%. This indicates the development of ferruginous bottom water conditions in a sulfate-poor setting, due to restriction of the basin by the encircling Brasiliano mountains that formed Gondwana. The restricted, oxygen-poor and nutrient-depleted conditions caused the demise of complex life forms and hampered the development of typical Ediacaran-Cambrian ecosystems. Basin re-connection might have occurred during deposition of the Lagoa do Jacaré Formation, with independent proxies such as local tidal facies indicating a return to more ventilated conditions in the upper Bambuí Group. Our results highlight the importance of basin restriction and connection over coupled redox-nutrients variations during the development of Ediacaran-Cambrian ecosystems.

Time harmonic analysis of concrete gravity dam-reservoir systems by mixed High order-Wavenumber approach for general reservoir bottom condition

Recently, mixed HO-WN (i.e., High order-Wavenumber) method was introduced for dynamic analysis of concrete gravity dam-reservoir systems. This is formulated by FE-(FE-TE) approach (i.e., Finite Element-(Finite Element-Truncation Element)). In this technique, dam and reservoir are discretized by plane solid and fluid finite elements. Moreover, the mixed HO-WN (i.e., High order-Wavenumber) condition is imposed at the reservoir truncation boundary. This task is formulated by employing a truncation element at that boundary. The method is derived by combining the High-order and Wavenumber approaches. The present study is an extension of mixed HO-WN approach which allows it to be effectively utilized in the case of absorptive as well as fully reflective reservoir bottom condition. The formulation is initially explained in details and three alternatives are presented for this method. Subsequently, the response of an idealized triangular dam-reservoir system is studied for an absorptive reservoir condition due to horizontal and vertical ground motions. For each alternative, responses are evaluated from accuracy point of view by comparing them against exact solutions for three different values of normalized reservoir length (i.e., L/H ratio). It should be emphasized that a very low value of L/H = 0.2 is also considered for this investigation which makes it a very challenging test for any kind of truncation boundary condition. Moreover, it is worthwhile to stress that although time harmonic analysis is adopted in the present study, the main part of formulation is explained in the context of time domain. Therefore, the approach can easily be extended for transient type of analysis.

Last interglacial seasonal hydroclimate in the North Sea–Baltic Sea region

The Last Interglacial (LIG) experienced substantial changes in seasonal insolation compared with the present day, which may have affected the hydrography and water-mass exchange in the North Sea and Baltic Sea region. Here we investigate the effects of solar radiation and greenhouse gas (GHG) forcing on the regional climate by analyzing model simulations of the LIG (127 ka BP), pre-industrial (PI, 1850 CE), and present-day (PD, 1990 CE) climates. We also interpret the reconstructed seasonal bottom water conditions using benthic foraminifera and geochemistry data.Our simulations reveal that during the LIG, the Baltic Sea region (including the Kattegat and the Danish Straits) experienced more saline and colder bottom waters than those in the PD, in agreement with the reconstruction data. This can be attributed to lower GHG levels and enhanced water exchange of cooler, saline North Sea water into the Baltic Sea during the LIG. The thermocline was stronger during the summer months in the LIG, mainly due to the higher sea surface temperature (SST) compared to that of the PD resulting from increased summer insolation.Further, the temperature anomalies (LIG–PD) show significant inverse correlations with the precipitation–minus–evaporation (P–E) at the Baltic Sea entrance. However, the P–E balance appears to have had minimal impact on salinity changes in the North Sea, the Baltic Proper, and the open sea area. Our findings indicate that monthly surface and bottom water salinity anomalies of LIG-PI exhibit strong positive correlations with the North Atlantic Oscillation (NAO) anomalies in the Baltic entrance region. During the LIG, a more positive phase of the NAO index in autumn played a crucial role in wind-driven major inflows and led to more intensive water exchange in the North Sea–Baltic Sea region compared to the late Holocene.

New Fetch- and Depth-Limited Forecasting Curves Depending on Bed Roughness

ABSTRACT Predicting wind waves within confined and shallow basins is very important, given the decisive role they play in the resuspension mechanisms of sediments and nutrients from the bottom, on which the main morphological and environmental changes depend. Pascolo, Petti, and Bosa (2019) proposed a set of wave forecasting curves for fully developed conditions in finite depth, which consider the bottom roughness as an additional variable, since it plays a fundamental role in the wave energy dissipation during the generation process. The present study incorporates and integrates the results previously obtained by Pascolo, Petti, and Bosa (2019) and provides the growth curves in the complete form, taking into account also the limitation on fetch. A numerical approach on a simplified domain has been adopted and statistical analyses on the fit of the curves to numerical results have been performed. The new set of equations confirms the variability of the wave heights and periods as a function of the bottom conditions, which can change due to the presence of bedforms, vegetation, or particle size differences. Applications at different conditions of depth, fetch, and roughness have been analyzed, in order to confirm the validity of the new growth curves.

Estimation of shallow stream bathymetry under varying suspended sediment concentrations and compositions using hyperspectral imagery

Hyperspectral remote sensing has the proven ability to provide bathymetric estimates over relatively clear water. High turbidity caused by suspended sediments scatters light, decreasing light penetration to depth and is thus regarded as the most confounding factor in remote sensing-based bathymetry. Therefore, the effect of varying sediment-laden flow conditions on remote sensing-based bathymetry measurements was investigated in this study to assess the applicability of hyperspectral imagery and a robust method was proposed to account for such conditions. To acquire spectral data under various suspended sediment and bottom conditions, experiments involving the injection of sand and yellow loess were performed in outdoor field-scale channels with three bottom conditions (coarse sand, vegetation, and fine sand) under shallow stream conditions (< 1 m). Using the acquired data, the random forest with recursive feature elimination (RF-RFE) method was used to select and learn the optimal spectral band combination for each bottom type. The results were then compared with those of the optimal band ratio analysis (OBRA) method, which has been most widely used for bathymetry measurements via remote sensing imagery. The reflectance spectra differed depending on the bottom type although they were similar regardless of the bottom type when high reflectance was distributed at high concentrations. Given such optically complex data, OBRA exhibited very low accuracy because it was substantially affected by suspended sediment. However, RF-RFE showed an accuracy of R2 ≥ 0.95 and mapped a stable bathymetry distribution under sediment-laden flow conditions by utilizing 6–12 spectral bands as the optimal combination, depending on the bottom type. This result demonstrated that although the contribution of bottom reflectance was weak when the suspended sediment concentration was high, hyperspectral remote sensing is still applicable if spectral bands of various wavelengths can be incorporated to account for nonlinearity. While the effectiveness of this method could be limited to the specific conditions of suspended sediment and bottom properties, it is expected to be more robust to various confounding factors after being trained under diverse spectral conditions.

Influence of abiotic and biotic factors on benthic marine community composition, structure and stability: a multidisciplinary approach to molluscan assemblages from the Miocene of northern Germany

AbstractThe Miocene mica‐clay deposits of Groß Pampau (northern Germany) are well known for their diverse assemblages of marine mammals. Despite numerous systematic and biostratigraphic studies, an in‐depth palaeoecological analysis of its molluscan assemblages and a comprehensive palaeoenvironmental reconstruction are lacking. Here, we integrate new faunal, sedimentological and geochemical data to reconstruct the marine palaeoecosystem of the Upper Miocene sedimentary succession of Groß Pampau, and to identify the drivers controlling the composition, ecological structure and temporal dynamics of its macrobenthic molluscan assemblages. Fossil evidence, coupled with analyses of clay mineral composition, grain size distribution and geochemical data (total organic carbon, total nitrogen, δ13C, δ18O, δ15N of sediment and shells), suggests a warm–temperate, mesotrophic, low‐energy, offshore marine setting mostly below storm wave base and a pronounced surface‐to‐bottom water temperature gradient. Low variability in sedimentological and geochemical signals indicates generally stable physicochemical conditions, whereas the occurrence of the opportunistic species Varicorbula gibba suggests occasionally unfavourable bottom conditions, possibly related to transient hypoxia. Canonical correspondence analysis indicates that the distribution of molluscan assemblages correlates with total organic carbon and nitrogen content, suggesting organic matter availability at the sea floor as a controlling factor. A pattern of repetitive punctuated stasis of molluscan assemblages is defined by the temporal persistence in taxonomic and ecological composition, occasionally interrupted by shifts to a different faunal configuration. We suggest that both stable environmental conditions and biotic interactions (i.e. the top‐down control exerted by carnivorous gastropods and environmental modification by ubiquitous burrowing deposit feeders) probably contributed to the observed temporal stability.

APLIKASI HIDROGEN PEROKSIDA DI SEDIMEN TERHADAP KUALITAS AIR DAN PERTUMBUHAN UDANG VANAME Litopenaeus vannamei

Pond bottom sediment conditions influence shrimp culture. As benthic organisms, shrimp are mainly on the surface of the pond bottom, so cultivation preparations related to improving sediment quality are essential. Pond bottom practice, such as drying, liming, and fertilizing, is common. However, in bottom pond conditions where total drying cannot be carried out, other treatments are needed, such as the addition of hydrogen peroxide. The purpose of this study was to determine the effect of adding hydrogen peroxide in pond sediments on the performance of shrimp growth and water quality. The study was conducted with five doses of hydrogen peroxide (0.25 mL, 0.5 mL, 1 mL, 2 mL) mixed with 350 g of pond soil sediment. Ten shrimps with an average weight of 0,27±0,03 g were put into the rearing container, which had been given pond bottom sediment according to the treatment. The results showed that the 2 mL hydrogen peroxide treatment gave the best results on the growth rate and average weight of Pacific whiteleg shrimp at the end of rearing. Water quality such as pH value, dissolved oxygen, and temperature were not significantly different between treatments. Hydrogen peroxide treatment can improve shrimp growth performance without affecting water quality during rearing.

A Simplified Numerical Method for Simulating the Generation of Linear Waves by a Moving Bottom

In this study, simplified linear numerical method that can simulate wave generation and transformation by a moving bottom is introduced. Numerical analysis is conducted in wave number domain after continuity equation, linear dynamic and kinematic free surface boundary conditions and linear kinematic bottom boundary condition are Fourier transformed, and the results are expressed in space domain by an inverse Fourier transform. In the wavenumber domain, the dynamic free water surface boundary condition and the kinematic free water surface boundary condition are numerically calculated, and the velocity potential in the mean water level (&lt;i&gt;z&lt;/i&gt; = 0) satisfies the continuity equation and the kinematic bottom boundary condition. Wave generation and transformation are investigated when the triangular and rectangular shape of bottoms move periodically. The results of the simplified numerical method are compared with the results of previous analytical solutions and agree well with them. Stability of numerical results according to the calculation time interval (△&lt;i&gt;t&lt;/i&gt;) and the calculation wave number interval (△&lt;i&gt;k&lt;/i&gt;) was also investigated. It was found that the numerical results were appropriate when △&lt;i&gt;t&lt;/i&gt;≤&lt;i&gt;T&lt;/i&gt;(period)/1000 and △&lt;i&gt;k&lt;/i&gt;≤π/100.

Early–Middle Jurassic brachiopods from Ponor Mountain, Western Balkan Mountains, Bulgaria; taxonomy, biostratigraphy and occurrence in the context of the early Toarcian Oceanic Anoxic Event

ABSTRACT An upper Pliensbachian–Aalenian brachiopod succession is reported from Ponor Mountain, Western Balkan Mountains, Bulgaria. This includes nine species (6 rhynchonellides and 3 terebratulides) from eight genera. A new genus Bulgariarhynchia and two new species, Bulgariarhynchia ponorensis and Capillirhynchia brezenensis, are formally described. A single species Homoeorhynchia ? aff. prona was found in the upper Pliensbachian. Most of the brachiopods derived from the Toarcian–Aalenian interval, and comprise: Pseudogibbirhynchia jurensis, Rhynchonelloidea angulata, Globirhynchia subobsoleta, Sphaeroidothyris uretae, Lobothyris? hispanica, and Telothyris jauberti. The brachiopod assemblages were dated using coeval ammonite biostratigraphy. Both ammonites and brachiopods display clear northwest European affinities. The new brachiopod taxa are considered autochthonous for the Balkan Mountains. Three biofacies (BF2, BF3 and BF5) were recognised and implied alternating suboxic to anoxic bottom water conditions. A few geochemical proxies are indicative of the early Toarcian Oceanic Anoxic Event (T-OAE) in the stratigraphic column. The main T-OAE pulse was fixed at the coeval positive δ13C and negative δ18O excursions, as well as increases in Hg/TOC ratios and redox-sensitive elements. The late Pliensbachian–earliest Toarcian time span was found to be the most hostile for the brachiopods. Above it, brachiopods lived in less stagnant environments.urn:lsid:zoobank.org:pub:22EF76B7-6A4B-4E54-A5BC-38C87125253E

Biodeposit dispersion around a deep cage finfish farm in the Northern Persian Gulf

Due to increasing demand for food, intensive mariculture of finfish is a fast developing industry in the Iranian part of the Persian Gulf (PG). The environmental impacts of cage fish farming largely involve release of excessive organic matter (biodeposits). Careful monitoring of fish farms to avoid anoxia and bottom “dead zones” is an essential part of a sustainable mariculture industry.Monitoring data were collected for a fish farm north of Kish Island that had been in full operation for a period of one year. The data were then incorporated into a hydrodynamic model in order to estimate the quantity and dispersion pattern of biodeposits around the farm.Our results show that the farm had significant impacts on local environmental conditions, including water transparency, sulfide levels, and Eh values. Bottom water clarity near the cages was >15 NTU. Underneath the cages, sediment sulfide values are >800 μmole, Eh is usually -100 or less, and the sedimentation rate is 6.8 g/m2/day. The number of live benthic foraminifera near the cages was 4.5/10 g aliquot, as opposed to 20 at a control site.Numerical modeling, combined with data from sediment traps, shows that the farm “footprint” is much larger than the actual area of the farm, and is elongated by tidal currents. Considering the relatively short operation of the farm, it is already close to generating anoxic bottom conditions over a 2 km wide area. This can potentially impact the fragile habitats of the Persian Gulf. Continued expansion of net pen fish farms in sensitive areas such as the PG should be carefully monitored.