Dispersion and recruitment of crab larvae in the Chesapeake Bay plume: Physical and biological controls     

Michael R. Roman  William C. Boicourt 《Estuaries and Coasts》1999,22(3):563-574

As part of the Microbial Exchanges and Coupling in Coastal Atlantic Systems (MECCAS) Project, crab larvae were collected in the shelf waters off Chesapeake Bay in June and August 1985 and April 1986. We conducted hydrographic (temperature, salinity, nutrients) and biological (chlorophyll, copepods) mapping in conjunction with Eulerian and Lagrangian time studies of the vertical distribution of crab larvae in the Chesapeake Bay plume. These abundance estimates are used with current meter records and drifter trajectories to infer mechanisms of larval crab dispersion to the shelf waters and recruitment back into Chesapeake Bay. The highest numbers of crab larvae were usually associated with the Chesapeake Bay plume, suggesting that it was the dominant source of crab larvae to shelf waters. Patches of crab larvae also were found in the higher salinity shelf waters, and possibly were remnants of previous plume discharge events. The distribution of crab larvae in the shelf waters changed on 1–2 d time scales as a consequence of both variations in the discharge rate of the Chesapeake Bay plume and local wind-driven currents. Downwelling-favorable winds (NW) intensified the coastal jet and confined the plume and crab larvae along the coast. In April during a downwelling event (when northwesterly winds predominated), crab zoeae were transported southward along the coast at speeds that at times exceeded 168 km d⁻¹. During June and August the upwelling-favorable winds (S, SW) opposed the anticyclonic turn of the plume and, via Ekman circulation, forced the plume and crab larvae to spread seaward. Plume velocities during these conditions generally were less than 48 km d⁻¹. The recruitment of crab larvae to Chesapeake Bay is facilitated in late summer by the dominance of southerly winds, which can reverse the southward flow of shelf waters. Periodic downwelling-favorable winds can result in surface waters and crab larvae moving toward the entrance of Chesapeake Bay. Approximately 27% of the larval crabs spend at least part of the day in bottom waters, which have a residual drift toward the bay mouth. There appears to be a variety of physical transport mechanisms that can enhance the recruitment of crab larvae into Chesapeake Bay.  相似文献   

Multidimensional Toxicity of Rhamnolipid Extracts Obtained From Creosote‐Contaminated Soil          下载免费PDF全文

Zuzanna Sydow  Piotr Lisiecki  Justyna Staninska‐Pięta  Anna Olejnik  Paweł Cyplik  Agnieszka Zgoła‐Grześkowiak  Roman Marecik  Jacek Nowak  Katarzyna Glazar  Agnieszka Piotrowska‐Cyplik 《洁净——土壤、空气、水》2018,46(5)

  相似文献   

Quantifying flow resistance in mountain streams using computational fluid dynamics modeling over structure-from-motion photogrammetry-derived microtopography     

Yunxiang Chen  Roman A. DiBiase  Nicholas McCarroll  Xiaofeng Liu 《地球表面变化过程与地形》2019,44(10):1973-1987

Flow resistance in mountain streams is important for assessing flooding hazard and quantifying sediment transport and bedrock incision in upland landscapes. In such settings, flow resistance is sensitive to grain-scale roughness, which has traditionally been characterized by particle size distributions derived from laborious point counts of streambed sediment. Developing a general framework for rapid quantification of resistance in mountain streams is still a challenge. Here we present a semi-automated workflow that combines millimeter- to centimeter-scale structure-from-motion (SfM) photogrammetry surveys of bed topography and computational fluid dynamics (CFD) simulations to better evaluate surface roughness and rapidly quantify flow resistance in mountain streams. The workflow was applied to three field sites of gravel, cobble, and boulder-bedded channels with a wide range of grain size, sorting, and shape. Large-eddy simulations with body-fitted meshes generated from SfM photogrammetry-derived surfaces were performed to quantify flow resistance. The analysis of bed microtopography using a second-order structure function identified three scaling regimes that corresponded to important roughness length scales and surface complexity contributing to flow resistance. The standard deviation σ_z of detrended streambed elevation normalized by water depth, as a proxy for the vertical roughness length scale, emerges as the primary control on flow resistance and is furthermore tied to the characteristic length scale of rough surface-generated vortices. Horizontal length scales and surface complexity are secondary controls on flow resistance. A new resistance predictor linking water depth and vertical roughness scale, i.e.  H/σ_z, is proposed based on the comparison between σ_z and the characteristic length scale of vortex shedding. In addition, representing streambeds using digital elevation models (DEM) is appropriate for well-sorted streambeds, but not for poorly sorted ones under shallow and medium flow depth conditions due to the missing local overhanging features captured by fully 3D meshes which modulate local pressure gradient and thus bulk flow separation and pressure distribution. An appraisal of the mesh resolution effect on flow resistance shows that the SfM photogrammetry data resolution and the optimal CFD mesh size should be about 1/7 to 1/14 of the standard deviation of bed elevation. © 2019 John Wiley & Sons, Ltd.  相似文献   

Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment          下载免费PDF全文

Valeriya Shulakova  Roman Pevzner  J. Christian Dupuis  Milovan Urosevic  Konstantin Tertyshnikov  David E. Lumley  Boris Gurevich 《Geophysical Prospecting》2015,63(1):55-69

4D seismic is widely used to remotely monitor fluid movement in subsurface reservoirs. This technique is especially effective offshore where high survey repeatability can be achieved. It comes as no surprise that the first 4D seismic that successfully monitored the CO₂ sequestration process was recorded offshore in the Sleipner field, North Sea. In the case of land projects, poor repeatability of the land seismic data due to low S/N ratio often obscures the time‐lapse seismic signal. Hence for a successful on shore monitoring program improving seismic repeatability is essential. Stage 2 of the CO2CRC Otway project involves an injection of a small amount (around 15,000 tonnes) of CO₂/CH₄ gas mixture into a saline aquifer at a depth of approximately 1.5 km. Previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions, near surface geology and farming activities. In order to improve time‐lapse seismic monitoring capabilities, a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability. A small‐scale trial of such an array was conducted at the Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1–12 m depth. In order to assess the gain in the signal‐to‐noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms. With such an amplified background noise level, we found that the noise level for buried geophones is on average 20 dB lower compared to the surface geophones. The levels of repeatability for borehole geophones estimated around direct wave, reflected wave and ground roll are twice as high as for the surface geophones. Both borehole and surface geophones produce the best repeatability in the 30–90 Hz frequency range. The influence of burying depth on S/N ratio and repeatability shows that significant improvement in repeatability can be reached at a depth of 3 m. The level of repeatability remains relatively constant between 3 and 12 m depths.  相似文献   

Application of diffracted wave analysis to time‐lapse seismic data for CO2 leakage detection     

Faisal Alonaizi  Roman Pevzner  Andrej Bóna  Mohammad Alshamry  Eva Caspari  Boris Gurevich 《Geophysical Prospecting》2014,62(2):197-209

Time‐lapse seismic analysis is utilized in CO₂ geosequestration to verify the CO₂ containment within a reservoir. A major risk associated with geosequestration is a possible leakage of CO₂ from the storage formation into overlaying formations. To mitigate this risk, the deployment of carbon capture and storage projects requires fast and reliable detection of relatively small volumes of CO₂ outside the storage formation. To do this, it is necessary to predict typical seepage scenarios and improve subsurface seepage detection methods. In this work we present a technique for CO₂ monitoring based on the detection of diffracted waves in time‐lapse seismic data. In the case of CO₂ seepage, the migrating plume might form small secondary accumulations that would produce diffracted, rather than reflected waves. From time‐lapse data analysis, we are able to separate the diffracted waves from the predominant reflections in order to image the small CO₂ plumes. To explore possibilities to detect relatively small amounts of CO₂, we performed synthetic time‐lapse seismic modelling based on the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway project data. The detection method is based on defining the CO₂ location by measuring the coherency of the signal along diffraction offset‐traveltime curves. The technique is applied to a time‐lapse stacked section using a stacking velocity to construct offset‐traveltime curves. Given the amount of noise found in the surface seismic data, the predicted minimum detectable amount of CO₂ is 1000–2000 tonnes. This method was also applied to real data obtained from a time‐lapse seismic physical model. The use of diffractions rather than reflections for monitoring small amounts of CO₂ can enhance the capability of subsurface monitoring in CO₂ geosequestration projects.  相似文献   

Evaluation of Liquefaction Potential Index Along Western Coast of South Korea Using SPT and CPT     

Min-Woo Seo  Scott M. Olson  Myoung-Hak Oh 《Marine Georesources & Geotechnology》2013,31(3):234-260

For South Korea, liquefaction potential along the western coast has not been widely assessed because South Korea is considered to be a low seismic hazard. However, recent earthquake events and historical records indicate that the seismic hazard of South Korea should not be ignored. Moreover, as artificial fills are extensively used along the western coast for development, liquefaction evaluation of the soils in this area is necessary. In this paper, we present: (1) the seismic characteristics of the study area; (2) procedures for evaluating liquefaction potential, focusing on the liquefaction potential index (LPI) approach; and (3) LPI distributions at several representative locations along the western coast of South Korea under various seismic scenarios. The liquefaction potential index represents the liquefaction potential over the upper 20 m of a boring or sounding. Using cone penetration test (CPT) and standard penetration test (SPT) data from two coastal sites, we compare and discuss CPT-based and SPT-based LPI values, particularly values computed in nonplastic, silt-rich soils. In these soils, it appears that the CPT yields lower liquefaction resistance, resulting in large LPI values. Finally, discussion and suggestions are provided for CPT- and SPT-based liquefaction assessment of low plasticity and high fines content soils.  相似文献   

Chlorinated Solvent Source‐Zone Remediation via ZVI‐Clay Soil Mixing: 1‐Year Results     

Mitchell R. Olson  Thomas C. Sale  Charles D. Shackelford  Christopher Bozzini  Jessica Skeean 《Ground Water Monitoring & Remediation》2012,32(3):63-74

ZVI‐Clay is an emerging remediation approach that combines zero‐valent iron (ZVI)‐mediated degradation and in situ stabilization of chlorinated solvents. Through use of in situ soil mixing to deliver reagents, reagent‐contaminant contact issues associated with natural subsurface heterogeneity are overcome. This article describes implementation, treatment performance, and reaction kinetics during the first year after application of the ZVI‐Clay remediation approach at Marine Corps Base Camp Lejeune, North Carolina. Primary contaminants included trichloroethylene, 1,1,2,2‐tetrachloroethane, and related natural degradation products. For the field application, 22,900 m³ of soils were treated to an average depth of 7.6 m with 2% ZVI and 3% sodium bentonite (dry weight basis). Performance monitoring included analysis of soil and water samples. After 1 year, total concentrations of chlorinated volatile organic compounds (CVOCs) in soil samples were decreased by site‐wide average and median values of 97% and >99%, respectively. Total CVOC concentrations in groundwater were reduced by average and median values of 81% and >99%, respectively. In several of the soil and groundwater monitoring locations, reductions in total CVOC concentrations of greater than 99.9% were apparent. Further reduction in concentrations of chlorinated solvents is expected with time. Pre‐ and post‐mixing average hydraulic conductivity values were 1.7 × 10^?5 and 5.2 × 10^?8 m/s, respectively, indicating a reduction of about 2.5 orders of magnitude. By achieving simultaneous contaminant mass depletion and hydraulic conductivity reduction, contaminant flux reductions of several orders of magnitude are predicted.  相似文献   

Rotation and strain seismology     

Roman Teisseyre 《Journal of Seismology》2012,16(4):683-694

Asymmetric continuum theory points to the equal roles of the rotation motions and those related directly to shear or confining strains. The strain motions could be quite independent or mutually related with the eventual phase shifts, while the displacements have only a mathematical sense; a real displacement may appear along the fracture slip only. Formally, any deformation could be presented as related to the displacements; however, its origin in a fracture source should be considered either as belonging to an individual process or to complex correlated events; in these cases, the confining, shear and rotation strains can be related mathematically to the different displacement fields. Some of these related deformations could be emitted from a source with a phase shift, while the observed displacements (deduced from records) result as a sum of these independent displacements. An important influence on a source process and on the premonitory micro-events has the material defects, their distribution, and mobility. The defect arrays lead to a concentration of stresses and their local reorganization. Thus, in this paper, we consider the induced stresses and strains related to defect content and to its modification and redistribution. Moreover, an important role in understanding the complex correlated events in a source plays the release?Crebound mechanism. The release?Crebound mechanism in an earthquake source processes leads to a possible direct or phase-shifted correlations between the emitted motions; in this aspect, a propagation of the coupled strain and rotation waves is discussed. In particular, we consider the point fracture events as related either to a confining load or/and to the shear and rotation processes; we discuss the related effects and their meaning when discussing the fault plane mechanism and emitted waves. In some important seismic regions, we have the recording system which permits to record the strains and rotations. However, we should point that the wordwide seismological network is not adequate to record the complex strain deformations released in the fracture processes and remains quite insufficient to understand the global stress changes and related strain waves of a very low period. Consideration on a recording mechanism of the long displacement waves indicates the insufficiencies of the present global recording system and points that recording of the global strain and rotation waves is an important and urgent task.  相似文献   

Differences in the abiotic parameters of water in coastal lakes in the light of the EU water framework directive: An example of the Polish southern Baltic coast     

Roman Cieśliński  Maciej Major 《Acta Geophysica》2012,60(4):1159-1179

Coastal lakes have a specific hydrological regime determined by the influence of sea and inland water and the local hydrographic conditions. There are several problems concerning the protection and assessment of water quality of these bodies. The most important features differentiating coastal lakes from other lakes are: high salinity, a wide range of seasonal and short-term water quality changes, and specific aquatic ecosystems adapted to these conditions. These matters have not been sufficiently taken into account in the existing classifications and typologies of lakes in Poland. The problem has not been solved by the establishment of the adequate reference conditions and new guidelines for the classification of water status (which are being prepared according to the Common Strategy for the Implementation of the Water Framework Directive) regarding inland surface waters (rivers and lakes) and marine waters (coastal and transitional). An important issue is to define criteria which would help to distinguish all those hydrographic objects and to establish water quality standards for them.  相似文献   

Intermittent generation of mafic enclaves in the 1991–1995 dacite of Unzen Volcano recorded in mineral chemistry     

Hiroaki?SatoEmail author  Francois?Holtz  Roman?E.?Botcharnikov  Setsuya?Nakada 《Contributions to Mineralogy and Petrology》2017,172(4):22

Mafic enclaves in the 1991–1995 dacite of Unzen volcano show chemical and textural variability, such as bulk SiO₂ contents ranging from 52 to 62 wt% and fine- to coarse-grained microlite textures. In this paper, we investigated the mineral chemistry of plagioclase and hornblende microlites and distinguished three enclave types. Type-I mafic enclaves contain high-Mg plagioclase and low-Cl hornblende as microlites, whereas type-III enclaves include low-Mg plagioclase and high-Cl hornblende. Type-II enclaves have an intermediate mineral chemistry. Type-I mafic enclaves tend to show a finer-grained matrix, have slightly higher bulk rock SiO₂ contents (56–60 wt%) when compared with the type-III mafic enclaves (SiO₂?=?53–59 wt%), but the overall bulk enclave compositions are within the trend of the basalt–dacite eruptive products of Quaternary monogenetic volcanoes around Unzen volcano. The origin of the variation of mineral chemistry in mafic enclaves is interpreted to reflect different degree of diffusion-controlled re-equilibration of minerals in a low-temperature mushy dacitic magma reservoir. Mafic enclaves with a long residence time in the dacitic magma reservoir, whose constituent minerals were annealed at low-temperature to be in equililbrium with the rhyolitic melt, represent type-III enclaves. In contrast, type-I mafic enclaves result from recent mafic injections with a mineral assemblage that still retains the high-temperature mineral chemistry. Taking temperature, Ca/(Ca?+?Na) ratio of plagioclase, and water activity of the hydrous Unzen magma into account, the Mg contents of plagioclase indicate that plagioclase microlites in type-III enclaves initially crystallized at high temperature and were subsequently re-equilibrated at low-temperature conditions. Compositional profiles of Mg in plagioclase suggest that older mafic enclaves (Type-III) had a residence time of ~100 years at 800 °C in a stagnant magma reservoir before their incorporation into the mixed dacite of the 1991–1995 Unzen eruption. Presence of different types of mafic enclaves suggests that the 1991–1995 dacite of Unzen volcano tapped mushy magma reservoir intermittently replenished by high-temperature mafic magmas.  相似文献