Enhanced attenuation of septic system phosphate in noncalcareous sediments

Review of phosphate behavior in four mature septic system plumes on similar textured sand has revealed a strong correlation between carbonate mineral content and phosphate concentrations. A plume on calcareous sand (Cambridge site, 27 wt % CaCO3 equiv.) has proximal zone PO4 concentrations (4.8 mg/L P average) that are about 75% of the septic tank effluent value, whereas three plumes on noncalcareous sand (Muskoka, L. Joseph, and Nobel sites, <1 wt % CaCO3 equiv.) have proximal zone phosphate concentrations (<0.1 mg/L P) that are consistently less than 2% of the effluent values. Phosphate attenuation at the noncalcareous sites appears to be an indirect result of the development of acidic conditions (site average pH 3.5 to 5.9) and elevated Al concentrations (up to 24 mg/L), which subsequently causes the precipitation of Al-P minerals such as variscite (AlPO4 x 2H2O). This is supported by scanning electron microscope analyses, which show the widespread occurrence of (Al+P)--rich secondary mineral coatings on sand grains below the infiltration beds. All of these septic systems are more than 10 years old, indicating that these attenuation reactions have substantial longevity. A field lysimeter experiment demonstrated that this reaction sequence can be readily incorporated into engineered waste water treatment systems. We feel this important P removal mechanism has not been adequately recognized, particularly for its potential significance in reducing P loading from septic systems in lakeshore environments.     

Natural and anthropogenic nitrogen uptake by bloom-forming macroalgae

The frequency and duration of macroalgal blooms have increased in many coastal waters over the past several decades. We used field surveys and laboratory culturing experiments to examine the nitrogen content and delta(15)N values of Ulva and Gracilaria, two bloom-forming algal genera in Narragansett Bay, RI (USA). The northern end of this bay is densely populated with large sewage treatment plant nitrogen inputs; the southern end is more lightly populated and opens to the Atlantic Ocean. Field-collected Ulva varied in delta(15)N among sites, but with two exceptions had delta(15)N above 10 per thousand, reflecting a significant component of heavy anthropogenic N. This variation was not correlated with a north-south gradient. Both Ulva and Gracilaria cultured in water from across Narragansett Bay also had high signals (delta(15)N= approximately 14-17 per thousand and 8-12 per thousand, respectively). These results indicate that inputs of anthropogenic N can have far-reaching impacts throughout estuaries.     

Internal multiple attenuation by Kirchhoff extrapolation

Surface‐related multiple elimination is the leading methodology for surface multiple removal. This data‐driven approach can be extended to interbed multiple prediction at the expense of a huge increase of the computational burden. This cost makes model‐driven methods still attractive, especially for the three dimensional case. In this paper we present a methodology that extends Kirchhoff wavefield extrapolation to interbed multiple prediction. In Kirchhoff wavefield extrapolation for surface multiple prediction a single round trip to an interpreted reflector is added to the recorded data. Here we show that interbed multiples generated between two interpreted reflectors can be predicted by applying the Kirchhoff wavefield extrapolation operator twice. In the first extrapolation step Kirchhoff wavefield extrapolation propagates the data backward in time to simulate a round trip to the shallower reflector. In the second extrapolation step Kirchhoff wavefield extrapolation propagates the data forward in time to simulate a round trip to the deeper reflector. In the Kirchhoff extrapolation kernel we use asymptotic Green's functions. The prediction of multiples via Kirchhoff wavefield extrapolation is possibly sped up by computing the required traveltimes via a shifted hyperbola approximation. The effectiveness of the method is demonstrated by results on both synthetic and field data sets.     

Interstation surface wave attenuation by autoregressive deconvolution

A new technique for calculating interstation Green's functions and attenuation coefficients for seismic surface waves is presented.The interstation Green's function is evaluated from the autocorrelation functions of the seismograms, which are obtained from a maximum entropy process.Since a data-invariant time window is not used, the evaluated Green's functions gives reliable information on both the amplitude and the phase spectra of the system.This new technique is compared with other methods by applying them to both synthetic and real data from a path in the Canadian shield.     

On the attenuation of sea waves by rain

Abstract

Some conflicting evidence on Reynolds' (1900) hypothesis that rain should attenuate any wave motion on the sea surface is discussed. It is concluded that rain drops ought to produce vortex rings in the sea which mix the water to a sufficient depth to affect most waves, as asserted by Reynolds. By introducing vertical and horizontal eddy viscosities to model the mixing process, an estimate is found for the rate of attenuation of wave energy by the rain. Consequently, the net effect on the wave field of attenuation by rain and generation by wind is calculated.     

Seasonal variation in di-nitrogen fluxes and associated processes (denitrification, anammox and nitrogen fixation) in sediment subject to shellfish farming influences

Seasonal patterns of di-nitrogen fluxes together with denitrification, anammox, and N-fixation rates were studied in sediment in an area subject to strong human pressure via waste water, tributaries and shellfish farming in the Mediterranean Sea (Carteau Cove, NW area of the Gulf of Lion). Ammonium concentration demonstrated no seasonal variation, however, a large increase in its concentration was observed over a 10 years period due to intense biodeposition of organic matter. In contrast, nitrate concentration demonstrated no seasonal or long-term (10 years) variation. The main processes affecting di-nitrogen flux magnitudes were denitrification and N-fixation. Anammox was only detected occasionally, nevertheless it represented at times up to 39% of the N₂-flux. Nitrate reducing processes were variable and denitrification showed a 20-fold increase over the past 10 years and might actually have reached its potential maximal activity. Rates of N₂ production (denitrification and anammox) were generally higher than those of N-fixation, leading to elimination of nitrogen from the ecosystem.     

Flood hydrograph attenuation induced by a reservoir system: analysis with a distributed rainfall‐runoff model

Spatially distributed hydrologic models can be effectively utilized for flood event simulation over basins where a complex system of reservoirs affecting the natural flow regime is present. Flood peak attenuation through mountain reservoirs can, in fact, mitigate the impact of major floods in flood‐prone areas of the lower river valley. Assessment of this effect for a complex reservoir system is performed with a spatially distributed hydrologic model where the surface runoff formation and the hydraulic routing through each reservoir and the river system are performed at a fine spatial and time resolution. The Toce River basin is presented as a case study, because of the presence of 14 active hydroelectric dams that affect the natural flow regime. A recent extreme flood event is simulated using a multi‐realization kriging method for modelling the spatial distribution of rainfall. A sensitivity analysis of the key elements of the distributed hydrologic model is also performed. The flood hydrograph attenuation is assessed. Several possible reservoir storage conditions are used to characterize the initial condition of each reservoir. The results demonstrate how a distributed hydrologic model can contribute to defining strategies for reservoir management in flood mitigation. Copyright © 2004 John Wiley & Sons, Ltd.     

Natural attenuation, biostimulation and bioaugmentation on biodegradation of polycyclic aromatic hydrocarbons (PAHs) in mangrove sediments

The biodegradability of a mixture of PAHs, namely fluorene (Fl), phenanthrene (Phe) and pyrene (Pyr), in mangrove sediment slurry was investigated. At the end of week 4, natural attenuation based on the presence of autochthonous microorganisms degraded more than 99% Fl and Phe but only around 30% of Pyr were degraded. Biostimulation with addition of mineral salt medium degraded over 97% of all three PAHs, showing that nutrient amendment could enhance Pyr degradation. Bioaugmentation with inoculation of a PAH-degrading bacterial consortium enriched from mangrove sediments did not show any promotion effect and the degradation percentages of three PAHs were similar to that by natural attenuation. Some inhibitory effect was observed in bioaugmentation treatment in week 1 with only 50% Fl and 70% Phe degraded. These results indicate that autochthonous microbes may interact and even compete with the enriched consortium during PAH biodegradation. Natural attenuation appeared to be the most appropriate way to remedy Fl- and Phe-contaminated mangrove sediments while biostimulation was more capable to degrade Pyr-contaminated sediments. The study also shows that although a large portion of the added PAHs (more than 95%) was adsorbed onto the sediments at the beginning of the experiment, most PAHs were degraded in 4 weeks, suggesting that the degraders could utilize the adsorbed PAHs efficiently.     

青岛震群体波衰减特性研究

随着观测能力的提高和观测手段的改善,反映地球介质特性Q值的研究不断深化和发展。利用山东数字测震台网记录的数字地震波资料,采用时间域P波脉冲宽度法对2003年和2004年青岛震群进行Q值计算,对初动半周期的两种不同获取方法进行了比较,总结了P波脉冲宽度法的适用条件及计算效果,得到青岛地区和胶东地区的Q值。     

Water‐bottom multiple attenuation by Kirchhoff extrapolation

Despite being less general than 3D surface‐related multiple elimination (3D‐SRME), multiple prediction based on wavefield extrapolation can still be of interest, because it is less CPU and I/O demanding than 3D‐SRME and moreover it does not require any prior data regularization. Here we propose a fast implementation of water‐bottom multiple prediction that uses the Kirchhoff formulation of wavefield extrapolation. With wavefield extrapolation multiple prediction is usually obtained through the cascade of two extrapolation steps. Actually by applying the Fermat’s principle (i.e., minimum reflection traveltime) we show that the cascade of two operators can be replaced by a single approximated extrapolation step. The approximation holds as long as the water bottom is not too complex. Indeed the proposed approach has proved to work well on synthetic and field data when the water bottom is such that wavefront triplications are negligible, as happens in many practical situations.     

钢筋混凝土框架结构体系抗震可靠度及其抗力衰减影响分析

结构体系可靠度分析面临的主要问题是失效模式多,但通过pushover分析方法在一定情况下可以得到结构的最弱失效模式。本文将结构体系抗力等效为与结构特定损伤状况相关的结构的顶点位移,结构的地震作用效应由pushover分析及能力谱法求得。考虑结构体系抗力随机性的主要影响因素以及地震作用的随机性,分别求得了结构抗力及地震作用效应的概率分布参数,通过一次二阶矩方法求得了结构体系可靠度,并进一步研究了结构层数变化及耐久性退化因素对结构体系可靠度的影响。研究发现,结构体系的抗震可靠度水平随着结构层数的增加有减小的趋势,结构体系的抗震可靠度水平随着结构使用期增加而降低,降低幅度与薄弱层个数有关,薄弱层越多,降低幅度越大。     

地铁诱发地面运动的衰减规律的研究分析

以地铁车站间的隧道为研究对象，在研究和分析有关资料的基础上，用快速拉格朗日有限差分法软件FLAC建立了二维数值分析模型，并以列车振动加速度时程作为模型输入，进行了隧道衬砌－地层的整体动力学分析，分析了列车运行产生的振动在地面的衰减规律，得到了一些结论，可为地面建筑的防振减振控制提供参考。     

Natural self-cleaning of oil-polluted beaches by waves

Changes in the magnitude of oil pollution on five prototype study beaches on Israel's northern Mediterranean coast had been monitored at 2- to 4-weekly intervals from 21 November 1980 to 19 March 1981. Statistical analyses of these changes were employed to rank the beaches in order of decreasing self-cleaning capacity. Records of storm-induced wave data records for the winter of 1980–1981 were correlated to incidence of change in the magnitude of subsurface tarball pollution and the rate of emplaced fuel sample dissipation on the study beaches. Specific wave breaking processes, overtopping of offshore obstacles and wave refraction were singled out as accelerating or retarding wave energy transfer to the polluted beaches. Attribution of the occurrence of specific local littoral processes to observed change in beach pollution magnitude made it possible to assess potential oil spill damage. Elucidation of the causative processes provided theoretical corroboration for beach sensitivity ranking established earlier by statistical analysis.     

Characterization of the light attenuation by periphyton in lakes of different trophic state

In order to measure the attenuation of light by periphyton a method has been developed which assures that natural periphyton architecture and therefore its optical characteristics remain preserved. This method has been applied to analyze the transmittance of periphyton of four lakes of different tropic states situated in the Osterseen Lake District (Upper Bavaria, Germany). The seasonal variation of the periphyton's transmittance has been studied using standard microscope glass slides exposed 1 m beneath the water surface within macrophyte beds. The study ran from February to November 1997 in two eutrophic lakes (Lake Waschsee, Lake Sengsee) and from May to November 1997 in the meso-oligotrophic Lake Eishaussee and in the oligotrophic Lake Herrensee.Generally the exposure-period, the seasonality, and the tropic state of the habitat affected the transmittance spectra of the periphyton. In all lakes the attenuation by periphyton increased with longer colonization times but at a different time scale. The periphyton of the nutrient-rich and the nutrient-poor lakes differed clearly in composition and architecture. The eutrophic lakes were characterized by a relatively thick but loosely attached, unstable periphyton community, which was translucent to a certain degree even at the end of the growth period. The transmittance of this periphyton fluctuated considerably and high percentages of filamentous green algae in this periphyton contributed to attenuation maxima within the range 400-500 nm and 650-700 nm due to photosynthetic pigments. By contrast, the periphyton of the meso-oligotrophic and of the oligotrophic lake was quite compact and nearly impervious to light.     

Natural attenuation of volatile organic compounds (VOCs) in the leachate plume of a municipal landfill: using alkylbenzenes as process probes

More than 70 individual VOCs were identified in the leachate plume of a closed municipal landfill. Concentrations were low when compared with data published for other landfills, and total VOCs accounted for less than 0.1% of the total dissolved organic carbon. The VOC concentrations in the core of the anoxic leachate plume are variable, but in all cases they were found to be near or below detection limits within 200 m of the landfill. In contrast to the VOCs, the distributions of chloride ion, a conservative tracer, and nonvolatile dissolved organic carbon, indicate little dilution over the same distance. Thus, natural attenuation processes are effectively limiting migration of the VOC plume. The distribution of C2-3-benzenes, paired on the basis of their octanol-water partition coefficients and Henry's law constants, were systematically evaluated to assess the relative importance of volatilization, sorption, and biodegradation as attenuation mechanisms. Based on our data, biodegradation appears to be the process primarily responsible for the observed attenuation of VOCs at this site. We believe that the alkylbenzenes are powerful process probes that can and should be exploited in studies of natural attenuation in contaminated ground water systems.     

应用烈度衰减关系进行烈度分布快速评估的偏差特性研究

地震发生后,一般都是用烈度衰减关系来初步评估烈度分布.为了研究该方法的偏差特性,首先利用138次地震事件回归出我国大陆地区的烈度衰减关系,然后应用该衰减关系,以我国大陆地区1966年以来震级在6.0级以上的43次地震事件的评估结果,总结出应用烈度衰减关系评估烈度分布时的偏差特性,并提出了相应的改进建议.     

Anisotropic attenuation of stratified viscoelastic media

An important cause of seismic anisotropic attenuation is the interbedding of thin viscoelastic layers. However, much less attention has been devoted to layer‐induced anisotropic attenuation. Here, we derive a group of unified weighted average forms for effective attenuation from a binary isotropic, transversely isotropic‐ and orthorhombic‐layered medium in the zero‐frequency limit by using the Backus averaging/upscaling method and analyse the influence of interval parameters on effective attenuation. Besides the corresponding interval attenuation and the real part of stiffness, the contrast in the real part of the complex stiffness is also a key factor influencing effective attenuation. A simple linear approximation can be obtained to calculate effective attenuation if the contrast in the real part of stiffness is very small. In a viscoelastic medium, attenuation anisotropy and velocity anisotropy may have different orientations of symmetry planes, and the symmetry class of the former is not lower than that of the latter. We define a group of more general attenuation‐anisotropy parameters to characterize not only the anisotropic attenuation with different symmetry classes from the anisotropic velocity but also the elastic case. Numerical tests reveal the influence of interval attenuation anisotropy, interval velocity anisotropy and the contrast in the real part of stiffness on effective attenuation anisotropy. Types of effective attenuation anisotropy for interval orthorhombic attenuation and interval transversely isotropic attenuation with a vertical symmetry (vertical transversely isotropic attenuation) are controlled only by the interval attenuation anisotropy. A type of effective attenuation anisotropy for interval TI attenuation with a horizontal symmetry (horizontal transversely isotropic attenuation) is controlled by the interval attenuation anisotropy and the contrast in the real part of stiffness. The type of effective attenuation anisotropy for interval isotropic attenuation is controlled by all three factors. The magnitude of effective attenuation anisotropy is positively correlated with the contrast in the real part of the stiffness. Effective attenuation even in isotropic layers with identical isotropic attenuation is anisotropic if the contrast in the real part of stiffness is non‐zero. In addition, if the contrast in the real part of stiffness is very small, a simple linear approximation also can be performed to calculate effective attenuation‐anisotropy parameters for interval anisotropic attenuation.     

Ultrasonic attenuation of pure tetrahydrofuran hydrate

Improved estimates of the amount of subsurface gas hydrates are needed for natural resource, geohazard, and climate impact assessments. To evaluate gas hydrate saturation from seismic methods, the properties of pure gas hydrates need to be known. Whereas the properties of sediments, specifically sands, and hydrate‐bearing sediments are well studied, the properties of pure hydrates are largely unknown. Hence, we present laboratory ultrasonic P‐wave velocity and attenuation measurements on pure tetrahydrofuran hydrates as they form with reducing temperatures from 25°C to 1°C under atmospheric pressure conditions. Tetrahydrofuran hydrates, with structure II symmetry, are considered as proxies for the structure I methane hydrates because both have similar effects on elastic properties of hydrate‐bearing sediments. We find that although velocity increased, the waveform frequency content and amplitude decreased after the hydrate formation reaction was complete, indicating an increase in P‐wave attenuation after hydrate formation. When the tetrahydrofuran hydrate was cooled below the freezing point of water, velocity and quality factor increased. Nuclear Magnetic Resonance results indicate the presence of water in the “pure hydrate” samples above the water freezing point, but none below. The presence of liquid water between hydrate grains most likely causes heightened attenuation in tetrahydrofuran hydrates above the freezing point of water. In naturally occurring hydrates, a similarly high attenuation might relate to the presence of water.