Assessing changes in nutrient status in the Richmond River estuary,Australia, using paleolimnological methods   总被引：1，自引：0，他引：1  

Brendan Logan  Kathryn H. Taffs  Bradley D. Eyre  Atun Zawadski 《Journal of Paleolimnology》2011,46(4):597-611

Eutrophication from nutrient over-enrichment is a serious problem for the coastal zone and the estuarine environment globally. Australian estuaries are generally oligotrophic, but assessing whether they are becoming more eutrophic over time is inhibited by a lack of long-term monitoring data. The Richmond River, Australia, provided an ideal example of an estuary under anthropogenic pressure where the use of paleoecological techniques may potentially be used to reconstruct changes in nutrient status over time. Five cores were extracted from depositional areas in the Richmond River, and subjected to paleo-magnetic profiling and loss-on-ignition testing to ensure the core of greatest integrity was selected for further analytical work. Results from diatom and stable isotope analyses combined with ²¹⁰Pb and AMS ¹⁴C dating show a strong indication that the total phosphorus levels in the Richmond River have fluctuated since 1940. Evidence also suggests that these fluctuations are most likely a function of climate. This study has successfully applied paleolimnological techniques to the estuarine environment to produce information that can be used by environmental managers to aid decision making in relation to nutrient control for the Richmond River. Further work using paleolimnological techniques should be aimed at the extraction of a core containing diatoms that pre-date European settlement and include analyses of specific lipids and fatty acid biomarkers.  相似文献   

Nonaxisymmetric instabilities in self-gravitating disks. II. Linear and quasi-linear analyses     

Kathryn Z. Hadley  Paul Fernandez  James N. Imamura  Erik Keever  Rebecka Tumblin  William Dumas 《Astrophysics and Space Science》2014,353(1):191-222

We studied global nonaxisymmetric hydrodynamic instabilities in an extensive collection of hot, self-gravitating polytropic disk systems, systems that covered a wide expanse of the parameter space relevant to protostellar and protoplanetary systems. We examined equilibrium disk models varying three parameters: the ratio of the inner to outer equatorial radii, the ratio of star mass to disk mass, and the rotation law exponent q. We took the polytropic index n=1.5 and examined the exponents q=1.5 and 2, and the transitional one q=1.75. For each of these sets of parameters, we examined models with inner to outer radius ratios from 0.1 to 0.75, and star mass to disk mass ratios from 0 to 10³. We numerically calculated the growth rates and oscillation frequencies of low-order nonaxisymmetric disk modes, modes with azimuthal dependence ∝e ^im? . Low-m modes are found to dominate with the character and strength of instability strongly dependent on disk self-gravity. Representatives of each mode type are examined in detail, and torques and mass transport rates are calculated.  相似文献   

The impact of an extra background of relativistic particles on the cosmological parameters derived from the cosmic microwave background     

R. Bowen  S. H. Hansen  A. Melchiorri  Joseph Silk  R. Trotta 《Monthly notices of the Royal Astronomical Society》2002,334(4):760-768

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Topology of the Universe from COBE–DMR – a wavelet approach     

G. Rocha  L. Cayón  R. Bowen  A. Canavezes  J. Silk  A. J. Banday  K. M. Górski 《Monthly notices of the Royal Astronomical Society》2004,351(3):769-778

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钙华非经典沉积的纳米生长过程与调控机制初探——以九寨沟—黄龙钙华形成为例     

董发勤  郑飞  代群威  李琼芳  陈禹衡  刘明学  蒋忠诚  张强  李博文  Alper Bab  Andelka Plenkovic-Moraj 《中国岩溶》2021,40(1):55-67

钙华是自然界重要的岩溶碳酸盐沉淀之一,其形成过程往往受到生命活动的影响,弄清钙华生物沉积作用有助于更好地理解钙华微岩相结构和地球化学特征的气候环境指示意义。本文以黄龙-九寨沟钙华形成为例,阐述黄龙-九寨沟现代钙华纳米结晶特征、纳米钙华的生长和集合体形态,分析模拟实验中生物有机质对钙华生长和形貌的调控原因,揭示了生物活动和代谢产物对纳米钙华成核、生长及钙华晶体形貌的调控两途径四阶段机制;为探究钙华成因、碳酸钙生长调控机制、钙华退化的因素及其保护和可持续利用钙华景观具有重要的科学价值。   相似文献   

A two-level perturbation method for connecting unstable periodic orbits with low fuel cost and short time of flight: application to a lunar observation mission     

George?A.?TsirogiannisEmail author  Kathryn?E.?Davis 《Celestial Mechanics and Dynamical Astronomy》2016,125(3):287-307

The proposed method connects two unstable periodic orbits by employing trajectories of their associated invariant manifolds that are perturbed in two levels. A first level of velocity perturbations is applied on the trajectories of the discretized manifolds at the points where they approach the nominal unstable periodic orbit in order to accelerate them. A second level of structured velocity perturbations is applied to trajectories that have already been subjected to first level perturbations in order to approximately meet the necessary conditions for a low \(\varDelta \text {V}\) transfer. Due to this two-level perturbation approach, the number of the trajectories obtained is significantly larger compared with approaches that employ traditional invariant manifolds. For this reason, the problem of connecting two unstable periodic orbits through perturbed trajectories of their manifolds is transformed into an equivalent discrete optimization problem that is solved with a very low computational complexity algorithm that is proposed in this paper. Finally, the method is applied to a lunar observation mission of practical interest and is found to perform considerably better in terms of \(\varDelta \text {V}\) cost and time of flight when compared with previous techniques applied to the same project.  相似文献   

A study of the observed shift in the peak position of olivine Raman spectra as a result of shock induced by hypervelocity impacts          下载免费PDF全文

Kathryn H. Harriss  M. J. Burchell 《Meteoritics & planetary science》2016,51(7):1289-1300

Kuebler et al. (2006) identified variations in olivine Raman spectra based on the composition of individual olivine grains, leading to identification of olivine composition from Raman spectra alone. However, shock on a crystal lattice has since been shown to result in a structural change to the original material, which produces a shift in the Raman spectra of olivine grains compared with the original unshocked olivine (Foster et al. 2013). This suggests that the use of the compositional calculations from the Raman spectra, reported in Kuebler et al. (2006), may provide an incorrect compositional value for material that has experienced shock. Here, we have investigated the effect of impact speed (and hence peak shock pressure) on the shift in the Raman spectra for San Carlos olivine (Fo₉₁) impacting Al foil. Powdered San Carlos olivine (grain size 1–10 μm) was fired at a range of impact speeds from 0.6 to 6.1 km s^?1 (peak shock pressures 5–86 GPa) at Al foil to simulate capture over a wide range of peak shock pressures. A permanent change in the Raman spectra was found to be observed only for impact speeds greater than ~5 km s^?1. The process that causes the shift is most likely linked to an increase in the peak pressure produced by the impact, but only after a minimum shock pressure associated with the speed at which the effect is first observed (here 65–86 GPa). At speeds around 6 km s^?1 (peak shock pressures ~86 GPa), the shift in Raman peak positions is in a similar direction (red shift) to that observed by Foster et al. (2013) but of twice the magnitude.  相似文献   

面向虚拟地理环境的Linux平台地理分析模型服务化封装方法     

谭羽丰  陈旻  张博文  沈超然  温永宁 《测绘学报》2018,47(8):1031-1042

地理分析模型是对现实世界中地理过程的抽象与表达,是虚拟地理环境能够反映真实世界的重要工具。随着地理学的发展,跨领域、多学科合作式地理建模逐渐成为地理学的研究趋势,地理分析模型共享与重用也已经成为研究热点之一。然而,地理分析模型运行平台的差异性导致了其在共享与重用上存在困难,表现在用户难以直接透明共享不同平台下的模型。目前,地理分析模型运行平台主要包含Windows与Linux,Linux平台上存在大量模型,但相关模型服务共享与重用研究相对较少。本文面向Linux平台不同操作系统,分析其差异性及安全性,设计模型服务化的安全策略;面向Linux平台下地理分析模型的异构特征,设计了模型基本信息描述接口、行为接口及部署接口,实现Linux系统下地理分析模型的服务共享与重用。本文以system for automated geoscientific analyses（SAGA GIS）中的网格分析模型为例,对所设计的Linux平台下地理分析模型服务化封装方法进行了验证,显示了所设计封装策略的可行性,为Linux平台下地理分析模型的共享与重用提供了理论与方法基础。  相似文献   

Effects of Docks on Salt Marsh Vegetation: an Evaluation of Ecological Impacts and the Efficacy of Current Design Standards     

John M. Logan  Amanda Davis  Charles Markos  Kathryn H. Ford 《Estuaries and Coasts》2018,41(3):661-675

Private docks are common in estuaries worldwide. Docks in Massachusetts (northeast USA) cumulatively overlie ~ 6 ha of salt marsh. Although regulations are designed to minimize dock impacts to salt marsh vegetation, few data exist to support the efficacy of these policies. To quantify impacts associated with different dock designs, we compared vegetation characteristics and light levels under docks with different heights, widths, orientations, decking types and spacing, pile spacing, and ages relative to adjacent control areas across the Massachusetts coastline (n = 212). We then evaluated proportional changes in stem density and biomass of the dominant vegetation (Spartina alterniflora and Spartina patens) in relation to dock and environmental (marsh zone and nitrogen loading) characteristics. Relative to adjacent, undeveloped habitat, Spartina spp. under docks had ~ 40% stem density, 60% stem biomass, greater stem height and nitrogen content, and a higher proportion of S. alterniflora. Light availability was greater under taller docks and docks set at a north-south orientation but did not differ between decking types. Dock height best predicted vegetation loss, but orientation, pile spacing, decking type, age, and marsh zone also affected marsh production. We combined our proportional biomass and stem elemental composition estimates to calculate a statewide annual loss of ~ 2200 kg dry weight of Spartina biomass (367 kg per ha of dock coverage). Managers can reduce impacts through design modifications that maximize dock height (> 150 cm) and pile spacing while maintaining a north-south orientation, but dock proliferation must also be addressed to limit cumulative impacts.  相似文献   

Pollen,biomarker and stable isotope evidence of late Quaternary environmental change at Lake McKenzie,southeast Queensland     

Pia Atahan  Henk Heijnis  John Dodson  Kliti Grice  Pierre Le Métayer  Kathryn Taffs  Sarah Hembrow  Martijn Woltering  Atun Zawadzki 《Journal of Paleolimnology》2015,53(1):139-156

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