Investigation of a eutrophic tidal basin: part 1—factors affecting the distribution and biomass of macroalgae     

D. Lowthion  P. G. Soulsby  M. C. M. Houston 《Marine environmental research》1985,15(4):263-284

The distribution and biomass of macroalgae, principally Enteromorpha spp., have been estimated in Langstone Harbour, a 19 km² tidal basin in southenrn England. Comprehensive mapping was carried out annually at the time of maximum biomass and monthly mapping of selected areas allowed seasonal changes to be studied. Aerial false-colour photography and ground-level mapping were used for assessing the area and density of cover of macroalgae, but have identified no continuous trends between 1973 and 1982. In nine years, some 48% of the intertidal mudflat has supported >75% macroalgal cover at some stage, but generally only one-third of this potential has been achieved annually. The average peak biomass was determined by a stratified sampling method and varied about a mean of 38.5 g dry weight per square metre and showed significant annual differences. The processes controlling macroalgal growth and distribution reviewed, but, in general, factors other than nutrient availability are effective in determining areas supporting high macroalgal cover in any particular year.  相似文献   

基于波动方程的广义屏叠前深度偏移   总被引：15，自引：7，他引：15       下载免费PDF全文

金胜汶  许士勇  吴如山 《地球物理学报》2002,45(5):684-690

地震波传播算子的计算效率和精度是制约三维叠前深度偏移的关键因素. 广义屏传播算子(GSP, Generalized Screen Propagator)是一种在双域中实现的广角单程波传播算子. 这一方法略去了在非均匀体之间发生的交混回响,但它可以正确处理包括聚焦、衍射、折射和干涉在内的各种多次前向散射现象. 通过背景速度下的相移和扰动速度下的陡倾角校正,广义屏算子能够适应地层速度的强烈横向变化. 这种算子可以直接应用于炮集叠前偏移,通过将广义屏算子作用于双平方根方程,还可以获得一种高效率、高精度的炮检距域叠前深度偏移方法,用于二维共炮检距道集和三维共方位角道集的深度域成像. 本文首先简述了炮检距域广义屏传播算子的理论,进而讨论了共照射角成像(CAI, Common Angle Imaging)条件,由此给出各个不同照射角(炮检距射线参数)下的成像结果,进而得到共照射角像集. 由于照射角和炮检距的对应关系,共照射角像集又为偏移速度分析和AVO(振幅随炮检距变化)分析等提供了有力工具.  相似文献   

再论各向异性介质转换波地震学,第一部分:理论     

Xiangyang Li  Jianxin Yuan British Geological Survey  West Mains Road  Edinburgh EH LA  UK. Formerly at British Geological Survey  now at PGS Inc.  Richmond Avenue  Suite  Houston  TX  USA. 《应用地球物理》2005,2(1)

我们业已研发了计算各向异性、非均质介质中P- SV转换波(C-波)的转换点和旅行时的新理论。据此 可以利用诸如相似性分析、迪克斯模型建模、克契 霍夫求和等常规方法来完成各向异性的处理和各向 异性处理,并使各向异性的处理成为可能。这里将 我们的新发展分作两部分来介绍。第一部分为理 论,第二部分为对速度分析和参数计算的应用。第 一部分理论包括转换点的计算和动校正的分析。  相似文献   

Urban re-generations: afterword to special issue on the politics of urban greening in Australian cities     

Donna Houston 《The Australian geographer》2020,51(2):257-263

ABSTRACT

‘Urban re-generations' is written as an afterword to the special issue of Australian Geographer on ‘The Politics of Urban Greening in Australian Cities'. The collection prompts a deep questioning of reparative and regenerative work associated with greening, green spaces and green infrastructures. The climate-driven 2019-2020 bushfire crisis and COVID-19 have amplified the visibility of the more-than-human connectivity of our cities and the deep underlying structures of social and environmental inequity underpinning a variety of urban green spaces and agendas. Inspired by the articles in this special issue, the afterword explores how we might call back the grammars and practices of regeneration from their service to the neo-liberal, settler-colonial city and instead nurture reparative de-colonial practices that aid in the collaborative work of re-composing, becoming into better relation with, and working in modes of situated historical and cultural difference, with green and just cities.  相似文献   

The Victoria Province Drought Relief Project, I. Geophysical Siting of Boreholes     

C. C. White  J.F.T. Houston  R. D. Barker 《Ground water》1988,26(3):309-316

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Gravity profiles across the Cheyenne Belt, a precambrian crustal suture in southeastern Wyoming     

R.A. Johnson  K.E. Karlstrom  S.B. Smithson  R.S. Houston 《Journal of Geodynamics》1984,1(3-5)

Geologic discontinuities across the Cheyenne Belt of southeastern Wyoming have led to interpretations that this boundary is a major crustal suture separating the Archaean Wyoming Province to the north from accreted Proterozoic island arc terrains to the south. Gravity profiles across the Cheyenne Belt in three Precambrian-cored Laramide uplifts show a north to south decrease in gravity values of 50–100 mgal. These data indicate that the Proterozoic crust is more felsic (less dense) and/or thicker than Archaean crust. Seismic refraction data show thicker crust (48–54 km) in Colorado than in Wyoming (37–41 km). We model the gravity profiles in two ways: 1) thicker crust to the south and a south-dipping ramp in the Moho beneath and just south of the Cheyenne Belt; 2) thicker crust to the south combined with a mid-crustal density decrease of about 0.05 g/cm³. Differences in crustal thickness may have originated 1700 Ma ago because: 1) the gravity gradient is spatially related to the Cheyenne Belt which has been immobile since about 1650 Ma ago; 2) the N-S gradient is perpendicular to the trend of gravity gradients associated with local Laramide uplifs and sub-perpendicular to regional long-wavelength Laramide gradients and is therefore probably not a Laramide feature. Thus, gravity data support the interpretation that the Cheyenne Belt is a Proterozoic suture zone separating terrains of different crustal structure. The gravity “signature” of the Cheyenne Belt is different from “S”-shaped gravity anomalies associated with Proterozoic sutures of the Canadian Shield which suggests fundamental differences between continent-continent and island arc-continent collisional processes.  相似文献   

Observations on the effects of sewage discharged into a tidal harbour     

P.G. Soulsby  D. Lowthion  M. Houston 《Marine pollution bulletin》1978,9(9):242-245

Portsmouth harbour, a partially enclosed tidal inlet, receives a large discharge of sewage effluent. Investigations involving the measurement of nutrient concentrations, dissolved oxygen, heavy metals in sediments and faunal distributions have shown that gross effects are confined to an area near the discharge point. Surveys over 3 years have shown most of the harbour to be capable of supporting large mats of macroalgae, probably stimulated by the nutrient in the effluent which is to be removed by 1980.  相似文献   

Groundwater recharge through an alluvial fan in the Atacama Desert,northern Chile: mechanisms,magnitudes and causes     

John Houston 《水文研究》2002,16(15):3019-3035

The Chacarilla fan in the Atacama Desert is one of several formed in the Late Miocene at the foot of the Pre‐Andean Cordillera overlying the large, complex, Pampa Tamarugal aquifer contained in the continental clastic sediments of the fore‐arc basin. The Pampa Tamarugal aquifer is a strategic source of water for northern Chile but there is continuing doubt over the resource magnitude and recharge. During January 2000 a 1 in 4 year storm in the Andes delivered a 34 million m³ flash flood to the fan apex where c. 70% percolated to the underlying aquifers. Groundwater recharge through the fan is calculated to be a minimum of 200 l/s or 6% of the long‐term catchment rainfall. These figures are supported by hydrochemical data that suggest that recharge may be 9% of long‐term rainfall. Isotopic data suggest groundwater less than 50 years old is transmitted westward through the permeable sheetflood sediments of the fan overlying the main aquifer. Analysis of this and other events shows that the hydrological system is non‐linear with positive feedback. The magnitude of groundwater recharge is dependent on climatic variations, antecedent soil moisture storage and changes in channel characteristics. Long‐term declines in groundwater level may partly result from climatic fluctuations and the causes of such fluctuations are discussed. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Time-Dependent Deformation Behavior of Jiangsu Marine Clay     

L. Miao  J. Zhang  F. Wang  S. L. Houston 《Marine Georesources & Geotechnology》2013,31(2):86-100

In this article, the mechanical behavior of a Jiangsu marine clay was investigated by drained triaxial tests, traixial rheological tests, and one-dimensional compression and swelling tests. A visco-plastic model, the Bingham model combining two yield surfaces model, was proposed to describe the time-dependent deformation behaviors of the marine clay. The governing equation of Biot's consolidation theory for the visco-plastic soil is solved using a finite element code which incorporates the visco-plastic model. Using the finite element method, settlements of a typical embankment on the Lianxu expressway in China are calculated. Settlement calculations using the visco-plastic model are in agreement with the measured settlements in the field. The results demonstrate that the visco-plastic model is appropriate for calculating the visco-plastic deformations of Jiangsu marine clay. Theoretical and experimental studies show that the visco-plastic deformation of Jiangsu marine clay is substantial.  相似文献   

Ground-Water Systems Simulation by Time-Series Techniques   总被引：2，自引：0，他引：2  

J.F.T. Houston 《Ground water》1983,21(3):301-310

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