The nature, extent and causes of land degradation in South Africa: legacy of the past, lessons for the future?     

M. E. Meadows  & M. T. Hoffman 《Area》2002,34(4):428-437

The aim of this paper is to reassess the land degradation and desertification problem in South Africa. The country has a wide range of interrelated environmental and development challenges existing in a socio–political context recently subject to substantial change. The paper outlines the fundamental environmental constraints and opportunities that underlie degradation phenomena and illustrates the nature, extent and geographical distribution of the major forms of soil and vegetation degradation in the country. The principal causes of degradation are identified and some important land use and land tenure questions that need to be addressed in the near future are posited.  相似文献   

The initial development of solar flares     

J. F. Vesecky  A. J. Meadows 《Solar physics》1969,6(1):80-85

The extent to which the early phases of solar-flare development can be accounted for by a simple high-temperature chromospheric explosion model is investigated without involving a particular energy source. A model is developed in which it is shown that a point explosion in the lower chromosphere can be treated as a virtually instantaneous release of energy throughout a volume of radius R 100 km, which subsequently expands as a classical hydrodynamic blast wave in which R~ t ( < 2/3). This model is in substantial agreement with areal growth-rate observations of disk flares. An explanation for the fact that limb-flare observations can imply > 2/3 is suggested by considering the effects of the large atmospheric density gradient in the lower chromosphere on an upward travelling shock wave.  相似文献   

Probabilistic flood risk analysis considering morphological dynamics and dike failure     

J. Oliver  X. S. Qin  O. Larsen  M. Meadows  M. Fielding 《Natural Hazards》2018,91(1):287-307

A comprehensive flood risk assessment should aim not only at quantifying uncertainties but also the variability of risk over time. In this study, an efficient modelling framework was proposed to perform probabilistic hazard and risk analysis in dike-protected river systems accounting for morphological variability and uncertainty. The modelling framework combined the use of: (1) continuous synthetic discharge forcing, (2) a stochastic dike breach model dynamically coupled to a stochastic unsteady one-dimensional hydraulic model (MIKE1D) describing river flows, (3) a catalogue of pre-run probabilistic inundation maps (MIKE SHE) and (4) a damage and loss model (CAPRA). The methodology was applied using continuous simulations to a 45-km reach of the Upper Koshi River, Nepal, to investigate the changes in breach and flood hazards and subsequent risks after 2 and 5 years of probable river bed aggradation. The study results indicated an increase in annual average loss of 4% per year driven by changes in loss distribution in the most frequent loss return periods (20–500 years). The use of continuous simulations and dike breach model also provided a more robust estimation of risk metrics as compared to traditional binary treatment of flood defence and/or the direct association of flow with loss return periods. The results were helpful to illustrate the potential impacts of dynamic river morphology, dike failure and continuous simulation and their significance when devising flood risk study methodologies.  相似文献   

Characterizing the changing environment of cropland in the Songnen Plain,Northeast China,from 1990 to 2015     

Zhang  Yuan  Zang  Shuying  Sun  Li  Yan  Binghe  Yang  Tianpeng  Yan  Wenjia  Meadows  Michael E.  Wang  Cuizhen  Qi  Jiaguo 《地理学报(英文版)》2019,29(5):658-674

Journal of Geographical Sciences - Quantitative characterization of environmental characteristics of cropland (ECC) plays an important role in maintaining sustainable development of agricultural...  相似文献   

Near infrared imaging spectroscopy of Venus with the Anglo-Australian Telescope     

Jeremy Bailey  S. Chamberlain  V.S. Meadows 《Planetary and Space Science》2008,56(10):1385-1390

We have obtained full-disk spatially resolved spectra of the Venus nightside at near-infrared wavelengths during July 2007 using the Anglo-Australian Telescope and Infrared Imager and Spectrograph 2 (IRIS2). The data have been used to map the intensity and rotational temperature of the O₂(a¹Δ_g) airglow band at . The temperatures agree with those obtained in earlier IRIS2 observations and are significantly higher than expected from the Venus International Reference Atmosphere (VIRA) profile. We also report the detection of the corresponding ν=0-1O₂ airglow band at with a similar spatial distribution to the ν=0-0 band. Observations in the thermal window have been used to image surface topography using two different methods of cloud correction. We have also obtained images that can be used to study cloud motion.  相似文献   

Mineralogic investigation into occurrence of high uranium well waters in upstate South Carolina, USA     

Richard Warner  Jason Meadows  Scott Sojda  Van PriceTom Temples  Yuji AraiChris Fleisher  Bruce CrawfordPeter Stone 《Applied Geochemistry》2011,26(5):777-788

High levels of U (up to 5570 μg/L) have been discovered in well waters near Simpsonville, South Carolina, USA. In order to characterize the mineralogical source of the U and possible structural controls on its presence, a deep (214 m) well was cored adjacent to one of the enriched wells. The highest gamma-ray emissions in the recovered core occur in coarse biotite granite at a depth just below 52 m. A slickenlined fault plane at 48.6 m and narrow pegmatite layers at depths of 113, 203 and 207 m also yield high gamma-ray counts. Thin sections were made from the above materials and along several subvertical healed fractures. Uraninite and coffinite are the principal U-rich minerals in the core. Other U-bearing minerals include thorite and thorogummite, monazite, zircon and allanite. Primary uraninite occurs in the biotite granite and in pegmatite layers. Secondary coffinite is present as tiny (<5 μm) crystals dispersed along fractures in the granite and pegmatites. Coffinite also occurs along the slickenlined fault plane, where it is associated with calcite and calcic zeolite and also replaces allanite. Coffinite lacks radiogenic Pb, hence is considerably younger than the uraninite.Dissolution of partially oxidized Ca-rich uraninite occurring in the surficial biotite granite (or secondary coffinite in fracture zones) is likely the main source for the current high levels of U in nearby area wells. The high-U well waters have a carbonate signature, consistent with pervasive calcite vein mineralization in the core. Aqueous speciation calculations suggest U transport as an uranyl (U⁶⁺) hydroxyl-carbonate complex. Later reduction resulted in secondary precipitation along fractures as a U⁴⁺ mineral (i.e., coffinite).  相似文献   

A late Pleistocene–Holocene multi‐proxy record of palaeoenvironmental change from Still Bay,southern Cape Coast,South Africa          下载免费PDF全文

Lynne J. Quick  Andrew S. Carr  Michael E. Meadows  Arnoud Boom  Mark D. Bateman  David L. Roberts  Paula J. Reimer  Brian M. Chase 《第四纪科学杂志》2015,30(8):870-885

  相似文献   

Global Climate Change — the Latest Assessment: Does Global Warming Warrant a Health Warning?     

RT Watson  AJ McMichael 《Global Change & Human Health》2001,2(1):64-75

Global climate change is a qualitatively distinct, and very significant, addition to the spectrum of environmental health hazards encountered by humankind. Historically, environmental health concerns have focused on toxicological or microbiological risks to health from local exposures. However, the scale of environmental health hazards is today increasing; indeed, the burgeoning human impact on the environment has begun to alter global biophysical systems (such as the climate system). As a consequence, a range of larger-scale environmental hazards to human population health has emerged. This includes the health risks posed by climate change, stratospheric ozone depletion, loss of biodiversity, stresses on terrestrial and ocean food-producing systems, changes in hydrological systems and the supplies of freshwater, and the global spread of persistent organic pollutants. Appreciation of this scale and type of influence on human health entails an ecological perspective — a perspective that recognises that the foundations of long-term good health in populations reside in the continued stability and functioning of the biosphere's "life-supporting" ecological and physical systems. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Observations of asteroids in the 3- to 4-μm region     

N. Eaton  S.F. Green  R.S. McCheyne  A.J. Meadows  G.J. Veeder 《Icarus》1983,55(2):245-249

Spectra of eleven asteroids (1, 2, 8, 10, 15, 16, 22, 83, 386, 433, 471) have been obtained in the 3- to 4-μm region. Of these, only 1 Ceres and 2 Pallas have previously been observed in this wave-length region. Spectra of the S- and M-type asteroids are generally featureless, but 8 Flora may be an exception. None of the three new C-type spectra show significant absorption.  相似文献   

The formation of the atmospheres of the terrestrial planets by impact     

A. Benlow  A. J. Meadows 《Astrophysics and Space Science》1977,46(2):293-300

It is generally supposed that the atmospheres of the terrestrial planets were formed by secondary degassing processes. We propose, instead, that they are of primary origin, forming as an immediate and necessary consequence of the final stages of planetary accretion. Once the planetary embryo reached a critical size, the impacting material began to vaporize. The atmosphere, so created, then decelerated other impacting material, thus limiting the rate of atmospheric growth. We show that, given reasonable assumptions concerning the chemical composition of the impacting material, an acceptable model for the early atmosphere of the Earth, and the present atmospheres of Venus and Mars results.A discussion of the noble gas data for the terrestrial atmosphere indicates that these can be readily reconciled with an impact origin.  相似文献