The Creation of a National Agricultural Land Use Dataset: Combining Pycnophylactic Interpolation with Dasymetric Mapping Techniques     

Alexis Comber  Chris Proctor  Steve Anthony 《Transactions in GIS》2008,12(6):775-791

Agricultural Census data is summarised over spatially coarse reporting units for reasons of farm confidentiality. This is problematic for research at a local level. This article describes an approach combining dasymetric and volume preserving techniques to create a national land use dataset at 1 km² resolution. The results for an English county are compared with contemporaneous aggregated habitat data. The results show that the accurate estimates of local agricultural land use (Arable and Grass) patterns can be estimated when individual 1 km squares are combined into blocks of > 9 squares, thereby providing local estimates of agricultural land use. This in turn allows more detailed modelling of land uses related to specific livestock and cropping activities. The dataset created by this work has been subject to extensive external validation through its incorporation into a number of other national models: nitrate leaching (e.g. MAGPIE, NEAP‐N), waste, and pathogen modelling related to agricultural activity.  相似文献   

Mechanisms of shrubland expansion: land use,climate or CO2?   总被引：11，自引：0，他引：11  

Steve Archer  David S. Schimel  Elisabeth A. Holland 《Climatic change》1995,29(1):91-99

Encroachment of trees and shrubs into grasslands and the thicketization of savannas has occurred worldwide over the past century. These changes in vegetation structure are potentially relevant to climatic change as they may be indicative of historical shifts in climate and as they may influence biophysical aspects of land surface-atmosphere interactions and alter carbon and nitrogen cycles. Traditional explanations offered to account for the historic displacement of grasses by woody plants in many arid and semi-arid ecosystems have centered around changes in climatic, livestock grazing and fire regimes. More recently, it has been suggested that the increase in atmospheric CO₂ since the industrial revolution has been the driving force. In this paper we evaluate the CO₂ enrichment hypotheses and argue that historic, positive correlations between woody plant expansion and atmospheric CO₂ are not cause and effect.Please direct all correspondence to the senior author.  相似文献   

A realistic model for point-sources imaged on array detectors: The model and initial results     

W. J. Merline  Steve B. Howell 《Experimental Astronomy》1995,6(1-2):163-210

We have constructed a computer model for simulation of point-sources imaged on two-dimensional detectors. An attempt has been made to ensure that the model produces data that mimic real data taken with 2-D detectors. To be realistic, such simulations must include randomly generated noise of the appropriate type from all sources (e.g. source, background, and detector). The model is generic and accepts input values for parameters such as pixel size, read noise, source magnitude, and sky brightness. Point-source profiles are then generated with noise and detector characteristics added via our model. The synthetic data are output as simple integrations (onedimensional), as radial slices (two-dimensional), and as intensity-contour plots (three-dimensional). Each noise source can be turned on or off so that they can be studied separately as well as in combination to yield a realistic view of an image. This paper presents the basic properties of the model and some examples of how it can be used to simulate the effects of changing image position, image scale, signal strength, noise characteristics, and data reduction procedures.Use of the model has allowed us to confirm and quantify three points: 1) The use of traditionalsize apertures for photometry of faint point-sources adds substantial noise to the measurement which can significantly degrade the quality of the observation; 2) The number of pixels used to estimate the background is important and must be considered when estimating errors; and 3) The CCD equation normally used by the astronomical community consistently overestimates the signal-to-noise obtainable by a measurement while a revised equation, discussed here, provides a better estimator.  相似文献   

Spectral reflectance change and luminescence of selected salts during 2–10 KeV proton bombardment: Implications for Io     

Robert M. Nelson  Douglas B. Nash 《Icarus》1979,39(2):277-285

Radiation damage and luminescence, caused by magnetospheric charged particles, have been suggested by several authors as mechanisms for explaining some of the peculiar spectral/albedo features of Io. We have pursued this possibility by measuring the uv-visual spectral reflectance and luminescent efficiency of several proposed Io surface constituents during 2 to 10-keV proton irradiation at room temperature and at low temperature (120 < T < 140°K). The spectral reflectance of NaCl and KCl during proton irradiation exhibits the well-known F-center absorption bands at 4580 and 5560 Å. Na₂SO₄ shows a generalized darkening which increases toward longer wavelengths. NaNO₃ shows a spectral reflectance change indicative of the partial alteration of NaNo₃ to NaNo₂. NaNO₂ shows no change. The luminescent efficiencies of NaCl and KCl are ～10^?4 at 300°K and increase by one-half order of magnitude at ～130°K. The efficiencies of K₂CO₃, Na₂CO₃, Na₂SO₄, and NaNO₃ are 10^?4, 10^?4, 10^?5 and 10^?6, respectively, at 300°K and they all decrease by one-half order of magnitude at ～130°K. These results indicate that magnetospheric proton irradiation of Io could cause spectral features in its observed ultraviolet and visible reflection spectrum if salts such as those studied here are present on its surface. However, because the magnitude of these spectral effects is dependent on competing factors such as surface temperature, incident particle energy flux, solar bleaching effects, and trace element abundance, we are unable at this time to make a quantitative estimate of the strength of these spectral effects on Io. The luminescent efficiencies of pure samples that we have studied in the laboratory suggest that charged-particle induced luminescence from Io's surface might be observable by a spacecraft such as Voyager when viewing Io's dark side.  相似文献   

Great earthquakes of variable magnitude at the Cascadia subduction zone   总被引：1，自引：0，他引：1  

Alan R. Nelson  Harvey M. Kelsey 《Quaternary Research》2006,65(3):354-365

Comparison of histories of great earthquakes and accompanying tsunamis at eight coastal sites suggests plate-boundary ruptures of varying length, implying great earthquakes of variable magnitude at the Cascadia subduction zone. Inference of rupture length relies on degree of overlap on radiocarbon age ranges for earthquakes and tsunamis, and relative amounts of coseismic subsidence and heights of tsunamis. Written records of a tsunami in Japan provide the most conclusive evidence for rupture of much of the plate boundary during the earthquake of 26 January 1700. Cascadia stratigraphic evidence dating from about 1600 cal yr B.P., similar to that for the 1700 earthquake, implies a similarly long rupture with substantial subsidence and a high tsunami. Correlations are consistent with other long ruptures about 1350 cal yr B.P., 2500 cal yr B.P., 3400 cal yr B.P., 3800 cal yr B.P., 4400 cal yr B.P., and 4900 cal yr B.P. A rupture about 700-1100 cal yr B.P. was limited to the northern and central parts of the subduction zone, and a northern rupture about 2900 cal yr B.P. may have been similarly limited. Times of probable short ruptures in southern Cascadia include about 1100 cal yr B.P., 1700 cal yr B.P., 3200 cal yr B.P., 4200 cal yr B.P., 4600 cal yr B.P., and 4700 cal yr B.P. Rupture patterns suggest that the plate boundary in northern Cascadia usually breaks in long ruptures during the greatest earthquakes. Ruptures in southernmost Cascadia vary in length and recurrence intervals more than ruptures in northern Cascadia.  相似文献   

Cripple Creek and other alkaline-related gold deposits in the southern Rocky Mountains, USA: influence of regional tectonics   总被引：1，自引：0，他引：1  

Karen D. Kelley  Steve Ludington 《Mineralium Deposita》2002,37(1):38-60

Alkaline-related epithermal vein, breccia, disseminated, skarn, and porphyry gold deposits form a belt in the southern Rocky Mountains along the eastern edge of the North American Cordillera. Alkaline igneous rocks and associated hydrothermal deposits formed at two times. The first was during the Laramide orogeny (about 70-40 Ma), with deposits restricted spatially to the Colorado mineral belt (CMB). Other alkaline igneous rocks and associated gold deposits formed later, during the transition from a compressional to an extensional regime (about 35-27 Ma). These younger rocks and associated deposits are more widespread, following the Rocky Mountain front southward, from Cripple Creek in Colorado through New Mexico. All of these deposits are on the eastern margin of the Cordillera, with voluminous calc-alkaline rocks to the west. The largest deposits in the belt include Cripple Creek and those in the CMB. The most important factor in the formation of all of the gold deposits was the near-surface emplacement of relatively oxidized volatile-rich alkaline magmas. Strontium and lead isotope compositions suggest that the source of the magmas was subduction-modified subcontinental lithosphere. However, Cripple Creek alkaline rocks and older Laramide alkaline rocks in the CMB that were emplaced through hydrously altered LREE-enriched rocks of the Colorado (Yavapai) province have ²⁰⁸Pb/²⁰⁴Pb ratios that suggest these magmas assimilated and mixed with significant amounts of lower crust. The anomalously hot, thick, and light crust beneath Colorado may have been a catalyst for large-scale transfer of volatiles and crustal melting. Increased dissolved H₂O (and CO₂, F, Cl) of these magmas may have resulted in more productive gold deposits due to more efficient magmatic-hydrothermal systems. High volatile contents may also have promoted Te and V enrichment, explaining the presence of fluorite, roscoelite (vanadium-rich mica) and tellurides in the CMB deposits and Cripple Creek as opposed to deposits to the south. Deep-seated structures of regional extent that formed during the Proterozoic allowed the magmas to rise to shallow crustal levels. Proterozoic sites of intrusions at 1.65, 1.4, and 1.1 Ga were also important precursors to alkaline-related gold deposits. Many of the larger gold deposits are located at sites of Proterozoic intrusions, and are localized at the intersection of northeast-trending ductile shear zones formed during Mesoproterozoic deformation, and an important north-trending fault formed during 1.1 Ga rifting.  相似文献   

Ludlow (Silurian) stromatoporoid biostromes from Gotland, Sweden: facies, depositional models and modern analogues   总被引：1，自引：0，他引：1  

Olof Sandström  Steve Kershaw† 《Sedimentology》2002,49(3):379-395

Stacked stromatoporoid‐dominated biostromes of the Ludlow‐age Hemse Group (Silurian) in eastern Gotland, Sweden, are 0·5–5 m thick and a few tens of metres to >1 km in lateral extent. They form one of the world's richest Palaeozoic stromatoporoid deposits. This study compiles published and new data to provide an overall facies model for these biostromes, which is assessed in relation to possible modern analogues. Some biostromes have predominantly in‐place fossils and are regarded as reefs, but lack rigid frameworks because of abundant low‐profile non‐framebuilding stromatoporoids; other biostromes consist of stromatoporoid‐rich rudstones interpreted here as storm deposits. Variation between these two `end‐members' occurs both between interlayered biostromes and also vertically and laterally within individual biostromes. Such variation produces problems of applying established reef classification terms and demonstrates the need for the development of terminology that recognizes taphonomic destruction of reef fabrics. An approach to such terminology is found in all four categories of a recent biostrome classification scheme that are easily recognized in the Hemse biostrome facies: autobiostromes (>60% in place); autoparabiostromes (a mixture of in‐place and overturned reef‐building organisms, 20–60% in place); parabiostromes (builders are overturned and damaged, <20% in place); and allobiostromes (transported and detrital reef material, nothing in place). These categories provide a broad taphofacies scheme for the Hemse biostromes, which are mostly autoparabiostrome to allobiostrome. The biostromes developed on crinoidal grainstone sheets and expanded laterally across relatively flat substrates in a marine setting of low siliciclastic input. Planar erosion surfaces commonly terminate biostrome tops. Three broadly similar modern analogues are identified, each of which has elements in common with the Hemse biostromes, but none of which is an exact equivalent: (a) laterally expanded and coalesced back‐barrier patch reefs behind the Belize barrier, an area influenced by limited accommodation space; (b) a hurricane‐influenced shelf, interpreted for Grand Cayman, where reef cores consist of rubble and lack substantial framework; the wide distribution of rounded pebbles and cobbles of stromatoporoids in the Hemse biostromes most probably resulted from hurricanes; (c) coral carpets in 5–15 m water depth of the northern Red Sea, where lateral expansion of low‐diversity frames dominated by Porites coral has produced low‐profile biostromes up to 8 m thick and several km long. Such carpets accumulated large amounts of carbonate, with little export, as in the Hemse biostromes, although the latter did not build frameworks because of the nature of growth of the stromatoporoids. The notable lack of algae in the Hemse biostrome facies is also a feature of Red Sea coral carpets; nevertheless, coral carpets are ecologically different. Hemse biostromes lack evidence of a barrier reef system, although this may not be exposed; the facies assemblage is consistent with either a storm/hurricane‐influenced mid‐ to upper ramp or back‐barrier system.  相似文献   

Kinetics of Mn(II) oxidation by Leptothrix discophora SS1     

Jinghao ZhangLeonard W Lion  Yarrow M Nelson  Michael L ShulerWilliam C Ghiorse 《Geochimica et cosmochimica acta》2002,66(5):773-781

The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O₂, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 μM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O₂ and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 μM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 μM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈μg/L) concentrations of Mn oxidizing bacteria.  相似文献   

Processes in microbial transport in the natural subsurface     

Timothy R. Ginn  Brian D. Wood  Kirk E. Nelson  Timothy D. Scheibe  Ellyn M. Murphy  T.Prabhakar Clement   《Advances in water resources》2002,25(8-12)

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Smart optics in ast     

Steve Welch  Alan Greenaway  Peter Doel  Gordon Love 《Astronomy& Geophysics》2003,44(1):1.26-1.29

Smart optics means much more than adaptive optics on telescopes: these new technologies are changing the way space instruments are built and operated and are bringing new technologies into everyday life in the form of cheaper, lighter and more robust optical systems. Steve Welch, Peter Doel, Alan Greenaway and Gordon Love summarize the work of the Smart Optics Faraday Partnership in the UK.  相似文献