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301.
Volker Prasuhn 《地球表面变化过程与地形》2020,45(7):1539-1554
Long-term field assessments of soil erosion on the landscape scale are very scarce. Such monitoring programmes create sound data regarding severity, extent, frequency and types of soil erosion and the vulnerability of particular crops. In a 20-year monitoring programme between 1997 and 2017, accurate erosion damage mapping was carried out on 203 fields on arable land in the Canton of Berne (Switzerland). During 115 field inspections, 4060 field years and 2165 mapped erosion systems were recorded. Because several soil conservation programmes were implemented during this period, two 10-year time periods (1st October 1997 to 30th September 2007 [P1] and 1st October 2007 to 30th September 2017 [P2]) were established and compared. The soil erosion rate was already low in P1 (mean: 0.74 t ha−1 year−1), but decreased significantly in P2 (mean: 0.20 t ha−1 year−1). During P1 and P2, respectively, 12 and 42% of the fields were without any visible erosion. Within 10 years, erosion occurred on each field on average 3.2 times in P1 and only 1.3 times in P2. Soil losses are spatially concentrated and linked to topographically defined pathways (thalwegs, slope depressions) or human-made flow pathways (wheel tracks, tramlines, headlands). Financial incentives, rising awareness among farmers, innovative contractor farmers and good extension service of cantonal agencies helped conserve 85% of the arable land in the study area with conservation tillage methods by 2015. As a result, soil erosion was significantly reduced. The field-based measurements show that a significant decrease in soil erosion is possible by changes in soil tillage practices and that erosion control is feasible almost everywhere under real-life conditions on farmers’ fields. In this respect, the Frienisberg region is a case example of successful erosion control. © 2020 John Wiley & Sons, Ltd. 相似文献
302.
Volker Springel Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1999,307(1):162-178
We study the formation of tidal tails in pairs of merging disc galaxies with structural properties motivated by current theories of cold dark matter (CDM) cosmologies. In a recent study, Dubinski, Mihos & Hernquist showed that the formation of prominent tidal tails can be strongly suppressed by massive and extended dark haloes. For the large halo-to-disc mass ratio expected in CDM cosmologies their sequence of models failed to produce strong tails like those observed in many well-known pairs of interacting galaxies. In order to test whether this effect can constrain the viability of CDM cosmologies, we construct N ‐body models of disc galaxies with structural properties derived in analogy to the recent analytical work of Mo, Mao & White. With a series of self-consistent collisionless simulations of galaxy–galaxy mergers we demonstrate that even the discs of very massive dark haloes have no problems developing long tidal tails, provided the halo spin parameter is large enough. For our class of models, the halo-to-disc mass ratio is not a good indicator of the ability to produce tails. Instead, the relative size of disc and halo or, alternatively, the ratio of circular velocity to local escape speed at the half mass radius of the disc is a more useful criterion. This result holds in all CDM models. While tidal tails can provide useful information on the structure of galaxies, it thus appears unlikely that they are able to constrain the values of the cosmological parameters within these models. 相似文献
303.
Oliver Ritter Volker Haak Volker Rath Eckardt Stein & Manfred Stiller 《Geophysical Journal International》1999,139(1):161-170
New magnetotelluric data from the Münchberg Gneiss complex in Southern Germany reveal a zone of extremely high electrical conductivity. 1-D modelling of the data is justified in the period range 0.01 to 10 s. At least three layers are required to explain the steepness of the apparent resistivity curves, and the best-fitting models comprise four layers with successively higher conductivities. The layers of highest conductivity at depths between 2.2 and 3.6 km correlate with pronounced bands of high seismic reflectivity (profile DEKORP 85-4N). The Münchberg complex is today widely recognized as a tectonic klippe, consisting of rocks whose metamorphic and stratigraphic order is inverted rather than overturned. The material was transported into its present position by predominantly horizontal tectonic forces along shear zones. We interpret the high conductivity and high reflectivity as remnants of this transport process. 相似文献
304.
Ocean Dynamics - Die Konvention zum Schutz der marinen lebenden Ressourcen der Antarktis (CCAMLR) wurde 1982 ins Leben gerufen. Im Hinblick auf die sich in der Antarktis rapide entwickelnde... 相似文献
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307.
TENG Jiwen LI Songying JIA Mingkui LIAN Jie LIU Honglei LIU Guodong WANG Wei Volker SCH?PE FENG Lei YAO Xiaoshuai WANG Kang YAN Yafen ZHANG Wanpeng 《《地质学报》英文版》2020,94(1):10-26
In order to effectively detect potential geology anomalous bodies in coal bearing formation, such as coal seam thickness variation, small faults, goafs and collapse columns, and provide scientific guidance for safe and efficient mining, the SUMMIT-II EX explosion-proof seismic slot wave instrument, produced by German DMT Company, was used to detect the underground channel wave with the help of transmission method, reflection method and transflective method. Region area detection experiment in mining face had been carried out thanks to the advantage of channel wave, such as its great dispersion, abundant geology information, strong anti-interference ability and long-distance detecting. The experimental results showed that: (1) Coal seam thickness variation in extremely unstable coal seam has been quantitatively interpreted with an accuracy of more than 80% generally; (2) The faults, goafs and collapse columns could be detected and predicted accurately; (3) Experimental detection of gas enrichment areas, stress concentration regions and water inrush risk zone has been collated; (4) A research system of disaster-causing geology anomalous body detection by in-seam seismic survey has been built, valuable and innovative achievements have been got. Series of innovation obtained for the first time in this study indicated that it was more effective to detect disaster-causing potential geology anomalies by in-seam seismic survey than by ground seismic survey. It had significant scientific value and application prospect under complex coal seam conditions. 相似文献
308.
Abel Amirbekyan Volker Michel Frederik J. Simons † 《Geophysical Journal International》2008,174(2):617-628
We present a mathematical framework and a new methodology for the parametrization of surface wave phase-speed models, based on traveltime data. Our method is neither purely local, like block-based approaches, nor is it purely global, like those based on spherical harmonic basis functions. Rather, it combines the well-known theory and practical utility of the spherical harmonics with the spatial localization properties of spline basis functions. We derive the theoretical foundations for the application of harmonic spherical splines to surface wave tomography and summarize the results of numerous numerical tests illustrating the performance of a practical inversion scheme based upon them. Our presentation is based on the notion of reproducing-kernel Hilbert spaces, which lends itself to the parametrization of fully 3-D tomographic earth models that include body waves as well. 相似文献
309.
Ascelina K. M. Hasberg Satria Bijaksana Peter Held Janna Just Martin Melles Marina A. Morlock Stephan Opitz James M. Russell Hendrik Vogel Volker Wennrich 《Sedimentology》2019,66(2):675-698
Lake Towuti on Sulawesi Island, Indonesia, is located within the heart of the Indo‐Pacific Warm Pool. This tropical lake is surrounded by ultramafic (ophiolitic) rocks and lateritic soils that create a unique ferruginous depositional setting. In order to understand modern sediment deposition in Lake Towuti, a set of 84 lake surface sediment samples was collected from across the entirety of the lake and samples were analyzed for their physical, chemical, mineralogical and biological constituents. End‐member analyses were carried out to elucidate modern sediment origin, transport and depositional processes. This study found that allochthonous sediment, characterized by the concentrations of the elements Mg, Fe, Si and Al, as well as the clay and serpentine minerals, is dominated by fluvial supply from five distinct source areas. Granulometric data and the occurrence of organic matter of a terrestrial origin suggest that, in the southern and north‐eastern parts of the lake the near‐shore sediments may additionally be influenced by mass wasting. This is due at least partly to the particularly steep slopes in these areas. Furthermore, sediment composition suggests that sediment transport into deeper parts of the lake, particularly in the northern basin, is partly controlled by gravitational and density‐driven processes such as turbidity currents. Directional sediment transport by persistent lake currents, in contrast, appears to be less important. Organic matter deposition in the ultra‐oligotrophic lake, albeit limited, is dominated by autochthonous production, but with some contribution of fluvial and gravitational supply. Biogenic silica deposition, primarily from diatom frustules and sponge spicules, is very limited and is concentrated in only a few areas close to the shoreline that are characterized by shallow waters, but away from the areas of high suspension loads at the mouths of the major inlets. The results of this study build upon current and published work on short piston cores from Lake Towuti. Conversely, the results will support the interpretation of the depositional history and past climatic and environmental conditions derived from the composition of much longer records, which were obtained by the Towuti Drilling Project in May 2015 and are currently under investigation. 相似文献
310.
Digital elevation models derived from airborne laser scanning point clouds: appropriate spatial resolutions for multi‐temporal characterization and quantification of geomorphological processes 下载免费PDF全文
Digital terrain models (DTMs) are a standard data source for a variety of applications. DTM differencing is also widely used for detection and quantification of topographic changes. While several investigations have been made on the accuracy of DTMs, calculated from different kinds of input data, little has been published on the error of DTM differencing, specifically for the quantification of geomorphological processes. In this study, an extensive, multi‐temporal set of airborne laser scanning (ALS) data is used to investigate the accuracy of topographic change calculations in a high alpine environment, caused by different geomorphic processes. Differences from DTMs with cell sizes ranging from 0.25 m to 10 m were calculated and compared to very accurate point‐to‐point calculations for a variety of processes and in nearby stable areas which show no significant surface changes. The representativeness of the DTM differences is then compared to the terrain slope and surface roughness of the investigated areas to show the influence of these parameters on the errors in the differences. Those errors are then taken into account for analyses of the applicability of different cell sizes for the investigation of geomorphic processes with different magnitudes and over different time periods. The analyses show that the error of DTM differences increases with lower point densities and higher roughness and slope values. The higher the error, the greater the differences between two elevation datasets have to be in order to quantify certain morphodynamic processes. Lower point densities and higher roughness and slope values require greater process rates or longer time intervals in order to obtain valid results. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献