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1.
The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo‐Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
2.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. 相似文献
3.
We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben. 相似文献
4.
Bo PENG Shurong XIE Meilian XIAO Fucheng WU Zhi SONG 《中国地球化学学报》2006,25(B08):23-24
The Taojiang Mn ore deposit was exploited in the early 1960s, and waste rocks were developed since then. Because the Mn ores were hosted within the metal-enriched black shales (Peng et al., 2004), the continuous mining has led to the exposure of an immense quality of black shales, which might cause serious impacts on environments. The present study deals with this environmental issue with samples from the waste rocks, and from the surrounding soils and surface water. The mineralogy of the waste rock was studied using EMPA, then a large number of elements in all waste rock, soil, and water samples were analyzed at a wide range of concentrations with high accuracy using an Elan6000 ICP-MS machine at Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. The waste rock is composed mostly of black shales, with minor Mn carbonates. Both black shales and Mn carbonates of the waste rock contain many sulfide minerals, mainly pyrite, with minor galena, sphalerite, chalcopyrite, and others. The waste rocks are enriched in many metals including Sc, V, Cr, Co, Ni, Fe, Mn, Cu, Zn, Pb, Th, U, Mo, Sb, Sn, Tl, and others, and the metals are mostly hosted within the sulfides. Weathering of waste rocks might cause emission of the following metals: V, Cd, Ni, Th, U, Mo, Sb, Tl, Sc, Cr, Cu, Zn, Sn, and minor Co, and Pb. The surrounding soils are highly enriched in Cr, Co, Cu, Zn, Mn, Mo, Cd, Tl, and Pb, with the enrichment factors of 2.67.3.8, 7.26, 7.27, 8.2, 5.7, 13, and 5.4, respectively. The element ratios (Rb/Cs, Fe/Mn, Nb/Zr, Hf/Zr, and Ba/Sr) and REE distribution patterns of the soils are similar to those of the waste rocks and bedrocks. 相似文献
5.
Natural environmental changes and human impact reflected in sediments of a high alpine lake in Switzerland 总被引:1,自引:0,他引:1
From the high alpine Sägistalsee (1935 m a.s.l.), 13.50 m of continuously laminated sediments comprising the last 9050 years, were analyzed. Even though Sägistalsee is a high elevation site, human-induced environmental changes start as early as 4300 cal. BP and leave a clearly detectable signal in the mineralogy of the sediments, which is much stronger than the signal from natural environmental changes that occurred before this time. Variations in the physical and mineralogical sediment properties of this clastic sequence reflect erosional changes in the catchment, where almost pure limestone contrasts with carbonaceous, quartz-bearing marl, and shist. The calcite/quartz (Cc/Qz) ratio was found to be most indicative of these changes, which occurred around AD 1850 and at 650, 2000, 3700, and 6400 cal. BP. The first four are interpreted as erosion events, which are related to human-induced changes in the vegetation cover and land use. We associate them to the recent development of tourism and grazing, the medieval intensification of pasturing, Roman forest clearance, and Bronze Age forest clearance, respectively. The Cc/Qz-ratio increases significantly within less than 100 years during these events, reflecting the erosion of unweathered or poorly weathered soils. The time intervals in between are characterized by a gradually decreasing Cc/Qz-ratio and reflect the stabilization or formation of new soils. Only the change at 6400 cal. BP, which represents the initial gradual stabilization of the catchment, is related to the immigration of Picea abies. 相似文献
6.
Geologic marks related to extraterrestrial impact events, such as impact split gravels, impact brecciate layers, impact dikes, microirghizites, microtektites, especially meteoritic residues, were discovered on the boundary between Sinian/Cambrian at Tianmenshan of Western Hunan, which may possibly demonstrate that an extraterrestrial impact event has ever occurred there on the S/C boundary. 相似文献
7.
Linda T Elkins-Tanton 《Earth and Planetary Science Letters》2004,222(1):17-27
Large volumes of mare basalts are present on the surface of the moon, located preferentially in large impact basins. Mechanisms relating impact basins and mare basalt eruptions have previously been suggested: lunar impacts removed low-density material that may have inhibited eruption, and created cracks for fluid flow [Icarus 139 (1999) 246], and lunar basins have long been described as catchments for magma (e.g., [Rev. Geophys. Space Phys. 18 (1980) 107] and references therein). We present a new model for melt creation under near side lunar basins that is triggered by the impacts themselves. Magma can be produced in two stages. First, crater excavation depressurizes underlying material such that it may melt in-situ. Second, the cratered lithosphere rises isostatically, warping isotherms at the lithosphere-asthenosphere boundary which may initiate convection, in which adiabatic melting can occur. The first stage produces by far the largest volume of melt, but convective melting can continue for up to 350 Ma. We propose that giant impacts account for a large portion of the volume and longevity of mare basalt volcanism, as well as for several compositional groups, including high alumina, high titanium, KREEP-rich, and picritic magmas. 相似文献
8.
Hossein Ghadiri 《地球表面变化过程与地形》2004,29(1):77-89
The process of crater formation by the impact of water drops on soil, sand and various other target material was studied. Craters of various shapes and sizes were observed on different target materials or conditions, ranging from circumferential depression to completely hemispherical shape. Crater shape was dependent upon target material, its ?ow stress or shear strength and the presence and thickness of water on the surface. Between 5 and 22 per cent of impact energy was spent on cratering, but the relationship between crater volume and kinetic energy of a raindrop was curvilinear, indicating a lower ef?ciency of impact energy in removing target material as the energy increases. Impact impulse, on the other hand, showed a more linear relationship with crater volume, and the ratio of impulse over crater volume (I/V) remained constant for the entire range of drop sizes, impact velocities, and surface conditions used in this study. Surface shear strength, represented by the penetration depth of fall‐cone penetrometer, appeared to be a key factor involved in this process. An equation was developed which related crater volume to cone penetration depth and impact impulse. Crater volume, which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount, can thus be predicted using this equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
Introduction Through many year's practices by vast numbers of scientific and technological workers andefforts from all aspects, the dynamic testing method of high-low strain has formally entered intothe technical code of foundation pile test of construction at last (The Industry Standards of thePeople's Republic of China, 2003). The striking mode of the dynamic testing method of high strainis stipulated as hammer in the code, the striking of rocket can also be used. The latter is widely… 相似文献
10.
Rural Hong Kong contains culturally protected enclaves of remnant woodlands that provide sanctuary for vegetation, wildlife and soil. This study focuses on the influence of natural and cultural factors on soil properties in woodlands with different human activities. At each of the nine selected sites, two pits were dug to collect soil samples for analysis of 24 physical and chemical properties. Analyses of variance between soil attributes and site factors suggest the prominence of woodland size, and important contribution of topography, aspect and parent material. Soil indicators of human impacts and the tenacity of woodland soil towards anthropogenic disturbance were demonstrated. 相似文献