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Surface Disturbance (surface + disturbance)
Selected AbstractsWind erosion characteristics of Sahelian surface typesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2010Thomas Maurer Abstract The assessment of wind erosion magnitudes for a given area requires knowledge of wind erosion susceptibilities of the dominant local surface types. Relative wind erosion potentials of surfaces can hardly be compared under field conditions, as each erosion event is unique in terms of duration, intensity and extent. The objective of this study was to determine and compare relative wind erosion potentials of the most representative surface types over a transect comprising most parts of southwestern Niger. For this purpose, mobile wind tunnel experiments were run on 26 dominant surface types. The effects of surface disturbance were additionally determined for 13 of these surfaces. The results, namely measurements of wind fields and mass fluxes, can be classified according to specific surface characteristics. Three basic surface groups with similar emission behaviour and aerodynamic characteristics were identified: (1) sand surfaces, (2) rough stone surfaces and (3) flat crusted surfaces. Sand surfaces feature a turbulent zone close to the surface due to the development of a saltation layer. Their surface roughness is medium to high, as a consequence of the loss of kinetic energy of the wind field to saltating particles. Sand surfaces show the highest mass fluxes due to the abundance of loose particles, but also fairly high PM10 fluxes, as potential dust particles are not contained in stable crusts or aggregates. Rough stone surfaces, due to their fragmented and irregular surface, feature the highest surface roughness and the most intense turbulence. They are among the weakest emitters but, due to their relatively high share of potential dust particles, PM10 emissions are still average. Flat crusted surfaces, in contrast, show low turbulence and the lowest surface roughness. This group of surfaces shows rather heterogeneous mass fluxes, which range from moderate to almost zero, although the share of PM10 particles is always relatively high. Topsoil disturbance always results in higher total and PM10 emissions on sand surfaces and also on flat crusted surfaces. Stone surfaces regularly exhibit a decrease in emission after disturbance, which can possibly be attributed to a reorganization which protects finer particles from entrainment. The results are comparable with field studies of natural erosion events and similar wind tunnel field campaigns. The broad range of tested surfaces and the standardized methodology are a precondition for the future regionalization of the experimental point data. Copyright © 2010 John Wiley & Sons, Ltd. [source] The factors influencing the abrasion efficiency of saltating grains on a clay-crusted playaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2001Christopher A. Houser Abstract The entrainment and subsequent transport of PM10 (particulate matter <10,µm) has become an important and challenging focus of research for both scientific and practical applications. Arid and semi-arid environments are important sources for the atmospheric loading of PM10, although the emission of this material is often limited by surface crusts. It has been suggested that the primary mechanisms through which PM10 is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities. To examine the importance of saltation abrasion in the emission of PM10, a series of field wind tunnel tests were conducted on a clay-crusted surface near Desert Wells, Arizona. In a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate, although there can be considerable variation in this relationship. This paper more closely examines the source of the variability in the abrasion efficiency, the amount of PM10 emitted by a given quantity of saltating grains. The abrasion efficiency was found to vary with the susceptibility of the surface to abrasion, the ability of the sand to abrade that surface and the availability of material with a caliper size <10,µm within the crust. Specifically, the results of the study show that the abrasion efficiency is related to the crust strength, the amount of surface disturbance and the velocity of the saltating grains. It is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models, and can make theoretical models too complex and impractical to be of use. Copyright© 2001 John Wiley & Sons, Ltd. [source] Analysis of suspended sediment yields after low impact forest harvestingHYDROLOGICAL PROCESSES, Issue 26 2007Norifumi Hotta Abstract Disturbances to forest catchments have profound effects on the environment of headwater streams and have an impact on suspended sediment (SS) management. Forest harvesting is a dominant factor in increasing SS yields. Road construction, skidder activity and ploughing associated with harvesting cause serious soil disturbance that results in SS increases. However, few studies have shown whether harvesting itself increases SS yields. This study examined how harvesting influenced SS yields in a steep forested area. During harvesting, soil surface disturbance was prevented as much as possible by using skyline logging treatments and piling branches and leaves at selected locations in the watershed. Using these methods, the representative SS rating curve did not change significantly after harvesting. The results also show that the characteristics of SS transport were related to the SS source area, and reveal that the riparian zone/stream bank was a dominant SS source area at the study site. Annual SS yields did not increase despite increasing annual water yields after harvesting. The limited water capacity of the soil at the study site likely led to only slight differences in pre- and post-harvest water discharge from heavy rainfall events. Most SS was transported during heavy rainfall events, and increases in SS yields were not detected after harvesting. We concluded that it is possible to prevent post-harvest SS increases by performing careful, low-impact harvesting procedures. Copyright © 2007 John Wiley & Sons, Ltd. [source] Acquisition of desiccation tolerance in developing wheat embryos correlates with appearance of a fluid phase in membranesPLANT CELL & ENVIRONMENT, Issue 11 2003E. A. GOLOVINA ABSTRACT Membrane behaviour in developing wheat (Triticum aestivum cv Priokskaya) embryos was studied in relation to the acquisition of desiccation tolerance, using spin probe techniques. Fresh embryos were able to develop into seedlings at day 15 after anthesis, but it took 18 d before fast-dried, isolated embryos could germinate. On the basis of membrane integrity measurements it was estimated that between 14 and 18 d after anthesis the proportion of embryonic cells surviving fast drying increased and the critical moisture content, to which embryonic cells could be dehydrated, decreased. Apparently, embryonic cells do not acquire the same level of desiccation tolerance simultaneously. Only when all cells had become desiccation tolerant was germination of air-dried embryos possible. Using 5-doxylstearic acid as the probe molecule, an approximately similar lipid,water interface ordering of membranes was observed in all hydrated embryos, irrespective of age. Dehydration had a dual effect on the lipid interface: further ordering of the major part of the interface and the appearance of additional, disturbed regions. The proportion of these regions correlated with the proportion of desiccation-tolerant cells. We propose that the membrane surface disturbance be caused by endogenous amphiphiles that partition from the cytoplasm into membranes during drying. The absence of such disturbed regions in dried, desiccation-sensitive embryos might reflect a lack of sufficient amphiphiles. The relevance of membrane surface disturbance for desiccation tolerance is discussed. [source] Patterns of permafrost formation and degradation in relation to climate and ecosystemsPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2007Y. L. Shur Abstract We develop a permafrost classification system to describe the complex interaction of climatic and ecological processes in permafrost formation and degradation that differentiates five patterns of formation: ,climate-driven'; ,climate-driven, ecosystem-modified'; ,climate-driven, ecosystem-protected'; ,ecosystem-driven'; and ,ecosystem-protected' permafrost. Climate-driven permafrost develops in the continuous permafrost zone, where permafrost forms immediately after the surface is exposed to the atmosphere and even under shallow water. Climate-driven, ecosystem-modified permafrost occurs in the continuous permafrost zone when vegetation succession and organic-matter accumulation lead to development of an ice-rich layer at the top of the permafrost. During warming climates, permafrost that has formed as climate-driven can occur in the discontinuous permafrost zone, where it can persist for a long time as ecosystem-protected. Climate-driven, ecosystem protected permafrost, and its associated ground ice, cannot re-establish in the discontinuous zone once degraded, although the near surface can recover as ecosystem-driven permafrost. Ecosystem-driven permafrost forms in the discontinuous permafrost zone in poorly drained, low-lying and north-facing landscape conditions, and under strong ecosystem influence. Finally, ecosystem-protected permafrost persists as sporadic patches under warmer climates, but cannot be re-established after disturbance. These distinctions are important because the various types react differently to climate change and surface disturbances. For example, climate-driven, ecosystem-modified permafrost can experience thermokarst even under cold conditions because of its ice-rich layer formed during ecosystem development, and ecosystem-driven permafrost is unlikely to recover after disturbance, such as fire, if there is sufficient climate warming. Copyright © 2007 John Wiley & Sons, Ltd. [source] Using LiDAR to detect cultural resources in a forested environment: an example from Isle Royale National Park, Michigan, USAARCHAEOLOGICAL PROSPECTION, Issue 3 2008Julie M. Gallagher Abstract This article discusses the use of light detecting and ranging (LiDAR) technology as an effective remote sensing tool for the location of cultural resources. Its use, particularly in Europe, has proven successful in the identification of archaeological sites obscured by dense vegetation or surface disturbances. This study used LiDAR-derived imagery to detect pre- and post-European contact sites, and their related features, in densely forested environments on Isle Royale, Michigan, USA. LiDAR bare-Earth models were used to ,see through' the vegetation in an effort to: (i) identify cultural features prior to the implementation of a pedestrian reconnaissance survey; (ii) aid in the development of a more informed survey strategy; and (iii) produce an overall safer, more efficient and more cost-effective research design. Three study areas were selected for investigation. Within these three study areas, a total of seven investigation locales containing 32 separate features were identified using LiDAR-derived imagery. Eighteen of the 32 features were found to have been previously recorded. Of the remaining 14 features, seven were confirmed in the field as being cultural features and were recorded for the first time as a result of this investigation. The remaining seven could not be located on the ground or were found to be non-cultural. The results of this study support the use of LiDAR as a viable method for the detection of cultural resources, particularly in remote and heavily forested environments. Despite its positive contributions, there is a limited range of archaeological (surface) features that can be detected using this technology. As applied to archaeology, LiDAR is not an exclusive investigatory technique. It must be part of a comprehensive research strategy that integrates field, laboratory and archival investigation in order to achieve the best possible interpretation of the archaeological record. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||