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141.
Bimodal grain-size distribution of Chinese loess, and its palaeoclimatic implications 总被引:14,自引:1,他引:14
Sun Donghuai Jan Bloemendal David K. Rea An Zhisheng Jef Vandenberghe Lu Huayu Su Ruixia Liu Tungsheng 《CATENA》2004,55(3):325-340
Grain-size analysis indicates that Chinese loess generally shows a bimodal distribution with a coarse and a fine component. The coarse component, comprising the main part of the loess, has pronounced kurtosis and is well sorted, which is interpreted to be the product of dust storms generated by low-altitude northwesterly winds. Its grain-size reflects the strength of the low-altitude circulation in the dust seasons of the year, and its percentage provides an indicator of the source area aridity and the frequency of dust storms. Conversely, the fine component has a wide grain-size range and is poorly sorted. Sedimentary illustrations based on the grain-size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high-altitude westerly airstreams. Its grain-size provides an estimate of the westerly air stream intensity. The coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain-size data, and this procedure constitutes an approach for reconstructing the palaeowind system of Northern China. 相似文献
142.
Anne Schmitt Jan Rodzik Wojciech Zgobicki Christian Russok Markus Dotterweich Hans-Rudolf Bork 《CATENA》2006,68(2-3):124
Key catchments of the Roztocze loess area in south-east Poland have a great potential of revealing the history of long-term soil erosion and changes in land use. The knowledge of how and when soil erosion took place in the past helps one understand the impact of land use changes on the landscapes [Bork, H.-R., 1989. Soil erosion during the past Millennium in Central Europe and its significance within the geomorphodynamics of the Holocene. Catena 15, 121–131]. The Jedliczny Dol gully system near the town Zwierzyniec in south-east Poland was investigated by using detailed field stratigraphy and radiocarbon dating of charcoal and wood.In connection with new settlements which were established between the 14th and 16th centuries, arable land was cultivated and forests were used much more intensively. As a consequence, the loess soils were strongly eroded during heavy rainfalls. Up to 4 m of colluvial sediments were deposited in the gully system during the 15th and/or 16th centuries. The thickness of the colluvial sediments indicate severe erosion which might be related to excessive timber exploitation for the local glass and iron production. With the foundation of the so-called Ordinariat Zamoyski at the end of the 16th century, some parts of the area were presumably reforested. High pressure on the land at the beginning of the 19th century enabled a second main phase of gulling before 1900.Since 1890 at the latest, almost the whole catchment is used as a forest, however, concentrated runoff on compacted forest roads can still be high after heavy rainfalls.In loess areas soil erosion caused by intensive land use, triggered by heavy rainfalls, can change the landscape drastically. These changes will continue to influence how catchments react, even if land use gets less intensive again. This knowledge should be considered regarding future, sustainable land use and recent changes in land use in the south-eastern Polish loess regions. 相似文献
143.
Klejdus B Mikelová R Petrlová J Potesil D Adam V Stiborová M Hodek P Vacek J Kizek R Kubán V 《Journal of agricultural and food chemistry》2005,53(15):5848-5852
An ultrafast HPLC/UV-vis DAD method working at 254 nm was applied for the determination of isoflavone aglycons and glycosides (genistin, genistein, daidzein, daidzin, glycitin, glycitein, ononin, formononetin, sissotrin, and biochanin A) in roots, stems, leaves, and soy pods of soy plants and in soybeans of five varieties (Korada, Quito, Rita, OAC Erin, and OAC Vison). An Atlantis dC18 ultrafast RP chromatographic column (20 mm x 2.1 mm, 3 microm particle size) was applied for separation of the isoflavone aglycons and glycosides. A flow rate of the mobile phase (0.1% (v/v) acetic acid, pH 3.75-solvent A and methanol-solvent B) was 0.35 mL min(-1), and the column temperature was 36 degrees C. A linear gradient profile from 13 up to 22% B (v/v) from zero to 2.5 min, up to 30% B to 3.21 min, up to 35% B to 4 min, up to 40% B to 4.5 min, up to 50% B to 5.14 min, and followed by negative gradient up to 13% B to 7.71 min was used. The absolute limits of detection per sample injection (5 microL) were the highest for biochanin A (166.2 fmol) and the lowest for genistin (17.0 fmol), respectively. An accelerated solvent extraction (ASE) in combination with sonication was applied for isolation of biologically active compounds. A solid-phase extraction procedure was used to purify the extracts in the case of analysis of soy plants parts. The recoveries of 96-106% were obtained for the different concentrations of the isoflavone aglycons and glycosides and the different matrixes (overall RSDs 2-9%). The highest isoflavone concentrations were found in roots (12.5 microg g(-1) dry weight), while the amounts were about 3-1100 microg g(-1) fresh weight in different varieties of soybeans. 相似文献
144.
145.
Management policies to save threatened species are not always successful, often due to the lack of a scientific basis and evaluation of the species response. We describe the ecological studies and the conservation actions taken between 1985 and 1992 on Cousin Island (29 ha, Seychelles) to safeguard the future of the highly threatened Seychelles warbler (Acrocephalus sechellensis), which until 1988 only occurred on this island. A detailed field study was designed to (1) identify the key processes influencing warbler demography, (2) identify appropriate management techniques to increase the warbler population, and (3), assess the influence of the resulting habitat management. Since 1980 the island has been saturated with c. 115 territories and c. 320 birds. The warbler is purely insectivorous. Morinda (Morinda citrifolia), the most insect rich tree, is preferred for foraging. The higher the insect abundance (and Morinda cover) in territories the higher the reproductive success and survival of warblers. Insect numbers were highest in the central part of Cousin and decreased towards the coast. Coastal territories protected by a salt tolerant hedge of Scaevola (Scaevola taccada) had more insects and higher reproductive success than unprotected territories. Between 1990 and 1992 Morinda trees were planted on the island and Scaevola along the coast. Although these habitat restoration measures have not resulted in higher numbers of adult warblers and territories due to habitat saturation, they have been successful in terms of improving the quality of existing breeding territories and with that the reproductive success of breeding birds (including the number of territories producing recruits), and the exchange of individuals (genetic material) between territories. We provide evidence that the high reproductive potential of this species is likely to improve the resilience of the species to catastrophic events. 相似文献
146.
147.
Soil acidification over the last three decades in three forest areas situated in northern Belgium (Region of Flanders), is assessed by comparing recent data of soil analysis with historical data. It is investigated whether acidification values of sites evenly spread over the region, averaged per soil group, can be used to assess acidification in specific forest areas. Results suggest that data obtained by this kind of geographical extrapolation do not differ significantly from measured data. In sandy soils however, a stop of acidification as measured by the pH(KCl), is observed at pH(KCl) values lower than 3.3. 相似文献
148.
149.
Young JF Rosenvold K Stagsted J Steffensen CL Nielsen JH Andersen HJ 《Journal of agricultural and food chemistry》2003,51(23):6877-6881
Polyunsaturated fatty acids (PUFAs) and exercise-induced stress are known to increase the oxidative susceptibility of lipids in muscle tissue. In contrast, antioxidative enzymes, e.g., catalase, superoxide dismutase, and glutathione peroxidase, are known to help sustain the delicate oxidative balance in biological tissue upon the application of stressors. The present study investigates the combined effect of different diet-induced muscle PUFA contents and preslaughter stress on the activity of antioxidative muscle enzymes and the oxidative stability of cooked meat. An increased content of unsaturated fatty acids in the tissue led to a decreased activity of lactate dehydrogenase in the plasma, indicating increased cell integrity. Catalase activity in the muscle tissue increased with increasing PUFA levels. However, this upregulation in antioxidative status of the muscle could not counteract the subsequent development of accelerated lipid oxidation in cooked meat as measured in terms of thiobarbituric acid reactive substances. Moreover, preslaughter stress induced increasing oxidative changes with elevated PUFA levels in the muscle tissue. 相似文献
150.
Wind erosion is not as significant or a widespread problem in Europe as in dryer parts of the world, but it can cause major damage in small areas. The hazard is greatest in the lowlands of northwestern Europe with more than 3 million ha at high-potential wind erosion risk. Crop damage and off-site damage have prompted farmers and policymakers to pay more attention to wind erosion control. A great variety of measures have been developed in the last decades. Most farmers, however, only use measures to protect their high value crops. In existing policies, little attention is paid to the off-site effects and long-term effects of wind erosion. There are no direct policy measures at a European level to control soil erosion, and few measures exist in individual Member States. Agricultural or environmental EC policies offer different policy tools to approach the wind erosion problems related to agricultural practices. Tools like subsidies for the re-afforestation of arable land can help regional policy makers with the implementation of wind erosion control measures. A case study concerning the ‘Code of Good Agricultural Practice’ shows that regional differences result in different control measures that fits best given the physical, social and economic context. The formulation of the practical details of such code should therefore remain a task of the local or regional government. The main objectives of a Code of Good Agricultural Practice could be formulated at national or European level. 相似文献