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31.
Research samples were taken from an ancient gravel stratum which is not only a representative soil layer along the middle-lower reaches of the Yangtze River in East China ,but also one of the primary Neozoic strata in Nanjing district.Located mostly on the second and third terraces,the ancient gravel strata formed the geomorphic landscapes of terrace and step.They were complex in constitution,varied widely in stability,of multiple sources,locally derived ,and associated with braided streams in the deposition environment ,A CIPW(Cross,Iddings,Pirsson and Washington) method modified by the author was used to analyze the soil-rock-forming materials of finer grains(less than 2 mm in size) of the ancient gravel stratum.Results of the analysis showed that the sandy grains were composed of apatite,ilmenite,potassium feldspar,plagioclase,enstatite and free quartz,the clay mainly of kaolinite,and the cement of a combination of silicon,aluminum and iron at a ratiof of 46:44:10.In the soil-rock-forming processes, including compactional solidifiation,water-stable illuviation-cementation,homogneous overgrowth and so on,the loose soil-rock-forming components gradually changed into consolidated soil and further to the early stage of lithification.Meanvwhile,from ,the analysis,we found that the ancient gravel stratum had been protected by overlying Xiashu loess or basalt and the overloading resulted in overconsolidated strata ,The modified CIPW method was applicale and effective for semi-quantitative analysis. 相似文献
32.
主要说明随机的广义Kuramoto-Sivashinsky方程的唯一解生成一个随机动力系统,这个系统在L^2(I)中有一个紧的随机吸引子. 相似文献
33.
试验以核桃仁和脱脂奶粉为原料,对核桃仁预处理、发酵剂的制备、酸奶原料配比及发酵时间等工艺进行了探讨,确定合理的制作工艺.研制出芳香浓郁,口感细腻的核桃酸奶。 相似文献
34.
通过田间试验研究了施用绿肥、猪粪及稻草后的稻田土壤供氮过程。绿肥耕翻后,前一阶段矿化氮量变化符合二次方程=-1.70+0.629x-0.0164x~2,峰值出现在压青后第20d,后一阶段自水稻分蘖盛期开始,绿肥氮在水稻根系影响下矿化,并大部分被水稻吸收,吸氮过程可用直线方程模拟,猪粪氮的矿化是缓慢较长的持续过程,早稻一季矿化率20.9%,猪粪氮与稻草氮的矿化量与施用后的天数有良好的直线关系 相似文献
35.
The fate of Amazonian forest fragments: A 32-year investigation 总被引:2,自引:0,他引:2
William F. Laurance José L.C. Camargo Regina C.C. Luizão Susan G. Laurance Stuart L. Pimm Emilio M. Bruna Philip C. Stouffer G. Bruce Williamson Julieta Benítez-Malvido Heraldo L. Vasconcelos Kyle S. Van Houtan Charles E. Zartman Sarah A. Boyle Raphael K. Didham Ana Andrade Thomas E. Lovejoy 《Biological conservation》2011,(1):56-67
We synthesize findings to date from the world’s largest and longest-running experimental study of habitat fragmentation, located in central Amazonia. Over the past 32 years, Amazonian forest fragments ranging from 1 to 100 ha have experienced a wide array of ecological changes. Edge effects have been a dominant driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage, fauna, and other aspects of fragment ecology. However, edge-effect intensity varies markedly in space and time, and is influenced by factors such as edge age, the number of nearby edges, and the adjoining matrix of modified vegetation surrounding fragments. In our study area, the matrix has changed markedly over the course of the study (evolving from large cattle pastures to mosaics of abandoned pasture and regrowth forest) and this in turn has strongly influenced fragment dynamics and faunal persistence. Rare weather events, especially windstorms and droughts, have further altered fragment ecology. In general, populations and communities of species in fragments are hyperdynamic relative to nearby intact forest. Some edge and fragment-isolation effects have declined with a partial recovery of secondary forests around fragments, but other changes, such as altered patterns of tree recruitment, are ongoing. Fragments are highly sensitive to external vicissitudes, and even small changes in local land-management practices may drive fragmented ecosystems in markedly different directions. The effects of fragmentation are likely to interact synergistically with other anthropogenic threats such as logging, hunting, and especially fire, creating an even greater peril for the Amazonian biota. 相似文献
36.
Threat syndromes and conservation of the Australian flora 总被引:1,自引:0,他引:1
The status of the Australian flora was reviewed by compiling published information on all critically endangered and endangered species listed federally in 2004. Threatening processes were categorised and their contributions to past, present and future declines were assessed. The information was cross-referenced against State agency information and field knowledge. Land clearance for agriculture (grazing and cropping) and urbanization have been the primary causes of range contractions and habitat loss in the past, responsible for the current status of the majority of threatened Australian plants. In the future, land clearance will remain important but new issues are emerging. Many species are now at risk from demographic and environmental uncertainty alone. Threats growing in importance include disease, salinity, invasive species and changed disturbance regimes. Many species are subject to common, landscape-level threats. A key issue to emerge from our analysis is that most species are threatened by a number of interacting factors - threat syndromes. Several future risks may be mitigated effectively by simple, low-cost changes in policy, such as more stringent controls on land clearance, strategic fire management, and firmer control on the importation of plant species. Other factors will require greater effort and new strategies to mitigate, including social and legal initiatives in urban landscapes and broad strategies for pathogens, climate change and other landscape-level processes. 相似文献
37.
许炯心 《中国水土保持科学》2007,5(6):1-7
为了解决黄河治理中迫切需要解决的粗泥沙来源和数量问题,依据大量实测资料,运用统计方法对无定河粗泥沙产沙量进行研究。结果表明:无定河流域d>0.05 mm粗泥沙产沙量呈现出减少趋势,这种减少与年降水量、年沙尘暴频率的减少和水土保持面积的增大有一定的因果关系;估算出最大30d降雨量和年沙尘暴频率的变化对d>0.05mm粗泥沙产沙量变化的贡献率分别为66.5%和33.5%,即沙尘暴特征的变化对粗泥沙产沙量变化的贡献率相当于暴雨特征的变化贡献率的1/2。建立了粗泥沙年产沙量与最大30d降雨量、年沙尘暴频率和水土保持措施面积之间的回归方程,表明粗泥沙年产沙量随最大30d降雨量、年沙尘暴频率的减小而减小,随水土保持面积的增大而减小。因此,20世纪50年代以来暴雨的减弱、沙尘暴的减弱和水土保持措施面积的增大是无定河流域粗泥沙产沙量减少的原因。 相似文献
38.
Interrill and rill erodibility in the northern Andean Highlands 总被引:2,自引:0,他引:2
There is a lack of quantitative information describing the physical processes causing soil erosion in the Andean Highlands, especially those related to interrill and rill erodibility factors. To assess how susceptible are soils to erosion in this region, field measurements of interrill (Ki) and rill (Kr) erodibility factors were evaluated. These values were compared against two equations used by the Water Erosion Prediction Project (WEPP), and also compared against the Universal Soil Loss Equation (USLE) erodibility factor. Ki observed in situ ranged from 1.9 to 56 × 105 kg s m− 4 whereas Kr ranged from 0.3 to 14 × 10− 3 s m− 1. Sand, clay, silt, very fine sand and organic matter fractions were determined in order to apply WEPP and USLE procedures. Most of the evaluated soils had low erodibility values. However, the estimated USLE K values were in the low range of erodibility values. Stepwise multiple regression analyses were applied to ascertain the influence of the independent soil parameters on the Ki and Kr values. After this, we yield two empirical equations to estimate Ki and Kr under this Andean Highlands conditions. Ki was estimated using as predictors silt and very fine sand, while Kr used as predictors clay, very fine sand and organic matter content. Relationship among Ki, Kr and K are described for the Highland Andean soils. 相似文献
39.
40.