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411.
412.
与长江1954 年洪灾相比较,1998 年洪灾具有“中水量、高水位、大灾害”的特征。流域内原始森林的过量采伐、大量湖泊的消亡、河道的普遍淤塞等生态系统的破坏引起了长江产流、汇流、洪水调蓄、行洪等水文条件的严重恶化。这是长江流域洪灾频繁,灾情加重的主要原因。 相似文献
413.
第16届国际土壤学大会包括全会和45个分会,内容涵盖土壤学所有分支并反映了本世纪土壤学的进展。本文综述了土壤学在全球资源与环境问题中的重要地位,分析了世纪之交土壤学面临的挑战和契机,提出土壤学只有拓展与其它学科以及社会的联系,服务于社会的可持续发展,保持自己的特色并在基础研究和应用研究中不断创新,才能在未来更好地生存和发展。 相似文献
414.
为了分析黄土塬区土地利用变化对土壤中NO3--N迁移规律的影响,在陕西长武黄土塬区沿东西方向设置6个样地,每个样地内均选择耕地、由耕地转变来的果龄10 a和20 a左右的苹果园(下称耕地、10 a果园和20 a果园)3种土地利用方式采集土壤样品,分析土地利用变化对NO3--N迁移的影响,并初步评估其对地下水污染的潜在风险. 结果表明:不同土地利用方式下土壤中NO3--N均出现累积现象,达到累积峰时的土层深度表现为果园>耕地,NO3--N最大累积量表现为20 a果园>10 a果园>耕地. 耕地、10 a果园和20 a果园土壤w(NO3--N)平均稳定深度分别为300、400和500 cm,平均稳定值分别为2.4、2.5和2.6 mg/kg. 地下水中ρ(NO3-)为15.3 mg/L,而3种土地利用方式下土壤中ρ(可移动态NO3-)分别为14.2、26.2和26.3 mg/L,可见,与耕地相比,果园土壤中NO3--N淋溶至地下水的风险更大. 但由于土地利用变化导致的土壤水分运动和地下水补给存在差异,各土地利用方式对地下水中NO3--N的贡献率尚需进一步量化. 相似文献
415.
416.
Erich Gebhart 《毒物与环境化学》2013,95(1-2):7-15
A very extensive and effective research in the fields of classical and molecular cytogenetics of cancer cells, during the past 10 years, has produced a rather concrete picture of the events and mechanisms rendering a normal cell a malignant one: Mutational changes in the control of so‐called cellular oncogenes play a fundamental role in cell transformation and tumor progression. These oncogenes are highly conservative and, therefore, important genes normally coding for a series of specific proteins particularly involved in growth control and differentiation processes. The most important alterations of these genes are: (1) Point mutations (e.g. base transitions) in essential base pairs of the respective proto‐oncogenes causing an uncontrolled expression of the latter, (2) translocations of specific chromosomal segments resulting in transfer of a proto‐oncogene from its normal (controlled) location into the area of highly active genes and by that in its activation, (3) amplification of DNA sequences including proto‐oncogenes which also can cause their over‐expression, (4) insertion of retroviral oncogenes into the DNA, (5) point mutations or deletions in “control genes” rendering the respective gene mutation homozygous or hemizygous. All these events are mutations in the strict sense the mutageneticist applies to the endpoints of his experimental studies. Above all, the fundamental importance of translocations and point mutations in the transformation process has clearly been evidenced by these data. Therefore, the design of experiments in mutagenicity testing should preferentially consider these types of mutations. Any mutagen, e.g. certain heavy metals or their compounds, inducing those types of mutations, must be considered suspicious not only concerning its mutagenicity in germ cells but also in somatic cells, and, by that, its carcinogenicity. 相似文献
417.
Zbigniew W. Kundzewim 《国际发展与全球生态学杂志》2013,20(4):290-298
SUMMARY The notion of sustainable development in the context of water resources is discussed. Facing the increasing pressures — population growth with consequences for settlements and production of food and fibre, and human aspirations to better living standards — the business-as-usual approach to water development and management cannot he globally sustainable. The need for curbing water demands and for ‘doing more with less’ are gaining growing recognition in our increasingly thirsty planet. An integrated approach to freshwater resources is needed, based on the perception of water as a natural resource, part of the ecosystem, and an economic and social good. It is discussed how hydrological extremes jeopardize sustainable development. Sustainability-related properties of drought and flood preparedness and mitigation measures are reviewed. Even if the term ‘sustainable development’ has been typically used in a qualitative sense, in order to compare how different options (e.g. flood protection alternatives) fare with regard to sustainable development, one needs at least rough quantitative measures. A sample of relevant indices is reviewed. It is advocated that hydrological observations should be recognized as an essential component of sustainable development and management of water resources. 相似文献
418.
SUMMARY The Lesser Himalaya, as the most densely populated part of the tectonically active and ecologically sensitive Himalayan mountain ranges, deserves specific attention to the conservation of the environment and the sustainable development of natural resources. Rapid growth of the human population during recent years, and the absence of any viable means of livelihood other than uneconomic crop farming have led to the uncontrolled exploitation of land areas and the consequent degradation and depletion of critical biophysical resources in the region. The need for sustainable development in Himalaya, therefore, makes it imperative to adopt a comprehensive land-use policy based on land capacity analysis that is scientific and practical. The main objective of this paper is to evolve an optimal land-use framework for the Gomti Watershed, situated in Kumaon, Lesser Himalaya. A detailed study of the traditional land use, regional agricultural system and the areas prone to environmental hazards was made throughout the watershed, through the preparation of large scale topographical forest and land record maps, field surveys and mapping. The average slope was considered as the principal parameter of land capacity, the potential for landslides and the intensity of erosion. Recognising the drastic changes that have taken place in the traditional land use, the watershed area has been proposed to be defined as protected forests (33.41%), community forests (32.86%), cultivation (23.33%) and horticulture (8.30%). 相似文献
419.
洱海入湖河流水体悬浮颗粒物有机碳氮来源特征 总被引:14,自引:4,他引:10
以洱海主要入湖河流水体悬浮颗粒物为研究对象,运用稳定同位素技术,研究了不同季节、不同河流水体悬浮颗粒物中有机碳、氮的来源,探讨了其与流域环境和人类活动之间的关系. 结果表明:①入湖河流水体悬浮颗粒物δ13C的离散程度为夏季<秋季<冬季<春季,变化范围分别为-25.1‰~-16.9‰、-30.0‰~-10.7‰、-20.9‰~-11.0‰和-28.6‰~-14.4‰;δ15N的离散程度为冬季>夏季>春季>秋季,变化范围分别为-0.5‰~8.8‰、5.4‰~10.6‰、3.4‰~7.9‰和6.2‰~8.7‰. ②入湖河流水体悬浮颗粒物有机质的来源,春季以陆源C3植物和自生有机质为主,并且C3植物来源的有机质贡献呈逐渐增大趋势;夏季主要来源于陆源C3植物;秋季仍以陆源C3植物和水生植物的混合来源为主,但水生植物来源有机质比例有所上升;冬季则以陆源C3、C4植物和水生植物来源有机质混合来源为主. ③入湖河流水体悬浮颗粒物中的氮,春季主要来源于土壤流失和水生植物残体,并且土壤流失氮比例逐渐升高;夏季主要来源于土壤流失;秋季来源于土壤流失、化学肥料和水生植物死亡的共同作用;冬季来源于化学肥料、土壤流失和水生植物,并且化学肥料带来的氮比例有所上升. 相似文献
420.
大别山区是中国南北地理生态过渡带东延余脉,山地系统表现出高度的异质性和敏感易变性,识别山地生境质量的空间特征对揭示自然和人为因素的时空驱动机制及差异具有重要指示意义.基于PLUS-InVEST以及地理探测器方法,分析大别山区2000~2020年生境质量的时空动态变化及驱动机制,并对2030年土地利用和生境质量进行多情景模拟预测.2000~2020年,区内土地利用类型以耕地(50%~54%)和林地(42%~45%)为主,荒地(2%~4%)面积占比最低,大别山区耕地变化最大,面积减少2 311.45 km2,林地和建设用地次之,面积分别增加1 431.37 km2和924.52 km2,灌木和荒地的变化较小,面积分别减少7.72 km2和19.10 km2;大别山区的生境质量与海拔高度呈正相关,中东部生境质量较高,北部和南部生境质量较差;2000~2010年生境质量均值从0.594上升到0.608,到2020年下降到0.603,生境质量出现了先上升后下降的趋势.地理探测器结果表明,影响大别山区生境质量的主要驱动因素是地形起伏度、土地利用强度和海拔,NDVI的影响随着时间逐渐增强.2030年生境质量的预测结果显示,4种发展情景下,区域内整体生境质量仍然呈现下降的趋势,并且在生态保护情景下,依旧呈现降低的趋势,只是降低的速率减小.研究结果可为大别山区未来土地利用类型空间规划提供优化策略. 相似文献