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61.
八宝喀斯特山区生态环境问题与治理措施 总被引:3,自引:1,他引:3
喀斯特峰丛山区生态系统特征有:结构简单,稳定性差,恢复困难等。其生态系统脆弱性表现为:(1)裸露型喀斯特山地坡度陡峻,土壤贫脊,耕地少而分散,水土保持能力差;(2)地下水文网发育导致地表水大量漏失,地下水位埋藏深,难以开采利用;(3)植被树种单一,生长缓慢,资源开发过程中易产生耕作粗放,水土流失,石漠化等环境问题,对其治理和恢复过程应是渐进式的:水-土-林,即首先要科学开发利用各种水资源,同时合理规划利用土地资源,其次要加速生态系统重建,使其形成良性循环发展方式。 相似文献
62.
中国地质公园地质背景浅析和世界地质公园建设 总被引:35,自引:3,他引:35
2000年以来,中国基于自身丰富的地质遗产资源和保护经验,正式分2批命名了44家国家地质公园,其分布和特征受地质构造背景和新构造运动的控制。地质遗迹的保护和开发产生了很好的社会、经济和环境效益,同时也为世界地质公园的申报创造了条件。 相似文献
63.
S. Gamito 《International Journal of Salt Lake Research》1997,6(2):145-173
The Ria Formosa lies in southern Portugal, extending for about 55 km. It is a true barrier island system, comprising mainland,
backbarrier lagoons, inlet deltas, barrier islands, barrier platforms and shoreface. Of the Ria Formosa system, which covers
a total area of 163 km2, 20 km2 are occupied by salinas and aquaculture ponds. The main water reservoir of thesalinas and the extensive aquaculture ponds behave like small lagoons where there are one or more openings to a tidal channel. These
small lagoons have the advantage of being easy to study and to model.
An ecological model was developed to estimate the potential production of the gilthead seabream in the Ria Formosa, in an
extensive aquaculture regime. This model was based on information concerning chemical and physical factors (forcing functions)
and secondary production estimates from four sites in the Ria Formosa with different environmental conditions, where extensive
aquaculture is practised. Published information on optimal growth parameters of the gilthead was used to build the model,
which was based on some assumptions concerning the detrimental effect of an excessive increase of salinity and other environmental
factors both on gilthead growth (one state variable) and on prey production (divided into two state variables), which is essentially
benthic macrofauna.
Reservoirs with low water renewal undergo large environmental fluctuations. The growth of gilthead or other fish can be difficult,
not only because of the adverse environmental conditions but also because of the low secondary production. The maximum yield
of fish is predicted to be less than 6 g m−2. In reservoirs where the water exchanges on almost every tide, the maximum yield of gilthead can be in excess of 22–25 g
m−2. Nevertheless, the high productivity of these sites in terms of secondary production of benthos and fish, as well as primary
production, can lead to oxygen depletion during the night or at day-break. An attempt to further improve fish production by
fertilisation or by adding food could provoke a rapid deterioration of the water quality and endanger all production. 相似文献
64.
Coloradoapos;s 1992 vote on Amendment Two was the first meaningful, broad-based test of attitudes on gay rights within the United States. Analysis of voting results distinguishes places of tolerance from places of rejection. Social differences separating these places reflect typical contrasts between “traditionalists” and “modernizers” found in cultural conflicts at the national level. Places showing support for gay rights are recreational-based mountain communities, urban areas, and university communities. Those showing opposition are rural, agriculturally based communities. Suburban areas produced a more ambivalent vote. 相似文献
65.
Metropolitan growth and labor markets in Mexico 总被引:1,自引:0,他引:1
Adrian Guillermo Aguilar 《GeoJournal》1997,43(4):371-383
The objective of this paper is to examine the main changes in the metropolitan labor markets associated with economic restructuring in Mexico during the late 1980s and beginning of the 1990s. The analysis refers particularly to the four largest metropoles of the country, Mexico City, Guadalajara, Monterrey and Puebla, looking for common characteristics in their emergent employment structures now strongly differentiated in terms of rewards, stability in employment relations and conditions of access to jobs. The analysis reveals that largest metropolitan areas have been the most profoundly affected by the economic restructuring resulting from globalization, through a rapid de-industrialization and the expansion of the tertiary sector. Metropolitan labor markets in Mexico, at the time that show signs of social polarization in the formal sector, put in evidence a general process of precarization – less labor stability, replacement of permanent by part-time jobs, and increasing subcontracting –, segmentation of the labor force, and an increasing informal conditions of economic activities with small businesses and unskilled, temporarly and poorly paid jobs. The labor force segmentation and its more precarious and casual conditions are mostly explained by the impact of recent neoliberal policies, and recurrent economic crisis during the 1980s and 1990s which highly contributes to social inequality. 相似文献
66.
67.
IntroductionItisdefinitelystipulatedintheLawofthePeople'sRepublicofChinaonProtectingagainstandMitigatingEarthquakeDisastersthattheseismicsafetyevaluationmustbemadeformajorprojects(includinglifelineprojects)and,accordingtotheresultsobtained,theseismicresistancerequirementsshouldbedetermined.Thenecessityofseismicsafetyevaluationhasbeenrecog-nizedgradually,butthetopicontheeffectofsafetyevaluationhasnotbeenreferredmuch.Gener-allyspeaking,althoughmostpeopleapprovethesocialeffectofsafetyevaluatio… 相似文献
68.
分析近20年来珠江河口水环境变异的特征,探讨珠江河口水环境与水生物相互联系和相互作用的关系。结果表明,珠江河口形态、地貌、水文情势和入河污染物等变异改变了珠江河口水生物的栖息条件,削弱了河口生态系统的自动调节修复能力和稳定性,对河口生态系统的物质循环、能量流动和发育演化平衡构成了重大影响。 相似文献
69.
Agriculture was the primary target of moves to deregulate the New Zealand economy in 1984. Within twelve-months all production
subsidies had been removed, including those for fertiliser and other inputs, as well as funding for drought relief, floods
and other natural weather disasters. Whereas at the start of 1984, subsidies were estimated to represent as much as 33% of
farm income, by 2003 this had fallen to less than 2% with most of this spent on agricultural research. The anticipated shift
of thousands of people off the land did not appear to occur, and by conventional measures at least New Zealand agriculture
in 2003 is a major success story. At the core of the changes imposed on agriculture was a commitment to remove all state or
government distortions from the system and to fully expose the agricultural sector to market forces. This included wide-ranging
and fundamental changes in the broad institutional context within which agriculture must operate. All this was achieved at
great social cost and with a significant impact on the environment. In many respects New Zealand agriculture is now very different
from that in 1984. Some sectors, such as dairying, have grown and become increasingly industrialised. On the other hand, sheep
farming, particularly for wool has struggled to maintain its market share, while other enterprises have emerged as significant
sources of income, including horticulture, viticulture and fruit. It is argued here that the trends evident in New Zealand
agriculture since 1984 pre-existed the reform period and that the apparent success of the reforms evident at a national scale
have not addressed or removed the fundamental problems which face New Zealand agriculture, just as they do modern agricultural
systems elsewhere.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
黄河流域坡高地系统最小生态需水研究 总被引:2,自引:0,他引:2
以保护和恢复流域坡高地生态系统为目的,对坡高地最小生态需水问题进行研究,提出了坡高地生态需水和生态缺水的计算方法。以黄河流域为实例,在GIS和遥感技术支持下对坡高地最小生态需水量和缺水量进行了计算,并从时空两个尺度揭示了黄河流域坡高地生态系统最小生态需水的变化规律,研究成果可为流域生态环境建设和水资源合理配置提供依据。 相似文献