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531.
Land-Use Systems and Resilience of Tropical Rain Forests in the Tehuantepec Isthmus,Mexico 总被引:1,自引:0,他引:1
Land-cover types were analyzed for 1970, 1990 and 2000 as the bases for determining land-use systems and their influence on the resilience of tropical rain forests in the Tehuantepec Isthmus, Mexico. Deforestation (DR) and mean annual transformation rates were calculated from land-cover change data; thus, the classification of land-use change processes was determined according to their impact on resilience: a) Modification, including land-cover conservation and intensification, and b) Conversion, including disturbance and regeneration processes. Regeneration processes, from secondary vegetation under extensive use, cultivated vegetation under intensive use, and cultivated or induced vegetation under extensive use to mature or secondary vegetation, have high resilience capacity. In contrast, cattle-raising is characterized by rapid expansion, long-lasting change, and intense damages; thus, recent disturbance processes, which include the conversion to cattle-raising, provoke the downfall of the traditional agricultural system, and nullify the capacity of resilience of tropical rain forest. The land-use cover change processes reveal a) the existence of four land-use systems (forestry, extensive agriculture, extensive cattle-raising, and intensive uses) and b) a trend towards the replacement of agricultural and forestry systems by extensive cattle-raising, which was consolidated during 1990–2000 (DR of evergreen tropical rain forest=4.6%). Only the forestry system, which is not subject to deforestation, but is affected by factors such as selective timber, extraction, firewood collection, grazing, or human-induced fire, is considered to have high resilience (2 years), compared to agriculture (2–10 years) or cattle-raising (nonresilient). It is concluded that the analysis of land-use systems is essential for understanding the implications of land-use cover dynamics on forest recovery and land degradation in tropical rain forests. 相似文献
532.
结合当前我国大气污染控制工作的严峻形势,分析了我国火电行业大气污染控制工作的进展情况、存在问题及控制措施等。 相似文献
533.
PETER M. CHAPMAN 《Environmental management》1997,21(2):197-201
/ Information provided by acid volatile sulfide (AVS) andequilibrium partitioning (EqP) theory is described, including two caseexamples, relative to hazardous waste site sediments. AVS and EqP are toolsin the toolbox, which can serve three main functions: screening,prioritization, and assisting in explaining observed effects. They should notbe used in isolation for decision making, particularly at hazardous waste orother sites where the sediments are contaminated by materials such as coal,coke, and pitch.KEY WORDS: Acid volatile sulfides; Equilibrium partitioning; Sediments;Hazardous waste 相似文献
534.
pH值是衡量降水酸性的重要指标。本文研究了都匀市降水pH值的变化趋势,并对其酸性降水的特征进行分析,提出了保护大气质量,降低酸雨频率的对策建议。 相似文献
535.
The operation policy for a single reservoir is applied to a rain water cistern system because the functions of a cistern are similar to a simple single reservoir. Since the cistern is a closed system, water loss is negligible. In this study, a dynamic programming analysis has been made to study the effects of the probable weekly rainfall and the water storage in the cistern towards the water consumption policy. The result of this study indicates that the water consumption rate should be adjusted into a lower rate when the water storage in the cistern is low and/or when the expected probable weekly rainfall is low if the owner of the cistern does not want to risk the chance of an empty cistern. The demand for a reliable method for forecasting weekly rainfall is evident in this study. 相似文献
536.
Stanley A. Changnon 《Journal of the American Water Resources Association》1977,13(6):1165-1174
ABSTRACT: Weather modification, both planned by man and that accidentally produced by man, has been under intensive study in Illinois for ten years. Most everyone in Illinois and the Midwest is living in a climate that now is modified inadvertently from its natural state. State atmospheric scientists have tackled weather modification through a series of interrelated studies beginning with climatic studies (to establish the background), experimental design studies, experimental field studies to verify changes and their causes, and finally socio-economic and environmental studies to measure the impacts of weather modification. Studies at St. Louis show that the city acts as a trigger of summer clouds and rainfall leading to 4 to 6 summer days with 3 cm or more rain somewhere just east of the city. Power plants and jet aircraft also accidentally produce climatic changes. A focus on planned weather modification has been on the design of needed midwestern experiments in rainfall enhancement and hail suppression including the societal and environmental impacts. 相似文献
537.
Year-to-year variation in SO4
2-,NO3
-, Ca2+, K+, and Mg2+concentrations in forest floor and mineral soil percolatefrom a forested, podzolic soil at the Turkey Lakes Watershedon the Precambrian Shield was assessed for monotonic trendsbetween 1986 and 1995. Our objective was to examine howrapidly ion concentrations in soil percolate equilibratedafter stabilization of SO4
2- concentrations inprecipitation. Significant negative trends were detected inmonthly Ca2+, and Mg2+ concentrations in forestfloor and SO4
2-, Ca2+, and Mg2+ inmineral soil percolate during the 10-year-period. Thedecline in Ca2+ and Mg2+ was greater than annualdecreases in SO4
2- and NO3
- in forestfloor percolate and proportional to the reduction inSO4
2- in mineral soil percolate. Response ofmineral soil percolate to a 15 molc L-1SO4
2- decrease in wet-only precipitation between1985 and 1986 was a gradual decline in SO4
2-concentration through 1995. The five-year meanSO4
2- concentration in bulk precipitation, forestfloor percolate, and mineral soil percolate decreased 8, 9and 18 molc L-1 from 1986–90 to 1991–95.Microbial (mineralization of organic S) and sorption(release from and/or retention in the pool of insolubleSO4
2-) processes in the soil were logicalexplanations for the observed changes in SO4
2- inmineral soil percolate. 相似文献
538.
Around the city of Izmir, Yamanlar – Manisa (north) Karabelen (south) andKemalpasa mountainous areas exist. The forested area in total covers 122,613.5 ha on these mountainous areas. This forested area has 6,146,387 m3 of wood potential. Industrial complex surroundingthe Aliaga, and thermo-electric power plants working with lignitecoal in the Soma region and some other small industrial establishmentsare located around Izmir and Manisa. These establishements have a vital importance in polluting the air. The forest, which suffers especially from SO2 pollution, consists of Pinus brutia and Pinus nigra. Sulphur contents in 1, 2, 3 yr old needles of the trees were determined to range between 2000–8000 ppm. Microscopic investigation of the tree needles revealed that black blights on the needles indicate destruction of the cells. Annual ring thickness of trees measured showed that there has been a reduction in the forest growth and thisreduction is becoming more serious each year. Reduction in the wood production causes hundreds of billions of Turkish lira of economic loss to the Forestry Administration. It has been concluded at the end of this study that in order to stop theharm that the forests suffer, industrial establishments must pay an `ecological costs' to be added to their product cost items. 相似文献
539.
540.