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231.
Francis J. Singer 《Environmental management》1981,5(3):263-270
Populations of introduced European wild boar, feral pigs, and combinations of both types (all Susscrola L.) inhabit thirteen areas in the National Park Service system. All parks have relatively stable populations, with the exception of Great Smoky Mountains National Park, which reported a rapidly expanding wild boar population. Suspected and documented impacts were apparently related to pig densities and sensitivity of the ecosystem; the three largest units with dense wild pig populations reported the most damage. Overall, wild pigs are a relatively minor problem for the Park Service; however, problems are severe in at least three parks, and there is potential for invasion of wild boars into several additional parks in the Appalachian Mountains. More specific information is needed on numbers of wild pigs and their impacts in the various parks. 相似文献
232.
Predicting the multiple pathways of plant succession 总被引:4,自引:0,他引:4
Peter J. Cattelino Ian R. Noble Ralph O. Slatyer Stephen R. Kessell 《Environmental management》1979,3(1):41-50
Classical concepts view succession as a deterministic, mechanistic regeneration of the disturbed community, and thus have limited applicability to fire-prone ecosystems, A recently developed multiple pathway succession model appears to have more realism and applicability in frequently disturbed ecosystems. It includes a set of species-specific attributes that are vital to reproduction and survival, and permits variable succession pathways depending on the stand's age (and thus species composition) when disturbed. Examples from Australia and the northern Rocky Mountains (USA) are presented, as are approaches to refining and improving the model. 相似文献
233.
Mark C. Scott Gene S. Helfman Matthew E. McTammany E. Fred Benfield Paul V. Bolstad 《Journal of the American Water Resources Association》2002,38(5):1379-1392
ABSTRACT: Streams integrate biogeochemical processes operating at broad to local spatial scales and long term to short term time scales. Humans have extensively altered those processes in North America, with serious consequences for aquatic ecosystems. We collected data on Upper Tennessee River tributaries in North Carolina to: (1) compare landuse and landscape geomorphology with respect to their ability to explain variation in water quality, sedimentation measures, and large woody debris; (2) determine if landscape change over time contributed significantly to explaining present stream conditions; and (3) assess the importance of spatial scale in examining landuse influences on streams. Stream variables were related to both landuse and landscape geomorphology. Forest cover accounted for the most variation in nearly all models, supporting predictions of nutrient enrichment, thermal pollution, and sedimentation caused by landscape disturbance. Legacy effects from past catchment disturbance were apparent in sedimentation measures. Nitrogen and phosphorus concentrations, as well as stream temperature, were lower where riparian buffers had reforested. Models of stream physicochemistry fit better when predictors were catchment wide rather than more localized (i.e., within 2 km of a site). Cumulative impacts to streams due to changes in landuse must be managed from a watershed perspective with quantitative models that integrate across scales. 相似文献
234.
本文分析了西南地区旅游资源的现状,探讨了西南旅游资源的分区,并结合我国当前大力发展第三产业的要求,提出了开发西南旅游资源的对策。 相似文献
235.
黑水河干旱河谷沿程土壤物理参数梯度变化特征研究 总被引:1,自引:0,他引:1
横断山区干旱河谷是具有典型的旱季和雨季的特殊气候特征的区域,本区域土壤退化和荒漠化极大制约了区域农业的发展。本文研究了金沙江干热河谷区支流黑水河从源头到河口未扰动土壤的物理参数变化特征。结果表明,沿河土壤物理呈现不同变化趋势,砾石在中游部分河段和河口段高,而〉5mm团聚体的变化则相反;5~1mm的团聚体变化不大;〈1mm团聚体河口和源头段高于其余地段;土壤容重沿程增大,非饱和导水率源头地段土壤最高。本研究初步揭示了干旱河谷土壤不均匀,不同水热条件及其组合可能对退化程度有至关重要的影响。这表明横断山区不同的干旱河谷地段土壤和植被退化途径、退化特征和退化过程不同,开发和治理途径与方式也应当不同。 相似文献
236.
川西古镇大气环境容量计算模型 总被引:1,自引:1,他引:1
通过对川西古镇大气环境污染特点的分析。根据箱体内污染物“物质守恒”原理,以箱式模型为基础,推导出箱体内污染物之浓度随时问和空间的变化规律。建立了适合于川西古镇大气环境容量的数值计算模型。在此基础上,根据污染物自身特点,引入k1、k2两个浓度修正系数,分别建立了适合于该区域的SO2和TSP环境容量计算的修正模型。当研究区域具有下垫面变化显著或大气污染源源强变化显著等特点时,应使用改进后的单箱模式。 相似文献
237.
Xianwei Wang Xiuzhen Li Yuanman Hu Jiujun Lv Ju Sun Zongmei Li Zhifeng Wu 《环境科学学报(英文版)》2010,22(7):1057-1066
Boreal peatlands represent a large global carbon pool.The relationships between carbon mineralization,soil temperature and moisture in the permafrost peatlands of the Great Hing'an Mountains,China,were examined.The CO2 emissions were measured during laboratory incubations of samples from four sites under different temperatures(5,10,15,and 20°C) and moisture contents(0%,30%,60%,100% water holding capacity(WHC) and completely water saturated).Total carbon mineralization ranged from 15.51 to 112.92 mg C under the treatments for all sites.Carbon mineralization rates decreased with soil depth,increased with temperature,and reached the highest at 60% WHC at the same temperature.The calculated temperature coefficient(Q10) values ranged from 1.84 to 2.51 with the soil depths and moisture.However,the values were not significantly affected by soil moisture and depth for all sites due to the different peat properties(P 0.05).We found that the carbon mineralization could be successfully predicted as a two-compartment function with temperature and moisture(R2 0.96) and total carbon mineralization was significantly affected by temperature and moisture(P 0.05).Thus,temperature and moisture would play important roles in carbon mineralization of permafrost peatlands in the Great Hing'an Mountains,indicating that the permafrost peatlands would be sensitive to the environment change,and the permafrost peatlands would be potentially mineralized under future climate change. 相似文献
238.
239.
240.
天山山地河流水体中微量重金属的分布特征及形态分析 总被引:4,自引:0,他引:4
为了解绿洲经济迅速发展背景下天山山地河流水体中重金属分布特征及形态特征,对乌鲁木齐-阿克苏、巴里坤-伊吾、昭苏-特克斯等3个区段河流干支流重金属Zn、Cu、Pb、Cr、As、Hg、Cd的分布、来源、污染状况及存在形态进行了分析.结果表明:1天山山地各取样河流的p H值大部分在8.0左右,为偏碱性的环境;各取样点水体的氧化还原反应电位值在150~200 m V之间,为弱氧化的环境.水质评价表明,3个采样区段河流中7种重金属的含量均低于国家Ⅰ类水质标准及WHO饮用水健康的建议标准.2多元统计分析表明,7种重金属可以归为3个主成分,其中PC1(Hg、Zn和Pb)主要受人为污染因素的影响;PC 2(Cr和As)主要受自然地质背景的影响;PC 3(Cd和Cu)同时受人为和自然因素的共同影响.3污染评价表明,天山山地河流中7种重金属的单因子污染指数值和综合污染指数值均小于1,属于安全等级,清洁水平.4形态分析表明,重金属Pb、Cd和Hg在天山中部的乌鲁木齐-阿克苏区段干支流,重金属As和Cu在天山东部的巴里坤-伊吾区段和天山西部的昭苏-特克斯区段干支流中溶解态的含量均大于50%,生物毒性较大.总体上,3个采样区段河流干支流重金属的总量及溶解态含量均较低,未造成污染.但在天山山地中部的乌鲁木齐-阿克苏区段,河流干支流中重金属Pb、Cd和Hg的总量及溶解态含量较高.应加强对该区域人类活动的合理规划以及河流水质监测,防止因人为污染而导致河流水体中重金属的含量过高,危害生态环境. 相似文献