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1.
Blue sucker Cycleptus elongatus (L.) in the upper Yazoo River basin, Mississippi, USA was studied using overnight hoop net sets (n = 4093) during 1988 and 1990–1998 to determine the influence of channel dredging. There were 264 blue suckers captured, ranging from 3 to 11 years of age. Length ranged from 265 to 700 mm and weight from 120 to 4700 g. Concurrent studies with smaller mesh hoop nets failed to capture any juvenile blue suckers. Catch‐per‐unit‐effort (CPUE: fish net?1) declined throughout the study in the Yalobusha River, a river subjected to channel dredging during 1988 and 1994. With the exception of limited hydraulic dredging in the Tallahatchie River, there was no dredging in the other Yazoo River tributaries, nor were there declines in blue sucker catch rates in these rivers. Throughout the upper Yazoo River basin, blue sucker stocks were dominated by adult fish, and there was little evidence of reproduction or recruitment. Conservation of the blue sucker in the upper Yazoo River basin should include actions that ensure the functional integrity of this floodplain river ecosystem and elimination of channel dredging throughout the basin. 相似文献
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研究了用下间作黄麻和苏丹草在不同树龄阶段的林木生长情况和作物产量,结果发现５－６ａ树龄时的林农复合系统具有树木的偏利作用,而６ａ树龄后的树木对农作物有偏害作用。 相似文献
3.
- Extensive assessments of a species distribution, its variation in density and demographic status across environments are crucial to develop successful conservation efforts.
- The freshwater pearl mussel (Margaritifera margaritifera) is considered one of the most endangered freshwater bivalves with many recovery efforts continuing throughout its geographic range. The distribution and conservation status of M. margaritifera are not well documented in the Iberian Peninsula. Galicia (NW Iberian Peninsula) represents nearly 70% of the historical distribution of the species in the southern limit of its European range.
- An extensive field survey was conducted in two phases at 2436 locations. The presence and density of M. margaritifera was determined at 555 sampling points spread across 54 rivers that belong to 23 drainage basins in Galicia. The present work has more than doubled the number of rivers known to provide habitat for this endangered species in the Iberian Peninsula.
- In Galicia the species is heterogeneously distributed with a highly variable density of individuals within and between rivers. For example, within the River Camba density ranged from 0.02 to 47.8 ind m‐2. The maximum density detected in a sample was 332 ind m‐2. Twelve rivers in Galicia are thought to have more than 5000 individuals, and small individuals were found in 11 rivers.
- High rates of decline and extinction of M. margaritifera populations are known in some areas and the main threat to unionoid bivalves is a lack of natural recruitment. Thus, Galician populations are important for providing new opportunities for conservation of the species in Europe because it is vitally important to find the reasons for recruitment failure.
4.
- Little has been done to identify key conservation areas in the Amazonian freshwater ecosystems of Colombia.
- This research constitutes the first attempt to systematically identify important conservation areas in the freshwater ecosystems of the South of the Colombian Amazonian Trapezium. This effort considered not only fine filter targets (species) as central elements of decision making, but coarse filter targets (habitats), ecosystem services and social benefits, and threats. Owing to the complexity of the study area, a multi‐criteria assessment constituted a good approach to tackle the issues affecting a complex ecological, cultural, social, economic and political territory.
- Five sites stood out and were considered important as areas for targeted management: the Tarapoto Lakes System, Yahuarcaca Lakes System, Loreto‐Yacu River, and Mocagua Island (Colombia) and Caballo Cocha Lake (Peru). Biodiversity conservation initiatives as well as livelihood improvement projects are currently in motion in the area aiming to find a balance between resource use and local development.
5.
研究分析了丁坝和护坦在沿河林区公路路基防护中的作用、防护原理、设置方法、应用条件和有效性问题。 相似文献
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宁夏平原湿地保护、利用的经验教训 总被引：5，自引：0，他引：5
汪一鸣 《干旱区资源与环境》2004,18(6):6-9
本文在分析宁夏平原湿地特点的基础上 ,总结了古代和当代保护、利用湿地的若干经验教训 ,为今后湿地的有效保护、合理利用指出发展方向。 相似文献
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采用随机区组设计,试验了氮、磷和钾水平不同组合的复合肥配方系列及尿素对赤水河流域毛竹林生产力的影响。结果表明：①不同处理对毛竹林出笋成竹量和成竹率、新竹平均胸径和胸高断面积、以及竹秆、枝叶等地上生物量有增产效应,差异不显著。综合效应指数排序为复合肥F （271．34％）＞尿素（228．33％）＞复合肥G （160．46％）＞对照（100．00％）。②复合肥F的出笋量、成竹量、新竹平均胸径、胸高断面积,秆材量和枝叶生物量分别为对照的110．53％、107．22％、103．61％、113．62％、114.93％和109．70％。除出笋量增幅仅中下水平外,成竹量、新竹质量和生物量增幅较大,适宜于毛竹林大径材培育。③复合肥G和尿素的出笋成竹量增幅较大,复合肥G的新竹质量和生物量增幅较小,不及尿素的中上水平,前者可作为笋用林和笋材兼用林培育肥种、肥效较低,后者肥效应较高、不利于地力维护,生产上宜慎用。 相似文献