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991.
Domestic animals potentially affect the reproductive output of plants by direct removal of aboveground plant parts but also could alter the structure and fertility of the upper soil and the integrity of biological crusts through trampling. We asked whether sheep selectivity of plant patches along grazing paths could lead to negative changes in biological crusts and soil seed banks. We randomly selected ten floristically homogeneous vegetation stands distributed across an area (1250 ha) grazed by free ranging sheep. Vegetation stands were differently selected by sheep as estimated through sheep-collaring techniques combined with remote imagery mapping. At each stand, we extracted 15 paired cylindrical soil cores from biological crusts and from neighboring soil without crusts. We evaluated the crust cover enclosed in each core and incubated the soil samples at field capacity at alternating 10-18 °C during 24 months. We counted the emerged seedlings and identified them by species. Sheep selectivity along grazing paths was largest at mid-distances to the watering point of the paddock. Increasing sheep selectivity was associated with the reduction of the cover of biological crusts and the size and species number of the soil seed bank of preferred perennial grasses under biological crusts. The size of the soil seed bank of annual grasses was reduced with increasing sheep selectivity under both crust and no crust soil conditions. We did not detect changes in the soil seed banks of less- and non- preferred species (shrubs and forbs) related to sheep selectivity. Our findings highlight the negative effects of sheep selectivity on biological crusts and the soil seed bank of preferred plant species and the positive relationship between biological crusts and the size of the soil seed bank of perennial grasses. Accordingly, the state of conservation of biological crusts could be useful to assess the state of the soil seed banks of perennial grasses for monitoring, conservation and planning the sustainable management of grazing lands. 相似文献
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994.
危险化学品运输路径优化选择模型研究 总被引:1,自引:0,他引:1
针对危险化学品运输的路径优化选择问题,将多目标格序决策理论引入到路径方案评价比选中,结合指标选取的综合性和可操作性原则,从6个方面构建危险化学品运输路径比选指标体系:影响区域水源保护性(p1)、影响区域途径区域名胜古迹保护性(p2)、影响区域生态环境保护性(p3)、影响区域人口规模(p4)、影响区域厂矿规模(p5)、运输路径综合运输效益(p6)。通过对各方案综合差异度的计算,实现了备选方案的格序化排序。此外在模型体系权重计算中采用了熵值法,实现了权重确定的客观性。最后,应用该模型结合算例对该模型进行了试算,证明了模型的合理性。 相似文献
995.
Alex Potapov Jim R. Muirhead Subhash R. Lele Mark A. Lewis 《Ecological modelling》2011,222(4):964-972
Freshwater aquatic systems in North America are being invaded by many different species, ranging from fish, mollusks, cladocerans to various bacteria and viruses. These invasions have serious ecological and economic impacts. Human activities such as recreational boating are an important pathway for dispersal. Gravity models are used to quantify the dispersal effect of human activity. Gravity models currently used in ecology are deterministic. This paper proposes the use of stochastic gravity models in ecology, which provides new capabilities both in model building and in potential model applications. These models allow us to use standard statistical inference tools such as maximum likelihood estimation and model selection based on information criteria. To facilitate prediction, we use only those covariates that are easily available from common data sources and can be forecasted in future. This is important for forecasting the spread of invasive species in geographical and temporal domain. The proposed model is portable, that is it can be used for estimating relative boater traffic and hence relative propagule pressure for the lakes not covered by current boater surveys. This makes our results broadly applicable to various invasion prediction and management models. 相似文献
996.
在回顾环境功能材料研究进展的基础上,将材料按功效分为固化/稳定化材料、氧化还原剂类材料以及催化剂类材料,重点对固化/稳定化材料进行了介绍。根据环境材料科学的发展前沿提出了污染场地环境修复功能材料的发展趋势,并总结了功能材料开发与应用中的一些问题。 相似文献
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998.
随着核工业的发展,含铀放射性废水的产生量越来越大,必须进行妥善处理与处置.微藻吸附技术是近年来放射性废水处理领域的研究热点,而获得吸附铀的优势藻种则是该技术得以研究和应用的基础.从工程应用的角度出发确定了筛选原则,并针对11株备选藻种进行了优势藻种筛选工作.栅藻LX1对铀的吸附容量最大,为40.7 mg·g~(-1);在m BG11培养基(模拟城镇污水处理厂污染物排放一级A标准的氮磷浓度限值)中的生物质产量较高,为0.32 g·L~(-1);生长进入稳定期后的沉降性能较好,沉降率为45.3%.综上,在本研究范围内,栅藻LX1为放射性废水处理中吸附铀的优势藻种. 相似文献
999.
为优化低温等离子体反应器设计、提高NO分解率,在低放电电压下通过改变介质阻挡放电参数(放电电压、介质材料、放电间隙等)考察其对分解NO的影响.研究结果表明:在低电压范围条件下(≤6.5 kV),放电电压对提高NO分解率的效果是非线性的,其影响随电压的升高而减弱;选择介电常数较大的介质材料更易获得较高的分解率;当反应器其它特征参数确定后,放电间隙并非越小越好,而是存在一个最佳值;实际应用中,应选用二次电子发射系数较大的电极材料;NTP反应器中加入填充材料不仅具有吸附和存储性能,还具有介质阻挡放电的功能,选择适合的填充材料能更大程度地提高能量利用率,提高NO分解率. 相似文献
1000.
In anarchistic honey-bee colonies, many workers’ sons are reared despite the presence of the queen. Worker-laid eggs are normally
eaten by other workers in queenright colonies. Workers are thought to discriminate between queen-laid and worker-laid eggs
by the presence or absence of a queen-produced egg-marking pheromone. This study compared the survival of three classes of
eggs (worker-laid eggs from anarchistic colonies, worker-laid eggs from non-anarchistic queenless colonies, and queen-laid
eggs) in both queenright normal colonies and queenright anarchistic colonies, in order to test the hypothesis that anarchistic
workers evade policing by laying more acceptable eggs. As expected, few worker-laid eggs from non-anarchistic colonies survived
more than 2 h. In contrast, worker-laid eggs from anarchistic colonies had much greater acceptability, which in some trials
equalled the acceptability of queen-laid eggs. Anarchistic colonies were generally less discriminatory than normal queenright
colonies towards worker-laid eggs, whether these originated from anarchistic colonies or normal queenless colonies. This indicates
that the egg-removal aspect of the anarchistic syndrome involves both worker laying of eggs with greater acceptability and
reduced discriminatory behaviour of policing workers.
Received: 19 July 1999 / Received in revised form: 3 November 1999 / Accepted: 20 November 1999 相似文献