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91.
92.
天津郊区农田降雨径流重金属的污染特征及来源分析 总被引:5,自引:0,他引:5
降雨条件下形成的农田径流是土壤与水体间物质交换的一种重要形式,是农业非点源污染的重要组成部分.2007-2008年,在强降雨条件下,定点采集了天津市郊农田降雨径流样品64个,并对其重金属含量进行了分析测定.结果显示:研究区农田降雨径流中Cr、Ni、Cd、Zn等4项重金属含量服从对数正态分布,Cu、As、Pb为偏态分布.... 相似文献
93.
Chunhong Zhao Jian'en Gao Yuefei Huang Guangqian Wang Mengjie Zhang 《Land Degradation \u0026amp; Development》2016,27(3):748-757
Vegetation plays an important role in soil erosion control, but few studies have been performed to quantify the effects of vegetation stems on hydraulics of overland flow. Laboratory flume experiments were conducted to investigate the potential effects of vegetation stems on Reynolds number, Froude number, flow velocity and hydraulic resistance of silt‐laden overland flow. Cylinders with diameter D of 2·0, 3·2 and 4·0 × 10−2 m were glued onto the flume bed to simulate the vegetation stems, and a bare slope was used as control. The flow discharge varied from 0·5 to 1·5 × 10−3 m3 s−1 and slope gradient was 9°. Results showed that Reynolds number on vegetated slope was significantly higher than that on bare slope because of the effect of vegetation stems on effective flow width. All the flows were supercritical flow, but Froude number decreased as D increased, implying a decrease in runoff ability to carry sediment. The mean flow velocity also decreased with D, while the velocity profile became steeper, and no significant differences were found in surface flow velocities among longitudinal sections on all slopes. Darcy–Weisbach friction coefficient increased with D, implying that the energy consumption of overland flow on hydraulic resistance increased. Reynolds number was not a unique predictor of hydraulic roughness on vegetated slopes. The total resistance on vegetated slopes was partitioned into grain resistance and vegetation resistance, and vegetation resistance accounted for almost 80% of the total resistance and was the dominant roughness element. Further studies are needed to extend and apply the insights obtained under controlled conditions to actual overland flow conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
94.
Amrakh I. Mamedov Benayahu Bar‐Yosef Irit Levkovich Rivka Rosenberg Avner Silber Pinchas Fine Guy J. Levy 《Land Degradation \u0026amp; Development》2016,27(6):1629-1639
Application of organic wastes to cultivated lands can replace mineral fertilizers but may also alter soil physical properties and enhance pollution potential. The objective of this study was to investigate the effects of biosolids [composted manure (MC) and activated sludge (AS)] and specific biosolid component [orthophosphate (OP), phytic acid (PA) and humic acid (HA)] application on soils differing in texture [loamy‐sand (Ramat‐HaKovesh, RH), loam (Gilat, GL) and clay (Bet‐Dagan, BD)], infiltration rate, runoff volume and soil sediment loss. The soils were packed in erosion boxes (400 × 200 × 40 mm) and subjected to six consecutive simulated rainstorms, each of 186 mm deionized water. The results showed that runoff volume and sediment loss from untreated soils increased with increasing clay contents. In treated soils, the response to AS application differed from the response to other amendments; in the BD clay and GL loam, it was the only amendment that caused a decrease in sediment removed by runoff. In the RH loamy‐sand, all amendments reduced the final infiltration rate, but only AS and HA increased the measured runoff. It is proposed that the difference in the response of the soils to the amendments is associated with the soil's ability to attenuate changes in the negative charge on the clay edges following the increase in the specific adsorption of charged anions, thus controlling clay swelling and maintaining aggregate integrity. The effects of amending soils with a source of organic matter in order to control runoff and soil erosion are not straight forward and depend on soil and amendment properties. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
95.
指出了土壤水分是影响地表径流产生重要因素之一 ,研究土壤水分在土壤中的分布、土壤水分动态变化规律以及影响土壤水分变化的因子 ,对林地的生态环境保护具有重要意义.土壤水分的分布受空间和时间的影响 ,不仅如此 ,土壤水分动态变化和分布规律还受到诸如气象因子、地形因子、地形利用因子、人为活动等因子的影响.这些影响因素都导致了土壤水分动态变化在空间和时间上的差异 ,从而导致了林地降雨-产流的差异.因此 ,深入研究影响土壤水分变化的各种因素 ,以及研究各种因素对土壤水分动态变化的作用规律 ,一方面能够为降雨-地表径流的发生规律提供参考 ,另一方面为保护林地植被生长提供了重要的条件. 相似文献
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针对树材气体渗透性与气体在管胞中的流动特性和规律紧密相关,研究管胞的气体渗透流阻,可以获得关于针叶树材气体渗透性更深入的认识。本文从针叶树材管胞解剖结构出发,运用流体力学理论,导出了管胞3个纹理方向渗透气体流阻的数学表达式,并由此计算了针叶树材管胞的气体渗透系数。计算结果表明,管胞流阻可以描述气体渗透阻力的分布情况,反映气体渗透性在3个纹理方向的差异,在木材细胞层次揭示针叶树材气体渗透性的机制。 相似文献
99.
Reproductive phenology was observed over three years in a Eucalyptus grandis seed orchard in Madagascar to determine the impact of geographic differences of parental selections on the expected genetic composition of seed crops. Pollen flow (observed pollen cloud) was deduced from a paternity assignment based on sampling from one year’s seed production. The two approaches were used to verify whether knowledge of phenology is sufficient to predict the genetic quality of the seeds collected. Despite the high flowering level, with a constant cycle over three years, the results demonstrated wide reproductive phenological differences associated with the parents’ origin, suggesting putative pollination disequilibrium. From both observed and expected pollen clouds, the results showed preferential mating among different provenances, which has consequences for seed crop composition. Phenological observations, which can be made inexpensively, can be used to promote methods of effective seed orchard management in order to improve the genetic quality of seeds. 相似文献
100.
我国鲜切花物流发展问题的探讨 总被引:7,自引:1,他引:7
鲜切花物流是指鲜切花从供应地向接受地的实体流动过程。经对我国鲜切花物流面临的问题作出分析,在借鉴其他国家和地区先进经验的基础上,结合我国的具体情况为鲜切花物流的发展提出了一些建议。 相似文献