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831.
Bayessa D. Letta Louis E. Attah 《Journal of environmental science and health. Part. B》2013,48(1):23-32
Residue levels of organochlorine pesticides (OCP) in a total of 90 cattle samples comprising meat, liver and kidney collected from carcasses slaughtered in six towns in West Shoa Zone, Ethiopia, (Ambo, Guder, Ginchi, Gedo, Holeta and Tikur Inchini), have been determined. The pesticides were extracted by solid phase extraction (SPE) and quantification was carried out using gas chromatography-mass spectrometry (GC-MS). A good linearity (r2 > 0.998) was found in the range 0.001–7.00 mg/kg for the samples studied. Most of the pesticides had recoveries in the range 81–99% and values of relative standard deviation (RSD) <7.2% for repeatability and reproducibility, showing good accuracy and precision of the method. The concentration level of the studied organochlorines followed the order: p, p’ dichloro-diphenyl-trichloroethane (DDT) > endosulfan>o,p′-DDT >lindane>dieldrin>endrin>aldrin>chlorothanolin while the order of contamination in the analyzed organs was liver > kidney > meat. Heat treatment of the meat, kidney and liver samples (boiling for 90 min.) produced an overall reduction of 62.2%, 44.5%, 37.7%, 29%, 31%, 34.3% and 30.8% in lindane, o, p′-DDT, endosulfan, p, p′-DDT, chlorothanolin, aldrin, dieldrin, and endrin, respectively. Although the residual contents of the organochlorines detected in all the contaminated samples analyzed from the six cities were below the respective maximal permissible levels set by international organizations, samples from Holeta town were more contaminated and may necessitate effective monitoring as bioaccumulation of these residues may pose health problems in human beings. 相似文献
832.
Saeed Khorram Mustafa Ergil 《Journal of the American Water Resources Association》2010,46(6):1065-1090
Khorram, Saeed and Mustafa Ergil, 2010. Most Influential Parameters for the Bed-Load Sediment Flux Equations Used in Alluvial Rivers. Journal of the American Water Resources Association (JAWRA): 46(6):1065–1090. DOI: 10.1111/j.1752-1688.2010.00468.x Abstract: Problems of bed-load sediment transport equations in alluvial rivers are addressed in this study where user-friendly parameters were developed. To determine the influences of 300 parameters on the final result, 52 selected bed-load equations for noncohesive particles (sand and gravel separately) were gathered and individually investigated. The influences of discrepancies among the computed and measured datasets were obtained by sensitivity analysis through multilinear regression method. The most influential parameters for the bed-load sediment flux equations used to describe sand particles in alluvial rivers are: the gravitational power due to Shields’ parameter with an energy slope, the universal stream power due to critical Shields’ parameter with an energy slope, the Shields’ parameter ratio, the critical unit stream power, and the Shields’ parameter with energy slope. For gravel particles, the most influential parameters are: the universal stream power due to critical Shields’ parameter with an energy slope, the Shields’ parameter ratio, the gravitational power due to Shields’ parameter with an energy slope, the Shields’ parameter with an energy slope, and the Froude number of the channel. It is expected that researchers working in this field will be able to use these predicted parameters to generate new bed-load sediment flux equations that give results that more closely agree with the actual values measured in alluvial rivers. 相似文献
833.
Wesely M. L. Song J. Mcmillen R. T. Meyers T. P. 《Water, Air, & Soil Pollution: Focus》2001,1(5-6):5-15
The parameterized subgrid-scale surface flux (PASS) modelprovides a simplified means of using remote sensing data from satellites and limited surface meteorological information to estimate the influence of soil moisture on bulk canopy stomatalresistances to the uptake of gases over extended areas.PASS-generated estimates of bulk canopy stomatal resistance were usedin a dry deposition module to compute gas deposition velocitieswith a horizontal resolution of 200 m for approximately 5000 km2 of agricultural crops and rangeland. Results were compared with measurements of O3 flux and concentrations made during April and May 1997 at two surface stations and from an aircraft. The trend in simulated O3 deposition velocityduring soil moisture drydown over a period of a few days matchedthe trend observed at the two surface stations. For areas underthe aircraft flight paths, the variability in simulated O3 deposition velocity was substantially smaller than the observedvariability, while the averages over tens of kilometers were usually in agreement within 0.1 cm s-1. Model results indicated that soil moisture can have a major role in depositionof O3 and other substances strongly affected by canopy stomatal resistance. 相似文献
834.
The results of field studies that measured the flux anddeposition velocity of SO2 and O3 are reported. Three of the studies were over agricultural crops (pasture, corn, and soybean), and two were over forest (a deciduous forest and a mixed coniferous–deciduous forest). In all cases the deposition velocity for SO2 was higher than that for O3. Diurnal cycles of SO2 deposition velocity were similar in shape, but not magnitude for all surfaces; however those for O3 showed some difference between forest sites where the peak was in the morning, and the agricultural sites where the peak occurred at mid-day. Seasonal cycles of SO2 were affected by deposition to surfaces when leaves were not active, yet surface conductance is significant, but not for O3 where stomatal uptake is the primary pathway for deposition.(On assignment to the National Exposure Research Lab., US EPA) (e-mail: 相似文献
835.
黄土丘陵小流域沟坡水热条件及其生态修复初探 总被引:8,自引:1,他引:7
在黄土丘陵沟壑区,沟坡是小流域尺度上水土流失最为活跃的部分,对其水热条件的了解是进行综合治理的基础。论文以黄土丘陵区甘肃定西安家沟小流域为例,观测了沟坡不同地形部位和植被类型土壤水分季节动态和剖面变化特征,同时观测了光照、大气湿度、温度和风速等小气候条件,并探讨了沟坡生态修复方式。结论与建议如下。①历次取样中,0~100cm平均土壤水分均以沟道灌木林地最高,沟坡中的阳坡和阴坡的草地和灌木林地次之,梁峁坡农地最低,且6种类型样地间有显著差异(P<0.01);对于相同的植被类型来说,阳坡的林草植被土壤水分均要小于阴坡,但没有显著差异(P>0.05);而在同一坡向,草地的土壤水分要显著高于灌木林地(P<0.01);和梁峁坡农地的土壤水分季节变化特征相比,沟坡植被土壤水分的季节变化不明显。②对于梁峁坡农地和阴坡的灌木林地来说,土壤水分在剖面内随着深度变化平缓,而其它4种类型样地土壤水分在剖面内随着深度呈增加的趋势。对于这6种类型样地,土壤水分剖面差异格局与0~100cm平均含水量相似;且随着深度的增加,6种类型样地间土壤水分的差异性增大。③对于梁峁坡和沟坡来说,4~5月份风速均是观测期内最大的,但沟坡风速要小于梁峁坡坡面;在观测期内,高湿期出现在5月,且沟坡大气相对湿度高于梁峁坡;和 相似文献
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840.
放牧对草原土壤N2O产生及微生物的影响 总被引:9,自引:1,他引:8
利用AIM乙炔抑制法,首次测试了我国内蒙古放牧和非放牧羊草草原土壤N2O产生的微生物过程;通过分析不同类型草原土壤N2O产生的微生物过程和相关微生物菌群的季节变化,研究了放牧行为对于草原土壤N2O微生物产生过程的影响.放牧行为改变了土壤结构,有利于土壤微生物反硝化作用的发生,在一定程度上降低了草原土壤N2O的排放.揭示了内蒙古草原土壤N2O产生是以异养硝化作用过程为主的微生物过程,解释了内蒙古典型草原土壤N2O通量较低和其季节变化的微生物学机理. 相似文献