共查询到20条相似文献,搜索用时 437 毫秒
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《四川环境》2021,(4)
采用3-D计算流体力学(CFD)技术模拟不同温度层结下城市街区内气流与污染物扩散规律,并与Uehara K等人风洞试验结果进行对比分析,应用Pontiggia M.等人基于Monin-Obukhov (M-O)理论添加外部源相方法对RNG k-ε模型k方程与ε方程进行修正,建立数值风洞模拟技术,结果表明,不同温度层结下,街区中下部速度非常低,为来流的1.5%左右,街区内部均形成一个稳定的涡,涡的强度受温度层结影响较明显,稳定层结下,街区内涡流较弱,不同温度层结下k/U2700最大值均出现在街区建筑物迎风角附近,较高归一化k/U2700出现在不稳定层结下。不同温度层结下街区内背风侧墙上污染物的浓度均大于与迎风侧墙浓度,较高归一化污染物浓度均出现在污染源的上风向。由于稳定层结抑制了垂直方向上气流的运动,近地面稳定层结归一化浓度值最大,而不稳定层结归一化浓度值最小。总之,温度层结对街区内流场结构与污染物扩散能力影响较为显著,不同温度层结下,由于街区内部与环境大气温度存在温度差,影响了街区内流场结构与湍流特征,从而影响了街区内污染物的扩散特征。 相似文献
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在对气田废水处理中产生的污泥进行处理时,普遍存在着干化周期长、含水率高等问题,严重影响了废水处理装置的处理能力。脱水剂优化选择实验以及污泥脱水性能实验结果表明:先加入聚合氯化铝并搅拌15 s,再加入阴离子聚丙烯酰胺并搅拌混合30 s,最后加入FO4190SH搅拌,混合凝聚30 s后静止分层,其凝聚效果较好。在污泥脱水性能的各项指标中,真空脱水均好于重力脱水,特别是对于新鲜污泥滤层,真空(45 kPa)脱水速度比重力脱水速度约高8倍。 相似文献
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吴姗姗 《环境保护与循环经济》2023,(5):59-63
河口是具有高生产力与多样性的水陆物质交换区域。受小流域环境的影响,不同入湖河口的地貌与水文特征差异显著,致使河口种类繁多。从自然地理与水动力两方面独立分析了影响入湖河口形态及冲淤变化的主要因素,分别以此为基础划分河口类型。根据水动力分类指标,得出环太湖河口的6种基本类型。针对不同的环境压力,预测入湖河口形态受人类活动影响的演变趋势,为建设入湖河口管理区与生态修复模式提供思路。 相似文献
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从系统整体出发,基于既有建筑节能改造市场发展研究全面规划视角,架构了总括、ESCO驱动力作用机理、政府作用力实施机理、总结四大模块、两大篇共10章的层次体系。结果发现:ESCO驱动力以作用效益为导向,以运行实践与行为规律、作用影响机理、ESCO驱动策略、效益评价与优化策略为核心要素,是内在动力;政府作用力以有效性为基准,以运行特征与政府行为、影响机理与博弈策略、实施影响机理与有效性评价、实施策略为核心要素,是外在动力。在揭示既有建筑节能改造市场动力机制的基础上,提出未来研究发展趋势。 相似文献
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本研究面向循环经济企业、园区、政府和相关社会公众,以实现循环经济发展模式的小循环、中循环和社会大循环的融合为最终目标,以构建信息服务协同管理平台为主要途径,重点分析了平台建设的四方面必要性和三方面可行性。在此基础上,设计了平台的功能定位和体系架构。平台功能包括活动数据采集、活动数据不确定性分析与校准、企业绿色投入产出分析、循环经济效率指标评价、物质流与能量流可视化分析、园区循环经济协同度分析、宏观物质流分析和循环经济公共信息服务,平台的体系架构由交互层、逻辑层和数据层组成。 相似文献
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Hobbs R 《Journal of environmental management》2009,90(9):2857-2865
In the latter half of the 20th century, native pine woodlands in Scotland were restricted to small remnant areas within which there was little regeneration. These woodlands are important from a conservation perspective and are habitat for numerous species of conservation concern. Recent developments have seen a large increase in interest in woodland restoration and a dramatic increase in regeneration and woodland spread. The proximate factor enabling this regeneration is a reduction in grazing pressure from sheep and, particularly, deer. However, this has only been possible as a result of a complex interplay between ecological, political and socio-economic factors. We are currently seeing the decline of land management practices instituted 150-200 years ago, changes in land ownership patterns, cultural revival, and changes in societal perceptions of the Scottish landscape. These all feed into the current move to return large areas of the Scottish Highlands to tree cover. I emphasize the need to consider restoration in a multidisciplinary framework which accounts not just for the ecology involved but also the historical and cultural context. 相似文献
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P. A. Glancy A. S. Van Denburgh S. M. Born 《Journal of the American Water Resources Association》1972,8(6):1157-1172
The Truckee River heads in the Sierra Nevada at Lake Tahoe, and terminates in Pyramid Lake. During the 1969 water year, flow about 9 miles upstream from the mouth (974,000 acre-ft) was almost four times the long-term average, due mainly to heavy winter rains and spring snowmelt. A short period of low-altitude rainfall produced the highest concentrations of suspended sediment, whereas a much longer subsequent period of snowmelt yielded a much greater total quantity of material. The upper 90 percent of the basin yielded about 260 acre-feet (630,000 tons) of sediment at the Nixon gage, whereas an estimated 2,800 acre-feet (6.8 million tons) was contributed by erosion of about 200 acres of river bank below the gage. Solute content at the gage ranged from 80 to 450 mg/l, dominated by calcium, sodium, and bicarbonate, plus silica in the most dilute snowmelt and chloride in the most concentrated low flows. Solute load totaled about 130,000 tons, of which the principal constituents in Pyramid Lake-sodium plus equivalent bicarbonate and chloride-amounted to almost 40,000 tons. The total solute load during a year of average flow may be 45,000-55,000 tons, including 18,000-22,000 tons of principal lake constituents. 相似文献
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Victor W. Lambou Stephen C. Hern William D. Taylor Llewellyn R. Williams 《Journal of the American Water Resources Association》1982,18(5):807-813
ABSTRACT: The relationship between chlorophyll u, total phosphorus, secchi disk depth, and trophic state were examined using data on U.S. lakes collected by U.S. EPA's National Eutrophication Survey. By comparing predicted secchi disk depths with observed summer secchi disk depths in 757 lakes, it was determined that in many lakes non-chlorophyll related light attenuation is important in controlling the amount of chlorophyll u produced per unit of total phosphorus. Ranking of 44 lakes by 18 different trophic state measurements and single and multivariable indices were compared with rankings provided by mean summer ambient total phosphorus and chlorophyll u. The trophic state measurements and indices were much more successful in ranking the lakes against total phosphorus than chlorophyll u, indicating that there are differences in the relative trophic rankings of many of the lakes depending upon whether primary nutrients or biological manifestations are used as the ranking mechanism. If the manifestations of nutrients rather than their absolute levels are the primary criteria for beneficial use of lakes, the use of many of the commonly employed trophic state measurements, which assume or imply that there is a constant relationship between total phosphorus or secchi disk and chlorophyll, can lead to erroneous conclusions and unnecessary costly management controls. Secchi disk measurements may be more useful as a predictor of ambient lake total phosphorus concentrations than of chlorophyll. 相似文献
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Iron oxides are important components influencing the adsorption of various inorganic and organic compounds in soils and sediments. In this study the adsorption on iron oxides of nonionic and ionic pesticides was determined as a function of solution pH, ionic strength, and pesticide concentration. The investigated iron oxides included two-line ferrihydrite, goethite, and lepidocrocite. Selected pesticides comprised atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea)], mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propionic acid], 2,4-D (2,4-dichlorophenoxyacetic acid), and bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. The adsorption of the nonionic pesticides (atrazine and isoproturon) was insignificant, whereas the adsorption of the acidic pesticides (mecoprop, 2,4-D, and bentazone) was significant on all investigated iron oxides. The adsorption capacity increased with decreasing pH, with maximum adsorption reached close to the pKa values. The addition of CaCl2 in concentrations from 0.0025 to 0.01 M caused the adsorption capacity to diminish. The adsorption of bentazone was significantly lower than the adsorption of mecoprop and 2,4-D, illustrating the importance of a carboxyl group in the pesticide structure. The adsorption capacity on the iron oxides increased in the order: lepidocrocite < goethite < two-line ferrihydrite. The maximum adsorption capacities of meco-prop and 2,4-D on goethite were found to be equivalent to the site density of singly coordinated hydroxyl groups on the faces of the dominant (110) form, suggesting that singly coordinated hydroxyl groups are responsible for adsorption. Differences in adsorption capacities between iron oxides can be explained by differences in the surface site density of singly coordinated hydroxyl groups. The maximum measured adsorption capacity of mecoprop on two-line ferrihydrite was equivalent to 0.2 mol/mol Fe. 相似文献
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Tillage, intercrop, and controlled drainage-subirrigation influence atrazine, metribuzin, and metolachlor loss 总被引:2,自引:0,他引:2
Gaynor JD Tan CS Drury CF Ng HY Welacky TW van Wesenbeeck IJ 《Journal of environmental quality》2001,30(2):561-572
Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] have been found with increasing occurrence in rivers and streams. Their continued use will require changes in agricultural practices. We compared water quality from four crop-tillage treatments: (i) conventional moldboard plow (MB), (ii) MB with ryegrass (Lolium multiflorum Lam.) intercrop (IC), (iii) soil saver (SS), and (iv) SS + IC; and two drainage control treatments, drained (D) and controlled drainage-subirrigation (CDS). Atrazine (1.1 kg a.i. ha-1), metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazine-5(4H)-one] (0.5 kg a.i. ha-1), and metolachlor (1.68 kg a.i. ha-1) were applied preemergence in a band over seeded corn (Zea mays L.) rows. Herbicide concentration and losses were monitored from 1992 to spring 1995. Annual herbicide losses ranged from < 0.3 to 2.7% of application. Crop-tillage treatment influenced herbicide loss in 1992 but not in 1993 or 1994, whereas CDS affected partitioning of losses in most years. In 1992, SS + IC reduced herbicide loss in tile drains and surface runoff by 46 to 49% compared with MB. The intercrop reduced surface runoff, which reduced herbicide transport. Controlled drainage-subirrigation increased herbicide loss in surface runoff but decreased loss through tile drainage so that total herbicide loss did not differ between drainage treatments. Desethyl atrazine [6-chloro-N-(1-methylethyl)-1,3,5-triazine-2,4-diamine] comprised 7 to 39% of the total triazine loss. 相似文献