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71.
Lynne Tolland Jaime G. Cathcart S. O. Denis Russell 《Journal of the American Water Resources Association》1998,34(4):787-794
ABSTRACT. Estimates of peak flows, with specified return periods, are needed in practice for the design of works that affect streams in forested areas. In the province of British Columbia (B.C.), Canada, the new Forest Practices Code specifies the 100-year instantaneous peak flow (Q100) for the design of bridges and culverts for stream crossings under forest roads; and many practitioners are engaged in making such estimates. The state of the art is still quite primitive, very similar to the state of urban hydrology 30 years ago, when popular estimating techniques were used with little consideration given to their applicability. Urban hydrology then evolved on a much more scientific basis, such that within about a 10-year period, standard approaches to design were developed. Forest hydrology should follow the same pattern, at least as far as estimating design flows is concerned. Popular present day design procedures include the rational method and other empirical approaches based on rainfall data, as use of the standard flood frequency approach is limited by the paucity of relevant flow data. Estimating procedures based on peak streamflow measurements and statistics are likely to evolve, and these will include distinctions for rain, snowmelt, and rain on snow floods. Guidelines will also be developed for selecting and applying appropriate procedures for particular areas. 相似文献
72.
渭河宝鸡市区段阴离子表面活性剂污染研究 总被引:2,自引:0,他引:2
本文采用改进的亚甲蓝分光光度法,对渭河宝鸡市区段阴离子表面活性剂进行监测分析。测定结果表明:渭河在进入宝鸡市至植物园断面时阴离子表面活性剂含量较低,日平均值为0.049mg/L,达到地面水环境质量I类标准(≤0.2mg/L)(GB3838-88.地面水环境质量标准);在流经市区新世纪桥、渭河桥断面时,由于分别有清姜河和金陵河两个支流的汇入,污染越来越严重.在这两个断面阴离子表面活性剂含量日平均值分别为0.34mg/L和0.54mg/L;在即将流出宝鸡市的斗鸡断面阴离子表面活性剂含量日平均值为0.424mg/L,已远远超过地面水环境质量V类标准(≤0.3mg/L)(GB3838-88,地面水环境质量标准)。从监测结果看:双休日阴离子表面活性剂含量普遍高于工作日;清姜河、金陵河污染严重,这两条支流的汇入对渭河水质影响巨大,要治理好渭河,须先治理好清姜河和金陵河这两条支流。 相似文献
73.
Cadmium accumulation and elimination in tissues of juvenile olive flounder, Paralichthys olivaceus after sub-chronic cadmium exposure 总被引:1,自引:0,他引:1
Experiments were carried out to investigate the accumulation and elimination of cadmium (Cd) in tissues (gill, intestine, kidney, liver and muscle) of juvenile olive flounder, Paralichthys olivaceus, exposed to sub-chronic concentrations (0, 10, 50, 100 microg l(-1)) of Cd. Cd exposure resulted in an increased Cd accumulation in tissues of flounder with exposure periods and concentration, and Cd accumulation in gill and liver increased linearly with the exposure time. At 20 days of Cd exposure, the order of Cd accumulation in organs was gill > intestine > liver > kidney > muscle and after 30 days of exposure, those were intestine > gill > liver > kidney > muscle. An inverse relationship was observed between the accumulation factor (AF) and the exposure level, but AF showed an increase with exposure time. During the depuration periods, Cd concentration in the gill, intestine and liver decreased immediately following the end of the exposure periods. No significant difference was found Cd in concentration in the kidney and muscle during depuration periods. The order of Cd elimination rate in organs were decreased intestine > liver > gill during depuration periods. 相似文献
74.
Low dissolved oxygen (DO) concentrations occur commonly in aerobic digesters treating thickened sludge, with benefits of smaller digester size, much reduced aeration cost, and higher digestion temperature (especially important for plants in colder areas). The effects of low DO concentrations on digestion kinetics were studied using the sludge from municipal wastewater treatment plants in Akron, Ohio, and Los Lunas, New Mexico. The experiments were conducted in both batch digestion and a mixed mode of continuous, fed-batch, and batch operations. The low DO condition was clearly advantageous in eliminating the need for pH control because of the simultaneous occurrence of nitrification and denitrification. However, when compared with fully aerobic (high DO) systems under constant pH control (rare in full-scale plants), low DO concentrations and a higher solids loading had a negative effect on the specific volatile solids (VS) digestion kinetics. Nonetheless, the overall (volumetric) digestion performance depends not only on the specific digestion kinetics, but also the solids concentration, pH, and digester temperature. All of the latter factors favor the low DO digestion of thickened sludge. The significant effect of temperature on low DO digestion was confirmed in the mixed-mode study with the Akron sludge. When compared with the well-known empirical correlation between VS reduction and the product (temperature x solids retention time), the experimental data followed the same trend, but were lower than the correlation predictions. The latter was attributed to the lower digestible VS in the Akron sludge, the slower digestion at low DO concentrations, or both. Through model simulation, the first-order decay constant (kd) was estimated as 0.004 h(-1) in the mixed-mode operations, much lower than those (0.011 to 0.029 h(-1)) obtained in batch digestion. The findings suggested that the interactions among sludges with different treatment ages may have a substantially negative effect on digestion kinetics. The use of multistage digesters, especially with small front-end reactors, may be advantageous in both "process" kinetics and "biological reaction" kinetics for sludge digestion. 相似文献
75.
76.
基于2016年3月对长江口及邻近海域的调查,剖析该海域CO2分压及相关参数的区域分布特征,估算其海-气界面CO2的交换通量,并探讨了源/汇分布特征背后的物理机制。研究表明,调查区域海表pCO2变化范围为321~575 μatm,整体呈现出近岸高、离岸低的分布趋势。至冬季末期,海表pCO2分布主要受控于低温低盐高pCO2的河口水与高温高盐低pCO2的东海陆架水的水团混合影响,水体垂直混合作用对海表pCO2影响不大。长江口及邻近海域冬季整体表现为大气CO2的弱汇,通量值为-4.43±7.41 mmol/m2/d。从区域碳汇强度看来,近岸长江冲淡水区近乎与大气保持平衡,黄东海混合水区和台湾暖流区表现为大气CO2的中/强汇,是冬季末期海洋吸收大气CO2的主要贡献区域。 相似文献
77.
Weiqing Meng Cui Hao Hongyuan Li Meiting Ju 《Frontiers of Environmental Science & Engineering in China》2010,4(2):203-212
This study presents a quantitative and ecological benefit evaluation of the Baiyangdian wetland in China between the years
2000 and 2006. Methods of EMERGY analysis were applied to illustrate the wetland ecosystem, to evaluate the economic and environmental
inputs and consequent yields, and to assess the sustainability of the Baiyangdian wetland. The indicators for the integrated
ecological and economic system, such as EMERGY yield ratio (EYR) (7.51), EMERGY investment ratio (EIR) (4.52), environmental
loading ratio (ELR) (2.92), EMERGY exchange ratio (0.41), and EMERGY sustainable indicator (ESI) (2.57) were calculated, compared,
analyzed, and discussed. The non-renewable investment in Baiyangdian was greater than renewable investment, leading to the
unsustainable development of the system. High EYR indicated that the Baiyangdian integrated system had created huge profits
for its people, while ELR and ESI revealed that human behavior has been a heavy burden on the environment, and countermeasures
should be taken by the Chinese government to relieve and resolve these problems. Potential management methods were also proposed
in this paper. 相似文献
78.
79.
80.
温度对膜生物反应器(MBR)污染物去除效果和膜污染速率都有很大的影响。采用两套相同的MBR蓑置在冬季运行,其中一套维持20℃的恒温,另一套水温与周围环境相同。对两套装置处理效果及膜污染速率进行对比,并通过反应器中溶解性微生物产物(SMF)、胞外聚合物(EPS)含量、污泥粒径分布扣膜面污染物的比较,分析温度对MBR运行的影响。研究结果表明膜对污染物的截留能有效补偿低温时微生物作用的不足,因此低温对出水水质并没有显著的影响。此外,低温时虽然SMP和EPS的释放增加,但并没有引起膜污来的加剧。相反地,低温时污泥粒径较高温时小,而粒径较大的颗粒更易沉积于膜表面,因此低温时膜面固体物质含量较低,膜污染速率反而比高温时低。 相似文献