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51.
David J. Wilson Robert D. Mutch Jr. Joanna I. Scott 《Environmental monitoring and assessment》1993,26(1):49-64
Simple mathematical models are developed to account for the rather slow mass transport of nonaqueous phase liquid (NAPL) into aqueous solution in groundwater during flushing operations. The models are based on the assumption that this bottleneck in the process is associated with diffusion in the aqueous phase in the porous medium from the location of the NAPL drops/ganglia in a region of relatively low permeability out into a region of substantially higher permeability, somewhat analogous to diffusion from a block of porous rock into a nearby fracture, where the fracture system overwhelmingly dominates the overall permeability. The models include batch flushing, flushing in a laboratory column, and a one-dimensional model for flushing by means of a single recovery well. 相似文献
52.
Jesse?Rush?O’HanleyEmail author David?Tomberlin 《Environmental Modeling and Assessment》2005,10(2):85-98
Removing small artificial barriers that hinder upstream migrations of fish is a major problem in riparian habitat restoration. Because of budgetary limitations, it is necessary to prioritize barrier removal and repair decisions. These have usually been based on scoring and ranking procedures, which, although simple to use, can be very inefficient in terms of increasing the amount of accessible instream habitat. We develop a novel decision-making approach, based on integer programming techniques, which optimizes repair and removal decisions. Results show based on real datasets of barrier culverts located in Washington State that scoring and ranking is over 25% below the optimum on average and a full 100% below in the worst case, producing no net habitat gain whatsoever. This is compared to a dynamic programming method that was able to find optimal solutions in less than a second, even for problems with up to several hundred variables, and a heuristic method, which found solutions with less than a 1% average optimality gap in even less time. 相似文献
53.
David J. Wilson 《Environmental monitoring and assessment》1982,2(3):309-330
The partial differential equations governing the migration of adsorbable pollutants undergoing 2-dimensional flow in saturated aquifers are presented. The analytical solution of these equations is rarely possible, and the use of mesh or grid techniques for numerical integration leads to so-called numerical dispersion, excessive dispersion which is an artifact associated with the numerical method. We discuss here the use of conformal mapping techniques to develop coordinate systems in which numerical dispersion transverse to the direction of flow is eliminated. Some simple illustrations are presented. 相似文献
54.
Gary H. Heinz David S. Miller Brian J. Ebert Kenneth L. Stromborg 《Environmental monitoring and assessment》1994,33(3):175-182
From 1977–1978 to 1990, concentrations of polychlorinated biphenyls (PCBs) and most organochlorine pesticides declined in eggs of red-breasted mergansers (Mergus serrator) nesting on islands in northwestern Lake Michigan. Total PCBs decreased 60% (from 21 ppm in 1977–1978 to 8.5 ppm in 1990) and p,p-DDE decreased 66% (from 6.5 to 2.2 ppm). Dieldrin decreased only 16% (from 0.82 to 0.69 ppm). In 1990, 79.1% of incubated eggs hatched, which was not significantly different from the 83.5% that hatched in 1977–1978.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
55.
David L.Findlay 《Ambio-人类环境杂志》2003,32(3):190-195
人们普遍推测控制SO2排放可以促进加拿大、美国和欧洲的酸化淡水湖泊的恢复.本文研究了1998~2000年间靠近安大略省基拉尼公园的22个湖泊(pH值范围4.5~7.7)的浮游生物群落变化,将结果与安大略省西北的实验湖泊区(ELA)人工酸化(pH值从6.7降至4.5)又恢复(pH升至6.0)的南302号湖的数据进行了对比,以评价酸化后的恢复效果.根据历史记录,基拉尼地区数个湖泊的pH值由先前酸化的5.0~5.5反弹到6.0.浮游生物量与pH不相关,但其物种的丰富度与pH值间呈显著相关.将所得到的物种多样性数据与历史数据加以组合,可观察到其中6个湖泊中的恢复轨迹.相关分析表明:pH值得到提高后,其中几个湖泊的浮游生物群落开始向中性环境中的典型群落转化. 相似文献
56.
气候确实在发生变化。以往人们随意地认为这与温室效应气体排放量的增加有关,现在这种观点已得到充分证实。自1991年以来.已出现了自有记录以来全球气温最高的十个年份.而在上个世纪,温度上升7约0.6摄氏度。在同一期间内,全球的海平面上升了约20厘米.部分原因是陆地上冰层融化.海洋自身发生热膨胀。许多山峰上的冰盖正在消失.最近几十年来,夏秋季节北冰洋的冰层厚 相似文献
57.
The density of red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), necessary to limit boll weevil abundance, Anthonomus grandis Boheman (Coleoptera: Curculionidae), below the action level was determined. An inaction level of 0.4 fire ants per shake bucket sample (i.e., four ants per 10 plant terminals) will provide boll weevil control approximately 90% of the time. A dynamic inaction level is also provided. Total mortality of boll weevil developmental stages including eggs through teneral adults averaged 97.9%. Of 100 boll weevil eggs deposited in cotton squares (flower buds), an average of two adults survive of which about half are female. Thus, the net replacement rate per generation (Ro is 1.0 which, in this case, indicates a stable boll weevil population. 相似文献
58.
The economics of climate change in agriculture 总被引:1,自引:0,他引:1
Zilberman David Liu Xuemei Roland-Holst David Sunding David 《Mitigation and Adaptation Strategies for Global Change》2004,9(4):365-382
This paper presents a conceptual frameworkof the impact of climate change onagriculture. It assumes that climatechange will result in a fertilizationeffect and a shift of agro-ecologicalconditions away from the Equator towardsthe Poles. The agro-ecological shift islikely to reduce yield because of reducedacreage and the fertilization effect willincrease yield. The aggregate effectdepends on whichever of the two dominates. The overall effect of climate change may beless significant than its distributionaleffects and the results are consistentwith previous empirical studies. Theimpact of climate change depends on itspace. Faster changes in climate willresult in higher cost. The assessment ofthe cost has to consider that climatechange is a dynamic phenomenon that mayrequire continuous adjustment. Environmental regulation that emphasizesconservation may increase cost ofadjustment and environmental policiesshould emphasize adaptation andflexibility. 相似文献
59.
Linda?Anderson-BerryEmail author David?King 《Mitigation and Adaptation Strategies for Global Change》2005,10(3):367-392
Community mitigation of hazard impact requires hazard knowledge and preparedness on the part of the members of diverse and
complex communities. Longitudinal research in the tropical cyclone prone north of Australia has gathered extensive datasets
on community awareness, preparedness and knowledge, in order to contribute to education campaigns and mitigation strategies.
Data have been used to identify issues of vulnerability to cyclones and capacity to deal with the hazard. This has been developed
as a community vulnerability and capacity model that may be applied to diverse communities in order to assess levels of capability
to mitigate and deal with the cyclone hazard. The model is presented here in a simplified form as its development is evolving
and ongoing. 相似文献
60.
Maguelone G. Forest Hervé Bétuel Philippe Couillin André Boué Michel David Daniel Floret René Francois Pierre Guibaud Henri Plauchu Raphaël Rappaport 《黑龙江环境通报》1981,1(3):197-207
Amniotic fluid (AF) levels of 17-hydroxyprogesterone (17OHP) and testosterone (T) were determined at 16–17 weeks in 17 pregnancies at risk for CAH and results compared to 75 normal controls. The fetus was predicted to be unaffected in 12 cases on the findings of normal AF levels of both 17OHP and T and the latter allowed a correct prediction of fetal sex in all instances. HLA typing confirmed normality in 12 cases revealing 5 carriers, 5 homozygous normal and 2 indeterminate. Steroid levels of the 2 groups were similar. Three fetuses were predicted to be CAH affected on unambiguously high levels of 17OHP and T (in female only). HLA typing was in agreement, and the diagnosis was confirmed in 2 abortuses and a female newborn by physical and hormonal studies. In the last 2 cases AF levels of OHP and T were normal but HLA (A/B/C) genotypes were identical to the CAH affected siblings. Normal physical and hormonal findings in the 2 aborted fetuses would exclude the possibility of an in utero virilizing form of CAH. The discrepancy could be explained on the basis that the fetuses had an allelic form of 21-hydroxylase deficiency or on the basis of recombination (not fully tested). It is concluded that a fully informative prenatal diagnosis of CAH should not rely entirely on HLA typing but on hormonal studies. 相似文献