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531.
Recent evidence indicates that acid rain is a growing environmental phenomenon of potentially far reaching consequences and increasing geographical extent in North America. Acid rain is but one aspect of the broader problem of atmospheric deposition which includes snow, fog, and dry deposition of material. First noticed and studied in the Scandinavian countries, acid precipitation has now been well documented in the United States, first in the northeast and more recently throughout much of the United States east of the Mississippi River. Numerous streams and lakes in regions with poorly buffered soils have become devoid of fish, have an impoverished aquatic flora and fauna, and are changing toward conditions of low aquatic productivity. Evidence also indicates that acid precipitation may cause damage to forest growth, crop production, wildlife, and man-made materials such as buildings, metals, paints, and statuary. 相似文献
532.
A simplistic aggregate model of global economic activity supports a 50-year visioning exercise with targets defined in terms of aggregate measures of global equity (convergence) and sustainability (contraction). Some ambitious combinations of these targets turn out to be infeasible even under the most favorable modeling assumptions. No contraction target (no reduction in fossil fuel consumption relative to the present) was possible, for example, if international capital transfers pushed per capita incomes in low-income countries above 33% of levels achieved in high-income countries. Lower prices for renewable alternatives to exhaustible resources generally made sustainability targets easier to achieve, but lower prices for renewable resources also made equity targets more difficult to achieve. Improved substitution between capital and labor made equity targets easier to achieve in relative terms, but improved substitution between capital and labor could make any given sustainability target more or less difficult to achieve. All the results suggest that it is possible to overstate the purported conflict between achieving sustainability and equity targets. The very transfers of international capital that would promote relative equity between high-income and low-income countries could also work to spread the incidence of achieving any sustainability target more evenly across their boundaries. 相似文献
533.
Gary D. Lynne 《Journal of the American Water Resources Association》1977,13(1):93-107
ABSTRACT: Society has many objectives, many of which are not commensurable. This incommensurability problem is generally referred to as the multiple objective problem and leads to the notion of tradeoffs. Various approaches to calculating tradeoffs in water resource development have been advocated by several authors. Many have made errors in the context of the conceptural model presented in this paper. It is argued the correct framework for tradeoff analysis is the neoclassical economic model. The relevant tradeoffs, then, are really price ratios. These, in turn, must be calculated in such a manner as to allow comparison of product mixes where the expenditure on resources is the same. This is where several authors have erred. An empirical example which illustrates the correct application of the model is presented. 相似文献
534.
Gary A. Campbell 《Resources Policy》1990,16(4)
The purpose of this article is to analyse the use of diversification and market specialization as corporate strategies by non-ferrous metal company managements as responses to adverse financial conditions. The analytical framework is provided by the financial theory of risk. Managements must deal with both company specific risk and market risk as they attempt to improve the profitability of their companies. Companies from the US copper industry are used as empirical examples. Deversification is a flexible but risky strategy. Specialization is a more restrictive strategy but it is less risky. The appropriate strategy to use depends on the particular situation of a company. 相似文献
535.
Translocations and the Preservation of Allelic Diversity 总被引:3,自引:0,他引:3
Translocation is a tool commonly used for the conservation of threatened and endangered fish species. Despite extensive use, the biological implications of translocation remain poorly understood. Of particular interest is the effect of translocation on genetic variability. Maintenance of genetic variability in these "refuge" populations is assumed to be important for both short- and long-term success. We examined allozyme variability at 16 loci for western mosquitofish ( Gambusia affinis ) populations with known histories of introduction. Refuge populations had significantly lower levels of heterozygosity. Refuge populations also had considerably lower levels of allelic diversity than parental populations. All losses were of relatively rare alleles (frequency less than 0.1 in parental population). These losses were probably due to an undocumented bottleneck early in the introduction history. These results were surprising because the initial transplant involved 900 fish and because mosquitofish have numerous reproductive traits that should minimize the effects of bottlenecks on genetic diversity. A literature review revealed that genetic variability is often reduced in refuge populations and that such reductions typically involve the loss of alleles. We suggest that translocated populations be examined periodically for losses of genetic variability. 相似文献
536.
A Decision-Support System for Prioritizing Restoration Sites on the Mississippi River Alluvial Plain 总被引:4,自引:0,他引:4
Daniel W. Llewellyn Gary P. Shaffer Nancy Jo Craig Lisa Creasman David Pashley Mark Swan Cindy Brown 《Conservation biology》1996,10(5):1446-1455
Conversion of forested wetlands to agricultural use and the resulting fragmentation of the landscape has led to concerns for the functional integrity of the Mississippi River Alluvial Plain ecosystem. We describe an effort spearheaded by The Nature Conservancy to initiate a multi-decade partnership dedicated to creating and implementing a viable, cooperative, landscape-level restoration project in the Mississippi River Alluvial Plain. Important phases of the process during the first 5 years were (1) initiation of the development of an extensive network of partners, including state and federal agencies, private land owners, conservation groups, academicians, and other interested citizens; (2) development of a geographic information system (GIS) for the entire extent of the ecosystem; and (3) for one watershed, the Tensas basin in northeastern Louisiana, refinement of a high resolution GIS to generate more detailed land-use conversion statistics to demonstrate the feasibility of a semi-objective, landscape-scale restoration planning procedure, including methodology for prioritization of existing wetland forest patches and areas most suitable for reforestation and connection via corridors. 相似文献
537.
Gary W. Evans Stephen V. Jacobs Neal B. Frager 《Journal of environmental psychology》1982,2(2):99-108
This study examines human adaptation to air pollution by comparing responses to photochemical smog of long-term residents and recent residents of the Los Angeles air basin. Long-term residents in comparison to recent migrants use a higher response criterion to identify smog in a visual signal detection task. There is no difference in visual sensitivity between the two residential groups in detecting the presence of air pollution in photographic slides. Thus for low levels of visual air pollution, both long-term residents of Los Angeles and new migrants are equally accurate in detecting the presence of smog. Long-term residents, however, are less likely to decide that smog is present in a scene. This response bias is interpreted in terms of adaptation level theory. Characteristics of the response bias differences between the two residential groups are examined in detail using signal detection procedures. 相似文献
538.
539.
Flood control failure: San Lorenzo River,California 总被引:2,自引:0,他引:2
The San Lorenzo River on the central California coast was the site of a major US Army Corps of Engineers flood control project in 1959. By excavating the channel below its natural grade and constructing levees, the capacity of the river was increased in order to contain approximately the 100 year flood. Production and transport of large volumes of sediment from the river's urbanizing watershed has filled the flood control project with sand and silt. The natural gradient has been re-established, and flood protection has been reduced to containment of perhaps the 30 year flood. In order for the City of Santa Cruz, which is situated on the flood plain, to be protected from future flooding,it must either initiate an expensive annual dredging program, or replan and rebuild the inadequately designed flood control channel. It has become clear, here and elsewhere, that the problem of flooding cannot simply be resolved by engineering. Large flood control projects provide a false sense of security and commonly produce unexpected channel changes. 相似文献
540.
In groundwater systems, dissolved natural organic matter (NOM) can influence the mobility of organic contaminants by altering the contaminant behavior in water and solid phases. The transport of anthracene and benz(a)anthracene (B(a)A) was studied in the presence and absence of NOM and/or soil organic matter (SOM) in column experiments. The results show that sorption are related to the properties of polycyclic aromatic hydrocarbons (PAHs), NOM and SOM. In the Fe-quartz media, the amount of NOM (20 mg/l) in solution had a little effect on increasing the apparent solubility of anthracene and countering increased anthracene sorption. In the natural (Bemidji) soil, Suwannee river fulvic acid (SRFA, 20 mg/l) and Suwannee river humic acid (SRHA) in water did not compete with SOM for anthracene, indicating that SOM has higher partition efficiency for anthracene. It was also observed that slow diffusion through an organic phase apparently caused most of the observed tailing in column breakthrough curves (BTCs). Even though the fOC of washed Bemidji sediment was very low, the transport of B(a)A was retarded significantly, however, and the transport of B(a)A was shown to be facilitated by dissolved NOM. 相似文献