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991.
We investigate a community of independent logistically growing populations under a common harvesting effort which leads to the total maximum sustainable yield (TMSY). It is surprising that in the case of two populations with approximately equal carrying capacities, TMSY is reached while both populations persist, although their biotic potential may differ substantially. In general, however, TMSY with a common harvesting effort implies suboptimal fishing of some populations, overfishing of others and extinction of the rest of the populations. Since extinction of populations is a rule rather than an exception and since a community of independent populations is more robust than an ecosystem with multiple trophic levels, we call for urgent retraction of all legal documents advocating MSY in ecosystems. 相似文献
992.
993.
Intelligent Databases Assist Transparent and Sound Economic Valuation of Ecosystem Services 总被引:1,自引:0,他引:1
Assessment and economic valuation of services provided by ecosystems to humans has become a crucial phase in environmental
management and policy-making. As primary valuation studies are out of the reach of many institutions, secondary valuation
or benefit transfer, where the results of previous studies are transferred to the geographical, environmental, social, and economic context of
interest, is becoming increasingly common. This has brought to light the importance of environmental valuation databases,
which provide reliable valuation data to inform secondary valuation with enough detail to enable the transfer of values across
contexts. This paper describes the role of next-generation, intelligent databases (IDBs) in assisting the activity of valuation.
Such databases employ artificial intelligence to inform the transfer of values across contexts, enforcing comparability of
values and allowing users to generate custom valuation portfolios that synthesize previous studies and provide aggregated
value estimates to use as a base for secondary valuation. After a general introduction, we introduce the Ecosystem Services
Database, the first IDB for environmental valuation to be made available to the public, describe its functionalities and the
lessons learned from its usage, and outline the remaining needs and expected future developments in the field. 相似文献
994.
Degradation of warmwater streams in agricultural landscapes is a pervasive problem, and reports of restoration effectiveness
based on monitoring data are rare. Described is the outcome of rehabilitation of two deeply incised, unstable sand-and-gravel-bed
streams. Channel networks of both watersheds were treated using standard erosion control measures, and aquatic habitats within
1-km-long reaches of each stream were further treated by addition of instream structures and planting woody vegetation on
banks (“habitat rehabilitation”). Fish and their habitats were sampled semiannually during 1–2 years before rehabilitation,
3–4 years after rehabilitation, and 10–11 years after rehabilitation. Reaches with only erosion control measures located upstream
from the habitat measure reaches and in similar streams in adjacent watersheds were sampled concurrently. Sediment concentrations
declined steeply throughout both watersheds, with means ≥40% lower during the post-rehabilitation period than before. Physical
effects of habitat rehabilitation were persistent through time, with pool habitat availability much higher in rehabilitated
reaches than elsewhere. Fish community structure responded with major shifts in relative species abundance: as pool habitats
increased after rehabilitation, small-bodied generalists and opportunists declined as certain piscivores and larger-bodied
species such as centrarchids and catostomids increased. Reaches without habitat rehabilitation were significantly shallower,
and fish populations there were similar to the rehabilitated reaches prior to treatment. These findings are applicable to
incised, warmwater streams draining agricultural watersheds similar to those we studied. Rehabilitation of warmwater stream
ecosystems is possible with current knowledge, but a major shift in stream corridor management strategies will be needed to
reverse ongoing degradation trends. Apparently, conventional channel erosion controls without instream habitat measures are
ineffective tools for ecosystem restoration in incised, warmwater streams of the Southeastern U.S., even if applied at the
watershed scale and accompanied by significant reductions in suspended sediment concentration. 相似文献
995.
A method for assessing environmental risk: A case study of Green Bay,Lake Michigan,USA 总被引:4,自引:0,他引:4
Hallett J. Harris Robert B. Wenger Victoria A. Harris David S. Devault 《Environmental management》1994,18(2):295-306
The Science Advisory Board of the US Environmental Protection Agency has recommended that risk reduction strategies become
the centerpiece of environmental protection. The goal in developing such strategies is to identify opportunities for greatest
reduction of ecological risks. This is a perspective that is significantly more comprehensive than the traditional focus on
human health risks arising from environmental degradation. The identification of ecological risks upon which environmental
protection efforts should be focused requires an ecological risk assessment methodology that is based on anthropogenic stressors
affecting an ecosystem and a set of impaired use criteria. A methodology based on this concept is developed and discussed
in this article. The methodology requires that risk values be assigned to each ecosystem stressor-impaired use pair that reflect
the degree to which the given stressor contributes to ecosystem risk as measured by the given impaired use criterion. Once
these data are available, mathematical analyses based on concepts from fuzzy set theory are performed to obtain a ranking
of ecosystem stressors. The methodology has been tested by applying it to a case study involving Green Bay of Lake Michigan.
A workshop was held in which 11 persons with extensive knowledge of the Green Bay ecosystem determined risk values through
a group-consensus process. The analytical portion of the methodology was then used to rank the ecosystem risks (stressors)
from several perspectives, including prevention management and remediation management. The overall conclusion of the workshop
participants was that the fuzzy set decision model is a useful and effective methodology for differentiating environmental
risk. 相似文献
996.
Gabriele Fava Romeo Fratesi Maria Letizia Ruello Daniela Sani 《Chemistry and Ecology》2002,18(3):223-232
The present work relates to galvanized structures with several years of time life subjected to atmospheric corrosion, like galvanized high tension steel pylons. The mass and fate of zinc released is evaluated both via empirical and experimental procedures. The corrosion rate determination requested atmospheric condition characterization, especially for SO 2 concentration and experimental activities focused on soil sampling around pylons. The soil zinc content, total and exchangeable, is determinates by different analytical procedures. The zinc diffusion in environment and the zinc extension under the top soil is evaluated using 1-dimensional mathematical model for miscible species in porous soil. 相似文献
997.
本文通过对我国1980~1989年热带气旋灾害的分析与评估,指出热带气旋灾害具有影响偏南、多集中于夏季且与冷空气等气象灾害重叠、加重灾情等特点,总结了以往防治台风灾害工作中的经验与教训。 相似文献
998.
/ Implemented in the context of a long history ofintense public debate, forestry practices applied on private forest land areregulated in some form by 38 states. State regulatory activities can involvemany agencies implementing numerous regulatory laws, a single forestry agencyadministering a comprehensive regulatory program, or a combination of thetwo. Regulatory programs are designed to protect resources such as soils,water, wildlife, and scenic beauty. Program administration often involvesrule promulgation, harvest plan reviews, coordination of interagency reviews,and pre- and postharvest on-site inspections. Forest practice rules usuallyfocus on reforestation, forest roads, harvest procedures, and wildlifehabitat protection. Emerging regulatory trends include growth of multiagencyregulatory authority and associated jurisdictional conflicts, increasedtendencies to narrowly specify standards in statutes and rules, emergence ofcontingent regulations, growing sensitivity to processes enabling theadoption of new forest practice technologies and an ability to addresscumulative effects, interest in collaborative rule-making stemming fromheightened concern over legalization of administration processes, and growingconcern over the constitutional foundations for regulatory programs and thegovernment and private sector cost of implementing such programs.KEY WORDS: Ecosystem management; Forestry practices; Private landowners;Regulatory programs; State government 相似文献
999.
针对如何评价和选择矿井安全监控系统装备的问题。运用科学的方法,就几种不同型号装备,做了定量和定性的阐述,还就建立监测系统装备的可靠性评价结构模型和数学分析模型做了分析。也对其他几个人为影响因素的性能指标提出了定性分析方法。 相似文献
1000.
用数量化理论(Ⅱ)[1]研究了矿井冒顶危险性评价问题,建立了一个实用的矿井冒顶危险性评价模型;并通过项目贡献分析,提出了一套降低冒顶危险程度的安全对策。 相似文献