首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
4.
We analyzed cadmium and lead levels in feathers of mated pairs of common terns (Sterna hirundo) and in their eggs to determine if metal levels in eggs correlated with female levels, and whether there were intrapair and intermetal correlations. Eggs had significantly lower lead levels (89 ng g-1) and cadmium levels (4.0 ng g-1) than adult feathers (500 and 50 ng g-1 respectively). Adult females had higher metal levels than males. Cadmium and lead levels were correlated across families for females, males and eggs. Lead, but not cadmium, levels were correlated in females and their eggs.  相似文献   

5.
6.
7.
8.
Surface disturbances: Their role in accelerating desertification   总被引:19,自引:0,他引:19  
Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.  相似文献   

9.
10.
This study examines defoliation and discoloration findings collected throughout the Italian Level I network between 1997 and 2000. Prior to this period no Quality Assurance procedures had been implemented, so that earlier findings cannot be considered reliable. The aim of the study is to compare differentindices used in reporting findings, in order to determine the full potential and limitations of each. In international surveys,findings are normally expressed in terms of individual trees presenting a defoliation level greater than 2 %; this criterion,however, has been challenged since it is not based on scientificevidence. By analysing the distribution of defoliation values(grouped in 5% classes) relating to the main species (Fagus sylvatica, Quercus pubescens, Quercus cerris, Picea abies), the study examines the behaviour of statistical indices such as the median, the mode and the mean. Instead of using the traditional 25% threshold to determine the part of the population with the highest defoliation values, a procedureis suggested whereby a different threshold can be determined foreach species. It is established based on the 90° percentile of cumulative defoliation values recorded over the four-year period. Each index used to report findings possessesits own information potential, and the findings may at times appear contradictory. The use of a combined defoliation and discoloration index (Ilce = Lacking Crown Equivalent Index) is also proposed, but the results obtained do not differin substance from the results relating to defoliation alone. Thefunctional limitations of this index are due mainly to the way the data are collected: for this reason suggestions are made onhow to improve the procedure in future surveys.  相似文献   

11.
A multinational collaborative study during the summer of 1983 addressed organizational alternatives in natural systems management. Participants were particularly interested in ways different governments attempted to resolve the disparity between the interconnected quality of nature and the compartmentalized structure of bureaucracies. Five patterns of organization have evolved to meet this challenge: mission agencies managing ecosystems; independent or interagency central environmental units: environmental units within mission agencies; environmental components within central planning units; and regional superagencies. The systems developed by five nations—the United States, Korea, Malaysia, the Philippines, and Thailand—are analyzed and compared in terms of these five patterns.  相似文献   

12.
13.
Fluoride in high concentration in groundwater has been reported from many parts of India. However, a systematic study is required to understand the behavior of fluoride in natural water in terms of local hydrogeological setting, climatic conditions, and agricultural practices. The present study is an attempt to assess hydrogeochemistry of groundwater in parts of Palar river basin pertaining to Kancheepuram district Tamil Nadu to understand the fluoride abundance in groundwater and to deduce the chemical parameters responsible for the dissolution activity of fluoride. The study area is geologically occupied by partly sedimentary and partly crystalline formations. A total of 50 dug cum borewell-water samples, representing an area of 2,628.92 km2. The results of the chemical analyses in September 2009 show fluoride abundance in the range of 1 to 3.24 mg/l with 86% of the samples in excess of the permissible limit of 1.5 mg/l. Presence of fluoride-bearing minerals in the host rock, chemical properties like decomposition, dissociation, and dissolution, and their interaction with water are considered to be the main causes for fluoride in groundwater. Chemical weathering with relatively high alkalinity favors high concentration of fluoride in groundwater. Villagers who consume nonpotable high fluoride water may suffer from yellow, cracked teeth; joint pains; and crippled limbs and also age rapidly.  相似文献   

14.
There is ongoing debate about the effectiveness of impact assessment tools, which matters both because of the threat to future practice of the tools which are frequently perceived to be ineffective, and because of the disillusionment that can ensue, and controversy generated, amongst stakeholders in a decision context where opportunities for meaningful debate have not been provided. In this article we regard debate about the meaning of effectiveness in impact assessment as an inevitable consequence of increased participation in environmental decision-making, and therefore frame effectiveness based on an inclusive democracy role to mean the extent to which impact assessment can accommodate civil society discourse. Our aim is to investigate effectiveness based on this framing by looking at one type of impact assessment – environmental impact assessment (EIA) – in two controversial project proposals: the HS2 rail network in England; and the A4DS motorway in the Netherlands. Documentary analysis and interviews held with key civil society stakeholders have been deployed to identify discourses that were mobilised in the cases. EIA was found to be able to accommodate only one out of four discourses that were identified; for the other three it did not provide the space for the arguments that characterised opposition. The conclusion in relation to debate on framings of effectiveness is that EIA will not be considered effective by the majority of stakeholders. EIA was established to support decision-making through a better understanding of impacts, so its ineffectiveness is unsurprising when its role is perceived to be broader. However, there remains a need to map discourses in different decision contexts and to analyse the extent to which the range of discourses are accommodated throughout the decision process, and the role of impact assessment in those processes, before recommendations can be made to either improve impact assessment effectiveness, or whether it is simply perceptions of effectiveness that need to be improved.  相似文献   

15.
The transformation, composition, and distribution characteristics of nutrients in natural wetlands are significantly affected by human activities, such as large-scale water conservancy projects and agricultural activities. It is necessary to reveal the composing and distribution characteristics of nutrients for elucidating its complex removal and retention mechanisms in natural wetlands. In this study, the composition and the spatial distribution characteristics of nitrogen in a natural wetland in central China were illustrated and analyzed. The self-organizing map (SOM) model was used in this study to assess the water quality dataset of the wetland. The relationships between nitrogen and other water quality parameters were revealed by the visualization function of the SOM model with the pre-processed data; the modeling result was in agreement with the linear correlation analysis. The results indicated that the SOM model was suitable for the assessment of field-scale date of natural wetlands, and finally a potential approach for predicting the nutrients concentrations in natural wetlands was also found.  相似文献   

16.
Debates concerning the relation between Sustainable Development Goals (SDGs) and environmental assessment (EA) have long suggested their integration in some form. The purpose of this paper is to go beyond conceptual debates to explore practices of environmental impact assessment and strategic environmental assessment in terms of how they change in response to the Agenda 2030. A thorough web search for EA reports integrating SDGs resulted in 45 cases from five continents, which were then analyzed using a framework on levels of integration to examine and reflect on practice. The results show that in the majority of reports, SDGs are merely mentioned with no further function, that there is a trend towards focusing on positive impacts and that there is a high variation in how contributions to SDGs are assessed and displayed. The paper concludes by identifying key directions for further research, such as ways to further understand practices and to close the gap between theoretical considerations and EA practice.  相似文献   

17.
Almost 2700 samples of human renal cortex have been collected from throughout the UK over a 16 year period from 1978 to 1993. The mean Cd concentration was 19 micrograms g-1 and the median 16 micrograms g-1. Smokers were, on average, about 5 micrograms g-1 higher than non-smokers. Cd increased from low concentration in the young to a maximum of 23 micrograms g-1 in middle age followed by a decrease in old age. Subjects who had died of renal disease had lower Cd concentrations. Geographical variations in the UK are small and the concentrations appear to be static over the 16 year period. Some 3.9% of the population had Cd concentrations > 50 micrograms g-1, the critical level at which beta 2-microglobulin appears in urine.  相似文献   

18.
This paper presents development of a first approximation of a Namibian, national level, land degradation monitoring system. The process involved a large number of stakeholders and led to the definition of four primary indicators that were regarded as related to land degradation in Namibia: population pressure, livestock pressure, seasonal rainfall and erosion hazards. These indicators were calculated annually for the period 1971–1997. Annual land degradation risk maps were produced for the same period by combining the indicators. A time series analysis of results generated by indicators was undertaken at two sites. The analysis revealed a general trend towards an increased land degradation risk over the period 1971–1997. A decrease in annual rainfall and an increase in livestock numbers caused this negative trend at one site, while decreased annual rainfall and increased human population were the causes at a second site. Evaluation of resulting maps through direct field observations and long-term monitoring at selected study sites with different conditions relevant for the indicators defined, is an essential next step.  相似文献   

19.
20.
Natural capital in ecology and economics: an overview   总被引:2,自引:0,他引:2  
The Brundtland Commission report, Our Common Future, defined sustainable development as development that meets the needs of the present without compromising the ability of futuregenerations to meet their own needs. Although the idea of sustainable development has been widely accepted, it has proveddifficult to identify and implement policies and practices thatpromote sustainable economic growth. Some economists, environmental scientists and policy analysts believe that they can transform the consensus about sustainability into manageablepractices. They propose to accomplish this feat with a set of new ideas about the relationships between the economy and theenvironment offered under the banner of 'natural capital'. An ideal account of natural capital would be one or more standard measures or models that would allow the direct comparison of environmental goods, like forests, fresh water and clean air, with economic goods, like money, capital and productivity. By bringing economic science and environmental science to an objective common ground, a natural capital model has the potentialto provide a concrete means of comparing the economic and ecological costs and benefits of particular policies and programmes. This paper offers a survey and analysis of several new contributions to the formation of the natural capital concept from economists, ecologists, policy analysts, biometricians, foresters and a philosopher. The paper concludes that existingmicroeconomic theory may be 'ungreenable', if it is not reformulated. While macroeconomic approaches to natural capitalhave been more successful, they share the limitation that ecosystems and species are valued solely in monetary terms. These problems are taken to suggest that the development of a successful natural capital model may require economic theory tobe recast to include non-monetary social preferences and values.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号