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排序方式: 共有209条查询结果,搜索用时 16 毫秒
171.
172.
基于生物可给性的某冶炼厂土壤重金属健康风险评价 总被引:1,自引:0,他引:1
为科学评价重金属污染场地的人体健康风险,以某冶炼厂土壤为研究对象,采用PBET(Physiologically-Based Extraction Test)和IVG(In-Vitro gastrointestinal)两种方法测定了As、Cd、Cu、Pb、Zn的生物可给性,并对比了只考虑重金属总量与基于生物可给性的人体... 相似文献
173.
174.
Abstract: We compared species diversity of plants and insects among grazed and ungrazed areas of Ponderosa pine–grassland communities in Arizona. Plant species richness was higher in two of three grassland communities that were grazed by native elk and deer and domestic cattle than in ungrazed areas inside a series of three large (approximately 40-ha) grazing exclosures. Similarly, plant species richness was higher in grazed areas relative to ungrazed areas at one of two series of smaller (approximately 25-m2 ) and short-term exclosure sites. Evenness of plant distribution, however, was greater inside ungrazed long-term exclosures but was reduced inside ungrazed short-term exclosures relative to grazed areas. Relative abundances of forbs, grasses, trees, and shrubs, and native and introduced plants did not differ between the long- and short-term grazing exclosures and their grazed counterparts. Relative abundances of some plant species changed when grazers were excluded, however. In contrast, insect species richness was not different between grazed and ungrazed habitats, although insect abundance increased 4- to 10-fold in ungrazed vegetation. Our results suggest that vertebrate grazing may increase plant richness, even in nutrient-poor, semi-arid grasslands, but may decrease insect abundances. 相似文献
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176.
Arctic Foundations, Inc. (AFI), of Anchorage, Alaska, has developed a freeze barrier system designed to hydraulically isolate a contaminant source area. The system can be used for long‐term or temporary containment of groundwater until appropriate remediation techniques can be applied. The technology was evaluated under the United States Environmental Protection Agency's (EPA's) Superfund Innovative Technology Evaluation (SITE) program at the United States Department of Energy's (DOE's) Oak Ridge National Laboratory (ORNL) facility in Oak Ridge, Tennessee. For the demonstration, an array of freeze pipes called “thermoprobes” was installed to a depth of 30 feet below ground surface around a former waste collection pond and keyed into bedrock. The system was used to establish an impermeable frozen soil barrier to hydraulically isolate the pond. Demonstration personnel collected independent data to evaluate the technology's performance. A variety of evaluation tools were used—including a groundwater dye tracing investigation, groundwater elevation measurements, and subsurface soil temperature data—to determine the effectiveness of the freeze barrier system in preventing horizontal groundwater flow beyond the limits of the frozen soil barrier. Data collected during the demonstration provided evidence that the frozen soil barrier was effective in hydraulically isolating the pond. 相似文献
177.
John Lyons Stanley W. Thimble Laura K Paine 《Journal of the American Water Resources Association》2000,36(4):919-930
ABSTRACT: Forestation of riparian areas has long been promoted to restore stream ecosystems degraded by agriculture in central North America. Although trees and shrubs in the riparian zone can provide many benefits to streams, grassy or herbaceous riparian vegetation can also provide benefits and may be more appropriate in some situations. Here we review some of the positive and negative implications of grassy versus wooded riparian zones and discuss potential management outcomes. Compared to wooded areas, grassy riparian areas result in stream reaches with different patterns of bank stability, erosion, channel morphology, cover for fish, terrestrial runoff, hydrology, water temperature, organic matter inputs, primary production, aquatic macroinvertebrates, and fish. Of particular relevance in agricultural regions, grassy riparian areas may be more effective in reducing bank erosion and trapping suspended sediments than wooded areas. Maintenance of grassy riparian vegetation usually requires active management (e.g., mowing, burning, herbicide treatments, and grazing), as successional processes will tend ultimately to favor woody vegetation. Riparian agricultural practices that promote a dense, healthy, grassy turf, such as certain types of intensively managed livestock grazing, have potential to restore degraded stream ecosystems. 相似文献
178.
Brian E. Haggard Daniel E. Storm Emily H. Stanley 《Journal of the American Water Resources Association》2001,37(5):1291-1299
ABSTRACT: We examined the effect of a point source (PS) input on water chemistry and nutrient retention in Spavinaw Creek, Arkansas, during summer baseflows in 1998 and 1999. The nutrient uptake length (Sw) concept was used to quantify the impact of nutrient inputs in the receiving stream. We used an artificial injection upstream of the PS inputs to estimate background S and used the natural decline in nutrient concentrations below the PS to estimate the net nutrient uptake length (Snet). Sw for soluble reactive phosphorus (SRP) in the upstream reference section was O.75 km, but Snet ranged from 9.0 to 31 km for SRP and 3.1 to 12 km for NO3‐N in the reach below the PS. Snet‐SRP was significantly correlated with discharge whereas Snet‐NO3‐N was correlated with the amount of NO3‐N enrichment from the PS. In order to examine specific mechanisms of P retention, loosely exchangeable P and P Sorption Index (PSI) of stream sediments were measured. Sediments exhibited little natural P buffering capacity (low PSI) above the PS, but P loading from the PS further reduced PSI. Loosely exchangeable P in the sediments also increased three fold below the PS, indicating sediments removed some water column P. The physical process of flow and sediment sorption apparently regulated P retention in Spavinaw Creek, whereas the level of N enrichment and possibly biotic uptake and denitrification influenced N retention. Regardless of the mechanism, Spavinaw Creek demonstrated little ability to retain PS‐added nutrients because net nutrient uptake lengths were in the km range. 相似文献
179.
A reclamation demonstration project at an abandoned deep mine 总被引:1,自引:0,他引:1
Stanley D. Zellmer B.Sc. Michael L. Wilkey B.Sc. 《Environmental geochemistry and health》1979,1(2):57-63
This project involves an evaluation of the reclamation process at a typical abandoned deep coal mine in the Midwest, U.S.A. The reclamation process included determining the final land use, collection of preconstruction environmental data, development of detailed construction plans, and implementation of the construction plans. A multidisciplinary approach is being used to evaluate post-construction conditions of the site. Current investigations are monitoring groundwater, surface water quality, aquatic ecosystems, revegetation, soil characteristics, erosion and runoff, soil microbial populations, wildlife, and economic effects of the reclamation. Data collected to date indicate a significant improvement in overall environmental quality, a substantial increase in the economic potential of the site and adjacent properties, and a genuine enhancement of the entire area's aesthetic value. This project will also provide design data for future reclamation efforts of this type.This project is financially supported by the following agencies: U.S. Department of Energy, Contract No. W31-109-Eng-38; Abandoned Mined Land Reclamation Council, State of Illinois Contract No. 31-109-38-3694L; Illinois Institute of Natural Resources, Contract No. 31-109-38-3702L. 相似文献
180.
The Science of Nature - The establishment of a carbon cycle was a necessary prerequisite for the evolution of higher forms of life. This could not have been achieved without the direct... 相似文献