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91.
Preface 总被引:1,自引:0,他引:1
Robert K. Dixon 《Mitigation and Adaptation Strategies for Global Change》2007,12(3):323-324
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Burger J Campbell KR Campbell TS Shukla T Dixon C Gochfeld M 《Environmental monitoring and assessment》2005,110(1-3):171-184
We compared the levels of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in a small species of fish (Central
stonerollers, Campostoma anomalum) collected from East Fork Poplar Creek (EFPC) and a reference site in eastern Tennessee. Stonerollers are minnows in the
Cyprinidae family that serve as prey for many carnivores in aquatic systems. Fish were collected from East Fork Poplar Creek
within the U.S. Department of Energy's Y-12 National Security Complex, part of the Oak Ridge Reservation, and from a reference
stretch of the Little River in East Tennessee. Whole fish were homogenized for analysis. Concentrations of all metals (except
arsenic) were significantly higher in stonerollers from EFPC compared to the reference site. Mercury levels in minnows from
EFPC averaged 0.4 ppm (μg/g), four times higher than the average for fish in the U.S. in general. This was higher than levels
in fish from the nearby Clinch River and higher than fillets of white bass (Morone chrysops) from the same creek. Most metal levels were inversely related to size and weight of the stonerollers, perhaps due to growth
dilution. 相似文献
94.
Monitoring global change: Comparison of forest cover estimates using remote sensing and inventory approaches 总被引:2,自引:0,他引:2
David P. Turner Greg Koerper Hermann Gucinski Charles Peterson Robert K. Dixon 《Environmental monitoring and assessment》1993,26(2-3):295-305
Satellite-based remote sensing offers great potential for frequent assessment of forest cover over broad spatial scales, however, calibration and validation using ground-based surveys are needed. In this study, forest cover estimates for the United States from a recently developed land surface cover map generated from satellite remote sensing data were compared to state-level inventory data from the U.S. National Resources Planning Act Timber Database. The land cover map was produced at the U.S. Geological Survey EROS Data Center and is based on imagery from the AVHRR sensor (spatial resolution 1.1 km). Vegetation type was classified using the temporal signal in the Normalized Difference Vegetation Index derived from AVHRR data. Comparisons revealed close agreement in the estimate of forest cover for extensively forested states with large polygons of relatively similar vegetation such as Oregon. Larger forest cover differences were observed in other states with some regional patterns in the level of agreement apparent.Comparisons in inventory- and remote sensing-based estimates of current forested area with potential vegetation maps indicated the magnitude of past land use change and the potential for future changes. The remote sensing approach appears to hold promise for conducting surveys of forest cover where inventory data are limited or where rates of vegetation change, due to human or climatic factors, are rapid. 相似文献
95.
L. J. Lane M. H. Diskin D. E. Wallace R. M. Dixon 《Journal of the American Water Resources Association》1978,14(5):1143-1158
ABSTRACT: Significant errors in estimating surface runoff and erosion rates are possible if a watershed is assumed to contribute runoff uniformly over the entire area, when actually only a portion of the entire area may be contributing. Generation of overland flow on portions of small semiarid watersheds was analyzed by three methods: an average loss rate procedure, a lumped-linear model, and a distributed-nonlinear model. These methods suggested that, on the average, 45, 60, and 50% of the drainage area was contributing runoff at the watershed outlet. Infiltrometer data support the partial area concept and indicate that the low infiltration zones are the runoff source areas as simulated with the distributed-nonlinear model. 相似文献
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97.
Wetlands are critical natural resources in developing countries where they perform a range of environmental functions and provide numerous socio-economic benefits to local communities and a wider population. In recent years, however, many wetlands throughout eastern Africa have come under extreme pressure as government policies, socio-economic change and population pressure have stimulated a need for more agriculturally productive land. Although wetland drainage and cultivation can make a key contribution to food and livelihood security in the short term, in the long term there are concerns over the sustainability of this utilization and the maintenance of wetland benefits. This article draws upon recent research carried out in western Ethiopia, which addressed the sustainability of wetland agriculture in an area of increasing food insecurity and population pressure. It discusses the impacts of drainage and cultivation on wetland hydrology and draws attention to local wetland management strategies, particularly those characterized by multiple use of wetlands, where agriculture exists alongside other wetland uses. The article suggests that where multiple wetland uses exist, a range of benefits can be sustained with little evidence of environmental degradation. Ways of promoting and empowering such sustainable wetland management systems are discussed in the context of the wider need for water security throughout the region. 相似文献
98.
Development of a MSW classification system for the evaluation of mechanical properties 总被引:5,自引:0,他引:5
To date, sparse information is available on the mechanical properties of municipal solid waste and the results of published work are often hard to compare due to differences in waste composition and therefore properties. To allow comparison, a unified classification system for waste is deemed crucial. Existing classification systems are presented and discussed. For a geotechnical classification, mechanical properties, size, shape and degradability potential of waste components have to be taken into account. A new and improved classification system for waste components is proposed, which complies with the requirements of a geotechnical classification system. It classifies waste components based on: (1) their material engineering properties (e.g., shear, compressive and tensile strength), (2) a size distribution of the components, (3) the component shape (reinforcing, compressible and incompressible), and (4) the degree of degradability. The proposed classification system is applied to data from the literature and methods for presenting classification information are demonstrated. Further work required to develop a full classification system for waste bodies is highlighted. 相似文献
99.
Taylor S. Roumeliotis Brad J. Dixon Bill J. Van Heyst 《Atmospheric environment (Oxford, England : 1994)》2010,44(31):3770-3777
This paper characterizes the emission rates of size fractionated particulate matter, inorganic aerosols, acid gases, ammonia and methane measured over four flocks at a commercial broiler chicken facility. Mean emission rates of each pollutant, along with sampling notes, were reported in this paper, the first in a series of two. Sampling notes were needed because inherent gaps in data may bias the mean emission rates.The mean emission rates of PM10 and PM2.5 were 5.0 and 0.78 g day?1 [Animal Unit, AU]?1, respectively, while inorganic aerosols mean emission rates ranged from 0.15 to 0.46 g day?1 AU?1 depending on the season. The average total acid gas emission rate was 0.43 g day?1 AU?1 with the greatest contribution from nitrous and nitric acids and little contribution from sulfuric acid (as SO2).Ammonia emissions were seasonally dependent, with a mean emission rate of 66.0 g day?1 AU?1 in the cooler seasons and 94.5 g day?1 AU?1 during the warmer seasons. Methane emissions were relatively consistent with a mean emission rate of 208 g day?1 AU?1.The diurnal pattern in each pollutant’s emission rate was relatively consistent after normalizing the hourly emissions according to each daily mean emission rate. Over the duration of a production cycle, all the measured pollutants’ emissions increased proportionally to the total live mass of birds in the house, with the exception of ammonia.Interrelationships between pollutants provide evidence of mutually dependent release mechanisms, which suggests that it may be possible to fill data gaps with minimal data requirements. In the second paper (Roumeliotis, T.S., Dixon, B.J., Van Heyst, B.J. Characterization of gaseous pollutants and particulate matter emission rates from a commercial broiler operation part II: correlated emission rates. Atmospheric Environment, 2010.), regression correlations are developed to estimate daily mean emission rates for data gaps and, using the normalized hourly diurnal patterns from this paper, emission factors were generated for each pollutant. 相似文献
100.