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991.
William L. Jackson Robert L. Beschta 《Journal of the American Water Resources Association》1984,20(4):527-533
ABSTRACT A flume study was conducted to examine (1)changes in the particle-size distribution of sediments in riffles due to the proportion of sand in transport and the total rate of bedload transport at the time the riffle is deposited and (2) the effect of high sand transport rates on the stability of gravel riffles. The median particle size of sediment deposited in the riffle was larger than that of the sediment in transport. Small but significant (a = 0.05) decreases in the median particle size of riffle sediments resulted as the sand-to-gravel ratio. Increased concentrations of sand in transport caused previously stable gravel riffles to undergo scour. These results, in combination with information from other studies, suggest that an alluvial channel with pool-riffle sequences and with sand and gravel beds may respond to an increased delivery of sand by reducing form roughness. Form roughness can be reduced by degrading riffles and filling pools. Subsequent responses may be increases in width-to-depth ratio and slope. 相似文献
992.
993.
Robert E. Foley 《Environmental monitoring and assessment》1992,21(1):37-48
Thirteen organochlorine compounds were detected in fat and breast muscle tissues of Canada goose and five species of ducks that were shot by sportsman in New York. Residues of DDE and PCB occurred most frequently and were positively identified along with DDT, heptachlor epoxide, trans-nonachlor, and hexachlorobenzene. Compounds that were detected but not positively confirmed by mass spectrometry were dieldrin, mirex, heptachlor, chlordane, oxychlordane, and endrin. Wood duck (Aix sponsa) and Canada goose (Branta canadensis) had significantly lower levels of DDE and PCB than black duck (Anas rubripes), mallard (Anas platyrhynchos), scaup (Athya sp.), and bufflehead (Bucephala albeola). Birds collected from Long Island and the Hudson River-Lake Champlain corridor carried highest concentrations. 相似文献
994.
995.
Charles J. Henny Lawrence J. Blus David J. Hoffman Robert A. Grove 《Environmental monitoring and assessment》1994,29(3):267-288
Mining and smelting at Kellogg-Smelterville, Idaho, resulted in high concentrations of lead in Coeur d'Alene (CDA) River sediments and the floodplain downstream, where American Kestrels (Falco sparverius), Northern Harriers (Circus cyaneus), Red-tailed Hawks (Buteo jamaicensis), Great Horned Owls (Bubo virginianus), and Western Screech-owls (Otus kennicotti) nested. Nestling American Kestrels contained significantly higher (P=0.0012) blood lead concentrations along the CDA River (0.24 µg/g, wet wt) than the nearby reference area (0.087 µg/g). A 35% inhibition of blood -aminolevulinic acid dehydratase (ALAD) in nestling Northern Harriers (P=0.0001), 55% in nestling American Kestrels (P=0.0001) and 81% in adult American Kestrels (P=0.0004) provided additional evidence of lead exposure in the CDA River population. In nestling American Kestrels and Northern Harriers, ALAD activity was negatively correlated with lead in blood. An earlier report on Ospreys (Pandion haliaetus) showed slightly less inhibition of ALAD than in American Kestrels, but no significant reduction in hemoglobin or hematocrit and no negative influence on production rates. The adult and nestling American Kestrels along the CDA River contained about twice as much blood lead as Ospreys during the same years (adult 0.46 vs. 0.20 µg/g, and nestling 0.24 vs. 0.09 µg/g), but adults showed a 7.5% reduction in hemoglobin (P=0.0356) and nestlings an 8.2% reduction in hemoglobin (P=0.0353) and a 5.8% reduction in hematocrit (P=0.0482). We did not observe raptor deaths related to lead, and although the production rate for American Kestrels was slightly lower along the CDA River, we found no significant negative relation between productivity and lead. Limited data on the other raptors provide evidence of exposure to lead along the CDA River. Several traits of raptors apparently reduce their potential for accumulating critical levels of lead which is primarily stored in bones of prey species.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
996.
Jeffrey L. Arthur Robert G. Haight Claire A. Montgomery Stephen Polasky 《Environmental Modeling and Assessment》2002,7(2):81-89
Two approaches to formulating the reserve site selection problem when species occurrence data is probabilistic were solved for terrestrial vertebrates in a small set of potential reserve sites in Oregon. The expected coverage approach, which maximizes the sum of the occurrence probabilities, yielded solutions that covered more species on average in Monte Carlo simulations than the threshold approach, which maximizes the number of species for which the occurrence probability exceeds some threshold. 相似文献
997.
Hong S Boutron CF Barbante C Do Hur S Lee K Gabrielli P Capodaglio G Ferrari CP Turetta C Petit JR Lipenkov VY 《Journal of environmental monitoring : JEM》2005,7(12):1326-1331
Lead (Pb), cadmium (Cd), copper (Cu) and zinc (Zn) have been measured by electrothermal atomic absorption spectrometry in various sections of the 3623 m deep ice core drilled at Vostok, in central East Antarctica. The sections were dated from 240 to 410 kyear BP (Marine Isotopic Stages (MIS) 7.5 to 11.3), which corresponds to the 3rd and 4th glacial-interglacial cycles before present. Concentrations are found to have varied greatly during this 170 kyear time period, with high concentration values during the coldest climatic stages such as MIS 8.4 and 10.2 and much lower concentration values during warmer periods, such as the interglacials MIS 7.5, 9.3 and 11.3. Rock and soil dust were the dominant sources for Pb, whatever the period, and for Zn and Cu and possibly Cd during cold climatic stages. The contribution from volcanic emissions was important for Cd during all periods and might have been significant for Cu and Zn during warm periods. 相似文献
998.
The removal of soluble contaminants from fractured porous bedrock by means of a recovery well is modeled by means of a lumped parameter approach. The diffusion of contaminant from immobile liquid within the pores of the fractured rock into the mobile liquid in the interstices is handled by means of a time constant the estimation of which is described. 相似文献
999.
James C. McFarlane Amy Cross Clyde Frank Robert D. Rogers 《Environmental monitoring and assessment》1981,1(1):75-81
Gaseous benzene was rapidly depleted in exposure chambers containing viable soils and plants. When separate components of the system were analyzed, no benzene was detected in soils, plants, or water. Soil microorganisms were shown to be responsible for metabolizing benzene, yielding CO2 as the main product. The rates were sufficiently rapid to suggest that this reaction forms a major pathway for the elimination of benzene from the environment.This work was sponsored and conducted at the Environmental Protection Agency-Environmental Monitoring Systems Laboratory, Las Vegas, Nevada, U.S.A. 相似文献
1000.
Watson RT Patz J Gubler DJ Parson EA Vincent JH 《Journal of environmental monitoring : JEM》2005,7(9):834-843
This paper reviews the background that has led to the now almost-universally held opinion in the scientific community that global climate change is occurring and is inescapably linked with anthropogenic activity. The potential implications to human health are considerable and very diverse. These include, for example, the increased direct impacts of heat and of rises in sea level, exacerbated air and water-borne harmful agents, and--associated with all the preceding--the emergence of environmental refugees. Vector-borne diseases, in particular those associated with blood-sucking arthropods such as mosquitoes, may be significantly impacted, including redistribution of some of those diseases to areas not previously affected. Responses to possible impending environmental and public health crises must involve political and socio-economic considerations, adding even greater complexity to what is already a difficult challenge. In some areas, adjustments to national and international public health practices and policies may be effective, at least in the short and medium terms. But in others, more drastic measures will be required. Environmental monitoring, in its widest sense, will play a significant role in the future management of the problem. 相似文献