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81.
Sherwood C. McIntyre 《Journal of the American Water Resources Association》1993,29(3):487-495
ABSTRACT: Long-term land use and reservoir sedimentation were quantified and linked in a small agricultural reservoir-watershed system without having historical data. Land use was determined from a time sequence of aerial photographs, and reservoir sedimentation was determined from cores with 137Cs dating techniques. They were linked by relating sediment deposition to potential sediment production which was determined by the Universal Soil Loss Equation and by SCS estimates for gullied land. Sediment cores were collected from Tecumseh Lake, a 55-ha reservoir with a 1,189-ha agricultural watershed, constructed in 1934 in central Oklahoma. Reservoir sediment deposition decreased from an average of 5,933 Mg/yr from 1934 to 1954, to 3,179 Mg/yr from 1954 to 1962, and finally to 1,017 Mg/yr from 1962 to 1987. Potential sediment production decreased from an average of 29,892 to 11,122 and then to 3,589 Mg/yr for the same time periods as above, respectively. Reductions in deposition and sediment production corresponded to reductions in cultivated and abandoned cropland which became perennial pasture. Together, cultivated and abandoned cropland accounted for 59 percent of the watershed in 1937, 24 percent in 1954, and 10 percent in 1962. Roadway erosion, stream bank erosion, stored stream channel sediment, and long-term precipitation were considered, but none seemed to play a significant role in changing sediment deposition rates. Instead, the dominant factor was the conversion of fields to perennial pastures. The effect of conservation measures on reservoir sedimentation can now be quantified for many reservoirs where historical data is not available. 相似文献
82.
根据加卸载响应比理论,通过对1991~1996年江苏省部分井孔观测资料固体潮加卸载响应比的计算发现,在中强地震前一年左右的时间震中区附近的井孔出现了响应比高值异常。通过空间图像扫描可以看出:在苍山地震前一年左右,徐州、宿迁地区出现了加卸载响应比的高值集中区;在南黄海地震前一年左右,在镇江、苏州地区出现了高值集中区,之后高值集中区有自西向东迁移即有向震中区迁移的迹象。 相似文献
83.
Bogaert J Salvador-Van Eysenrode D Impens I Van Hecke P 《Environmental management》2001,27(4):493-500
A method is proposed to quantify disturbance impact on isolated habitats. For every landscape patch, the breakpoint distance,
defined as the penetration distance for which equality of interior and edge habitat is observed, can be calculated. Disturbance
with equal impact at all patch sides is assumed. Effects of patch compactness, size, convolution, and perforation are discussed.
The potential use of the measure for nature reserve design is discussed. The breakpoint distance follows the reserve design
guidelines for individual patches, based on island biogeography and is consistent with the form and function principle. A
large breakpoint distance is preferred for natural habitats. Small size, small compactness, intense convolution, and the occurrence
of many gaps depress the breakpoint distance. 相似文献
84.
污泥掺烧技术在煤粉炉上应用的试验研究 总被引:2,自引:0,他引:2
通过污泥掺烧技术在煤粉炉上的应用试验,得出污泥的含水率对锅炉制粉系统的影响.掺烧前后对炉膛温度没有大的影响,随着污泥比例的增加,燃烧效率下降,烟尘浓度和SO2浓度降低. 相似文献
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87.
Michael V. Martin Louise M. Arthur 《Journal of the American Water Resources Association》1982,18(3):481-484
ABSTRACT: The period of time from identification of a possibly desirable inland waterway transportation project to its actual implementation has been observed to be inordinately long. It is Hypothesized that at Least one cause of delays in project approval and implementation is a analytical credibility associated with project feasibility analysis conducted by the U.S. Army Corps of Engineers. This paper examines this hypothesis in terms of the proposal to construct a new, expanded lock at the Bonneville Dam on the Columbia River. The principle finding is that the analysis conducted by the Corps is conceptually flawed, methodologically questionable, internally inconsistant, and inappropriately narrow in scope. 相似文献
88.
FRANCISCO PALOMARES JOSÉ ANTONIO GODOY JOSÉ VICENTE LÓPEZ‐BAO ALEJANDRO RODRÍGUEZ SEVERINE ROQUES MIREIA CASAS‐MARCE ELOY REVILLA MIGUEL DELIBES 《Conservation biology》2012,26(4):689-697
Abstract: Theory suggests that demographic and genetic traits deteriorate (i.e., fitness and genetic diversity decrease) when populations become small, and that such deterioration could precipitate positive feedback loops called extinction vortices. We examined whether demographic attributes and genetic traits have changed over time in one of the 2 remaining small populations of the highly endangered Iberian lynx (Lynx pardinus) in Doñana, Spain. From 1983 to 2008, we recorded nontraumatic mortality rates, litter size, offspring survival, age at territory acquisition, and sex ratio. We combined these demographic attributes with measures of inbreeding and genetic diversity at neutral loci (microsatellites) and genes subjected to selection (major histocompatibility complex). Data on demographic traits were obtained through capture and radio tracking, checking dens during breeding, track surveys, and camera trapping. For genetic analyses, we obtained blood or tissue samples from captured or necropsied individuals or from museum specimens. Over time a female‐biased sex ratio developed, age of territory acquisition decreased, mean litter size decreased, and rates of nontraumatic mortality increased, but there were no significant changes in overall mortality rates, standardized individual heterozygosity declined steadily, and allelic diversity of exon 2 of class II major histocompatibility complex DRB genes remained constant (2 allelic variants present in all individuals analyzed). Changes in sex ratio and age of territory acquisition may have resulted from demographic stochasticity, whereas changes in litter size and nontraumatic mortality may be related to observed increases in inbreeding. Concomitant deterioration of both demographic attributes and genetic traits is consistent with an extinction vortex. The co‐occurrence, with or without interaction, of demographic and genetic deterioration may explain the lack of success of conservation efforts with the Doñana population of Iberian lynx. 相似文献
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