排序方式: 共有33条查询结果,搜索用时 15 毫秒
31.
Weiping Chen Lianqing Li Andrew C. Chang Laosheng Wu Rufus L. Chaney Richard Smith Husein Ajwa 《Agriculture, ecosystems & environment》2009,129(1-3):212-220
In risk assessment models, solid–solution partition coefficient, Kd, and plant uptake factor, PUF, are often employed to depict the fate and transport of trace elements in soils. The trustworthiness of risk assessments depends on the reliability of the parameters used. In this study, we examined Kd and PUF for As, Cd and Pb based on soils and plant tissues obtained from 70 crop production fields in California. We also examined the California portion of a nationwide survey of trace elements in cropland soils conducted by the Soil Survey, Natural Resources Conservation Service, USDA. Results showed that the Kd and PUF for cropland soils are probabilistic in nature and follow log-normal distributions. The trace element concentration of the soil solution did not appear to be a more appropriate estimator of PUF than the total soil element content. The Kd used in the CDFA (California Department of Food and Agriculture) study had a much wider range than that could occur in California croplands while the PUF used in the CDFA risk assessment was comparable to patterns observed in the field measurements. 相似文献
32.
33.
《Atmospheric environment(England)》1986,20(7):1325-1332
A crosswind integrated K-model with wind- and K-profiles described by Monin-Obukhov similarity expressions is solved for a continuous surface release to yield the vertical spread of the plume as a function of the surface roughness z0 and the Monin-Obukhov length L for a given downwind distance. The vertical spread of the plume is translated into σz, and lines were traced in a (z0, L−) plane for which the σz of the K-model matched the corresponding σz of Pasquill's system. By this technique a new classification scheme is constructed. Knowing z0 and L, the scheme tells which σz curve in the Pasquill system should be used to describe the dispersion.This dispersion classification scheme is used to organize 3 years of data from two meteorological masts, one placed directly at a shoreline and the other roughly 1 km inland. Differences in the dispersion climatology over land and water are studied by averaging the data selectively. The large differences for water and land surfaces between the seasonal and diurnal variation of the dispersion class distributions are illustrated. It is found that the water surface influences the dispersion climatology as far as 20 km inland. 相似文献