[Magnetic Responses of Heavy Metals in Street Dust of Typical Mine-Based City, Northwest China].

Magnetic characteristics and heavy metal properties of 43 street dust samples collected from Baiyin City, northwest of China were systematically analyzed. The results revealed that the main magnetic minerals were low-coercivity magnetite and maghemite with coarse pseudo single domain (PSD) and multi-domain (MD) in magnetic grain size. Compared with the domestic comprehensive cities, low frequency magnetic susceptibility(χlf) value of street dust samples in Binyin varied from 43. 75 x 10(-8) m3.kg-1 to 1 340. 08 x 10(-8) m3.kg-1 with the average value of 245. 98 x 10(-8) m3.kg-1, the magnetic mineral content in street dust samples of Binyin was low relatively, hut it varied among distinct districts with industrial district was the highest and the stripe traffic area was more higher than those of other regions(commercial district, new district). Different functional zones of Baiyin had a single pollution source relatively. Additionally, the contribution to strong magnetic minerals was predominated by industrial pollution and the distribution of pollution degrees in Bainyin showed a significant spatial difference. Concentrations of heavy metals(Cu, Pb, Zn) were generally high in Baiyin street dust. The significantly positive correlation between magnetic parameters(χlf, χARM, SIRM, SOFT) and pollution load index(PLI) and their consistent spatial characteristics confirm that magnetic concentration parameters can effectively monitor urban heavy metals pollution and determine the bounds and areas of pollution, providing a valuable tool for further urban pollution control.

[Magnolia liliiflora whole-tree sap flow in response to multiple environmental variables in Beijing].

In order to clarify the environmental factors affecting the water use of typical urban tree species Magnolia liliflora, an investigation was conducted on the responses of M. liliiflora whole-tree sap flow to the air temperature, air relative humidity, radiation, wind speed, soil temperature and water content, and precipitation in Beijing from April to October, 2008. The eight environmental factors affecting M. liliiflora whole-tree sap flow could be divided into three categories, i.e., evaporative demand index, soil index, and precipitation index. The evaporative demand index (air temperature, air relative humidity, total radiation, wind speed, and vapor pressure deficit) could explain 60% of the variation in the sap flow of individual trees, which presented S-type change trend, i.e., the sap flow reached an asymptote where higher light and evaporative demands could not cause sap flow to increase further. Soil index (soil temperature and water content) and precipitation index (precipitation amount) had little influence on the sap flow.