Magnetic Properties Of Top Soils In Beijing, And Their Environmental Implications

The two studied regions locate around the Shisanling reservoir in Changpingdistrict (non-polluted area) and along the bank of Yongding river in Shijingshandistrict (industrial polluted area) in Beijing. Detailed environmental magneticmeasurements were carried out on soil sections selected from these two areas.It was concluded that significant differences of the magnetic susceptibility curvesexist between the soil sections from the two regions. The susceptibility values of topsoils from the non-polluted area are low (<10E-3SI) and varies slightly with depth.While distinct magnetic enhancement was observed at top soils from Yingshan ForestGarden, in western Beijing city (belonging to polluted area). The top soils have thehigh magnetic susceptibility values up to 5.0×10E-3SI, as much 3-6 times as that ofthe substratum and decreases sharply downward the section. The susceptibility valuesof soils are small and having little variations at a depth of >8cm in the YingshanForest Garden.At the exit of ash water current from Shijingshan Power Plant, the curve ofmagnetic susceptibility versus depth of the sediment section shows that magneticsusceptibility is more than 4.0×10E-3SI and increases with the depth. The magneticminerals, contained in both the polluted soil and the unpolluted soil, are dominated bymagnetite;while magnetic minerals have much more concentration in the pollutedsoils than in the unpolluted soils. The magnetic minerals are larger in the pollutedsoils than that in the unpolluted soils.In Yingshan Forest Garden, the polluting material is mainly transported by theforce of wind, the polluted soil is limited in the surface soils that having a depthsmaller than 8 cm, indicating the vertical transfering distance of polluting material isvery limited. While at the exit of ash water current from Shijingshan Power Plant, thedepth of polluted sediments is obviously enlarged (>50cm), which may result fromtwo reasons, firstly the polluting material deposited quickly and secondly thedownword tranfering depth of polluting material is larger, aided by the penetratingeffect of water.