Characters of River Sediment of Urban Area in Lanzhou
兰州市城区河道表层沉积物磁性特征研究

A total of 23 deposits samples were collected from 8 selected the river sediments in Lanzhou urban area as researching objects of magnetic property and organic matter measure. The results indicate that: (1) the magnetic property controlled by magnetite which is ferrimagnetic mineral, and anti-ferromagnetic component such as hematite and goethite; (2) the value of samples' magnetic parameters (such as: chi, SIRM, magnetic hysteresis loops and M-T curves) increased from upstream to downstream in Paihong River, Shier River and Yuer River, Shuimo River; decreased in Qili River and Lanni River; and contrasting above-mentioned, the value of samples' magnetic parameters were low in Luoguo River and Dasha River. Based on the variation of magnetic parameters, such as chiFD, chiARM, chiFD/Ms and chiARM/Ms, we divided the rivers into three groups according to the contribution originating from anthropogenic activities into spatial river sediments: first type, such as Paihong River, Shier River, Yuer River and Shuimo River, called downstream concentrate type; second type, such as Qili River and Lanni River, called upstream concentrate type; third type, such as Luoguo River and Dasha River, called less affected type. Bulk samples also demonstrate a strong linear positive correlation between magnetic parameters chiFD, chiARM and the content of organic matter, which reflected the content of superparamagnetic and single domain grains were nice proxy parameters of the content of organic matter of river sediments.