Magnetic Properties of Farmland Soils in Arid Regions in Northwest China and Their Environmental Implications

: In order to understand the feasibility of environmental magnetism methods in farmland soil pollution monitoring in the northwest arid areas of China, the environmental magnetic properties of 102 farmland soil samples from four typical agricultural regions, namely Linze county, Ganzhou district, Minle county, and Shandan county in Zhangye City were systematically analyzed. The results show that the main magnetic mineral of farmland soil samples is ferrimagnetic magnetite, and the main magnetic grain sizes are coarse-grained pseudo single domain (PSD) and multidomain (MD), mainly between 0.2-1 μm in equivalent diameter. The low frequency magnetic susceptibility (χlf) value of farmland soil samples ranged from 22.27×10-8 m3·kg-1 to 188.36×10-8 m3·kg-1, with the average value of 63.85×10-8 m3·kg-1. Overall, the magnetic mineral content of farmland soil samples was low, but it had large spatial variation. The spatial distribution of the magnetic parameters show that the magnetic mineral contents in Ganzhou district, Minle county, and Shandan county are higher than in Linze county, and three relatively high-value areas are present in central Ganzhou district, the southwest side of Minle county, and the west side of Shandan county. High magnetic value in central Ganzhou district is mainly controlled by human activities, such as industrial production, whereas the high magnetic values in the southwest side of Minle county and west side of Shandan county are more related to strong natural pedogenesis. Therefore, systematic comprehensive analysis of magnetic parameters can effectively distinguish and delimit the man-made pollution range in farmland soil and provide a basis for farmland soil pollution prevention and control.