Magnetic responses to heavy metal pollution and its statistics significance for site 722 soil vertical profile in eastern Beijing

Two short cores were obtained from a tree nursery in eastern Beijing city, and gray-black pollutants can be found within the uppermost 37 cm of the soil profile. All of them were measured, and one of them, profile BJ722 of 90 cm length, is discussed in detail in this paper. Magnetic measurements, element contents and grain size analysis were carried out to understand the vertical characteristics of magnetic minerals and heavy metals in soil from anthropogenic pollutants, as well as the relationship between magnetic parameters and heavy metals. Magnetic proxies show similar pattern comparing to heavy metal elements, with higher concentration above 37cm. Index cluster and principal component analysis indicate that strong correlation between magnetic parameters and Pb, Zn, Sr, Ba and Cu (R2>0.90, membership>80%). Fuzzy C-means cluster analysis (FCM) shows that anthropogenic pollutants accumulated and enriched above 37 cm. Below 37 cm, soil is unpolluted. Our work demonstrates that magnetic measurements can be used to delineate anthropogenic pollution in the soil profile and to identify the migration depth and the depth of unpolluted soil with the help of multivariate statistics.