Wolfgang Rösler

Topsoil Magnetic Susceptibility Mapping: Data Reproducibility and Compatibility, Measurement Strategy

Magnetic susceptibility measurements on topsoils have often been used during the last few years to detect anthropogenic pollution. In most cases, a Bartington susceptibility meter for field measurements was used. However, up to now, no standard procedure has been developed for carrying out such investigations. The purpose of our study was to test the compatibility of different set-ups of instruments used for this purpose and the possible influences of subjective (human) factors. Field magnetic susceptibility measurements, carried out with four different Bartington MS2D instruments in strictly defined positions, are very consistent both for low and high values. The correlation coefficient between the magnetic susceptibility values recorded with different Bartington MS2D probes reached 97–98%. A test area was mapped independently by two groups, without any restrictions concerning the choice and distribution of the measured points, but respecting a few standard conditions (e.g., measuring at a distance from tree trunks; on the flattest place possible; recording between 10–30 values per point). The resulting susceptibility maps show the same general features in both cases, suggesting that the measuring strategy applied is suitable for topsoil magnetic screening. The methodology proposed can be used to map magnetic susceptibility on a larger scale—for example Europe—providing large sets of representative data and eliminating border-transition biases and human errors.

Magnetic survey of soil pollution around meishan steel mill in Nanjing, China

High resolution magnetic survey around Meishan steel mill in Nanjing (SE China) was carried out after a preliminary magnetic study which proved that paddy soil could be a suitable target for environmental study on heavy metal pollution. Magnetic susceptibilities were measured on the surface and along down holes at 100 soil sites around Meishan steel mill. In vertical profiles, geochemical and magnetic results show an obvious boundary at a depth of 20cm or so (plough pan). It means there is no transmission of heavy metals below plough pan. The low susceptibility blow plough pan can be taken as background, and the high susceptibility in the upper part can be thought as an average polluted signal. Surface measurement of magnetic susceptibility at paddy field around the steel mill shows a decreasing trend with the increasing distance from the main emission zone of steel mill. With the help of geochemistry, correlation between zinc content and magnetic susceptibility of top soil is proved to be significant. It indicates paddy soil can be used as an effective object to map heavy metal pollution. To some extent, our research expands the magnetic object for heavy metal pollution, and makes it possible to carry out a large scale magnetic scanning for heavy metal pollution in China, since undisturbed soil with low magnetic background is not easy to find.