Use of variograms for field magnetometry analysis in Upper Silesia Industrial Region

Measurements of topsoil magnetic susceptibility are often used for quick assessment of soil contamination of anthropogenic origin, with heavy metals or other pollutants. However, because of complicated correlations between low-field magnetic susceptibility (shortened to magnetic susceptibility) of topsoil and soil pollution, the outcome of a field magnetometry survey can not be related directly to soil pollution. For each case study, the results should be interpreted on their own taking into account not only the type of pollution but also pedogenic, biogenic and environmental factors. In practice, it is very difficult to measure and consider all these factors. Here we illustrate the merit of geostatistical methods, which are focused on the spatial variability of a phenomenon, in the interpretation of soil magnetometry results. This article presents the analysis of spatial variability of top soil layers magnetic susceptibility-within the Upper Silesia Industrial Region (USIR)-using semivariance analysis. It also explains how to adjust the sampling density of field magnetometry measurements to spatial variability of the soil pollution as well as to the spatial scale of the investigated area. For this purpose, the values of magnetic susceptibility have been measured by using various sampling densities at areas of different size located within USIR. This enabled to determine the main scales of magnetic susceptibility spatial variability of soils within USIR using semivariance. A few distinct scales of variability were found from the site scale to a more regional scale. Variability ranges of 30 km, 12 km, and 5 km refer to the large regional scale, whereas smaller ranges of few hundreds down to a few tens of meters, can be attributed to the local (site) scale. In addition, the precision of the measuring campaigns, performed within USIR with different sampling densities, was compared through the analysis of the spatial variability of the soil magnetic susceptibility signal by using ordinary kriging. jarek97@yahoo.com, piotr.fabijanczyk@is.pw.edu.pl