Historical anthropogenic layers identification by geophysical and geochemical methods in the Old Town area of Krakow (Poland)

In the Middle Ages, trade and craft started developing intensely in Krakow, a significant metropolis of Central Europe. This led to a considerable demand for water, which resulted in the creation of an elaborate network of artificial watercourses. Their course, until today, has not been sufficiently studied. Non-invasive geophysical methods combined with a small diameter borehole drilling technique and geochemical analyses can identify the presence of structures connected with historical moats, millstreams, etc. on the basis of historical sediment recognition. The research carried out in 2010 involved measurements with two geophysical methods, i.e. the ground-penetrating radar (GPR) and the cesium magnetometer. Due to the high attenuation of electromagnetic waves by anthropogenic soil and magnetic disturbances connected with a tram line, additional measurements were undertaken using the electrical resistivity tomography (ERT) technique. This method allowed the detection of structures buried under anthropogenic layers. Based on the use of borehole drilling and the acquisition of ground profiles, it was possible to present a more precise interpretation. In consequence, the location of historical watercourses was determined and the course of their fragments was mapped more precisely. The measurement of the basic physicochemical proprieties of the ground samples (pH, Eh, EC) and determining the metal concentration with atomic absorption spectroscopy (AAS), enabled to identify anthropogenic-origin metals, such as Cu and Pb, and also those of the geogenic origin, like Fe, in the medium. The measured values were correlated with the measurement results of magnetic susceptibility, which allowed for lithological classification of the layers.