Application of OSL dating and 137Cs measurements to reconstruct the history of water erosion: A case study of a Holocene colluvium in Świerklany, south Poland

Slopes used agriculturally at medium latitudes in European loess areas are modelled mainly by washing processes. The thickness of colluvium depends on the intensity of washing processes and the length of time of agricultural use, and it ranges from tens of centimetres to several meters in extreme cases. In southern Poland, anthropogenic deforestation of some slopes, and consequently washing processes, begun as early as 5 ka. However, in many places these processes began much later. As a result, colluvium accumulated at the foot of the slopes corresponds to different stages of the prehistoric and historical anthropopressure. Those specific stages of anthropogenic prehistoric erosion can be distinguished by dating methods. Dating may be used to establish the beginning of the prehistoric agricultural activity in a particular area and to determine the extent of areas used for agriculture in the past.To study Holocene colluvium, the Świerklany site was selected mainly due to an archeological-rescue excavation associated with the construction of the highway in the vicinity of Świerklany village. For laboratory study, four sample profiles were collected from key points of the study area. Two of them were located at the foot of slopes, one at the eroded part of the slope and one in a former pond area on the extension of the one of the tested slopes. Beside this, 10 cores were collected to measure 137Cs activity concentration as a modern erosion tracer. In the laboratory, analyses of 137Cs activity concentration, grain size distribution and luminescence characteristics were done. The quartz extracted from the collected colluvial sediment was suitable for age determination based on the OSL SAR protocol. The OSL results for the lower part of the profiles indicate that fossil soils developed about 10 ka. Younger results from overlying materials were used to infer a range of erosion and transport processes since deforestation associated with the establishment of Świerklany village, in the thirteenth century. The most modern phase of landscape activation are described by the 137Cs measurements, because 137Cs is present on the slope deposits to plough depth. The soil layer which contains 137Cs was dated by the OSL method for a period of 25–75 years, and the results obtained with both methods are in good agreement Results of investigations of the colluvium in Świerklany area clearly document good bleaching of OSL signal for sediments derived from washing (slope sediment).