Human‐induced overbank sedimentation in the foreland of the Eastern Sudety Mountains

Abstract

AbstractAnalysis of a 2–3 m thick vertical sequence of fine‐grained overbank alluvial sediments on the foreland of the Eastern Sudety Mountains reveals that these sediments resulted from human land use changes. Following the Holocene climatic amelioration the first farmers and breeders, migrating northward from the Danube Basin, crossed the limit of the Sudety–Carpathians and settled the loess‐covered Glubczyce Plateau about 7000 years ago. The farming and breeding tribes of Early Bronze Age created the compact settlement structure of the Lusitian culture here about 1600–1300 years BC. The first forest clearance began at this time. Slavic settlements existed here in Early Medieval times from at least the 6th and 7th centuries onwards. Later, economic expansion of the Opole Duchy and increased population density (up to 20–30 persons/km2) caused an increase in soil erosion and flood amplitudes.Investigation of small‐radius palaeomeander infills adjacent to the main channels indicates that fossilization of organic material that filled these palaeochannels started in Early Medieval times due to more frequent flood waves and an increased rate of overbank sedimentation. In channel undercuts, ‘older’ alluvia have well‐developed cambic gleyo‐fluvisols while ‘younger’ homogenous alluvia do not have traces of soil processes. Analysis of heavy metal concentrations in ‘older’ and ‘younger’ deposits indicates very similar concentrations of cadmium, copper, lead and zinc. This indicates that the source of these alluvia was the transfer of sediments from the mainly deforested part of the drainage basin. Therefore, since at least Early Medieval times, and possibly even earlier, the Glubczyce Plateau has been a deforested region. Despite the mountainous character of the headwater area of rivers in the Eastern Sudety foreland, sediment transfer from sub‐mountainous loess‐covered uplands, induced by human activity, is clearly marked in the granulometric and geochemical properties of the vertical sequences of overbank deposits. Copyright © 2002 John Wiley & Sons, Ltd.