BayCEER Workshop 2023

Changing river dynamics in the Eger/Röslau catchment since the late Middle Ages – investigations using three human induced metals as tracers (Hg, Fe, Sn)

River systems in the Middle-European uplands have undergone significant changes in their structure and dynamics due to different types of human impact. Our aim is to unravel the change of river dynamics of the upper Eger and its tributaries in the Fichtelgebirge uplands (Upper Franconia, Germany) driven by land-use and mining history. From 1788 until 1985, the chemical factory Marktredwitz contaminated the river system with mercury. Even earlier the region was rich with mining and metalworking, starting in the Middle Ages. The most important metals were tin (peaking 1300-1450) and iron (peaking 1400-1750), connected with hammer mills and hydropower. As a result, the floodplains have been severely modified and chemically imprinted.

We use these metals from three different time periods as tracers to determine the age and mixing of river and floodplain sediments as well as their overall dynamics through time. Based on an evaluation of historical maps, aerial- and ortho-photos and mapping of current erosion, we defined cross sections along the river course to perform sediment coring and geophysical surveys (geoelectrics/ERT, ground-penetrating radar/GPR). Sediment coring provides an overview of the sedimentary architecture, grain size distributions and provides the samples for chemical analysis (XRF, ICP). ERT and GPR extend drill core information on thickness, lateral extent and architecture of fluvial and floodplain deposits. Erosion mapping and chemical analyses will be compared to a study on mercury contamination conducted 2011, to reveal current dynamics.

First results show a great variability of the character of floodplain sediments, especially in their grain size distribution, implying spatial and temporal differences in erosion and sedimentation along the river. Variability close to the rivers (<1m) is significantly higher than further away (1-10m), indicating concentration of present-day river dynamics in the immediate vicinity of the rivers. Results of the chemical analyses will be presented on the poster.