Autor:innen:
Obaida Assida | Georg-August-Universität Göttingen, Geographisches Institut | Germany
Dr. Daniel Schwindt | Georg-August-Universität Göttingen, Geographisches Institut | Germany
Prof. Dr. Daniela Sauer | Georg-August-Universität Göttingen, Geographisches Institut | Germany
Alluvial and colluvial sediments represent a valuable archive of landscape development. Using this archive, we aimed to reconstruct the Holocene erosion-sedimentation dynamics in the catchment of the Aue river, a tributary to the Leine river in southern Lower Saxony, with an area of about 112 km2. Our goal was to establish a chronology of phases of varying sedimentation rates, and to determine the underlying driving factors. This catchment is particularly suitable for this purpose, because its loess-covered slopes are highly prone to erosion, thus responding highly sensitively to land-use change, while subrosion along the valley (due to soluble salts at some depth) makes the floodplain an efficient sediment trap that accumulated an unusually thick sediment sequence.
Based on a high-resolution DEM and field observation, the catchment was divided into several sub-catchments: (1) the main Aue catchment, having the widest floodplain and thickest deposits; (2) the Eboldshausen sub-catchment, having a narrow alluvial plain; (3) the Westerhof sub-catchment, including a paleolake; (4) the Düderode sub-catchment having a v-shaped valley and no distinct alluvial plain. We described 70 drill cores (mostly reaching 5-6 m depth) along the floodplain, across adjacent slopes, and from the paleolake. 50 samples (mostly charcoal or plant fragments) were subjected to radiocarbon dating to create a chronological framework of the different erosion/sedimentation phases.
We found a very low to negligible sedimentation rate during the early Holocene. The mid-Holocene witnessed a slight increase in sedimentation rate within the main Aue catchment. At that time, the Pleistocene fluvial gravel was covered by sandy deposits, followed by alluvial loam. The sediments of the paleolake area in the Westerhof sub-catchment, consisting of alternating peat and lacustrine sediments, show high mid-Holocene sedimentation activity.
The late Holocene, especially after 3800 cal BP (Iron age), witnessed a significant increase in sedimentation rates in the main Aue catchment. However, the maximum geomorphological changes started in the high Medieval time, after 1200 cal BP, and lasted until the modern period, with deposition of up to 3-5 m alluvial loam in some parts of the catchment. Increasing human activities in the catchment since the Iron age played the main role in driving these changes in the geomorphological dynamics.