Past climate changes in Lake Constance – lessons for the future
Objectives
A flood chronology of the last 5000 years
Sediment cores from the Friedrichshafen Bay will enable a high resolution reconstruction of the discharge history of the Alpine Rhine and the flood history of Lake Constance. The well-laminated sediment archives allow the identification of natural climate changes and the reconstruction of a flood chronology reaching far back into the past. The analysis of sediment archives allows the assessment and the classification of flood risks at Lake Constance – particularly against the background of anthropogenic climate change.
Research approach
The sediments of Lake Constance as an archive of environmental changes
The sediments of Lake Constance are a high-resolution archive of environmental change that extends far beyond the periods documented by historical sources and measurement data (from 1817 onwards). They enable us to obtain and analyse information on the lake ecosystem for periods without measurement records including periods without human impact (land use, hydropower, hydraulic engineering, eutrophication, climate change). By comparing periods of natural dynamics with the last few centuries, heavily influenced by humans activities, it will become possible to better understand the extent of the changes observed today and the human influence in order to prepare for expected future changes.
The investigation of past ecosystem changes in Lake Constance provide the unique opportunity to learn from the past in order to shape the future and to enable a sustainable development.
Sediment cores along a transect from Friedrichshafen Bay to the mouth of the Alpine Rhine. The increase in sediment thickness to the east is clearly recognisable. The sedimentation dynamics increase sharply near the mouth of the Rhine where the signal of individual, easily identifiable flood years gives way to thick event deposits. Using gravity corers (blue dots) the spatial distribution of the sediment thickness is mapped and with the discharge records of the Alpine Rhine a numerical flood model will be calibrated.
Ecosystem changes
Information about past ecosystem functioning can be derived from shells, diatoms, mussel crustaceans and remains of cladocerans, which have been preserved in the sediment of Lake Constance for thousands of years and are analysed on a regular basis for around 50 years. Classical methods (identification and counting of physically preserved organism remains such as diatoms and ostracods) and new methods (analysis of organism groups with sedimentary DNA fragments) have already been used to reconstruct trophic changes in the Lake Constance ecosystem (Wessels et al. 1999, Ibrahim et al. 2019, Milan et al. 2022, Wang et al. in press). These methods will be applied specifically to periods of natural climate fluctuations in order to understand the reactions of aquatic communities to natural climate dynamics.
First results
Core extraction
Short gravity cores
In preparation for the sub-project, around 40 short – up to approx. 1 m long – sediment cores have been taken between the current mouth of the Rhine and Friedrichshafen Bay since 2023. A drop-lot consists of a core tube (plastic tube/liner) which penetrates the soft sediment surface due to its own weight and enables relatively undisturbed sampling of the seabed.
Long core sampling locations between Friedrichshafen Bay and Kressbronn using a miniVibroCorer and a piston corer.
miniVibroCorer
In cooperation with the companies limknow GmbH and K.U.M. Umwelt- und Meerestechnik Kiel GmbH, a newly developed “miniVibroCorer” was deployed and ten sediment cores up to 4.5 metres long were extracted. The miniVibroCorer was lowered from on board the institute’s own research vessel Kormoran to a depth of up to 200 metres. A 6 metre long core chamber was pushed into the soft sediments by the weight and the vibrations of a small motor.
Core extraction with the miniVibroCorer from on board the research vessel Kormoran in collaboration with limknow GmbH and K.U.M.
(Photo: Martin Wessels, ISF)
Sampling using a piston corer was carried out on a floating platform of the Institute of Geology and Mineralogy of the University of Cologne with the support of the 2024 student practical training course.
(Photo: Martin Wessels, ISF)
Analyses
The cores are stored in the cold room of the Institute of Lake Research at approx. 4°C. After opening, the sediment layers are photographed, measured and described. Selected cores are currently being further characterised using non-destructive examination methods (high-resolution line scan camera, X-ray fluorescence analysis (XRF) to determine element distribution, magnetic volume susceptibility). Distinctive flood layers are identified and analysed for their grain size composition, main minerals and carbon content. The results will be compared with existing studies of earlier cores (Wessels 1995, 1998, Wang et al. in press) to ensure the representativeness of the analyses and statements.
To assess past ecosystems in Lake Constance, periods with high hydrological and climatic dynamics will be analysed in detail for organism remains in order to understand the reaction of aquatic communities to environmental changes.
Well-preserved sediment layers of the 4.5 m long core BO24-53 off Langenargen. Cracks and gaps are due to a high gas content. The eutrophic phase with high nutrient input in the middle of the 20th century is clearly recognisable in the upper part.
Cooperation within the SeeWandel-Climate project
Modelling the flood chronology (kup, sub-project 5).
Support for quagga mussel monitoring in the pelagic and littoral zone of Lake Constance (Eawag, sub-project 6A).
Coordination of the SeeWandel-Climate thematic working group “Water level dynamics and littoral”. This working group brings together knowledge on the expected impact of climate change with regard to water level changes and the shallow water zone.
Associated project partners
State Office for the Preservation of Monuments in the Regional Council of Stuttgart (LAD), Department of Wetland Archaeology, Germany
International Rhine Regulation (IRR), Rhine Engineering Management Austria
In collaboration with
apl. Prof. Dr. habil. Bernd Wagner, Institute of Geology and Mineralogy, University of Cologne, Germany
Piston corer sampling as part of a practical student training & XRF measurements on half cores
Prof. Dr. Flavio Anselmetti, Institute of Geological Sciences, University of Bern, Switzerland
Whole-core MSCL logging to determine magnetic susceptibility and gamma-density
Dr. Christian Zeeden, Leibnitz Institute for Applied Geophysics (LIAG-Grubenhagen), Germany
Measurement of paleomagnetic parameters
Prof. Dr. Laura Epp, Limnological Institute, University of Konstanz, Germany
eDNA assessment
Prof. Dr. Claudia Wrozyna, Institute of Geography and Geology, University of Greifswald, Germany
Ostracod determination
limknow GmbH & Co. KG, Germany
Sampling with the miniVibroCorer
Umwelt- und Meerestechnik Kiel GmbH (K.U.M.), Germany
Sampling with the miniVibroCorer
