Sediment cores from Bichelsee and Hüttwilersee, two lakes in the canton of Thurgau, Switzerland, were studied by an interdisciplinary team of researchers from the University of Basel, EAWAG Dübendorf, the University of Bern, ETH Zurich...
moreSediment cores from Bichelsee and Hüttwilersee, two lakes in the canton of Thurgau,
Switzerland, were studied by an interdisciplinary team of researchers from the
University of Basel, EAWAG Dübendorf, the University of Bern, ETH Zurich and the
Canton of Thurgau’s Office of Archaeology between 2019 and 2023. Based on various
scientific analyses of the lake sediments the research aimed to reconstruct past environmental changes and the influence of human activity on ecosystems and
landscapes in the Canton of Thurgau. The research project «Climate, Environment,
Man in Thurgau» (KUMIT) was financed by the Walter-Engist-Fund.
The sediment cores, up to 13 metres long, provided a complete sedimentary sequence
from the end of the Würmian glaciation to the present day at both lakes and
together covered the past 16,000–17,000 years. A total of 201 radiocarbon dates,
137Cs/210Pb analyses in the upper sections and evidence of the Laacher See Tephra
layer were available to constrain the age of the sediments and enabled high-resolution
depth-age modelling for the sequences. The analyses provided new insights
into the terrestrial and aquatic environmental history and allowed the comparison
of archaeological and historical data with the palaeoecological analyses: The results
indicate, for example, Neolithic and Bronze Age settlement phases at the two lakes
that have not yet been documented by archaeological finds. They reveal phases of
land opening and changes in the agricultural use of the landscape in the vicinity of
the lakes over millennia. They further document the immigration and the changing
importance of various tree species in the forests around the lakes, but also, for example, that certain trees, such as European spruce, were not as common at these
sites as one would expect based on archaeological wood from building surveys in
the Lake Constance region. The spread of neophytes and the influence of modern
agriculture on the lakes and their surroundings can also be recognised based on
analyses of the youngest sections of the records. Aquatic indicators show how the
lake ecosystems of Bichelsee and Hüttwilersee have changed over long time scales,
indicate when, from today’s perspective, undesirable conditions (e.g. oxygen depletion,
high nutrient concentrations) became established and document when the
lakes have changed as a result of human activities, but also how they recovered after
these have subsided or as a result of lake restoration measures. From a lake history
perspective, the very early human influence on the ecosystem of Hüttwilersee,
with a pronounced eutrophication phase as early as the Neolithic period, and the
early establishment of at least seasonally low-oxygen conditions in the deep water
of both lakes from the early to mid-Holocene onwards, are of particular interest.
The recent eutrophication phases and the rising levels of soot particles in the 20th
century that are clearly visible in both profiles show how increasing human pressure
led to negative impacts on our environment and ecosystems. At the same time,
the recovery of the lakes from this eutrophication and the stabilisation or decrease
in soot particles in the uppermost sediment layers also demonstrate how environmental policy, social debate and environmental legislation and measures have led to a recovery of the lake ecosystems and improvements in air quality.
The KUMIT research project has significantly improved the information on the environmental history of the canton of Thurgau, and particularly provided information
on the long-term, off-site development of ecosystems, i.e. at locations that have not
been investigated in detail by archaeological excavations, but represent the largescale
development of the landscape, vegetation and lake ecosystems. It is expected
that future comparisons with comparable data sets from the western Central Swiss
Plateau, the southern German Alpine foothills and Upper Austria will provide exciting
new insights into the supra-regional environmental development of this region.