19 Feb. 2013 - Liisa Nevalainen

Sedimentary invertebrate remains disentangle long‐term hydrolimnological changes in Austrian mountain lakes

Presenta: Liisa Nevalainen (Department of Environmental Sciences, University of Helsinki, Finland)

Mountain lakes in the Austrian Alps were investigated with the paleolimnological approach. The aim was to utilize sedimentary invertebrate assemblages (Chironomidae, Cladocera, Oribatida) to infer hydrolimnological alterations under the post Little Ice Age (LIA) climate warming. Short sediment sequences were cored from three case study lakes across the tree‐line: Oberer Landschitzsee, Twenger Almsee, and Moaralmsee, and a surface sediment dataset was sampled from Moaralmsee. In Moaralmsee, intralake calibration models based on subfossil invertebrate assemblages and linear models based on oribatid mites and loss‐on‐ignition were used to reconstruct past lake level fluctuations. The inferred lake level trends strongly correlated with each other showing periods of low lake level for ca. 1600‐1650 AD and 1700‐1900 AD, and high lake level ca. 1650‐1700 AD and 1900 AD‐present. The sediment profile from Oberer Landschitzsee showed a complete and simultaneous invertebrate community turnover from ca. 1850 AD onward. The faunal shifts corresponded with reduced benthic quality, higher organic content of the sediment, and the progressive climate warming, superimposed with Alpine land‐use changes, that likely were indicative of changes in summer stratification. In Twenger Almsee, there was a threshold crossed at ca. 1850 AD, when invertebrate taxa tolerant of oxygen deficiency disappeared, oxybiontic taxa began to dominate, and the zooplankton community exhibited a species turnover. These ecological changes were most likely caused by improved oxygen conditions following the deepening of the depth of the summer stratification layer, and ultimately driven by the increased air temperatures. Overall, the collective core results showed significant community shifts in all the three case study lakes around 1850‐1900 AD and pronouncedly during the late 20th century, coinciding with the Alpine temperature increase and suggesting that significant climate‐driven hydrolimnological and ecological thresholds have been crossed.

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