Diatom-based paleoenvironmental reconstruction in Lake Balaton, Hungary (Tó34f)

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A high-resolution diatom assemblage’s database was built on a 65 cm long sediment core (Tó34f), obtained from the Siófok Basin of Lake Balaton in 2017. Light microscope photo-documentation was developed out of 15,797 diatom valves. The pictures were arranged according to taxonomy from centric diatoms via araphids, monoraphids to biraphid forms. 30 categories were established to group the diatom taxa instead of species level identification requiring high level of expertise. Some (1) characteristic, and easily identifiable taxa (Karayevia clevei, Cavinula scutelloides) were distinguished on species level, (2) taxa were grouped at genus level (like Amphora, Aulacoseira, Neidium), while (3) were joined based on their morphological features. Two large groups were created based on this approach, the “light fragilarioids” and the “heavy fragilarioids”. Both groups contain diatoms with taxonomic problems, e.g. Staurosira, Staurosirella genera and other fragilarioids. This approach allowed us to make paleo-ecological reconstruction on (1) rough taxonomic data and (2) apply trait-based methods. Diatom assemblage’s zones were defined by CONISS clustering method, validated by the broken stick model. Though the planktonic trait (referring the high lake level) is insignificant (< 5%) in most of the studied record, but some peaks (>35%) point to high water level. The most recent trend of increasing number of planktonic diatoms is hypothesized to be due to the recent global warming. We demonstrated that traits are a good alternative to time and expertise demanding species-level determination of diatoms, thus a quick method is found for paleo-ecological reconstructions, while the photo-base good for detailed taxonomic work at a future time.