oa Persistent Roman Impact on Algal Community in Murtensee (Switzerland)

During the 2nd century before common era, human activity led to significant disturbances (soil erosion, cultural eutrophication, changes of local vegetation) of Murtensee and its catchment, which persisted for centuries, providing an ideal context to analyze not only the immediate effects but also the potential recovery capability of the algal community following such a disturbance.

We present a record spanning 10,000 years of the relative abundance of lipid biomarkers, which we used to reconstruct the ratio between eukaryotic algae and cyanobacteria and to provide insights about the diversity among eukaryotes. Our results reveal a prominent shift towards cyanobacteria during the Roman period, and a substantial decrease of specific phytosterols indicative of dinoflagellates and diatoms. We complement our analyses of biomarker distributions with compound-specific hydrogen isotope measurements of fatty acids, n-alkanols, and phytol, and use the offsets among these to further distinguish ecological changes in the lake. In addition to our organic geochemical data, we analyzed sedaDNA using a metabarcoding approach targeting cyanobacteria.

Although human pressure was reduced following the Roman period, the effect on the algal community composition was long-lasting, with persistent reduced diatom abundance for at least three centuries, and reduced dinoflagellate presence for over 1,500 years.