Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics in Rotsee (Switzerland)

Reconstructions of past changes in algal community composition provide important context for future alterations in biogeochemical cycling. However, many existing phytoplankton proxies are indicative of individual algal groups and are not fully representative of the whole community. Here, we evaluated hydrogen isotope ratios of algal lipids (δ2Hlipid) as a potential proxy for phytoplankton community composition. We sampled the water column of Rotsee, a small eutrophic lake in Switzerland, every second week from January 2019 to February 2020 and analyzed distributions and the relative offsets between δ2Hlipid values (ε2Lipid1/Lipid2) from short-chain fatty acids, phytosterols and phytol. Comparing these data with phytoplankton cell counts, we found ε2C16:0/sterol and ε2sterol/phytol values reflect shifts in the eukaryotic algal community. To assess whether the selected phytoplankton groups were the main sources of the selected lipids, we further modeled algal ε2Lipid1/Lipid2 values based ..., Water and biomass samples were taken biweekly from the water column of Rotsee at 1 m depth and the chlorophyll maximum depth over a one-year period. For biomass samples, lake water was filtered through glass fiber filters. The chlorophyll maximum depth on each sampling date was determined based on the turbidity maximum measured by a multi-parameter CTD probe. The temperature at the two different sampling depths was estimated by the mean of temperatures measured by the CTD probe from 0.5 m above to 0.5 m below the respective depth. Cell counts of phytoplankton and microzooplankton species were conducted from water samples and the biovolume of individual taxonomic groups was calculated based on cell densities and the mean per-cell biovolume. δ2Hwater values of filtered water samples were measured by a high-temperature conversion/elemental analyzer (TC/EA) coupled with isotope ratio mass spectrometry (IRMS). Nutrient concentrations of filtered water samples were measured via spectrophotome..., , # Algal lipid distributions and hydrogen isotope ratios reflect phytoplankton community dynamics in Rotsee (Switzerland)

[https://doi.org/10.5061/dryad.9s4mw6mrm ](https://doi.org/10.5061/dryad.9s4mw6mrm)

## Description of the data and file structure

This dataset comprises different parameters measured biweekly in the water column of Rotsee during a one-year sampling period.
Measurements occurred at 1 m depth (A) and the chlorophyll maximum depth at the respective sampling date (B). Sample names include the lake name (ROT), the date (yy-mm-dd), and the sampling depth (A or B). Different specifications were made for biovolume data, i.e., all phytoplankton including cyanobacteria, eukaryotic algae excluding cyanobacteria, and biovolume with and without microzooplankton contribution. 

The following files contain (1) phytoplankton and microzooplankton biovolume (absolute values), (2) nutrient concentrations and temperature, (3) concentrations of different algal lipids (fatty acids, ster...