EGU24-9025, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

A new lipid-based proxy for the reconstruction of past phytoplankton ecological dynamics

Antonia Klatt1, Cindy De Jonge2, Daniel B. Nelson3, Marta Reyes4, Ricardo N. Santos1, Fatemeh Ajallooeian2, Carsten J. Schubert5,6, Nathalie Dubois2,7, and S. Nemiah Ladd1
Antonia Klatt et al.
  • 1Department of Environmental Sciences, Organic Geochemistry, University of Basel, Basel, Switzerland (
  • 2Department of Earth Sciences, ETH Zurich, Zurich, Switzerland
  • 3Department of Environmental Sciences, Botany, University of Basel, Basel, Switzerland
  • 4Department Aquatic Ecology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland
  • 5Department Surface Waters – Research and Management, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Kastanienbaum, Switzerland
  • 6Department of Environmental System Science, ETH Zurich, Zurich, Switzerland
  • 7Department Surface Waters – Research and Management, Sedimentology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland

The composition of lacustrine phytoplankton communities plays a key role for biogeochemical cycling of carbon, nitrogen, and phosphorus. Through the linkage between lakes and terrestrial ecosystems, especially via carbon cycling and freshwater supply, changes in algal ecology can affect even non-aquatic habitats. To investigate past phytoplankton dynamics, paleolimnologists often rely on microscopic algal remains preserved in the sediment, e.g., diatom frustules. However, only few taxa produce fossil remains, and might not be fully representative for the phytoplankton community. Other studies have reconstructed phytoplankton dynamics based on source-specific algal lipids, but many lipids are not as source-specific as initially thought. Rather than focusing on specific lipid biomarkers, a more holistic analysis of algal lipid distributions and their isotopic composition might highlight shifts in the past phytoplankton community with a greater robustness.

In this study, we introduce a new lipid-based proxy to reconstruct past phytoplankton community changes based on the abundance and hydrogen isotope ratios (δ2H) of short-chain fatty acids, phytosterols and phytol. Previous culturing and mesocosm experiments have shown that the relative offset between δ2H values of different algal lipids (εlipid1-lipid2) strongly differs among phytoplankton groups. For instance, εpalmitic acid-phytol values for green algae and cyanobacteria were ~150 ‰ higher than for other taxa. To validate these results in a natural system, we collected algal biomass samples from the water column of Lake Rot, a small eutrophic lake in central Switzerland, every second week from 2019 to 2020. Phytoplankton and microplankton cell counts were conducted for every sampling date. εlipid1-lipid2 values and algal lipid distributions were measured and related to biovolume changes of different algal groups. We used algal δ2Hlipid values from previous culturing studies weighted by phytoplankton biovolume in Lake Rot to model algal εlipid1-lipid2 values. To assess the potential heterotrophic impact on εlipid1-lipid2 values, we created a second model to simulate εlipid1-lipid2 values incorporating δ2Hlipid values from algae and microplankton. For this, we included hydrogen isotope fractionation between algal and plankton lipids as well as microplankton biovolume in Lake Rot. Modeled εlipid1-lipid2 values showed generally a good agreement with measured εlipid1-lipid2 values, validating εlipid1-lipid2 values as a potential proxy for phytoplankton dynamics. Moreover, measured εlipid1-lipid2 values were clearly represented by modeled algal εlipid1-lipid2 values suggesting that δ2Hlipid values in eutrophic lakes primarily reflect phytoplankton community composition with a negligible impact from microplankton. Our analysis of algal lipid distributions in the water column of Lake Rot revealed a significant positive correlation between the ratios of phytol and phytosterols (phytol:sterol ratio) as well as the sum of C18 fatty acids and C16:0 (C18:C16 ratio) and cyanobacterial biovolume.

We further apply our new lipid-based approach to a ~14 m long sediment core from Lake Rot, enabling a paleoecological reconstruction of phytoplankton community dynamics during the past ~13 kyr. Sedimentary phytol:sterol ratios, C18:C16 ratios, and εpalmitic acid-phytol indicate rising cyanobacterial biovolume during the last ~4000 years. Moreover, we compare the magnitude of change in the algal community in response to 20th century eutrophication with the natural variability throughout the Holocene.

How to cite: Klatt, A., De Jonge, C., Nelson, D. B., Reyes, M., Santos, R. N., Ajallooeian, F., Schubert, C. J., Dubois, N., and Ladd, S. N.: A new lipid-based proxy for the reconstruction of past phytoplankton ecological dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9025,, 2024.