POSTER Session 1

Identifying phytoplankton groups from absorption spectra – a regional approach based on data from the Baltic Sea and Estonian lakes

Determining Chl-a from optical measurements and using it as a proxy for total phytoplankton biomass has been ongoing for a long time. However, different phytoplankton groups occupy unique positions in the ecosystem, and thus, there is a need to distinguish them. Some groups, such as the cyanobacteria, cryptophytes, chrysophytes, chlorophytes, dinoflagellates and diatoms, can be discriminated via unique photoactive pigments (markers). These are typically measured using High-Performance Liquid Chromatography (HPLC), an arduous, expensive, and time-consuming process. Obtaining information about the presence and concentration of ’marker’ pigments from absorption spectra would allow for quicker and cheaper analysis of the phytoplankton dynamics. Here, different approaches to derive pigment concentration have been undertaken – a chl-based model, a Gaussian decomposition model, and a model based on principle component analysis (PCA). The pigment concentration was also linked with the measured biomass. The analysis relies on the data gathered during a research cruise on the Baltic Sea and special optical monitoring campaigns of Estonian lakes. Preliminary results indicate that different models are better at distinguishing various pigments. The Gaussian decomposition model has shown an overall better performance than the other models, especially for photoprotective carotenoids (PPC) derived from absorption at 498 nm (r2=0.86). Meanwhile, the chl-a model showed promising results for discerning zeaxanthin (r2=0.72), a key pigment in cyanobacteria. A comparison between regional models for deriving marker pigment concentration has been undertaken, and implications for phytoplankton group biomass have been discussed.

*Ian-Andreas Rahn, University of Tartu, Estonia, https://orcid.org/0000-0001-9590-0623

Kersti Kangro, University of Tartu, Estonia, https://orcid.org/0000-0001-6143-9330

Krista Alikas, University of Tartu, Estonia, https://orcid.org/0000-0003-3855-6525

Rüdiger Röttgers, Helmholtz-Zentrum HEREON, Germany

Martin Hieronymi, Helmholtz-Zentrum HEREON, Germany

Rene Freiberg, Estonian University of Life Sciences, Estonia, https://orcid.org/0000-0002-8645-0031

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