The silicification value: a novel diatom-based indicator to assess climate change in freshwater habitats

Abstract

Formation of diatom frustules depends on the process of silicification. In many planktonic species of algae, ambient temperature and nutrients are already known to affect growth and morphology, making them suitable bioindicators. In this study, a similar indicator function of benthic diatoms is proposed based on the principle that cell wall thickness is inversely proportional to temperature and nutrients. Therefore, higher turnover rates at warmer temperatures are hypothesized to favour smaller and lighter diatoms due to their shorter regeneration time. Accordingly, benthic diatom species were classified into seven categories according to their intensity of silicification, referred to as ‘Silicification Value’. For each diatom assemblage, an abundance-weighted average silicification value was calculated and tested for its applicability to assess global change impact on mountain lakes in the northern calcareous Alps of Europe. Surface sediment diatom samples and morphometric and ecological parameters of 41 lakes from a wide altitudinal range in the Bavarian and Tyrolian Alps were collected and analysed. Statistical tests revealed that temperature conditions in a lake and its altitude were the most decisive proxies related to the ‘Silicification Value’. Moreover, trophic status and the presence of macrophytes had some influence. This supported the hypothesis that lakes, which are warmer and richer in nutrients, show a weaker average silicification in diatom assemblages. A dependence of silicification on valve size could be shown but appears to be negligible in climatological issues. In particular, the correlation with temperature makes the silicification value an applicable palaeoecological proxy to assess climate change impact in freshwater lakes.

Keywords:

• diatoms
• temperature
• climate change
• mountain lakes
• silicification

Acknowledgments

The authors want to thank our colleague Andrea Hofmann for providing diatom and environmental data of the mountain lakes. Moreover, thanks to our students, who enthusiastically helped with the fieldwork, hydrochemical analyses and some diatom counts: Yvonne Bernauer, Moritz Bissinger, Joachim Hilber, Lena Hofmeister, Ben Horsmann, Lena Nowotny, Sabrina Pitschi, Melina Stegbauer, Lorenz Tschampel, Melina Weger and Lukas Zwosta. Special thanks also to John Smol, who inspired our work on the valve size effect.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental data for this article can be accessed at https://doi.org/10.1080/0269249X.2020.1722246

ORCID

Wolfgang Kuefner http://orcid.org/0000-0002-9827-7950

Stefan Ossyssek http://orcid.org/0000-0002-3632-5478

Juergen Geist http://orcid.org/0000-0001-7698-3443

Uta Raeder http://orcid.org/0000-0002-2982-3196

Additional information

Funding

This study was funded by Bavarian State Ministry of the Environment and Consumer Protection terms of the project ‘Climate Change in Bavarian mountain lakes’.