The silicification value: a novel diatom-based indicator to assess climate change in freshwater habitats
2020
Kuefner, Wolfgang | Ossyssek, Stefan | Geist, Juergen | Raeder, Uta
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.
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