Ecological responses of the diatom species Asterionella formosa to climate change and resource availability in a shallow eutrophic lake of Chinese Loess Plateau

Diatoms have long been recognized as strong ecological indicators for climate and environmental changes. Asterionella formosa Hassall is a cosmopolitan diatom species around the world, but its ecological preferences are still unclear and its palaeolimnological interpretations are strongly disputed. This species is often considered to be driven by nutrient enrichment, whereas it was recently proposed that the increasing abundance of this species is linked to warming-induced lake thermal stratification. To improve its ecological interpretation, we examine the possible driving factors of this species through diatom seasonal monitoring in an alpine, shallow and eutrophic lake (Lake Mayinghai) on the Chinese Loess Plateau. Our data show that the compositional dominance of A. formosa in the late-autumn and winter months indicates that this species can tolerate both mixing and ice-covered stable water conditions and further suggests that it has a preference to low light availability. The dominance of this species is not associated with an increase in nutrients, and does not support that this species can be used as an indicator of nutrient enrichment. However, given low diatom production in the cold season, increased lake thermal stability in the growing season induced by warming is a more probable explanation, and it is likely that a eutrophic, turbid condition or an oligotrophic, other algae-dominant low-light condition may be a requisite for its interpretation as a signal of warming.