Non-uniform responses of small fragilarioid taxa to environmental changes in global mountain lakes during the last century

Abstract

Global environmental changes have accelerated the degradation of remote mountain lake ecosystems during the Anthropocene. Small fragilarioid taxa (SFT), a group of benthic diatoms encompassing genera such as Staurosirella, Staurosira, Pseudostaurosira, may respond sensitively to global environmental changes. However, knowledge regarding such SFT responses at the continental scale remains limited. This study explored spatiotemporal changes of SFT in sedimentary records of 78 mountain lakes during the last century. There was a net increasing trend in global-scale SFT abundance since the 20th century, and hence global changes have accelerated diatom flora shifts during recent decades. Generally, SFT increased in high-elevation mountain lakes, but decreased in low-elevation mountain lakes. In high-elevation lakes that are less influenced by human activities, SFT respond more strongly to climate change and anthropogenic disturbances. According to the results of correlation analyses and generalized additive models, climate change and local human activities played a major role in recent changes in SFT in mountain lakes. In terms of spatial distribution, SFT were more dominant in small shallow lakes in comparison with large deep counterparts, and thus their utility as an ecological indicator is likely mediated by lake morphometry. Although accurate identification of SFT to species level is challenging because many SFT appear similar in lateral view, our results highlight that SFT as a group can be a useful bioindicator for tracking past environmental changes in mountain lakes, especially in small shallow lakes at high elevations.