Bacterial communities in pre-alpine headwater streams

Microbial communities play a vital role in the functioning of stream ecosystems. However, the factors that control their composition and diversity in headwater streams remain poorly understood. In this study, we investigated the hydrological and biogeochemical controls on microbial composition and diversity at different seasons in the Oberer Seebach catchment in Austria. Here we show that bacterial community composition and diversity is strongly influenced by variations in precipitation and discharge. We found that the free-flowing bacterial communities found in streams during flood events differed depending on whether the event was the result of a summer storm or snowmelt. During summer high flow events, the bacterial diversity in the Oberer Seebach increased by 8% compared to communities during snowmelt. In soils and biofilms, bacterial diversity and species richness were more affected by dissolved organic carbon quality or pH than a change in discharge. Our results demonstrate that soil water, streams, and biofilm communities respond differently to an increase in discharge and a change in season despite them being intricately connected.