Lake Sediment Microbial Communities in the Anthropocene

Abstract

Since the Industrial Revolution at the end of the 18th century, anthropogenic changes in the environment have shifted from the local to the global scale. Even remote environments such as the high Arctic are vulnerable to the effects of climate change. Similarly, anthropogenic mercury (Hg) has had a global reach because of atmospheric transport and deposition far from emission point sources. Whereas some effects of climate change are visible through melting permafrost, or toxic effects of Hg at higher trophic levels, the often-invisible changes in microbial community structures and functions have received much less attention. With recent and drastic warming-related changes in Arctic watersheds, previously uncharacterized phylogenetic and functional diversity in the sediment communities might be lost forever. The main objectives of my thesis were to uncover how microbial community structure, functional potential and the evolution of mercury specific functions in lake sediments in northern latitudes (>54ºN) are affected by increasing temperatures and Hg deposition. To address these questions, I examined environmental DNA from sediment core samples and high-throughput sequencing to reconstruct the community composition, functional potential, and evolutionary responses to historical Hg loading. In my thesis I show that the microbial community in Lake Hazen (NU, Canada) sediments is structured by redox gradients and pH. Furthermore, the microbes in this phylogenetically diverse community contain genomic features which might represent adaptations to the cold and oligotrophic conditions. Finally, historical Hg pollution from anthropogenic sources has likely affected the evolution of microbial Hg resistance and this deposition can be tracked using sediment DNA on the Northern Hemisphere. My thesis underscores the importance of using culture-independent methods to reconstruct the structure, functional potential and evolution of environmental microbial communities.