Microbial communities as indicators of anthropogenic impacts in Antarctic lakes

Fildes Peninsula is one of the Antarctic regions having the highest intensity of human activity, and the region is also greatly influenced by global warming. The ice-free area of the peninsula is the site of numerous lakes, some of which are used as water sources for Antarctic stations. I studied a series of lakes of the Fildes Peninsula using a combined limnological-paleolimnological approach in order to assess and reconstruct microbial community structure before and after the onset of human presence and activity in Antarctica. This thesis consists of three chapters: In the first chapter, I studied seven lakes around Fildes Peninsula through the analysis of phytoplankton and bacterioplankton communities when the lakes were ice-cover (spring) and before the summer, when the lakes were ice-free. We found that seasonal differences were the main causes structuring microbial diversity. These results suggest that longer ice- free periods such as those predicted for the future, and the presence of contaminants due to the increase in human impact in the area, may affect microbial communities and thus overall system functioning. The second chapter asses the anthropogenic effect in Fildes Peninsula evaluating the pre- and post-anthropic sediments of the same lakes, by estimating metal enrichment and changes in bacterial communities before and after the establishment of year-round human presence in the area. Two lakes very close to roads and airport infrastructure showed increases of metals as well as bacteria taxa associated with polluted environments. This study confirms that bacterial DNA is well preserved in Antarctic lake sediments and is a good sedimentary proxy for inferring changes related to anthropogenic impacts. The third chapter evaluated detailed sedimentary profiles of metal concentrations, bacterial DNA and diatom diversity and teratologies in two of the impacted lakes close to logistics and scientific infrastructure, and in one lake more distant to the stations. Diatom and bacteria changes observed in the lake more distant from infrastructure were shown to be related to climate change, while we confirmed human impacts in the other lakes from the observed increase in metal concentrations, changes in diatom taxa and diatom teratologies related to metal enrichment. This study helps to better understand how human activities and climate change have affected the local landscape around Fildes Peninsula and how the region's ecosystems will respond to future changes. This thesis demonstrates that microbial communities are sentinels of adaptive response to environmental change related both to climate change as well as to local human impacts. Moreover, it contributes to the growing awareness of the impact that human beings are having on sensitive Antarctic ecosystems.