Disentangling sources and variation of organic matter in soda lakes from Nhecolândia (Pantanal, Brazil) based on hydrocarbons and bacterial composition

The Nhecolândia, in the middle of Pantanal-Brazil, is known for the co-existence of soda lakes and freshwater lakes. The distribution and ocurrence of n-alkanes in three cores from the soda and freshwater lakes were studied in order to assess the variation in organic matter. Additionally, variations in bacteria populations were associated with changes in alkalinity or salinity of the studied lakes. Results show a significant change in n-alkanes distribution. Long carbon chain predominated in the uppermost part of the cores (C24 to C33), while short carbon chain prevailed in the deepest parts (C17 to C22), which correspond to ∼3200 yr BP. It is documented that the soda lakes became highly alkaline at some point during the Holocene, causing changes in the microbiota, which is currently dominated by bacteria in the three cores, independently of salinity and alkalinity characteristics. Whereas the NHP and BB2 cores, both from soda lakes, exhibit a relatively high number of different bacteria, with averages of 335 and 300, the BTP core, from a freshwater lake, presented 123 bacteria. Thus, cores from soda lakes show a greater diversity of the bacterial community in comparison to freshwater lakes, despite the existence of an extreme saline environment.