Relevance of bacterial exudates for flocculation and carbon sequestration in freshwaters
Microbial Ecology and Applied Microbiology
Final Report Abstract
The fellowship`s topic was “Relevance of bacterial exudates for flocculation and carbon sequestration in freshwaters”. I aimed to link bacterial activities and their dissolved organic carbon (DOC) production, particularly in the form of extracellular polymeric substances which form transparent exopolymer particles (TEP), to particle formation in boreal freshwaters. In the initial proposal, it was planned to investigate the role of bacteria and their release of extracellular polymeric substances in laboratory incubations and finally evaluate the relevance in a field study. During the course of the fellowship, first laboratory incubations did not suggest a major role of extracellular polymeric substances for flocculation of terrestrial organic matter. In addition, collaborations within Uppsala University and the group of Lars Tranvik offered the possibility to examine particle degradation and transparent exopolymeric particle (TEP) concentrations in a variety of boreal freshwaters across Sweden. Furthermore, participation in a project including a huge number of scientists from the Limnology group at Uppsala University gave the opportunity to investigate the role of light and terrestrial organic matter inputs for bacterial activities and TEP concentrations in a mesocosm experiment over a course of one month. The results from the mesocosm experiment and the field study revealed a minor role of bacteria for TEP production and thus a minor contribution to flocculation in boreal freshwaters. The high aquatic-terrestrial coupling in boreal freshwaters renders the influence of bacteria and algae onto aquatic TEP production almost negligible. I could show that particles along the boreal aquatic continuum are active sites of organic carbon processing and flocculation potentially plays a large role for particle renewal to sustain POC concentrations (I). However, the role of bacterial or algal production for TEP concentrations and ultimately flocculation seems to be very small and the high TEP concentrations in boreal freshwaters are mainly driven by terrestrial organic matter inputs (II). Furthermore, flocculation is supposedly a major process in headwater systems receiving huge amounts of terrestrial organic matter from wetlands (III) which is driven mostly by changes in the redox potential and iron availability. Finally, a review and meta-analysis about the aquatic priming effect revealed differences between organic carbon processing in soils versus aquatic ecosystems and highlights difference between terrestrial and aquatic concepts of organic carbon processing (IV). In summary, the results from this fellowship contributed to a better understanding of the role of microbes for flocculation and particle dynamics in boreal freshwaters. Flocculation of allochthonous organic matter is an important process of organic matter transformations in boreal freshwaters. Aquatic microorganisms thereby degrade large amounts of particulate organic carbon but do not play a large role in the production of extracellular polymeric substances and other factors such as the redox potential or iron availability seem to be more important than bacteria or algae in headwater systems. The results from this fellowship highlight the need to focus on both, microbial as well as physical and chemical processes for flocculation of terrestrial organic matter and ultimately carbon burial in aquatic ecosystems.
Publications
- (2018) Organic Carbon Processing During Transport Through Boreal Inland Waters: Particles as Important Sites. J. Geophys. Res. Biogeosci. (Journal of Geophysical Research: Biogeosciences) 123 (8) 2412–2428
Attermeyer, Katrin; Catalán, Núria; Einarsdottir, Karolina; Freixa, Anna; Groeneveld, Marloes; Hawkes, Jeffrey A.; Bergquist, Jonas; Tranvik, Lars J.
(See online at https://doi.org/10.1029/2018JG004500)
