Ausmass und Einflussfaktoren der Methanproduktion von Bachsedimenten in Europa
Zusammenfassung der Projektergebnisse
Fluvial systems (i.e. streams and rivers) have been recently recognized as a globally significant source of atmospheric methane (CH4). However, the various pathways of CH4 fluxes to the atmosphere as well as the large spatial and temporal variability of these fluxes lead to large uncertainties in (annually) averaged flux estimates. An alternative approach is to assess the processes contributing to the emission of CH4 from these systems, namely potential CH4 production and oxidation rates (PMP and PMO) while for now neglecting the final pathway(s) how the net produced CH4 will reach the atmosphere. However, driving factors of these processes and their spatial variability are not well understood. In this project, we measured sediment PMP at a standardized incubation temperature of 16 °C and PMO along with sediment characteristics of three sediment areas differing in grain size (fine, middle, coarse) in 16 stream sites across Europe. Furthermore, we performed a substrate mapping and measured physical and chemical water parameters, as well as hydrogeomorphological stream and catchment characteristics. PMP and PMO showed a very high spatial variability ranging between 0.05 and 3.40 gCH4 m^-3 d^-1 and 1.06 and 21.04 %CH4 d^-1, respectively. The variability of PMP and PMO within streams was similar to the variability among streams, which shows the big challenge for up-scaling exercises. This spatial variability of PMP was driven by sediment organic carbon content and depth, i.e. higher sediment organic carbon content and less deep sediments show higher PMP. PMO was driven by a combination of proportion grain size class clay, sediment organic carbon to nitrogen ratio, and organic carbon content. The identification of these drivers can potentially be used to build a process-based model to calculate PMP and PMO of streams across Europe. Net PMP (i.e. depth-integrated PMP minus PMO calculated spatially weighted for the investigated 50 m stretches) showed as well a high spatial variability among the 16 stream sites, ranging between 0.02 mg CH4 d^-1 m^-2 in Scotland to 318.91 mg CH4 d^-1 m^-2 in Italy. This spatial variability could best be explained by the proportion of fine sediments (silt/loam/clay, <6 μm) in the stream stretch and Strahler stream order via a generalized linear model. Interpreting the model coefficients shows that while keeping the other variable constant, an increase of 1% fine sediments in the stream stretch results in an on average 3% (95% confidence interval (CI), 2 to 5%) increase of net PMP, while a an increase of one Strahler stream order results in an on average 53% (95% CI, 30 to 76%) increase. These identified drivers may be used to up-scale net PMP in streams across Europe. Overall, this project successfully assessed magnitudes and influencing parameters of the major processes driving the CH4 cycle in stream ecosystems at stream reach and European scale. These results enhance our current understanding of CH4 production and oxidation in stream ecosystems and facilitate the up-scaling of net PMP at the European scale.
Projektbezogene Publikationen (Auswahl)
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Sediment Methane Production and Oxidation in Streams Across Europe: Magnitudes and Drivers (2018) Association for the Sciences of Limnology and Oceanography (ASLO), Victoria, BC, Canada
Pascal Bodmer, ..., Andreas Lorke
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Distribution and abundance of methanogenic and methanotrophic microorganisms across European streams (2019) Symposium for European Freshwater Sciences (SEFS), Zagreb, Croatia
Magdalena Nagler, ..., Pascal Bodmer
