Solid and dissolved organic matter redox properties as controls of anaerobic Respiration in organic soils

• Applicant: Professor Dr. Klaus-Holger Knorr
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Soil Sciences
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 346018319

Anaerobic decomposition of organic matter is quantitatively important in wetlands, peatlands, sediments, and other water saturated systems. Thereby, based on thermodynamic constraints, presence or absence of alternative electron acceptors for oxidation of organic matter (OM) determines the competitiveness of methanogenesis. As commonly considered inorganic electron acceptors, such as nitrate, iron, and sulfate mostly do not suffice to explain observed production of carbon dioxide (CO2), the role of dissolved (DOM) and solid organic matter (SOM) as electron acceptors is increasingly acknowledged. Nevertheless, (OM) redox properties has been in the focus of only a small number of studies and we are lacking data on ranges of electron accepting (EAC) and donating capacities (EDC) of OM and their relation to OM properties. Such data would be needed to implement OM redox processes into models of anaerobic carbon mineralization. Additionally, knowledge about typical re-oxidation kinetics of DOM and DOM would be needed to understand the impact of naturally occurring redox fluctuations. Moreover, preliminary work suggests that the redox state of DOM and SOM cannot be assumed similar and an assessment of both may be necessary. Finally, it is yet unknown if redox properties of OM are related to thermodynamics in a given environmental system, as has been demonstrated for carbon mineralization using inorganic electron acceptors. This proposal addresses these important knowledge gaps, by conducting i) controlled incubations of a range of peat materials of different quality and origin, ii) incubations under controlled conditions to calculate electron budgets for carbon mineralization, iii) controlled, kinetic OM re-oxidation experiments, and iv) incubations to relate the redox state of OM to dissolved H2 concentrations as an indicator for thermodynamic conditions. From this project, I expect a substantial contribution to our current understanding of organic carbon mineralization in organic-rich systems and under anaerobic conditions.

• DFG Programme: Research Grants