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Methane and Ammonium Removal In redoX transition zones

Periodic Reporting for period 2 - MARIX (Methane and Ammonium Removal In redoX transition zones)

Reporting period: 2021-09-01 to 2022-09-30

Earth’s geochemical evolution was shaped by an enormous microbial metabolic diversity. One of the urgent scientific grand challenges is to decipher the key geochemical pathways, with the ultimate aim to obtain a truly predictive understanding of the response of the Earth System to global change. Rapid advances in geochemistry and microbiology have revealed the unique and critical role of sharp redox transitions in marine environments as prime sites for the removal of toxic ammonium and the greenhouse gas methane. Yet, the redox reactions, microbial players, and key controls remain largely unexplored.The ERC synergy project MARIX will unite the complementary expertise required to gain a fundamental and mechanistic understanding of the geochemistry of these redox zones and the complex in-situ microbial interactions that together strongly impact our environment. By combining highly innovative fieldwork, cutting-edge laboratory experiments and state-of-the-art modeling for a range of carefully selected and representative coastal ecosystems we will unravel the geochemistry and novel microbial pathways that remove methane and ammonium through oxidation with metal oxides. Furthermore, we will determine the impact of the novel microbial pathways of methane and ammonium oxidation on the dynamics of nutrients, oxygen and other key elements. lastly, we will develop innovative gene-centric biogeochemical models for coastal sediments and overlying waters, to improve projections of the impacts of eutrophication and climate change.
The MARIX project will lead to major breakthroughs in the understanding of the key role that microorganisms play in modulating Earth’s biogeochemistry with far-reaching implications for a wide range of research fields.
A review paper on microbial methane cycling in coastal sediments was published (Wallenius et al. 2021).

NIne sea-going sampling campaigns were organized and performed in Marine Lake Grevelingen in 2020 (2x) and 2021 (7x) to study the seasonal cycling of methane and ammonium in a seasonally hypoxic coastal system. A large number of samples were collected and a wide range of geochemical and microbiological analyses were performed. Preliminary results were presented at various conferences. Because of covid, sampling outside the Netherlands was not possible. Hence, the field work planned for the Stockholm Archipelago and Bothnian Sea had to be postponed. Some work was carried out on existing samples from the two aforementioned field areas and one paper was pubished (Dalcin-Martens et al. 2021).
We have obtained extremely high resolution water and sediment profiles for Lake Grevelingen as proposed in the project. We have also acquired and applied new in-situ equipment for the measurement of methane fluxes across the sediment-water interface and the sea-air interface. We are combining a range of techniques/analyses that have not been combined previously.