249 Synthesis and discussion C (SO4 -2) Anaerobic digester High-rate activated sludge Nitritation Sulfide oxidation Sulfate reduction Anammox N-DAMO dCH4 NH4 + NO3 - NO2 - (SO4 -2) (Saline) Waste NH4 + C O2 Figure 2. High-rate activated sludge two-stage Waste Water Treatment Plant (WWTP) schematic embedding brackish nitrate/nitrite-dependent anaerobic methane oxidation (N-DAMO) - anaerobic ammonium oxidation (anammox) (N-DAMO-anammox) culture from Chapters 3 and 5 for methane and ammonium removal. dCH4 (dissolved methane). Parenthesis indicate sulfate presence with increased saline waste water. Inspired by Wang et al. (2017). IMPLICATIONS OF COASTAL STRESSORS ON METHANE CYCLING IN AQUATIC ECOSYSTEMS (CHAPTER 5 AND 6) In Chapters 5 and 6, we investigate the physiological response of “Ca. Methanoperedens” to stressors such as sulfide and salt, which are increasingly relevant in coastal aquatic ecosystems. As presented in Chapter 1, is expected that due to global warming and melting of glaciers the seawater level will rise (IPCC, 2023; Kaushal et al., 2021). This will lead to unavoidable intrusion of saline water into freshwater ecosystems having a broad impact on methane cycling, particularly in the context of osmotic and sulfide stress. By focusing on “Ca. Methanoperedens”, we were able to attribute specific responses to this key anaerobic methanotroph under specific stress conditions. To maintain experimental clarity, we simplified some of our methodologies. For instance, in Chapter 5, we used sulfate-free artificial seawater, while in Chapter 6, we removed iron from the medium to prevent FeS precipitates. These modifications were made to isolate the effects of sulfide and salinity on methane 8
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