250 Chapter 8 oxidation, allowing us to focus on the physiological adaptations of interest. However, this approach does not fully account for the complex environmental pressures that coastal ecosystems face. In broader environmental terms, factors such as sea-level rise will contribute to increased osmotic pressure, changes in chloride concentrations, and enhanced sulfate availability (Figure 3). These changes will intensify competition between methanogens and sulfate-reducing bacteria (SRB) for organic carbon, with SRB likely gaining an advantage due to the thermodynamic favorability of sulfate reduction over methanogenesis and the increased availability of sulfate (Figure 3). Elevated sulfide levels and salinity (chloride) concentrations are known to inhibit methanogenesis (Karhadkar et al., 1987), potentially likewise inhibiting but also diminishing the role of anaerobic oxidation of methane (AOM) in these environments. These reflections also raise the question of whether SRB-driven sulfate-dependent AOM (S-AOM) will co-exist or dominate over nitrate-dependent AOM (N-AOM) in these altered conditions. Bioremediation with N-DAMO amendment on ditches and peat soils of varying salinities were recently tested. (Legierse et al., 2023) amended a stable N-DAMO culture (same as the one employed in Chapter 5) to a brackish and freshwateradapted peatland ditch and a sandy-clay ditch. Here, the brackish peatland N-DAMO amendment showed promising results on methane and nitrate removal compared to freshwater-fed peatland ditches or sandy-clay ditches. This led to conclude that the role of efficient heterotrophic denitrifers could play a role as competitive nitrate reducer with AOM. In this regard, environments may require different interventions depending on the native microbial community. Taken together, even though AOM might adapt to these coastal stressors, the competition with SRB and the inhibition of methanogenesis could reduce the relevance of methane-oxidizing processes in high-sulfide environments. Moreover, while methane emissions may be mitigated, the increase in sulfide could disrupt ecosystem services in coastal and agricultural ecosystems, affecting plant health, microfauna, and fish populations (Riesch et al., 2015). This highlights a
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