Does energy, water and gas transport determine carbon sequestration and methane release in anoxic peatland soils? - Testing a novel hypothesis.
Zusammenfassung der Projektergebnisse
Within this project we demonstrated that burial of peat and accumulation of CO2 and CH4 in deep deposits strongly inhibited anaerobic respiration and methanogenesis. Under this inhibitory effect, peat material decomposed much slower than currently estimated. This project also demonstrated that both column and incubation experiments are suitable to investigate this effect, although the column approach showed more limitations in the exact determination of respiration rates than the incubation experiment. Advective vertical transport had the potential ease end-product accumulation and the inhibitory effect to some extent, suggesting that residence times of dissolved CO2 and CH4 may be indicators of potential respiration in deep peat. Formation of trapped bubbles and ebullition, artificially simulated in the incubation experiment, similarly had a strong effect in removing the inhibitory effect and in restoring CO 2 and CH4 although a preferential removal of CH4 into the gas phase hampered an exact determination of production rates and the identification of fully methanogenic conditions, i.e., a 1:1 production ration of CO 2 and CH4 which could be observed under undisturbed conditions without bubbles or headspace. The concomitant decrease in CO2 and CH4 production and Gibbs free energy of methanogenesis indicated a thermodynamic control on decomposition and end-product inhibition. Nevertheless, Gibbs free energy levels, as well as H2 partial pressures were apparently biased and could not be exactly determined, presumably due to formation of micro-niches and microbial clusters. These indicators have thus inherent limitations in characterizing the predominant TEAPs and the inhibitory effect. On the other hand, stable isotope fractionation factors of 13C in CO2 and CH4 and the redox state of organic matter were apparently promising indicators to identify redox conditions and the onset of end-product inhibition in peat.
