Modelling the specific pathway of CH₄ and CO₂ formation using carbon isotope fractionation: an example for a boreal mesotrophic fen

<p>We described mathematically the process of peat methanization in a boreal mesotrophic fen. Gaseous and dissolved CH₄ and CO₂ as well as their δ¹³C signatures were considered in the dynamic equations for incubation bottles. In accordance with the model, acetate, H₂, and CO₂ were produced during cellulose hydrolysis and acidogenesis. ¹³C/¹²C in CO₂ was a key variable reflecting dynamic changes in the rates of cellulose hydrolysis and acidogenesis, acetoclastic and hydrogenotrophic methanogenesis. As CO₂ is the substrate in hydrogenotrophic methanogenesis, <i>δ</i>¹³C–CO₂ increased from the start till the dissolved hydrogen concentration became very low. Thereafter, the rate of acetoclastic methanogenesis with the significant current acetate concentration dominated over the rate of hydrogenotrophic methanogenesis leading to the decreasing <i>δ</i>¹³C–CO₂ and the increasing <i>δ</i>¹³C–CH₄. The model was validated by describing the system’s dynamics under strong and weak inhibition of acetoclastic and hydrogenotrophic methanogenesis by methyl fluoride, respectively. During peat methanization at the lowered temperature of 10 °C, the processes of hydrogenotrophic methanogenesis and homoacetogenesis competing for H₂ may occur. However, based on dynamics of the carbon isotope signatures, especially on dynamics of <i>δ</i>¹³C–CO₂, the model showed no significant contribution of homoacetogens in peat methanization.</p