Carbon gas (CH₄ and CO₂) cycling in sediments of the Tonteich, a Northern German acid pond

Abstract

Dissolved carbon gases and bacterial metabolism in the sediments of the highly acid, shallow pond Tonteich were evaluated during the period 1985–1986. Concentrations of pore water CO₂ (0.3-3.6 mM) were at least 10 times higher than CH₄ (0–0.4 mM) resulting in a greater diffusive flux to overlying waters: 1600–9100 mmol m⁻² d⁻¹ for CO₂ versus 52–200 mmol m⁻² d⁻¹ for CH₄. This high CO₂ flux fueled an increased level of productivity near the bottom than in surface waters because of the lack of inorganic carbon at ambient acidity (pH 3.3-3.8). Even though rapid neutralization occurred in surface sediments and sulfate was >0.2 mM at a depth of 16 cm, endogenous methanogenesis was poor. Some microbial populations showed a preference for methanol while others preferred CO₂/H₂ during sediment incubation experiments. Even though the highest potential for methane oxidation was observed in surface sediments, methanogenic activity was relatively high, as compared to deeper strata, when samples were treated in vitro under anaerobic conditions with substrates. This suggested a latent ability of the microbial population to counterbalance disturbances, such as acidification, in the carbon cycle.