Above and Belowground Carbon Dynamics of a Degraded Mountain Peatland

Abstract

Peatlands are typically net CO₂ sinks and CH₄ sources under intact or undisturbed conditions due to near-surface water tables, which create anoxic conditions that limit aerobic decomposition and promote methanogenesis. However, disturbances can disrupt this balance by altering hydrology and vegetation. In Australian mountain Sphagnum peatlands, vegetation change is often used to assess biophysical condition, but the effects of degradation on carbon dynamics remain poorly understood. Therefore, this study aimed to investigate the above- and below-ground carbon dynamics of a degrading Australian mountain Sphagnum peatland. We used the manual chamber method to measure CO₂ and CH₄ fluxes from moss-present and moss-absent areas of the peatland, over six measurement occasions in the growing season, across 2 years. A 14-month in situ mesh bag incubation experiment was also conducted to assess the decomposition rates of two peat substrates (fresh and degraded) at three different depths (5, 15, and 30 cm). The results indicated that both moss-present and moss-absent areas of the peatland acted as net CO₂ sources due to lowered water table levels than intact peatlands, moss-vegetation loss, and altered peat structure. Both areas had reduced CH₄ emissions due to the low water table and the absence of aerenchyma plants in the peatland. Organic matter decomposition rates of the peatland are mainly affected by the water table level and secondarily by substrate quality and peat depth. This study concluded that the carbon balance of degrading mountain peatlands is mainly controlled by the water table level, vegetation composition, and the quality of the substrate being decomposed.