CO2, CH4 and N2O balances of restored forestry-drained and natural peatlands in Estonia

Natural peatlands are significant reservoirs and sequesters of carbon, important modifiers of local hydrology through their high water retention capacity, and unique habitats of rich biodiversity. The exploitation of peatlands by drainage for land-use purposes, such as peat mining or forestry, disrupts the original peatland ecosystem and leads to the degradation of the peat carbon storage, turning the soil from a sink into a source of greenhouse gases. Restoring drained peatlands aims to improve the water regime and carbon sink functions by re-establishing pre-disturbance conditions, ultimately restoring the ecosystem to a state where peat accumulation resumes. How fast and to what extent restoration goals are reached depend e.g. on the properties of the pristine peatland before drainage as well as the level of disturbance by the post-drainage land-use. Quantifying the greenhouse gas balances of restored peatlands is crucial for assessing the effectiveness of restoration as a climate change mitigation strategy, but it necessitates long-term monitoring of greenhouse gas exchanges. However, due to their vast diversity, there is limited research coverage on the various types of peatlands undergoing restoration, as well as a lack of data from the from periods beyond the first five years after rewetting. 

This study presents and compares the annual balances of CO2, CH4 and N2O for two forestry-drained bogs restored five years ago and two natural bogs, located in Estonia. For this we apply a field measurement-based modelling approach, utilising data from manual soil surface measurements of greenhouse gas fluxes conducted bi-weekly from November 2023 to October 2024, accompanied by continuous measurements of soil water content, soil water table level, soil and air temperatures and photosynthetically active radiation. The year-round CH₄ and N₂O fluxes, as well as the non-growing season net ecosystem exchange (NEE), were determined from series of gas samples collected from static, opaque chambers and analysed by gas chromatography. During the growing season, NEE was derived from gas flux measurements using a transparent dynamic chamber connected to a portable CO2 gas analyser. To account for spatial heterogeneity, the gas flux measurements were conducted across different microtopographical features and vegetation: hummocks, hollows, and spots dominated by cotton grass (Eriophorum vaginatum). The annual greenhouse gas balances are compiled from daily-level fluxes, which are modelled based on their dependencies with the environmental parameters.