Carbon balance in a drained forest-marsh ecosystem

Peat bogs, swamps and mires cover about 3% of the world's land area, but they contain twice as much carbon as all the world forests. Drained peat bogs release this accumulated carbon into the atmosphere. However, the impact of peat bogs on forest carbon stocks is a subject of varying interpretations. There are difficulties in accurately accounting of soil carbon balance all aspects. We have made an attempt to assess, at least in the first approximation, the change of the carbon balance under the conditions of experimental long-term drainage of the dwarf-shrub sphagnum Scots pine forest. It is known that the decrease of peat thickness after the construction of canals and the lowering groundwater table consists of the compaction of peat (physical process) and its mineralization (biochemical process). The total peat thickness decrease ranged from 6 to 38 cm in the middle of the inter-channel distances over the entire period after drainage (56 years) in different experimental variants, including from 0 to 20 cm as a result of peat mineralization. The greatest carbon loss occurred 15 to 20 years after drainage, followed by a gradual decrease in the rate of carbon loss, indicating that the process had been stabilized. The estimated time for compensating carbon losses ranged from zero (205 m between channels) to 44-45 years after drainage (45 m between channels). It happens in dependance on the intensity of drainage, the stratigraphy of the peat deposit, and the growth of woody biomass. It has been found that the optimal distances between channels are within 65-130 m for draining a complex-structured peat deposit in order to achieve high efficiency of hydro-reclamation. It allows restoration the positive carbon balance as quickly as possible (20-30 years). An increase in distances of more than 130 m leads to a loss of the forestry effect. A decrease (to 45 m or less) leads to a sharp increase in the cost of building a drainage network, a lack of improvement in the growth of tree stands, and an increase in the time required to compensate the loss of carbon in peat up to 40-50 years after the start of forest drainage. Based on the results of an almost half-century-long experiment, it can be concluded that medium-intensity drainage with a ditch density of 65-130 m in this particular case was environmentally positive in terms of the overall carbon balance, with the productivity of the stands increase from Va to II-III site index. Therefore, the drainage of wet forests and peat bogs, with the necessary and sufficient increase in the productivity of forest stands, can be neutral or even positive in terms of the carbon balance.

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