Carbon accumulation in a drained boreal bog was decreased but not stopped by seasonal drought

Abstract

Abstract. Drainage of peatlands is expected to turn these ecosystems to carbon sources to the atmosphere. We measured carbon dynamics of a drained forested peatland in southern Finland over four years, including one with severe drought during 10 growing season. Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured with eddy covariance method from a mast above the forest. Soil and forest floor CO2 and methane (CH4) fluxes were measured from the strips and from ditches with closed chambers. Biomasses and litter production were sampled, and soil subsidence was measured by repeated levellings of the soil surface. The drained peatland ecosystem was a strong sink of carbon dioxide in all studied years. Soil CO2 balance was estimated by subtracting the carbon sink of the growing tree stand from NEE, and it showed that also the soil was a sink 15 of carbon. A drought period in one summer significantly decreased the sink through decreased gross primary production.Drought also decreased ecosystem respiration. The site was a small sink for CH4, even when emissions from ditches were taken into account. Despite the continuous carbon sink, peat surface subsided slightly during the 10-year measurement period, which was probably mainly due to compaction of peat. It is concluded that even fifty years after drainage this peatland site acted as a soil C sink due to relatively small changes in water table and in plant community structure compared to similar 20 undrained sites, and the significantly increased tree stand growth and litter production. Although the site is currently a soil C sink, simulation studies with process models are needed to test whether such sites could remain C sinks when managed for forestry over several tree-stand rotations.

Five‐Year Measurements of Net Ecosystem CO2 Exchange at a Fen in the Zoige Peatlands on the Qinghai‐Tibetan Plateau

“…Rainfall can be an important climate determinant of peatland CO 2 flux. First, rainfall impact on growing seasons NEE can be reflected in photosynthesis levels (clouds affect sunlight), and GPP variation can affect NEE much more than other climate factors (Hirano et al, ; Minkkinen et al, ; Zhao et al, ). We found that cumulative monthly rainfall correlated significantly with cumulative monthly NEE from 2013 to 2015, but not in 2016 or 2017 (Table ).…”

Impacts of drainage, restoration and warming on boreal wetland greenhouse gas fluxes

“…In addition to lower water table, the sites differ from each other in that drained sites have significant amount of tree roots, which are lacking from undrained sites. Based on estimate from a Finnish forestry drained mire, 10 to 20 % of the respiration may be produced by tree roots (Minkkinen et al 2018). In addition to increased respiration rates, drainage decreased the photosynthetic capacity (PMAX) of the field layer vegetation and shifted production to the growing tree stand.…”

“…In some forestry drained mires, the growth of the tree stand has exceeded the C release from the decomposing peat, resulting in a large C sink (e.g. Lohila et al 2011;Ojanen et al 2013;Hommeltenberg et al 2014;Minkkinen et al 2018;Ojanen et al unpublished data,). All such sites have been nutrient poor but still able to support intensive tree growth.…”