Carbon balance and radiative forcing of Finnish peatlands 1900–2100 – the impact of forestry drainage

Abstract

Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO2) and releasing methane (CH4) to the atmosphere; in contrast fluxes of nitrous oxide (N2O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry‐drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a‐‐1 in 1900, when all peatlands were undrained, to 3.6 Tg a‐‐1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH4‐‐C a‐‐1, while those of N2O have increased from 0.0003 to 0.005 Tg N2O‐‐N a‐‐1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m‐‐2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO2 sequestration in peat (‐‐0.5 mW m‐‐2), tree stands and wood products (‐‐0.8 mW m‐‐2), decreases in CH4 emissions from peat to the atmosphere (‐‐1.6 mW m‐‐2), and only a small increase in N2O emissions (+0.1 mW m‐‐2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry‐drained peatlands occur outside Finland.

Experimental drying intensifies burning and carbon losses in a northern peatland

“…However, rates of peat accumulation also are dependent on carbon inputs to soils. Others also have found that long-term drainage can stimulate above-and below-ground tree productivity, and soil carbon sequestration as silvic peat [27][28][29] .…”

“…28). In some boreal regions, then, the sustained drying or drainage of peatlands in the absence of wildfire could have a negative feedback to climate change, at least in the short term, although reduced carbon uptake by trees as stands mature could diminish this effect 28 .…”

Soil carbon stock changes in transitional mire drained for forestry in Latvia: a case study

“…Management of organic soils may alter carbon cycling. The main threat for carbon storage is drainage, causing increased CO 2 emissions (Minkkinen et al, 2002;Hooijer et al, 2009). Drainage helps to remove the excess water and, consequently, the upper soil layer is enriched with oxygen.…”

Effects of Drainage Ditches on Water Table Level, Soil Conditions and Tree Growth of Degraded Peatland Forests in West Kalimantan

“…The changes of biomass, growth, and mortality of trees could reflect a distribution of responses Months Months to resource availability and site condition dynamics (Feeley et al, 2007) and diversity shifting (Astiani, 2016). Our previous study demonstrated that reduced rainfall in peatlands lowered the water table (R= -0.44) from the peat surface (Astiani, 2014) which has been demonstrated to have positive effects on Net Primary Production in some northern peatlands (Laiho & Laine, 1997;Minkkinen, Korhonen, Savolainen, & Laine, 2002;Laiho, Vasander, Penttilä, & Laine, 2003). Even though lowering of the water table level due to the establishment of drainage ditches reduced the biomass growth of the trees, when we calculated cumulatively within the six years of assessments (before and post canal presence) it showed that a significant additional growth occurred, whereby stand basal area of trees increased by 27%.…”