Geoscience for Society 125th Anniversary Volume Edited by Keijo Nenonen and Pekka A. Nurmi Geological Survey of , Special Paper 49, 163–170, 2011

THE SUFFICIENCY OF PEAT FOR ENERGY USE ON THE BASIS OF CARBON ACCUMULATION

by Markku Mäkilä

Mäkilä, M. 2011. The sufficiency of peat for energy use on the basis of carbon accumulation. Geological Survey of Finland, Special Paper 49, 163–170, 6 figures and 1 table.

The purpose of this study was to compare the average annual carbon accumulation of surface peat layers younger than 100 years with the estimated use of energy peat by separate provinces of Finland in the year 2020. The annual carbon accumulation of surface peat layers is 3.44 million tonnes for the mire area of 6.737 million hectares that is accumulating peat. This is of the same size as the estimated use of peat carbon in the year 2020, i.e. 28.2 TWh, which approximates to 3.28 million tonnes of carbon. Carbon accumulation is higher than the estimated use in the regions of and Pohjanmaa-, whereas in the remaining regions carbon accumulation is lower than the estimated annual use of energy peat carbon.

Keywords (GeoRef Thesaurus, AGI): mires, peat, carbon, deposition, fuel peat, utiliza- tion, sustainable development, Finland

Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland

E-mail: [email protected]

163 Geological Survey of Finland, Special Paper 49 Markku Mäkilä

INTRODUCTION

There has been considerable discussion of the bal- living surface vegetation to be used in the growth ance between peat carbon accumulation and the use of new plant biomass, which after a few years will of energy peat. The purpose of the study presented again start to decay. Rapid carbon accumulation in this paper was to compare the average annual and turnover of peat carbon occur in young surface carbon accumulation of surface peat layers younger layers in the same way as in a growing forest. The than 100 years with the estimated use of energy peat climate impact of surface peat layers is indistin- in the year 2020. New peat accumulates all the time guishable from the impact of the forest, so the use on most of the mires in Finland. This accumulating of surface carbon in accumulation calculations can layer is still in the rapid gas exchange zone, where be considered reasonable.

CO2 released in the decay process is captured by the

Peat formation

Sphagnum (moss) and Carex (sedge) peat form in constituents are roots (Figure 2). A certain propor- different ways. Sphagnum moss grows from the tion of roots dies and regenerates, so besides living apical bud and respectively lower layers die and roots there are roots of different ages in the same form peat (Figure 1). In Carex peat (and also in the peat volume. Finally all roots die and form peat. formation of other high plants), the most important

Figure 1. Formation of Sphagnum peat. Picture drawn by Harri Figure 2. Formation of Carex peat. Picture drawn by Harri Kutvonen. Kutvonen.

164 Geological Survey of Finland, Special Paper 49 The sufficiency of peat for energy use on the basis of carbon accumulation

Peat layers are in a dynamic state. Relatively peat layers below ground thus consist of different thick (up to 40 cm) surficial layers consist of living components, which have different climate impacts. and dead biomass, which slowly changes (decom- Moisture, especially its temporal distribution, is poses) to peat. It is also well known that the living the main factor controlling Sphagnum production. roots of sedges can penetrate down to a depth of two Thus, both the amount of precipitation and the dis- metres in the peat layers, making even deeper layers tance to the groundwater level are important for a mixture of peat and living biomass. Although the Sphagnum production. However, other climatic fac- biomass of these deep-growing roots is relatively tors (e.g. the mean annual growing season tempera- small, they may contribute significantly to the ac- ture and growing degree-days) have also been shown cumulation of carbon, because decomposition in the to correlate with moss growth. The fact that carbon anoxic layers (catotelm) is slow (Saarinen 1996). accumulation rates are higher in coastal Sphagnum As the decomposition continues slowly under an- bogs than in older raised bogs is not only due to cli- oxic conditions, a small proportion of the carbon mate, but also to the fact that coastal bogs are in the deposited in the catotelm is subsequently converted early phase of their development (Figure 3). This to methane (CH4). Methane is a 25-fold stronger type of young bog produces more moss on the sur- greenhouse gas than carbon dioxide. This anoxic face and the amount of peat decayed and compacted layer is still in the slow gas exchange zone. The in the entire bog is lower than in an old bog.

Figure 3. A coastal bog from Storslättmossen, Mustasaari, where the Sphagnum peat layer is growing rapidly. Two metres of peat has accumulated during 800 years. Photo: Markku Mäkilä.

165 Geological Survey of Finland, Special Paper 49 Markku Mäkilä

The rate of carbon accumulation is higher in the roots of sedges, where it contributes to the de- raised bogs than in minerotrophic aapa mires. Aero- cay of peat layers. As far as northern aapa mires are bic decay is more efficient in aapa mires that receive concerned, the short growing season, severe win- nutrients and oxygenated water from adjacent min- ters with a strong frost action and often the highly eral soils (Figure 4), whereas ombrotrophic raised permeable subsoil have resulted in a lower rate of bogs are only fed by rainwater. In minerotrophic carbon accumulation and highly compressed peat aapa mires, oxygen is transported into the peat via deposits (Figure 4).

Figure 4. A northern aapa mire from Luovuoma, Enontekiö, where the Carex peat layer is growing slowly. Almost two metres of peat has accumu- lated during 9800 years. Photo: Markku Mäkilä.

MATERIAL AND METHODS

The starting point for this study was the estimated examined with 433 radiocarbon dates using bulk use of energy carbon by separate provinces of Fin- density and carbon pool measurements from 86 peat land in the year 2020 (Flyktman 2009). The average columns (Figure 5). The peat columns represented annual carbon accumulation in the last 100 years mires varying in depth, age, natural state and nutri- was used to calculate the rate of peat carbon accu- ent conditions, from both aapa mire and raised bog mulation (Mäkilä & Goslar 2008). In addition, some regions in southern and , as well as samples were taken from Lapland during 2009 and four peat columns from Russian Karelia. The cali- added to the study material. The average annual bration program and age-depth modelling devel- carbon accumulation during the last 100 years was oped at Poznan Radiocarbon Laboratory was used.

166 Geological Survey of Finland, Special Paper 49 The sufficiency of peat for energy use on the basis of carbon accumulation

Figure 5. Numbered regions of mire complex types in Finland and location of the studied mires. Study points are marked with red points. The region to the south of the black line contains a raised Sphagnum bog area; to the north of the line is a Carex aapa mire area.

RESULTS

Mire area

According to the latest statistics, the total area of ish Forest Research Institute, we obtain a peat ac- peatlands in Finland is 9.29 million ha (http://www. cumulating mire area of 6.737 million hectares. On gtk.fi/luonnonvarat2/turve/turvemaat.html) (Finn- transformed mires, the ground vegetation consists ish Statistical Yearbook of Forestry 2009, Kaakinen of upland vegetation. There is practically no accu- & Salminen 2008, verbal knowledge (TTL, 02/2010 mulation of new peat on the mire surface in many and MTT, 11/2009). When organic croplands (0.33 places. However, there is still some accumulation of million hectares) and the peat production area (0.06 organic material in the peat layer because of forest million hectares) are deducted from this peatland litter from the root system. Transformed mires can area, we obtain a mire area of 8.90 million hectares actually release more carbon that they accumulate, pertaining to forest science (VMI 10). When the as the dried peat layers rapidly decompose in oxy- area of transformed mires (2.163 million hectares) is gen rich conditions and thus release more CO2 than deducted from the mire area pertaining to the Finn- in natural wet conditions.

Estimated use of energy peat in the year 2020

The CO2 emission from peat combustion is 0.381 tonnes of carbon (IPCC seminar 2008) are lost in t CO2/MWh (105.9 g CO2/MJ) (Vesterinen 2003). production fields and stocks. The use of 28.2 TWh The total emission from energy peat combustion is of energy peat consumes 3.28 million tonnes of car-

10.74 million tonnes CO2, which means 2.97 mil- bon (Table 1 and Figure 2). The carbon emission lion tonnes of carbon per year if the estimated use during the production phase is included in the cal- of energy peat carbon is 28.2 TWh in the year 2020. culations of carbon use.

Besides this, over 1 million tonnes of CO2 or 0.3

167 Geological Survey of Finland, Special Paper 49 Markku Mäkilä

Table 1. The estimated use of energy peat carbon in the year 2020 and the average annual carbon accumulation of the surface peat layers younger than 100 years on the basis of regions demarcated by Forest centres.

Region Province Estimated use Carbon of carbon year 2020 accumulat. provincially regionally regionally TWh mill. t. C mill. t. C mill. t. C/yr , Ahvenanmaa 0.51 0.06 Varsinais-Suomi 0.50 0.06 Itä-Uusimaa 0.08 0.01 1.73 0.20 0.67 0.19 1. Southern Kanta-Häme 0.47 0.05 Päijät-Häme 0.39 0.05 0.78 0.09 Etelä-Karjala 1.26 0.15 1.34 0.16 Etelä-Pohjanmaa 2.40 0.28 2. Western Pohjanmaa 2.05 0.24 1.14 0.53 Keski-Pohjanmaa 0.52 0.06 Keski-Suomi 3.48 0.40 Etelä-Savo 0.75 0.09 3. Eastern Pohjois-Savo 1.88 0.22 0.37 0.30 Pohjois-Karjala 0.59 0.07 4. Kainuu – Pohjanmaa Kainuu 0.60 0.07 0.84 1.18 Pohjois-Pohjanmaa 6.64 0.77 5a. Lapland, S Lappi 2.24 0.26 0.26 1.10 5b. Lapland, N Lappi (Enontekiö, 0.14 Utsjoki, Inari) 5. Lapland Lappi, total 1.24 Total 28.2 3.28 3.28 3.44

Carbon accumulation

The average annual carbon accumulation of surface Western and Southern Finland (1 and 2), being 0.70 peat layers younger than 100 years and the estimat- t/ha and 0.67 t/ha, respectively. The lowest carbon ed use of energy peat carbon in the year 2020 have accumulation is 0.24 t/ha in the regions of North- been divided into five regions on the basis of For- ern Lapland (5a) and 0.42 t/ha in Southern Lapland estry centres (Table 1 and Figure 6.) Furthermore, (5a). The carbon accumulation is 0.53 t/ha in the re- the Lapland area has been divided into Southern gion of Eastern Finland and 0.60 t/ha in the region and Northern Lapland. Peat columns were collect- of Kainuu-Pohjanmaa. The carbon accumulation of ed from study sites of varying depth, age, nutrient all regions is obtained by multiplying the amount of conditions and degree of natural state typical for carbon by the rate of peat accumulation in each mire the peat layers of each region. The highest annual area (Finnish Statistical Yearbook of Forestry 2009) carbon accumulation is in Sphagnum-dominated (Table 1 and Figure 6).

168 Geological Survey of Finland, Special Paper 49 The sufficiency of peat for energy use on the basis of carbon accumulation

Figure 6. The estimated use of energy peat carbon in the year 2020 and the average annual carbon accumulation of surface peat layers younger than 100 years in different regions and in the whole country. The distribution of mires is shown by the darker areas in the inset map.

CONCLUSIONS

According to the large and accurate radiocarbon dat- in 2020, i.e. 28.2 TWh, which approximates to 3.28 ing material of GTK, the annual carbon accumula- million tonnes carbon. The rate of carbon accumu- tion of the vitally living surface peat layers younger lation is higher than the rate of use in the regions than 100 years is 3.44 million tonnes for the Finnish of Lapland and Pohjanmaa-Kainuu, whereas in the mire area (6.737 million hectares) that is still effec- remaining regions, carbon accumulation is lower tively accumulating peat. The carbon accumulation than the annual estimated use of energy peat carbon rate is the same as the estimated use of peat carbon (Table 1 and Figure 3).

169 Geological Survey of Finland, Special Paper 49 Markku Mäkilä

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