peatlands 1 taitto.indd - International Peat Society

A lot of under 300-year-old peat layers
in Finland Text: Markku Mäkilä
Markku Mäkilä from the
Geological Survey of Finland
analyzes the carbon storage
abilities of Finnish mires
according to their age, type
and location.
Geological peatland covers an area
of 5.1 million ha in Finland, having
a mean depth of 1.4 m. The Finnish
national peat reserves total 69.3 billion
m 3 in situ, while the carbon storage of
Finnish mires is 3.2 billion t (627 t per
hectare). The original peatland area
covered ca. 10 million hectares.
The long-term peat increment of
Finnish mires has been calculated on
the basis of 520 dated peat columns.
The calibrated radiocarbon ages
correspond to the present time, as
50 years were added to them. The
long-term peat increment in Finnish
mires varies considerably, depending
on many factors. For example, the rate
of increment is higher in geologically
young mires than in old ones (Fig. 1),
higher in southern and western than
in eastern and northern Finland, and
higher in ombrotrophic bogs of southern
Finland (Sphagnum area) than in
minerotrophic mires (sedge area) of
northern Finland (Fig. 1).
The highest recorded rates are 2-3
mm yr -1 in young coastal bogs and the
lowest, under 0.1 mm yr -1 , in the uplands
of northern and eastern Finland,
where the bottom soil topography is
sloping. The average peat increment
rate is 0.32 mm yr -1 . The rate in areas
of peat deeper than 2 metres is 0.4
mm yr -1 , when northern aapa and palsa
areas are excluded.
The vertical peat increment rate
was determined from 39 dated peat
columns mainly representing the thickest
peat layers of mires. Several datings
were performed from separate levels
in each column. The rate has varied
greatly during the last 10 000 years
(Fig. 2). Variations in peat increment
rates can mainly be explained by the
changes in vegetation composition and
decomposition rates due to natural
mire succession and variations in local
conditions, especially moisture and
nutrient conditions. However, the role
of the climate cannot be ignored. Usually,
about 5-20% of the plant biomass
production is deposited as peat. Most
of the biomass decays in the oxic peat
layer at the surface and returns to the
atmosphere as carbon dioxide (CO 2) .
The proportion of the carbon
store of mires contained in the surface
peat layer (age 50-430 years, average
250 years) was
examined in 25
peat columns of
known age, dry
bulk density and
carbon content.
This proportion
was found to
vary considerably
(2-37%),
approximately
corresponding to
the proportion of
virgin peat but not
the proportion of
the energy content
in the surface
layer. However,
due to the natural
conditions, especially
the moisture
and nutrient
conditions, areal
differences were
substantial and the
proportion differed
greatly even
between adjacent
mires. In addition
to the age of the
surface peat layer,
the carbon store
also depends on
many other fac-
tors such as the thickness of both the
surface (0.1-1.0 m) and the total peat
layer (0.5-7.8 m), and the age (710-10
440 years) and carbon store of the
total peat layer (180-2790 t ha -1 ).
The highest proportions of carbon
in the surface peat layer (>20%) were
found in quite young mires under 1000
years old in the coastal bogs of the
highest uplift area. For example, in this
type of bog the carbon content of surface
peat layers aged 160 years was 114
t ha -1 on average. The carbon accumulation
(g m -2 yr -1 ) of this type of young
bog can be compared to the annual
carbon accumulation of young birch
Fig. 1. The variability of long-term peat increment rates in various
parts of Finland.
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