According to
Wikipedia:
“Peat is an accumulation of partially decayed vegetation
or organic matter. It is unique to natural areas called peatlands, bogs, mires,
moors, or muskegs.”
Peat is a
formative stage in the eventual formation of lignite coal. Peatlands have
specific plant communities such as sphagnum moss. Peat is used in horticulture and
gardening to help grow plants. By volume, there are about 4 trillion cubic meters
of peat in the world. Global peatland ecosystems cover 3.7 million square
kilometers (1.4 million square miles). They are considered to be the most efficient
carbon sink on the planet. The peatland plants capture CO2 naturally released
from the peat, maintaining an equilibrium. According to Wikipedia:
“In natural peatlands, the "annual rate of biomass
production is greater than the rate of decomposition", but it takes
"thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m
[4.9 to 7.5 ft], which is the average depth of the boreal [northern]
peatlands",[2] which store around 415 gigatonnes (Gt) of carbon (about 46
times 2019 global CO2 emissions).[12] Globally, peat stores up to 550 Gt of
carbon, 42% of all soil carbon, which exceeds the carbon stored in all other vegetation
types, including the world's forests, although it covers just 3% of the land's
surface.”
Centuries of
burning peat for heat and draining peatlands for agriculture has emitted
massive amounts of CO2 to the atmosphere. There is a need for peatlands
restoration and conservation.
Peatlands vary
with the types of plant material that decompose to make it up. Peat forms in
acidic and anaerobic conditions. Most current peatlands formed about 12,000
years ago in high latitudes after the glaciers retreated. They also occur in
some tropical and temperate regions. Peat accumulates at a rate of about 1mm
per year. Thus, it is not a renewable resource since it regenerates very
slowly.
Peatlands in
the form of bogs and other wetlands make up 50-70% of wetlands globally. Peatlands
make up 3% of the Earth’s land and freshwater surface. Peatlands contain one-third of the world’s soil carbon and 10% of global freshwater resources. Around
7% of global peatlands have been exploited for agriculture and forestry. A 2024
paper increases that amount considerably:
“…at the global scale, ~11–13% of near-pristine
peatlands have been lost due to drainage for croplands, forestry, grasslands
production (to support livestock grazing and herbage production, or peat
extraction.”
The map below from PEATMAP, a GIS
shapefile dataset, shows the global distribution of peatlands.
Peat has many
uses, past and present. It was once burned for heat. It was also used in
medieval metallurgy. In Sweden, it is used to absorb excrement for farm animals
kept indoors in winter. Importantly, peatlands are major drinking water
sources, 4% of the global total. In the U.K. 43% of the population derives
drinking water from peatlands. In Ireland, the total is 68%. Peatlands help with
flood mitigation in some areas. Peat is also used in freshwater aquariums. Peat
spas and peat baths are utilized traditionally for health in some European
countries.
About half of
the northern peatlands are affected by permafrost and make up about 10% of permafrost
lands and contain about 10% of permafrost carbon. Dry peat is a good insulator
and helps protect permafrost from thawing.
Peatland Drainage: Increases Atmospheric CO2 but Also Decreases
Atmospheric Methane
When peatlands
are drained for agriculture, forestry, or peat extraction the organic matter,
previously underwater is exposed to air, and CO2 is released. Pristine undrained peatlands also
emit significant amounts of methane as a result of anaerobic decomposition. The net effect of peatland drainage, however,
is an increase in total greenhouse gases and global warming potential. According
to Wikipedia:
“The global CO2 emissions from drained peatlands have
increased from 1,058 Mton in 1990 to 1,298 Mton in 2008 (a 20% increase). This
increase has particularly taken place in developing countries, of which
Indonesia, Malaysia and Papua New Guinea are the fastest-growing top emitters.”
Peat Fires
The totals above
do not include emissions from peat fires. Like coal fires, peat fires can burn
under low moisture conditions. They can burn below ground and undetected for
years. Burning of peatlands to clear land for agriculture such as planting trees
for palm oil is a major source of atmospheric CO2 accumulation from places like
Indonesia.
“It is estimated that in 1997, peat and forest fires in
Indonesia released between 0.81 and 2.57 gigatonnes (0.89 and 2.83 billion
short tons; 0.80 and 2.53 billion long tons) of carbon; equivalent to 13–40
percent of the amount released by global fossil fuel burning, and greater than
the carbon uptake of the world's biosphere. These fires may be responsible for
the acceleration in the increase in carbon dioxide levels since 1998.[70][71]
More than 100 peat fires in Kalimantan and East Sumatra have continued to burn
since 1997; each year, these peat fires ignite new forest fires above the
ground.”
Peat fires have
been problematic in Canada and the Florida Everglades during droughts and in
Russia during summer heatwaves. Peatland CO2 emissions, including peat fire emissions,
are discussed below.
“…at least 4,000 Mton/CO2-eq./yr for south-east Asia).
With 174 Mton/CO2-eq./yr, the EU is after Indonesia (500 Mton) and before
Russia (161 Mton), the world's second-largest emitter of drainage-related
peatland CO2 (excl. extracted peat and fires). Total CO2 emissions from the
worldwide 500,000 km2 of degraded peatland may exceed 2.0 Gtons (including
emissions from peat fires), which is almost 6% of all global carbon emissions.”
Thus, peatland management, restoration, extinguishing, and preventing peat fires can have a major effect in reducing global carbon emissions.
Restoring, Rewetting, and Reforesting Peatlands to
Improve Carbon Uptake and Quantifying Net Greenhouse Gas Effects
Peatlands are
protected as wetlands. The U.N. Convention on Biological Diversity recognizes
peatlands as ecosystems to be preserved and protected. The main method of
restoring peatlands is simply blocking drainage channels and allowing natural
vegetation to recover. This allows peatlands to be rewetted. A November 2023
paper in Nature Scientific Reports exploring peatland rewetting in Sweden notes:
“Drainage for forestry has created ~ 1 million km of artificial
waterways in Sweden, making it one of the largest human-induced environmental
disturbances in the country. These extensive modifications of both peatland and
mineral soil dominated landscapes still carry largely unknown, but potentially
enormous environmental legacy effects”
Since ditching is
commonly used to drain peatlands, rewetting them involves ditch management.
Blocking off is the main method. Ditch cleaning involves removing the sediments
accumulated in ditches and the increased vegetation along the ditch. This is
done in forestry to increase the survival rate of newly planted seedlings. It
has been shown to have some negative consequences since sediment and nutrients increase
downstream. Its greenhouse gas balance is also not well known. Finland, Russia,
and Sweden have the most peatland drained for forestry in the world. Much of it
was drained in the first half of the 1900s. Peatland rewetting still needs more studies to quantify its effects better. This is especially true since rewetting
increases methane emissions as well as reducing CO2 emissions. The effects of
rewetting can vary considerably by area. The researchers in Sweden compared cleaned,
left-alone, and filled ditches in consideration of the best way to manage those 1
million km of ditches. Ditch cleaning also affects water quality and its effect
on sediment, nutrient, and metal loads can be considerable.
“While ditch cleaning in general seems to have had a
mitigating influence on the negative effects of the clear-cut for most
variables, the 700% increase in sediment load is potentially detrimental to
downstream fish habitats and spawning grounds.”
“Continued monitoring will be necessary to provide a more
solid base for future management decisions, and in the meantime, these
management decisions should be made more cautiously and carefully given the
little published information we have on their outcomes in a Swedish context.”
Studies also show that some effects of rewetting and
restoring will take years to accurately evaluate and other factors may prevent drained
peatlands from returning fully to their previous ecological state.
A study published in October 2024 in Nature Communications Earth & Environment explored the CO2 and methane emissions of these drainage ditches. The authors found that ditch methane emissions result in retaining about 12% of the emissions of the undrained peatlands while making up 3.1-4.4% of the peatland area. Thus, the ditch emissions are 3-4 times greater than area alone would account for.
“{The authors} conducted a global meta-analysis by
compiling annual methane emissions from paired near-pristine peatlands and
terrestrial portion of drained peatlands and ditches to address this issue.
Results showed that ditches occupy approximately 3.8 (95% confidence interval:
3.1~4.4)% of all drained peatlands. Ditches emit 695 (511~898) kg ha−1 yr−1
methane overall, with the highest emissions observed in (sub)tropics. Globally,
ditch emissions offset approximately 12 (10~14)% for reductions in methane
emissions from peatland drainage. Our findings demonstrate the importance of
including ditch methane emissions to quantify emission factors for regional to
global peatlands affected by drainage.”
References:
Peat.
Wikipedia. Peat - Wikipedia
Ditch
emissions partially offset global reductions in methane emissions from peatland
drainage. Dezhao Gan, Zelong Zhang, Huinan Li, Dongsheng Yu, Zheng Li, Ruijun
Long, Shuli Niu, Hongchao Zuo, Xianhong Meng, Jinsong Wang & Lei Ma. Nature
Communications Earth & Environment volume 5, Article number: 640 (October
29, 2024). Ditch emissions partially offset
global reductions in methane emissions from peatland drainage | Communications
Earth & Environment
Potential
of continuous cover forestry on drained peatlands to increase the carbon sink
in Finland. Aleksi Lehtonen, Kyle Eyvindson, Kari Härkönen, Kersti Leppä, Aura
Salmivaara, Mikko Peltoniemi, Olli Salminen, Sakari Sarkkola, Samuli
Launiainen, Paavo Ojanen, Minna Räty & Raisa Mäkipää .Scientific Reports
volume 13, Article number: 15510 (2023). Potential of continuous cover
forestry on drained peatlands to increase the carbon sink in Finland |
Scientific Reports
Consequences
of rewetting and ditch cleaning on hydrology, water quality and greenhouse gas
balance in a drained northern landscape. Hjalmar Laudon, Virginia Mosquera,
Karin Eklöf, Järvi Järveoja, Shirin Karimi, Alisa Krasnova, Matthias Peichl,
Alexander Pinkwart, Cheuk Hei Marcus Tong, Marcus B Wallin, Alberto Zannella
& Eliza Maher Hasselquist. Scientific Reports volume 13, Article number:
20218 (2023). Consequences of rewetting and ditch
cleaning on hydrology, water quality and greenhouse gas balance in a drained
northern landscape | Scientific Reports
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