Peat bogs are somewhat misunderstood ecosystems. Although peat bogs or peatlands consist of dying plant material, their conservation and restoration could help provide a potential lifeline for the world’s climate change mitigation needs. Or, in a warming world - propose a risk to mitigation efforts as a source of greenhouse gas (GHG) emissions.
Peatlands, bogs or fens?
Peatlands go by several different names: peatlands, fens, swamps, mires - to name a few. There is no globally accepted definition for peatlands. But fundamentally, they are a type of terrestrial wetland that has a build-up of peat soil, where the amount of organic matter produced, exceeds the amount that decomposes. Beneath the surface water of wetlands, anoxic conditions persist. It is here, where plants such as mosses and shrubs cannot fully decompose and remain suspended in a state of partial decomposition. After many years, the process of accumulation, compression, and partial decomposition forms layered soil known as peat (Figure 1).
Figure 1 – formation of tropical peatlands by Nieves Lopez Izquierdo. Image taken from the United Nations Environment Programme
Why are peatlands important?
Peatlands are home to rare and specialised biodiversity, filter freshwater and absorb carbon dioxide (CO2). As layers of plant mass decay, CO2 is released. Some CO2 acts as a substrate for the plant layers above to absorb. The rest remains trapped and stored as carbon within the partially decomposing peat. Thus, creating a carbon sink.
Carbon sequestration in almost every the nation
Although they cover approximately 3% of the world’s terrestrial ecosystems, peatlands are found on every continent and in 180 countries (Figure 2). These ecosystems can sequester 0.37 gigatonnes of CO2 per year, making them the most powerful terrestrial vegetation for carbon sequestration per unit of area. Overall, peatlands store twice as much carbon as all the world’s forests combined.
Figure 2 - a map of global peatland coverage shows peatlands occupy 2.84% of terrestrial land, with the majority spread across boreal, northern latitudes. However, the most significant proportion are found in Indonesia - taken from Xu et al.
Threats and complications
Although a readily accessible climate mitigation solution for ~92% of the world’s nations, peatland conservation is under threat from agriculture and climate change. A lack of awareness of the mitigation potential of these ecosystems has lead to drainage to provide water for agriculture. Globally, ~15% of the world’s wetlands have been drained, emitting around 1.3 gigatonnes of CO2 per year. After drainage, peatlands dry out, becoming flammable. The land can then be burned to grow crops like paper and palm oil, particularly in Indonesia. Alternatively, the peat is extracted and sold as fuel or fertiliser. All of these processes result in the return of CO2 to the atmosphere.
Even though they are widespread and able to store carbon, peatlands also have a dark side. The waterlogged nature of decaying and productive plant matter leads to the release of methane (Figure 3). Methane is thirty times more potent in its heat-trapping potential than CO2. The methane generated in the anoxic areas of the soil can escape to the atmosphere by travelling up through air channels in plants growing in the oxic peat layer.
Figure 3 - Processes involved in carbon storage and methane emissions in peatlands taken from Dean et al., 2018
Peatland restoration
Research by Joosten et al. finds that rewetting of peatlands can lead to an initial increase in methane emissions. But in the long-term, peatlands will reduce net GHG emissions through carbon storage. However, future climate change is a risk for peatlands in two ways. Firstly, research by Dean et al. finds that dried peatlands - in warmer temperatures - will allow previously-stored carbon to mix with atmospheric oxygen and form CO2. This turns a carbon sink into a source. Secondly, warming temperatures are likely to increase the stimulation of bacteria which catalyses methane production in peatlands. Thus, leading to increased methane emissions even when these ecosystems are hydrated and restored.
What next for peat?
To remain a carbon sink - rather than a source - peatlands must remain moist. Although moist peatlands may facilitate carbon storage, an overly waterlogged peatland, can emit large amounts of methane, particularly in a warming world. The IUCN has released a booklet of successful restoration case studies in the U.K., to inspire safe, sustainable management and future safeguarding for climate change mitigation. However, as the climate warms - peatlands should be monitored closely to manage changes in CO2 and methane fluctuations.
Similar to the challenges facing tropical forests, sufficient political awareness, legislation, and enforcement are required for protection. Until then, these areas are at risk of exploitation, mismanagement and becoming an emissions source, rather than a solution.
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