Peatlands & geoengineering: an unlikely pair

Whilst researching the carbon sequestration potential of peatlands for my dissertation, I came across the concept of "peatland geoengineering". The concept of peatland geoengineering is a recent and niche addition to the growing field of geoengineering. I have to admit I was intrigued: I would never have associated peatlands with geoengineering. 

Peatlands are extensive accumulations of slow-decaying organic matter formed under waterlogged conditions in the absence of oxygen. They are primarily distributed in the northern hemisphere: Europe, North America and circumpolar regions, as well as in tropical South East Asia (Figure 1) (Cris et al, 2014).

Figure 1: Global distribution of peatlands (Source: IUCN)

Although they only constitute 3% of the Earth’s surface – approximately 400 million ha – they store 1/3 of the global soil carbon pool (Kochy et al, 2015). Peatlands have a higher carbon storage density per unit than any other ecosystem in the world. In total, global peatlands are estimated to store 450-600 gigatonnes of carbon (Yu et al, 2011).

Thus, the carbon storage potential of peatlands is powerful. This is due to the primary productivity exceeding the slow decomposition rate of plant litter. Due to anaerobic decay suppressing decomposition, partially decaying plant remains store carbon as peat (Zhang et al, 2016). The below video explores this in greater detail. 

Keystone peatland species

Sphagnum is a genus of peat moss – characterised by its spongy texture and large water absorption potential. They are principal peat-forming species due to their role in ecosystem functioning; by strongly influencing the cycling of carbon, water and nutrients. This contributes to an acidified, anoxic and waterlogged state (Kotska, 2016). 

Figure 2: Sphagnum moss in a peat-bog in Yorkshire, England (Source: Me)

Due to their large carbon sequestration potential, Sphagnum can dominate primary productivity in northern peatlands. Approximately 50% of northern peat volume is made up of decaying Sphagnum (Turetsky, 2003); thus making it one of the most efficient plants for carbon storage and peat formation (Gunnarsson, 2013). 

Manipulation of carbon storage potential

The following are proposed manipulation techniques to optimise carbon storage potential (Freeman et al, 2012):

1)    Installing dams to increase waterlogging and reduce oxygen availability

2)   Acid fertilisaiton, e.g. ammonium sulphate, to increase competitive advantage of keystone species such as Sphagnum by aiding productivity

3)   Genetic modification of Sphagnum to enhance phenolic production, which would further slow decomposition.

4)   Inserting forestry waste into peatland to prevent timber decomposition which would re-release CO₂ into atmosphere.

Potential risks

In a warming climate, the potential for drought occurrence is much greater (IPCC, 2007).  This is particularly worrying for peatlands as drought stimulates aerobic decomposition. This would result in large carbon loss, we are talking in terms of gigatonnes, from peatlands and contribute to current CO₂ emissions (Fenner and Freeman, 2011). Peatlands could therefore become a large positive feedback mechanism for global warming (Cris et al, 2014).   Furthermore, a decrease in water table can release large amounts of CH₄: a much more potent greenhouse gas than CO₂ (Brown et al, 2013). 

Whilst ammonium sulphate fertilisers may increase peatland carbon sequestration potential, excess fertiliser runoff into river catchments can prove detrimental for the aquatic ecosystem (Higashino and Stefan, 2014). An excess of nutrients can cause toxic algal blooms and decrease water quality (Chislock et al, 2013). This is particularly troublesome in the UK as many large cities rely on upland peat-catchments for clean drinking water. 

Unfortunately, I feel that advocators of nitrogen fertilisation as a means to capture CO₂ are missing a crucial point. As nitrogen is a limiting nutrient in peatland ecosystems, there is a potential for ‘nitrophilous’ (nitrogen-loving) species to capitalise on high influxes (Stevens et al, 2016). This is a well documented phenomenon in European peatlands; which have exhibited a decrease in biodiversity and species richness (Bobbink et al, 2010). Declines in the key stone Sphagnum species, associated with nitrogen deposition, can significantly undermine the formation, and thus carbon sequestration, of peat (Sheppard et al, 2014).

In conclusion, I think it is too early to rule out peatland geoengineering, as there is still so much we don’t know about peatland ecosystem functioning. At this stage in time, I am not too convinced and feel more research needs to be dedicated to this field.