Peatlands, the carbon cycle and climatic change

What are peatbogs?

In the UK there are two main types of peatbogs: “blanket bogs” and “raised bogs”. Blanket bogs occur on hill tops which receive over 2000mm of rain a year and are called blanket bogs as they appear to be draped across the underlying topography. Raised bogs occur in valley bottoms where water flow is retarded allowing the establishment of bog species which further retards water flow leading to an accumulation of plant material. Raised bogs are called raised because the accumulation of plant material forms a raised dome above the surrounding topography and water table.

Peatlands are historic sinks of carbon, removing CO2 from the atmosphere and storing it in recalcitrant forms of carbon where acidic and water logged conditions prevent decomposition. Peatland environments are the UK’s largest store of carbon. The carbon stored in UK peatlands is equivalent to 8 years of total UK carbon emissions. Therefore, it is critical to preserve these peatlands and restore damaged peatlands to carbon sinks once more.

As peatlands are large carbon stores concerns have been raised over the future stability of these stores due to climate change. Climate change in the UK predicts warmer summer temperature, increased frequency of summer drought, and increased frequency and intensity of winter rainfall. It is predicted that climate change will affect peatbogs and the resilience of peatbogs to change is unknown.

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Ecological Continuity Trust interview with Dr James Rowson at the Cors Fochno long-term experiment on climate change near Aberystwyth:

Field scale manipulation experiment

In response to this gap in knowledge a field scale manipulation experiment was established in 2009, where a raised bog was continually warmed using a passive warming system and increased summer drought frequency of 4-5 weeks in length with 4 drought seasons completed during this period.  A variety of variables have been measured such as carbon dioxide and methane, water table depths, air and soil temperatures, soil pore water chemistry, vegetation changes, carbon and nitrogen isotopes, plant decomposition rates, as well as cores for palaeo analysis.  This experiment is on going with plenty of fascinating questions raised from the results collected so far.  We have seen so far that the response of peatlands to both warming and drought is greater than either warming or drought individually.  This raises concerns for the future of peatlands, not just in the UK but further afield in places like eastern Europe, Russia and Canada.  We are potentially seeing a legacy effect of droughts on peatland where plots that have been previously droughted show that water table depths drop faster with increasing drought frequency.  This have implications on greenhouse gases that are released, as plots with deeper water table depths have a large aerobic zone and release more carbon dioxide.

Peatlands in the UK have been damaged in a variety of ways. The south Pennine blanket bogs have been subjected to decades of pollution from both Manchester and Sheffield, this pollution has led to widespread reduction in peat forming plants species. The southern Pennines has a history of wildfire events which removes the vegetation from the peat surface exposing the peat below. This led to subsequent rapid and widespread erosion of the peat creating gullies up to 3 meters deep with a loss of 2cm per meter squared from the peat surface. Raised bogs have suffered a similar fate having been commercially extracted for the horticultural industry leaving large areas of bare peat.

Tree planting on peatlands has been a management objective to increase productivity of these lands.  We now understand that tree planting on peatlands if often sustainable because drainage and soil acidification had significant impacts on water quality with increased fluvial and gaseous carbon losses from the peat which is not off set by the growth of the trees.  A shift in management focus has led to interest in restoration of these afforested areas.  Results show from a chronosequence that sites can be restored in terms of vegetation and water table depth but below ground biodiversity in microbial soil predators (testate amoeba) still show differences more that 20 years after restoration.  This raises questions about the effectiveness of restoration methods and further investigation is needed to establish whether these areas would benefit from further management intervention by introducing certain vegetation species or even inoculating soils from undisturbed areas.

Dr James Rowson’s research investigates the restoration potential and climate change resilience using a combination of environmental sampling and modelling techniques. Environmental monitoring consists of a suite of techniques including greenhouse gas monitoring, soil pore water sampling for pH, conductivity and cation and anion concentrations all of which are modelled against data collected continuously by dataloggers to provide ecosystem responses to climate change and restoration.

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