Nature’s natural fix to the ticking carbon time bomb in the peatlands

Figure courtesy of geograph.org.uk

Figure courtesy of geograph.org.uk

Finally some good news on the climate change front! After reporting on global warming research for long enough, I begin to feel  like a perpetual bearer of bad news.  But new research in Nature Climate Change provides a glimpse of hope for a particular case that many portend to be especially dire:  the disastrous carbon loss from warming peatlands.  Although many have seen carbon loss as inevitable in these regions due to global warming, new research shows not only how natural adaptations intrinsic to the environment prevent such loss but also hint at how we can promote carbon storage in peatlands as temperatures rise.

Peatlands are thick layers of organic soil made from decaying plants that often occur in wetlands and the northern tundra.   These are dense sources of carbon, accounting for one third of the global CO2 total stored in soil even though peatlands only make up 3% of the land on Earth.  Luckily for us, most of this carbon is stored underwater, protected from atmospheric oxygen that would break down the organic material and release CO2 into the air.  But with recent global warming trends and predictions for increasing temperatures, scientists have worried that droughts and extensive water evaporation in these wetlands would lead to a scary positive feedback loop where these massive stores of carbon are exposed to the air, further increasing temperature and leading to more evaporation and CO2 loss.  Essentially an atmospheric CO2 bomb waiting to happen!

Research hasn’t been definitive about this conclusion, however.  Some sites have shown no change or decreased CO2 emissions in peatlands with decreased water levels, whereas other regions indeed showed the positive feedback between drought and increased emissions.  So what’s causing such different trends?

Wang and colleagues believe they’ve found the smoking gun: shrubs and trees that grow in response to decreased water levels and provide a buffer against CO2 release from the soil.  Comparing soil samples from several sites across the southeast United States, the authors compared regions with dense shrubs to those with mainly Sphagnum moss.  They found that the shrub-filled peatlands had more concentration of phenolics that slow down CO2 decomposition even when oxygen is present.  The authors note that shrubs are known to produce longer chain phenolics that don’t break down as easily in the wetland environment.  This allows them to stick around longer to prevent organic decomposition.

As additional confirmation of their field findings, the authors also  brought soil samples into the laboratory and compared decomposition rates of soil with Sphagnum moss (low phenolic content) to shrub-filled peat.  The Sphagnum soil dramatically decomposed 20-150 times faster than the peat with shrubs!

This seems to be a decisive answer to the question of why such varied CO2 decomposition rates are seen in Nature.  Nature appears to have a natural negative feedback cycle set up to prevent massive CO2 losses as peatlands are exposed to air.  As water levels decrease from increasing temperatures and evaporation, the environment is more conducive to larger shrubs and tree growth, leading to increased phenolic concentrations.  Such a feedback cycle should provide resilience to short-term droughts in peatlands.  Furthermore, these results indicate a conservation approach we can take to mitigate CO2 soil loss – plant more trees!

Questions about why phenolics actually prevent CO2 decomposition remain, but these findings should open up a whole line of research to find out why.  Furthermore, if we discover the mechanism, we may be able to find ways to apply it to vulnerable regions to promote carbon storage and prevent further CO2 loss to the atmosphere!  This could be an excellent natural method of carbon sequestration that provides a bit of hope in an otherwise ominous future.

References

1)

Wang, H., Richardson, C., & Ho, M. (2015). Dual controls on carbon loss during drought in peatlands Nature Climate Change DOI: 10.1038/nclimate2643

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