Carbon Accumulation Rates Over the Holocene in Flow Country Peatlands and the Direct Comparison of Open and Afforested Peatland Carbon Stocks Using Tephrochronology

Abstract

No other terrestrial biome stores carbon as efficiently as peatland. Covering 2-3% of global land surface they are estimated to store as much as half the carbon contained in the atmosphere. With >30% peatland cover, Scotland has more blanket bog than any other country in Western Europe and are estimated to contain carbon equivalent to almost one hundred years of anthropogenic emissions. When damaged and disturbed, these same peatlands can nevertheless turn into a significant source of carbon to the atmosphere. In the UK, it is estimated that around 80% of peatlands are disturbed. For instance, approximately 20% of UK peatlands has been drained and afforested with coniferous trees. While it is recognised that this may be a threat to the long-term carbon reserves stored in afforested peatland, there are very few studies measuring the effects of afforestation on the carbon balance of naturally open, nutrient poor peatland such as we have in the UK. This thesis presents a novel, quick and robust method that could be used to compare carbon stocks between forested and open peatlands, based on tephrochronology, the identification and use of volcanic ash layers to reliably match stratigraphy. We successfully applied this method to four pairs of afforested and open blanket bog sites in the Flow Country. First, ITRAX scanning was tested as a tool for finding tephra within peat and we found it be a highly efficient technique, both in terms of success rate and time. Three tephra layers were located across the Flow Country, improving our knowledge of tephra geochemistry and distribution as well as improving the accuracy of our paleoecological carbon accumulation estimates. The ubiquitous nature of some of these tephra suggest this study could be replicated across the north of Scotland. Along with the chronology, carbon content and bulk density data were then used to compare stocks between afforested and open sites. Our data highlighted a high variability between sites and thus that a higher level of replication than we were able to achieve in this short study alone will be required to effectively assess the impact of afforestation on carbon stocks. Finally, we have demonstrated how data generated from this method can be integrated in Bayesian age-depth models to reconstruct paleoecological rates of carbon accumulation, which are almost entirely lacking for UK peatlands. We have done this for one core located within the Flow Country, providing a much needed context in which to view contemporary carbon flux measurements. Overall, we have demonstrated the potential for ITRAX scanning to be used for rapid detection of tephra layers in peat in the North of Scotland and other areas where volcanic ash deposition occurs. However, more work and especially a higher level of replication at the site level will be required to assess the impact of afforestation on carbon stocks. This should then be integrated to studies looking at carbon balance using flux-based approaches, and used to inform policy development in the future.

Date of Award	31 Jul 2016
Original language	English
Awarding Institution	University of the Highlands and Islands
Sponsors	The Carnegie Trust for the Universities of Scotland
Supervisor	Roxane Andersen (Supervisor), Richard Payne (Supervisor) & Stuart Gibb (Supervisor)