Oxidation state of a peatland

Abstract

The oxidative ratio [ORterra] is the amount of O2 released relative to the CO2 sequestered by the terrestrial biosphere and can be used to assess the magnitude of the terrestrial carbon [C] sink. The Intergovernmental Panel on Climate Change [IPCC] use a value of 1.10±0.05 for the ORterra; this value is from one study [Severinghaus 1995]. The value of the ORterra is hence imperative in the calculation of carbon flux to land; an overestimation of OR would result in an underestimation of C flux to land. Peatlands represent the most important terrestrial C store and are predicted to be amongst the ecosystems worst affected by climate change; predicted impacts include lowering of water tables and wildfires. Recent research has found the accepted value of the ORterra to be higher than the value measured in several ecosystems [e.g., Worrall et al. 2013]. The accuracy of the use of 1.10±0.05 for peatland ecosystems and the effects of wildfire on peat soils is assessed here.
An outline of the current understanding of the ORterra and the C sink nature of peatland ecosystems is given in Chapter 1. Gaseous flux analysis of the OR of a field peatland ecosystem is performed in Chapter 2. Contributions towards overcoming difficulties in measurement of OR by gaseous flux analysis identified in Chapter 2 are made by measuring OR of an artificial peatland regularly by the same method and by elemental analysis in Chapter 3. Variation in OR with depth and location of Austrian peatlands is analysed in Chapter 4. The effects of wildfire on oxidation state and composition of peat soils from Swineshaw moorland, UK is assessed in Chapter 5.
This study finds a significant difference in OR measured by gaseous flux analysis and elemental analysis. The method of gaseous flux measurement of OR was limited by the detection limit of the apparatus and this approach would require long measurement times. Measurement of gas fluxes under dark conditions prior to light conditions increases the rate of photosynthesis. OR measurement by gaseous flux analysis would be best focused on times and locations with high photosynthesis. The accepted value of ORterra is found to be at the maximum extent of values measured by this study and is not representative of the range of values measured in peatland ecosystems. Use of the IPCC’s value for ORterra may be resulting in an underestimation of the global terrestrial C sink. Change in OR with depth and location of peatland ecosystems, and burnt status is found to show significant and complex variation in the samples analysed.
Increase in the degree of unsaturation [Ω] and decrease in H/C with depth in peat soils is a result of condensation reactions which occur with burial. Changes to these compositional indicators, and others e.g., C/N in peat soils affected by wildfire, are suggested to be more appropriate for assessing the C-sink nature of peatland ecosystems than the oxidation state or OR.