Hydrological & Inhibitory Regulators of Carbon Sequestration in Peatlands

Abstract

Wetlands are considered to be of high importance because of the role they play in carbon sequestration. These soils are major sources and sinks of greenhouse gases including nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2).
Furthermore, they are also characterised by a high capacity for carbon storage. This is because the rate of production of organic material in peatlands exceeds that of decomposition, making peatlands unbalanced ecosystems. Some studies have shown that peatlands almost include 20-30% of global soil carbon stocks, which equates to 60 % of the carbon pool in the atmosphere.

Recent lab studies have indicated that addition of phenolics in the form of wood can further suppress decomposition.

In this thesis, a first study showed that in a UK fen, adding wooden spatulas (as a source of phenolic inhibitors) was able to suppress decomposition. Interestingly, the high cation concentrations in fens (especially Mg) appear to counteract the inhibitor effect on extracellular enzymes, although the direct inhibitory effect on microbial cell metabolism persisted. Nevertheless, the inhibitor additions did slow decomposition and the release of CO2.

Further studies in the thesis focussed on experiments in Canada, where peat harvesting is a major business that creates land that needs to be restored, and which is therefore highly suitable as a test location for experiments at a field scale. A second study showed that phenolics in liquid form can have an inhibitory effect. Phenolics were supplied from waters draining from a peat extraction site adjacent to a Sphagnum farm which had been installed on a harvested peatland, as part of activities to restore normal peatland functions to the site.
The liquid phenolics were highly effective as inhibitors, especially when they were supplied through peripheral channels that supplied the phenolics from all 4 sides (but was less effective when liquids were only supplied through the centre).

Identification of the beneficial effects of irrigation with phenolics through peripheral channels was followed by a study to see if these benefits would be maintained when the plots were subjected to lower water tables (as needed to favour the growth of some Sphagnum species). The experiment showed an adverse effect that could counteract the benefits of irrigation with phenolics. This was particularly so in the peripherally irrigated systems.

A follow-up study investigated whether the adverse effects of water table drawdown could be overcome by adding a similar woody phenolic treatment to the one applied in the first experiment in Cors Goch Wales. Focussing exclusively in the peripherally irrigated plots, wood chips were applied from 2 tree species, spruce and cedar. Cedar was the most effective, showing an effect that may be further improved by soaking the wood chips in lignin.

A final experiment studied the hydrological controls on decomposition rates in more detail. It investigated the effects of stable water tables at different depths, and of water tables that fluctuated in depth quickly or slowly. All of these were found to result in a loss of phenolics and a consequent increase in decomposition. Based on previous studies, these changes were expected to result in stimulated phenol oxidase activities, which would then have eliminated the phenolics. However, it appears from the study that non-enzymic processes can be effective in eliminating phenolics as phenol oxidase was not involved.

Overall this series of experiments revealed three important new additions to our knowledge. Firstly, phenolics in either solid (wood) or liquid (drainage waters) can slow decomposition. Second, the importance of hydrology was clearly demonstrated in that irrigation channels had a large effect by bringing phenolics inhibitors into the peat. Finally, there is evidence that a previously unrecognised mechanism can be important in eliminating phenolics inhibitors - a non-enzymic physical loss of phenolics in the drainage waters. And also that it is possible for the inhibitory effects of phenolics to occur even when the external conditions do not cause a suppression of extracellular enzyme activities.

Date of Award	10 Sept 2025
Original language	English
Sponsors	University of Tabuk
Supervisor	Chris Freeman (Supervisor)