The role of terminal electron acceptors in peatland restoration.

The role of alternative terminal electron acceptors in peatland restoration.

Emily Fearns-Nicol, Catherine Hirst, Julia Knapp, Fred Worrall

Department of Earth Sciences, Durham University, Science Laboratories, South Road, Durham, DH1 3LE, UK. 

 

The existence of peatlands relies on the balance of primary productivity and oxidation of organic matter. Oxidation requires a terminal electron acceptor (TEA). The most energetically favourable TEA is O₂ followed, in order of reducing energy return, by NO₃, Mn, Fe, and SO₄. Organic matter itself can become a TEA with the production of methane (CH₄). Organic matter will degrade faster the better access to the more energetically favourable TEAs. Therefore, the fate of the organic matter turnover in peatlands is related to the supply of TEAs. We hypothesize that if the supply of TEAs can be limited, then more organic matter could be preserved, and so enhance carbon sinks. Typically, water tables are raised to limit the access of TEAs into the peat porewater, however, it is not only high water tables that are required but also stagnant water tables otherwise fresh TEAs are brought into the porewater.

Bunds are used in peatlands to manipulate the water table to create environments for peat-forming species such as sphagnum mosses. However, bunds may also create areas of high and stable water table, and therefore allowing us to test our hypothesis. To test the hypothesis that stagnant water tables control organic matter storage, this study considered a peat covered hillslope where bunds had been installed. Monthly monitoring of these bunds, started in January 2024 and is being undertaken for soil water chemistry (pH, conductivity, absorbance, DOC, cations, anions), CO₂ gas fluxes and water table depth. The site enables us to consider 9 bunded plots, alongside 9 control plots, with each plot having monitoring upslope, within and downslope of the bund.

There was a significant difference in ecosystem exchange down the hillslope, but no difference within individual bunds. Ecosystem respiration showed no signifncnat difference down the hillslope or relative to the individual bunds. There was a significant difference in absorbance and DOC down the hillslope, but no difference relative to the individual bunds. Equally, there was no significant difference in iron or sulphate concentration down the hillslope or relative to the individual bunds. Water tables were not significantly changed by the presence of the bunds nor was conductivity. In this blanket bog we are seeing that high water tables and swift transport pathways persist despite the presence of multiple bunds.