Carbon balance of a restored and cutover raised bog: Implications for restoration and comparison to global trends

Abstract

The net ecosystem exchange (NEE) and methane ( CH4) flux were measured by chamber measurements for five distinct ecotypes (areas with unique eco-hydrological characteristics) at Abbeyleix Bog in the Irish midlands over a 2-year period. The ecotypes ranged from those with high-quality peat-forming vegetation to communities indicative of degraded, drained conditions. Three of these ecotypes were located in an area where peat was extracted by hand and then abandoned and left to revegetate naturally at least 50 years prior to the start of the study. Two of the ecotypes were located on an adjacent raised bog, which although never mined for peat, was impacted by shallow drainage and then restored (by drain blocking) 6 years prior to the start of the study. Other major aspects of the carbon (C) balance, including dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and open-water CO2 evasion, were quantified for a catchment area at the study site over the same 2-year period. The ecotype average annual ecotype C balance ranged from a net C sink of - 58 ± 60 gCm ĝ'2 yr ĝ'1, comparable to studies of intact peatlands, to a substantial C source of + 205 ± 80 gC m ĝ'2 yr ĝ'1, with NEE being the most variable component of the C balance among the five ecotypes. Ecotype annual CH4 flux ranged from 2.7±1.4 gC- CH4 m ĝ'2 yr ĝ'1 to 14.2±4.8 gC- CH4 m ĝ'2 yr ĝ'1. Average annual aquatic C losses were 14.4gCm ĝ'2 yr ĝ'1 with DOC, DIC, and CO2 evasion of 10.4gCm ĝ'2 yr ĝ'1, 1.3gCm ĝ'2 yr ĝ'1, and 2.7gCm ĝ'2 yr ĝ'1, respectively. A statistically significant negative correlation was found between the mean annual water table (MAWT) and the plot-scale NEE but not the global warming potential (GWP). However, a significant negative correlation was observed between the plot-scale percentage of Sphagnum moss cover and the GWP, highlighting the importance of regenerating this keystone genus as a climate change mitigation strategy in peatland restoration. The data from this study were then compared to the rapidly growing number of peatland C balance studies across boreal and temperate regions. The trend in NEE and CH4 flux with respect to MAWT was compared for the five ecotypes in this study and literature data from degraded/restored/recovering peatlands, intact peatlands, and bare peat sites.