Role of the aquatic pathway in the carbon and greenhouse gas budgets of a peatland catchment

Many previous studies have highlighted the importance of peatland soils to the global greenhouse gas (GHG) balance through their role in carbon sequestration and methane emission. However such studies often overlook the drainage system as a pathway for dissolved organic carbon (DOC) and GHG release. Surface waters associated with peatlands have repeatedly been shown to be highly and consistently supersaturated in CO2 and CH4 with respect to the atmosphere. Therefore in addition to downstream losses, degassing from the water surface (evasion) has the potential to act as an important pathway directly linking the peatland carbon pool to the atmosphere, and hence altering the perceived greenhouse gas and carbon balances of the catchment. Here we present both the carbon and GHG budgets for Auchencorth Moss, an ombrotrophic peatland in South East Scotland, including losses through the aquatic pathway. The catchment functioned as a net sink for GHGs and a net source of carbon. Downstream DOC export was the largest component of the carbon budget; the greatest flux of GHGs was via net ecosystem exchange (NEE). Terrestrial emissions of CH4 and N2O combined returned only ~5% of CO2-equivalents captured by NEE to the atmosphere, whereas evasion of CO2, CH4 and N2O from the stream surface returned ~40%. The budgets clearly show the importance of lateral (downstream) and vertical (evasion) aquatic fluxes at Auchencorth Moss and highlight the potential for significant error in source/sink strength calculations if they are omitted. Furthermore, a process based understanding of soil-stream connectivity, suggests that the aquatic flux pathway may play an increasingly important role in the sink-source function of peatlands under future management and climate change scenarios.