Carbon and GHG budgets of an ombrotrophic peatland – importance of surface drainage water as a flux pathway

Peatlands represent a major store of soil carbon and as such play an important role in global atmospheric CO2 and CH4 cycling. Much previous peatland research has focussed primarily on land-atmosphere fluxes. Where aquatic fluxes have been considered, they are often in isolation from the rest of the catchment and usually focus on downstream losses, ignoring evasion (degassing) from the water surface. However, as peatland streams have been repeatedly shown to be highly supersaturated in both CO2 and CH4 with respect to the atmosphere, they potentially represent an important pathway for catchment greenhouse gas (GHG) losses. The primary aims of this study were: a) to create a complete GHG (CO2, CH4, N2O) and carbon budget for Auchencorth Moss, an ombrotrophic peatland in south east Scotland, and in doing so identify the relative importance of aquatic fluxes and b) to understand what controls aquatic fluxes in order to predict how they will respond to changes in both land management practices and future climate scenarios. Using both empirical modelling and the examination of streamwater CO2 concentration-discharge hysteresis loops, a number of distinct CO2 sources were identified within the catchment. These included the input of deep peat/ground water containing high concentrations of dissolved CO2, through-flow from the shallow peat, and water originating from an area of deep peat/peat extraction upstream of the study site. Temporal variability in both CO2 and CH4 could be well modelled using discharge and temperature data alongside the inclusion of an antecedent rainfall variable, indicating the importance of flow path in controlling the source of catchment derived gaseous carbon. The catchment functioned as a net sink for GHGs (212 g CO2-eq m-2 yr-1) and carbon (30.7 g C m-2 yr-1) (Figure 1) . The greatest flux in both the GHG and C budget was net ecosystem exchange (NEE). Terrestrial emissions of CH4 and N2O combined returned only 1.6% of CO2-equivalents captured b