Sources and sinks of aquatic carbon in a peatland stream continuum

Streams draining peatland systems contain a number of different C-species, all of which are linked either directly or indirectly to the cycling of C in the terrestrial environment. Concentrations and fluxes of dissolved, particulate and gaseous forms of carbon were measured along a network of streams draining an acidic peatland catchment (46.3km2) in NE Scotland. The main aim was to identify sources and sinks of all the major forms of C in the drainage network and use this to develop a conceptual understanding of the evolution of streamwater chemistry along a peatland stream continuum. The investigation included a small-scale intra-catchment study of three contiguous sites in a 1.3km2 headwater catchment (Brocky Burn) and a larger scale integrated study of seven sites. Mean annual fluxes of the main carbon species varied from 115–215 (DOC), 8.15–97.0 (POC), 0.32–6.90 (HCO3--C) and 2.62–10.4 (free CO2-C)kgCha–1year–1; all contributed to the overall carbon flux to varying degrees. Methane-C was only measurable at sites within areas of deep peat (<0.01–0.09kgCha–1year–1). Downstream spatial changes in the intra-catchment study (Brocky Burn) were characterised by a decrease in DOC, CO2-C and CH4-C and an increase in POC fluxes over a distance of 1.1km from the Upper to the Lower sites. In the context of the integrated catchment study estimated losses and gains of carbon from the water column showed no net change in DOC, a large decrease in POC (–55%) and a slight increase in (HCO3--C) (+7.7%) and CO2-C (+4.5%). A significant decrease in the CO2-C flux: HCO3-C flux ratio with distance downstream from the stream source, illustrates the importance of outgassing of CO2 from streams draining peatland C reservoirs. These data are interpreted in the context of losses and gains of the various components of the aquatic C flux along the peatland stream continuum.