The controls on concentrations and fluxes of gaseous, dissolved and particulate carbon in upland peat dominated catchments
A programme of field sampling was undertaken to quantify total carbon fluxes (DOC, POC, HCO3, free CO2 and CH4) from peatland catchments in Glen Dye, NE Scotland and Plynlimon, Mid-Wales. This was integrated with temporal and spatial sampling to investigate controls on contrasting concentrations and fluxes and to determine carbon sources or sinks within the stream system. Microcosms containing radiolabelled ( 14C) biofilms were also used to investigate removal of DOC from streamwater. Carbon fluxes from acidic peatlands were dominated by DOC (115-215 kg C ha-1 yr-1) and POC (8.15-97.0 kg ha -1 yr-1). In the majority of headwaters studied, DIC was exported as free CO2 (2.62-8.49 kg ha-1 yr -1). Methane-C fluxes at the outlets of catchments were <0.01 kg ha-1 yr-1. Small-scale (diurnal) temporal variations in free CO2, HCO3- and pH at the NE Scotland catchments were small compared to more productive systems; DOC showed no diurnal fluctuations. In addition, diurnal patterns were masked by marked variations in discharge. Small-scale downstream spatial changes in Brocky Burn, NE Scotland and the Upper Hafren, Mid-Wales showed that variation in climate, in particular precipitation, was also a major controlling factor on concentrations and fluxes of the different forms of carbon. However, the actual amount of carbon stored within the soils acted as an initial control on the potential DOC load within the streamwater. A peatland stream continuum linked to terrestrial carbon cycling is presented. Initially terrestrial inputs of DOC, POC, free CO2 and CH 4 dominated the upper headwaters. The soil-stream linkage was progressively reduced downstream due to autochthonous and atmospheric factors. A critical area in the peatland stream continuum occurred approximately 1 km downstream from the gaseous carbon-rich peats.