A comparison of particulate, dissolved and gaseous carbon in two contrasting upland streams in the UK

Concentrations and fluxes of particulate, dissolved and gaseous forms of hydrologic carbon were measured in two contrasting acidic upland streams in NE Scotland and Mid-Wales. Sampling was undertaken at the outlet of each catchment, on a weekly or biweekly basis over 2 years. In addition, spatial variations in concentrations of total organic carbon (TOC). dissolved inorganic carbon (DIC), free CO2 and CH4 are presented for both streams along 14 contiguous sites between the source and the outlet of each catchment. Concentrations of carbon determinants along each stream reflected increasing inputs of TOC and gaseous forms of carbon from soil-pore water emanating from deep peat areas; these concentrations subsequently decreased downstream due to changing soil characteristics and in-stream processes.

The total annual carbon flux was 191 kg C ha(-1) yr(-1) from the NE Scotland site compared to 121 kg C ha(1) yr(1) from the Mid-Wales stream, mainly due to significantly higher dissolved organic carbon (DOC) concentrations (p < 0.001) found in the Scottish stream. DOC dominated the carbon flux at both the NE Scotland (88.4%) and Mid-Wales (69.0%) sites, reflecting the importance of organic carbon sources in both catchments. Particulate organic carbon ( 18.5 and 27.4 kg C ha(1) yr(-1) for NE Scotland and Mid-Wales, respectively), HCO3--C (1.12 and 1.28 kg C ha(1) yr(1)) and free CO2-C (2.62 and 8.75 kg C ha(-1) yr(-1)) also contributed to the overall carbon flux. The CH4-C flux at the outlet of each catchment was less than 0.01 kg C ha(-1) yr(-1). Climatic differences between the two sites were expressed in terms of significantly higher discharge and temperature, which caused an increase in CO2 and CH4 export from the warmer and wetter Mid-Wales catchment. (C) 2002 Elsevier Science B.V. All rights reserved.