The role of rivers and lakes in the transport of organic carbon and carbon dioxide

A programme of field sampling was undertaken to quantify annual organic carbon fluxes at a range of sites on the River Dee and River Don in NE Scotland. The annual fluxes of both DOC and POC in the R. Dee and R. Don were found to increase cumulatively with distance down the river system. In headwater and tributary catchments of the R. Dee, annual DOC fluxes were positively related to the coverage of peat in the catchment area. This work as supplemented by a desk study in which organic carbon exports in 1993 were calculated for 85 large British rivers, using archive information. The resulting estimates, along with data on the soil carbon content of 17 river catchments were used to develop a predictive model of British riverine DOC fluxes. Calculated and predicted DOC fluxes and estimates of POC export based on suspended solids data, were combined to produce estimates of the annual British riverine organic carbon export during 1993. The 'non-storm' flux of DOC in British rivers in tidal waters during 1993 was estimated at 0.69 Mt +/- 0.28 Mt; the corresponding POC flux estimate was 0.2 Mt. A direct method for measuring dissolved CO2 in river and lake waters was developed. Preliminary studies of rivers in NE Scotland and lakes in Northern Wisconsin, USA, suggested that lakes may act as conduits for CO 2 transport, particularly in catchments containing substantial wetland. In conclusion, soil carbon content appears to be a useful integrative measurement for predicting annual DOC fluxes in British rivers. The establishment of a link between soil carbon stores and riverine fluxes, should help to improve future modelling of the carbon cycle. These findings suggests that rivers (and lakes) may regulate increases in soil carbon pools induced by climate change.