The Flux of Dissolved Organic Carbon From UK Rivers

The rise in DOC concentrations in the Northern Hemisphere in recent decades has been taken to indicate increased turnover of terrestrial carbon, particularly in the vital carbon reserve of peat. We propose that, although trends in concentration have been the main focus of attention, it is trends in DOC flux that need to be examined to understand changes in terrestrial carbon storage. This study uses data from 208 rivers over the period 1975-2003 to calculate the trend of DOC flux from Great Britain. The DOC flux peaks at 1.68 Mt C/yr, or an export of 6.6 tonnes C/km2/yr. The trend in flux is inconsistent with the pattern of atmospheric deposition, but regression analysis shows that the major control is total annual runoff followed by an underlying upward, linear temporal trend. There is a small but significant effect related to drought and storage effects. This suggests that there is additional biogeochemical production as result of drought but that the overwhelming control in DOC flux is controlled by hydrological throughput overprinting an underlying increase in trend in DOC production. The underlying trend is consistent with increases in air temperature and atmospheric CO2.