The flux of DOC from the UK – Predicting the role of soils, land use and net watershed losses

SummaryThe estimation of flux of dissolved organic carbon (DOC) from the terrestrial biosphere has been of concern because of its importance for the status of carbon storage in soils and the potential impact on atmospheric CO2 levels. However, these studies have tended to focus on the flux at the tidal limit and from organic soils, without considering the losses at the soil source or processing within the watershed. This study constructs a database of 194 catchments where DOC export was predicted as a function of soil, land-use and hydrological characteristics of each catchment. By comparing across catchments of differing sizes while accounting for the effects of differences in soil and land use this study can estimate the export of DOC at the soil source and the net removal across the watershed. The study can show that although the dominant source of DOC was organic soils, there was significant DOC export from urban and grazed land on mineral and organo-mineral soils, but not from arable land. The average export at source from peat soils was 40 ± 4 tonnes C/km2/yr. The average estimated annual DOC flux between 2001 and 2007 from the UK was 909 ± 354 ktonnes C/yr which was within the error of previous estimates. The study was able to estimate the loss of DOC at the soil source as between 3100 and 4000 ktonnes C/yr, with a net watershed loss of DOC between 2200 and 3100 ktonnes C/yr, equivalent to between 9.0 and 12.7 tonnes C/km2 of UK land area/yr.

► The average export at source from peat soils was 40 ± 4 tonnes C/km2/yr.
► The average estimated annual DOC flux between 2001 and 2007 from the UK was 909 ± 354 ktonnes C/yr.
► The loss of DOC at the soil source as between 3100 and 4000 ktonnes C/yr.
► There was a net watershed loss of DOC equivalent to 78% of inputs.