Leaching of dissolved organic carbon from mineral soils plays a significant role in the terrestrial carbon balance

The leaching of dissolved organic carbon (DOC) from soils to the river network is an overlooked component of the terrestrial soil C budget. Measurements of DOC concentrations in soil, runoff and drainage are scarce and their spatial distribution highly skewed towards industrialized countries. The contribution of terrestrial DOC leaching to the global-scale C balance of terrestrial ecosystems thus remains poorly constrained. Here, using a process based, integrative, modelling approach to upscale from existing observations, we estimate a global terrestrial DOC leaching flux of 0.28 +/- 0.07 Gt C year(-1) which is conservative, as it only includes the contribution of mineral soils. Our results suggest that globally about 15% of the terrestrial Net Ecosystem Productivity (NEP, calculated as the difference between Net Primary Production and soil respiration) is exported to aquatic systems as leached DOC. In the tropical rainforest, the leached fraction of terrestrial NEP even reaches 22%. Furthermore, we simulated spatial-temporal trends in DOC leaching from soil to the river networks from 1860 to 2010. We estimated a global increase in terrestrial DOC inputs to river network of 35 Tg C year(-1) (14%) from 1860 to 2010. Despite their low global contribution to the DOC leaching flux, boreal regions have the highest relative increase (28%) while tropics have the lowest relative increase (9%) over the historical period (1860s compared to 2000s). The results from our observationally constrained model approach demonstrate that DOC leaching is a significant flux in the terrestrial C budget at regional and global scales.

Automated summary

The leaching of dissolved organic carbon (DOC) from soils to river networks is a significant but overlooked component of the terrestrial carbon budget, contributing to about 15% of the terrestrial Net Ecosystem Productivity (NEP) globally. Through modeling, a global terrestrial DOC leaching flux of 0.28 Gt C year(-1) was estimated, with regions like the tropical rainforest exporting as much as 22% of their terrestrial NEP as leached DOC. Despite boreal regions having the highest relative increase (28%) in DOC leaching inputs to river networks, the tropics showed the lowest relative increase (9%) over the historical period from 1860 to 2010.