Mobilization of aged and biolabile soil carbon by tropical deforestation

• Published in: Nature geoscience Vol. 12; no. 7; pp. 541 - 546
• Main Authors: Drake, Travis W., Van Oost, Kristof, Barthel, Matti, Bauters, Marijn, Hoyt, Alison M., Podgorski, David C., Six, Johan, Boeckx, Pascal, Trumbore, Susan E., Cizungu Ntaboba, Landry, Spencer, Robert G. M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2019; Nature Publishing Group
• Subjects: 704/286; 704/47/4113; 706/134; Agricultural expansion; Agricultural land; Agriculture; Carbon; Carbon 14; Carbon cycle; Carbon dioxide; Carbon dioxide concentration; Catchment area; Catchments; Chemical composition; Deforestation; Dissolved organic carbon; Dissolved organic matter; Earth and Environmental Science; Earth Sciences; Earth System Sciences; Geochemistry; Geology; Geophysics/Geodesy; Lakes; Land use; Mass spectrometry; Mass spectroscopy; Organic carbon; Organic matter; Organic soils; Rainy season; Rivers; Soil; Soil horizons; Soil organic matter; Sulfur; Sulphur; Tropical climate; Water analysis; Wet season; agriculture; soil organic carbon; Congo; dissolved organic carbon; deforestation
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/s41561-019-0384-9

In the mostly pristine Congo Basin, agricultural land-use change has intensified in recent years. One potential and understudied consequence of this deforestation and conversion to agriculture is the mobilization and loss of organic matter from soils to rivers as dissolved organic matter. Here, we quantify and characterize dissolved organic matter sampled from 19 catchments of varying deforestation extent near Lake Kivu over a two-week period during the wet season. Dissolved organic carbon from deforested, agriculturally dominated catchments was older ( 14 C age: ~1.5 kyr) and more biolabile than from pristine forest catchments. Ultrahigh-resolution mass spectrometry revealed that this aged organic matter from deforested catchments was energy rich and chemodiverse, with higher proportions of nitrogen- and sulfur-containing formulae. Given the molecular composition and biolability, we suggest that organic matter from deforested landscapes is preferentially respired upon disturbance, resulting in elevated in-stream concentrations of carbon dioxide. We estimate that while deforestation reduces the overall flux of dissolved organic carbon by approximately 56%, it does not significantly change the yield of biolabile dissolved organic carbon. Ultimately, the exposure of deeper soil horizons through deforestation and agricultural expansion releases old, previously stable, and biolabile soil organic carbon into the modern carbon cycle via the aquatic pathway. Tropical deforestation induces the loss and transport of old and biolabile soil organic carbon into rivers, suggest analyses of dissolved organic matter in deforested and pristine catchments in the Congo Basin. The mobilized soil carbon is likely to turn into a carbon source.