Abstract
Black carbon (BC) is a recalcitrant form of organic carbon (OC) produced by landscape fires. BC is an important component of the global carbon cycle because, compared to unburned biogenic OC, it is selectively conserved in terrestrial and oceanic pools. Here we show that the dissolved BC (DBC) content of dissolved OC (DOC) is twice greater in major (sub)tropical and high-latitude rivers than in major temperate rivers, with further significant differences between biomes. We estimate that rivers export 18 ± 4 Tg DBC year−1 globally and that, including particulate BC fluxes, total riverine export amounts to 43 ± 15 Tg BC year−1 (12 ± 5% of the OC flux). While rivers export ~1% of the OC sequestered by terrestrial vegetation, our estimates suggest that 34 ± 26% of the BC produced by landscape fires has an oceanic fate. Biogeochemical models require modification to account for the unique dynamics of BC and to predict the response of recalcitrant OC export to changing environmental conditions.
Highlights
Black carbon (BC) is a recalcitrant form of organic carbon (OC) produced by landscape fires
The dissolved BC (DBC) content of dissolved OC (DOC) was significantly greater in minor channels draining savannah (15.2 ± 5.0%) and peatland (14.8 ± 2.3%) than in channels draining tropical forest (8.6 ± 3.3%) and wetland (8.3 ± 2.7%) and in all of these channel classes when compared to channels draining temperate forest (4.4 ± 2.5%), temperate grassland (3.3 ± 0.6%) and glaciers (2.1 ± 1.0%)
The DBC content of DOC in rivers draining boreal forest (5.4 ± 1.1%) was neither significantly lower than in channels draining tropical forest and wetland nor significantly greater than in channels draining temperate forest, temperate grassland and glaciers. These systematic differences in the DBC content of DOC demonstrate that the dynamics of BC and OC are not uniformly coupled across biomes and latitudes
Summary
Black carbon (BC) is a recalcitrant form of organic carbon (OC) produced by landscape fires. While rivers export ~1% of the OC sequestered by terrestrial vegetation, our estimates suggest that 34 ± 26% of the BC produced by landscape fires has an oceanic fate. 1234567890():,; Globally, terrestrial net primary production (NPP) sequesters around 60 Pg C year−1 from the atmosphere to stocks of organic carbon (OC) in biomass[1,2,3]. The majority of this carbon returns to the atmosphere from the terrestrial biosphere over decadal timescales, through fire emissions, herbivory or by entering soils as dead organic matter and undergoing microbial decomposition[4,5,6]. Estimates of the BC contribution to global oceanic DOC stocks do not differ substantially from estimates of the total terrigenous fraction of DOC (
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