Two black carbon pools transported by the Changjiang and Huanghe Rivers in China. Issue 12 (3rd December 2016)

• Record Type: Journal Article
• Authors: Wang, Xuchen; Xu, Caili; Druffel, Ellen M.; Xue, Yuejun; Qi, Yuanzhi
• Is Part Of: Global biogeochemical cycles. Volume 30:Issue 12(2016:Dec.)
• Page Start: 1778
• Page End: 1790
• Publication Date: 2016-12-03
• Subjects: black carbon -- dissolved organic carbon -- particulate organic carbon -- radiocarbon -- Changjiang River -- Huanghe River; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2016GB005509
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Major rivers play important roles in transporting large amounts of terrestrial organic matter from land to the ocean each year, and the organic matter carried by rivers contains a significant fraction of black carbon (BC). A recent study estimated that 0.027 Gt of BC is transported in the dissolved phase by rivers each year, which accounts for ~10% of the global flux of dissolved organic carbon. The relative sources of this large amount of riverine dissolved black carbon (DBC) from biomass burning (young, modern 14 C) and fossil fuel (old, 14 C free) combustion are not known. We present radiocarbon measurements of BC in both dissolved and particulate phases transported by the Changjiang and Huanghe Rivers, the two largest rivers in China, during 2015. We show that two, distinct BC pools (young and old) were carried by the rivers. The DBC pool was much younger than the particulate BC (PBC) pool. Mass balance calculations indicate that most (78–85%) of the DBC in the Changjiang and Huanghe Rivers was derived from biomass burning, and only 15–22% was from fossil fuel combustion. In contrast, PBC from biomass burning and fossil fuel combustion were approximately equal in these two rivers. Export of PBC and DBC by the rivers are decoupled, and fluxes of PBC were 4.1 and 6.7 times higher than DBC in the Changjiang and Huanghe Rivers, respectively. The 14 C age differences of the two BC pools suggest that BC derived from biomass burning and fossil fuel combustion are mobilized in different phases and on different time scales in these rivers. Key Points: Combined 14 C and 13 C study to quantify black carbon in both dissolved and particulate phases for two largest rivers in China We identified two black carbon pools with distinct C‐14 ages transported in the rivers River dissolved BC was younger and mainly derived from biomass burning; particulate BC was largely from the fossil fuel combustion