[A-HW22] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW22-10] Riverine transport of dissolved pyrogenic carbon from land to ocean

★Invited Papers

*Youhei Yamashita^1,2, Keisuke Hattori², Daiki Kojima², Natsumi Yoshida² (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Graduate School of Environmental Science, Hokkaido Univeristy)

Keywords:river, Dissolved Organic Matter, Dissolved Pyrogenic Carbon

Pyrogenic carbon (PyC) is a pyrolyzed product derived from incomplete oxidation of biomass burning and fossil fuel combustion. The major products of PyC through biomass burning and fossil fuel combustion are charcoal and soot, respectively. PyC is known to be related to global warming as well as global carbon cycle. Since soot absorbs sunlight, soot emission into atmosphere heats the surrounding air, and soot deposition on snow or ice changes the albedo. A major fraction of charcoal produced with landscape fires is biologically recalcitrant, and thus, can accumulate in soils. Therefore, production of PyC by landscape fires can be considered carbon sequestration in the global carbon cycle. However, it is well known that some of the PyC accumulated in soils is transported to rivers and eventually reaches the ocean as particulate PyC or dissolved PyC. The transport of particulate PyC from land to rivers is known to be controlled by erosion, but the mechanism of transport of dissolved PyC from land to rivers is not well understood. We measured quantity and quality of DPyC determined by a benzenepolycarboxylic acids method in the mainstream and tributaries of the Ishikari River including the streams in Hokkaido University’s Uryu Experimental Forest which catchments were not affected by landscape fire for at least 110 years. DPyC concentration in the mainstream increased from upstream to downstream. DPyC was also detected in the streams in Uryu Experimental Forest throughout the year. The qualitative parameter of DPyC, namely ratio of benzenehexacarboxylic acid (B6CA) to benzenepentacarboxylic acid (B5CA), suggested that DPyC in the streams was likely derived from leaching from deposited soot. DPyC concentrations showed a linear relationship with dissolved organic carbon (DOC) concentrations in the entire Ishikari River basin and in all streams in the Uryu Experiment Forest. Such linkage between DPyC and DOC concentrations, implying the coupling of DPyC and bulk DOC transports from soils to streams.