[M-IS11] Biogeochemistry

[MIS11-01] Source of dissolved black carbon in streams

*Youhei Yamashita^1,2, Daiki Kojima², Natsumi Yoshida², Hideaki Shibata^3,2 (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Graduate School of Environmental Science, Hokkaido University, 3.Field Science Center for Northern Biosphere, Hokkaido University)

Keywords:Pyrogenic carbon, Dissolved black carbon, soot

Pyrogenic carbon (PyC) is pyrolyzed product derived from incomplete combustion during biomass burning as well as fossil fuel combustion and plays an important role as carbon sink in the global carbon cycle. A major fraction of PyC produced with landscape fire is initially deposited to on-site soils. Atmospheric deposition of soot is also known to be important source of soil PyC. Transport of dissolved fraction of oxidized PyC in soil, defined as dissolved black carbon (DBC), to stream has been considered to be one of the important loss pathways of PyC in soil, while the mechanism is not well documented. We measured quantity and quality of DBC determined by a benzenepolycarboxylic acids method together with quantitative and qualitative parameters of bulk DOM in streams in Hokkaido University’s Uryu Experimental Forest, Hokkaido, northern Japan, which catchments were not affected by landscape fire for at least 110 years. DBC having relatively less polycondensed signature occurred in the streams, irrespective of differences in watershed characteristics and seasons, suggesting that atmospheric deposition of PyC to the catchment is probably a major source of stream DBC. The DBC concentration was linearly related to the DOC concertation, irrespective of differences in watershed characteristics and seasons. Furthermore, an index of the polycondensation degree of DBC was correlated with qualitative parameters of bulk DOM. That is, the polycondensation degree of DBC was positively correlated with specific UV absorbance (SUVA) and DOC/DON ratio, while negatively correlated with spectral slope ratio (S_R) and fluorescence index. Such quantitative and qualitative relationships between DBC and bulk DOM imply that transfer mechanism from soils to streams is similar between thermally altered polycondensated DBC and higher plant derived high molecular weight aromatic DOM.