The University of Arizona

Variation of Δ14C and δ13C Values of Dissolved Humic and Fulvic Acids in the Tokachi River System in Northern Japan

Seiya Nagao, Takafumi Aramaki, Nobuhide Fujitake, Hiroki Kodama, Takayuki Tanaka, Shinya Ochiai, Masao Uchida, Yasuyuki Shibata, Masayoshi Yamamoto

Abstract


Characteristics of dissolved humic and fulvic acids in river waters were studied during 2003–2005 at 4 sites located in the headwaters and in the upper and lower Tokachi River, including a lowland tributary site. Fulvic acids from the headwaters to downstream areas have similar elemental composition and 13C-NMR spectra. Humic acids have similar characteristics in the Tokachi River system. In contrast, δ13C and Δ14C values exhibit a decreasing trend from the upper to the lower and tributary sites, although the headwater site has heavier δ13C and lower Δ14C values than the upper site. Fulvic acids had similar δ13C values from the upper to lower sites, but 123‰ higher in Δ14C than those of humic acids on average. The δ13C and Δ14C values exhibited differences in downward variation for humic and fulvic acids. In the Tokachi River system, these results suggest that differences in transport pathways and residence times of humic and fulvic acids reflect differences in the δ13C and Δ14C values in a single river basin.

DOI: 10.2458/azu_js_rc.55.16372


Keywords


humic substances; carbon isotopes; river waters; downward variation

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