title: Carbon isotope composition of dissolved humic and fulvic acids in the Tokachi River system.
abstract: This study reports carbon isotopic ratios (Δ(14)C and δ(13)C) of dissolved humic and fulvic acids in the Tokachi River system, northern Japan. These acids have a refractory feature and they represent the largest fraction of dissolved organic matter in aquatic environments. The acids were isolated using the XAD extraction method from river water samples collected at three sites (on the upper and lower Tokachi River, and from one of its tributaries) in June 2004 and 2005. δ(13)C values were -27.8 to -26.9 ‰ for humic and fulvic acids. On the other hand, the Δ(14)C values ranged from -247 to +26 ‰ and the average values were -170 ± 79 ‰ for humic acid and -44 ± 73 ‰ for fulvic acid. The difference was attributed to the residence time of fulvic acid in the watershed being shorter than that of humic acid. The large variation suggested that humic substances have a different pathway in each watershed environment.
authors.affiliation: Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Wake, Nomi, Ishikawa 923-1224, Japan. nagao37@staff.kanazawa-u.ac.jp
authors.forename: Seiya
authors.initials: S
authors.lastname: Nagao
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kodama
authors.forename: Takafumi
authors.initials: T
authors.lastname: Aramaki
authors.forename: Nobuhide
authors.initials: N
authors.lastname: Fujitake
authors.forename: Masao
authors.initials: M
authors.lastname: Uchida
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shibata
mesh_terms: D001578:Benzopyrans / Q000032:analysis* / Q000302:isolation & purification; D002247:Carbon Isotopes / Q000032:analysis*; D004784:Environmental Monitoring; D006812:Humic Substances / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*
chemical_list: D001578:Benzopyrans; D002247:Carbon Isotopes; D006812:Humic Substances; C005023:fulvic acid