Seasonal Variation in Sources of Dissolved Organic Carbon in a Lacustrine Environment Revealed by Paired Isotopic Measurements (Δ14C and δ13C)

• Published in: Radiocarbon Vol. 49; no. 2; pp. 767 - 773
• Main Authors: Nara, Fumiko, Imai, Akio, Yoneda, Minoru, Matsushige, Kazuo, Komatsu, Kazuhiro, Nagai, Takashi, Shibata, Yasuyuki, Watanabe, Takahiro
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, US Cambridge University Press 2007; University of Arizona
• Subjects: Applications; Earth sciences; Earth Systems and Climate; Earth, ocean, space; Exact sciences and technology; Geochronology; Isotope geochemistry. Geochronology; Far East; Asia; Honshu; Japan; rivers; tributaries; stable isotopes; C-13/C-12; springs; carbon cycle; C-14; lacustrine environment; dating; radioactive isotopes; lakes; residence time; seasonal variations; dissolved organic carbon; chemical analysis methodology
• ISSN: 0033-8222; 1945-5755
• DOI: 10.1017/S0033822200042648

To investigate the sources and cycling of dissolved organic carbon (DOC) in a lacustrine environment, isotopic measurements of 14C and 13C in DOC were carried out for Lake Kasumigaura—which is famous as a very eutrophic and shallow (mean depth 4.0 m) lake in central Japan—and its tributary rivers. Lake and river samples were collected in the spring and autumn (May and September) of 2003. The Δ14C measurements of DOC were performed using the accelerator mass spectrometer at the National Institute for Environmental Studies (NIES-TERRA), Japan. In September, the 14C values of DOC were light (around −200%) and did not differ significantly between lake and river water samples, indicating that DOC in Lake Kasumigaura and its tributary rivers yields older 14C ages than the age expected from the lake-water residence time (average 200 days). This result suggests that terrestrial sources are important contributors to DOC in Lake Kasumigaura. Nevertheless, δ13C values indicated that during spring, DOC in the lake is mainly autochthonous. Thus, sources and cycling of DOC in Lake Kasumigaura may vary seasonally.