Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW23] Hydrology & Water Environment

Wed. May 29, 2019 9:00 AM - 10:30 AM 103 (1F)

convener:Isao Machida(Geological Survey of Japan), Dai Yamazaki(Institute of Industrial Sciences, The University of Tokyo), Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Keisuke Fukushi(Institute of Nature & Environmental Technology, Kanazawa University), Chairperson:Takeshi Hayashi(Faculty of Education and Human Studies, Akita University)

9:30 AM - 9:45 AM

[AHW23-14] Study on transport of particulate organic matter in a small river with forest and paddy filed by using carbon isotopes (δ13C and Δ14C)

*Seiya Nagao1, Ryunosuke Tahara2, Shinya Ochiai1, Akiko Goto3, Takashi Hasegawa3 (1.Institute of Nature and Environmental Technology, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University, 3.Institute of Science and Engineering, Kanazawa University)

Keywords:Radiocarbon, stable carbon isotope ratio, Particulate organic matter

Radioactive and stable isotopes of carbon (14C and 13C) can serve as powerful tools for identifying sources and estimating turnover times of organic matter in aquatic systems. The present study aims to investigate variations in the characteristics of riverine particulate organic matter running through forests and paddy fields, corresponding to a typical Japanese river system. We selected the Kumaki River located in the central part of the Noto Peninsula in Ishikawa Prefecture, Japan. The river research was conducted at a fixed site of the midstream Kumaki River from April 2016 to March 2018.

Total organic carbon and nitrogen content was measured using the elemental analyzer after the 0.1 M HCl treatment to remove inorganic carbonates. 14C measurements were performed by accelerator mass spectrometry. Final 14C activities are reported in Δ14C. δ13C values were determined for sub-samples of the CO2 gas generated during graphite production, using an isotope ratio mass spectrometer.

δ13C and Δ14C values of organic matter in the riverine POC of Kumaki River show the range of –27.2‰ to –25.1‰, and –130 to +3 ‰, respectively. There are two negative correlations (correlation factor of 0.78) between the δ13C and Δ14C values at winter and the other season except for summer in July and August in 2017. The results indicate that particulate organic matter is mixed with two end-members such as surface forest soil and paddy field soil.