Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

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

[A-HW22] Hydrological Cycle and Water Environment

Thu. May 24, 2018 9:00 AM - 10:30 AM 104 (1F International Conference Hall, Makuhari Messe)

convener:Seiya Nagao(Institute of Nature and Environmental Technology, Kanazawa University), Isao Machida(Geological Survey of Japan), Shin'ichi Iida(国立研究開発法人森林研究・整備機構森林総合研究所森林研究部門森林防災研究領域水保全研究室, 共同), Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Chairperson:Hayashi Takeshi(Faculty of Education and Human Studies, Akita University), Iida Shin'ichi(Forestry and Forest Products Research Institute), Machida Isao(Geological Survey of Japan, AIST), Nagao Seiya(Institute of Nature and Environmental Technology, Kanazawa University)

10:15 AM - 10:30 AM

[AHW22-12] Dynamics of particulate organic matter in a small lagoon, Lake Kiba, in Japan

*Seiya Nagao1, Hong Tuoi Bui2, Tomoyo Suzuki2, Yuriko Kawai2, Shinya Ochiai1, Keisuke Fukushi1 (1.Institute of Nature and Environmental Technology, Kanazawa University, 2.Graduate School of Natural Science and Technology, Kanazawa University)

Keywords:radiocarbon, suspended solids, carbon isotopes

Lake Kiba is located at Ishikawa prefecture, Japan, and a shallow, semi-closed lagoon. The lake has been suffering organic pollutant. COD concentration is two times higher than the standard level of class A (< 3 mg/L, Environmental quality standards for conservation of the living environment in Japan) during the last decade. The objectives of this study are to elucidate the characteristics of particulate organic matter (POM) in Lake Kiba using carbon isotopes: δ13C and Δ14C. The carbon isotope composition is basic and useful information to clarify organic pollutants affecting shallow lakes and lagoons.
Water samples were monthly collected at the central lake in the periods of 2014-2016. The percentage and concentration of particulate organic carbon (POC), particulate nitrogen (PN) were measured and calculated from freeze-dried suspended solid which was pretreated from approximately 60 liters of water sample by using continuous flow centrifugation method.
Particulate organic carbon (POC) concentrations of 0.44–5.01 mg/L, δ13C and Δ14C values were, respectively, –32.0 to –22.8 ‰ and –157 to –33 ‰. The organic matter in suspended solid samples consistently showed depleted 14C. The carbon isotopes showed seasonal variation, higher in summer, with positive correlation to POC contents. These results indicate that the POC characteristics are controlled by a mixture of two endmembers, organic matter produced by phytoplankton activity within the lake and the watershed organic matter. However, the relation between Δ14C and δ13C values in 2014 and 2015 is different from that in 2016. The similar difference is observed for the relation between Δ14C and POC content for suspended solids. We will discuss about the variation of carbon isotope signatures based on primary production and climate condition.