[AOS18-03] Downward variation of δ13C and Δ14C in riverine particulate organic matter at Kumaki River, a small river in Noto Peninsula
Keywords:stable carbon isotope, radiocarbon, riverine suspended solids
δ13C and Δ14C values of organic matter in the riverine suspended solids of Kumaki River show the range of –27.2‰ to –25.1‰, and –130 to +3 ‰, respectively. The carbon isotope composition shows three groups corresponding the up-, mid- and down-stream sites at normal flow condition. After rain events, the carbon isotope values are shifted to lower value of δ13C and higher value of Δ14C at the three sites under higher flow condition. There is a positive correlation between particulate organic carbon concentrations and thier Δ14C values, and a negative correlation between the δ13C and Δ14C values at mid and down-stream sites. All data shows downward variation of carbon isotope composition from upstream to downstream. The Δ14C values decrease along the river line, but the δ13C increased downward in the Kumaki River. The results indicate that particulate organic matter at each sampling site is mainly supplied from each watershed area. The higher contribution from surface forest soil was observed at all sampling sites after rain events. Therefore, water discharge and land use type of the watershed are related to the transport of particulate organic matter in the small river system.