Sediment and carbon storages in the Yahagi River Delta during the Holocene,central Japan |
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| Authors: | Kiyoshi Fujimoto Kumiko Kawase Shigehiro Ishizuka Koji Shichi Akio Ohira Hiroshi Adachi |
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| Institution: | 1. Faculty of Education, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan;2. Tono Geoscience Center, Japan Atomic Energy Agency, Toki, Gifu 509-5102, Japan;3. Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan;4. Department of Environmental and Life Sciences, School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan;5. Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan;6. National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Japan;7. Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Wake, Nomi, Ishikawa 923-1224, Japan;8. Shikoku Research Center, Forestry and Forest Products Research Institute, 2-915 Asakura-Nishimachi, Kochi, 780-8077, Japan |
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| Abstract: | We estimated stored sediment and carbon during the Holocene for each layer of the Yahagi River Delta, central Japan and discussed the provenance of stored carbon. To estimate the bulk density and the carbon content of each layer, we collected two 30 m deep undisturbed cores. The volume of each layer was calculated using ArcView 3D analyst. Although the volume ratio of each layer to the total volume was calculated to be 9.5% for the top mud layer, 34.9% for the upper sand layer, 32.8% for the middle mud layer and 22.9% for the lower sand layer, the mass ratio of each layer to the total mass was calculated to be 8.5, 40.9, 25.2 and 25.4%, respectively, and the stored carbon ratio in each layer to the total stored carbon was 20.4, 4.7, 55.9 and 18.9%, respectively. These results suggest that the top mud and middle mud layers have a significant role as a place for carbon sequestration during postglacial time. Total stored carbon in the study area of only 92.1 km2 was estimated at 26 Tg C, which is equivalent to 0.003% of atmospheric carbon. This suggests that deltas on the globe have accumulated a massive amount of carbon during the evolution. The inorganic carbon ratio to total carbon reached more than 45% around the boundary between the middle mud and lower sand layers. The increasing trend in the Corg/Ntotal ratio accompanied with a decrease in δ13C from the bottom to the top horizon in the middle mud layer indicates a gradual increase in terrestrial organic matter contribution. The relative proportion of terrestrially derived materials decreases with increasing distance seaward. |
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