Evaluation of sediment and carbon storage functions in the formative processes of alluvial plains

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In order to clarify the sediment and carbon storage in the alluvium, non-disturbed boring cores which reach the Lower sand layer were collected in the Lower Tokachi River Plain in Hokkaido, the Lower Yahagi River Plain in central Japan and the Lower Oyodo River Plain in southeastern Kyushu and bulk density and carbon contents in each layer of alluvium were clarified. On the other hand, the volume in each layer was estimated using ArcView 3D Analyst for the Lower Tokachi River Plain and the Lower, Yahagi River Plain. Stored sediment and carbon were calculated using the bulk density, carbon contents and the estimated volume in each layer for the two alluvial plains. The total stored carbon in the alluvium in each plain was estimated to be 0.5 to 0.6 % of present global emission of fossil carbon. Stored carbon in mangrove sediments in the Asia-Pacific region was also compiled and the carbon sequestration ability was evaluated.In order to estimate the source of stored carbon, pollen and σ^<13>C analyses were applied for the boring cores. As a result, it was indicated that the relative contribution of each source, such as terrestrial plants, marine-non-marine planktons, and so on will be possible to estimate by combining CN ratio and σ^<15>N value.The relative sea-level changes were clarified in the Lower Furen River Plains, eastern Hokkaido. Sea-level rise between 5000 and 4000 cal BP and sea-level fall between 4000 and 2000 cal BP, which are common trends in the Asia-Pacific Region, were found out. Three abrupt events of sea-level fall, which are seemed to have been caused by seismic uplift, were also detected.