Study on Accumulation and Transportation of Refractory Organic Materials in Terrestrial Area

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An important part of global organic carbon cycle is the flux of terrestrial organic carbon from the continents to the oceans. The potential importance of coastal systems in global and regional organic budgets is still unclear because of the inherent complexity and variability of rivers, estuaries and coastal zones. Therefore, it is important to understand the organic matter cycling in estuaries and coastal systems, especially characteristics and dynamics of river DOM and POM. But the DOM and POM is not homogeneous in terms of size or chemical characteristics so that we can't evaluate the linkage of terrestrial and coastal environments. The objective of this study is to understand the transport behavior of dissolved and particulate organic matter from terrestrial region to ocean. This study used carbon isotopic ratios (Δ^<14>C and δ^<13>C values) as tracers of organic carbon because the simultaneous use of these values adds a second dimension to isotopic studies of carbon cycling in surface aquatic environments.Refractory organic materials, humic substances, were isolated from the river waters in Scotland, Ukraine, Japan and Indonesia by the XAD extraction. The Δ^<14>C values of dissolved humic substances ranged from -316‰ to +209‰, indicating spatial and temporal distribution.To understand transport of POM in river systems, we selected three river systems (Tokachi, Ishikari and Kuji River systems) with different watershed conditions and carried out the observation at a fixed point in each river. The Δ^<14>C values range from -111 to -286‰ for the Tokachi River in northeast Hokkaido, -103〜-364‰ for the Ishikari River in southeast Hokkaido and -18.7〜-94.4‰ for the Kuji River in Kanto area in Japan. The paired Δ^<14>C vs. δ^<13>C distributions vary with rivers and seasons. These results suggest that the difference in paired Δ^<14>C vs. δ^<13>C distributions may reflect the water discharge and watershed environments.