Permalink :  http://hdl.handle.net/2115/45170

This paper reviews recent advances in using the 17O anomalies (Δ17O) to trace the fate of atmospheric nitrate that had deposited onto a forest ecosystem, especially for the recent studies by Tsunogai et al.［2010］in which the fate of atmospheric nitrate deposited onto a forest ecosystem have been successfully traced by Δ17O for the first time in East Asia. In the study, the stable isotopic compositions of nitrate in precipitation (wet deposition) and groundwater (spring, lake, and stream water) were determined for the island of Rishiri, Japan, which is a representative background forest ecosystem for East Asia. The deposited nitrate had large 17O anomalies with Δ17O values ranging from ＋20.8 ‰ to ＋34.5 ‰ (n＝32) with ＋26.2 ‰ being the annual average. On the other hand, nitrate in groundwater had small Δ17O values ranging from ＋0.9 ‰ to 3.2 ‰ (n＝19), which corresponds to an mixing ratio of atmospheric nitrate to total nitrate of 7.4±2.6 %. Comparing the inflow and outflow of atmospheric nitrate in groundwater within the island, Tsunogai et al.［2010］estimated that the direct drainage accounts for 8.8±4.6% of atmospheric nitrate that has deposited on the island and that the residual portion has undergone biological processing before being exported from the forest ecosystem.

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