[A-CG42] 沿岸海洋生態系─１．水循環と陸海相互作用

[ACG42-P04] 硝酸イオンの窒素・酸素同位体比を用いた北川・南川流域の窒素動態解析

*杉本 亮¹、坪井 智子¹、藤田 素子² (1.福井県立大学海洋生物資源学部、2.京都大学東南アジア研究所)

キーワード：硝酸イオン、安定同位体、窒素飽和、森里海連環

The Kita and Minami Rivers are non-urbanized adjacent rivers which are located in the central Japan facing to the Sea of Japan. Recent deposition rates of atmospheric nitrogen onto the two river basins are serious. However, export ratios and their seasonality of atmospheric nitrate versus microbial nitrate from forest soils to streams have not yet been quantified. Furthermore, influence of local nitrogen sources and internal biogeochemical processes are still unclear. To elucidate the influence of watershed properties and atmospheric N deposition on nitrate dynamics in two basins, we have conducted seasonal synoptic surveys by using the dual isotopes of nitrate. Nitrogen and oxygen isotopes of nitrate showed that nitrate remineralized through nitrification in the forest soil was likely dominant source in both basins from the stream to downstream waters. Moreover, net mass balance calculations showed nitrate supplied from the forest occupied large amounts of nitrate outflows from the two basins to the coastal sea.