[A-HW22] 流域圏生態系における物質輸送と循環：源流から沿岸海域まで

[AHW22-17] 崩壊地から駿河湾に流れる都市型河川安倍川の低溶存有機炭素濃度:狩野川との比較

*宗林 留美¹、波多野 太一¹、山岡 希海¹、久保 篤史¹、石川 義朗²、加藤 憲二¹、塚越 哲¹ (1.静岡大学、2.環境科学技術研究所)

キーワード：炭素循環、地下水、浮遊粒子

The Abe River is one of the major three rapid stream rivers in Japan. It originates in the Oya-Kuzure landslide, a part of the Cenozoic Setogawa Group, and runs through an urban area of Shizuoka City with half a million of population toward the Suruga Bay. Downstream water of the Abe River is famous for its high turbidity, but we found the concentration of dissolved organic carbon (DOC) was low through the year (13.1– 30.7 μmol C l^-1; average ± standard deviation, 20.0 ± 5.2 μmol C l^-1). In the upstream water, concentrations of DOC (4.2 – 11.5 μmol C l^-1) and suspended solids (SS) (1.4 – 2.4 mg l^-1) were lower than in the downstream water where SS concentration varied between the left and right bank (63 and 1.2 mg l^-1, respectively) likely due to the difference in the flow volume. Groundwater and river-bed water also exhibited low DOC concentration (5.0 – 7.5 μmol C l^-1), but groundwater from a shallow well and river-bed water contained a specific fluorescent component of protein-like DOM which was not detected in the upstream and midstream waters but in the downstream water. This result reveals that DOC in the river water is diluted with upwelling shallow groundwater and river-bed water with low DOC concentration in the downstream area. We collected suspended particles in the downstream water of the Abe River and added them into the downstream water of the Kanogawa River and the surface seawater of the Suruga Bay whose DOC concentrations were higher than the Abe River (49.6 and 69.6 μmol C l^-1, respectively). The Kanogawa River is originated from the Izu-peninsula and outflows to the northeastern part of the Suruga Bay with the confluent waters from the tributaries containing the spring water of the Mt. Fuji. Concentration of DOC of the Kanogawa River was decreased by 6.8% after stirring for 30 minutes and this result indicates that suspended particles in the Abe River has a potential to adsorb DOC in the river water. However, DOC in the seawater was not decreased after 2 hours of stirring. It is inferred that the downstream water of the Abe River keeps DOC concentration low by dilution with upwelling water and adsorption to the particles that are likely originated from the landslide catchment area, and the outflow of the Abe River may dilute DOC in the surface Suruga Bay without redistribution of organic carbon between dissolved and particulate forms.