[A-CG51] [JJ] 沿岸海洋生態系──１．水循環と陸海相互作用

[ACG51-08] 別府湾および大槌湾の浅海域の一次生産速度に地下水湧出が及ぼす影響

*本田 尚美¹、杉本 亮²、三島 壮智³、大沢 信二³、小路 淳⁴、富永 修²、谷口 真人¹ (1.総合地球環境学研究所、2.福井県立大学海洋生物資源学部、3.京都大学大学院理学研究科付属地球熱学研究施設、4.広島大学大学院生物圏科学研究科)

キーワード：一次生産速度、ラドン222、海底湧水、浅海域

In recent years, a number of studies have shown that submarine groundwater discharge (SGD) is an alternative nutrient pathway and can drive primary production in coastal seas. However, little is known about a relationship between input of nutrients through the groundwater and response of primary production. To clarify the relationship, we conducted in situ measurements of primary productivity (PP) using stable ¹³C tracer method under different strength sites of SGD at nearshore coasts in Beppu Bay and Otsuchi Bay during the summer in 2016. Considering the differences of light intensity and water temperature at each site, we have also incubated the bottles taken from each site under same conditions of light and water temperature on land. In both bays, significant positive relationships between in situ PP and ex situ PP (r > 0.91, p < 0.01) indicated that in situ PP would be controlled by nutrient availability. In Beppu Bay, in situ PP and ²²²Rn activity ranged from 4.4 to 23.3 µg C L^-1 h^-1 and 69.8 to 586.8 Bq m^-3, respectively. Although there was no clear relationship between in situ PP and ²²²Rn activity, biomass specific PP (P_B, µg C µg chl a^-1 h^-1) showed the positive correlation with ²²²Rn activity. In Otsuchi Bay, in situ PP and ²²²Rn activity ranged from 4.5 to 10.7 µg C L^-1 h^-1 and 298 to 765.8 Bq m^-3, respectively. ²²²Rn activity did not related to in situ PP and P_B. This could be due to low phosphate concentrations in terrestrial confined groundwater. Our experimental studies suggested that the mechanism by which SGD affects phytoplankton production differs from one ecosystem to another.