[A-HW18] 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

[AHW18-P08] Spatial variation in groundwater discharge on a tidal flat in an island of western japan

*高 啓迪¹、小野寺 真一¹、齋藤 光代¹、友澤 裕介¹、松原 怜哉² (1.広島大学大学院先進理工系科学研究科、2.広島大学総合科学部)

キーワード：海底地下水湧出、空間分布、干潟、海島

To manage and conserve the seagrass bed and ecosystem in tidal flats, this study examined to confirm spatial distribution in groundwater (SGD) on tidal flats with the area of around 100 m square in a small and steep island. Various groundwater and nutrient discharges were observed at the W and E sites. 1) Based on the water budget, the groundwater flux was estimated to be 8.68 m/yr or 23.9 mm/day in E, and 17.75 m/yr or 48.6 mm/day in W, respectively. 2) Spatial distributions of groundwater contribution ratio (%) in pore water at W was around 60% in average, which was 8 times of that in E site. 3) The NO₃-N concentration in pore water at W site was about 30 times of that at E because of the low attenuation rate with high groundwater velocity. 4) The temporal variation in groundwater flux with tidal fluctuation indicated 2.5 m/day in maximum and -4.0 m/day in minimum. This huge difference between the average flux and maximum indicated also large seawater recirculation and heterogeneous distribution of SGD. This heterogeneous distribution at this tidal flat would contribute to the activity of seagrass and diversity of ecosystem.

Acknowledgment
This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito) and Fostering Joint International Research (A) (No. 20KK0262, PI: Mitsuyo Saito).