[A-HW24] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW24-06] Effect of seagrass-seaweed bed dynamics on carbon and nitrogen cycles on a tidal flat scale

*Mitsuyo Saito¹, Shin-ichi Onodera², Fujio Hyodo¹, Kazuki Iwamoto³, Takuya Akinaga¹ (1.Graduate School of Environmental and Life Science, Okayama University, 2.Graduate School of Advanced Science and Engineering, Hiroshima University, 3.Faculty of Environmental Science and Technology, Okayama University)

Keywords:Seagrass-seaweed beds, Tidal flat, Carbon and nitrogen cycles

In this study, we aimed to examine the spatial and temporal variations in seagrass-seaweed beds on the tidal flat scale, and to clarify this dynamics on carbon and nitrogen cycles. The spatial distributions of SSB and bottom sediments were examined and these samples were collected at dozens of stations on a tidal flat in Ikuchijima Island, western Japan. The surveys have been conducted from 2014 to 2021. The bottom sediments in the target area have become coarser recently, and the highest ratio of gravel points was observed in 2021. In 2014, larger size of eelgrass was dominant, however it has decreased year by year, and green macro algae (e.g. Ulva) is dominant recently. The results of principal component analysis indicated that SSB is significantly influenced by the type of bottom sediment, and also suggested that green algae is influenced by submarine groundwater dischrage (SGD). The results of stable isotope analysis supported that green algae is significantly influenced by SGD-derived nitrogen and organic carbon derived from green algae is deposited on the sediments in the western area.

Acknowledgement: This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito).