Koichi Sugimatsu

Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea

To help evaluate the sequestration and carbon dioxide storage function of seagrass meadows, we describe the processes by which carbon is sequestered in eelgrass beds and transported from shallow coastal waters to the deep sea. A part of the carbon taken up by eelgrass is decomposed and returned to biological production or the water column’s dissolved inorganic carbon pool, some is accumulated and stored in the shallow sea bottom, and the rest flows out into the deep sea. Here, we describe the growth of eelgrasses and the processes of decomposition, sedimentation, and transportation of eelgrass-derived organic carbon using the Seto Inland Sea as a model site. We estimated the amount of carbon sequestered and stored in eelgrass beds, the fate of eelgrass-derived organic carbon, and the amounts accumulated in the shallow coastal water and transported to the deep sea. According to our estimates based on calculations from tracking carbon over a 1-year period, of the 73,000 tons of carbon sequestered by eelgrass annually in the Seto Inland Sea, 40.9% is accumulated in the Seto Inland Sea and 8.3% flows out to the deep sea. In other words, the eelgrass beds in the Seto Inland Sea have an annual potential capacity of 36,000 tons of carbon storage. In addition, most of the organic carbon was accumulated in the shallow coastal waters rather than in the deep sea.

A Study of Damage Mechanism on Fishery Port Facilities at Taro Fishery Port due to TOHOKU Earthquake Tsunami

In order to investigate the damage mechanism on fishery port facilities at Taro fishery port, field surveys were conducted and stabilities of the facility bodies was examined using the tsunami simulation modeled with flooding. The east and south breakwaters were found to be collapsed inward of the port, wave-dissipating blocks were found scattered in all directions and the breakwater substructions were also destroyed. The modeled results were verified with the flood areas as well as with the height of the watermarks. The results revealed that the height of the watermarks could not be reproduced without the facility collapses in the model. The stability analysis of structures was consistent with the survey results well, in which the east, south and west breakwaters collapsed while the offshore breakwater was intact.