Kyoko Hata

Evaluation of eelgrass bed nitrogen cycle using an ecosystem model

Abstract An eelgrass bed ecosystem model incorporating epiphyte and epifauna compartments has been developed and applied to the Lake Notoro eelgrass bed. The model could reproduce the nitrogen cycle in the eelgrass bed ecosystem reasonably well. In terms of a nitrogen cycling in the eelgrass bed, the representative nitrogen cycle in the water column was identified as inorganic nitrogen in the water column–epiphyte–epifauna–inorganic nitrogen, whereas the one in the benthic system was identified as inorganic nitrogen in the interstitial water–eelgrass–detritus–bacteria–inorganic nitrogen in the interstitial water. Just outside of the eelgrass bed, the nitrogen cycle was very simple and the magnitude of fluxes between state variables was very low compared to that of the eelgrass bed.

Subtidal frequency fluctuations of current velocity and sea level in the Japan Sea

Abstract An analysis of the sea level and the velocity fluctuations along the Japanese coast in the Japan Sea was conducted. The sea level and velocity fluctuations with periods of 5 days were dominant. As far as sea level was concerned, the propagation of fluctuations with speeds of about 20 km/h between Shimonoseki and Maizuru was an obvious feature, whereas to the east of Maizuru the fluctuations appeared to be in phase. The average velocity over one month in Ishikari Bay, Akita Bay and Niigata coast suggested that the velocity field along the Japanese coast was strongly influenced by the first branch of Tsushima Current.