Effect of Geological Succession on Macrophyte and Microbiota in Aquifer Ecosystem in Urban Coastal Zone

Abstract

This study was conducted to investigate the effect of geological succession of sediment on macrophyte and microbiota in aquifer ecosystem. The research field was selected as Yatsu Tidal Flat where located in urban coastal zone in Tokyo Inner Bay. This tidal flat has been registered under Wildlife Protection Area of Japan in 1988 and the Ramsar Convention in 1993, and just as the tidal flat that was left from reclamation of waterfront zone of urban area. It is very important to obtain some information about these ecosystem characteristics of such nature left in urban area, because creation of artificial tidal flat is recognized as one of important enterprises to construct urban ecosystem. In recent years, a large chlorophyceae, Ulva spp. (mainly Ulva pertusa and Ulva japonica) which is recognized as a biotic indicator of eutrophicated sea area, has become observed in Yatsu tidal flat, and it is considered that Ulva spp. give a large effect to water quality. Ulva spp. has high absorbent potential of nutrient salts at its growth phase, so this macrophyte is considered to place the microbiota such as zooplankton and phytoplankton under its control. In the first place, the geological succession as muddy to sandy occurred because of water quality change as fresh water to sea water. This water change resulted from the decrease of drainage with the sewer system service in basin area, and lead oligotrophication of the sediment. Ulva spp. is one of the biological indicater for sea water and sandy sediment and eutrophicated environment. Because of the irregular growth of Ulva spp., the quantity of phytoplankton decreased drastically, and the dominant species of phytoplankton and zooplankton transited from ideal to unsuitable food organisms for macrobenthos which is important food for the migratory birds, and the production potential of this aquifer ecosystem became in fragility.