The Microcosm enclosure devices (l=5m, φ=1m, V=4m3) were set in the coastal area at the mouth of the Tokyo Bay.
　The sea water was separated and enclosed by the Microcosm device, which has transparent nontoxic vinyl-sheet wall. The change of the water quality and the particulate concentration inside the Microcosm had been monitered for 10 days during each summer season in 1983 and 1984. The ecological dynamics were analyzed through the data of these field observations.
　In the surface of the observed sea, the main part of the suspended particles is diatom and organic detritus. The change of the particle concentration is governed primarily by the decomposition and settling processes, while grazing pressure by the zooplankton is estimated very small in the magnitude. After the separation of the total settling flux into the sediment flux and the phytoplankton flux, contribution of the phytoplankton is estimated very large at the surface while sediment flux at the bottom layer is dominant.
　With some accompanied experiments, the Microcosm and Sediment Trap experiments are effectively utilized to analyze the eutrophication processes.