Estimation of Dynamic Characteristics of Water Environmental Elements in a Brackish and Fresh Water Lake and Development of an Ecosystem Model in Closed Water Area

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The field observation, hydraulic model experiment and numerical modeling were carried out for an estimation, characterization and prediction of the behavior of water quality items in enclosed water area. The consequences were summarized as follows.1)Variability of water quality in a brackish lakeA continual measurement of water quality and micrometeorological items was carried out in Lake Koyama from 2003 to 2005. We examined the variability of DO by the wavelet analysis. Also, the prediction in short-term the time transition of DO was done using a Local Approximation method developed in the chaos engineering field. In addition, a 3-dimensional analytical model was constructed by utilizing the operator splitting method to examine lake currents and salinity dispersion, and was applied to Lake Togo.2)Numerical modeling of environmental behavior in a semi-closed bayA mathematical model was developed for predicting the daily variation of creek water quality (nitrogen and phosphorus) in the … More flat low-lying paddy-cultivated area during irrigation period by considering ecosystem processes. Also, the environmental behavior and fate of TBT-containing antifouling paints in the northern Ariake Sea were assessed by numerical simulations. Furthermore, the 2-dimensional depth-averaged finite difference numerical models have been developed for predicting the tidal flow and SS in the Ariake Sea, Japan.3)Hydraulic model experiment for density current in closed water areaWe experimentally investigated the effect of the surface coverage of floating vegetation on the turbulent structure based on the mechanical disturbance of wind-induced flow in a closed water body. As a result, the presence of floating vegetation had a significant effect on the scale of the turbulent entrainment. When the water surface was partially covered with floating vegetation, the turbulent energy in horizontal direction was decreased at water surface and neighborhood of density interface as the surface coverage of floating vegetation increased. Less