Abstract
We launched the research project in order to build a scientific and technological framework for comprehensively assessing and framing policies to restore the environment of a semi-closed coastal water area substantially affected by surrounding river basins. Setting Mikawa Bay and its river basins as the target field, first, we chose N and P as primary materials that play substantial roles in the ecosystem of the water area, and then estimated the latest four-decade transition in composition of the materials and their supply to the bay. Comparing the transition and the time series of direct impacts on the water area with the environmental deterioration of the bay, we identified a scenario composed of four stages to explain the deterioration process with respect to material cycles, and validated it with a water/material movement simulation model. By defining "good material cycle" as the state under which oxygen deficient water is much less likely to expand in the water area, and by using the scale of oxygen deficient water as a common index to measure the environmental soundness, we materialized the aforementioned framework, whereby the best mix between policies to be executed in river basins and a coastal water area can be examined.
