A Fundamental Study in the Characteristics of Water Quality for Improvement in the Urban Closed Water Body

The historic site, Edo Castle outer moat is a precious place that has one of the few water and greenery in Tokyo urban areas. However, the outer moat water quality is exceed the environmental standards of water quality by the Ministry of the Environment. Moreover, offensive odors emitting from decomposition processes of blue-green algae. Because of the existing special sewage system in the area, the water quality become deterioration. When the rainfall amount more than the capacity of treatment, a lot of untreated wastewater is released into the outer moat. It is important issue that the place with such a problem in the urban area. In order to grasp the actual state of the water environment in the outer moat, continuous field observation of the main water quality items is carried out and each of the observation results is reviewed. By the observation of Chlorophyll-a (Chl-a), T-N, T-P and COD, we revealed the seasonal variation of each water quality item near 1 year. The concentration of T-N and T-P are showed from 0.2 to 9.7 mg L-1 and 0.27 to 2.68 mg L-1 respectively. In addition, a modified ecosystem model applied in the study to simulate the water quality of the outer moat. The results are confirmed to present the reproducibility of the model and the effect of pollution load from the sewer network of vicinity of the catchment area.