Generation and Extinction Condition of Blue-Green Algal Bloom in the Ponds at the Nara Park

A lot of ponds exist in Nara Park, and the occurrence of a water bloom is frequently confirmed in recent years in the pond. Therefore, it is thought that the preservation of aqueous environment and a view is important. One of the factors of the water pollution in these ponds considers the excrement of a deer or the food of a carp and a tortoise. It is considered that it has large influence on the ecosystem of these ponds because generating of water bloom produces a bad smell and lack of oxygen in the water. In this study, in order to clarify the generation and extinction of water bloom, we carried out the monthly observation of water quality and the continuous observation of the water temperature from June, 2007 to December. It was found that the rainfall, temperature, solar radiation had a large influence on the generation and the extinction of water bloom from this analysis result. Moreover, it makes to the oxygen depression to cover the water surface with Wolffia arrhiza and Azolla japonica in St.4, and it was thought that the amount of the dissolved ion is larger than other points