流域荒廃の影響を受ける閉鎖性海域の水環境

摘要

わが国は1970年代の高度経済成長に伴って自然改変と環境破壊が各地で著しく進行し，死の海と呼ばれる内湾・内海が出現した。都市には人口が集中して市域を拡大させ，逆に人口流出の著しい中山間地では過疎化と高齢化が進行していった。このため，都市域から発生する汚濁物質は増加し，過疎地では人間活動による汚濁物賓の発生量は減少したものの，若い労働力を失い管理の行き届かない山林，放棄されて荒地化する農地など土地利用の変化によって流域が荒廃し汚濁量を増加させた。%In the 1970s, high economic growth enabled the industrialization of Japan. This led to the alteration and destruction of the natural environment. Furthermore, it caused large changes in the social structure. Urban areas were expanded because of the increasing population and industrialization in cities. On the other hand, rural areas became depopulated with an ageing society and there was a subsequent decline in agricultural and forestry industries. Moreover, Japan is located in the northernmost region of the Asian monsoon zone, and tends to suffer from serious floods due to the heavy rain during the rainy season and frequent typhoons. Volcanic activity has damaged river basins and influenced the water environment of enclosed coastal seas. The various human activities and natural disasters also damaged river basins and generated pollutants. It is thought that these phenomena have had a large impact on the water environment of the Ariake Sea. As a result, approximately 4% water quality in the Ariake Sea was deteriorated by the desolation of river basins. Approximately 75% of the water quality (COD values) of the Ariake Sea was deteriorated by the impact of the change in social conditions. In addition, approximately 25% of the water quality of the Ariake Sea was deteriorated by natural disaster.