||Appropriate Water Quality Environment for Protecting the Coastal Ecosystem in the Ariake Sea, Japan
Tabata, Toshinori ,
Hayashi, Wataru ,
Otsubo, Emi ,
Hiramatsu, KazuakiHarada, Masayoshi
E-proceedings of IAHR World Congress
9 , 2017-12-02
The resource of bivalve has been decreasing drastically since 1970s in the Ariake Sea located in Kyushu Island, Japan. Also, water quality environment in the sea has been changed in decades. However, even the data of water quality or the amount of bivalve catchment have been collected for more than 30 years, these data have never been assessed before. In this research, the change of decennial characteristics was assessed in order to identify the environmental change. Using kriging method, all point data of water quality items interpolated into the entire area. Then, each area was classified into six groups by cluster analysis. The result showed that the water quality environment in the Ariake Sea have been significantly changed in these 30 years. It was revealed that the amount of nutrient (DIN, DIP) and organic matter (COD) has been decreased importantly in this area. Then, the relationship between water quality items and bivalve catchment was investigated using Artificial Neural Network (ANN) model with sensitive analysis. ANN model reproduced the annual bivalve catchment well from 10 of annual average water quality items. And sensitive analysis was conducted to evaluate which water quality item is affecting the bivalve catchment the most. The result showed that decreasing amount of nutrients is inducing the decreasing bivalve catchment in the Ariake Sea. This result coincides with the result from cluster analysis. In Japan, the technologies of waste water treatment or sewage coverage have been improved so much that the water qualities in the river become clean which means less nutrients in the water. There are water quality standard to protect the coastal area from eutrophication, but there are no standard to protect the area from oligotrophication in Japan. Therefore, appropriate standard of the water quality items must be established to protect coastal ecosystems in Japan.