Author(s): Toshinori Tabata, Wataru Hayashi, Emi Otsubo, Kazuaki Hiramatsu, Masayoshi Harada
Linked Author(s): Toshinori Tabata
Keywords: Kriging, cluster analysis, artificial neural network, sensitive analysis, water quality
Abstract: The resource of bivalve has been decreasing drastically since 1970s in the Ariake Sea located in Kyushu Island, Japan. Water quality of environment in the sea has been changed in decades. Even though, 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 is assessed in order to identify the environmental change. Using kriging method, all data point of water quality items are 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 past 30 years. It was revealed that the amount of nutrient (DIN, DIP) and organic matter (COD) has been decreasing rapidly in this area. Then, the relationship between water quality items and bivalve catchment is 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. 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 decrease of bivalve catchment in 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
Year: 2017