Masami Ohashi

Influence of a river flood on the environment of fishing ground in the Mukawa coast, Hokkaido

To elucidate the influence of flood event on the habitat of Japanese surf clam, field observation of water quality and fingerprinting sources of suspended sediment and bed material were conducted in the Mukawa coast, the Pacific Ocean of northern Japan. Nitrate-nitrogen in the surface water was insufficient for the aquatic ecosystem before the flood and then recovered after the flood. However, the primary productivity was limited by scattering of light by suspended sediment. Although the suspended sediment, found to be from midto down-stream areas in the Mu River watershed, can decrease the primary productivity temporarily during flood event, the bed material provided from the upstream area and the nutrients are necessary for the Japanese surf clam.