宍道湖における消波堤造成を伴うヨシ植栽事業が湖岸表層底質環境に与えた影響

Abstract

In this study, the effects of a reed planting project with construction of breakwaters in Lake Shinji were investigated on surface sediments using chemical analysis. Compared with that in areas with and without breakwaters at Rokuonji, the sediment inside the breakwaters exhibited higher organic carbon, nitrogen, and total phosphorus concentrations. At the western shore where the reeds were planted, organic carbon, nitrogen, and total phosphorus levels in the surface sediment were higher on the offshore side than inside the water area in the reed community. Furthermore, the total sulfide concentration inside the breakwaters at Rokuonji was approximately 60 times higher than that of Torigasaki as a reference point.In a lake where the bottom surface is disturbed by waves, the grain size is normally sand, and an aerobic environment is maintained. However, comparison between the inside and outside of the breakwater in the Rokuonji area showed that the organic matter and sulfide levels increased and the bottom sediment became more finegrained in the lakeshore, which is inside the breakwaters. These results suggest that the reeds did not directly cause organic pollution of the surface sediment in Lake Shinji; rather, the change in hydraulic conditions caused by the construction of the breakwater was the causative factor.