2018 Volume 24 Issue 1 Pages 1-24
Izonoura — located in the inner area of Matoya bay in Shima City, Mie Prefecture — prospered in the aquaculture of green laver (Monostroma nitidum). However, the production decreased rapidly after the 1980s, and the fishermen have demanded an investigation into its cause. We (Tasaki. et al., 2017) conducted continuous observations of several environmental elements and weather throughout the spring and summer in 2014, which revealed that the cause of the decrease in laver production amount was turbidity and clarified the generation mechanism of high turbidity. As a result, lowering of river discharge that was caused by the past dam construction in the basin is one of the reasons for the bottom sediment condition (Tasaki et al., 2017). In this study, we constructed SS-Diffusion models to reproduce the behavior of the SS observation numerically, and then examined some improvement cases to reduce turbidity in Izonoura. As a result, a decrease in the river flow quantity with past dam construction promoted SS habitation in Izonoura and confirmed that it was a factor in the quality of bottom aggravation. However, as a technique of environmental improvement, the simple recovery of the river flow quantity under the present situation promoted resuspension for the existing sedimentation and promoted environmental degradation. Therefore, having greatly restrained resuspension by the sediment removal of the old route and improving the bottom sediment quality in Izonoura, and then restoring river flow quantity, it was considered possible to restart Monostroma nitidum culture and autonomously improve the turbidity of Izonoura.
