Growing of Asian Clams and the Difference of Water Qualities of Miyagawa Irrigation Network System in Main Pipeline System via Pond or Not

The terminal pipelines of the Miyagawa irrigation network system are being clogged due to the accumulation of Asian clams. To counteract this clogging, the Miyagawa land improvement district conducts sludge discharge operations. In this study, the government-managed No. 1 main channel via a pond and the government-managed No. 2 main channel not via a pond were set as the study area. From the estimated growth curve, the growth of Asian clams in the pipeline was considered. As the result, it indicated the possibility that Asian clams were reproducing during all seasons excluding severe cold season. In addition, the water sampling were carried out in discharge operations. Some water qualities were analyzed. As the results, it was found that the pond had the effect of increasing Chl-a and DO. It was shown that Miyagawa irrigation network system provide the water quality environment suitable for the habitat of Asian clams within the pipeline. In addition, it was shown that total nitrogen, total phosphorus, and COD in the downstream increase until the middle of the irrigation period, due to the presence of Asian clams in the pipeline.