The Impact of Watershed Land Use on the River Quality of Notsuke Bay's inflowing Rivers

Abstract

Notsuke Bay is a bay where eelgrass (Zostera marina) grows, and is a fishing ground for Hokkai shrimp(Pandalus latirostris). We examined how the water quality of the rivers flowing into Notsuke Bay affects the eelgrass and Hokkai shrimp. We then examined the factors that affect the quality of the river water. The T-N concentrations in Tobikari River and Kumushi River are 0.6-0.9 mg/L, and the reduction rates in the number of eelgrass and Hokkai shrimp in the vicinity of the mouths of these rivers were small. On the other hand, the T-N concentrations in Tohoro River and Chashikotsu River are 1.7-4.7 mg/L, and the reduction rates in the number of eelgrass and Hokkai shrimp in the vicinity of the mouths of these rivers were large. The T-N concentrations in river water have had a tendency to increase with the increase of the river basin's nitrogen input. The river basin's nitrogen input has increased due to an increase in dairy farmers purchasing feed and fertilizer.