This study clarifies the water quality characteristics of stagnant, eutrophic water bodies that freeze in winter, based on our surveys and simulations, and examines how climate change may influence those characteristics. The survey found that climate-change-related increases in water temperature were suppressed by ice covering the water area, which also blocked oxygen supply. It was also clarified that the bottom sediment consumed oxygen and turned the water layers anaerobic beginning from the bottom layer, and that nutrient salts eluted from the bottom sediment. The eluted nutrient salts were stored in the water body until the ice melted. Climate change was surveyed as having caused decreases in nutrient salts concentration because of the shortened ice-covered period; however, Biochemical Oxygen Demand (BOD) showed a tendency to increase because of the proliferation of phytoplankton that was promoted by the climate-change-related increase in water temperature in spring.
To forecast the water quality by using these findings, particularly the influence of climate change, we constructed a water quality simulation model that incorporated the freezing-over of water bodies. The constructed model showed good temporal and spatial reproducibility and enabled water quality to be forecast throughout the year, including during the ice-covered period. The forecasts using the model agreed well with the survey results of the shortened ice period and climate-change-related increase in the BOD in spring.
2016 Japan Society of Civil Engineers