Host: Abstracts of Annual Meeting of the Geochemical Society of Japan
Pages 255-
The concentrations and seasonal changes of dissolved constituents of small rivers in Hirakawa City, Aomori Prefecture have been investigated. The effects of human activities such as agriculture were evaluated. The surveyed rivers are Biwata-River, Roppa-River, Hirofune-River, Asai-River and Hikiza-River, which is sourced from mountainous area of Hirakawa City, flow through the plains, and flow into a large Hirakawa-River. The survey was carried out from April to November in 2018 and resumed from April, 2019. The annual mean concentration of dissolved silica was higher in the upstream stations and lower in the downstream stations. It showed a significant seasonal change. Since the river water is taken and used for rice cultivation, the uptake of rice in the paddy field might cause the concentration decrease in summer season. In 2019, we set up a test paddy field and have started observation of the concentration of dissolved silica in supplying, in-paddy and outflow waters. The water is supplied to the upper paddy field, flows into the lower paddy, and is discharged. As the result of chemical analysis, the concentrations were generally in the following order; supplying water, upper paddy water, lower paddy water, and discharge water. It was suggested that dissolved silica in the supplied water was absorbed by the rice plant in accordance with its growth.
