Host: The Association of Japanese Geographers
Name : Annual Meeting of the Association of Japanese Geographers, Autumn 2020
Date : October 10, 2020 - November 22, 2020
The tributaries of the Abukuma River flowing down Fukushima and Miyagi prefectures have some points with high electrical conductivity (EC) values which we think are attributed to the contamination of domestic wastewater and influence of field fertilization (Yamagata et al., 2020). In this study, we clarified the relationship between water quality and land use in the basins of tributaries, as well as the chemical composition of river water, following monthly site investigations from Oct. of 2019 to Jul. of 2020.
The results showed that some tributaries such as Kameda Riv., Ouse Riv. and Higashine Riv. have high EC values with large levels of coefficient of variation (CV) (Fig. 1). On the other hand, tributaries such as Surikami Riv., Uchi Riv. and Kijio Riv. have low EC with small CV. In comparison with the land use ratio of each basin, a positive correlation between EC of tributaries on the right bank and the sum of land for buildings, paddy fields and other agricultural land is observed. This indicates a negative correlation between EC and forest land at the same time. Although no correlation between EC and land use on the left bank was found, EC was low in some tributaries with wide forest land.
As for the composition of river water, tributaries except for Higashine Riv. on the right bank were categorized into Ca-HCO3 type, a typical Japanese river water (Fig.2). Tributaries on the left bank were divided into Ca-SO4, Ca-HCO3 and Na-Cl types. Ca-SO4 type includes the rivers such as Ara Riv. and Matsu Riv. on the left bank flowing down from volcanoes. Na-Cl type includes two rivers with high EC and one river with low EC. The former is considered to be caused by the contamination of NaCl from domestic wastewater. The latter, Surikami Riv., which is characterized by the fact that forest land occupies approximately 90% of its basin, should be examined in the future.
In this study, the relationship between river water quality and land use was clearly implied in tributaries on the right bank. We will examine the water characteristics further by considering the size of catchment areas and geology.
