Host: The Association of Japanese Geographers
Name : Annual Meeting of the Association of Japanese Geographers, Autumn 2019
Date : September 21, 2019 - September 23, 2019
In order to clarify the hydrological characteristics of the islands of Nagasaki Prefecture, we have been conducting research with the Goto, Tsushima, Iki, and Hirado Islands since 2014. In this paper, the similarities and differences in water quality formation on the islands are discussed based on the results of statistical analysis of the survey results.
The riverbed gradient differs between Iki and the other three islands. In Iki, the concentration of dissolved ingredients is high from the upper reaches, while in Tsushima, sea salt has a particularly strong effect on rivers in the basin around Mt. Yatate in the southern part of Shimojima. Because of its steep topography, it is considered that the wind-swept salt and rainfall with a lot of seawater remained, and the same tendency can be seen in Ikitsuki Island in Hirado and Azuchi Oshima Island.
Statistical analysis was performed on the observation results and main dissolved components, and the main components were calculated for each island. It can be said that the main components related to EC and the amount of main dissolved components were the first main components, and the concentration of the main dissolved components is considered to be a major factor in the difference in water quality. The second and third principal components are considered to be the principal components that indicate the relationship between pH and RpH and water temperature, or the principal components that indicate water pollution relatively. Cluster analysis revealed that water quality was divided by region to some extent, and comparison with principal component scores suggested regional water quality characteristics. In Tsushima, the topography and geology, and in Iki, many reservoirs and rivers with low water flow were considered to have formed the same cluster, and residence time influenced, and in Tsushima, the topography and geology can be said to classify water quality clusters (Figure 1).
