Changes in Water Quality of Springs and Rivers in Aso Caldera in Relation to the 2016 Kumamoto Earthquake

Abstract

　We investigated changes in the water quality of springs and rivers in Aso caldera related to the 2016 Kumamoto earthquake. We used data available for the three or more years before and after the earthquake, respectively. Using these data, we preformed statistical analyses to assess differences. Results show that the pH of all spring and river waters was higher throughout the caldera after the earthquake. At springs located in the southern part of the caldera, electric conductivity, RpH−pH, and the concentration of SiO₂ were all greater after the earthquake. Specifically, it is considered that the groundwater residence time was longer after the earthquake. Analysis of the pH of rivers in the northern part of the caldera suggests that the discharge point of high SO₄^2- groundwater changed, which is consistent with the results obtained from earlier studies.