Abstract
On April in 2018, huge eruption at Iouyama in Kirishima mountain range was happened, and the mountain erupted for the first time in 250 years. By this large explosion, many of eruptions were contaminated into rivers, which killed massive amount of fishes due to lower pH and contamination of several heavy metals and anions. Therefore, people who live close to the rivers decided to stop cultivation in paddy fields because the cultivation requires river water. In this study, to understand actual in situ situation, we evaluated influence of water contaminated with eruption of Iouyama in Kirishima mountain range into river environments and rice cultivation. Water quality analysis during 2019–2020 indicated that concentration of Fe and Mn were often higher than threshold of Japanese environmental standard of river. For the As, although beginning concentration was higher than the standard, the concentration became lower than the standard after October in 2019. By 16S rRNA gene analysis, species richness of sediment observed from upstream river closer to Iouyama were significantly lower than downstream rivers, and strong acidophilic bacteria and archaea were predominant in the sediments. Rice cultivation test indicated that total As concentration in brown rice was 0.40 ± 0.11 mg/kg using 10-fold diluted Akago river water during 2018–2019, suggesting that some brown rice may contain As equal to or higher than codex standard value (0.35 mg/kg). Overall, we could assess in situ situation closer to Iouyama in terms of water quality, microbiology, and plant cultivation.
