10:45 AM - 12:15 PM
[MIS09-P05] Factors of Neutralization of Acidic Lake Inawashiro, Fukushima Prefecture : Focusing on the temporal change in Water Quality of Inflow Rivers
Keywords:Lake Inawashiro, Land use, pH, Total nitrogen, Total phosphorus
Lake Inawashiro, Fukushima Prefecture, was one of the volcanically acidic lakes in Japan. From 1990 to 2010, however, the neutralization of Lake Inawashiro has been observed, and its causes are still unclear. Lake water quality is affected by inflow rivers, which are strongly controlled by geographical and human-related factors. In this study, we investigated temporal changes in the water quality of Lake Inawashiro and major rivers flowing into the lake from open data archive, and analyzed the relationships between water quality changes and land-use history in the river watershed. Then we aim to elucidate the possible causes of lake water neutralization from two aspects: volcanic activity and human activity. Inflow river watershed boundaries were extracted from the 10m DEM data, and the watershed land-use and vegetation classification were based on the land-use maps and vegetation classification maps from past to present. The ratio of an area of the respective land-use category to the whole watershed area was calculated using Q-GIS.
As Sutani et al. (2013) pointed out, a slight increase in pH with decreasing the sulfate concentration was detected in the strongly acidic rivers flowing from the mouth of the active volcano (Mt. Adatara), which would be due to the gradual change in the volcanic activity. In addition, we found that the significantly temporal increase in pH and total nitrogen and phosphorus concentrations in originally pH neutral rivers, of which watersheds are covered with the paddy field and urban land. The possible reason for this temporal change is the expansion of land use which is strongly influenced by human activities. Increases in total nitrogen and phosphorus concentrations in river and lake water can induce a further increase in pH of Lake Inawashiro owing to bicarbonate uptake by phytoplankton. From our study, not only the change in volcanic activity but also the intensification of human activities may have contributed to the increase in pH of the Lake Inawashiro.
As Sutani et al. (2013) pointed out, a slight increase in pH with decreasing the sulfate concentration was detected in the strongly acidic rivers flowing from the mouth of the active volcano (Mt. Adatara), which would be due to the gradual change in the volcanic activity. In addition, we found that the significantly temporal increase in pH and total nitrogen and phosphorus concentrations in originally pH neutral rivers, of which watersheds are covered with the paddy field and urban land. The possible reason for this temporal change is the expansion of land use which is strongly influenced by human activities. Increases in total nitrogen and phosphorus concentrations in river and lake water can induce a further increase in pH of Lake Inawashiro owing to bicarbonate uptake by phytoplankton. From our study, not only the change in volcanic activity but also the intensification of human activities may have contributed to the increase in pH of the Lake Inawashiro.