11:15 〜 11:30
[AHW27-09] Origin and fate of groundwater nitrate-nitrogen pollution in the Kumamoto area based on isotopic ratio and metagenomic analysis
In the Kumamoto area, which is the study area of this study, nitrate contamination of groundwater mainly occurs in the eastern and central parts of Kumamoto City. Previous studies have shown the spatial distribution of nitrate ion concentration and δ15NNO3 in groundwater in the Kumamoto region, as well as evaluated the seasonal variations in nitrate ion concentration in groundwater in the eastern part of the Kumamoto region.
However, no study has evaluated the seasonal variations of nitrate ion concentrations, δ15NNO3 and δ18ONO3 in groundwater over a wide area in the Kumamoto region.
In this study, we measured nitrate ion concentrations, δ15NNO3 and δ18ONO3 in groundwater from a wide area in Kumamoto region, and evaluated their seasonal variations to clarify the overall picture of nitrogen dynamics in groundwater in Kumamoto region. And tried to clarify bacterial species and functional genes by using metagenome analysis.
The results showed that nitrate ion concentrations were constant throughout the season at all sites, while δ15NNO3, δ18ONO3 showed large fluctuations only at sites with low nitrate ion concentrations. At the sites with low nitrate ion concentrations, the low DO values suggested the possibility of denitrification. The origin of nitrogen pollution was estimated using δ15NNO3, and the origin characteristics did not change throughout the season. And metagenomic analysis showed that the abundance of functional genes working in nitrate reduction and denitrification was higher at sites with lower nitrate ion concentrations.
This study suggested that there is a limit to what can be learned from isotopic ratio measurements alone, since denitrification varies in intensity and functional genes at different sites. Therefore, it was thought that the characteristics of denitrification at each site could be elucidated in more detail by combining isotope ratio measurements with metagenomic analysis.
However, no study has evaluated the seasonal variations of nitrate ion concentrations, δ15NNO3 and δ18ONO3 in groundwater over a wide area in the Kumamoto region.
In this study, we measured nitrate ion concentrations, δ15NNO3 and δ18ONO3 in groundwater from a wide area in Kumamoto region, and evaluated their seasonal variations to clarify the overall picture of nitrogen dynamics in groundwater in Kumamoto region. And tried to clarify bacterial species and functional genes by using metagenome analysis.
The results showed that nitrate ion concentrations were constant throughout the season at all sites, while δ15NNO3, δ18ONO3 showed large fluctuations only at sites with low nitrate ion concentrations. At the sites with low nitrate ion concentrations, the low DO values suggested the possibility of denitrification. The origin of nitrogen pollution was estimated using δ15NNO3, and the origin characteristics did not change throughout the season. And metagenomic analysis showed that the abundance of functional genes working in nitrate reduction and denitrification was higher at sites with lower nitrate ion concentrations.
This study suggested that there is a limit to what can be learned from isotopic ratio measurements alone, since denitrification varies in intensity and functional genes at different sites. Therefore, it was thought that the characteristics of denitrification at each site could be elucidated in more detail by combining isotope ratio measurements with metagenomic analysis.