Spatial characteristics of groundwater flow mechanisms and their seasonal variations in Kumamoto area revealed by stable isotope analysis of water

<p>In the Kumamoto area, where this study was conducted, the recent decline in the water table due to groundwater pumping and water pollution, such as nitrate-nitrogen contamination, have become problems. Groundwater has long been associated with people's daily lives, and groundwater currently provides almost 100% of the water supply for the region. In previous studies on groundwater flow in this area, various studies have been conducted, including measurement of groundwater level and hydrogeology, but analysis in recharge areas such as the Otsu-Kikuyo area has not progressed, and there are still problems in understanding the groundwater system as a whole. In this study, we were able to obtain the cooperation of several municipalities and companies, which made it possible to collect water more comprehensively than in previous studies. Therefore, we analyzed the obtained groundwater samples for stable isotopes of hydrogen and oxygen in order to obtain a broad and detailed understanding of groundwater flow in this region, where groundwater is closely connected to people's daily lives. Based on the characteristics of the flow mechanism obtained from the analysis, 13 sites were selected, and monthly isotope analysis has been continued since April 2022.</p>