Evaluation of the mechanism of residence time change of Shimabara springs based on high frequency water sampling survey

It is essential to clarify the groundwater flow system and its scale for the sustainable use and management of local water resources. One effective method is to estimate the residence time of groundwater. The Shimabara springs exist in Nagasaki Prefecture, Japan, and its water quality has been characterized over time. However, there have been few studies on water quality characteristics and isotope variations with fine resolution in a region such as Japan, where seasonal changes in precipitation are observed. Therefore, we conducted periodic water sampling at five locations in the Shimabara Springs at a frequency of about once a month, and evaluated water quality characteristics and isotope variations. CFC-12, an age dating tracer, was also used for a multifaceted study. During the observation period, we observed precipitation that was more than five times larger than the normal year, and in response to this, we were able to identify springs that showed changes in various hydrologic parameters. In the presentation, we will discuss the relationship between precipitation, residence time, and water quality, and present a schematic diagram of the mechanism of this spring discharge.