[A-HW22] Material transportation and cycling in watershed ecosystems; from headwaters to coastal areas

[AHW22-P10] Estimation of groundwater and lake water interaction in the deeper zone of Lake Biwa, using ¹⁸O and D in pore water and groundwater

*Shin-ichi Onodera¹, Mitsuyo Saito², Yusuke Tomozawa¹, Takuya Ishida¹, Syuhei Ban³, Noboru Okuda⁴ (1.Graduate School of Advanced Science and Engineering, , Hiroshima University, 2.Okayama University, 3.The University of Shiga Prefecture, 4.Kobe Univesity)

Keywords:groundwater discharge, deep zone, isotope

We examined to estimate groundwater and lake water interaction in the deeper zone of Lake Biwa, using ¹⁸O and D in pore water and groundwater to confirm groundwater discharge and nutrient flux. We collected groundwater samples at production and observation boreholes several depths on the eastern coastal area of the lake and the pore water samples in bottom sediment cores at the sites of an eastern and western slopes with the depths of 5m, 10m, 20m, 60m in a northern lake, respectively. The water isotopic ratios in groundwater were lower than those in lake water, and those in deep groundwater were lower than those in shallow groundwater, respectively. The d-values which is a y-intercept on the ¹⁸O and D plot with the slope of 8 were larger in groundwater and deep, respectively. The isotopic ratios in spring water of headwater indicated the altitude effect which isotopic ratios in the spring with the higher altitude has lower, and d-values in summer precipitation has smaller than those in winter. These indicated the deeper groundwater came from the mountain slope with the higher altitude. The pore water at the site with the depth of 20m had the larger d-values than those at the site with the shallower depth. This suggested the deeper groundwater contributes to the groundwater discharge at the deep zone of the lake.
* This research was supported by JSPS project (PI Ban,S).