[A-HW22] 流域生態系における物質輸送と循環：源流から沿岸まで

[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

*小野寺 真一¹、齋藤 光代²、友澤 裕介¹、石田 卓也¹、伴 修平³、奥田 昇⁴ (1.広島大学大学院先進理工系科学研究科、2.岡山大学、3.滋賀県立大学、4.神戸大学)

キーワード：地下水流出、深層、同位体

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).