日本地球惑星科学連合2018年大会

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[EE] ポスター発表

セッション記号 A (大気水圏科学) » A-HW 水文・陸水・地下水学・水環境

[A-HW20] 流域の物質輸送と栄養塩循環-人間活動および気候変動の影響-

2018年5月21日(月) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:齋藤 光代(岡山大学大学院環境生命科学研究科)、小野寺 真一(広島大学大学院総合科学研究科)、細野 高啓(熊本大学大学院先導機構、共同)、Adina Paytan(University of California Santa Cruz)

[AHW20-P25] Observation for the groundwater inflow to the lagoons connected to Lake Biwa

*齋藤 光代1小野寺 真一2友澤 裕介2Wang Kunyang2伴 修平3奥田 昇4 (1.岡山大学大学院環境生命科学研究科、2.広島大学大学院総合科学研究科、3.滋賀県立大学、4.総合地球環境学研究所)

キーワード:地下水流入、内湖、琵琶湖

There are more than 20 lagoons around Lake Biwa which were originally a part of the lake. These lagoons are regarded to have important functions as settling ponds of inflowing loads from the catchments to Lake Biwa, refuges for shallow water ecosystems and so on. Because these lagoons are connected to Lake Biwa, evaluation of nutrient budget is important for the nutrient cycle in the lake. Groundwater inflow is one of the potential nutrient paths from a catchment to water environments. Some researchers have pointed out the presence of lacustrine groundwater discharge (LGD) in littoral area of Lake Biwa. However, it has not been evaluated for the lagoons around the lake. In the present research, we aimed to examine the groundwater inflow to the lagoons connected to Lake Biwa using the multi-tracer method.

The field campaign was conducted in December 2017 for two lagoons (Noda-Numa and Hasu-Ike) located on northeastern shore of Lake Biwa. The volume of inflow and outflow, water temperature, electric conductivity, chlorophyll-a and radon (222Rn) concentration were measured in these lagoons. 222Rn is a radioactive element of uranium (238U) series with 3.8 day of half-life. 222Rn is a useful tracer of groundwater discharge because it generally enriched in groundwater than surface water. Water samples were collected at the inlet, outlet and near the center of the lagoons and natural springs and groundwater wells around the lagoons. Also bottom sediment samples were collected in the lagoons. These samples have been analyzed for nutrients (nitrogen, phosphorus and silicate) and stable isotope ratios of oxygen and hydrogen (δ18O and δD) for water.
δ18O and δD for water were plotted on the different meteoric lines between Noda-Numa an Hasu-Ike. This result suggests these water are originated from different watersheds with different groundwater flow systems. Besides, these values were lower at the inlet than the center and outlet of the lagoons and was lowest in the groundwater around the lagoons. These results suggest the presence of groundwater inflow to these lagoons and the signal decreased from the inlet to the outlet.