Relationship between underground structure and the deep spring water at the bottom of Lake Biwa and evaluation of effects of the spring on the lake environment

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H01974
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17020:Atmospheric and hydrospheric sciences-related
• Research Institution: The University of Shiga Prefecture
• Principal Investigator: Koizumi Naoji 滋賀県立大学, 環境科学部, 教授 (00215154)
• Co-Investigator(Kenkyū-buntansha): 岸 和央 立正大学, 環境科学研究所, 客員研究員 (40802468) ; 山野 誠 東京大学, 地震研究所, 教授 (60191368) ; 丸尾 雅啓 滋賀県立大学, 環境科学部, 教授 (80275156) ; 細井 祥子 (田辺祥子) 滋賀県立大学, 環境科学部, 准教授 (80423226) ; 後藤 忠徳 兵庫県立大学, 理学研究科, 教授 (90303685) ; 笠谷 貴史 国立研究開発法人海洋研究開発機構, 海洋機能利用部門(海底資源センター), グループリーダー (90373456) ; 後藤 慎平 東京海洋大学, 学術研究院, 助教 (90772939)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 琵琶湖 / 湖底湧水 / 湖底地下構造 / 湖底環境

Outline of Final Research Achievements

To elucidate the relationship between the deep lake bottom spring water in Lake Biwa and the subsurface structure of the lake bottom, and to evaluate the effects of the spring water on the lake bottom environment, we conducted underwater acoustic survey, lake bottom thermal survey, lake bottom observation by ROV, and surveys of lake water quality and bacteria. As a result, it was assumed that the spring water flows along the unconformity surface between the bedrock and the lake-bottom sediments. Therefore it is conceivable that the temperature in the path becomes higher than the surroundings. As a result, methanogens are activated, using the surrounding organic matter to produce methane, which may be released to the bottom of the lake with the spring water. Although the spring water usually has little effect on the lake bottom environment, it was found that the spring water occasionally may have some effect.

Free Research Field

地震地下水学

Academic Significance and Societal Importance of the Research Achievements

琵琶湖の深部湖底湧水の湖底環境への影響は，通常は軽微だが，時期によってはある程度の影響を与えている可能性がある事がわかった