2022 Fiscal Year Final Research Report

Influence of changes in lake water circulation processes due to global warming on denitrification in the sediment at Lake Biwa

Research Project

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Project/Area Number	20H04311
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Review Section	Basic Section 63010:Environmental dynamic analysis-related
Research Institution	The University of Shiga Prefecture
Principal Investigator	Osaka Ken'ichi 滋賀県立大学, 環境科学部, 准教授 (30455266)
Co-Investigator(Kenkyū-buntansha)	佐藤祐一滋賀県琵琶湖環境科学研究センター, 総合解析部門, 専門研究員 (30450878) 後藤直成滋賀県立大学, 環境科学部, 教授 (40336722) 中村高志山梨大学, 大学院総合研究部, 准教授 (60538057) 西田継山梨大学, 大学院総合研究部, 教授 (70293438) 細井祥子 (田辺祥子) 滋賀県立大学, 環境科学部, 准教授 (80423226) 木庭啓介京都大学, 生態学研究センター, 教授 (90311745)
Project Period (FY)	2020-04-01 – 2023-03-31
Keywords	窒素循環 / 温暖化 / 成層 / 同位体 / 微生物 / 溶存酸素
Outline of Final Research Achievements	We developed the column method to clarify the effect of dissolved oxygen concentration in the lake bottom on the rate of dissolved nitrogen exchange between lake bottom sediments and lake water. Using this method, the dissolved nitrogen exchange rate between lake sediments and lake water in Lake Biwa was measured. It was found that about 10% of the total dissolved nitrogen in the water of Lake Biwa is supplied from the lake bottom sediments to the lake water in one year, and this amount increases with a decrease in the dissolved oxygen concentration in the lake bottom. However, the amount of dissolved nitrogen pooled in Lake Biwa water in 2019 and 2020, when the winter total circulation was weaker than usual and the dissolved oxygen concentration in the lake bottom was lower than usual, was lower than usual. This suggests that consumption of dissolved nitrogen in the lake occurred more than the increased supply of dissolved nitrogen from the lake bottom sediments to the lake water.
Free Research Field	陸水学
Academic Significance and Societal Importance of the Research Achievements	世界各地の湖沼において、地球温暖化により表層水温が上昇することで湖水の鉛直循環過程が変化し、それによる湖水深層での溶存酸素濃度の低下や栄養塩の放出が問題となっている。本研究は湖水深層での溶存酸素濃度の低下が湖底堆積物と湖水間の窒素化合物交換速度に与える影響を明らかにするための手法を提示し、今後の地球温暖化に対する湖沼の応答に関する研究分野に貢献した。また近畿1400万人の飲料水を賄っている琵琶湖における窒素動態に関する重要な知見を得ることができた。