Evaluation of the effects of toxic substances in Lake Tazawa-Tamagawa river system using biological responses of aquatic organisms

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K04325
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 22060:Environmental systems for civil engineering-related
• Research Institution: Akita National College of Technology
• Principal Investigator: KIM Juhyun 秋田工業高等専門学校, その他部局等, 教授 (20302193)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 短期慢性毒性 / 水生生物 / 生物応答 / 玉川中和処理施設 / 玉川ダム / 田沢湖

Outline of Final Research Achievements

A strongly acidic spring with a pH 1.2 that gushes out from Tamagawa hot spring in Akita Prefecture flows into Lake Tazawa, aquatic organisms became extinct, including the endemic species of Oncorhynchus kawamurae. As a countermeasure, Tamagawa neutralization treatment plant (TNTP) is in operation, but pH value of Lake Tazawa is lower than the water environmental standards.
In this study, we conducted a short-term chronic toxicity test using aquatic organisms at three locations in Lake Tazawa-Tamagawa river system and compared before and after adjusting the pH to 6.7. As a result, the toxicity unit (TU) in the downstream direction of TNTP, Tamagawa Dam, and Lake Tazawa showed a tendency to decrease, and in particular, the decrease in TU value up to Tamagawa Dam and the immediate improvement in toxicity were significant. Regarding the pH adjustment effect, a positive effect was observed in the treated water of TNTP. Al concentration was strongly involved in changes of toxicity unit.

Free Research Field

土木環境システム

Academic Significance and Societal Importance of the Research Achievements

本研究により玉川-田沢湖水系の酸性区間における毒性物質群の挙動及び水生生物の生物応答により得られた毒性レベルの変化をpH調整前後で比較検討を行った結果、玉川中和処理施設における中和処理目標の向上は酸性化問題を解決できる他、アルミニウム、フッ素等の毒性物質群の低減効果が同時に期待できるため、クニマスの「里帰り」が可能な玉川-田沢湖水系の水質管理に有効であることを明らかにした。
現状の玉川中和処理施設における目標pH3.5では、毒性物質群の凝集・沈殿効果が小さく、田沢湖のpHが5.2付近で推移していることから、中和処理の目標を上げて田沢湖本来のpH6.2～6.7に戻す中和処理対策が必要と考える。