Study on the formation and maintenance mechanisms governing micro-structure of low dissolved oxygen water areas in a lake

湖泊低溶氧水域微观结构形成与维持机制研究

• 批准号: 20244079
• 负责人: KUMAGAI Michio
• 金额: $ 31.12万
• 依托单位: Lake Biwa Environmental Research Institute
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (A)
• 财政年份: 2008
• 资助国家: 日本
• 起止时间: 2008 至 2010
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-20244079/
• 关键词: 湖底泥; 水温; 溶存酸素濃度; 消散係数; 湖底境界層; 数値モデル; 内部波; 琵琶湖

We had the following results from this study ;(1) We deployed a lake bottom platform several times at about 90m depth in Lake Biwa to measure the dissolved oxygen concentration (DO) in the bottom sediments. We found thin layers of 2-3mm thickness between oxic water and anoxic sediment and conclude that these layers correspond to viscous sub-layers. The recovery of DO in sediments depends on the temperature difference between the water and sediment. It is not easy to oxidize bottom sediments completely once they become anoxic,(2) We also deployed an ADCP-TP-1200F to measure mean and turbulent flows in benthic boundary layers (BBL). After calculation of Reynolds stress in the layers, we found the stress on the surface of bottom sediments was not great enough to re-suspend sediments. This suggests that turbidity in the BBL is not caused by shear instability, but originated from bottom sediment ebullition such as hydrothermal vents detected by the AUV "Tantan",(3) We developed a three dimensional numerical simulation model based on a hydrodynamics and ecosystem coupling scheme to understand the formation and maintenance mechanisms of low dissolved oxygen water areas near the lake bottom. Using this model, we found the oscillation flow due to internal waves periodically moved the anoxic water over a rather wide area. This result can be important, because it is deeply related with the generation of low DO water areas and their influence on benthic animals endemic to Lake Biwa.

本研究得到以下结果：（1）在琵琶湖水深约90m处多次部署湖底平台，测量湖底沉积物中的溶解氧浓度（DO）。我们在含氧水和缺氧沉积物之间发现了 2-3 毫米厚的薄层，并得出结论，这些层对应于粘性子层。沉积物中 DO 的回收取决于水和沉积物之间的温差。底部沉积物一旦缺氧就不容易完全氧化。(2)我们还部署了ADCP-TP-1200F来测量底栖边界层(BBL)的平均流和湍流。经过层内雷诺应力计算，我们发现底部沉积物表面的应力不足以使沉积物重新悬浮。这表明BBL中的浑浊度不是由剪切不稳定引起的，而是源于AUV“探探”探测到的热液喷口等底部沉积物沸腾。(3)我们开发了基于水动力和生态系统耦合方案的三维数值模拟模型，以了解湖底低溶解氧水域的形成和维持机制。使用该模型，我们发现由于内波而产生的振荡流周期性地将缺氧水移动到相当大的区域。这一结果可能很重要，因为它与低溶解氧水域的形成及其对琵琶湖特有的底栖动物的影响密切相关。

项目成果

深水湖の全循環の将来予測

未来深水湖泊总循环量预测

• 发表时间: 2010
• 作者: 吉田大紀;家森俊彦;大槻憲四郎;北澤大輔
• 通讯作者: 北澤大輔

The Dynamics of Dead Zone in Lake Biwa, Japan

日本琵琶湖死区动态

• 发表时间: 2009
• 作者: Suzuki;S.;K.Hosokawa;T.F.Shibata;K.Shiokawa;Y.Otsuka;N.Nishitani;T.Ogawa;A.V.Koustov;B.M.Shevtsov;関山剛;荻野竜樹;M.Kumagai
• 通讯作者: M.Kumagai

The dynamics of benthic boundary layer in Lake Biwa

琵琶湖底栖边界层动力学

• 发表时间: 2010
• 作者: Gahlan;H. A.;Arai;S.;Abu El-Ela;F. F. and Tamura;A.;熊谷道夫
• 通讯作者: 熊谷道夫

Impacts of Climate Change on the Lake Biwa Ecosystem.

气候变化对琵琶湖生态系统的影响。

• 发表时间: 2008
• 作者: S.Ikeda;M.Nakajima;K.Horioka;熊谷道夫
• 通讯作者: 熊谷道夫

Physical and biological controls of vertical gradients in phytoplankton

• DOI: 10.1215/21573698-1267403
• 发表时间: 2011-04
• 期刊: Limnology and Oceanography
• 影响因子: 4.5
• 作者: J. Prairie;P. Franks;J. Jaffe;M. Doubell;H. Yamazaki