Evaluation of material circulation in lakes by continuous tracking of river water

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 16540397
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Meteorology/Physical oceanography/Hydrology
• Research Institution: Shiga University
• Principal Investigator: ENDOH Shuichi Shiga University, Faculty of Education, Professor, 教育学部, 教授 (30111884)
• Project Period (FY): 2004 – 2005
• Keywords: River water / Material circulation / Lake Biwa / Density current / Electric conductivity / Dissolved oxygen

Research Abstract

Hydrological observation has been carried out in Lake Biwa to evaluate the material circulation caused by inflowing river water, especially focused on the River Yasu, which has a maximum catchment area among river flowing into Lake Biwa. In every month of 2005, three dimensional distribution of water quality, such as water temperature, electric conductivity, turbidity, chlorophyll, dissolved oxygen, were measured by vertical profiler in the lake. Continuous measurements of water current and water quality were also made off the river mouth.
Water quality of the River Yasu is rather good in the upstream area, but is getting worse especially downstream of the branch of "Omoi gawa River", where many industrial waste water released into the river. As a result, water quality of the River Yasu at the river mouth is worse than that of the lake.
In the spring season, river water inflows in the surface layer because river water is warmer (denser) than lake water. In this case, river water spreads in a radial manner. On the other side, river water sinks at the river mouth and deflect to the right in the season of summer, fall, and winter. This is due to the Coriolis effect on the density current.