2003 Fiscal Year Final Research Report Summary
A model analysis for nonpoint pollutant reduction in paddy field watersheds
| Project/Area Number |
12660221
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Irrigation, drainage and rural engineering/Rural planning
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| Research Institution | Shimane University |
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Principal Investigator |
TAKEDA Ikuo Shimane University, Department of life and environmental science, Professor, 生物資源科学部, 教授 (60227022)
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| Project Period (FY) |
2000 – 2003
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| Keywords | watershed / nonpoint source pollution / pollutant reduction / water quality / circular irrigation / pollution load |
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| Research Abstract |
Investigations on water quality and hydrology were conducted in a paddy field and forest watersheds and essential factors, which can be useful for establishing a water purification model, were extracted. In the forest watershed, runoff volume was about 1 mm/d during non rainy days, whereas it declined to be 0.5 mm/d during draught seasons. However, runoff showed relatively sharp increase during rainy days and decreased to be about 1 mm/d rapidly. The ration of runoff to the amount of rainfall was about 30 %, indicating that about 70 % of rainfall amount was evapotranspiration. Then the reliability of this phenomenon was discussed. Furthermore, pollution loads from the investigation sites were quantified. In the paddy field watershed with a circular irrigation system, the concentrations of nitrogen, phosphorus and COD in the Hii River were lower than those in other sites of drainage rivers. The concentrations of phosphorus and COD tended to decrease with the river flowing whereas that of nitrogen did not show such decreasing trend. On the other hand, the concentration of DO in the Hii River was the highest and oxygen in the river can contribute decomposition of organic matters. There was not clear relationship between concentration decrease with the river flowing and amounts of rainfall of total nitrogen, total phosphorus and COD. The concentration decrease was caused by precipitation in drainage rivers and retention ponds and aerobic decomposition. The amounts of removed pollutants tended to increase with increasing hydraulic retention time with a few exceptions.
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