2007 Fiscal Year Final Research Report Summary
Study on structure of environmental problems in an inner bay from viewpoint of long-term change of watershed, estuary and ocean. -Arase study in Hamana Lake
| Project/Area Number |
17360234
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | Toyohashi University of Technology |
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Principal Investigator |
AOKI Shin-ichi Toyohashi University of Technology, Faculty of Engineering, Professor (60159283)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Takanobu Toyohashi Univ. of Tech, Faculty of Engineering, Professor (00184755)
KATO Shigeru Toyohashi Univ.of Tech, International Corpoartion Center for Engineering Education Development, Assistant Professor (40303911)
TSUSHIMA Koji Toyobashi Univ. of Tech, Faculty of Engineering, Assistant Professor (70391612)
YAMADA Toshiro National Institute of Public Health, Faculty of Engineering, Senior Researcher (30335103)
FURUYAMA Shoichi Toyama College of Maritime Technology, Lecturer (90321421)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Conservation of Ocean Environment / Analysis of Environment / Dynamics of Environment / Environment of Inner Bay |
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| Research Abstract |
(i) High nitrogen and phosphate concentrations were observed in the river water through the citrus orchard area. The phosphate and ammonium concentrations have increasing trends with the application of fertilizer. The phosphorus loads, especially particulate phosphorus, increase with rain. Annual nutrient loads are estimated.
(ii) Water exchange between Inohana and Hamana Lakes is dependent upon wind forcing. Both of the flow in the channel and vertical distribution of phosphorus have distinct two-layer structures, which contribute to the exchanges of water and material(nutrient)strongly. By developing a box model, the flows and budgets of waters and phosphorus are quantitatively discussed.
(iii) From the long-term field data for 50 years and simulation results, several causes of entrophication and hypoxia occurrances were suggested. Prior to 1980, jetties construction made the water exchange better, as a result the water quality was improved. However, the water quality has been worse since 1980. This study suggests that one of the cause for it is the increase in water temperature.
(iv)A numerical simulation method was developed using the adaptive mesh refinement method and applied to the shallow water region in Hamana Lake. The effectiveness of the method was confirmed.
(v) Long-term changes of nutrient loads from the fertilization in citrus orchards around Inohana and Hamana lakes were estimated. Since mid-1970s, nitrogen load has been decreasing due to decrease in fertilization quantity around Inohana Lake and due to decrease in area of orchard around Hamana Lake.
(vi) Since 1993, the clam spat has been frequently observed in northern area of Hamana Lake. This is considered due to increase in water exchange rate by constructing the inner jetties. It also induced increase of clam-eating shellfish
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Research Products
(39 results)
