Evaluating the effects of drainage from paddy fields on Lake Biwa ecosystem
| Project/Area Number |
16310011
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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 |
Environmental dynamic analysis
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| Research Institution | The University of Shiga Prefecture |
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Principal Investigator |
BAN Syuhei The University of Shiga Prefecture, School of Environmental Science, Associate Professor, 環境科学部, 助教授 (50238234)
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| Co-Investigator(Kenkyū-buntansha) |
OHTA Kei-ichi The University of Shiga Prefecture, School of Environmental Science, Associate Professor, 環境科学部, 教授 (80022250)
SUDO Miki The University of Shiga Prefecture, School of Environmental Science, Associate Professor, 環境科学部, 講師 (50206570)
KUMAGAI Michio Lake Biwa Environmental Research Institute, Chief Scientist, 環境科学研究センター, 統括研究員 (40234512)
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| Project Period (FY) |
2004 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥15,100,000 (Direct Cost: ¥15,100,000)
Fiscal Year 2006: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2005: ¥4,300,000 (Direct Cost: ¥4,300,000)
Fiscal Year 2004: ¥9,100,000 (Direct Cost: ¥9,100,000)
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| Keywords | Drainage from paddy fields / Lake Biwa / Subsurface maximum of ammonium / Phytoplankton production / Internal Kelvin wave / Nitrogen stable isotope / Material transport / Bottom sediments / セストンδ^<13>C / セストンのδ^<15>N / アンモニア / 植物プランクトン / 内部波 / アンモニアの排出 / 動物プランクトン |
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| Research Abstract |
In north basin of Lake Biwa, subsurface maximum of ammonium was found across the east to west transect of the lake from late April to early July. Phytoplankton was relaxed from nutrient limitation and primary production was enhanced in mid-May just after rice planting. According to stable isotope analysis, suspended particles originated from paddy fields run into the lake, and seemed to deposit to the bottom of the littoral area, where ammonium, and probably together with phosphate, was released from the bottom sediments, used by phytoplankton production. Experiments for zooplankton excretion showed that regenerated nitrogen from micro-and mesozooplankton may contribute to the subsurface maximum of ammonium, and that regenerated phosphate was not enough for phytoplankton growth. This does not necessarily suggest that the subsurface maximum of ammonium is proxy as supplying nutrients from littoral to pelagic area.
Survey using ADCP and thermister-chain showed that internal Kelvin wave was found after mid-May. Vertically mixing and wavy motion produced by the internal Kelvin wave can induce wavy motion oscillating to the shoreline due to the effect of the slope of the bottom, and it can transport materials such as nutrients from littoral to pelagic area of the lake. Pesticides as indicator of the water from paddy were found even at 20 m depth as well as at the surface in the lake. It also supports horizontal transportation under the thermocline, ca. 20 m. These results provide a scenario as described below. In Lake Biwa, turbid drainage from paddy fields just after rice planting run into the lake, and suspended materials from the paddy deposits on the bottom sediments. Nutrients, such as ammonium and phosphate, released from the interstitial water in the sediments by disturbance due to internal wave are transported to the pelagic area and enhance phytoplankton production. To confirm this hypothesis, further studies for analyzing nitrogen stable isotope are needed.
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Report
(4 results)
Research Products
(8 results)
