2004 Fiscal Year Final Research Report Summary
Relationships among groundwater flow system, discharge types, and nitrate attenuation zone in upland-lowland boundary region
| Project/Area Number |
14380030
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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 |
自然地理学
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| Research Institution | University of Tsukuba |
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Principal Investigator |
TASE Norio University of Tsukuba, Graduate School of Life and Environmental Sciences, Professor, 大学院・生命環境科学研究科, 教授 (40133011)
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| Co-Investigator(Kenkyū-buntansha) |
TSUJIMURA Maki University of Tsukuba, Graduate School of Life and Environmental Sciences, Assistant Professor, 大学院・生命環境科学研究科, 講師 (10273301)
SUGITA Fumi Chiba University of Commerce, Associate Professor, 商経学部, 助教授 (40275962)
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| Project Period (FY) |
2002 – 2004
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| Keywords | nitrate nitrogen / groundwater contamination / attenuation / denitrification / groundwater flow / upland / wetland / spring |
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| Research Abstract |
Transitional zones from upland to lowland have been focused as an important attenuation zone of nitrate in groundwater. We have been studying relationships among geology, landform, groundwater flow and nitrate concentration, in order to clarify nitrate fate in a typical small hillslope-wetland zone in Tsukuba, through intensive observation network of wells and piezometers.
The results are summarized as follows :
1)Groundwater flow system in this region is controlled basically by landform, that is, water table is consistent with landform.
2)High nitrate(-100mg/L) in groundwater is attenuated near or below the black clay layer distributed in the small valley bottom. The attenuation zone or front is distributed like horseshoe-shaped along the valley bottom.
3)The attenuation process is attributed to denitrification by organic carbon as an electron donor under anaerobic condition. The black clay layer with high organic contents supplies dissolved organic carbon and reduced groundwater.
4)The attenuation front moves forward or backward with low or high hydraulic gradients in the black clay layer. That is, when downward flow is dominant in the black clay layer to the sand layer, attenuation occurs actively and the front moves backward or upstream.
5)There are three types of spring, that is, seepage, upwelling, and pipe-flow types in this region. The nitrate concentrations are generally higher in pipe-flow type than others. The seepage type is subject to natural attenuation.
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