事例研究 CASE　STUDY

千葉県船橋市近郊における谷津の土地利用と河川水質の関係

金子是久¹⁾・ 大野啓一²⁾・ 森内栄一³⁾・ 西岡孝雄³⁾

1)〒333-0801　川口市東川口2-14-24
2) 横浜国立大学大学院環境情報研究院　〒240-8501　横浜市保土ヶ谷区常盤台79-7
3) 船橋市環境保全課　〒273-8501　船橋市湊町2-10-25

Korehisa KANEKO¹⁾, Keiichi OHNO²⁾, Eiichi MORIUCHI³⁾ and Takao NISHIOKA³⁾: Relationship between river water quality and land uses in Yatsu located in the suberbs of Funabashi City, Chiba, Japan. Ecol. Civil. Eng. 7(1), 81-92, 2004.

1) 2-14-24 Higashi-kawaguchi, Kawaguchi 333-0801, Saitama, Japan
2) Institute of Environmental Information Research, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Kanagawa Japan
3) Environmental Conservation Section, Funabashi City, 2-10-25 Minatomachi, Funabashi 273-8501, Chiba, Japan

Abstract:The water quality of three Yatsu （Funabashi City in Chiba Prefecture, Japan） having different land uses, were compared. These three Yatsu are the natural type, semi-natural type, and the city-type. (1) The natural type Yatsu is swamps in the bottom of a valley and is surrounded by woods on a plateau and the plateau's slope. (2) The semi-natural type Yatsu is also marshland in the bottom of a valley, but is surrounded by residential areas and woods where ruderal plant community is locally distributed. (3) The city-type Yatsu is situated in a valley bottom where agricultural fields and residential areas have been developed. The water quality values, such as Cl, TN, TP, and COD, in the natural Yatsu are low in comparison with those in the semi-natural type and city-type Yatsu. The rate of the wooded area around the natural Yatsu was the highest among the three Yatsu. We considered that this area may have a high water-holding capacity, and that an abundant supply of spring water into the river may enhance the water quality. As for the semi-natural type and city-type Yatsu, although the woods occupy a part of the plateau slope, the wastewater from the densely-populated areas upstream of the Yatsu degrade the water quality flowing into this Yatsu. For this reason, even if spring water is supplied from the edge of the Yatsu, the waters in these types of Yatsu have become polluted in comparison with the natural type Yatsu.

Key words: land use, water quality, natural type Yatsu, semi-natural type Yatsu, city-type Yatsu

摘要

本研究は，千葉県船橋市近郊に位置する土地利用の異なる3つの谷津の水質について比較検討した．3つの谷津は，(1)谷底が過湿地であり，周辺の斜面台地及び台地に樹林が広がる自然型の谷津，(2)谷底の大部分は湿地であるが，その周辺の大部分が住宅地，人為裸地で占められている半自然型の谷津，(3)谷底の大部分が畑地または造成地であり，周辺は住宅地または畑地で占められている都市型の谷津の3タイプに分けられた．
　3つの谷津の水質（Cl，TN，TP，COD）を比較した結果，自然型の谷津は，半自然型，都市型の谷津に比べて水質が良好である傾向を示した．これは，自然型の谷津周辺における樹林の面積率が3つの谷津の中で最も高く，樹林による保水力もあると推察されたことから，豊富な湧水が流れ込み，水質の良好な河川を形成していると考えられる．また，半自然型の谷津と都市型の谷津では，樹林地が台地斜面に一部残されているが，谷頭周辺では住宅地が密集し，生活雑排水が流入していたことから，周辺から湧水が流入しても，自然型の谷津に比べて水質汚濁が進行していたと考えられる．

2003年11月10日受付，2004年6月10日受理
1) e-mail: k_kaneko@hotmail.com