Case Study

: 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 marsh-land 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 wa-ters in these types of Yatsu have become polluted in comparison with the natural type Yatsu.