関屋　幸一・赤崎　いずみ・迫　昭男・ 徳山　和秀・青山　好文

An Assessment of the Water Quality Including Seasonal Variations of the Kiyotake River Based on Zoobenthos (II)

Koichi SEKIYA, Izumi AKAZAKI, Akio SAKO, Kazuhide TOKUYAMA, and Yoshifumi AOYAMA

Abstract
We have examined the ASPT (Average Score Per Taxon) value and DI (Diversity Index), and water quality in regard to the rivers of this prefecture since 1996.

In 2003 as we did in 2002, we investigated 5 points ranging from the upper and lower parts of the Kiyotake river which is situated in the central part of the prefecture.

The results of the investigation were as follows.

1. At all 5 points the ASPT value was 5.7〜6.9, and DI was 1.6〜2.9 throughout the year.
2. We compared the ASPT value found in the 1996, 2002 and 2003 surveys. We found that the water quality at all 5 points was not as good relatively in 2002 and 2003 as it was in 1996. The main reason for this decline in quality was thought to be due to the increasing unnatural influence on the environment exerted by human activity.
3. Both the PPD (Points to Proper Degree) /ASPT value and the PPD/DI coefficients of correlation were lower in 2003 than in 2002, however it is believed that the PPD can be used to measure water quality.

Key words : ASPT, DI, zoobenthos, seasonal variations

はじめに
当所では、大型底生動物（以下「底生動物」と略す）による河川水域環境評価方法を用いて平成8年度から県内の河川の水質状況を、その季節的変動もあわせて調査してきた。

第1報（以下 「前報」 と称する）で報告したように、清武川について平成14年度から16年度までの3か年継続調査を計画した。初年度 （以下 「前年度」 と称する）に引き続き平成15年度 （以下 「今年度」 と称する） の調査を実施したので、その概要を報告する。