Organic pollution of the Ina River and it's branches, the Minoh River and the Yono River, was estimated numerically by using the diatom assemblage index (DAIpo). And the water quality charts of each river were made using DAIpo. Results were the following.
(1) The Ina River: DAIpo values decreased gradually toward the dow n stream. The DAIpo value of the point of water source for Ikeda City was ca.60 (α-oligosaprob) and for Toyonaka City was ca.55 (α-oligosaprob). River pollution index (RPI
D), whose value is able to be shown the general degree of pollution of river system, was 63.
(2) The Minoh River: DAIpo values of two sampling sites in the upstream were very high but decreased rapidly toward the downstream. The DAIpo value of the point of water source for Minoh City was ca.70 (β-oligosaprob), and the RPI
D was 67.
(3) The Yono River: DAIpo values were lower in the up s tream rather than in the downstream. The DAIpo value of the point of water source for Ikeda City was 59 (α-aoligosaprob), and the RPID was 56.
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