The River Godani, a tributary of the River Kakehashi which joins with main stream of the River Kakehashi about 5km downstream, is known for its pollution due to the mining water. Typhoon No.7 passed through Ishikawa Prefecture on September 22 in 1998 with locallized torrential down pour.
In this study, Vie examined the effect of the Typhoon No.7 on those Rivers from the viewpoint environmental factors of the river water and the ecological viewpoint based on the change of the epilithic diatom assemblages on the river bed.
Each of the four surveys <1998-1999> showed a tendency, in its measurement of EC values decreasing from upperstream to downstream in order.
The concentration of heavy metals increased in all sites after 6 months. At each sampling site 6 months after flood, the concentration of Cu was 1.3-2.0 higher, and that of Zn was 1.3-3.3 times greater than those obtained before flood, while the concentration of Cd showed no district difference from those obtained before flood.
The concentration of heavy metals in attached materials was far higher than that of heavy metals in the mud of river bed. This may be due to the fact that the greatest part of attached material consist of epilithic algae (organic materia1) and the rest is silt (inorganic material), while in the case of mud the volume of silt is much greater, than that of residue of epilithic algae. After all weight of epilithic algae per unit volume is small compared with silt, but they absorbs heavy metals. On the other hand, inorganicsilt only absorbs heavy metals but no process of concentration occurs.
Three surveys, B (November 2, 1988), C (December 21, 1988) and D (March 24, 1999) were after flood.
In the survey B,
Achnanthes minutissima which has strong tolerance to heavy metals was the most abundant taxon in almost all sampling sites.
It is noticeable that in all sites of D (150 days after flood), the most abundant taxon was
A. minutissima. The tempomry change of the most abundant taxon at Sites 3, 4 (cf. Fig.2) is considered to be due to the fact that materials on the river bed easily came off and were carried downstream and pilled up there temporarily.
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