In the upperstream basin of the River Nabetani, Ishikawa Prefecture, there are deposit areas of pottery stone containing pyrites as one of the inpurites. This mineral used to make the river water in the upperstream strongly acidic (pH 3.6) . And the effect of this waste water from the mine extended to considerbly wide dowmstream areas.
The water of the R.Edadani, one of the tributaries of the R, Nabetani was also weekly acidic, although there is no working mine in its vicinity.
Hattori Ltd. in order to neutralize the effect of the mine waste water installed mine waste water treatment facilities which started to operate in December 1993.
This six-year survey of R. Nabetani and its tributaries was made to evaluate the effect of the tratment facilities; before the operation of the facilities from 1990 to 1993 (Survey I) and after its operation from 1994 to 1995 (Survey II) .
In each sampling site, the attached diatom assemblage on river bed was collected and some physicochemical variables of the river water measured. The result are summarized as follows:
1. pH values of Sites 1-5 in Survey II showed slightly increasing tendency when compared with those of Survey I.
2. In Survey I the SO₄^2- values of river water decreased in order from upperstream to downstream.
3. After the operarion of the treatment facilities, T-Fe and EC valu es showed a distinctly clear reduction.
4. As shown Fig.7, the specific composition of diatom assembiage in each sampling site in the main stream, the R.Nabetani showed a distinct change after the operation of the treatment facilities.
In areas about 5km between Site 1 and Site 4, diatom assemblages resistant to mine pollution appeared before the operation of treatment facilities on November 1990 (Surbey I) . But after the operation on August 1995 (Survey II) such diatom assemblages were reduced to with in the range of ab. 2km from Site I to Site 2, and replaced by common species usually occurring in comparatively pollution-free water area. Such a change of specific composition of diatom assemblages seems to suggest that range of ab. 3km from Site 3 to Site 4 was made free from the effect of mine pollution and recovered to ordinary pollution-free water course.

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Seasonal changes of developmental patterns of algal mats of slow sand filters (Someya water works, Ueda city, Wakata water works, Takasaki city and Nabeya-ueno, Nagoya city) were examined. The water sources of Someya water works and Wakata water works were a surface water of a stream and the water source of Nabeya-ueno was a reservoir water. In the cases of slow sand filters which water sources were stream water, an algal mat of filamentous diatom of Melosira grew well due to high nutrient concentration in raw water. It was remarkable in summer when there was high nutrient concentration. However in the case of a slow sand filter which water source was a reservoir water, the developmental rate of algal mat was extremely slow. The dominant species of algal flora on the algal mat on the filter bed were almost same as the flora in the inflow water from the reservoir. Algal mat on the filter bed was just accumulated with phytoplankton which was grown in the reservoir. The low growth rate of algal mat was due to lack of available phosphorus in the inflow water.

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Ashford Common浄水場の緩速ろ過池砂層内における抑留物質の深度分布を調査して染屋浄水場と比較した結果、以下のことが明かになった。
1) Ashford Common浄水場と染屋浄水場とではTOC、Chl、Pheoの深度分布が異なることが判明した。いずれの抑留物質もAshford Common浄水場の方が量的に多く砂層内に侵入し抑留されていた。
2) 砂層内での抑留物質の減少率は、Ashford Common浄水場、染屋浄水場共にクロロフィルa>フェオフイチンa>全有機炭素>の順であった。このことから抑留物質に対する分解能が物質によって異なると考えられた。
3) 藻体の分解物質の侵入割合は、染屋浄水場よりもAshford Common浄水場の方が多かった。このことから緩速ろ過池流入水の水質とろ過継続日数の違いによって砂層内の懸濁物質の侵入度合が異なることが判明した。

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