Assessment of Neutralization of Acidic Water using Attached Diatom Assemblage
In the River Nabetani, Ishikawa Prefecture
1997 Volume 33 Issue 2 Pages 65-80
Details
1997 Volume 33 Issue 2 Pages 65-80
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 SO42- 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.
