Abstract
The significance of epilithic microorganisms (algae and Sphaerotilus natans) in estimating the degree of organic pollution in streams are examined on the basis of the results of investigations in Toyama Prefecture from 1979 to 1985. Relationships between carbon content of epilithic microorganisms and water quality indexes (BOD, TIN and PO4-P) show that these indexes influence the quantity of epilithic microorganisms. Species of the epilithic microorganisms examined can be classified into five types (Types IV) on the basis of the ranges of concentrations of BOD, TIN and PO4-P in the stations where they are found. Concentrations of BOD, TIN and PO4-P in streams can be estimated from the types of the epilithic microorganisms. Fourteen cases of such estimation of water quality are shown. Observed concentrations of BOD, TIN and PO4-P are almost all within the ranges of their estimated concentrations, except one case of BOD.
It's shown that the epilithic microorganisms have the following advantage and disadvantage as indicators of water quality. The BOD range of 1.0 mg·l-1 and over can be effectively distinguished with the species of Types IV and V. On the contrary, the ranges of estimated concentrations of TIN and PO4-P are rather wide, and the estimation of lower range of BOD concentration such as below 1.0 mg·l-1 is impossible.
