ON THE WATER POLLUTION OF THE SMALLER RIVERS IN AICHI PREFECTURE

Abstract

Examplifing the smaller river basins in Aichi Prefecture where many typical inland industries are formed, the author investigated the relationships between the chemical composition of river water and the annual production of industries as well as the resi-dential population per unit area (1km2) in the catchment area upstream from the observation station. The results are briefly summarized as follows: (1) Close relationships were obtained between the density of industrial production (annual production of industries per unit area in ten million yen/km2, year) and the concentration of dissolved matters in river waters. That is, with rise of the density of industrial production, the COD value and the concentration of NH4-N, PO4-P, SO'' and Fe''+'' increase progressively, on the other hand, the saturation level of DO de-creases gradually. Correlation was not obtained between the density of industrial production and the concentration of Cl', whereas a significant relationship was found between the population density of residents and the concentration of Cl' (See Figs. 3a_??_3g and 4a). (2) There were different tendencies in the increases of the concentration of a certain dissolved matter. I t was found that the difference in the increasing tendencies depended on the difference of the types of industries dominating in river basins (See Figs. 5a and 5b). (3) Examining the relationship between the density of industrial production and the COD value for the type of industries dominating in river basins, the density of industrial production corresponding to 10mg/l of COD are shown as below: _??_ (4) The density of industrial production corresponding to 50% of DO saturation was nearly equal to the value mentioned in (3). (5) As to the relationship between the population density of residents and the concentration of dissolved matters in river waters, correlations were not found for the basins where COD load by industrial waste waters is four or five times larger than that of domestic discharges. However, in the case of treating all rivers it was observed that the concentration of dissolved matters (exclusive of DO) began to increase when the population density of residents became larger than 100_??_200 persons per km2. (6) Examining the relationship between the population density of residents and the COD value in river basins where COD loads by industrial waste waters were relatively small, the population density of residents corresponding to 5mg/l of the lowest COD value was within the range of 2, 000_??_3, 000 persons per km2 (See Fig. 4c). Therefore, for urbanized regions where industrialization was not remarkable, it would be safe to consider that the population density of residents corresponding to 10mg/l of the lowest COD value will be the order of 10, 000 persons per km2 in Aichi Prefecture. (7) Considering the relationship between the COD value in river waters and the sum of daily COD load by industrial waste waters and that by domestic sewage per unit area, COD loads corresponding to 10mg/l of the lowest COD was around 100kg/ km2. day (See Fig. 6).