The Transition of Water Qualities in The Lake Togo with Establishment of Sewage Treatment Systems and Changes of Land Use Type

Abstract

Sewage treatment systems have been established for a countermeasure of eutrophication of the Lake Togo, located at the middle part of Tottori prefecture, and improvement of the living environment of inhabitants in this region. All of these systems has started the operation in 1995.
In this report, the transition of water qualities in the Lake Togo from 1971 to 1993 was analyzed. Moreover pollutant loads in this region were calculated by using the unit loading factors.
In this study, the following points are cleared :
(1) The water qualities tend to improve slightly. The main reason is because a lot of pollutant loads was transported to the regional sewage treatment system in the other region and treated. (2) The amount of loads, decreased by the rural sewage treatment systems in this region, is almost same as that of nonpoint source pollutant loads increased by changes of land utilities. (3) It is possible that the effect of establishment of the systems will be offset by increasing the nonpoint source pollutant loads.