Evaluation of Water Pureness by Horizontal Transparency

Abstract

People usually evaluate the amenity of water environment by transparence to look at water. Water transparence is measured by transparency or transparency by cylinder test. However, these methods have some defects such as difficulties in measuring at shallow and clean waters, because transparency is limited by water depth and transparency by cylinder test is limited by length of a cylinder. Moreover, the lack of objectivity is pointed out, since transparency measuring is due to personal sensitivity. To conquer these problems, we designed a measuring method of horizontal transparency, and developed a measuring equipment by using an eye-test chart and a waterproof camera. We applied this method to water quality investigation of Matsushima Bay, Miyagi prefecture, and studied the characteristics of horizontal transparency comparing with transparency, transparency by cylinder test and so on. The results obtained were as follows; (1)Horizontal transparevcy has superior objectivity, because evaluation by plural number of people diminish personal errors. (2)Horizontal transparency is possible to express water transparence quantitatively without any limits, though conventional methods cannot apply to relatively clear and shallow waters. (3)Horizontal transparency has a very good correlation between not only transparency but also turbidity and suspended solids that are mainly affect to transparency. (4)The sense of visitors and fishermen about the water quality of Matsuhima Bay can be represented by horizontal transparency.