STUDIES ON VITAMIN B₁₂ IN NATURAL WATER-VII

RELATION BETWEEN THE FERTILITY AND THE VITAMIN B₁₂ CONTENT OF LAKES

Abstract

There has been adopted a view that lakes and marsches can be classified according to their contents of nutritive salts into eutrophic, mesotrophic and oligotrophic ones. In order to find how the trophic level or fertility of these land waters is connected with vitamin B₁₂ content of their water, the authors carried out the measurement of the latter, selecting as an object of research 10 members of lakes and marsches in Japan. As seen from the data obtained in the present research (see Table 1), the level of vitamin B₁₂ content found as several mγ/l to about 10 mγ/l for typical eutrophic lakes as, for example, Lake Kasumigaura and Lake Suwa and that estimated as only 1 mγ/l and below for typical oligotrophic lakes as, for example, Lake Ikeda, Lake Biwa, Lake Towada and Lake Toya are in striking contrast to each other, that of Pond Unagiike, a typical mesotrophic lake in Kagoshima Prefecture being situated in the middle of the space between the former two.
It may hence be given a conclusion that as regards the trophic type of lakes and marches there exists likely an intimate relation between the content level of nutritive salts and that of vitamin B₁₂.