| Abstract: | The vertical profiles of chemical and biological parameters, including urea concentration, have been measured periodically since February of 1977 at a central station in Lake Suwa, which is one of the typical eutrophic lakes in Japan. The seasonal trend in the standing stock of urea in the central water column, together with the ratio of urea versus total inorganic nitrogen in the euphotic zone from 12 March, 1977 to 25 July, 1978, are presented. The possible importance of bacterial decomposition of dead phytoplankton as a urea source in natural waters is demonstrated by this study. At times, a highly significant correlation between the vertical profile of urea and vertical distributions of other chemical and biological parameters which were also measured was found. An apparent in situ utilization of urea by phytoplankton is suggested on the basis of vertical profiles of urea and other chemical and biological parameters. |
