UREA DECOMPOSITION ASSOCIATED WITH THE ACTIVITY OF MICROORGANISMS IN SURFACE WATERS OF THE NORTH HAN RIVER, KOREA

The rate of urea decomposition in relation to activities of microorgan isms was measured in surface water of the North Han River, Korea. The decomposition rate of urea was 0.2 to 3.1 mu mol urea m(-1) hr(-1) in the light. Much higher decomposition rates were observed in the pollut ed eutrophic waters, which were affected by sewage from a large city. The urea decomposition rates in the upper reaches of the river were ob viously higher in the light condition than in the dark, while the poll uted waters showed no such difference. Whereas only a negligible level in the phase of carbon incorporation was observed in the upper reache s, a significant value was obtained in the polluted areas. The present results indicate that in unpolluted waters the decomposition of urea occurred in connection with the photosynthesis of phytoplankton rather than bacteria activity. In polluted eutrophic waters, on the other ha nd, urea seemed to decompose under the competitive action of bacteria and phytoplankton.