抄録
Vertical distributions of urea and DON were studied in the northern area of Hiroshima Bay from April to December 1981. It was found that the concentration of urea was remarkedly low in bloom season. On the other hand, relatively high concentration of urea was observed in sea waters above 3m and under 13m from the latter half of July to September. The concentration of urea in the rivers inclined to get larger with an approach to the river mouth. This suggests that domestic and industrial waste waters containing urea inflow into the rivers. The ratios of urea to DON ranged from 2 to 30% (average 15.3%) and fairly high correlation coefficient between them was found.
From the biodegradation experiment of filtered sea water, a part of urea was certified to be produced from the decomposition of DON and its apparent biodegradation rate constant at 15°C was 0.166 day-1 Urea was observed to be similarly taken into the cells with NH4+and N03- in the culture of Skeletonema costatum. Additive effect of urea on the growth of Skeletonema costatum and Heterosigma sp. were relatively large in the range of 2-10 μg-at N/l.
