Abstract
Diel variations in urea decomposing activity in the euphotic zone of brackish Lake Nakaumi were measured under fixed light intensity. The decomposition rate of urea was 17 to 44 μ mol urea m−3 h−1 in the light and 10 to 27 μ mol urea m−3 h−1 in the dark. Higher decomposition rates were obtained in the upper euphotic zone. A clear diel periodicity in the urea decomposition rate was observed, with high rates from 1200 to 1600 and low rates from 0000 to 0400. Chlorophyll a specific decomposing activity ranged from 12 to 21 μg urea C mg chl.a −1 h−1 in the light and 7 to 13 μg urea C mg chl.a −1 h−1 in the dark. In the light, high values were obtained from 1600 to 2000 and low values from 0400 to 0800. The diel change in specific decomposing activity exhibited a similar pattern to that of the photosynthetic assimilation number, following the diel change in photosynthetic activity.
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Received: March 10, 1999 / Accepted: October 22, 1999
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Mitamura, O., Ishida, N., Seike, Y. et al. Diel variation in urea decomposing activity in the euphotic zone of brackish Lake Nakaumi. Limnology 1, 151–157 (2000). https://doi.org/10.1007/s102010070001
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DOI: https://doi.org/10.1007/s102010070001