Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer |
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| Authors: | Akihiro Shiomoto Katsuyuki Sasaki Toru Shimoda Satsuki Matsumura |
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| Institution: | (1) National Research Institute of Far Seas Fisheries 7-1, Orido 5 chome, Shimizu-shi, 424 Shizuoka, Japan;(2) National Research Institute of Fisheries Science, Fukuura 2 chome, Kanazawa-ku, Yokohama-shi, 236 Kanagawa, Japan |
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| Abstract: | The maximum uptake rate ( max) and affinity constant (K
s) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average max/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average max/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the max/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of  new production to total production was estimated by maxmax–No3/(max–NO3+max–NH4)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04). |
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