Carbon isotope ratio and photosynthetic activity of phytoplankton in the eutrophic Mikawa Bay,Japan |
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Authors: | Kazushi Takahashi Eitaro Wada Mitsuru Sakamoto |
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Institution: | (1) Water Research Institute, Nagoya University, Chikusa-ku, 464-01 Nagoya;(2) Laboratory of Biogeochemistry and Sociogeochemistry, Mitsubishi Kasei Institute of Life Sciences, Minamiooya 11, Machida, 194 Tokyo, Japan;(3) Present address: Center for Ecological Research, 4-1-23 Shimosakamoto, Ohtsu, 520-01 Shiga, Japan |
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Abstract: | Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural
carbon isotope ratio (δ
13C) and short-term carbon uptake rates (13C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates,
which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ
13C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction
(−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more
negativeδ
13C values (−22 to −18‰). Highδ
13C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the
increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the
nannoplankton fractions with higher POC values have relatively lowδ
13C values. |
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Keywords: | carbon isotope ratio photosynthesis phytoplankton |
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