Ammonium regeneration by microzooplankton in the Oslofjord |
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Authors: | E Paasche S Kristiansen |
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Institution: | (1) Department of Marine Biology and Limnology, University of Oslo, Blindern, P.O. Box 1069, Oslo 3, Norway |
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Abstract: | Concentrations of dissolved inorganic nitrogen compounds above the pycnocline in the Oslofjord are very low in the summer, with turnover times of the inorganic N pools of no more than a few hours. To investigate the possibility that continued phytoplankton growth in the summer depends on ammonium excretion by microzooplankton, rates of NH
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regeneration and assimilation were measured by a 15N isotope dilution method. Daytime regeneration rates at 0–2 m depth were 0–28% of the calculated assimilation rates at ambient NH
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concentrations. Regeneration was faster during a dinoflagellate bloom in August than in mixed diatom-dinoflagellate blooms in June and September. Most of the NH
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appeared to be produced by juvenile copepods, rotifers, tintinnids, and heterotrophic dinoflagellates in the size fraction 45–200 m. |
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