Nutrient regeneration at bottom after a massive spring bloom in a subarctic coastal environment,Funka Bay,Japan |
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| Authors: | Isao Kudo Takeshi Yoshimura Choon-Weng Lee Mitsuru Yanada Yoshiaki Maita |
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| Institution: | (1) Graduate School of Environmental Sciences, Hokkaido University, Sapporo 060-0813, Japan;(2) Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Japan;(3) Present address: Central Research Institute of Electric Power Industry, Abiko 270-1194, Japan;(4) Present address: Institute of Biological Sciences, University of Malaya, Kuala Lumpur, 50603, Malaysia |
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| Abstract: | Nutrient regeneration and oxygen consumption after a spring bloom in Funka Bay were studied on monthly survey cruises from
February to November 1998 and from March to December 1999. A high concentration of ammonium (more than 4 μmol l−1) was observed near the bottom (80–90 m) after April. Phosphate and silicate gradually accumulated and dissolved oxygen decreased
in the same layer. Salinity near the bottom did not change until summer, leading to the presumption that the system in this
layer is semi-closed, so regenerated nutrients were preserved until September. Nitrification due to the oxidation of ammonium
to nitrate was observed after June. Nitrite, an intermediate product, was detected at 4–7 μmol L−1 in June and July 1999. Assuming that decomposition is a first order reaction, the rate constant for decomposition of organic
nitrogen was determined to be 0.014 and 0.008 d−1 in 1998 and 1999, respectively. The ammonium oxidation rate increased rapidly when the ambient ammonium concentration exceeded
5 μmol L−1. We also performed a budget calculation for the regeneration process. The total amount of N regenerated in the whole water
column was 287.4 mmol N m−2 in 4 months, which is equal to 22.8 gC m−2, assuming the Redfield C to N ratio. This is 34% of the primary production during the spring bloom and is comparable to the
export production of 25 gC m−2 measured by a sediment trap at 60 m (Miyake et al., 1998). |
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| Keywords: | Remineralization nitrification oxygen consumption stoichiometry Funka Bay |
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