Phosphorus and nitrogen cyclings in the pelagic system of hiroshima bay: Results of numerical model simulation |
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| Authors: | Jutarat Kittiwanich Tamiji Yamamoto Toshiya Hashimoto Keiko Tsuji Osamu Kawaguchi |
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| Institution: | (1) Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima 739-8528, Japan |
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| Abstract: | A numerical ecosystem model expressing both phosphorus and nitrogen cyclings in the pelagic system of Hiroshima Bay, Japan,
was developed in order to investigate the seasonal variations of these elements and their annual budgets. Based on the geophysical
and chemical structures of the bay, Hiroshima Bay was divided into northern and southern boxes, themselves divided into two
layers of an upper 5 m and a lower layer according to the stratification of the water column. The model consists of equations
representing all relevant physical and biological processes. The results revealed that the internal regeneration of materials
was an important source of bioavailable nutrients for phytoplankton growth in the water column. The incorporation of phytoplankton
aggregation improved the accuracy of the outputs in comparison to the observed data, especially during the stratified summer
season. The results also indicated that phosphorus limitation of phytoplankton growth occurs in the upper layer during summer
while light limitation occurs in the lower layer. In addition, physical processes such as diffusion and advection were also
important as they ensured that most of regenerated nutrients in the lower layer were transported to the upper layer. Thus,
these processes might support the high primary production and the production of oysters that are extensively cultured in this
bay. Considering the informative results obtained, the model used in this study provides a sound basis and tool to describe
the dynamics of phosphorus and nitrogen cyclings in Hiroshima Bay. |
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| Keywords: | Hiroshima Bay phosphorus nitrogen pelagic system ecosystem model numerical simulation |
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