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★ [ACG33-01] Iron and spring water which have been ignored in material cycles in coastal marine ecosystems
Keywords:nutrient, material cycle, iron, spring
In enclosed coastal seas of Japan, the number of red tide occurrence has been decreased and the transparency has also significantly been increased by reduction measures of material loads from land. There are several areas in which the growth of fish and other organisms is depressed by nutrient depletion, which is called "oligotrophication".
Unexpectedly, the anoxic water mass is still formed in the bottom layer of coastal areas whereas the material loads was reduced. This evidenced that the anoxic water mass may be formed not only by decomposition of organic matter but also by chemical oxidation of hydrogen sulfide. This also suggests that depletion of iron which is an essential element for the growth of algae.
The author recently determined the concentration of dissolved iron from the upper area of the Ohta River which flowing into Hiroshima Bay to lower river and seawater of the bay. Iron and nutrient concentrations in a spring in the bay were also investigated. The author hopes the presentation would be a hook to promote material cycle study of coastal seas.