大阪湾の貧酸素底層水における無機栄養塩濃度について

概要

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In summer, oxygen-deficient layer is being formed extensively in the waters of the lower strata of Osaka Bay, from the interior to the east part of the bay. A large amount of inorganic nutrients are found in such lower waters. Based on the accumulated dada obtained from 1972 to 1982 by us, a remarkable regularity was observed as to the concentrations of inorganic nutrients and dissolved oxgen (DO) in the water. Plots of dissolved inorganic phosphorus (DIP) versus apparent oxygen utilization (AOU) are approximately on tow straight lines with an intersection at AOU ca. 2-4ml/l, whereas dissolved in organic nitrogen (DIN) is plotted versus AOU on a single straight line. However the abundance ratio of DIN in oxidized forms(NO2-N+NO8-N) decreases with the increase of AOU in the lower waters with AOU above ca.4ml/l. It mya be concluded that the generation of DIP and DIN in the decomposition process of organic materials accompanies the DO consumption at a definite rate in oxic waters. In the oxygendeficient lower waters, DIP increases in its concentraation by the liberation from the lower sediments, and DIN remains in the reduced form(NH4-N)by the suppressed oxidation process.