Comparison of nutritional environment of closed coastal seas in western Kyushu

Abstract

Bays in western Kyushu face to open sea and have their own characteristics. The author compared data on dissolved inorganic nitrogen (DIN) and chlorophyll a among three typical closed bays, Fukuoka Bay surrounded by a big city, Imari Bay holding large mariculture sites, and Kagoshima Bay divided into two parts, viz. extremely closed inner part and mid-closed outer part. The values from Fukuoka Bay indicated particular relations that is high chlorophyll - low DIN in summer, and low chlorophyll - high DIN in winter season. Values from Imari Bay distributed in wide range of the relations. In Kagoshima Bay, DIN values were not so different between two parts, however chlorophyll values were distinctly higher in the inner part. The composition of nitrogen as divided into three parts, DIN, DON, and PON in seawater varied by the seasons. He also compared these results with the data collected from various sea areas in the world, and got some suggestions that coastal water provides over production against equivalent DIN values, which is probably caused by some organic enrichment accompanied with human activities, and that characteristics of each bay seem to be consistently influenced by their social backgrounds and topographical features.