有明海湾奥部におけるノリ養殖の生産状況と窒素の収支

摘要

Ariake Bay has a surface area of 1,700 km' and an average water depth of approximately 20 m. The production of dried nori (Porphyra spp.) is a major industry in the inner area of the Ariake Bay. The total annual production in Saga and Fukuoka prefecture is about 3 billion sheets. Recently, the nori production in the Ariake Bay has been comparatively stable due to the high level of dissolved inorganic nitrogen (DIN) concentration in the cultivation period. The loads of nutrients from rivers and the fertilization of nori cultivation into the Ariake Bay are estimated to be 6,770 and 235 ton/year for DIN, respectively. Furthermore, nutrients are supplied with the nitrogenous water from a sewage treatment plant and the drain from dams. On the other hand, nitrogen uptake by dried nori, fish, and bivalve are 711, 46, and 30 ton/year, respectively. Accordingly, the stable production of dried nori and the increase in the catch of fish and bivalve are very important for preservation of the environment in the Ariake Bay.