RIVERINE INPUT OF BIOAVAILABLE IRON SUPPORTING PHYTOPLANKTON GROWTH IN KESENNUMA BAY (JAPAN)

The effects of riverain iron and nutrient inputs on phytoplankton grow th in Kesennuma Bay were studied. The effects of iron and Fulvic acid- iron complex additions on phytoplankton growth were studied in iron-en riched and -limited culture experiments of coastal marine diatom Chaet oceros sp. (the dominant species inside and outside of the bay) using media prepared from bay and outer waters. Bay water is not iron-limite d. The addition of Fe(III) to bay water or autoclaved bay water gave n o increase in cell yield. However, when bay water was autoclaved after UV-irradiation, there was little growth. This suggests that the UV ir radiation destroyed organic compounds that affected iron bioavailabili ty. Outer water is iron-limited. The addition of Fe(III) to outer wate r increased cell yield and iron-enriched outer water prepared by autoc laving after adding fulvic acid-Fe increased also cell yield. When out er water after adding Fe(III) was autoclaved, there was little growth. This suggests that fulvic acid made the iron bioavailable. The rivera in inputs of organically bound iron, such as fulvic acid-Fe, and nutri ents probably play an important role for supporting phytoplankton grow th in the bay. (C) 1998 Elsevier Science Ltd. All rights reserved.