Limiting Nutrients of Algal Growth in Ushiku Marsh

Abstract

Determination of water quality, Algal Growth Potential (AGP) and limiting nutrients in Ushiku Marsh and related rivers ; lnari, Higashiyata, and Nishiyata were carried out using Microcystis flos-aquae, M. aeruginosa, and Selenastrum capricornutum in order to clarify the difference between Ushiku Marsh where water bloom occurs very rare and Lake Kasumigaura where high density of water bloom occurs every year. T- P concentration of Ushiku Marsh was the same level of Lake Kasumigaura. However, T- N content in Ushiku Marsh was significantly higher than in Lake Kasumigaura. AGPs of the filtrated samples in Ushiku Marsh were very lower values than those of autoclaved ones. Autoclaving was done at 121°C and for 15 min. The limiting nutrients in Ushiku Marsh and related rivers were P and EDTA through the year for M. flos- aquae and M. aeruginosa. However, Lake Kasumigaura water did not need the EDTA for the growth of M. flos- aquae and M. aeruginosa in summer season. Lake Kasumigaura contained more chelate compunds which were growthstimulating than Ushiku Marsh. This may be one of the important reasons why the water bloom did not occur in Ushiku Marsh.