栄養塩添加湖水中における尿素分解 Urea Decompotion during Phytoplankton Growth in Enriched Water from Lake Biwa

Decomposition rate of urea and assimilation rate of urea nitrogen by phytoplankton, after enrichment of nitrogen and phosphorus in surface water collected from eutrophic area of Lake Biwa, were investigated. The rate of urea carbon incorporation into the narticulate matter and urea decomposition (as sum of carbon incorporation rate and CO_2 liberation rate) corresponded to chlorophyll-a amount and hotosynthetic rate. This suggests that urea in water is decomnosed by phytoplankton associated with photosynthesis. A close relationship between the decompositon rate of urea carbon and the assimilation rate of urea nitrogen was observed. The decompositon of urea seems to be enuivalent to the utilization of urea nitrogen by phytoplankton.