Nitrogen metabolism in the brackish lake nakanoumi japan i. uptake rate of inorganic nitrogen by phytoplankton
Seike, Y.; Kondo, K.; Date, Y.; Ishida, Y.
Japanese Journal of Limnology 47(2): 121-132
The uptake rates of ammonium and nitrate by the natural phytoplankton community in the shallow brackish lake Nakanoumi were measured thirteen times from August 1983 to July 1984 using the 15N tracer technique. Ammonium was uptaken in preference to nitrate, and nitrate use began when ammonium was depleted to about 3 .mu.g N .cntdot. liter-1. The result of the mutliple regression analysis implied that the uptake of ammonium was modified primarily by water temperature, phytoplankton standing stock (POC concentration) and ambient concentration of ammonium. Nitrogen appears to be the most important limiting element for the phytoplankton growth in the euphotic layer at the central part of Lake Nakanoumi from May to December, because the halocline acts as an effective barrier for the vertical transport of enriched nitrogen nutrient in the overlying water. The seasonal pattern of nitrate concentration in the euphotic layer at the central part of Lake Nakanoumi is also discussed relative to nitrate uptake rate by the phytoplankton standing stocks.