Uptake of dissolved nitrogen by phytoplankton in a eutrophic subtropical lake

Abstract

Uptake rates for ammonium, nitrate, urea and dinitrogen by phytoplankton in Lake Okeechobee ranged from 0.58 to 1.52 μmol l-1 h-1 among four representative stations during a short-term study period. Ammonium accounted for 53% of the uptake rates, followed by nitrate (19%), urea (16%) and dinitrogen (12%). Half-saturation constants for nitrogen (N) uptake ranged from 8.70 μmol l-1 for ammonium, 2.07 μmol l-1 for urea and 2.21 μmol l-1 for nitrate at South station. This study reveals spatially varying N uptake rates, particularly N fixation, within a large eutrophic lake.