Temporal and spatial variability in nitrogen uptake kinetics during harmful dinoflagellate blooms in the East China Sea

Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO3−), ammonium (NH4+), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using 15N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO3− (Vmax 0.044 h−1; Ks 60.8 μM-N) was an important N source before it was depleted. NH4+ (Vmax 0.049 h−1; Ks 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom (Vmax 0.020 h−1; Ks 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom (Vmax 0.025 h−1; Ks 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations.