|Urea as a nitrogen source for the phytoplankton in the Oslofjord|
Kristiansen, S. (1983). Urea as a nitrogen source for the phytoplankton in the Oslofjord. Mar. Biol. (Berl.) 74(1): 17-24
In: Marine Biology. Springer: Heidelberg; Berlin. ISSN 0025-3162, more
Fjords; Kinetics; Phytoplankton; Seasonality; Temperature effects; Urea; Marine
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Ambient concentrations of urea in the inner Oslofjord, Norway, showed a pronounced yearly cycle in 1980, with values in the range 0.1 to 10.0 mu g-at N l-1: this cycle resembled that of ammonia although urea concentrations were usually lower. The uptake of urea by phytoplankton was investigated using 15N. Urea was usually a less important N source than NH+4, and accounted for 0 to 53% (mean 19%) of summed NH+4 + NO3- urea uptake reates from April to October. Absolute as well as relative (specific) uptake rates of urea were higher in the summer (June-August) than at other times. Uptake of urea was inhibited by NH+4 concentrations higher than 1 to 2 mu g- at N l-1. The summed NH+4 + NO3- urea uptake rate was exponentially related to temperature.