A Method for Estimating Uptake and Production Rates for Urea in Seawater using [ 14 C] Urea and [ 15 N] Urea

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Hansell, Dennis A., Goering, John J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1989
• Subjects: Bering Sea
• Online Access: http://dx.doi.org/10.1139/f89-027; http://www.nrcresearchpress.com/doi/pdf/10.1139/f89-027

Improved estimates of the rates of urea production and uptake by natural populations of phytoplankton were made after determining the change in 15 N-atom% enrichment of urea during incubations. A [ 14 C] urea method is described by which the change in enrichment is measured. Estimates of uptake rates are increased (relative to uptake rates determined without correction for isotope dilution) by up to 83% using a 15 N accumulation model and by >210% using a 15 N disappearance model. A discrepancy exists between [ 15 N] urea removed from the aqueous phase and 15 N accumulated in the particulate phase at stations occupied in the northeastern Bering Sea. The ability to find in the particulate fraction the 15 N removed from solution as [ 15 N] urea was improved by 72% following removal of the >20-μm particulate fraction. This corresponded to only a 4% reduction in the concentration of chlorophyll a and a 37% reduction in the concentration of particulate N. Removal of microzooplankton may have improved the efficiency of urea-N retention by phytoplankton.