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Title: The Rate of Utilization of Urea, Ammonium, and Nitrate by Natural Populations of Marine Phytoplankton in a Eutrophic Environment 
Author: Harvey, Wayne A.; Caperon, John
Date: 1976-10
Publisher: University of Hawaii Press
Citation: Harvey WA, Caperon J. 1976. The rate of utilization of urea, ammonium, and nitrate by natural populations of marine phytoplankton in a eutrophic environment. Pac Sci 30(4): 329-340.
Abstract: The utilization rates of ammonium, nitrate ion, and urea were
determined for 18 samples of water from the southern sector of Kaneohe Bay,
Oahu, Hawaiian Islands. The samples were collected from 14 May through
23 August 1974. The mean daytime uptake rates for this period were 0.040,0.033,
and 0.013 hr-1 for ammonium, urea, and nitrate, respectively. Dark uptake rates
for ammonium, urea, and nitrate from two samples were approximately 50, 30, and
0 percent of the daytime uptake rates. The uptake data indicate that the phytoplankton
growth rate is not limited by the availability of fixed nitrogen. This
conclusion is supported by the data on the carbon: nitrogen ratio of the phytoplankton,
which show that the plants were more heavily enriched in nitrogen than
they had been during previous studies of this part of the bay. Mass balance calculations
show that the supply of fixed nitrogen to the nutrient pool from stream
runoff and municipal waste discharge was only 3.5 percent of the total uptake
rate by phytoplankton, and, therefore, suggest that the in situ regeneration of
nutrients is far larger than the new nutrients added to the bay from these sources.
ISSN: 0030-8870

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