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Nitrogenous nutrients and primary production in a tropical oceanic environment

DRS at CSIR-National Institute of Oceanography

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Title Nitrogenous nutrients and primary production in a tropical oceanic environment
 
Creator Wafar, M.V.M.
Wafar, S.
Devassy, V.P.
 
Subject Aquatic Ecology, Productivity
euphotic zone
nitrogen
urea
zooplankton
phytoplankton
marine environment
primary production
nutrients (mineral)
nitrogen compounds
ISW, Laccadive Sea
 
Description Measurements of the concentrations of nitrogenous nutrients and primary production were made at 10 stations along 8 degrees N and 10 degrees N in the tropical oceanic Lakshadweep waters Inorganic nitrogen (NO3, NO2 and NH4) accounted for less than 10%, and dissolved organic nitrogen (DON) for more than 90%, of the total dissolved N in the euphotic zone Urea formed a nearly constant fraction of total dissolved N (17-18%) and DON (19-20%) Addition of NO3, NH4 and urea as N source stimulated carbon fixation at all stations and at all depths This, together with the low ambient concentrations of inorganic nitrogen compounds, demonstrates that the phytoplankton in these waters are nitrogen limited Nitrate flux into the euphotic zone, computed from the vertical eddy diffusion coefficient and NO3 gradient data, showed that the production associated with NO3 assimilation varied from 11 to 60% (average 37%) of the observed primary production Zooplankton regenerated NH4 at an average rate of 0.59 mu g-at N (mg dry wt)-1d-1 Assimilation of this quantity of NH4 would account for 9-50%(average 23%) of the measured primary production Stimulation of carbon fixation on addition of urea was, on an average, as much as with either NO3 or NH4 addition, demonstrating a potential for urea uptake by phytoplankton in these waters Zooplankton regenerated urea at an average rate of 0.32 mu g-at N (mg dry wt)-1d-1, providing nitrogen for 5-27% (average 13%) of the primary production Excluding urea, the rest of the DON, though abundant, does not appear to be directly available for phytoplankton assimilation
 
Date 1995-06-13T10:01:21Z
2017-09-29T13:48:20Z
1995-06-13T10:01:21Z
2017-09-29T13:48:20Z
1986
 
Type Journal Article
 
Identifier Bulletin of Marine Science, vol.38; 1986; 273-284
0007-4977
http://drs.nio.org/drs/handle/2264/6220
 
Language en
 
Relation B Mar Sci
SCI
 
Publisher Rosenstiel School of Marine and Atmospheric Science of the University of Miami