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Seasonal variations in uptake and in situ regeneration of nitrogen in mangrove waters

DRS at CSIR-National Institute of Oceanography

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Title Seasonal variations in uptake and in situ regeneration of nitrogen in mangrove waters
 
Creator Dham, V.V.
Heredia, A.M.
Wafar, S.
Wafar, M.V.M.
 
Subject mangrove swamps
phytoplankton
nitrogen
seasonal variations
nutrients (minerals)
food chains
 
Description Seasonal changes of uptake of nitrogenous nutrients (NH sub(4) sup(+), NO sub(3) sup(-), NO sub(2) sup(-), and urea) and regeneration (NH sub(4) sup(+) and NO sub(2) sup(-) production) in the plankton fraction of a mangrove ecosystem on the west coast of India were investigated. Nitrate was the major fraction of assimilable N (72%), followed by NH sub(4) sup(+) (16%), NO sub(2) sup(-) (6%), and urea (6%). Changes of nutrient concentrations followed clear seasonal cycles and were mainly regulated by in situ biological processes. The plankton took up NO sub(3) sup(-) and NH sub(4) sup(+) in more or less equal proportions (39 and 44% respectively), followed by urea (11%) and NO sub(2) sup(-) (6%). Seasonal patterns of uptake were distinct, with a dominance of NO sub(3) sup(-) and NO sub(2) sup(-) uptake in the postmonsoon followed by a dominance of NH sub(4) sup(+) and urea uptake in the premonsoon. The high and prolonged use of NO sub(3) sup(-) at the beginning of the productive season was due to a strong allochthonous supply of NO sub(3) sup(-), dominance of microplankton, and low NH sub(4) sup(+) regeneration rates. Heterotrophs may take up all four nutrients and could account for half of the annual total N uptake. Ammonium and NO sub(2) sup(-) regeneration rates were among the highest known from nearshore waters and showed clear seasonal patterns. Production and use of NH sub(4) sup(+) were closely coupled. Nitrite production rates were related to NH sub(4) sup(+) production rates in a rectangular-hyperbolic fit. Nitrogen balance analyses showed that proximity to mangrove vegetation enhanced the flux rates, noninclusion of nitrification may lead to an overestimation of new production by 30%, and regeneration in the plankton fraction provided about 40% more N than was assimilated.
 
Date 2008-08-09T11:37:01Z
2008-08-09T11:37:01Z
2002
 
Type Journal Article
 
Identifier Limnology and Oceanography, Vol. 47(1); 241-254p.
http://drs.nio.org/drs/handle/2264/1424
 
Language en
 
Rights American Society of Limnology and Oceanography, Inc.
 
Publisher American Society of Limnology and Oceanography