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Short Term Nitrogen Dynamics in a Small Brazilian Wetland (Lago Infernao, Sao Paulo)
Clive Howard-Williams, F. de Esteves, J. E. Santos and M. T. Downes
Journal of Tropical Ecology
Vol. 5, No. 3 (Aug., 1989), pp. 323-335
Published by: Cambridge University Press
Stable URL: http://www.jstor.org/stable/2559435
Page Count: 13
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We have studied a number of related processes of the nitrogen cycle in a Brazilian floodplain lake to identify the major pools and pathways over a short time period. The study was centred on the littoral zone dominated by the floating plant Eichhornia azurea, which has a large epiphyte algal community of which heterocystous cyanobacteria were the major components. The water column was continuously undersaturated with oxygen although some elevated values (to 60% saturation) were recorded in the macrophyte beds in the afternoon. Marked diel temperature changes were documented. NH4-N dominated the dissolved N component in the water with maximal values (60 mg m-3) at lowest O2 concentrations early in the morning. Nitrogen fixation (acetylene reduction) of the epiphyte community showed marked diel changes with daily values of 5 mg N fixed m-2 day-1 (based on 3:1 C2H4:N2 ratio). Macrophyte NH4-N uptake rates (in situ incubations) were 93 mg N m-2 day-1. The activities of nitrifying bacteria could not be detected with the nitrapyrin block on dark CO2 fixation but denitrification (acetylene block technique) was recorded in the sediments when enhanced with NO-3. The major pathways of aquatic nitrogen involved macrophyte uptake and sediment release of NH4-N.
Journal of Tropical Ecology © 1989 Cambridge University Press