Nitrate reduction in sediments of a lowland tropical streams draining swamp forest in Costa Rica: An ecosystem perspective.
Abstract: Nitrate reduction and denitrification were measured in swamp forest
streams draining lowland rain forest on Costa Rica's Atlantic slope
foothills using the C2H2-block assay and sediment-water nutrient
fluxes. Denitrification assays using the C2H2-block technique indicated
that the full suite of denitrifying enzymes were present in the
sediment but that only a small fraction of the functional activity
could be expressed without adding NO;. Under optimal conditions,
denitrification enzyme activity averaged 15 nmoles cm(-3) sediment
h(-1). Areal NO, reduction rates measured from NO3- loss in the
overlying water of sediment-water flux chambers ranged from 65 to 470
umoles m(-2) h(-1). Oxygen loss rates accompanying NO3- depletion
averaged 750 umoles m(-2) h(-1). Corrected for denitrification of NO3-
oxidized from NH4+ in the sediment, gross NO3- reduction rates increase
by 130 umoles m(-2) h(-1), indicating nitrification may be the
predominant source of NO; for NO, reduction in swamp forest stream
sediments. Under field conditions approximately 80% of the increase in
inorganic N mass along a 1250-m reach of the Salto River was in the
form of NO3- with the balance NH4+. Scrutiny of potential inorganic N
sources suggested that mineralized N released from the streambed was a
major source of the inorganic N increase. Despite significant NO,
reduction potential, swamp forest stream sediments appear to be a
source of inorganic N to downstream communities.
Duff, J. H., C. M. Pringle and F. J. Triska. 1996. Nitrate reduction in sediments of a lowland tropical streams draining swamp forest in Costa Rica: An ecosystem perspective. Biogeochemistry 33: 179-196.
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