Nitrate reduction in sediments of lowland tropical streams draining swamp forest in Costa Rica: An ecosystem perspective |
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Authors: | John H Duff Catherine M Pringle Frank J Triska |
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Institution: | (1) U.S. Geological Survey, Water Resources Division, Mail Stop 496, 345 Middlefield Road, Menlo Park, California 94025-3591, USA;(2) Institute of Ecology, University of Georgia, 308 Biological Sciences Building, Athens, Georgia 30602-2607, USA |
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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 NO3
–. Under optimal conditions, denitrification enzyme activity averaged 15 nmoles cm–3 sediment h–1. Areal NO3
– 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 NO3
– for NO3
– 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 NO3
– reduction potential, swamp forest stream sediments appear to be a source of inorganic N to downstream communities. |
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Keywords: | NO3
– reduction denitrification nitrification swamp forest lowland rain forest tropical streams Costa Rica |
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