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Denitrification Associated with Stream Periphyton: Chamber Estimates from Undisrupted Communities¹

ABSTRACT

Undisrupted periphyton communities from a N-rich (NO₃^– = 63 µmol L^–1) and pristine (NO₃^– = 2.9 µmol L^–1) stream were assayed for denitrifying activity (acetylene-blockage technique) in 40-L chambers incubated at in situ temperature and nutrient concentrations. Nitrous oxide formation associated with periphyton from the N-rich stream was immediate and linear (52.1 µmol N₂O m^–2 h^–1) in the dark, anaerobic chamber (50 kPa C₂H₂). In the corresponding light, aerobic chamber (50 kPa C₂H₂), N₂O production was inhibited by 82% (9.3 µmol N₂O m^–2 h^–1). Nitrous oxide formation was not associated with periphyton from the pristine stream incubated in situ, either with or without NO^3– amendment.

Denitrification estimates made with undisrupted periphyton communities at in situ temperature and nutrient concentrations (40-L chambers) were less variable than estimates made with periphyton "scrapings" in small flasks (room temperature). The calculated diel periphyton-associated denitrification rate based on a 14-h light-10-h dark day was 651 µmol N₂O m^–2 d^–1. The data suggest denitrification within periphyton mats may contribute toward removal of NO^3– from N-rich fluvial environments.

Key Words: acetylene inhibition • nitrate removal • fluvial environments

¹ This research was supported by the U.S. Geological Survey, Menlo Park, CA 94025.

² Hydrologist, hydrologist, and microbiologist, U.S. Geological Survey, Water Resources Division, Menlo Park, CA 94025.

Received for publication October 6, 1983.

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