Undisrupted periphyton communities from a N-rich (NO3- = 63 ??mol L-1) and pristine (NO3- = 2.9 ??mol 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 ??mol 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 ??mol N2O m-2 h-1). Nitrous oxide formation was not associated with periphyton from the pristine stream incubated in situ, either with or without NO3- 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 ??mol N2O m-2 d-1. The data suggest denitrification within periphyton mats may contribute toward removal of NO3- from N-rich fluvial environments.
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Denitrification associated with stream periphyton: Chamber estimates from undisrupted communities