Denitrification associated with stream periphyton: Chamber estimates from undisrupted communities

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 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 µmol N₂O m⁻² d⁻¹. The data suggest denitrification within periphyton mats may contribute toward removal of NO³⁻ from N‐rich fluvial environments.