Diurnal pattern in nitrous oxide emissions from a sewage-enriched river

Abstract Estimates of N 2 O emission based on limit measurements could be highly inaccurate because of considerable diurnal variations in N 2 O flux due to rapid transformation of nutrients and diel change of dissolved oxygen (DO). In the present study, the N 2 O fluxes, dissolved N 2 O concentrations, and the controlling variables were measured hourly for 3 d and night cycles at five sites on a typically sewage-enriched river in the Taihu region. There were no significant diurnal patterns in N 2 O emissions and dissolved N 2 O saturation, with respective mean value of 56.1 μg N 2 O–N m −2  h −1 (range = 41.1 μg N 2 O–N m −2  h −1 to 87.7 μg N 2 O–N m −2  h −1 ) and 813% (range = 597–1372%), though distinct diurnal patterns were observed in DO concentration and river chemistry. However, the mean N 2 O emissions and the mean dissolved N 2 O saturation during the day (61.7 μg N m −2  h −1 for N 2 O fluxes and 0.52 μg N L −1 for dissolved N 2 O saturation) were significantly higher than those during the night (50.1 μg N m −2  h −1 for N 2 O fluxes and 0.44 μg N L −1 for dissolved N 2 O saturation). Factors controlling the N 2 O flux were pH, DO, NH 4 + , SO 4 2 - , air temperature, and water temperature. Sampling at 19:00 h could well represent the daily average N 2 O flux at the studied river.