N2O Fluxes and Rates of Nitrification and Denitrification at the Sediment–Water Interface in Taihu Lake, China

Because of global concerns regarding pollution and eutrophication in fresh water, China’s Taihu Lake has gained attention both for these issues and as a source of nitrous oxide (N2O) emissions. In this study, we investigated N2O fluxes and nitrification and denitrification rates at the sediment–water interface and analyzed monthly the relationships between these processes in different areas of Taihu Lake over a one-year period. Annual maximum nitrification and denitrification rate and N2O flux were observed during June in an algae-dominated area of the lake and measured 17.80, 235.51, and 31.49 µmol N m−2 h−1, respectively. The nitrification rate ranged from 0 to 1.18 µmol N m−2 h−1 at other sampling sites, with less variation. The denitrification rate showed clear seasonal variation, with lower levels between August and January (0.01–8.57 µmol N m−2 h−1; average = 1.49 µmol N m−2 h−1) and a rapid increase between February and July (1.03–235.51 µmol N m−2 h−1; average = 41.73 µmol N m−2 h−1).The N2O flux ranged from −0.64 to 1.5 µmol N m−2 h−1, with little variability except for a much higher rate (31.49 µmol N m−2 h−1) in June in algae-dominated areas. N2O flux was significantly positively correlated with nitrification and denitrification rates in most lake zones. By comparing the slopes of the regression equations, we found that N2O emissions from the sediment–water interface were influenced predominantly by nitrification, suggesting that lower N2O fluxes from the sediment–water interface in Taihu Lake are caused primarily by lower nitrification rates.