Coregulation of nitrous oxide emissions by nitrogen and temperature in China's third largest freshwater lake (Lake Taihu)

Abstract

Abstract Nitrous oxide (N 2 O) is a potent greenhouse gas and contributes to the loss of stratospheric ozone. However, the role of inland waterbodies in the dynamics of atmospheric N 2 O is poorly understood. We investigated N 2 O fluxes and their controlling factors in Lake Taihu, a large and shallow (2400 km 2 , 1.9 m depth) eutrophic lake in eastern China. Long‐term measurements (2011–2016) revealed spatial and temporal variations in the lake surface N 2 O fluxes. The mean N 2 O flux from the lake was 3.5 ± 1.8 (mean ± SD) μ mol m −2 d −1 , with an annual N 2 O budget of 134.4 ± 69.8 Mg (10 6 g) yr −1 . The highest N 2 O fluxes occurred in the eutrophic zone with significant anthropogenic N inputs, and the lowest fluxes occurred in the noneutrophic zone with no external N inflow. A seasonal pattern in N 2 O fluxes was observed only in the noneutrophic zone and was strongly correlated with water temperature. No seasonality in the N 2 O fluxes was observed in the eutrophic zone with high N concentrations in the water, indicating that N concentrations play a dominant role in regulating N 2 O fluxes compared to water temperature. The average N 2 O emission factor in Lake Taihu was 0.18%, with temporal and spatial variations negatively associated with N concentration but positively associated with the mass ratio of dissolved organic carbon to dissolved inorganic nitrogen. Our results suggest that anthropogenic activities strongly affect N 2 O fluxes in freshwater lakes.