N2O emissions from a multi-habitat lake: Patterns and controls

Abstract

Lakes are a significant source of N₂O emissions, and the spatial and temporal variability of lake N₂O emissions contributes to the uncertainty in global N₂O budget estimates. Currently, researchers have a limited understanding of N₂O emission patterns and controlling factors in different habitats of large, shallow lakes. This study focused on the phytoplankton-dominated zone (PDZ), submerged plants-dominated zone (SDZ), and emergent plants-dominated zone (EDZ) of Lake Taihu, China. The N₂O fluxes in each lake zone were recorded monthly for one year using the static floating chamber method, to explore the spatio-temporal variations in N₂O emissions and their controlling factors in lakes with complex habitat types. Additionally, a microcosm experiment was used to identify the effect of algal addition on the water column nitrogen (N) load and N₂O emissions. Results showed that the annual average N₂O fluxes at the water–air interface were 0.66 ± 0.62 μmol m⁻² h⁻¹, 0.09 ± 0.06 μmol m⁻² h⁻¹, and 0.56 ± 0.93 μmol m⁻² h⁻¹, from the PDZ, SDZ, and EDZ, respectively. The N₂O fluxes in the PDZ were significantly (p < 0.05) higher than those from the SDZ (p < 0.05), while those in the EDZ did not differ significantly from the other two zones. During summer, the N₂O concentrations and fluxes in all lake zones were higher than those in the other seasons. Statistical analysis indicated that water TN, temperature (T_W), and TP are crucial factors regulating N₂O emissions. The algae addition experiment demonstrated that phytoplankton aggregation promoted N₂O emissions by altering DO content and water column N load. Overall, this study emphasizes the importance of considering habitat differences in regional and global lake N₂O emission estimates.