Suspended particles potentially enhance nitrous oxide (NO) emissions in the oxic estuarine waters of eutrophic lakes: Field and experimental evidence.

Estuaries are considered hot spots for the production and emissions of nitrous oxide (NO) and easily occur suspended particles (SPS), however, current understanding about the role of SPS in the NO emissions from the oxic estuarine waters of lacustrine ecosystems is still limited. In this study, field investigations were performed in the estuaries of hypereutrophic Taihu Lake, and laboratory simulations were simultaneously conducted to ascertain the characteristics of NO emissions with different SPS concentrations. The results showed that the NO emission fluxes ranged from 9.75 to 118.38 μg m h, indicating a high spatial heterogeneity for the NO emissions from the estuaries of Taihu Lake. Although the dissolved oxygen (DO) concentrations were up to 7.85 mg L in the estuarine waters, from where the NO emissions fluxes were approximately three times that of the lake regions. Multiple regression model selected the total nitrogen (TN), SPS, and DO concentrations as the crucial factors influencing the NO emission fluxes. Particularly for SPS, the simulation results showed that the NO concentrations increased gradually with the increase in the SPS concentrations of an oxic water column containing 4 mg L of NO-N, indicating that a high SPS concentration can accelerate the NO emissions. It was related to the change of denitrifying bacteria population in the SPS, as evidenced by its significantly positive correlation with NO emissions (p < 0.01). Our findings will draw attentions to the role of SPS playing in the NO productions and emissions in eutrophic lakes, and its effect on nitrogen cycle should be considered in the future study.