Dissolved oxygen stratification changes nitrogen speciation and transformation in a stratified lake

Dissolved oxygen (DO) stratification is a natural phenomenon in lakes, which potentially influences nitrogen (N) biogeochemical cycle. However, the specific effects of DO stratification on N speciation and transformation behaviors in different water layers are still poorly understood. Here, we reported that DO stratification remarkably influenced N species and transformation pathways in different water columns by high frequency sampling during summers in Longjing Lake, China. Results showed that DO stratification in the lake created three water layers: epilimnion (1-3 m), oxycline (4-11 m), and hypolimnion (12-20 m). In the epilimnion, N speciation was mainly controlled by phytoplankton assimilation and organic N dominated in this layer. Oxycline was the major place for N transformations and had the most notable N removal…