Spatial characteristics of nitrogen forms in a large degenerating lake: Its relationship with dissolved organic matter and microbial community

It is crucial to clarifying the interactions among nitrogen, dissolved organic matter, and microorganisms to understand the ecological response mechanisms of degenerating large shallow lakes. This study focused on the spatial patterns of several nitrogen forms in Honghu Lake (Hubei province, China) in combination with the sediment physical and chemical properties. The dissolved organic matter (DOM) composition, the humification degree and the bacterial and eukaryotic communities responses were analyzed. The results showed that the spatial distribution of nitrogen was related to the particle size composition. The maximum mean value of total nitrogen appeared in the southwest region (4813.77 mg kg−1). DOM was mainly composed of humic-like substances, with a high degree of humification at the entrance of the inflowing lake (projection value peaked at 2.22). Structural equation model analysis also showed that the direct and indirect effects of the microenvironment physical and chemical properties and nitrogen and DOM jointly explained the changes in bacterial community diversity. However, there were no similar spatial distribution characteristics between eukaryotes and environmental parameters, suggesting a single, irregular dominant species and a low level of diversity. This suggests an internal ecological response of nitrogen, DOM, and microorganisms in the degenerating lake environment.