[Spatial and Temporal Heterogeneity and Ecological Health Evaluation of Diatom Community Based on eDNA]

In recent years, environmental DNA (eDNA) has been widely used in aquatic biodiversity monitoring, and how to establish a river ecological health assessment method based on eDNA has become a hot topic. This study was intended to develop a molecular diatom index based on eDNA to indicate the ecological health status of rivers under the influence of human activities. Firstly, the diatom community composition and structural changes in the Shaying River basin in spring and autumn were monitored through eDNA, and the driving environmental factors of the diatom community were diagnosed. Further, four strategies (OTU-taxonomy, OTU-free, ASV-taxonomy, and ASV-free) based on eDNA metabarcoding data were compared, and a molecular diatom index suitable for ecological health assessment in the Shaying River basin was constructed. The results showed that: ① there were seasonal differences in diatom community structure, and Discostella pseudostelligera, Nitzschia amphibia, Diatoma vulgaris, and other groups were the main factors to distinguish the seasonal differences. ② Mn, Fe, and TN were the main environmental factors affecting diatom community structure in spring, whereas COD and Cu were the main environmental factors affecting diatom community structure in autumn. ③ Among the four strategies, the diatom index calculated based on OTU-free data better reflected the environmental gradient change; the diatom index showed that the ecological health status of the Shaying River Basin was better in autumn than that in spring in time and better in the upstream than that in the downstream in space. In conclusion, this study monitored diatom community in Shaying River in spring and autumn through eDNA and constructed the molecular diatom index in the Shaying River basin, which promoted the application of eDNA to evaluate river ecological health.