Spatio‐Temporal Assessment of Fish Biodiversity in High‐Density Cascade Dam Rivers Using Environmental DNA Metabarcoding

ABSTRACT

The biodiversity of rivers with cascade dams undergoes significant changes due to alterations in hydrological conditions caused by the development of hydropower projects. However, complex hydrology and strong spatial heterogeneity in mountainous rivers with dense cascade dams make biodiversity assessments challenging, leaving their biodiversity patterns poorly understood. In the context of fishing bans for river conservation and hydropower impacts, suitable monitoring methods are required to guide policy implementation. The eDNA technology offers new opportunities for biodiversity assessment and ecosystem‐scale evaluation. Here, we conducted high‐resolution spatiotemporal eDNA sampling along the Bailong River in Gansu Province, China, covering spatial, temporal, and habitat dimensions. A total of 351 water samples were collected from 117 sites to investigate the spatiotemporal patterns of biodiversity in a typical cascade‐dammed mountainous river. We identified 97 fish species from 12 orders, 29 families, and 71 genera using eDNA metabarcoding. Spatially, fish diversity indices were correlated with river distance, but seasonal differences in spatial diversity patterns were observed. Temporally, eDNA detection rates for fish species were similar between summer and winter, yet molecular operational taxonomic unit (MOTU) abundance varied significantly between seasons. Habitat‐wise fish communities showed no significant differences in response to different habitat types. This study not only highlights the potential of eDNA metabarcoding in monitoring fish biodiversity but also offers valuable methodological insights for biodiversity assessments in other rivers with similar hydrological conditions.