Sediment eDNA reveals damming triggered changes in algal and fish communities at the Three Gorges Reservoir in China

With the rapid development of water conservation projects around the world, the potential impacts of damming on river ecosystems have attracted widespread attention. Here, we employed the environmental DNA (eDNA) records of the sediment core profiles to explore the effects of the dam construction on algal and fish community structure and biodiversity in the Three Gorges Reservoir in China for the past few decades. We detected 242 genera of algae and 62 species of fish in the sediment cores of the Xiangxi River estuary, the main tributary of the reservoir. The structure of algal and fish communities was changed significantly before and after damming. The dominant species in the algal community shifted from Cyanophyta to Bacillariophyta, while the dominant species in the fish community remained Cypriniformes, and the species diversity fluctuated greatly after damming. In addition, the Non-metric Multidimensional Scaling (NMDS) analysis showed that the composition of algal communities differed significantly among different sequences, while the differences among fish community groups were relatively small. The total nitrogen (TN) and total phosphorus (TP) in sediments were expected to be the main factors, affecting the abundance of eDNA in algae and fish in sediments. Our research emphasizes the progressiveness of sediment eDNA in retrieving the historical dynamics of biological communities, and especially, obtaining the temporal succession trend of biological communities is crucial to understanding the impact of dam construction on the reservoir ecosystem.