Influence of south-to-north water transfer project on ecology of typical water receiving area-Xiashan reservoir, China

• The trophic diversity was higher in transferred reservoir than that in non-transferred reservoir. • Half of the fish species in transferred reservoir exhibited changes in trophic level compared to historical data. • δ 15N and δ 13C values in transferred reservoir showed stronger correlations with environmental factors • The SNWTP enhanced nutrient diversity within the biotic communities of transferred reservoir. Inter-basin water transfers are known to profoundly modify the ecological structure of aquatic systems, however, comparative studies assessing the ecological impacts on transferred versus non-transferred water bodies remain limited, particularly within the framework of large-scale projects such as the South-to-North Water Transfer Project (SNWTP). The present study examined the trophic dynamics of two reservoirs: Xiashan (XS) reservoir, receiving water via the eastern route of the SNWTP, and Mushan (MS) reservoir, a non-transferred reference reservoir. Using stable isotope analysis, the trophic structures of functional communities in both systems were characterized. Our findings revealed a lower isotope overlap in the XS Reservoir compared to the MS Reservoir. Additionally, the fish community in the XS Reservoir exhibited longer food chains, greater isotopic diversity, wider ecological niches, and a more even trophic distribution relative to the MS Reservoir. These findings implied that water transfer operations under the SNWTP may enhance community diversity, expand ecological niches, and promote a more uniform distribution of nutrients within recipient reservoirs, which provides critical insights into the ecological consequences of inter-basin water transfers and supports informed management of impacted aquatic ecosystems.