Century-scale littoral-to-pelagic shift and environmental driving mechanisms in Baiyangdian Lake (Northern China)

Abstract Subfossil Cladocera zooplankton preserved in lake sediments provide valuable insights into long-term ecological and environmental change and offer a robust basis for defining reference conditions for lake restoration. We analyzed a 42-cm long sediment core collected from Baiyangdian Lake, northern China, and established an age–depth model using 210 Pb and 137 Cs dating. Subfossil Cladocera were examined from the upper 34 cm of the core, spanning approximately 1917–2020. A total of 26 Cladocera taxa were identified, with Chydorus sphaericus dominating the assemblage, followed by Bosmina longirostris and Alona spp. Stratigraphic analysis revealed a major reorganization of the Cladocera community around the early 1960s, characterized by a shift from a predominantly littoral, macrophyte-associated assemblage to a community, increasingly dominated by planktonic taxa. The environment attributed as the improved habitat, shifted back to a macrophyte-dominated littoral zone since 1995. Multivariate analyses indicated that total organic carbon and total nitrogen were strongly associated with changes in Cladocera composition, while climatic variables such as precipitation played a secondary role. Prior to the 1960s, community dynamics were largely consistent with natural hydrological variability under low nutrient conditions, whereas subsequent changes were closely associated with increased nutrient enrichment and organic matter accumulation. These findings demonstrate the value of paleolimnological records for distinguishing natural variability from anthropogenically associated change and for establishing realistic reference conditions for the management and restoration of shallow lake ecosystems.