Water regulation weakens the relationship between biodiversity and ecosystem multifunctionality: Insights from a highly managed Chinese lake

Water diversions can mitigate water scarcities by strategically reallocating water resources. Despite their benefits, these interventions may profoundly affect biodiversity and multiple ecological functions ("multi- functionality") within highly managed lake systems. However, the specific impact of such interventions on the relationship between biodiversity and multifunctionality remains elusive, which limits our grasp of how water regulation shapes the dynamics of managed lake ecosystems. In this study, we investigated the differences in biodiversity and ecological functions between periods with and without water regulation in a highly managed lake, and extended this analysis by calculating diversity and multi-diversity indices and assessing the ecosystem's multifunctionality, with the goal of improving our understanding of how water regulation affects the ecological integrity of such lakes. We found that the diversity and multi-diversity indices both decreased markedly during the regulation period, indicating a negative impact on biodiversity. Conversely, multifunctionality remained stable. To clarify these responses, we developed linear mixed-effects models that incorporated multi-diversity indices and multifunctionality. Our analysis uncovered a robust positive correlation between multi-richness and multifunctionality. However, this relationship weakened during the periods with water regulation. Finally, we established structural equation models based on trophic cascade theory to pinpoint the key biological groups that sustained multifunctionality. We found that plants and omnivorous fish were instrumental in supporting multifunctionality during the non-regulation period, whereas planktivorous fish played a crucial role during the regulation period. These findings significantly enhance our understanding of how water regulation influences both biodiversity and multifunctionality, and provide insights for future management of regulated lakes.