Enhancing water quality through biomanipulation: Insights into energy flow and nitrogen cycling from a subtropical eutrophic lake for sustainable management

Addressing the growing threat of harmful algal blooms driven by eutrophication and climate change, biomanipulation via fish has emerged as a promising strategy to enhance water quality in lake ecosystems. While biomanipulation is often evaluated by its impact on algal control, the influence of food web structure and function on water quality requires further mechanistic understanding. This study pioneers a 22-year ecosystem-scale analysis using Ecopath with Ecosim (EwE) model to quantify how a dual biomanipulation strategy involving filter-feeding fish and piscivorous fish reshapes energy flow pathways and nitrogen cycling dynamics in a subtropical eutrophic lake. The findings indicate that the introduction of filter-feeding fish (silver carp, Hypophthalmichthys molitrix, and bighead carp, Aristichthys nobilis) suppress cyanobacterial blooms by redirecting 52.7% of nitrogen to fisheries, while piscivorous fish (bass, Lateolabrax japonicus, and eel, Anguilla japonica) amplify trophic cascades, enhancing zooplankton-mediated microalgal regulation. Food web connectivity increased (connectance: 0.12 to 0.21), minimizing nitrogen flux to detritus and improving water quality by 38%, driven by cyanobacterial biomass suppression, enhanced energy transfer efficiency, and fish-mediated nitrogen removal. These results demonstrate that integrated biomanipulation balances fishery yields with eutrophication control, offering a climate-resilient framework for restoring subtropical lakes globally. This work advances mechanistic insights into nutrient-energy synergies and provides actionable strategies for sustainable aquatic management in warming ecosystems.