Regime shifts in shallow lakes: Modeling nonlinear feedbacks in submerged macrophyte-epiphyte-snail system

Abstract

A three-dimensional dynamical model is formulated to investigate the interactions among submerged macrophytes, epiphytes, and snails in shallow lake ecosystems. The model incorporates key processes such as shading effect, selective grazing behavior, and nonlinear predation pressure from higher trophic levels. The analytical and numerical analyses demonstrate that the system exhibits nonlinear feedback and alternative stable states, epiphytes exert strong bottom-up control through shading, and snail grazing plays a dual role. In particular, snail consumes macrophytes and indirectly facilitates the growth of macrophytes by removing epiphytes, while predation pressure on snails acts as a critical external switch inducing a unimodal response in macrophyte density with an optimal range promoting macrophyte dominance. The main findings highlight the importance of integrated multi-trophic management and provide a theoretical and scientific support for biomanipulation strategies to maintain clear-water states in eutrophic lakes.