Unstable Ecological-Economic Equilibria: The Effects of Invasive Species and Ecosystem Restoration on Nutrient Management Compromise in Lake Erie

Together, lake ecosystems and local human activity form complex ecological-economic systems characterized by feedback loops and discontinuous change. Researchers in diverse fields have suggested that complex systems do not have single stable equilibria in the long-term due to inevitable perturbation. During this study, we sought to address the general question of whether or not stable ecological-economic equilibria exist in highly stressed and managed lacustrine systems. Using an integrated human-biophysical model, we investigated the impacts of a species invasion and ecosystem restoration on ecological-economic system equilibrium, defined here as a compromise in phosphorus (P) management between opposing stakeholders, in western Lake Erie. Our integrated model is comprised of a calibrated ecological sub-model representing Sandusky Bay and a P management sub-model that reflects the societal benefits and costs of P regulation. These two sub-models together form a dynamic feedback loop including freshwater ecology, ecosystem services, and P management. We found that the invasion of dreissenid mussels decreased ecosystem resistance to eutrophication, necessitating increased P management to preserve ecosystem services and thus creating the potential for multiple unstable ecological-economic equilibria. Additionally, our results suggest that net benefits in the region following the invasion of dreissenids may never again reach the pre-invasion level if on-site P control is the sole management lever. Further demonstrating system instability, large-scale wetland restoration shifted points of management compromise to states characterized by less on-site P management and higher environmental quality, resulting in a significant increase in net benefits in the region. We conclude that lacustrine ecological-economic systems are open and dynamic and we recommend that future models of these systems emphasize site-specific perturbation over equilibrium, thereby aiding the development of management plans for building system resistance that are both flexible and sustainable in an unknowable future.