Short-term decisions in lake restoration have long-term consequences for water quality

Abstract

Ecological regime shifts from clear to turbid water states in shallow temperate lakes are quite well-investigated phenomena but critical time lags from human interaction with the lake and restoration activities are much less understood. This is a complex challenge for institutions who manage lakes but are usually less familiar with non-linear dynamics, slow and fast influences on water quality and how to manage those from a social-ecological perspective. We extend a well-known minimal model of shallow lake regime shifts to enable simulations over time with short- and long-term management measures (nutrient reduction, trawling, planting of aquatic vegetation). While we explore the mathematical conditions for ecological bistability, we also identify the necessary and sufficient extent of measures to restore the clear water state. Restoration scenarios evaluated by trajectories in the state space demonstrate the increased effectiveness from combined measures even when considering countereffective activities such as pike fishing. But, single measures alone may delay or even miss the overall restoration target. Our analysis demonstrates the importance of understanding transient dynamics where stable state analyses alone remain elusive about alternative ways to interact with bistability. We conclude that successful management of bistable systems, and particularly shallow temperate lakes, needs careful balancing between short-term improvements and long-term influence on the systems state.