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.
Highlights
Large-scale, persistent and often unexpected changes in a system are referred to as regime shifts (Scheffer et al 2001)
We extend a model of shallow lake bistability (Scheffer 1989) to examine the effect of measures for lake restoration which operate at different time scales
We extended a well-known minimal model for shallow lake regime shifts to investigate how interlinked dynamics of bream, pike and vegetation are affected by the combination of measures to restore the clear water state
Summary
Large-scale, persistent and often unexpected changes in a system are referred to as regime shifts (Scheffer et al 2001). Ecological regime shifts are a prominent phenomenon occurring in different ecosystems with negative implications for human well-being and the sustainability of socialecological systems (Biggs et al 2018; Rocha et al 2015; Gunderson et al 2006). This article is part of the Topical Collection in Sustainability of social-ecological systems. In most shallow temperate lakes, the accumulation of nutrients in the water column and sediments is the main driver for the shift towards the turbid water state (Scheffer et al 1993), which has been the most serious environmental threat to lakes in the temperate zone over the last century (Jeppesen et al 2007). Management measures often addressed the nutrient sources such as over-fertilization in agriculture or insufficient urban wastewater treatment (Jeppesen et al 2007). Multiple measures have been tested for restoring lakes that have shifted into a turbid state (Mehner et al 2004; Carpenter et al 2001). Often, a combination of measures is advisable to accelerate lake restoration but these combinations are so far rarely investigated
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