Regime Shift Analysis and Numerical Simulation for Effective Ecosystem Management

Abstract

—Ecosystems are constantly subject to shifts among multiple locally stable and unstable states. Such regime shifts or bifurcations are fascinating ecological phenomena, involving multiple causes and many variables that change at different spatial-temporal scales, potentially altering the direction of feedbacks. They are crucial for effective ecosystem management because regime shifts may impair valuable ecosystem services provided by nature and because recovery of desired states may be difficult and costly. Lakes may undergo regime shifts between two alternative steady states, oligotrophic or eutrophic, due to the strong interaction between exogenous phosphorus (P) input and endogenous interaction between water and sediment P. Many lakes exhibit either a desirable oligotrophic clear-water state with abundant macrophytes and low chlorophyll concentrations, or an undesirable eutrophic turbid condition with high chlorophyll concentrations and sparse macrophytes. A regime shift from a clear-water oligotrophic state to a turbid eutrophic condition may occur in response to a combination of increased exogenous nutrient loading and a strong feedback involving P release from the sediments. This paper presents water and sediment quality data for a small shallow stagnant lake in Selangor Malaysia indicating progressive deterioration of water quality arising from intensification of eutrophication due to accumulated nutrient loading from a relatively large human settlement over three decades. It then provides numerical simulations and analytical synthesis for explaining and predicting the prognosis of lake eutrophication regime shifts. The paper concludes with a practical and sustainable remediation measure for rehabilitating lake eutrophication.