Abstract

Ecosystems are constantly subject to shifts amongmultiple locally stable and unstable states. Such regime shifts orbifurcations are fascinating ecological phenomena, involvingmultiple causes and many variables that change at differentspatial-temporal scales, potentially altering the direction offeedbacks. They are crucial for effective ecosystem managementbecause regime shifts may impair valuable ecosystem servicesprovided by nature and because recovery of desired states maybe difficult and costly. Lakes may undergo regime shifts betweentwo alternative steady states, oligotrophic or eutrophic, due tothe strong interaction between exogenous phosphorus (P) inputand endogenous interaction between water and sediment P.Many lakes exhibit either a desirable oligotrophic clear-waterstate with abundant macrophytes and low chlorophyllconcentrations, or an undesirable eutrophic turbid conditionwith high chlorophyll concentrations and sparse macrophytes. Aregime shift from a clear-water oligotrophic state to a turbideutrophic condition may occur in response to a combination ofincreased exogenous nutrient loading and a strong feedbackinvolving P release from the sediments. This paper presentswater and sediment quality data for a small shallow stagnantlake in Selangor Malaysia indicating progressive deteriorationof water quality arising from intensification of eutrophicationdue to accumulated nutrient loading from a relatively largehuman settlement over three decades. It then provides numericalsimulations and analytical synthesis for explaining andpredicting the prognosis of lake eutrophication regime shifts.The paper concludes with a practical and sustainableremediation measure for rehabilitating lake eutrophication.