ALTERNATIVE EQUILIBRIA IN SHALLOW LAKES

The turbidity of lakes is generally considered to be a smooth function of their nutrient status. However, recent results suggest that over a range of nutrient concentrations, shallow lakes can have two alternat ive equilibria: a clear state dominated by aquatic vegetation, and a t urbid state characterized by high algal biomass. This bi-stability has important implications for the possibilities of restoring eutrophied shallow lakes. Nutrient reduction alone may have little impact on wate r clarity, but an ecosystem disturbance like foodweb manipulation can bring the lake back to a stable clear state. We discuss the reasons wh y alternative equilibria are theoretically expected in shallow lakes, review evidence from the field and evaluate recent applications of thi s insight in lake management.