The Theory of Alternative Stable States in Shallow Lake Ecosystems

The concept of alternative stable states within ecosystems was first forwarded in the 1960s. The current view with respect to shallow lakes is that over a range of nutrient concentrations, two alternative stable states can exist. One state comprises of clear water dominated by submerged macrophytes, whereas the other is a turbid phytoplankton-dominated state. Each of the stable states has a number of buffer systems that maintain that state through top-down and bottom-up processes. As many of the buffers and thus forward and reverse switches are well understood, attempts are sometimes made to influence these processes and thus force a change from one state to another, which is especially true during lake restoration projects when it can be desirable to turn a turbid algal-dominated lake into a clear water macrophyte-dominated lake. Keywords: algal dominated; alternative stable states; bottom-up; buffer system; feedback loops; lake restoration; macrophyte dominated; shallow lake; top-down