Successful Restoration Of A Shallow Lake: A Case Study Based On Bistable Theory

Eutrophication of shallow lakes provides an excellent example of alternative stable states. Clear water, macrophyte-dominated stages can alternate with turbid conditions characterized by high algal concentrations. Stable states can switch from one to the other domination through alterations of natural factors such as changes in water level and reduction in throughflow. Forward switches are often associated with anthropogenic pressure. In such cases, backward shift to the original, macrophyte-dominated stage may be difficult. Return times are often prolonged due to hysteresis as a result of resilience. The theory is exemplified with results from a shallow, urban, seepage lake 'Old Danube,' which is within the city limits of Vienna. Causes and consequences of switches between stable states including resilience and hysteresis are discussed. The remediation measures are explained and the success of the restoration is explained in detail.