Controlling internal phosphorus loading in lakes by physical methods to reduce cyanobacterial blooms: a review

The aim of this paper was to summarize the current knowledge on how physical methods can reduce or control internal P release from sediments in lakes and reservoirs. Particular emphasis is given to the role of internal phosphorus load in fueling cyanobacterial blooms which are predicted to increase in frequency and intensity in response to climate change and eutrophication. We present selective case studies (both successful and unsuccessful) to assess the applicability and efficiency of major physical approaches used for decades to reduce internal loading in different systems of various morphology. In particular, we concentrate on where and when (1) hypolimnetic aeration/oxygenation, (2) hypolimnetic withdrawal and (3) sediment dredging are likely to reduce cyanobacterial blooms and whether these methods have an adverse impact on other organisms. We conclude that each method has its strength and weakness depending on the system considered. Sufficient knowledge of all lake nutrient sources and their dynamics together with detailed lake and sediment characteristics is an essential prerequisite for choosing an appropriate control method. We also report that many experiences demonstrated that a combination of restoration methods is often more successful than a single method.