Preventing or predicting cyanobacterial blooms: Iron addition as a whole lake restoration tool

Abstract

Internal phosphorus loading has become a major problem in many freshwater lakes due to the build-up of nutrient stocks in the sediment over the past decades. Iron is a natural capping agent which naturally binds to P and can enhance sediment P binding capacity. Various restoration experiments using iron addition have been a success by reducing P availability and shifting a lake from an algal dominated state to a macrophyte dominated state. Adding iron to a lake could, however, also negatively affect lake ecosystems, as iron could impose toxic effects on the biota. Differences in the response of species to iron addition might lead to a change in community composition, favouring the more iron-tolerant species. Long term effects of addition on the biotic community are, however, relatively unknown. Nonetheless, iron addition can indirectly induce a shift from a eutrophic to a mesotrophic system that might eventually have the most important effect on the diversity of the aquatic community. To guarantee long term success of iron addition, the constraining chemical and biological factors that might reduce long term sediment P retention or inhibit macrophyte return should be addressed before or during iron application. Whereas iron addition can shift a lake from a cyanobacterial dominated state to a macrophyte dominated state, in some cases these effects are only visible on a longer term. Therefore, in order to bridge the years before water quality is fully restored, prediction of cyanobacterial scum occurrence could be a solution to protect the public from contact with these toxic scums.