Aluminum Sulfate Application to Improve Under-Water Light Condition for Native Submersed Macrophyte Restoration: Alum to Phosphorus Binding Ratio Considerations

PURPOSE: Native submersed macrophyte growth is often limited by underwater light availability in eutrophic aquatic systems. Control of canopy-forming exotic species does not necessarily lead to greater light penetration because eutrophic systems usually sustain high algal biomass in the form of cyanobacterial blooms that can rapidly attenuate light near the lake surface. High phosphorus (P) loading from bottom sediments often represents an important source for algal uptake that needs to be controlled in order to drive aquatic systems toward P-limitation of growth and improve underwater light condition for restoration of native submersed macrophyte populations. Aluminum (Al) sulfate application represents an effective management technique for binding P in sediment and reducing flux into the water column for algal uptake. However, research is needed to determine the dosage of alum required to bind sediment P. The objective of this research was to examine Al:P stoichiometry in relation to extractable forms of sediment P in order to improve the accuracy of alum dosage determination to control sediment P loading in aquatic systems.