Effects of Alum Treatments on Native and Exotic Macrophyte Density and Potential for Biological Control of Eurasian watermilfoil

Project Staff: 

Principal Investigators: Raymond M. Newman, Professor, Department of Fisheries, Wildlife, and Conservation Biology and Patrick L. Brezonik, Professor, Department of Civil Engineering, University of Minnesota


Minneapolis Park and Recreation Board

Project Duration: 

July 1999 - March 2004


Alum (aluminum sulfate, Al2(SO4)3 · 14 H2O) has been used successfully to control internal phosphorus loading and improve water clarity in lakes. The alum can form an Al(OH)3 "blanket" over the sediments, reducing P release from the sediments to the water column. If internal loading supplies significant phosphorus to the water column, the alum treatment should reduce water column phosphorus and thus planktonic algae, resulting in increased water clarity. Increased water clarity may result in increases in growth of aquatic macrophytes, particularly nuisance plants such as Eurasian watermilfoil (Myriophyllum spicatum). Furthermore, if extensive growths of exotic species such as Eurasian watermilfoil translocate nutrients from beneath the alum blanket, the effectiveness of the alum treatments may be short lived.

The aim of this project is to investigate and document the efficacy of alum treatments in four Minneapolis lakes (Cedar, Lake of the Isles, Calhoun, and Harriet), determine the response of the plant community to changes in water quality, determine if these changes affect internal nutrient loading, and determine if improvements to water clarity will enhance the effectiveness of the watermilfoil biocontrol agent Euhrychiopsis lecontei. The project will also inform the public and management professionals of the project results and findings.