Reducing Internal Phosphorus Loading in Minnesota Lakes- Can augmenting iron in lake sediment help?

Poornima Natarajan, Research Associate, St. Anthony Falls Laboratory, University of Minnesota

High internal phosphorus loading in lakes combined with watershed input of phosphorus can cause serious water quality issues like algal blooms. Reduction of both external and internal sources of phosphorus is necessary to regulate the trophic state of a lake. In-lake restoration measures such as alum application and hypolimnetic aeration are relatively more common than dosing iron salts to treat lakes. Iron can naturally bind phosphorus, and lakes with high levels of iron have been observed to release less phosphorus from sediments. In this talk, results of experimental addition of zero-valent iron filings to lake sediments to control internal phosphorus release will be presented. Using laboratory mesocosms, the effectiveness of increased iron supply in the sediment was investigated under oxic-anoxic regime. The dose-response relationship was studied to help determine the quantity of iron filings needed to decrease the flux of phosphorus from sediments and the water column phosphorus concentrations. The application of iron filings has the potential to sequester phosphorus in lake sediments, and could be a new lake management tool for Minnesota lakes and beyond.