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Phosphorus Removal by Plant Harvesting on Lake Minnetonka October 22, 2004 <br />John M. Barten, Three Rivers Park District <br />phosphorus. It would require the construction of a 4.5 acre-foot NURP pond treating <br />stormwater runoff from approximately 700 acres of residential area to achieve a <br />comparable phosphorus reduction. Viewed in this manner, the amount of phosphorus <br />removed by the milfoil harvesting program is significant. <br />The effect of the phosphorus removal by the LMCD harvesting program on the water <br />quality of Lake Minnetonka is more difficult to estimate. Previous studies have shown <br />that, in the short term, removal of phosphorus through plant harvesting is not a viable <br />water quality improvement technique. Generally, plants obtain phosphorus and other <br />nutrients from lake sediments. Therefore, removal of plants does not necessarily remove <br />phosphorus from the water column. However, the long term effect of annual plant <br />removal on a large scale on water column phosphorus concentrations has not been <br />determined. Theoretically, annual plant harvesting in the same area for an extended time <br />period could mine phosphorus from the sediments and increase their ability to adsorb <br />phosphorus from the water column. Future data from the ongoing monitoring program <br />should be analyzed to determine if phosphorus reductions in bays with extensive <br />harvesting are occurring. <br />C.I Usersl GabriellDownloadslMinnetonka Premovharvesting.doc p. 6 of 6 <br />