Year 2000 White Bear Lake Aquatic Plant Survey Summary

Aquatic Plant Survey. Aquatic plant checks to survey Eurasian watermilfoil growth were conducted on April 27, May 30, July 11, and August 14 and a whole lake aquatic plant survey was conducted on October 9, 2000. For the whole lake survey, a total of 122 stations on 42 transects were surveyed for plants. We sampled three depths for most transects with depth intervals ranging from 0-5, 6-10, and 11-15 feet. Some transects had less than three sampling stations, depending on water depths.

In 2000, Eurasian watermilfoil was common in White Bear Lake, based on occurrence, showing up in 69 stations out of 125 (55% occurrence). This is an increase compared to the 1999 survey where it was found at 35% of the stations (Table A). In mid-August, Eurasian watermilfoil matted at the surface in three areas, generally in water less than 6 feet deep, representing about three surface acres total. Areas of nuisance milfoil growth were found in areas of high lake sediment nitrogen concentration. Overall, the milfoil density in the matted areas appeared to be less compared to 1998 and 1999. Eurasian watermilfoil at other stations was one to four feet below the water surface with a canopy height similar to the other native plants. Milfoil was not a recreational nuisance at these sites.

Five areas were examined for evidence of milfoil damage by the milfoil weevil, Euhrychiopsis lecontei. Damage appeared to occur in the Matoska Marsh area, but weevils were not observed. Another survey is scheduled for 2001. At this time it is difficult to assign any level of milfoil control to the weevil.

Aquatic Plant Review. Eurasian watermilfoil has been in White Bear Lake since 1988. As of 2000, Eurasian watermilfoil is still found growing with native plants and has not been found to be displacing native plant species. Eurasian watermilfoil distribution was widespread in 2000, and although greater in occurrence to what was documented in 1999 it was similar to 1998 abundance. Growth in 1998 and 2000 probably represented a "heavy" milfoil season and growth in 1997 and 1999 probably represented a "light" milfoil season. Many factors influence milfoil growth and the length of the growing season and possible buildup of nutrients are two primary factors. In the future, we expect milfoil growth to vary from year to year depending on growing season variables, lake sediment fertility dynamics, and competition with native plants.

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