2007 National Lake Survey - Wisconsin Results

Aquatic Plant Surveys

A portion of the National Lake Survey funds granted to Wisconsin was also directed to enhance the WDNR aquatic plant monitoring program. The lakes sampled using the point-intercept sampling approach described below were selected based one of three criteria: 1) National Lake Survey lakes that had not been previously sampled, 2) ‘reference-condition’ lakes of appropriate size and access, and 3) lakes part of the Eurasian water milfoil monitoring project.

Sampling method

Using lake specific parameters, such as total acreage and shoreline sinuosity, a unique, GIS-based sampling grid was developed over the surface of each lake. These points were then uploaded into a handheld GPS and navigated to by WDNR staff. At each grid point a double-headed rake on an adjustable pole was first used to measure the depth of station and substrate type (e.g. sand, muck). By twisting two full turns of the rake head, the sampler collected aquatic plants from approximately 0.75 meters along the bottom. A similar rake head attached to a rope was constructed to collect plants from sites deeper than 4.5 meters.

After pulling the plants to the surface, the rake was assigned a fullness rating of 1 to 3 to estimate overall density of plant growth. Each individual plant species on the rake as well as any dislodged and floating were given similar fullness ratings to estimate abundance. Visual sightings of species within a two meter radius of the sample point were also recorded. Any additional species seen in the lake during a general boat survey were recorded separately from the point-intercept data.