These data were collected by Karen A. Wilson as part of her PhD work in Northern Wisconsin, (Vilas and Onieda Counties) during July and August of 1998 and 1999. Details of field collections can be found in Wilson, K.A. 2002. Impacts of the invasive rusty crayfish (Orconectes rusticus) in northern Wisconsin lakes. Ph.D. Dissertation. University of Wisconsin, Madison. Karen was assited by Carrie Byron, an undergraduate at UW-Madison at the time, who should be acknowledged.
Submersed and floating macrophytes were surveyed along a transect running perpendicular to shore at two sites representative of muck (organic) and sand substrate macrophyte communities. We avoided sites that were obviously impacted by boat launches, swimming beaches or lakeshore cottages and chose sites where plants were clearly present. Transects extended offshore to 100 m or a depth of 4 m, whichever came first. Divers noted the presence of macrophyte species within a 0.25 m2 circular quadrat at 1 m intervals along each transect. We sampled a minimum of ten quadrats within each depth range (0 - 1 m, 1 - 2 m, 2 - 3 m, 3 - 4 m). An additional ten 0.25 m2 quadrats were located parallel to shore at 1, 2, 3, and 4 m depths (N = 40) adjacent to the transect (or at equivalent spacing on transects less than 4 m deep). The additional ten quadrats were located approximately 1 m apart and placed by allowing the quadrat to drift down from above.
To calculate species frequency of occurrence for each lake, we summed the number of quadrats in which a species was found and divided by the total number of quadrats sampled in the lake. Species identifications followed Crow and Hellquist (2000). Uncommon or unknown species were collected for identification and voucher specimens. Many species in north temperate lakes reproduce infrequently via seed or are sterile and reproduce only vegetatively. Therefore not all plants were identifiable to species because reproductive structures were often absent. Thus, in addition to readily identified species, we used several genus-level categories. For example, except the readily identifiable Myriophyllum tenellum, all other Myriophyllum spp. were grouped together. These categories represent a conservative measure of the number of species in many lakes (for details see Wilson, 2002).