A proposed aquatic plant community biotic index for Wisconsin lakes

The Aquatic Macrophyte Community Index (AMCI) is a multipurpose tool develo ped to assess the biological quality of aquatic plant communities in lakes. It can be used to specifically analyze aquatic plant communities or as par t of a multimetric system to assess overall lake quality for regulatory, pl anning, management, educational, or research purposes. The components of th e index are maximum depth of plant growth; percentage of the littoral zone vegetated; Simpson's diversity index; the relative frequencies of submersed , sensitive, and exotic species; and taxa number. Each parameter was scaled based on data distributions from a statewide database, and scaled values w ere totaled for the AMCI value. AMCI values were grouped and tested by ecor egion and lake type (natural lakes and impoundments) to define quality on a regional basis. This analysis suggested that aquatic plant communities are divided into four groups: (1) Northern Lakes and Forests lakes and impound ments, (2) North-Central Hardwood Forests lakes and impoundments, (3) South eastern Wisconsin Till Plains lakes, and (4) Southeastern Wisconsin Till Pl ains impoundments, Driftless Area Lakes, and Mississippi River Backwater la kes. AMCI values decline from group 1 to group 4 and reflect general water quality and human use trends in Wisconsin. The upper quartile of AMCI value s in any region are the highest quality or benchmark plant communities. The interquartile range consists of normally impacted communities for the regi on and the lower quartile contains severely impacted or degraded plant comm unities. When AMCI values were applied to case studies, the values reflecte d known impacts to the lakes. However, quality criteria cannot be used uncr itically, especially in lakes that initially have low nutrient levels.