A century of change in Minnesota’s lake plant communities

Abstract

Aquatic plant communities are good indicators of lake conditions, and persistent changes to those communities are indicative of environmental change. Our study used historical and recent lake plant surveys to detect changes in Minnesota’s lake plant communities over the last century. We did not find taxa richness estimates useful for change detection and suggest that recent richness values were higher than historical due to increased search effort rather than real change. The primary signal of change was the failure to relocate taxa in lakes where they were historically common. In 55 % of the lakes, surveyors did not relocate at least one taxon that was reported in an historic survey. We found that emergent plant taxa were most likely to have been lost; for lakes where emergents were reported historically, 45% had at least one emergent taxon that was not redetected compared to 30% of lakes where at least one floating-leaf taxon was not redetected and 42% of lakes where at least one submerged taxon was not redetected. Lakes in the southwestern and central ecoregions of the state were most likely to have gross and persistent aquatic plant losses. Eutrophication was the most likely reason for losses, with substantial declines in the probability of presence of many taxa with greater increases in lake phosphorus concentrations. We identified limitations with these datasets and recommend survey method changes to improve future collection of lake plant lists.