A multi-index macrophyte-based assessment approach for lakes in the metropolitan region of Minnesota

Macrophytes are an important component of lake ecosystems and approaches to assess these communities are needed, yet many existing aquatic-macrophyte-based indices fail to account for invasive species, single-species dominance, and relative abundance. We developed a comprehensive multi-index macrophyte-based assessment for lakes in the Twin Cities Metro area of Minnesota, integrating Beck’s Index of Biotic Integrity (B-IBI) with two new indices: the Invasive Species Index and the Single-Species Dominance Index. The B-IBI addresses macrophyte community health with seven macrophyte metrics. The Invasive Species Index incorporates the frequency and density of invasive macrophytes, while the Single-Species Dominance Index measures the frequency and density of the most abundant species. Combined, there are 27 possible outcomes. Applied to case study lakes, the indices effectively captured distinct ecological responses to management interventions. Herbicidal treatments led to improvements in invasive species and dominance scores, reflecting successful control of nuisance species, whereas aluminum sulfate treatments primarily improved B-IBI scores, indicating enhanced macrophyte community health, without affecting invasive species or single species dominance scores. Compared to single-metric approaches, this multi-index system provides a more comprehensive assessment by separating community health from nuisance species dominance. Our assessment demonstrates that these indices can be used to guide lake management by evaluating the effectiveness of past interventions and informing targeted strategies for maintaining or restoring macrophyte communities.