Beck, M. W., B. Vondracek, and L. K. Hatch. 2013. Environmental clustering of lakes to evaluate performance of a macrophyte index of biotic integrity. Aquatic Botany 108:16–25.
A primary objective of biological assessment (bioassessment) is to determine the condition of living organisms using their response to environmental changes. Accurate bioassessment requires practitioners to determine the proportions of biological response attributed to natural variation and human-induced degradation. The absence of approaches for defining comparable groups of aquatic systems that are expected to have similar communities in the absence of anthropogenic stressors can prevent the extraction of useful information from biological surveys. The macrophyte-based index of biotic integrity was developed to assess the condition of Minnesota lakes but also exhibits responses to both environmental and anthropogenic variables. The objectives of the current study were to determine the explicit effects environmental factors have on macrophyte index response and to determine if the existing scoring criteria are adequate for accurate bioassessment. A comprehensive set of environmental variables was evaluated and used in a multivariate framework to identify comparable groups of lakes. Variance partitioning analyses were used to identify the fractions of variation of macrophyte response that could be attributed to environmental and/or anthropogenic variables. We found that lakes could be grouped by ecoregion, but these groups did not fully account for the variation in macrophyte communities. Additionally, a majority of the biological response could not be differentiated between environmental and anthropogenic variables due to substantial correlations among the explanatory variables. However, IBI scores exhibited stronger signals to anthropogenic variables than the component metrics, suggesting the index has potential for accurate bioassessment provided comparable groups of lakes are identified. Relevant variables to consider for improving biological assessment and additional approaches for further validation of the index are suggested. Although this information is applicable to Minnesota, this approach is relevant for any agency concerned with accurate bioassessment.