Consistency Among Biotic Indices to Represent Environmental Conditions: Implications for Biotic Assessments

Biotic indices are quantitative tools used to infer stream health. Since, they need to be tailored to a specific faunal group (e.g. fish or aquatic invertebrates) for similar stream sizes and regions, many different indices have been created. Therefore, understanding if there is consistency among index interpretations within and across faunal groups is needed. Investigating these differences may shed light on the consistency and limitations of individual indices and help managers select an index that will most accurately portray environmental conditions. We compared two fish (Index of Biotic Integrity, IBI, and Species Richness) and two aquatic invertebrate indices (Hilsenhoff Biotic Index, HBI, and Ephemeroptera, Plecoptera, and Trichoptera richness, EPT) calculated for 148 sites in rivers and streams in Midwest national parks. Overall, each of the indices were highly correlated in the Ozarks (r=0.47-0.16, p= <0.01-0.07) but less so in the Plains (r=0.53-0.04, p= 0.02-0.86). Additionally, local habitat variables best explained each of the indices when compared to segment and watershed scale variables.  Because of the inconsistency among indices, managers may need to consider their objectives to determine the most appropriate stream health index to meet their goals.