The performance of OEPA’s Invertebrate Community Index (ICI) and a family-level Macroinvertebrate Aggregate Index for Streams (MAIS) was compared in 40 streams of varying impact throughout the Western Allegheny Plateau (WAP). In addition, the effect of 3 levels of subsampling on MAIS scores was evaluated.
There was a significant correlation (rho = 0.719) between the ICI and MAIS. When grouped in OEPA’s biological condition categories the indices were only significantly correlated (rho = 0.703) at severely degraded sites. The indices rated 81% of sites similarly as “attaining” or “non-attaining”, but there was less agreement (37.80%) when comparing the 4 biological condition categories of each index. Subsampling had little effect on mean MAIS scores and no consistent effect on within-category score variation. Findings give support for the reliability of family-level indices, and suggest that the MAIS may be useful in degraded streams of the WAP and other streams upon recalibration.