Development and evaluation of a diatom-based biological monitoring index for streams in Cook Inlet Basin, Alaska

Benthic diatom assemblages in streams may respond simultaneously to both natural variation in stream habitat and to anthropogenic habitat degradation and are ideal organisms for biological monitoring. The overarching goal of this study was to examine the utility of diatoms for monitoring Cook Inlet region aquatic systems and to develop the criteria for its interpretation. Within that framework, the main objectives of this project were to (1) ascertain the variability of diatom assemblages caused by natural factors, (2) separate natural variation from that attributed to urban development, and (3) assess the seasonal variability of diatom assemblages. There are several natural patterns that occur spatially within the Cook Inlet Basin Ecoregion, including differences in water chemistry and stream bed slope. Diatom assemblages at reference sites with a slope of less than 2% were significantly different than those of greater than 2%. The final diatom-based index of biological integrity (IBI) provides an integrative index reflective of overall ecological health of Cook Inlet Basin streams.