An Evaluation of Indices of Biotic Integrity for Algal and BMI Assemblages in Streams of the Los Angeles Region

Abstract

ABSTRACTThe Los Angeles region contains a number of heavily altered watersheds, resulting in the degradation of both water and habitat quality along numerous streams. Assessing the impacts of these anthropogenic stressors on biological communities has primarily focused on the California Stream Condition Index (CSCI), a measure of the biotic integrity of benthic macroinvertebrate assemblages. To complement the CSCI an Algal Stream Condition Index (ASCI) was developed to assess the biotic integrity of both soft‐bodied and diatomaceous algal assemblages. Using random forest modeling, we evaluated the performances of the CSCI, the ASCI for diatom assemblages (D_ASCI), and the ASCI for hybrid assemblages containing both diatoms and soft‐bodied algae (H_ASCI). We found that our models of the D_ASCI and H_ASCI could account for approximately 77% and 78% of their observation variation across the watersheds of the Los Angeles region, nearly as high as the 82% accounted for by the CSCI. This indicates the future potential of using indices of biotic integrity based on, or in part, diatom assemblages for streams in this region as additional forms of bioassessment.