Using bioassessment in highly urbanized areas – a case study of Southern California

The Santa Ana and San Jacinto Rivers in Southern California both originate in relatively undisturbed mountainous areas and flow through highly urbanized areas of the Los Angeles basin.  We sampled 190 probabilistic sites between 2006 and 2011 using standard bioassessment protocols.  We identified four bioregions using nonparametric multivariate statistics on benthic macroinvertebrate community data.  We then characterized each bioregion with respect to physical habitat parameters and water chemistry and related these data to indices of biotic integrity.  This analytical strategy was effective for our highly variable dataset and may be a viable option for other similarly heterogeneous datasets.