Long term bioassessment multiple stressors study in a residential California stream

The relationship of various benthic metrics to physical habitat metrics, pyrethroids, metals and sediment parameters was evaluated for a 10 year data set in Pleasant Grove Creek (Roseville, California) using univariate linear models, stepwise multiple regressions, and canonical correlation analysis. In general, total physical habitat scores in this residential stream were considered to be marginal to suboptimal. The most dominant benthic taxa were generally considered to be tolerant of environmental stressors and the benthic communities were rated as impaired based on a benthic index. Potentially toxic sediment concentrations of cadmium, chromium, copper, nickel and zinc were reported at various sites based on a comparison with existing threshold effect levels. The sum of pyrethroid Toxics Units (TUs) indicated that 10 of 21 sites based on a sensitive Hyalella laboratory toxicity test had TUs greater than one thus suggesting toxicity at various sites. In summary, the effects of the physical habitat, as reflected by certain habitat metrics that were indicative of stream-flow, hydrology, habitat diversity, and substrate quality overshadowed any apparent effects of pyrethroids and metals on shaping resident benthic communities when all environmental variables were considered in multivariate analyses.