Water quality of selected effluent-dependent stream reaches in southern Arizona as indicated by concentrations of periphytic chlorophyll a and aquatic-invertebrate communities

Concentrations of chlorophyll a and indices computed for aquatic- invertebrate communities in two effluent-dependent stream reaches on the Santa Cruz River and one on the Salt River were compared to those in noneffluent-dependent streams to examine potential differences in water quality. Periphytic chlorophyll a from riffle habitats and aquatic-invertebrate communities from riffle and multiple habitats were used for the comparison. Concentrations of chlorophyll a from effluent-dependent streams were elevated compared with concentrations in noneffluent- dependent streams. Aquatic-invertebrate communities from effluent-dependent streams were characterized by an abundant, yet taxonomically depauperate fauna of tolerant organisms; whereas, noneffluent-dependent streams supported a diverse assemblage of aquatic invertebrates including taxa considered sensitive to water-quality degradation. These results indicate that water quality of the effluent-dependent streams is poor compared with water quality of noneffluent-dependent streams. Patterns of taxonomic composition of aquatic-invertebrate communities and abundances of aquatic invertebrates from effluent- dependent streams are the same as patterns discussed in the scientific literature.