Evaluating the potential of treated effluent as novel habitats for aquatic invertebrates in arid regions

Increasing anthropogenic demands for freshwater have altered many aquatic systems, including the drying of formerly perennial streams. The discharge of treated effluent has returned perennial flow in some of these streams, especially in arid and semi-arid regions, but the ability of treated effluent to support diverse aquatic communities is poorly understood. We examined the potential of treated effluent to create aquatic invertebrate habitat using the effluent-dependent Santa Cruz River in southern Arizona, USA as a case study. We identified 92 invertebrate taxa across our ten sampling sites and two sampling dates. Community composition was primarily shaped by water quality but also by stream drying (on daily time scales) and benthic substrate. Specifically, Linear Mixed-Effects models revealed a strong positive relationship between dissolved oxygen and taxonomic richness and a strong negative relationship between stream drying and invertebrate density. Although there are unique challenges to biota in effluent-dependent systems, our results suggest that treated wastewater could be managed to augment or recreate aquatic habitats that have been otherwise diminished or lost.