Turnitin: Prosiding SCRRD 2018 - Implications of Using Treated Wastewater as Habitat for Desert Fishes

Abstract

Discharge of treated wastewater and upgrades to water reclamation facilities have been instrumental in returning aquatic biodiversity and riparian habitat to the previously dry Santa Cruz River. The endangered Gila topminnow has recently recolonized the effluent-dependent reaches of the river, but the long-term health effects of living in effluent and the potential for these fish to persist in effluent reaches are unknown. Using non- native Western Mosquitofish in the lower Santa Cruz River as a proxy for native topminnow, we explore the challenges of living in effluent-dependent streams, including (1) fluctuating water levels, (2) the potential for microplastics to impact diet, and (3) the effects of emerging contaminants on sexual maturation. Diurnal fluctuations in discharge of effluent create daily drying events in the lower reaches of the river, which can result in the stranding and death of fish. Furthermore, in drift samples we have found microplastic concentrations as high as 5.56 particles/m3. However, in our diet analysis on a subset of 200 mosquitofish, we only documented one ingested plastic microfiber. Among the expected prey items that occur in the water column, such as midge larvae, we have also found taxa such as aquatic snails, which suggest some benthic foraging by mosquitofish. Finally, our preliminary analysis has revealed a sex ratio heavily biased towards females (10.1:1), which is higher than ratios from published studies of natural systems (4.4:1). We hypothesize this pattern could be due to estrogen compounds, which can be common in effluent-dominated systems, inhibiting the sexual maturation of males. Faced with increasing population growth and uncertainties of climate change, effluent-dominated systems will become increasingly important sources of aquatic habitat, but further studies are needed to assess their ability to support native fish.