Turnitin: Prosiding SCRRD 2021 - Microplastic pollution in the effluent-dependent lower Santa Cruz River during baseflow and post-flood conditions

Abstract

Microplastics are an emerging contaminant of potential ecological concern in waterbodies across the world. One important point source of microplastic pollution is treated wastewater; after treatment, this effluent is often discharged directly into streams. In southern Arizona, effluent discharge supports perennial flow and riparian habitat in the Santa Cruz River but also brings microplastic pollution and its potential ecological challenges. In this project, we examined microplastic concentrations in the water column and benthic sediment, and microplastic consumption by mosquitofish (Gambusia affinis) at 10 sites along a ~40 km stretch of the lower Santa Cruz River. We quantified these factors across two time periods: baseflow (effluent only) and post-flood (effluent baseflow immediately following urban runoff). We found four types of microplastics in the Santa Cruz River: fibers, fragments, film, and beads. In total, across both sampling periods, we detected microplastics in 95% of water column samples, 99% of sediment samples, and 6% of mosquitofish stomachs. Flow status (baseflow vs post-flood) was the only significant predictor of microplastic presence and concentrations in our models. Across all sites, microplastic concentration in the water column was ~33% higher during post-flood, with most pieces (≥80%) being fibers in both seasons. However, microplastic concentrations in the benthic sediment were 55% lower in post-flood vs baseflow samples, with fibers and fragments being the most common types. During baseflow, only 1.5% of mosquitofish sampled had ingested microplastics (all fiber), while post-flood 10% did (85% fiber, 10% film, 5% fragment). This project provides the first evidence that microplastics are common in the water column and sediment of the lower Santa Cruz River, and that resident mosquitofish are more likely to ingest microplastics post-flood. Future studies should assess the long-term impacts of these microplastics on the health and populations of aquatic species.