Impact of wastewater treatment plant effluent on the winter thermal regime of two urban Colorado South Platte tributaries

Wastewater treatment plant effluent can increase stream water temperature from near freezing to 5°C–12°C in winter months. Recent research the South Platte River Basin Colorado showed that this warming alters reproductive timing of some fishes. However, spatial extent and magnitude are unknown. Thus, we created models both upstream downstream inputs for two urban tributaries River, Big Thompson St. Vrain Creek. We examined influence air temperature, discharge, distance on over period (December–February). The were also used predict absence based predictions 2052 2082. Effluent was largest driver effluent, while impact comparatively small. Streams cooled after an initially sharp increase, though still predicted be ∼2°C greater than they would at ∼0.5 km. Predicted temperatures 2082 had a negligible effect suggesting mitigating is key protecting thermal regimes effluent-impacted rivers. Our gain insight into small streams provide baseline other watersheds larger scales.