Jase Hixson, Adam Scott Ward , Christina Remucal , Megan McConville

Predicting environmental fate requires an understanding of the underlying, spatiotemporally variable interaction of transport and transformation processes. Photolytic compounds, for example, interact with both time-variable photolysis and the perennially dark hyporheic zone, generating potentially unexpected dynamics that arise from time-variable reactivity. This interaction has been found to significantly impact environmental fate but is commonly oversimplified in predictive models. Our primary objective was to explore how time-variable photolysis and hyporheic storage interact across a range of photolysis rates to control the fate and transport of photolytic solutes in stream-hyporheic systems. In this study, we simulated variable release timing and durations of photolytic compounds spanning half-lives of 2.8 minutes to 908 hours. To contextualize these results, we interpret results 3-trifluoromethyl-4-nitrophenol (TFM), as its photolysis rate is controlled by environmental conditions and is known to vary by several orders of magnitude. Ultimately, we found the environmental fate and transport of photolytic compounds is highly variable as a function of release timing, which controls when, where, and for how long solute is stored in the hyporheic zone or exposed to in-channel photolysis. This knowledge can be used to improve predictions for photolytic compounds or assess potential impacts for an anticipated discharge or treatment.