Heat transport in dynamically-changing hyporheic zones

Understanding heat transport within hyporheic zones and its implications for flow and biogeochemical processes is critical for river management and habitat restoration. In this study, we use a reduced-order model to simulate fully-coupled hyporheic flow and heat transport driven by dynamic discharge events. A systematic analysis of discharge and temperature time series along the Mississippi River Basin were used to propose a series of generic scenarios constrained by observations in a real fluvial system. Our results indicate that the heat transport strongly affects the dynamic response of hyporheic zones to stage fluctuations. We also find that the correlation between channel discharge and temperature play an important role in the exchange process. For example, thermal dampening is maximum when heat and stage fluctuations are synchronized. Similarly, we observe that changes in density and viscosity, caused by temperature variability, result in enhanced hyporheic exchange fluxes and larger extent and penetration of hyporheic zones. This work has important implications for understanding local variability in hyporheic exchange and its implications for thermal refugia and ecosystem functioning. Moreover, it highlights a critical process that is needed to up-scale hyporheic exchange processes to the reach and catchment scales.