Modeling the Effects of Turbulence on Hyporheic Exchange and Local‐to‐Global Nutrient Processing in Streams

New experimental techniques are allowing, for the first time, direct visualization of mass and momentum transport across the sediment‐water interface in streams. These experimental insights are catalyzing a renaissance in our understanding of the role stream turbulence plays in a host of critical ecosystem services, including nutrient cycling. In this commentary, we briefly review the nature of stream turbulence and its role in hyporheic exchange and nutrient cycling in streams. A simple process‐based model, borrowed from biochemical engineering, provides the link between empirical relationships for grain‐scale turbulent mixing and nutrient processing at reach, catchment, continental, and global scales.

Streams transport excess nitrogen and phosphorous from point and non‐point sources in a watershed to downstream receiving waters. But streams are not pipes. Microorganisms living in streambed sediments catalyze a broad range of redox reactions that reduce the impacts of nutrient pollution, or in some cases exacerbate it. In this commentary we discuss recent advances in our understanding of how turbulence influences the transport and biogeochemical processing of nutrients in streambed sediments, and explore how these concepts might be incorporated into stream network models of nutrient fate and transport at local‐to‐global scales.