Alternative Reference Frames in River System Science

Understanding environmental processes begins with mental conceptualizations of system components and interactions. Conceptualizing rivers begins with adopting one of two reference frames for observing movement: Eulerian, wherein the flux of objects is observed in a spatially bounded area, or Lagrangian, wherein specific objects are tracked through time. Mechanistic studies include Eulerian and Lagrangian data, with some negotiation of how much Eulerian and Lagrangian information may be needed to maximize the accuracy of understanding processes and the efficiency of data collection. Most studies rely on a presupposed reference frame, yet we suspect breakthroughs lurk in explicit alterations of presupposed reference frames. We analyze the importance of reference frames by contrasting the extent to which alternative reference frames have been used and combined in studies of sediment transport, fish migration, and river biogeochemistry. We show how adopting alternative or nonintuitive reference frames can facilitate novel research questions and observations, potentially triggering new research trajectories.