CH 18 SOLUTE TRANSPORT ALONG STREAM AND RIVER NETWORKS data throughout respective basins. Thus, our current understanding of solute transport at the river network scale is limited.In this chapter, we focus on the processes that control solute transport in rivers and explore how those controls change from headwaters to higher-order streams. Fluvial geomorphologists have long studied how channel geometry and resulting hydraulics change predictably along the network continuum (Leopold and Maddock, 1953). We propose that the predictable changes in morphology and hydraulics have predictable impacts on the physical processes of stream-solute transport. This issue is critical to understanding stream ecology and contaminant transport at the network scale. For example, network-scale solute transport is important to conceptual ecological models, such as the River Continuum Concept, that propose ecosystem processes and forcing factors along streams vary systematically with location along the river due to changes in river size and connectivity to the adjacent landscape (Vannote et al., 1980;Fisher et al., 1998). Thus, we have structured this chapter to open with an introduction of solute-transport processes in streams (see Fischer et al. (1979) andRutherford (1994) for additional details). We then link these processes to morphologic and hydraulic domains within the stream network. Finally, we offer a perspective on future research foci that will improve our understanding of solute transport from headwater streams to large rivers.