Headwater stream networks dynamically expand and contract in response to precipitation inputs and periods of drought. Climate-mediated changes in patterns of network expansion and contraction have the potential to interact with material processing within headwater networks and change material export to downstream waters. We hypothesized that headwaters in more arid settings would have higher and more variable influence on outlet solute exports over time because dynamic expansion and contraction connects the stream network to varied solute sources and sinks. To test this hypothesis, we used coordinated monthly synoptic campaigns and ecohydrological metrics across five headwater catchments to capture spatial and temporal variability in headwater contributions to downstream exports. Our sites span the United States’ cross-continental aridity gradient and include headwater watersheds in New Hampshire, Alabama, Arkansas, New Mexico, and Nevada. Preliminary results support our hypothesis that headwaters in more arid settings have more variable influence on solute exports at watershed outlets. However, whether this variability corresponds to stream network expansion and contraction dynamics remains unclear. Continuing work across our hydro-biogeochemical observatory network and complementary hydrologic model development aim to provide predictive models of the spatial patterns of changing headwater network structure, determine how these spatial patterns influence material fluxes, and explore how dynamic expansion and contraction controls the scaling behavior of material export from headwaters.