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This study focuses on characterizing the contributions of key terrestrial pathways that deliver dissolved organic carbon (DOC) to streams during hydrological events and on elucidating factors governing variation in water and DOC fluxes from these pathways. We made high‐frequency measurements of discharge, specific conductance (SC), and fluorescent dissolved organic matter (FDOM) during 221 events recorded over 2 years within four Vermont (USA) watersheds that range in area from 0.4 to 139 km². Using the SC measurements, together with statistical information on discharge, we separated the event hydrographs into contributions from three terrestrial pathways, which we refer to as riparian quickflow, subsurface quickflow, and slow‐flow groundwater. The pathway discharges were used as input to a mixing model that closely approximated sub‐hourly streamwater DOC concentrations as measured with the FDOM sensors. Subsurface quickflow, comprised of pre‐event water, was the leading contributor to streamwater DOC fluxes, while riparian quickflow, comprised of event water, was the second‐leading contributor to streamwater DOC fluxes, despite comprising the smallest proportion of streamflow yield among the three end‐member pathways. Fixed‐effects regression analysis revealed that the relationship between DOC fluxes from the end‐member pathways and event magnitude was consistent across the four watersheds. This analysis also showed that DOC fluxes from the quickflow pathways increased significantly with temperature and varied inversely, but weakly, with catchment antecedent wetness. We believe that our approach, which leverages in‐stream sensors that enable high‐frequency measurements over extended periods, may be applicable for evaluating controls on DOC export from other watersheds within and beyond our study region.

Streams and rivers are significant sources of carbon dioxide (CO₂) and methane (CH₄) to the atmosphere. However, the magnitudes of these fluxes are uncertain, in part, because dissolved greenhouse gases (GHGs) can exhibit high spatiotemporal variability. Concentration‐discharge (C‐Q) relationships are commonly used to describe temporal variability stemming from hydrologic controls on solute production and transport. This study assesses how the partial pressures of two GHGs—pCO₂andpCH₄—vary across hydrologic conditions over 4 yr in eight nested streams and rivers, at both annual and seasonal timescales. Overall, the range ofpCO₂was constrained, ranging from undersaturated to nine times oversaturated, whilepCH₄was highly variable, ranging from 3 to 500 times oversaturated. We show thatpCO₂exhibited chemostatic behavior (i.e., no change withQ), in part, due to carbonate buffering and seasonally specific storm responses. In contrast, we show thatpCH₄generally exhibited source limitation (i.e., a negative relationship withQ), which we attribute to temperature‐mediated production. However,pCH₄exhibited chemostasis in a wetland‐draining stream, likely due to hydrologic connection to the CH₄‐rich wetland. These findings have implications for CO₂and CH₄fluxes, which are controlled by concentrations and gas transfer velocities. At highQ, enhanced gas transfer velocity acts on a relatively constant CO₂stock but on a diminishing CH₄stock. In other words, CO₂fluxes increase withQ, while CH₄fluxes are modulated by the divergentQdynamics of gas transfer velocity and concentration.