Soil CO ₂ Controls Short‐Term Variation but Climate Regulates Long‐Term Mean of Riverine Inorganic Carbon

The evasion of CO2 from inland waters, a major carbon source to the atmosphere, depends on dissolved inorganic (DIC) concentrations. Our understanding DIC dynamics across gradients climate, geology, and vegetation conditions however have remained elusive. To understand its large-scale patterns drivers, we collated instantaneous mean (multiyear average) concentrations about 100 rivers draining minimally-impacted watersheds in contiguous United States. Within individual sites, (C) measured at daily seasonal scales exhibit near-universal response changes river discharge (Q) negative power law form. High occur low when DIC-enriched groundwater dominates discharge; under high flow relatively DIC-poor shallow soil water predominates discharge. Such echo widely observed increase with depth shallow-and-deep hypothesis that emphasizes importance paths chemistry. Across (Cm) decrease increasing (Qm), long-term climate measure, reachs maxima around 200 mm/yr. A parsimonious model reveals arises accumulation rates DIC-generating reactions are compared export fluxes arid climates. Although similarly discharge, results here highlight their distinct drivers: seasonal-scale concentration variations controlled by subsurface distribution over (from below), whereas regulated above). emphasize significance land-river connectivity via paths. They also underscore characterizing illuminate belowground processes order project future cycles warming climate.