Contribution of a Headwater Stream to the Global Carbon Budget

The carbon cycle has been subject of numerous studies in recent years, primarily due to the role of CO₂ and CH₄ in global warming. Understanding the components and processes contributing to the global carbon cycle across a landscape is essential to understand climate change drivers and predicting future climate. Although the role of streams and rivers in transporting and processing nutrients from the land to the ocean has been widely recognized, most climate models still consider riverine systems as mere conduits without processing capacity. Evasion of carbon dioxide from inland waters has only been recently acknowledged to be an important source of carbon to the atmosphere and still, these estimations don’t take into account evasion from headwater streams due to a lack of data. Here we present a 10-year C budget for a small headwater stream draining a 96-ha watershed in western Oregon, USA. This stream exported ~5000 g C per m² of stream area, approximately 9% of the ecosystem production of the catchment (NEP). Export is dominated by evasion of CO₂ to the atmosphere (~2200 g C per m²/y) and by downstream transport of dissolved inorganic carbon (DIC, ~1300 g per m²/y). Although highest in-stream pCO₂ and DIC concentrations happen during summer low-flows, most stream export happens during winter high flows indicating at least a seasonal lag between CO₂ production (i.e., respiration) and carbon export.