Stream metabolism sources a large fraction of carbon dioxide to the atmosphere in two hydrologically contrasting headwater streams

Headwater streams are control points for carbon dioxide (CO2) emissions to the atmosphere, with relative contributions CO2 emission fluxes from lateral groundwater inputs widely assumed overwhelm those in-stream metabolic processes. We analyzed continuous measurements of stream dissolved and oxygen (O2) concentrations during spring early summer in two Mediterranean headwater which we evaluated contribution net ecosystem production (NEP) emission. The exhibited contrasting hydrological regimes: one was non-perennial relatively small inflows, while other perennial received significant inputs. strong inverse coupling between instantaneous daily O2 concentrations, a correlation aerobic respiration (ER) gross primary (GPP) despite persistent negative NEP. At stream, CO2–O2 relationship varied largely over time, ER GPP were uncorrelated, NEP, consistently negative, increased increasing temperature. Mean NEP 51% 57% at respectively. Although these proportions assumptions about stoichiometry concentration, substantially contributed total atmospheric flux both streams. conclude that metabolism can be more important driving C cycling some than previously assumed.