Dynamic contribution by aquatic metabolism to carbon dioxide emissions from a low‐land mixed land‐use catchment

Abstract

Carbon dioxide (CO ₂ ) emissions from streams are globally significant despite their limited areal extent and rival those from terrestrial ecosystems. Agricultural land represents 40% of the world's landmass; still, the magnitude and source dynamics of CO ₂ emissions from streams draining agricultural‐influenced landscapes are poorly understood. We used high‐frequency measurements of CO ₂ and dissolved oxygen in a temperate low‐land mixed land‐use catchment (21% agricultural) to estimate emissions and the contribution of in‐stream metabolism. Although CO ₂ concentrations were high (median 3520 μ atm), emissions were relatively low (median 4.0 g C m ² day ⁻¹ ) due to consistently low gas transfer velocities ( k ₆₀₀ ). In‐stream metabolism accounted for 46% of the emissions on average, which was higher than expected for a third‐order stream. Emissions peaked during late summer despite low k ₆₀₀ . Emissions were instead driven by high CO ₂ concentrations, highlighting the importance of CO ₂ supply over physical drivers. We show that low‐elevation human‐impacted streams exhibit distinct emission dynamics, underscoring the need to account for biological drivers in carbon budgets for these landscapes.