Carbon dioxide and methane emissions of Swedish low‐order streams—a national estimate and lessons learnt from more than a decade of observations

Abstract Low‐order streams are suggested to dominate the atmospheric CO2 source of all inland waters. Yet, many large‐scale stream estimates suffer from methods not designed for gas emission determination and rarely include other greenhouse gases such as CH4. Here, we present a compilation of directly measured CO2 and CH4 concentration data from Swedish low‐order streams (> 1600 observations across > 500 streams) covering large climatological and land‐use gradients. These data were combined with an empirically derived gas transfer model and the characteristics of a ca. 400,000 km stream network covering the entire country. The total stream CO2 and CH4 emission corresponded to 2.7 Tg C yr−1 (95% confidence interval: 2.0–3.7) of which the CH4 accounted for 0.7% (0.02 Tg C yr−1). The study highlights the importance of low‐order streams, as well as the critical need to better represent variability in emissions and stream areal extent to constrain future stream C emission estimates.