Enhanced total carbon in runoff following rewetting of drained boreal and hemi‐boreal wetlands

Abstract Rewetting of drained wetlands is promoted as an efficient nature‐based solution to combat multiple environmental challenges. Yet, how rewetting influences the total lateral carbon export via runoff across diverse landscapes is rarely studied. Here we show by paired (rewetted/drained) sampling of 66 wetlands along a large geographical‐ and climatic range of boreal and hemi‐boreal Sweden that rewetted sites had higher (on average 1.5–5.5 times) runoff concentrations of all major carbon forms (total organic carbon [TOC], carbon dioxide [CO 2 ], and methane [CH 4 ]) than drained sites. While the rewetting effect varied considerably across site pairs, the effects on TOC and CO 2 were weakly related (negatively) to aquatic carbon to nitrogen ratio (C/N) and latitude, though only during autumn season. No such relationship was observed for CH 4 , regardless of season. These findings suggest that rewetting enhances lateral carbon export, with potential implications for climate benefit assessments and downstream water quality.