Carbon emissions from rivers may be underestimated: evidence from European drying networks

Rivers receive substantial amounts of terrestrial organic carbon and a large fraction is released as CO 2 or CH 4 to the atmosphere. Global estimates of CO 2 or CH 4 emissions from inland waters are based on perennial rivers, although more than half of the global river length is prone to flow intermittence (lacking flowing water part of the year). The contraction of the flowing phase, with final fragmentation of river networks by drying of non-perennial reaches, can reduce or promote emissions at the local-(river reach) or regional-(river network) scale. We quantified CO 2 and CH 4 emissions from flowing water and dry riverbeds across six European drying river networks (DRNs, 120 reaches) and three seasons providing a unique dataset with 443 measurements. We identified drivers of emissions among local and regional variables and metrics describing local drying patterns and network-scale fragmentation. We also upscaled net CO 2 emissions to the 6 DRNs and annual timescale. CO 2 and CH 4 emissions from flowing water in non-perennial reaches were affected by drying severity indicating a legacy effect, even after flow resumption. At the network scale, dry riverbeds contributed to annual emissions up to 77%, indicating an urgent need to include non-perennial rivers when assessing global greenhouse gas emissions.