Background

In the last decade, the contribution of inland water bodies to the global carbon cycle has come into focus of climate change research. A recent estimate suggests that up to 3,000,000,000,000 kg C per year is emitted as CO2 from global inland waters, which is on similar levels as the global soil carbon sink (Raymond et al., 2013). Thus, the understanding of inland water carbon emissions and related mechanisms are of high relevance and can contribute to improving future predictions and models on the global carbon cycle. However, the data needed for accurate regional and global flux estimates are spatially and temporally sparse which highlights the requirement for high quality direct CO2 flux measurements in inland waters.

Considering all inland waters, up to 70% of the global CO2 flux is assigned to running waters (Raymond et al., 2013), identifying these systems as ”hotspots” of greenhouse gas emissions. Recent assessments of global CO2 fluxes from running waters are considerably higher than previously calculated, with an increase from 750,000,000,000-1,200,000,000,000 kg C per year (Cole et al., 2007, Battin et al., 2009) to 2,100,000,000,000-3,280,000,000,000 kg C per year (Aufdenkampe et al., 2011, Raymond et al., 2013). However, the magnitude is likely to change again caused by higher precision of large scale estimates combined with continuous improvements of methods and higher number of field measurements. First attempts were done to determine large-scale CO2 fluxes, for example, for Africa (Borges et al., 2015) and the conterminous United States (Butman and Raymond, 2011, Butman et al., 2016). However, none of these studies were able to measure CO2 fluxes directly across a whole continent with the same method and at similar timespans.

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