Anthropogenic activities significantly increase annual 1 greenhouse gas (GHG) fluxes from temperate headwater 2 streams in Germany 3

18 Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; 19 CO 2 , CH 4, and N 2 O) budgets, yet the mechanisms driving these increases are still not well constrained. In this 20 study, we quantified year-long GHG concentrations and fluxes, as well as water physico-chemical variables from 21 23 streams, 3 ditches, and 2 wastewater inflow sites across five headwater catchments in Germany contrasted by 22 land use. Using mixed-effects models, we determined the overall impact of land use and seasonality on the intra- 23 annual variabilities of these parameters. We found that land use was more significant than seasonality in 24 controlling the intra-annual variability of GHG concentrations and fluxes. Agricultural land use and wastewater 25 inflows

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