Fig. 4: Temperature dependence of diffusive CH₄ emissions.

a, The relationship of water temperature with measured diffusive CH₄ emissions in GRiMeDB¹³ coloured by latitude. The solid coloured lines are linear fits for sites that have more than 20 observations and the black solid line is the linear model for all data. The dashed black line represents the slope from the average activation energy of other aquatic systems from ref. ¹. The x axis shows the standardized temperature following ref. ¹, where k is the Boltzmann constant, T is the water temperature in kelvin and T_c is 15 °C. The colour scale shows the absolute values of latitudinal decimal degrees. b, A kernel density plot (y axis represents the relative number of observations) of the apparent activation energy—that is, the slope of the lines in a—for rivers (this study) and other freshwater systems compiled in ref. ¹. The vertical dashed line shows the zero x intercept.