Fig. 3. CO₂ levels are highly variable among African lakes and patterns depend on primary production.

Surface water pCO₂ in several African tropical lakes versus pelagic aquatic primary production (A), Chl-a concentration (B), oxygen saturation level (%O₂) (C), cyanobacteria abundance (D), carbon stable isotope composition of dissolved inorganic carbon (δ¹³C-DIC) (E), DOC (F), water temperature (G), and CDOM SR (H). Dotted lines and solid lines as in Fig. 2. The black dotted line gives the relation of pCO₂ versus DOC from a global dataset (2), while the black dotted line in the inset gives the relation of pCO₂ versus temperature from a dataset of tropical lakes (9). For lakes where multiple measurements were made, the symbol shows the median (n indicates the number of pCO₂ measurements).