We surveyed the carbonate system along the main channel of the Chesapeake Bay in June 2016 to elucidate carbonate dynamics and the associated sources of oxygen‐consuming organic matter. Using a two endmember mixing calculation, chemical proxies, and stoichiometry, we demonstrated that in early summer, dissolved inorganic carbon (DIC) dynamics were controlled by aerobic respiration in the water column (43%), sulfate reduction i...