Program

The combined effects of anthropogenic and biological carbon dioxide (CO₂) inputs may lead to a much greater pH decrease in coastal than open ocean waters, due to eutrophication and subsequent respiration and oxygen depletion in bottom environments withpotential detrimental effects on organisms and ecosystems. How redox reactions in coastal waters would contribute to acidification, however, is not clear. Here we report estuarine acidification based on oxygen (O₂), hydrogen sulfide (H₂S), pH, dissolved inorganic carbon (DIC) and total alkalinity (TA) data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia,and low pH over the past half century. We show that a pH minimum occurs in the low O₂water where acids are generated as a result of H₂Soxidation in watersmixed upward from the deep depths. Our analyses also suggest a large synergistic effect from river-ocean mixing, global and localCO₂ uptake from the atmosphere, and CO₂ and acid production from respiration and redox reactions.Together they lead to a pooracid buffer capacity and the observed acidification and carbonate mineral dissolution in the largest bay in the United States and likely estuaries elsewhere in the world.