Award: OCE-0961825

This project looked at the role of river input in altering pH and controlling carbonate mineral saturation states in Casco Bay Estuary, Gulf of Maine. In addition, we evaluated the role of sediment geochemistry on the recruitment success of small, commercially important bivalves (the soft shell clam, Mya arenaria) in a mud flat in the estuary. Through both field and laboratory work we showed that river input significantly depresses the buffering capacity of the recieving water, lowering carbonate saturation states to levels which impart significant stress on planktonic clam larvae. We also showed that surface sediments in coastal mud flats of Maine are sites of intense carbonate minerral dissolution due to the production of metabolic acids. Small clams can actually dissolve in some regions. Further offshore we document the tight coupling of CO2 consumption and production in surface and bottom water, respectively, and the associated changes in saturation state in these distinct zones during summer-time water column stratification. During summer, photosynthesis in the photic zone consumes CO2, raising both pH and saturation states. This occurs during the time when larval clams are in the surface water and may provide for thermodynamically favorable conditions for their growth and survivorship. Conversely, the bottom water, decoupled from the surface water due to the formation of a strong thermocline, shows a corresponding significant increase in CO2 and decreases in pH and saturations states, making these waters far less thermodynamically favorable to carbonate bearing fauna. Turnover during spring and fall homogenizes the chemistry of the water column. Last Modified: 08/16/2014 Submitted by: Mark A Green