MEASURING INORGANIC CARBON FLUXES FROM CARBONATE MINERAL WEATHERING FROM LARGE RIVER BASINS: THE OHIO RIVER BASIN

Rising atmospheric CO₂ concentrations have motivated efforts to better quantify reservoirs and fluxes of Earth’s carbon. Of these fluxes from the atmosphere, one that has received relatively little attention is the atmospheric carbon sink associated with carbonate mineral dissolution. Osterhoudt (2014) and Salley (2016) explored new normalization techniques to improve and standardize a process for measuring this flux over large river basins. The present work extends this work to the 490,600 km² Ohio River drainage basin and 11 subbasins. The study estimated the DIC flux leaving these basins between October 1, 2013 and September 30, 2014 based on secondary hydrogeochemical, geologic, and climatic data. The total annual DIC flux for the Ohio River basin was estimated to be 7.54 x 10¹² g carbon (C). The time-volume normalized value of DIC flux for the Ohio basin was 3.36 x 10⁸ g C/km³ day, where the km³ refers to the amount of water available during the year. This was within 71.4% agreement of that of the Barren River (Salley, 2016) and within 63.9% agreement of that for the Green River (Osterhoudt, 2014). In general, normalized DIC flux values of sub-basins containing at least modest amounts (more than 8%) of exposed carbonates (Tennessee, Cumberland, Green, Kentucky, Licking, Monongahela, and Allegheny) were in strong agreement with the normalized DIC flux of the Ohio River basin, whereas inclusion of basins with little or no near surface carbonates (Wabash, Great Miami, Scioto and Kanawha) yielded poor agreement. Regression analysis yielded strong agreement between DIC flux and the normalization parameters for the carbonate-bearing sub-basins (R² = 0.97, p = <0.001). Therefore, the normalization procedure appears to be an effective means of estimating DIC flux where surface carbonates serve as the primary source of alkalinity, even though these can constitute even a relatively small percentage of rock outcrop area. However, the normalization technique does not appear to be as effective among basins that do not receive alkalinity from interactions with surface carbonates. Additional study is required to refine this technique to become more broadly applicable in generating estimates of atmospheric C flux from carbonate mineral weathering processes.