The chemistry, fluxes, and sources of carbon dioxide in the estuarine waters of the Satilla and Altamaha Rivers, Georgia

Abstract

The pH, alkalinity (Alk), and dissolved inorganic carbon (DIC) in estuarine waters of several rivers of Georgia in the southeastern United States are reported. Although they discharge into a narrow area in the South Atlantic Bight, the rivers along the coast of Georgia differ significantly in their drainage area (Piedmont rivers vs. coastal plain rivers), chemical composition (contents of carbonate and humics), and discharge rates. Large differences in pH, DIC, and Alk between these rivers clearly reflect the differences of material inputs to the rivers. Dramatic pH increases in the early stage of mixing (more obvious for the coastal plain rivers) reflect the low buffering capacity of the river waters despite the high content of humic substances. Flux of riverine DIC to the South Atlantic Bight is estimated to be 52.5 × l09 mol yr−1. We suggest that the presently available world total riverine DIC flux to the ocean could have much uncertainty if the small river fluxes are important. Calculated pC0, values from the pH and DIC measurements are extremely high in low‐salinity areas (1,000 to >6,000 patm at salinity < 10) as are the corresponding CO2 fluxes to the atmosphere (20 to >250 mol m−2 yr−1 at salinity <l0). Data presented suggest that the most likely causes that sustain the high pCO2 values and high water‐to‐air fluxes in the estuaries are CO2 inputs from organic carbon respiration in the tidally flooded salt marshes and groundwater.