Solute Export and Carbon Dioxide Trends of the Altamaha River Basin

The Altamaha River Basin (ARB), a major drainage of the Atlantic seaboard, was monitored near Jesup, Georgia, on a biweekly frequency during April 2006 through June 2007. Alkalinity, pH, temperature, and Total Dissolved Solids (TDS) were measured in the field. Geographic Information Systems and historical precipitation and stream flow were used to calculate mean annual: (1) precipitation flux into the basin; (2) runoff from the basin; (3) solute export; and (4) partial pressure of carbon dioxide (pCO2). The mean annual precipitation flux to the ARB is 46.4 km3. Runoff near the mouth of the Altamaha River is 12.1 km3 or about 26% of the precipitation input, implying that roughly three quarters of all the rain that falls on the basin is lost to evapotranspiration. The ARB has discharge-weighted average TDS concentration of 53.3 mg/L and annually exports 646,445 metric tons of dissolved solutes to the Atlantic Ocean. The pCO2 values range between close to atmospheric equilibrium in May to 106 times above atmospheric equilibrium in December. For the rising limb of the hydrograph, pCO2 trend mimics stream flow with pCO2 peak occurring about a month ahead of discharge. The low values probably indicate CO2 drawdown by aquatic photosynthesis and higher values indicate discharge of wastewater/shallow groundwater charged with bacterially respired carbon dioxide. Thus, the ARB was a net source of carbon dioxide to the atmosphere during the water year 2006-2007.