Relationship between the carbon isotope composition of soil CO2 and dissolved carbonate species in groundwater

Authors:
  • CRCraig T. Rightmire
    Craig T. Rightmire
  • BHBruce B. Hanshaw
    Bruce B. Hanshaw
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Abstract
To understand the carbonate geochemistry of an aquifer system, it is helpful to determine the sources of carbon in the dissolved carbonate species. Samples of ground litter, soil organic matter, soil CO2, and groundwater were collected in the area of recharge to the principal artesian aquifer of central Florida and were analyzed for 13C content. Analytical results yield consistent 13C/12C values for soil organic matter, δ13CPDB = 23 ±1‰. The 13C/12C ratio of the litter samples ranges from δ13CPDB of −18.2 to −29.5‰ and indicates the presence of both Calvin and Hatch‐Slack cycle plants. The 13C/12C of the soil CO2 ranges from −14.7 to −21.3‰, which is consistent with the trend observed in the litter. The relationship between 13C/12C of the dissolved carbonate and the percent calcite saturation indicates that the δ13CPDB of the source CO2 is within the range of −25 ± 5‰, as is expected for a humid, subtropical environment.

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