Bacterial metabolism and the δ¹³C composition of ground water, Floridan aquifer system, South Carolina Available to Purchase

Viable bacteria are present (10⁵-10⁷ cells per gram sediment) in the clastic water-table and Hawthorn aquifers that overlie and recharge the Floridan aquifer near Hilton Head Island, South Carolina. Incubation of cored sediments shows that indigenous bacteria are capable of producing carbon dioxide (CO₂) as they metabolize sedimentary organic material. Estimated in situ CO₂ production rates, based on dissolved inorganic carbon (DIC) changes and ground-water flow rates, are in the range of 10^-2 mmol . L^-1, yr^-1.

Two independent lines of evidence, (1) isotope balance calculations on DIC along ground-water flow paths and (2) direct measurement of the isotopic composition of CO₂produced by incubation of Hawthorn sediment, suggest that bacterially produced CO₂ in the Hawthorn aquifer is much heavier isotopically (δ¹³C ∼ -10‰ to -15‰) than associated sedimentary organic material (δ¹³C ∼ -21‰). The relatively heavy δ¹³C values of DIC in water from the Floridan aquifer, which receives much of its recharge from the overlying Hawthorn, reflect this source of isotopically heavy CO₂.