Carbon Dioxide Fluxes in a Forest Soil in the Citronelle Oil Field of South Alabama: II.

Forest soils play a major role as terrestrial sources or sinks of CO₂. The main sources of soil CO₂ fluxes are decomposition of organic matter and respiration from roots and associated soil fauna. Soil is the largest terrestrial sink of atmospheric C, containing about 1500 Pg of C worldwide. Geological sinks in forest soils of south Alabama have a huge potential for sequestering billions of metric tons of CO₂ through enhanced CO₂ oil recovery (EOR). Enhanced CO₂ oil recovery offers an opportunity to safely and permanently store CO₂ in natural carbon sinks such as brine-filled geological formations and compounds such as lime (CaCO₃ and CaCO₃.MgCO₃), thereby reducing the atmospheric concentration of this greenhouse gas. In order for the concept of geological sequestration of CO₂ injected into oil wells to be environmentally sound, it is important that the CO₂ being injected into the ground will not escape back into the atmosphere. This paper discusses baseline soil CO₂ fluxes in a forest soil around five oil wells before CO₂ injection for EOR in the Citronelle Oil Field in south Alabama between August 2008 and March, 2009. Soils CO₂ fluxes at all the wells were highest in August 2008 with values ranging from 0.53 to 2.28 mg CO₂ m^-2 min^-1. These values declined significantly with decrease in soil temperatures from August 2008 to March 2009. The soil at one well was a NET sink of atmospheric CO₂ at one well in September and October, 2008 and at another well in March, 2009. Our data also show that the soils around the wells at the study location are deficient in soil C from 15cm depth and below, hence a potential for geological sequestration.