Partial pressures of CO2, O2, N2, and Ar were monitored at two locations in the Ogallala aquifer system on the Southern High Plains of Texas. Samples were collected monthly during parts of 1980–1981 from nine depths ranging from 0.6 to 36 meters below land surface. PCO2 was observed to be greater at depth than in the active soil zone and thus appears to contradict the normal process in which CO2 is generated in the soil zone and diffuses upward to the atmosphere and downward to the water table. The δ13C of the CO2 gas was quite uniform and averaged −17.9 per mil. PO2 declined with depth, suggesting in situ generation of CO2 by the oxidation of carbon. Several hypotheses were considered to explain the origin of the CO2 at depth. It was concluded that the most probable hypothesis was that dissolved and particulate organic carbon introduced by recharging water was oxidized to CO2 by the aerobic microbial community that utilized oxygen diffusing in from the atmosphere. This hypothesis is consistent with the CO2 concentration profile, calculated production profile of CO2, δ13C values of CO2 gas, caliche, soil humic acid fraction, and dissolved carbonate in groundwater. The abundance of CO2, its concentration profile, and its probable origin provide information for evaluating the observed complex sequence of caliche dissolution and precipitation known to occur in the aquifer.
Additional publication details
|Publication Subtype||Journal Article|
|Title||Origin and distribution of carbon dioxide in the unsaturated zone of the southern High Plains of Texas|
|Series title||Water Resources Research|
|Publisher||American Geophysical Union|
|Contributing office(s)||Toxic Substances Hydrology Program|
|Other Geospatial||Southern High Plains|