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, caliche, soil humic acid fraction, and dissolved carbonate in groundwater.-from Authors
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Origin and distribution of carbon dioxide in the unsaturated zone of the southern High Plains of Texas.