| Summary: | The occurrence of dissolved oxygen concentrations of 4.4 to 7.3 milligrams per liter in ground waters from artesian aquifers within the semi-arid Upper San Pedro basin, Arizona, supports recent research documenting the occurrence of oxygenated ground waters. These findings are in conflict with earlier hypotheses postulating that dissolved oxygen in recharge waters is rapidly reduced to negligible concentrations by chemical and biochemical processes in the soil and aquifer environments. However, the reported concentrations of dissolved oxygen become theoretically plausible upon consideration of the physical, chemical, and biological processes occurring within the water-soil-aquifer complex of the study area. These processes may also be dominant factors controlling the chemistry of dissolved oxygen in the ground waters of other semi-arid basins similar to the Upper San Pedro basin.
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