Evidence of partial denitrification during ground-water recharge, Southern High Plains, Texas

Comparison of data from several playas on the Southern High Plains suggests a correlation between extractable NO₃^- concentrations in sediments and land use. Highest concentrations are associated with discharge of human and animal wastes, and the lowest with runoff from uncultivated lands. NO₃^- concentrations, typically highest within 1 m of the playa surface, exhibit secondary peaks with depth; concentrations within the top meter tend to increase with proximity to points of wastewater discharge. Results from two playas (Playa 5 and Pantex Lake) indicate that counts of denitrifying bacteria decrease within 5 m of land surface. Although more numerous populations of denitrifying bacteria at Playa 5 may result from relatively recent wastewater discharge, contamination of the Ogallala aquifer beneath Playa 5 suggests that denitrification may only partly reduce NO₃^- concentrations in wastewater discharged to playas.