Effects of Bacteria on Nitrate and Nitrite Concentrations in Groundwater of the Ogallala Aquifer

The Ogallala Aquifer of the eastern High Plains of New Mexico has been examined for groundwater contamination. Previous studies have indicated the presence of numerous bacteria and many insidious chemical species. The origin of some contaminants were obvious (e.g. coliforms and fecal coliforms). High levels of nitrate concentration were resolved with the probable origin being 1 and application of fertilizer or leaching from septic sewage systems. The life span of the nitrate contamination in the Ogallala, however, has always been short-lived, and quite variable between sampling intervals. Determining cause of the observed variation was an objective of this investigation. Nitrate ions can be converted to nitrite ions through microbial action. An inverse variation between these two chemical contaminants would indicate a microbial conversion, while directly proportional variation would be indicative of a chemical cause.

The potential microbial responsibility for the fluctuations in nitrate and nitrite ions was examined in this project. Fluctuations were observed to be inversely proportional . Coliforms were not sufficiently numerous to explain the rapidity of the fluctuations. Consequently, the presence and quantitation of other nitrate-reducing organisms were determined.

Large numbers of bacteria were found which were capable of reducing nitrate. Their numbers fluctuated in direct proportion to the observed nitrate concentrations. Nitrate concentrations, regardless of source, were short-lived, highly variable, and were apparently reduced as a result of microbial populations, other than coliforms, occurring in the Ogallala Aquifer.

Project No. 1345630