Origin and distribution of soil nitrates on the Nevada Test Site

Abstract

Unusually high nitrate concentrations were found in soils of Yucca and Frenchman Flats. A maximum concentration of 11,100 mg/kg was found within the 2-6 inch soil depth on Frenchman playa. Maximum nitrate concentrations in the playa soils generally occurred within the 6 inch to 2 foot soil depth. The maxima for all playa sampling sites averaged 4,693 mg/kg nitrate. Soils from the bajada had lower nitrate concentrations, with an average maximum concentration of 588 mg/kg. Nitrogen fixation by blue-green algae was found to occur at 79 percent of the randomly chosen sample sites. Under optimum laboratory conditions nitrogen fixation ranged from 4.1 to 46,100g N2/acre/day. Average nitrogen fixation in soil cores was 359g N2/acre/day whereas, the average fixation by algal crusts was 5,527g N2/acre/day. Where nitrate was found to accumulate there was generally an associated decrease in the pH of the soil (from about 9.0 to 7.0) possibly indicating the oxidation of atmospheric nitrogen fixed by algae to nitrate by Nitrosomonas and Nitrobacter.