Isotopic fractionation associated to nitrate attenuation by ferrous iron containing minerals

Abstract

Biotic and abiotic laboratory experiments of nitrate and nitrite reduction by Fe-containing minerals were performed and the isotopic fractionation of the different reactions was calculated in order to determine whether it is possible to distinguish biotic and abiotic reactions involving N compounds. Results of biotic experiments showed nitrate reduction up to 96 % with transient NO2- accumulation and no significant N2O production. No significant nitrate attenuation was observed in abiotic nitrate reduction experiments. Abiotic experiments of nitrite reduction showed a rapid decrease in nitrite concentrations in those experiments with added Fe2+ coupled with a significant N2O production. Preliminary results of the N and O isotopic fractionation of the biotic experiments of nitrate reduction show differences in the ε15NNO3 and ε18ONO3 when different minerals were added. The abiotic experiments of nitrite reduction contrarily, showed similar ε15NNO2 in all the experiments.