Isotopic fractionation associated to nitrate attenuation by ferrous iron containing minerals

¹ Grup MAIMA, SGR Mineralogia Aplicada, Geoquímica i Geomicrobiologia, Departament de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona (UB), Martí i Franquès s/n, 08020 Barcelona (Spain)
² Serra Húnter Fellowship, Generalitat de Catalunya, Spain

^* Corresponding author: notero@ub.edu

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 NO_2^- 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 ε¹⁵N_NO3 and ε¹⁸O_NO3 when different minerals were added. The abiotic experiments of nitrite reduction contrarily, showed similar ε¹⁵NNO2 in all the experiments.