Isotopic fractionation associated to nitrate attenuation by ferrous iron containing minerals

Rosanna Margalef-Marti,Albert Soler,Neus Otero,Raul Carrey,O Chudaev,O Shouakar-Stash,R Millot,Y Kharaka,R Harmon

doi:10.1051/e3sconf/20199812013

Rosanna Margalef-Marti, Albert Soler + Show 7 more

Open Access

https://doi.org/10.1051/e3sconf/20199812013

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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.

Highlights

Numerous studies have pointed to the coexistence of biotic and abiotic reactions involving the N and Fe biogeochemical cycles in natural environments [1, 2]
As the enzymatic Fe2+ oxidation by NO3- dependent Fe2+ oxidation (NDFO) microorganisms has not yet been proven, it is unknown whether the Fe2+ oxidation is caused by an enzymatic activity, due to an abiotic reaction mediated by N intermediates from denitrification or a combination of both [1, 5, 6]
Transient NO2- accumulation and no significant N2O production were observed in all the biotic experiments

Summary

Introduction

Numerous studies have pointed to the coexistence of biotic and abiotic reactions involving the N and Fe biogeochemical cycles in natural environments [1, 2]. The NO2- reduction by Fe2+ oxidation has been well documented [3,4]. Fe2+ minerals have been suggested to enhance biotic denitrification through the NO3- dependent Fe2+ oxidation (NDFO) process, which is still not well constrained [5]. As the enzymatic Fe2+ oxidation by NDFO microorganisms has not yet been proven, it is unknown whether the Fe2+ oxidation is caused by an enzymatic activity, due to an abiotic reaction mediated by N intermediates from denitrification or a combination of both [1, 5, 6]. The same pattern is expected throughout the reduction of all N intermediate products

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