wAbstract
@In batch experiments, we studied the isotope fractionation of
nitrogen and oxygen during denitrification of two bacterial strains
(Azoarcus sp. strain DSM 9056 and Pseudomonas pseudoalcaligenes
strain F10). Denitrification experiments were conducted with succinate
and toluene as electron donor in three waters with a distinct
oxygen isotope composition. Nitrate consumption was observed in
all batch experiments. Reaction rates for succinate experiments
were more than six times higher than those for toluene experiments.
nitrogen and oxygen isotopes became progressively enriched in
the remaining nitrate pool in the course of the experiments; the
nitrogen and oxygen isotope fractionation varied between 8.6-16.2
and 4.0-7.3ρ, respectively. Within this range, neither electron
donors nor the oxygen isotope composition of the medium affected
the isotope fractionation process. The experimental results provide
evidence that the oxygen isotope fractionation during nitrate
reduction is controlled by a kinetic isotope effect which can
be quantified using the Rayleigh model. The isotopic examination
of nitrite released upon denitrification revealed that nitrogen
isotope fractionation largely follows the fractionation of the
nitrate pool. However, the oxygen isotope values of nitrite are
clearly influenced by a rapid isotope equilibration with the oxygen
of the ambient water. Even though this equilibration may in part
be due to storage, it shows that under certain natural conditions
(re-oxidation of nitrite) the nitrate pool may also be indirectly
affected by an isotope equilibration.
Keywords: Nitrate; Nitrite; Denitrification; Nitrogen isotopes;
Oxygen isotopes; Kinetic isotope fractionation; Isotope exchangex
Introduction
Experimental settings and methods
@Batch experiments
@Chemical and isotope analyses
Results and discussion
@Nitrate reduction in batch experiments
@Nitrogen isotope fractionation during denitrification
@Oxygen isotope fractionation during denitrification
Summary and conclusions
Acknowledgements
References