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Analysis of 15N-NO3 Via Anoxic Slurries Coupled to MIMS Analysis: An Application to Estimate Nitrification by Burrowing Macrofauna

Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124 Parma, Italy
Facultad de Minas, OCEANICOS, Universidad Nacional de Colombia, Medellín 050036, Colombia
Department of Life Sciences and Biotechnology, University of Ferrara, 44121 Ferrara, Italy
Marine Science and Technology Center, University of Klaipeda, 92294 Klaipeda, Lithuania
Author to whom correspondence should be addressed.
Water 2019, 11(11), 2310;
Received: 19 September 2019 / Revised: 27 October 2019 / Accepted: 1 November 2019 / Published: 4 November 2019
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
The increasing use of the stable isotope 15N-NO3 for the quantification of ecological processes requires analytical approaches able to distinguish between labelled and unlabeled N forms. We present a method coupling anoxic sediment slurries and membrane inlet mass spectrometry to quantify dissolved 15N-NO3 and 14N-NO3. The approach is based on the microbial reduction of 14N-NO3 and 15N-NO3 mixed pool, the determination of the produced 29N2 and 30N2, and the calculation of the original 15N-NO3 and 14N-NO3 concentrations. The reduction is carried out in 12 mL exetainers containing 2 mL of sediment and 10 mL of water, under anoxia. To validate this approach, we prepared multiple standard solutions containing 15N-NO3 alone or in combinations with 14N-NO3, with final concentrations varying from 0.5 to 3000 µM. We recovered nearly 90% of the initial 14N-NO3 or 15N-NO3, over a wide range of concentrations and isotope ratios in the standards. We applied this method to a 15N-NO3 dilution experiment targeting the measurement of nitrification in sediments with and without the burrower Sparganophilus tamesis. The oligochaete did not stimulate nitrification, likely due to limited ventilation and unfavorable conditions for nitrifiers growth. The proposed method is reliable, fast, and could be applied to multiple ecological studies.
Keywords: 15N-NO3, slurry; denitrification; MIMS; nitrification; Sparganophilus tamesis 15N-NO3, slurry; denitrification; MIMS; nitrification; Sparganophilus tamesis
MDPI and ACS Style

Carpintero Moraes, P.; Arroyave Gòmez, D.M.; Vincenzi, F.; Castaldelli, G.; Fano, E.A.; Bartoli, M.; Benelli, S. Analysis of 15N-NO3 Via Anoxic Slurries Coupled to MIMS Analysis: An Application to Estimate Nitrification by Burrowing Macrofauna. Water 2019, 11, 2310.

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