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Online measurement of denitrification rates in aquifer samples by an approach coupling an automated sampling and calibration unit to a membrane inlet mass spectrometry system
Author(s) -
Eschenbach Wolfram,
Well Reinhard
Publication year - 2011
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.5066
Subject(s) - denitrification , chemistry , mass spectrometry , tracer , inlet , aquifer , nitrate , isotope ratio mass spectrometry , environmental chemistry , analytical chemistry (journal) , groundwater , nitrogen , chromatography , geotechnical engineering , geology , physics , organic chemistry , geomorphology , nuclear physics
Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N‐fluxes within these anthropogenic ecosystems. Here, a newly developed automated online 15 N‐tracer system is presented for measuring (N 2 +N 2 O) production due to denitrification in aquifer samples. The system consists of a self‐developed sampler which automatically supplies sample aliquots to a membrane‐inlet mass spectrometer. The developed system has been evaluated by a 15 N‐nitrate tracer incubation experiment using samples (sulphidic and non‐sulphidic) from the aquifer of the Fuhrberger Feld in northern Germany. It is shown that the membrane‐inlet mass spectrometry (MIMS) system successfully enabled nearly unattended measurement of (N 2 +N 2 O) production within a range of 10 to 3300 µg N L –1 over 7 days of incubation. The automated online approach provided results in good agreement with simultaneous measurements obtained with the well‐established offline approach using isotope ratio mass spectrometry (IRMS). In addition, three different 15 N‐aided mathematical approaches have been evaluated for their suitability to analyse the MIMS raw data under the given experimental conditions. Two approaches, which rely on the measurement of 28 N 2 , 29 N 2 and 30 N 2 , exhibit the best reliability in the case of a clear 15 N enrichment of evolved denitrification gases. The third approach, which uses only the ratio of 29 N 2 / 28 N 2 , overestimates the concentration of labelled denitrification products under these conditions. By contrast, at low 15 N enrichments and low fractions of denitrified gas, the latter approach is on a par with the other two approaches. Finally, it can be concluded that the newly developed system represents a comprehensive and simply applicable tool for the determination of denitrification in aquifers. Copyright © 2011 John Wiley & Sons, Ltd.