title: Error assessment of nitrogen and oxygen isotope ratios of nitrate as determined via the bacterial denitrification method.
abstract: Currently, bacterial denitrification is becoming the accepted method for delta(15)N- and delta(18)O-NO(3)(-) determination. However, proper correction methods with international references (USGS32, USGS34 and USGS35) are needed. As a consequence, it is important to realize that the corrected isotope values are derived from a combination of several other measurements with associated uncertainties. Therefore, it is necessary to consider the propagated uncertainty on the final isotope value. This study demonstrates how to correctly estimate the uncertainty on corrected delta(15)N- and delta(18)O-NO(3)(-) values using a first-order Taylor series approximation. The bacterial denitrification method errors from 33 batches of 561 surface water samples varied from 0.2 to 2.1 per thousand for delta(15)N-NO(3)(-) and from 0.7 to 2.3 per thousand for delta(18)O-NO(3)(-), which is slightly wider than the machine error, which varied from 0.2 to 0.6 per thousand for delta(15)N-N(2)O and from 0.4 to 1.0 per thousand for delta(18)O-N(2)O. The overall uncertainties, which are composed of the machine error and the method error, for the 33 batches ranged from 0.3 to 2.2 per thousand for delta(15)N-NO(3)(-) and from 0.8 to 2.5 per thousand for delta(18)O-NO(3)(-). In addition, the mean corrected delta(15)N and delta(18)O values of 132 KNO(3)-IWS (internal working standard) measurements were computed as 8.4 +/- 1.0 per thousand and 25.1 +/- 2.0 per thousand, which is a slight underestimation for delta(15)N and overestimation for delta(18)O compared with the accepted values (delta(15)N = 9.9 +/- 0.3 per thousand and delta(18)O = 24.0 +/- 0.3 per thousand). The overall uncertainty of the bacterial denitrification method allows the use of this method for source identification of NO(3)(-).
authors.affiliation: Laboratory of Applied Physical Chemistry-ISOFYS, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium. dongmei.xue@ugent.be
authors.forename: Dongmei
authors.initials: D
authors.lastname: Xue
authors.forename: Bernard
authors.initials: B
authors.lastname: De Baets
authors.forename: Jan
authors.initials: J
authors.lastname: Vermeulen
authors.forename: Jorin
authors.initials: J
authors.lastname: Botte
authors.forename: Oswald
authors.initials: O
authors.lastname: Van Cleemput
authors.forename: Pascal
authors.initials: P
authors.lastname: Boeckx
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000378:metabolism*; D002623:Chemistry Techniques, Analytical / Q000379:methods / Q000592:standards*; D009566:Nitrates / Q000032:analysis* / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis* / Q000378:metabolism; D010103:Oxygen Isotopes / Q000032:analysis* / Q000378:metabolism; D012015:Reference Standards; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism
chemical_list: D009566:Nitrates; D009573:Nitrites; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D014874:Water Pollutants, Chemical