Oxygen exchange between (de)nitrification intermediates and H₂O and its implications for source determination of NO and N₂O: a review

Abstract

Stable isotope analysis of oxygen (O) is increasingly used to determine the origin of nitrate (NO(3)-) and nitrous oxide (N(2)O) in the environment. The assumption underlying these studies is that the (18)O signature of NO(3)- and N(2)O provides information on the different O sources (O(2) and H(2)O) during the production of these compounds by various biochemical pathways. However, exchange of O atoms between H(2)O and intermediates of the (de)nitrification pathways may change the isotopic signal and thereby bias its interpretation for source determination. Chemical exchange of O between H(2)O and various nitrogenous oxides has been reported, but the probability and extent of its occurrence in terrestrial ecosystems remain unclear. Biochemical O exchange between H(2)O and nitrogenous oxides, NO(2)- in particular, has been reported for monocultures of many nitrifiers and denitrifiers that are abundant in nature, with exchange rates of up to 100%. Therefore, biochemical O exchange is likely to be important in most soil ecosystems, and should be taken into account in source determination studies. Failing to do so might lead to (i) an overestimation of nitrification as NO(3)- source, and (ii) an overestimation of nitrifier denitrification and nitrification-coupled denitrification as N(2)O production pathways. A method to quantify the rate and controls of biochemical O exchange in ecosystems is needed, and we argue this can only be done reliably with artificially enriched (18)O compounds. We conclude that in N source determination studies, the O isotopic signature of especially N(2)O should only be used with extreme caution.

Role of Microorganisms in Emission of Nitrous Oxide and Methane in Pulse Cultivated Soil Under Laboratory Incubation Condition

“…Our study is in accordance with earlier reports, as significant N 2 O emission has been observed at 80 % WFPS (Fig. 2) which supports the augmentation of both nitrifier and denitrifier population, in absence of C 2 H 2 [31]. Experimental set with C 2 H 2 exposure showed a different result.…”

“…Presence of a low concentration of C 2 H 2 , has a direct deleterious impact on the nitrification and an indirect one on denitrification process, with relation to availability of nitrate. But further investigation is necessary to determine the accuracy of low partial pressures of C 2 H 2 having inhibitory effects only on nitrification process [31].…”

Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in Eastern Asia using Δ<sup>17</sup>O

“…On the contrary, the present results suggest that the remineralized nitrate have δ 18 O values substantially larger than those of the groundwater (δ 18 O = (−13±1)‰) within the island, probably owing to the contribution of oxygen atoms from oxygen molecules (O 2 ) having δ 18 O values of +23.88‰ (Barkan and Luz, 2005) or more during nitrification in the forest soil. The exchange of oxygen atoms between nitrification intermediates and the ambient water is limited by some environmental conditions (Kool et al, 2007). Yamaguchi et al (1975) On the other hand, the Rishiri National Acid Rain Monitoring Station quantified the annual deposition rate of NO − 3 (atm) as 12.7 mmol m −2 a −1 (average total deposition rate from 2000 to 2007), which corresponds to a total deposition rate of NO − 3 (atm) of 2.3×10 6 mol a −1 on the island (EANET, 2008).…”

Nitrate sources and dynamics in a salinized river and estuary – a δ<sup>15</sup>N–NO<sub>3</sub><sup>−</sup> and δ<sup>18</sup>O–NO<sub>3</sub><sup>−</sup> isotope approach

“…For δ 18 O-NO − 3 values, NO − 3 produced by nitrification in aquatic environments usually takes similar δ 18 O values to the ambient water (Casciotti et al, 2002;Sigman et al2005). There is evidence that O can exchange between H 2 O and intermediate compounds of nitrification (Andersson et al, 1982;DiSpirito and Hooper, 1986;Kool et al, 2007). Since the δ 18 O of estuarine water is expected to be higher than that of river water (Miyajima et al, 2009)…”