Applying cavity ring‐down spectroscopy for the measurement of dissolved nitrous oxide concentrations and bulk nitrogen isotopic composition in aquatic systems: Correcting for interferences and field application. (18th May 2015)

• Record Type: Journal Article
• Authors: Erler, D. V.; Duncan, T. M.; Murray, R.; Maher, D. T.; Santos, I. R.; Gatland, J. R.; Mangion, P.; Eyre, B. D.
• Is Part Of: Limnology and oceanography, methods. Volume 13:Number 8(2015:Aug.)
• Page Start: 391
• Page End: 401
• Publication Date: 2015-05-18
• Subjects: Limnology -- Methodology -- Periodicals; Oceanography -- Methodology -- Periodicals; 551.48
• DOI: 10.1002/lom3.10032
• Languages: English
• ISSNs: 1541-5856

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Laser spectroscopy is an emerging technology for measuring nitrous oxide (N<sub>2</sub>O) dynamics in the environment, but most studies have focused on atmospheric applications. We have coupled a commercially available cavity ring‐down spectroscope (CRDS) (Picarro G5101‐<italic>I</italic> isotopic N<sub>2</sub>O analyzer) to an air/water gas equilibration device to collect continuous in situ dissolved N<sub>2</sub>O molar concentration and bulk nitrogen isotopic (δ<sup>15</sup>N‐N<sub>2</sub>O) data. The δ<sup>15</sup>N‐N<sub>2</sub>O values measured by the CRDS unit were found to be significantly affected by changes in the mixing ratios of O<sub>2</sub>, CO, CH<sub>4</sub>, and CO<sub>2</sub>. There was also an effect of N<sub>2</sub>O mixing ratio on δ<sup>15</sup>N‐N<sub>2</sub>O. A series of equations was developed to correct for the matrix effect of O<sub>2</sub> and the spectral interference by CH<sub>4</sub>. Chemical traps effectively prevented interferences by CO and CO<sub>2</sub>. The maximum corrections required for N<sub>2</sub>O mixing ratio and O<sub>2</sub> matrix effects, were 1‰ (at a mixing ratio of 1.2 ppmv), and 11‰ (at 0% O<sub>2</sub> content), respectively. The CH<sub>4</sub> correction only became important at mixing ratios greater than 500 ppmv (>0.5‰). Measurements of N<sub>2</sub>O molar concentration and δ<sup>15</sup>N‐N<sub>2</sub>O from the CRDS isotopic N<sub>2</sub>O analyzer were similar to those measured with isotope ratio mass spectrometry. We demonstrated the utility of the laser‐based system with field deployments in three estuarine tidal creeks in subtropical Australia. Future work in this field should focus on the application of the laser‐based system to the measurement of N<sub>2</sub>O isotopologues in aquatic habitats, allowing for further constraints to be placed on the pathways of N<sub>2</sub>O cycling in aquatic system.</p> </abstract>