Global research alliance N2O chamber methodology guidelines: Flux calculations

Authors: Venterea, Rodney - Rod; PETERSEN, SOREN - Aarhus University; DE KLEIN, CECILE - Agresearch; PEDERSON, ASGER - Aarhus University; NOBLE, ALASDAIR - Agresearch; REES, ROBERT - Sruc-Scotland'S Rural College; Gamble, Joshua; Parkin, Timothy

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2020
Publication Date: 6/30/2020
Citation: Venterea, R.T., Petersen, S., de Klein, C., Pederson, A.R., Noble, A., Rees, R., Gamble, J.D., Parkin, T.B. 2020. Global research alliance N2O chamber methodology guidelines: Flux calculations. Journal of Environmental Quality. 49(5):1141-1155. https://doi.org/10.1002/jeq2.20118.
DOI: https://doi.org/10.1002/jeq2.20118

Interpretive Summary: Nitrous oxide (N2O) is a potent greenhouse gas and important ozone depleting chemical. A necessary and critical step in determining soil-to-atmosphere N2O exchange using chambers is converting the ‘raw’ chamber concentration versus time data into a flux value for each set of chamber time series data using a flux-calculation (FC) scheme. It is well-documented that different FC schemes can produce substantially different flux estimates for a given set of chamber data, and that selection of a FC scheme can be a major source of uncertainty in cumulative emissions estimates. The various available FC schemes differ in the theoretical basis of their underlying model, their computational requirements, and their performance in terms of both accuracy (bias) and precision. In this chapter, we describe the most commonly used FC schemes followed by a set of practical recommendations for applying and selecting among them. The theoretical underpinnings, mathematical structure, and advantages and limitations of the different FC schemes are presented as a foundation for the recommendations. Several example calculations in the form of spreadsheets and R script are provided as supplemental information to assist researchers with error analysis, determination of minimum detection limits and implementation of the different calculation methods. Recommendation for selection and implementation of a FC scheme are provided in the form of a decision tree and are based primarily on the availability of soil physical property data and number of samples collected during each chamber measurement. Additional criteria for selection among available non-linear FC schemes are provided based on analysis reported in parallel with this chapter which considers performance with respect to both accuracy and precision under different measurement conditions. The methods described here will result in improved estimates of N2O emissions and in turn will be useful for developing accurate global change models and developing mitigating practices.

Technical Abstract: A necessary and critical step in determining soil-to-atmosphere nitrous oxide (N2O) exchange using chambers is converting the ‘raw’ chamber concentration versus time data into a flux value for each set of chamber time series data using a flux-calculation (FC) scheme. It is well-documented that different FC schemes can produce substantially different flux estimates for a given set of chamber data, and that selection of a FC scheme can be a major source of uncertainty in cumulative emissions estimates. The various available FC schemes differ in the theoretical basis of their underlying model, their computational requirements, and their performance in terms of both accuracy (bias) and precision. In this chapter, we describe the most commonly used FC schemes followed by a set of practical recommendations for applying and selecting among them. The theoretical underpinnings, mathematical structure, and advantages and limitations of the different FC schemes are presented as a foundation for the recommendations. Several example calculations in the form of spreadsheets and R script are provided as supplemental information to assist researchers with error analysis, determination of minimum detection limits and implementation of the different calculation methods. Recommendation for selection and implementation of a FC scheme are provided in the form a decision tree and are based primarily on the availability of soil physical property data and number of samples collected during each chamber measurement. Additional criteria for selection among available non-linear FC schemes are provided based on analysis reported in parallel with this chapter which considers performance with respect to both accuracy and precision under different measurement conditions.