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Title:   Author  item
                                            Parkin, Timothyitem
                                            Venterea, Rodney

                                                         - *Rod*item
                                            HARGREAVES, SARAH - Iowa State University
  Submitted to: Journal of Environmental Quality
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/24/2012
                                    Publication  Date: 5/1/2012
                                    Citation: Parkin, T.B., Venterea, R.T., Hargreaves, S.K. 2012. Calculating the detection limits of chamber-based soil greenhouse gas flux measurements. Journal of Environmental Quality. 41(3):705-715. DOI:10.2134/jeq2011.0394.Interpretive Summary: Greenhouse gas emissions from soil in agricultural cropping systems contribute to global climate change. Measurement of greenhouse gas emissions from soil can be complicated, because emissions can vary substantially from spot to spot in the field. In order to determine which emissions are real and which are just background noise there needs to be a determination of the theoretical emission detection limit. This paper evaluated several common mathematical procedures used to compute emission rates. Through this analysis a procedure was developed by which a minimum emission detection limit can now be determined. This information will help scientists assess the significance of their greenhouse gas emissions measurements, and lead to better information on the contribution of agriculture to global climate change.
                                Technical Abstract: Renewed interest in quantifying greenhouse gas emissions from soil has lead to an increase in the application of chamber-based flux measurement techniques. Despite the apparent conceptual simplicity of chamber-based methods, nuances in chamber design, deployment, and data analyses can have marked effects on the quality of the flux data derived. In many cases fluxes are calculated from chamber headspace vs. time data sets consisting of 3 or 4 points. Several mathematical techniques have been used to calculate a soil gas flux from time course data. This paper explores the influences of sampling and analytical variability associated with trace gas concentration quantification on the flux estimated by linear and nonlinear models. Specifically, we used Monte Carlo simulation to calculate the minimum detectable fluxes (a = 0.05) of linear regression (LR), the Hutchinson/Mosier method (H/M), the quadratic method (QUAD), the HMR model, and restricted versions of the Quad and H/M methods over a range of analytical precisions and chamber deployment times for data sets consisting of 3 or 4 time points. We found that linear regression had the smallest detection limit thresholds and was the least sensitive to analytical precision and chamber deployment time. The HMR model had the highest detection limits and was most sensitive to analytical precision and chamber deployment time. Equations were developed which enable the calculation of the flux detection limits of any gas species if the analytical precision, the chamber deployment time, and the ambient concentration of the gas species are known.


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