Using automated non-steady-state chamber systems for making continuous long-term measurements of soil CO₂ efflux in forest ecosystems

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• 作者：Rachhpal S. Jassal^a ; ^{rachhpal.jassal@ubc.ca} ; T. Andrew Black^a ; Zoran Nesic^a ; David Gaumont-Guay^b
• 关键词：Soil respiration ; Soil CO2 efflux ; Automated chamber systems ; Effective chamber volume ; Data quality checks ; Linear and non-linear regression ; A model of soil CO2 efflux
• 刊名：Agricultural and Forest Meteorology
• 出版年：2012
• 期刊代码：2_01681923
• 类别：abs
• 出版时间：15 August, 2012
• 卷：161
• 期：Complete
• 页码：57-65
• 文件大小：930 K

摘要

Automated measurements of forest soil CO₂ efflux (F) using non-steady-state chamber systems are necessary to study the short- and long-term responses of soil respiration to temporal variations in abiotic and biotic variables. Increased use of automated chamber systems in regional flux networks results in large data sets that demand an efficient and reliable protocol to ensure good quality measurements, efficient and robust calculations, and post-processing data-quality control.

Using half-hourly measurements and simulations with a process-based model, we show that underestimation of efflux due to disturbance of the soil CO₂ diffusion gradient arising from chamber closure for periods of up to 3 min is much less (<4%) than is often assumed. Also, we found that use of simple linear regression for calculating the rate of change in the chamber headspace concentration is the best method in comparison to non-linear models; it is robust and, for lid closure periods <3%of the chamber-soil system time constant, results in <2%underestimation of the efflux, which is smaller than the overestimation using some non-linear methods.

The effective volume of a chamber is significantly higher than its geometric volume and varies markedly seasonally so its determination is important for accurate efflux measurements. A procedure is described for determining the effective volume, which we recommend should be followed at least once a day. We also describe various steps to ensure accurate measurements, including the use of a seasonal threshold value of the ratio of root mean square error of the linear fit to headspace concentration versus time to its slope for rejecting questionable measurements, and demonstrate the use of a procedure combining the use of automated and manual quality assurance/quality control in removing questionable measurements.