Abstract
Abstract. Soils play an important role in Earth's climate system through their regulation of trace greenhouse gases. Despite decades of soil gas flux measurements using manual chamber methods, limited temporal coverage has led to high uncertainty in flux magnitude and variability, particularly during peak emission events. Automated chamber measurement systems can collect high-frequency (subdaily) measurements across various spatial scales but may be prohibitively expensive or incompatible with field conditions. Here we describe the construction and operational details for a robust, relatively inexpensive, and adaptable automated dynamic (steady-state) chamber measurement system modified from previously published methods, using relatively low cost analyzers to measure nitrous oxide (N2O) and carbon dioxide (CO2). The system was robust to intermittent flooding of chambers, long tubing runs (>100 m), and operational temperature extremes (−12 to 39 ∘C) and was entirely powered by solar energy. Using data collected between 2017 and 2019 we tested the underlying principles of chamber operation and examined N2O diel variation and rain-pulse timing that would be difficult to characterize using infrequent manual measurements. Stable steady-state flux dynamics were achieved during 29 min chamber closure periods at a relatively low flow rate (2 L min−1). Instrument performance and calculated fluxes were minimally impacted by variation in air temperature and water vapor. Measurements between 08:00 and 12:00 LT were closest to the daily mean N2O and CO2 emission. Afternoon fluxes (12:00–16:00 LT) were 28 % higher than the daily mean for N2O (4.04 vs. 3.15 nmol m−2 s−1) and were 22 % higher for CO2 (4.38 vs. 3.60 µmolm-2s-1). High rates of N2O emission are frequently observed after precipitation. Following four discrete rainfall events, we found a 12–26 h delay before peak N2O flux, which would be difficult to capture with manual measurements. Our observation of substantial and variable diel trends and rapid but variable onset of high N2O emissions following rainfall supports the need for high-frequency measurements.
Highlights
Soils play a critical role in Earth’s carbon (C) and nitrogen (N) cycles
The results were minimally impacted by measurement error due to water vapor and were robust to changes in air temperature
CO2 emissions were best approximated during the same time interval, the difference between peak emissions and the daily average was less pronounced and displayed less variability than observed for N2O
Summary
Soils play a critical role in Earth’s carbon (C) and nitrogen (N) cycles. Reliable trace gas measurements are critical for informing management. Manual soil gas flux measurements have been collected for several decades, the high temporal and spatial variability of emissions has often plagued attempts to obtain accurate and precise flux estimates needed to calculate annual budgets (Davidson et al, 2002; Groffman et al, 2009; Hutchinson and Mosier, 1981). Sampling at higher frequency than is practical with manual measurements may be required to constrain the role of soils in global biogeochemical cycles and validate the impacts of management practices on trace gas emissions (Barton et al, 2015; Merbold et al, 2015; Parkin, 2008). Highfrequency automated flux measurements that can span the large (> 100 m) spatial scales that frequently accompany local topographical and hydrological variation at a site may be Published by Copernicus Publications on behalf of the European Geosciences Union
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