|GRIFFIS, TIMOTHY - University Of Minnesota
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2012
Publication Date: 2/11/2013
Citation: Fassbinder, J.J., Schultz, N.M., Baker, J.M., Griffis, T.J. 2013. Automated, low-power chamber system for measuring nitrous oxide emissions. Journal of Environmental Quality. 42(2):606-614.
Interpretive Summary: Nitrous oxide is a potent greenhouse gas, with 300 times the global warming potential of carbon dioxide, and agriculture is the primary source of it. Research on ways to reduce nitrous oxide production has been hampered by a lack of reliable data, because it is episodic in nature and difficult to measure. Here we describe an automated system, capable of continuous, unattended measurement and powered by solar panels and a wind turbine. The latter means that it can be deployed in remote field locations where AC power is not available. The system uses a relatively new analyzer that is much less expensive than previous analyzers, coupled to commercially available automated chambers originally developed to measure soil respiration. Results demonstrate that the system is accurate and reliable, and can measure nitrous oxide production continuously over the course of a growing season. In the spring and fall, when available solar power diminishes, the system has more frequent power outages, particularly at night, but this could be reduced or eliminated with a larger bank of batteries. The cumulative data from the system were also used to estimate the accuracy of cumulative emissions estimated from infrequent manual measurement, which is the more common approach. Results show that this approach is prone to errors that depend on the time of day that samples are collected and whether sampling days happen to follow heavy rains. This system will be useful for other scientists studying the impact of management practices on nitrous oxide emissions.
Technical Abstract: Continuous measurement of soil emissions is needed to constrain estimates of N2O loss to the atmosphere. Here, we describe the performance of a low-power, automated chamber system that can continuously measure N2O soil emissions, powered by wind and solar power. Laboratory testing of the Teledyne N2O analyzer revealed significant temperature sensitivity, causing zero drift of -10.6 ppb °C-1. However, temperature induced span drift is negligible, so the associated error in flux measurement for a typical chamber sampling period is on the order of only 0.016 nmol m-2 s-2. The 1 Hz precision of the analyzer over a 10 minute averaging interval, following wavelet decomposition, was 1.5 ppbv, equal to that of a tunable diode laser N2O analyzer. The power system performed well during summer, but system failures increased in frequency in spring and fall, usually at night. Although increased storage capacity would decrease down time, supplemental power from additional sources may still be needed to continuously run the system during spring and fall. The cumulative hourly flux data were used to assess the accuracy of integrated estimates derived from manually sampling static chambers at various frequencies (once every 4 days up to every 22 days) and at various times during the day. For all frequencies, cumulative estimates using only afternoon measurements were 15% to 43% greater than estimates using only morning measurements. Only the 7 and 19 day sampling frequencies happened to capture a spike in emissions following heavy rain on September 23, emphasizing the importance of continuous sampling.