Micrometeorology and Greenhouse Gas Flux Measurement from Four Pasture Sites at GSL
Xiangmin Sun, School of Natural Resources Micrometeorologist
With funding support from the University of Nebraska–Lincoln Advancing Development of Assessments, Practices and Tools (ADAPT) project, four micrometeorological measurement sites have been established and began operating at the Gudmundsen Sandhills Laboratory in 2025. Two sites are upland dry sites, and the other two are in the lowland meadow area. These sites were installed to measure the greenhouse gas emissions from grazing cattle to support sustainability in beef production. Continuous ground-based measurements could reveal the temporal pattern and magnitude of fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The carbon footprint results could provide defensible and actionable support for ranch management decisions.
Micrometeorology is the study of small-scale atmospheric processes near the Earth's surface. It focuses on interactions between the atmosphere and the surface (in this case, grazing pasture) and on greenhouse gas exchanges (fluxes). The technology for these micrometeorological sites is called eddy covariance, which records atmospheric eddies (swirling pockets of air) at very high frequency (usually 10 Hz, or 10 times per second). The core instruments or sensors are typically placed on a tower above a canopy to record data.
The core instruments include a 3-dimensional sonic anemometer to measure exact wind speed and direction, and fast-response gas analyzers to track the concentration of target gases. Our state-of-the-art site setup includes three gas analyzers. The LI-7500DS Analyzer is a non-dispersive infrared gas analyzer that simultaneously measures the densities of carbon dioxide (CO2) and water vapor (H2O) in ambient air. The LI-7700 CH4 Analyzer is a gas analyzer for measuring methane fluxes using wavelength modulation spectroscopy. Southwest Sciences. Inc has pioneered a breakthrough laser analyzer for nitrous oxide (N2O). This innovative N2O analyzer has just become commercially available, and we plan to install it in the summer of 2026. These remote sites are powered by a customized solar power management system.
Preliminary results of evapotranspiration (ET), CO2, and CH4 flux are shown in Figure 2. Monthly averaged diurnal patterns of these greenhouse gases show divergence between dryland and meadow sites. With relatively high soil moisture in meadow areas, water loss is much higher during the warm months than at upland sites. With more active vegetation and photosynthesis in October 2025 and April 2026, the meadow sites also show a stronger carbon sink, as expected. Due to logistics and maintenance challenges, we currently cannot draw definitive conclusions from CH4 records. But with a preemptive maintenance plan and continuous data collection in the summer of 2026, we expect a robust, comprehensive dataset to support informed conclusions.
Figure 2. Preliminary results of greenhouse gas budgets (ET, CO2, and CH4 flux) from the four micrometeorological measurement sites at GSL.
Figure 1. Core instruments deployed at one of four GSL eddy covariance sites as part of the ADAPT project.