EAGER: Collaborative Research: Development of a New Technique to Measure Ecosystem-level Soil Nitrous Oxide Fluxes using Micrometeorological Towers

Michigan State University, East Lansing MI

Investigators

Abstract

Nitrous oxide is the third most important greenhouse gas in the atmosphere, with an atmospheric lifetime of about 114 years and a global warming impact per molecule that is about 300 times greater than that of carbon dioxide. Atmospheric concentrations of nitrous oxide are increasing, primarily due to agriculture, which is thought to be responsible for about half of the total output to the atmosphere that can be attributed to human activities. Current trends in land-use change and agricultural intensification (in particular increasing fertilizer use) suggest that an additional 20% increase in global nitrous oxide emissions will occur by 2030. However, difficulties in measuring the output of nitrous oxide from ecosystems make it hard to manage and predict nitrous oxide production from major human sources. This project we will test a promising new technique to measure the ecosystem-level exchange of nitrous oxide with the atmosphere using a laser sensor. This novel approach will provide opportunities to measure whole system nitrous oxide dynamics at hourly to daily time scales over areas that are too large to effectively sample with traditional techniques. With this novel approach, a new understanding of the factors that control the production and consumption of nitrous oxide in forests, grasslands, and agricultural lands may be possible. This would lead to much better ability to manage and minimize the production of this important greenhouse gas, because management is currently hampered by significant uncertainties in the measurement of nitrous oxide. A major barrier to understanding and mitigating emissions of nitrous oxide from agricultural and other managed soils is the difficulty with which fluxes are measured, given temporal and spatial variability that often exceeds an order of magnitude at scales of meters and hours. In this project, open-path quantum cascade laser sensors will be integrated with standard micrometeorological measurements to develop a solar-powered measurement system to quantify nitrous oxide fluxes. This novel approach will provide opportunities to measure whole system nitrous oxide fluxes at hourly to daily time scales over multi-hectare areas, and thereby resolve and integrate the spatial and temporal variability that makes this flux so difficult to quantify and model in situ. A newly developed open-path quantum cascade laser (OP-QCL) sensor will be used on each of two existing carbon dioxide micrometeorological eddy covariance towers to measure ecosystem-level nitrous oxide exchange. In addition to the OP-QCL sensors, multiple standard static chambers will be deployed within the study area to perform ground based validation of the OP-QCL measurements. One of the sensors will be deployed in a high-emission fertilized continuous corn system; the other will be deployed in grassland that has not been farmed for 25 years. In addition to validating the micrometeorological method, the project will test hypotheses related to the temporal variability of fluxes at diurnal to seasonal scales, which cannot be answered without continuous observations. Specific project objectives include 1) to develop, test, and validate an OP-QCL sensor for ecosystem-level measurements of nitrous oxide fluxes using micrometeorological towers; and 2) to relate and assess the significance of changes in nitrous oxide flux with temporal environmental variability, including daily, seasonal, and episodic events such as large rain events and management activities such as tillage and fertilization in cropped systems.