A Stable Isotope and Eddy Covariance System for Monitoring Ecosystem Metabolism

Northern Arizona University, Flagstaff AZ

Investigators

Abstract

Non-Technical Abstract A grant has been awarded to Northern Arizona University to acquire eddy covariance towers and a stable isotope ratio mass spectrometer. The eddy covariance equipment will be used to measure carbon, water, and energy exchange between southwestern ecosystems and the atmosphere. These fluxes are critical regulators of ecosystem processes, such as decomposition, nutrient cycling, consumer activity, and groundwater recharge to riparian ecosystems. They also influence regional and global climate and are of increasing interest to policy-makers concerned with management of greenhouse gases. Previous eddy covariance studies emphasize determining net fluxes in pristine ecosystems. The two major goals of this project are 1) to use stable isotope techniques to determine the mechanisms responsible for changing net fluxes (e.g., for carbon dioxide, determining how overstory trees versus understory grasses contribute to total ecosystem photosynthesis and respiration), and 2) using large-scale experiments, to determine how fluxes of carbon, water, and energy respond to disturbance and land use practices. Eddy covariance and stable isotope measurements will be conducted in two experimental settings. First, tracts of Ponderosa Pine forest that have been thinned to reduce fire danger will be compared with dense, control forests, documenting the impacts of so-called 'forest restoration' on fluxes of carbon, water, and energy. Second, grasslands under varying grazing management practices will be compared to assess which land management practices, for example, are more effective at conserving water and storing carbon. In these experiments, instruments on towers will be used to measure 'eddies' (turbulent air movements) carrying pockets of air upwards, downwards, and sideways. Measuring vertical air movements and the amount of carbon dioxide, water vapor, and heat they contain enables one to calculate the net fluxes of these constituents between the ecosystem and the atmosphere. The isotope ratio mass spectrometer will be used to analyze the stable isotope composition of carbon dioxide and water vapor in samples of air throughout the canopy. Stable isotopes of carbon, hydrogen and oxygen provide characteristic fingerprints of how individual components of ecosystems contribute to overall fluxes measured by eddy covariance, so coupling these two techniques will enable researchers to determine which ecosystem components are responsible for altering net fluxes. This equipment will be used to address research questions ranging from the effects of climate on ecosystem functioning to the implications of large-scale forest restoration for regional climate and site water balance. Once established, this new flux measurement array will attract additional researchers working on issues as diverse as design of new range management programs to regional influences of globally important phenomena such as El Nino and the Pacific Decadal Oscillation. Undergraduate students from underrepresented groups will be recruited to participate in the proposed research through an NSF funded UMEB program already in place at NAU. The theme of the UMEB program includes specific research activities that dovetail nicely with the research enabled by this instrumentation grant (e.g., Carbon Balance of Colorado Plateau Ecosystems, and Livestock Management, Productivity, and Diversity of Southwestern Grasslands). Minority students recruited into the UMEB program will work with mentors involved with the flux and isotope studies and will attend special classes in which the findings of the ecosystem experiments are presented. In sum, the equipment funded by this grant will increase opportunities for training students of diverse backgrounds at NAU in state-of the-art techniques and research relevant to important issues in ecology and environmental biology